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Direct Modulation/Waveform Generating, 6.1 GHz Fractional-N Frequency Synthesizer
ADF4158
FEATURES
RF bandwidth to 6.1 GHz 25-bit fixed modulus allows subhertz frequency resolution Frequency and phase modulation capability Sawtooth and triangular waveforms in the frequency domain Parabolic ramp Ramp superimposed with FSK Ramp with 2 different sweep rates Ramp delay Ramp frequency readback Ramp interruption 2.7 V to 3.3 V power supply Separate VP allows extended tuning voltage Programmable charge pump currents 3-wire serial interface Digital lock detect Power-down mode Cycle slip reduction for faster lock times Switched bandwidth fast-lock mode
GENERAL DESCRIPTION
The ADF4158 is a 6.1 GHz, fractional-N frequency synthesizer with modulation and waveform generation capability. It contains a 25-bit fixed modulus, allowing subhertz resolution at 6.1 GHz. It consists of a low noise digital phase frequency detector (PFD), a precision charge pump, and a programmable reference divider. There is a sigma-delta (-) based fractional interpolator to allow programmable fractional-N division. The INT and FRAC registers define an overall N-divider as N = INT + (FRAC/225). The ADF4158 can be used to implement frequency shift keying (FSK) and phase shift keying (PSK) modulation. There are also a number of frequency sweep modes available, which generate various waveforms in the frequency domain, for example, sawtooth and triangular waveforms. The ADF4158 features cycle slip reduction circuitry, which leads to faster lock times, without the need for modifications to the loop filter. Control of all on-chip registers is via a simple 3-wire interface. The device operates with a power supply ranging from 2.7 V to 3.3 V and can be powered down when not in use.
APPLICATIONS
FMCW radar Communications test equipment
FUNCTIONAL BLOCK DIAGRAM
AVDD DVDD VP RSET
ADF4158
REFIN x2 DOUBLER 5-BIT R-COUNTER /2 DIVIDER VDD DGND LOCK DETECT MUXOUT OUTPUT MUX VDD RDIV CE TXDATA NDIV N-COUNTER THIRD-ORDER FRACTIONAL INTERPOLATOR CLK DATA LE RFINA RFINB FLO SWITCH + PHASE FREQUENCY DETECTOR - REFERENCE SW2
CHARGE PUMP CSR
CP
HIGH-Z
SW1
32-BIT DATA REGISTER
FRACTION REG
MODULUS 225
INTEGER REG
AGND
DGND
CPGND
Figure 1.
Rev. 0
Information furnished by Analog Devices is believed to be accurate and reliable. However, no responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other rights of third parties that may result from its use. Specifications subject to change without notice. No license is granted by implication or otherwise under any patent or patent rights of Analog Devices. Trademarks and registered trademarks are the property of their respective owners.
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ADF4158 TABLE OF CONTENTS
Features .............................................................................................. 1 Applications ....................................................................................... 1 General Description ......................................................................... 1 Functional Block Diagram .............................................................. 1 Revision History ............................................................................... 2 Specifications..................................................................................... 3 Timing Specifications .................................................................. 4 Absolute Maximum Ratings............................................................ 6 ESD Caution .................................................................................. 6 Pin Configuration and Pin Function Descriptions ...................... 7 Typical Performance Characteristics ............................................. 8 Circuit Description ......................................................................... 10 Reference Input Section ............................................................. 10 RF Input Stage ............................................................................. 10 RF INT Divider ........................................................................... 10 25-Bit Fixed Modulus ................................................................ 10 INT, FRAC, and R Relationship ............................................... 10 R-Counter .................................................................................... 10 Phase Frequency Detector (PFD) and Charge Pump ............ 11 MUXOUT and LOCK Detect ................................................... 11 Input Shift Registers ................................................................... 11 Program Modes .......................................................................... 11 Register Maps .................................................................................. 12 FRAC/INT Register (R0) Map .................................................. 14 LSB FRAC Register (R1) Map ................................................... 15 R-Divider Register (R2) Map .................................................... 16 Function Register (R3) Map...................................................... 18 Test Register (R4) Map .............................................................. 20 Deviation Register (R5) Map .................................................... 21 Step Register (R6) Map .............................................................. 22 Delay Register (R7) Map ........................................................... 23 Applications Information .............................................................. 24 Initialization Sequence............................................................... 24 RF Synthesizer: A Worked Example ........................................ 24 Reference Doubler and Reference Divider ............................. 24 Cycle Slip Reduction for Faster Lock Times ........................... 24 Modulation .................................................................................. 25 Waveform Generation ............................................................... 25 Additional Features .................................................................... 27 Fast-Lock Timer and Register Sequences ............................... 30 Fast Lock: An Example .............................................................. 30 Fast Lock: Loop Filter Topology ............................................... 30 Spur Mechanisms ....................................................................... 31 Low Frequency Applications .................................................... 31 Filter Design--ADIsimPLL ....................................................... 31 PCB Design Guidelines for the Chip Scale Package .............. 31 Application of ADF4158 in FMCW Radar ................................. 32 Outline Dimensions ....................................................................... 33 Ordering Guide........................................................................... 33
REVISION HISTORY
4/10--Revision 0: Initial Version
Rev. 0 | Page 2 of 36
ADF4158 SPECIFICATIONS
AVDD = DVDD = 2.7 V to 3.3 V, VP = AVDD to 5.5 V, AGND = DGND = 0 V, TA = TMIN to TMAX, dBm referred to 50 , unless otherwise noted. Table 1.
C Version 1 Parameter RF CHARACTERISTICS RF Input Frequency (RFIN) Min 0.5 Typ Max 6.1 Unit GHz Test Conditions/Comments -10 dBm min to 0 dBm max; for lower frequencies, ensure slew rate (SR) > 400 V/s -15 dBm min to 0 dBm max for 2 GHz to 4 GHz RF input frequency For f < 10 MHz, use a dc-coupled CMOS-compatible square wave, slew rate > 25 V/s If an internal reference doubler is enabled Biased at AVDD/2 2
REFERENCE CHARACTERISTICS REFIN Input Frequency
10
260 16 AVDD 10 100 32
MHz MHz V p-p pF A MHz
REFIN Input Sensitivity REFIN Input Capacitance REFIN Input Current PHASE DETECTOR Phase Detector Frequency 3 CHARGE PUMP ICP Sink/Source High Value Low Value Absolute Accuracy RSET Range ICP Three-State Leakage Current Matching ICP vs. VCP ICP vs. Temperature LOGIC INPUTS VINH, Input High Voltage VINL, Input Low Voltage IINH/IINL, Input Current CIN, Input Capacitance LOGIC OUTPUTS VOH, Output High Voltage VOH, Output High Voltage IOH, Output High Current VOL, Output Low Voltage POWER SUPPLIES AVDD DVDD VP IDD
0.4
5 312.5 2.5 2.7 1 2 2 2 1.4 0.6 1 10 1.4 VDD - 0.4 100 0.4 2.7 AVDD AVDD 23 5.5 32 3.3 10
mA A % k nA % % % V V A pF V V A V V V mA
Programmable With RSET = 5.1 k With RSET = 5.1 k Sink and source current 0.5 V < VCP < VP - 0.5 V 0.5 V < VCP < VP - 0.5 V VCP = VP/2
Open-drain output chosen; 1 k pull-up to 1.8 V CMOS output chosen IOL = 500 A
Rev. 0 | Page 3 of 36
ADF4158
C Version 1 Parameter NOISE CHARACTERISTICS Normalized Phase Noise Floor 4 Phase Noise Performance 5 5805 MHz Output 6
1 2
Min
Typ -213 -93
Max
Unit dBc/Hz dBc/Hz
Test Conditions/Comments
@ VCO output @ 5 kHz offset, 32 MHz PFD frequency
Operating temperature for C version: -40C to +125C. AC-coupling ensures AVDD/2 bias. 3 Guaranteed by design. Sample tested to ensure compliance. 4 This figure can be used to calculate phase noise for any application. Use the formula -213 + 10 log(fPFD) + 20 logN to calculate in-band phase noise performance as seen at the VCO output. 5 The phase noise is measured with the EVAL-ADF4158EB1Z and the Agilent E5052A phase noise system. 6 fREFIN = 128 MHz; fPFD = 32 MHz; offset frequency = 5 kHz; RFOUT = 5805 MHz; INT = 181; FRAC = 13631488; loop bandwidth = 100 kHz.
TIMING SPECIFICATIONS
AVDD = DVDD = SDVDD = 2.7 V to 3.3 V; VP = AVDD to 5.5 V; AGND = DGND = SDGND = 0 V; TA = TMIN to TMAX, dBm referred to 50 , unless otherwise noted. Table 2. Write Timing
Parameter t1 t2 t3 t4 t5 t6 t7 Limit at TMIN to TMAX (C Version) 20 10 10 25 25 10 20 Unit ns min ns min ns min ns min ns min ns min ns min Test Conditions/Comments LE setup time DATA to CLK setup time DATA to CLK hold time CLK high duration CLK low duration CLK to LE setup time LE pulse width
Write Timing Diagram
t4
CLK
t5
t2
DATA DB31 (MSB) DB30
t3
DB2 (CONTROL BIT C3) DB1 (CONTROL BIT C2) DB0 (LSB) (CONTROL BIT C1)
t7
LE
t1
LE
t6
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Figure 2. Write Timing Diagram
Rev. 0 | Page 4 of 36
ADF4158
Table 3. Read Timing
Parameter t1 t2 t3 t4 t5 t6 Limit at TMIN to TMAX (C Version) 20 10 10 25 25 10 Unit ns min ns min ns min ns min ns min ns min Test Conditions/Comments TXDATA setup time DATA (on MUXOUT) to CLK setup time DATA (on MUXOUT) to CLK hold time CLK high duration CLK low duration CLK to LE setup time
Read Timing Diagram
TXDATA
t1 t4
CLK
t5
t2
t3
DB2 DB1
MUXOUT
DB36
DB35
DB0
t6
LE
Figure 3. Read Timing Diagram
Rev. 0 | Page 5 of 36
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ADF4158 ABSOLUTE MAXIMUM RATINGS
TA = 25C, GND = AGND = DGND = SDGND = 0 V, VDD = AVDD = DVDD = SDVDD, unless otherwise noted. Table 4.
Parameter VDD to GND VDD to VDD VP to GND VP to VDD Digital I/O Voltage to GND Analog I/O Voltage to GND REFIN, RFIN to GND Operating Temperature Range Industrial (C Version) Storage Temperature Range Maximum Junction Temperature LFCSP JA Thermal Impedance (Paddle Soldered) Reflow Soldering Peak Temperature Time at Peak Temperature Rating -0.3 V to +4 V -0.3 V to +0.3 V -0.3 V to +5.8 V -0.3 V to +5.8 V -0.3 V to VDD + 0.3 V -0.3 V to VDD + 0.3 V -0.3 V to VDD + 0.3 V -40C to +125C -65C to +125C 150C 30.4C/W
Stresses above those listed under Absolute Maximum Ratings may cause permanent damage to the device. This is a stress rating only; functional operation of the device at these or any other conditions above those indicated in the operational section of this specification is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability.
ESD CAUTION
260C 40 sec
Rev. 0 | Page 6 of 36
ADF4158 PIN CONFIGURATION AND PIN FUNCTION DESCRIPTIONS
24 23 22 21 20 19
CPGND AGND AGND RFINB RFINA AVDD 1 2 3 4 5 6
PIN 1 INDICATOR
CP RSET VP SW2 SW1 DVDD
18 17 16 15 14 13
ADF4158
TOP VIEW (Not to Scale)
SDVDD MUXOUT LE DATA CLK CE
AVDD 7 AVDD 8 REFIN 9 DGND 10 SDGND 11 TXDATA 12
NOTES 1. THE LFCSP HAS AN EXPOSED PADDLE THAT MUST BE CONNECTED TO GND.
Figure 4. LFCSP Pin Configuration
Table 5. Pin Function Descriptions
Pin No. 1 2, 3 4 5 6, 7, 8 9 10 11 12 13 14 15 16 17 18 19 20 , 21 22 23 Mnemonic CPGND AGND RFINB RFINA AVDD REFIN DGND SDGND TXDATA CE CLK DATA LE MUXOUT SDVDD DVDD SW1, SW2 VP RSET Description Charge Pump Ground. This is the ground return path for the charge pump. Analog Ground. This is the ground return path of the prescaler. Complementary Input to the RF Prescaler. Decouple this point to the ground plane with a small bypass capacitor, typically 100 pF. Input to the RF Prescaler. This small-signal input is normally ac-coupled from the VCO. Positive Power Supply for the RF Section. Place decoupling capacitors to the digital ground plane as close as possible to this pin. AVDD must have the same voltage as DVDD. Reference Input. This is a CMOS input with a nominal threshold of VDD/2 and an equivalent input resistance of 100 k. It can be driven from a TTL or CMOS crystal oscillator, or it can be ac-coupled. Digital Ground. Digital - Modulator Ground. Ground return path for the - modulator. Tx Data Pin. Provide data to be transmitted in FSK or PSK mode on this pin. Chip Enable. A logic low on this pin powers down the device and puts the charge pump output into three-state mode. Serial Clock Input. This serial clock is used to clock in the serial data to the registers. The data is latched into the shift register on the CLK rising edge. This input is a high impedance CMOS input. Serial Data Input. The serial data is loaded MSB first with the three LSBs being the control bits. This input is a high impedance CMOS input. Load Enable, CMOS Input. When LE is high, the data stored in the shift registers is loaded into one of the eight latches, with the latch being selected using the control bits. Multiplexer Output. This pin allows either the RF lock detect, the scaled RF, or the scaled reference frequency to be accessed externally. Power Supply Pin for the Digital - Modulator. This pin should be the same voltage as AVDD. Place decoupling capacitors to the ground plane as close as possible to this pin. Positive Power Supply for the Digital Section. Place decoupling capacitors to the digital ground plane as close as possible to this pin. DVDD must have the same voltage as AVDD. Switches for Fast Lock. Charge Pump Power Supply. This should be greater than or equal to VDD. In systems where VDD is 3 V, it can be set to 5.5 V and used to drive a VCO with a tuning range of up to 5.5 V. Connecting a resistor between this pin and ground sets the maximum charge pump output current. The relationship between ICP and RSET is
I CPmax =
25.5 RSET
24 25
CP EPAD
where: ICPmax = 5 mA. RSET = 5.1 k. Charge Pump Output. When enabled, this provides ICP to the external loop filter, which in turn drives the external VCO. Exposed Paddle. The LFCSP has an exposed paddle that must be connected to GND.
Rev. 0 | Page 7 of 36
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ADF4158 TYPICAL PERFORMANCE CHARACTERISTICS
-40
5.87 5.86
-60
5.85 5.84
FREQUENCY (GHz)
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PHASE NOISE (dBc/Hz)
-80
5.83 5.82 5.81 5.80 5.79
-100
-120
-140
5.78 5.77
1k 10k 100k FREQUENCY OFFSET (Hz) 1M 10M
-0.005
0 TIME (s)
0.005
0.010
Figure 5. Phase Noise at 5805 MHz, PFD = 32 MHz, Loop Bandwidth = 100 kHz
Figure 8. Delay Between Ramps for Sawtooth Waveform, PFD = 32 MHz, INT = 181, FRAC = 0, DEV Offset = 4, DEV Word = 20972, Step Word = 200, CLK DIV = 10, MOD Divider = 125, DEL Start Word = 1025
5.86 5.85 5.84 NO DELAY DELAY
5.86 5.85 5.84
FREQUENCY (GHz)
5.83 5.82 5.81 5.80
FREQUENCY (GHz)
5.83 5.82 5.81 5.80 5.79 5.78
5.79 5.78 -0.025
5.77
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-0.015
-0.005
0.005
0.015
0.025
0
0.005
TIME (s)
0.010 TIME (s)
0.015
0.020
Figure 6. Triangular Waveform, PFD = 32 MHz, INT = 181, FRAC = 0, DEV Offset = 4, DEV Word = 20972, Step Word = 200, CLK DIV = 10, MOD Divider = 125
5.87
Figure 9. Delayed Start of Triangular Burst, PFD = 32 MHz, INT = 181, FRAC = 0, DEV Offset = 4, DEV Word = 20972, Step Word = 200, CLK DIV = 10, MOD Divider = 125, DEL Start Word = 1000
5.810 5.808
5.85
5.806
FREQUENCY (GHz)
5.804 5.802 5.800 5.798 5.796 5.794
FREQUENCY (GHz)
5.83
5.81
5.79
5.77
5.792
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-0.005
0 TIME (s)
0.005
0.010
Figure 7. Sawtooth Waveform, PFD = 32 MHz, INT = 181, FRAC = 0, DEV Offset = 4, DEV Word = 20972, Step Word = 200, CLK DIV = 10, MOD Divider = 125
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5.75 -0.010
5.790 -0.010
-0.005
0 TIME (s)
0.005
0.010
Figure 10. Dual Ramp Rate Waveform, PFD = 32 MHz, INT = 181, FRAC = 0, Ramp1: DEV Offset = 3, DEV Word = 16777, Step Word = 100, Ramp2: DEV Offset = 3, DEV Word = 20792, Step Word = 80
Rev. 0 | Page 8 of 36
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5.76
08728-039
-160
5.76 -0.010
ADF4158
5.8004 5.8003
-5 0
5.8002
FREQUENCY (GHz)
5.8000 5.7999 5.7998 5.7997
POWER (dBm)
5.8001
-10
-15
-20
-25
5.7996
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5.7995 -0.010
-0.005
0 TIME (s)
0.005
0.010
-30 0.185
1.185
2.185
3.185
4.185
5.185
6.185
7.185
FREQUENCY (GHz)
Figure 11. FSK Superimposed on Rising Edge of Triangular Waveform; Ramp Settings: PFD = 32 MHz, INT = 181, FRAC = 0, DEV Offset = 4, DEV Word = 20972, Step Word = 200, CLK DIV = 10, MOD Divider = 125; FSK Settings: DEV Offset = 3, DEV Word = 4194
5.80010 5.80005 5.80000 ICP (mA)
Figure 13. RFIN Sensitivity-Average Over Temperature and VDD
6 4 2 0 -2 -4 -6 -8
TIME (ms)
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FREQUENCY (GHz)
5.79995 5.79990 5.79985
5.79980 5.79975 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
0
1
2
3 vCP (V)
4
5
6
Figure 12. FSK; Settings: Frequency Deviation = 100 kHz, Data Rate = 3 kHz
Figure 14. Charge Pump Output Characteristics
Rev. 0 | Page 9 of 36
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ADF4158 CIRCUIT DESCRIPTION
REFERENCE INPUT SECTION
The reference input stage is shown in Figure 15. SW1 and SW2 are normally closed switches. SW3 is normally open. When power-down is initiated, SW3 is closed and SW1 and SW2 are opened. This ensures that there is no loading of the REFIN pin on power-down.
POWER-DOWN CONTROL 100k TO R-COUNTER BUFFER SW3 NO
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25-BIT FIXED MODULUS
The ADF4158 has a 25-bit fixed modulus. This allows output frequencies to be spaced with a resolution of fRES = fPFD/225 where fPFD is the frequency of the phase frequency detector (PFD). For example, with a PFD frequency of 10 MHz, frequency steps of 0.298 Hz are possible. (1)
NC REFIN NC SW1
INT, FRAC, AND R RELATIONSHIP
The INT and FRAC values, in conjunction with the R-counter, make it possible to generate output frequencies that are spaced by fractions of the phase frequency detector (PFD). The RF VCO frequency (RFOUT) equation is RFOUT = fPFD x (INT + (FRAC/225)) (2) where: RFOUT is the output frequency of external voltage controlled oscillator (VCO). INT is the preset divide ratio of binary 12-bit counter (23 to 4095). FRAC is the numerator of the fractional division (0 to 225 - 1). fPFD = REFIN x [(1 + D)/(R x (1 + T))]
AVDD 2k
SW2
Figure 15. Reference Input Stage
RF INPUT STAGE
The RF input stage is shown in Figure 16. It is followed by a 2-stage limiting amplifier to generate the current-mode logic (CML) clock levels needed for the prescaler.
BIAS GENERATOR 1.6V
(3)
2k
RFINA
where: REFIN is the reference input frequency. D is the REFIN doubler bit. T is the REFIN divide-by-2 bit (0 or 1). R is the preset divide ratio of the binary, 5-bit, programmable reference counter (1 to 32).
RF N-DIVIDER FROM RF INPUT STAGE N = INT + FRAC/MOD TO PFD N-COUNTER THIRD-ORDER FRACTIONAL INTERPOLATOR
RFINB
AGND
Figure 16. RF Input Stage
08728-015
RF INT DIVIDER
The RF INT CMOS counter allows a division ratio in the PLL feedback counter. Division ratios from 23 to 4095 are allowed.
INT REG
MOD REG
FRAC VALUE
08728-016
Figure 17. RF N-Divider
R-COUNTER
The 5-bit R-counter allows the input reference frequency (REFIN) to be divided down to produce the reference clock to the PFD. Division ratios from 1 to 32 are allowed.
Rev. 0 | Page 10 of 36
ADF4158
PHASE FREQUENCY DETECTOR (PFD) AND CHARGE PUMP
The PFD takes inputs from the R-counter and N-counter and produces an output proportional to the phase and frequency difference between them. Figure 18 shows a simplified schematic of the PFD. The PFD includes a fixed delay element that sets the width of the antibacklash pulse, which is typically 3 ns. This pulse ensures that there is no dead zone in the PFD transfer function and gives a consistent reference spur level.
HIGH D1 U1 +IN CLR1 Q1 UP
INPUT SHIFT REGISTERS
The ADF4158 digital section includes a 5-bit RF R-counter, a 12-bit RF N-counter, and a 25-bit FRAC counter. Data is clocked into the 32-bit shift register on each rising edge of CLK. The data is clocked in MSB first. Data is transferred from the shift register to one of eight latches on the rising edge of LE. The destination latch is determined by the state of the three control bits (C3, C2, and C1) in the shift register. These are the three LSBs--DB2, DB1, and DB0--as shown in Figure 2. The truth table for these bits is shown in Table 6. Figure 20 and Figure 21 show a summary of how the latches are programmed.
PROGRAM MODES
DELAY U3 CHARGE PUMP CP
Table 6 and Figure 22 through Figure 29 show how to set up the program modes in the ADF4158. Several settings in the ADF4158 are double buffered. These include the LSB fractional value, R-counter value, reference doubler, current setting, and RDIV2. This means that two events must occur before the part uses a new value for any of the double-buffered settings. First, the new value is latched into the device by writing to the appropriate register. Second, a new write must be performed on Register R0. For example, updating the fractional value can involve a write to the 13 LSB bits in R1 and the 12 MSB bits in R0. R1 should be written to first, followed by the write to R0. The frequency change begins after the write to R0. Double buffering ensures that the bits written to in R1 do not take effect until after the write to R0. Table 6. C3, C2, and C1 Truth Table
C3 0 0 0 0 1 1 1 1 Control Bits C2 0 0 1 1 0 0 1 1 C1 0 1 0 1 0 1 0 1 Register R0 R1 R2 R3 R4 R5 R6 R7
HIGH
CLR2 DOWN D2 Q2
08728-017
U2 -IN
Figure 18. PFD Simplified Schematic
MUXOUT AND LOCK DETECT
The output multiplexer on the ADF4158 allows the user to access various internal points on the chip. The state of MUXOUT is controlled by the M4, M3, M2, and M1 bits (see Figure 22). Figure 19 shows the MUXOUT section in block diagram form.
THREE-STATE OUTPUT DVDD DGND R-DIVIDER OUTPUT N-DIVIDER OUTPUT MUX DIGITAL LOCK DETECT SERIAL DATA OUTPUT CLK DIVIDER OUTPUT R-DIVIDER/2 N-DIVIDER/2 DGND
08728-009
DVDD
CONTROL
MUXOUT
Figure 19. MUXOUT Schematic
Rev. 0 | Page 11 of 36
ADF4158 REGISTER MAPS
FRAC/INT REGISTER (R0)
RAMP ON
MUXOUT CONTROL 12-BIT MSB FRACTIONAL VALUE (FRAC) CONTROL BITS 12-BIT INTEGER VALUE (INT)
DB31 DB30 DB29 DB28 DB27 DB26 DB25 DB24 DB23 DB22 DB21 DB20 DB19 DB18 DB17 DB16 DB15 DB14 DB13 DB12 DB11 DB10 DB9 DB8 DB7 DB6 DB5 DB4 DB3 DB2 DB1 DB0 R1 M4 M3 M2 M1 N12 N11 N10 N9 N8 N7 N6 N5 N4 N3 N2 N1 F25 F24 F23 F22 F21 F20 F19 F18 F17 F16 F15 F14 C3(0) C2(0) C1(0)
LSB FRAC REGISTER (R1)
13-BIT LSB FRACTIONAL VALUE (FRAC) (DBB) CONTROL BITS
RESERVED
RESERVED
DB31 DB30 DB29 DB28 DB27 DB26 DB25 DB24 DB23 DB22 DB21 DB20 DB19 DB18 DB17 DB16 DB15 DB14 DB13 DB12 DB11 DB10 DB9 DB8 DB7 DB6 DB5 DB4 DB3 DB2 DB1 DB0 0 0 0 0 F13 F12 F11 F10 F9 F8 F7 F6 F5 F4 F3 F2 F1 0 0 0 0 0 0 0 0 0 0 0 0 C3(0) C2(0) C1(1)
R-DIVIDER REGISTER (R2)
REFERENCE DOUBLER DBB PRESCALER
DBB DBB CONTROL BITS
RESERVED
RESERVED
CP CURRENT SETTING
RDIV2 DBB
CSR EN
5-BIT R-COUNTER
12-BIT MOD DIVIDER
DB31 DB30 DB29 DB28 DB27 DB26 DB25 DB24 DB23 DB22 DB21 DB20 DB19 DB18 DB17 DB16 DB15 DB14 DB13 DB12 DB11 DB10 DB9 DB8 DB7 DB6 DB5 DB4 DB3 DB2 DB1 DB0 0 0 0 CR1 CPI4 CPI3 CPI2 CPI1 0 P1 U2 U1 R5 R4 R3 R2 R1 D12 D11 D10 D9 D8 D7 D6 D5 D4 D3 D2 D1 C3(0) C2(1) C1(0)
FUNCTION REGISTER (R3)
POWER-DOWN CP THREE-STATE COUNTER RESET PSK ENABLE FSK ENABLE RAMP MODE RESERVED PD POLARITY SD RESET N SEL
LDP
RESERVED
CONTROL BITS
DB31 DB30 DB29 DB28 DB27 DB26 DB25 DB24 DB23 DB22 DB21 DB20 DB19 DB18 DB17 DB16 DB15 DB14 DB13 DB12 DB11 DB10 DB9 DB8 DB7 DB6 DB5 DB4 DB3 DB2 DB1 DB0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 NS1 U12 0 0 RM2 RM1 PE1 FE1 U11 U10 U9 U8 U7 C3(0) C2(1) C1(1)
NOTES 1. DBB = DOUBLE-BUFFERED BIT(S).
Figure 20. Register Summary 1
Rev. 0 | Page 12 of 36
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ADF4158
TEST REGISTER (R4)
RESERVED READBACK TO MUXOUT
LE SEL
CLK DIV MODE
12-BIT CLOCK DIVIDER VALUE
RESERVED
CONTROL BITS
DB31 DB30 DB29 DB28 DB27 DB26 DB25 DB24 DB23 DB22 DB21 DB20 DB19 DB18 DB17 DB16 DB15 DB14 DB13 DB12 DB11 DB10 DB9 DB8 DB7 DB6 DB5 DB4 DB3 DB2 DB1 DB0 LS1 0 0 0 0 0 0 0 0 R2 R1 CK2 CK1 D12 D11 D10 D9 D8 D7 D6 D5 D4 D3 D2 D1 0 0 0 0 C3(1) C2(0) C1(0)
DEVIATION REGISTER (R5)
TX RAMP CLK FSK RAMP EN RESERVED INTERRUPT RAMP 2 EN PAR RAMP
DEV SEL
4-BIT DEV OFFSET WORD
16-BIT DEVIATION WORD
CONTROL BITS
DB31 DB30 DB29 DB28 DB27 DB26 DB25 DB24 DB23 DB22 DB21 DB20 DB19 DB18 DB17 DB16 DB15 DB14 DB13 DB12 DB11 DB10 DB9 DB8 DB7 DB6 DB5 DB4 DB3 DB2 DB1 DB0 0 0 TR1 PR1 I2 I1 FRE1 R2E1 DS1 DO4 DO3 DO2 DO1 D16 D15 D14 D13 D12 D11 D10 D9 D8 D7 D6 D5 D4 D3 D2 D1 C3(1) C2(0) C1(1)
STEP REGISTER (R6)
STEP SEL
RESERVED
20-BIT STEP WORD
CONTROL BITS
DB31 DB30 DB29 DB28 DB27 DB26 DB25 DB24 DB23 DB22 DB21 DB20 DB19 DB18 DB17 DB16 DB15 DB14 DB13 DB12 DB11 DB10 DB9 DB8 DB7 DB6 DB5 DB4 DB3 DB2 DB1 DB0 0 0 0 0 0 0 0 0 SSE1 S20 S19 S18 S17 S16 S15 S14 S13 S12 S11 S10 S9 S8 S7 S6 S5 S4 S3 S2 S1 C3(1) C2(1) C1(0)
DELAY REGISTER (R7)
DEL START EN RAMP DEL FL DEL CLK SEL RAMP DEL
RESERVED
12-BIT DELAY START DIVIDER
CONTROL BITS
DB31 DB30 DB29 DB28 DB27 DB26 DB25 DB24 DB23 DB22 DB21 DB20 DB19 DB18 DB17 DB16 DB15 DB14 DB13 DB12 DB11 DB10 DB9 DB8 DB7 DB6 DB5 DB4 DB3 DB2 DB1 DB0 0 0 0 0 0 0 0 0 0 0 0 0 0 RDF1 RD1 DC1 DSE1 DS12 DS11 DS10 DS9 DS8 DS7 DS6 DS5 DS4 DS3 DS2 DS1 C3(1) C2(1) C1(1)
NOTES 1. DBB = DOUBLE-BUFFERED BIT(S).
Figure 21. Register Summary 2
Rev. 0 | Page 13 of 36
08728-110
ADF4158
FRAC/INT REGISTER (R0) MAP
With Register R0 DB[2:0] set to [0, 0, 0], the on-chip FRAC/INT register is programmed as shown in Figure 22.
12-Bit MSB Fractional Value (FRAC)
These 12 bits, along with Bits DB[27:15] in the LSB FRAC register (Register R1), control what is loaded as the FRAC value into the fractional interpolator. This is part of what determines the overall feedback division factor. It is also used in Equation 2. These 12 bits are the most significant bits (MSB) of the 25-bit FRAC value, and Bits DB[27:15] in the LSB FRAC register (Register R1) are the least significant bits (LSB). See the RF Synthesizer: A Worked Example section for more information.
Ramp On
Setting DB31 to 1 enables the ramp, setting DB31 to 0 disables the ramp.
MUXOUT Control
The on-chip multiplexer is controlled by DB[30:27] on the ADF4158. See Figure 22 for the truth table.
12-Bit Integer Value (INT)
These 12 bits control what is loaded as the INT value. This is used to determine the overall feedback division factor. It is used in Equation 2. See the INT, FRAC, and R Relationship section for more information.
RAMP ON
MUXOUT CONTROL
12-BIT INTEGER VALUE (INT)
12-BIT MSB FRACTIONAL VALUE (FRAC)
CONTROL BITS
DB31 DB30 DB29 DB28 DB27 DB26 DB25 DB24 DB23 DB22 DB21 DB20 DB19 DB18 DB17 DB16 DB15 DB14 DB13 DB12 DB11 DB10 DB9 DB8 DB7 DB6 DB5 DB4 DB3 DB2 DB1 DB0 R1 M4 M3 M2 M1 N12 N11 N10 N9 N8 N7 N6 N5 N4 N3 N2 N1 F25 F24 F23 F22 F21 F20 F19 F18 F17 F16 F15 F14 C3(0) C2(0) C1(0)
R1 RAMP ON 0 1 RAMP DISABLED RAMP ENABLED
M4 M3 M2 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 0 0 0 0 1 1 1 1 0 0 0 0 1 1 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1
M1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1
OUTPUT THREE-STATE OUTPUT DVDD DGND R-DIVIDER OUTPUT N-DIVIDER OUTPUT RESERVED DIGITAL LOCK DETECT SERIAL DATA OUTPUT RESERVED RESERVED CLK DIVIDER OUTPUT RESERVED FAST-LOCK SWITCH R-DIVIDER/2 N-DIVIDER/2 READBACK TO MUXOUT
F25 0 0 0 0 . . . 1 1 1 1
F24 0 0 0 0 . . . 1 1 1 1
.......... .......... .......... .......... .......... .......... .......... .......... .......... .......... .......... ..........
F15 0 0 1 1 . . . 0 0 1 1
F14 0 1 0 1 . . . 0 1 0 1
MSB FRACTIONAL VALUE (FRAC)* 0 1 2 3 . . . 4092 4093 4094 4095
*THE FRAC VALUE IS MADE UP OF THE 12-BIT MSB STORED IN REGISTER R0, AND THE 13-BIT LSB REGISTER STORED IN REGISTER R1. FRAC VALUE = 13-BIT LSB + 12-BIT MSB x 213.
N12 0 0 0 0 . . . 1 1 1
N11 0 0 0 0 . . . 1 1 1
N10 0 0 0 0 . . . 1 1 1
N9 0 0 0 0 . . . 1 1 1
N8 0 0 0 0 . . . 1 1 1
N7 0 0 0 0 . . . 1 1 1
N6 0 0 0 0 . . . 1 1 1
N5 1 1 1 1 . . . 1 1 1
N4 0 1 1 1 . . . 1 1 1
N3 1 0 0 0 . . . 1 1 1
N2 1 0 0 1 . . . 0 1 1
N1 1 0 1 0 . . . 1 0 1
INTEGER VALUE (INT) 23 24 25 26 . . . 4093 4095
08728-011
4094
Figure 22. FRAC/INT Register (R0) Map
Rev. 0 | Page 14 of 36
ADF4158
LSB FRAC REGISTER (R1) MAP
With Register R1 DB[2:0] set to [0, 0, 1], the on-chip LSB FRAC register is programmed as shown in Figure 23. These 13 bits are the least significant bits (LSB) of the 25-bit FRAC value, and Bits DB[14:3] in the INT/FRAC register are the most significant bits (MSB). See the RF Synthesizer: A Worked Example section for more information.
13-Bit LSB FRAC Value
These 13 bits, along with Bits DB[14:3] in the FRAC/INT register (Register R0), control what is loaded as the FRAC value into the fractional interpolator. This is part of what determines the overall feedback division factor. It is also used in Equation 2.
Reserved Bits
All reserved bits should be set to 0 for normal operation.
RESERVED
13-BIT LSB FRACTIONAL VALUE (FRAC) (DBB)
RESERVED
CONTROL BITS
DB31 DB30 DB29 DB28 DB27 DB26 DB25 DB24 DB23 DB22 DB21 DB20 DB19 DB18 DB17 DB16 DB15 DB14 DB13 DB12 DB11 DB10 DB9 DB8 DB7 DB6 DB5 DB4 DB3 DB2 DB1 DB0 0 0 0 0 F13 F12 F11 F10 F9 F8 F7 F6 F5 F4 F3 F2 F1 0 0 0 0 0 0 0 0 0 0 0 0 C3(0) C2(0) C1(1)
F13 0 0 0 0 . . . 1 1 1 1
F12 0 0 0 0 . . . 1 1 1 1
.......... .......... .......... .......... .......... .......... .......... .......... .......... .......... .......... ..........
F2 0 0 1 1 . . . 0 0 1 1
F1 0 1 0 1 . . . 0 1 0 1
LSB FRACTIONAL VALUE (FRAC)* 0 1 2 3 . . . 8188 8189 8190 8191
08728-012
*THE FRAC VALUE IS MADE UP OF THE 12-BIT MSB STORED IN REGISTER R0, AND THE 13-BIT LSB REGISTER STORED IN REGISTER R1. FRAC VALUE = 13-BIT LSB + 12-BIT MSB x 213. NOTES 1. DBB = DOUBLE-BUFFERED BITS.
Figure 23. LSB FRAC Register (R1) Map
Rev. 0 | Page 15 of 36
ADF4158
R-DIVIDER REGISTER (R2) MAP
With Register R2 DB[2:0] set to [0, 1, 0], the on-chip R-divider register is programmed as shown in Figure 24.
RDIV2
Setting DB21 to 1 inserts a divide-by-2 toggle flip-flop between the R-counter and the PFD. This can be used to provide a 50% duty cycle signal at the PFD for use with cycle slip reduction.
Reserved Bits
All reserved bits should be set to 0 for normal operation.
Reference Doubler
Setting DB20 to 0 feeds the REFIN signal directly to the 5-bit RF R-counter, disabling the doubler. Setting this bit to 1 multiplies the REFIN frequency by a factor of 2 before feeding the signal into the 5-bit R-counter. When the doubler is disabled, the REFIN falling edge is the active edge at the PFD input to the fractional synthesizer. When the doubler is enabled, both the rising edge and falling edge of REFIN become active edges at the PFD input. The maximum allowed REFIN frequency when the doubler is enabled is 30 MHz.
CSR Enable
Setting this bit to 1 enables cycle slip reduction. This is a method for improving lock times. Note that the signal at the PFD must have a 50% duty cycle in order for cycle slip reduction to work. In addition, the charge pump current setting must be set to a minimum. See the Cycle Slip Reduction for Faster Lock Times section for more information. Also note that the cycle slip reduction feature can only be operated when the phase detector polarity setting is positive (DB6 in Register R3). It cannot be used if the phase detector polarity is set to negative.
5-Bit R-Counter
The 5-bit R-counter allows the input reference frequency (REFIN) to be divided down to produce the reference clock to the phase frequency detector (PFD). Division ratios from 1 to 32 are allowed.
Charge Pump Current Setting
DB[27:24] set the charge pump current setting (see Figure 24). Set these bits to the charge pump current that the loop filter is designed with.
12-Bit MOD Divider
Bits DB[14:3] are used to program the MOD divider, which determines the duration of the time step in ramp mode.
Prescaler (P/P + 1)
The dual-modulus prescaler (P/P + 1), along with the INT, FRAC, and MOD counters, determines the overall division ratio from the RFIN to the PFD input. Operating at CML levels, it takes the clock from the RF input stage and divides it down for the counters. It is based on a synchronous 4/5 core. When set to 4/5, the maximum RF frequency allowed is 3 GHz. Therefore, when operating the ADF4158 above 3 GHz, the prescaler must be set to 8/9. The prescaler limits the INT value. With P = 4/5, NMIN = 23. With P = 8/9, NMIN = 75.
Rev. 0 | Page 16 of 36
ADF4158
REFERENCE DOUBLER DBB
RESERVED
RESERVED
RDIV2 DBB
CSR EN
DBB CP CURRENT SETTING
PRESCALER
DBB 5-BIT R COUNTER 12-BIT MOD DIVIDER CONTROL BITS
DB31 DB30 DB29 DB28 DB27 DB26 DB25 DB24 DB23 DB22 DB21 DB20 DB19 DB18 DB17 DB16 DB15 DB14 DB13 DB12 DB11 DB10 DB9 DB8 DB7 DB6 DB5 DB4 DB3 DB2 DB1 DB0 0 0 0 CR1 CPI4 CPI3 CPI2 CPI1 0 P1 U2 U1 R5 R4 R3 R2 R1 D12 D11 D10 D9 D8 D7 D6 D5 D4 D3 D2 D1 C3(0) C2(1) C1(0)
CR1 0 1
CYCLE SLIP REDUCTION DISABLED ENABLED
U1 0 1
REFERENCE DOUBLER DISABLED ENABLED D12 0 0 0 0 . . . 1 1 1 1 D11 0 0 0 0 . . . 1 1 1 1 .......... D2 .......... .......... .......... .......... .......... .......... .......... .......... .......... .......... .......... 0 0 1 1 . . . 0 0 1 1 D1 0 1 0 1 . . . 0 1 0 1 12-BIT MOD DIVIDER VALUE 0 1 2 3 . . . 4092 4093 4094 4095
U2 0 1
R DIVIDER DISABLED ENABLED
P1 0 1
PRESCALER 4/5 8/9
ICP (mA) CPI4 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 CPI3 0 0 0 0 1 1 1 1 0 0 0 0 1 1 1 1 CPI2 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 CPI1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 5.1k 0.31 0.63 0.94 1.25 1.57 1.88 2.19 2.5 2.81 3.13 3.44 3.75 4.06 4.38 4.69 5
08728-013
R5 0 0 0 0 . . . 1 1 1 0
R4 0 0 0 0 . . . 1 1 1 0
R3 0 0 0 1 . . . 1 1 1 0
R2 0 1 1 0 . . . 0 1 1 0
R1 1 0 1 0 . . . 1 . 1 0
R-COUNTER DIVIDE RATIO 1 2 3 4
29 30 31 32
NOTES 1. DBB = DOUBLE-BUFFERED BITS.
Figure 24. R-Divider Register (R2) Map
Rev. 0 | Page 17 of 36
ADF4158
FUNCTION REGISTER (R3) MAP
With Register R3 DB[2:0] set to [0, 1, 1], the on-chip function register is programmed as shown in Figure 25.
Phase Detector (PD) Polarity
DB6 sets the phase detector polarity. When the VCO characteristics are positive, set this bit to 1. When the VCO characteristics are negative, set this bit to 0.
Reserved Bits
All reserved bits should be set to 0 for normal operation.
Power-Down
DB5 provides the programmable power-down mode. Setting this bit to 1 performs a power-down. Setting this bit to 0 returns the synthesizer to normal operation. While in software powerdown mode, the part retains all information in its registers. Only when supplies are removed are the register contents lost. When a power-down is activated, the following events occur: 1. 2. 3. 4. 5. 6. All active dc current paths are removed. The synthesizer counters are forced to their load state conditions. The charge pump is forced into three-state mode. The digital lock-detect circuitry is reset. The RFIN input is debiased. The input register remains active and capable of loading and latching data.
N SEL
This setting is used to circumvent the issue of pipeline delay between an update of the integer and fractional values in the N-counter. Typically, the INT value is loaded first, followed by the FRAC value. This can cause the N-counter value to be at an incorrect value for a brief period of time equal to the pipeline delay (about four PFD cycles). This has no effect if the INT value has not been updated. However, if the INT value has been changed, this can cause the PLL to overshoot in frequency while it tries to lock to the temporarily incorrect N value. After the correct fractional value is loaded, the PLL quickly locks to the correct frequency. Introducing an additional delay to the loading of the INT value using the N SEL bit causes the INT and FRAC values to be loaded at the same time, preventing frequency overshoot. The delay is turned on by setting Bit DB15 to 1.
Charge Pump Three-State
DB4 puts the charge pump into three-state mode when programmed to 1. It should be set to 0 for normal operation.
SD Reset
For most applications, DB14 should be set to 0. When DB14 is set to 0, the - modulator is reset on each write to Register R0. If it is not required that the - modulator be reset on each Register R0 write, set this bit to 1.
Counter Reset
DB3 is the RF counter reset bit. When this bit is set to 1, the RF synthesizer counters are held in reset. For normal operation, set this bit to 0.
Ramp Mode
DB[11:10] determine the type of generated waveform.
PSK Enable
When DB9 is set to 1, PSK modulation is enabled. When set to 0, PSK modulation is disabled.
FSK Enable
When DB8 is set to 1, FSK modulation is enabled. When set to 0, FSK modulation is disabled.
Lock Detect Precision (LDP)
When DB7 is programmed to 0, 24 consecutive PFD cycles of 15 ns must occur before digital lock detect is set. When this bit is programmed to 1, 40 consecutive reference cycles of 15 ns must occur before digital lock detect is set.
Rev. 0 | Page 18 of 36
ADF4158
POWER-DOWN CP THREE-STATE COUNTER RESET
U8 U7
RAMP MODE
RESERVED
PD POLARITY
PSK EN
FSK EN
SD RESET
N SEL
LDP
RESERVED
CONTROL BITS
DB31 DB30 DB29 DB28 DB27 DB26 DB25 DB24 DB23 DB22 DB21 DB20 DB19 DB18 DB17 DB16 DB15 DB14 DB13 DB12 DB11 DB10 DB9 DB8 DB7 DB6 DB5 DB4 DB3 DB2 DB1 DB0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 NS1 U12 0 0 RM2 RM1 PE1 FE1 U11 U10 U9 C3(0) C2(1) C1(1)
NS1 0 1
N SEL N WORD LOAD ON SDCLK N WORD LOAD DELAYED 4 CYCLES - RESET ENABLED DISABLED FE1 0 1 FSK ENABLE DISABLED ENABLED U10 0 1 PD POLARITY NEGATIVE POSITIVE U8 0 1 U11 0 U12 0 1 1 LDP 24 PFD CYCLES 40 PFD CYCLES
U7 0 1
COUNTER RESET DISABLED ENABLED
CP THREE-STATE DISABLED ENABLED
RM2 RM1 0 1 1 1 0 1 1 1
RAMP MODE CONTINUOUS SAWTOOTH CONTINUOUS TRIANGULAR SINGLE SAWTOOTH SINGLE TRIANGULAR PE1 0 1 PSK ENABLE DISABLED ENABLED U9 0 1 POWER-DOWN DISABLED ENABLED
08728-014
Figure 25. Function Register (R3) Map
Rev. 0 | Page 19 of 36
ADF4158
TEST REGISTER (R4) MAP
With Register R4 DB[2:0] set to [1, 0, 0], the on-chip test register (R4) is programmed as shown in Figure 26.
CLK DIV Mode
Depending on the settings of DB[20:19], the 12-bit clock divider may be a counter for the switched R fast-lock ramp (CLK2), or it may be turned off.
LE SEL
In some applications, it is necessary to synchronize LE with the reference signal. To do this, DB31 should be set to 1. Synchronization is done internally on the part.
12-Bit Clock Divider Value
DB[18:7] are used to program the clock divider, which determines how long the loop remains in wideband mode while the switched R fast-lock technique is used. See the Fast Lock: Loop Filter Topology section for more details.
Reserved Bits
All reserved bits should be set to 0 for normal operation.
Readback to MUXOUT
DB[22:21] enable or disable the readback to MUXOUT function. This function allows reading back the synthesizer's frequency at the moment of interrupt.
READBACK TO MUXOUT
LE SEL
RESERVED
CLK DIV MODE
12-BIT CLOCK DIVIDER VALUE
RESERVED
CONTROL BITS
DB31 DB30 DB29 DB28 DB27 DB26 DB25 DB24 DB23 DB22 DB21 DB20 DB19 DB18 DB17 DB16 DB15 DB14 DB13 DB12 DB11 DB10 DB9 DB8 DB7 DB6 DB5 DB4 DB3 DB2 DB1 DB0 LS1 0 0 0 0 0 0 0 0 R2 R1 CK2 CK1 D12 D11 D10 D9 D8 D7 D6 D5 D4 D3 D2 D1 0 0 0 0 C3(1) C2(0) C1(0)
LS1 0 1
LE SEL LE FROM PIN LE SYNC WITH REF
R2 R1 0 1 0 0
READBACK TO MUXOUT DISABLED ENABLED D12 0 0 0 0 . . . 1 1 1 1 D11 0 0 0 0 . . . 1 1 1 1 .......... D2 .......... .......... .......... .......... .......... .......... .......... .......... .......... .......... .......... 0 0 1 1 . . . 0 0 1 1 D1 0 1 0 1 . . . 0 1 0 1 CLOCK DIVIDER VALUE 0 1 2 3 . . . 4092 4093 4094 4095
CK2 CK1 CLOCK DIVIDER MODE 0 0 1 1 0 1 0 1 CLOCK DIVIDER OFF FAST-LOCK DIVIDER RESERVED RAMP DIVIDER
Figure 26. Test Register (R4) Map
Rev. 0 | Page 20 of 36
08728-115
ADF4158
DEVIATION REGISTER (R5) MAP
With Register R5 DB[2:0] set to [1, 0, 1], the on-chip deviation register is programmed as shown in Figure 27.
FSK Ramp Enable
Setting DB25 to 1 enables the FSK ramp. Setting DB25 to 0 disables the FSK ramp.
Reserved Bits
All reserved bits should be set to 0 for normal operation.
Ramp 2 Enable
Setting DB24 to 1 enables the second ramp. Setting DB24 to 0 disables the second ramp.
Tx Ramp CLK
Setting DB29 to 0 uses the clock divider clock for clocking the ramp. Setting DB29 to 1 uses the Tx data clock for clocking the ramp.
Deviation Select
Setting DB23 to 0 chooses the first deviation word. Setting DB23 to 1, chooses the second deviation word.
PAR Ramp
Setting DB28 to 1 enables the parabolic ramp. Setting DB28 to 0 disables the parabolic ramp.
4-Bit Deviation Offset Word
DB[22:19] determine the deviation offset. The deviation offset affects the deviation resolution.
Interrupt
DB[27:26] determine which type of interrupt is used. This feature is used for reading back the INT and FARC value of a ramp at a given moment in time (rising edge on the TXDATA pin triggers the interrupt). From these bits, frequency can be obtained. After readback, the sweep might continue or stop at the readback frequency.
16-Bit Deviation Word
DB[18:3] determine the signed deviation word. The deviation word defines the deviation step.
FSK RAMP EN
TX RAMP CLK
INTERRUPT
RESERVED
RAMP 2 EN
PAR RAMP
DEV SEL
4-BIT DEV OFFSET WORD
16-BIT DEVIATION WORD
CONTROL BITS
DB31 DB30 DB29 DB28 DB27 DB26 DB25 DB24 DB23 DB22 DB21 DB20 DB19 DB18 DB17 DB16 DB15 DB14 DB13 DB12 DB11 DB10 DB9 DB8 DB7 DB6 DB5 DB4 DB3 DB2 DB1 DB0
0 0 TR1 PR1 I2 I1 FRE1 R2E1 DS1 DO4 DO3 DO2 DO1 D16 D15 D14 D13 D12 D11 D10 D9 D8 D7 D6 D5 D4 D3 D2 D1 C3(1) C2(0) C1(1)
FRE1 FSK RAMP ENABLE TR1 TX RAMP CLK 0 1 CLK DIV TX DATA PR1 0 1 PAR RAMP DISABLED ENABLED 0 1 DISABLED ENABLED
DS1 0 1
DEV SEL DEV WORD 1 DEV WORD 2
D16 0 . 0 0 0 0 1 1 1 . 1
D14 1 . 0 0 0 0 1 1 1 . 0
.......... D2 .......... .......... .......... .......... .......... .......... .......... .......... .......... .......... .......... 1 . 1 1 0 0 1 1 0 . 0
D1 1 . 1 0 1 0 1 0 1 . 0
16-BIT DEVIATION WORD 32,767 . 3 2 1 0 -1 -2 -3 . -32,768
I2 0 0 1 1
I1 0 1 0 1
INTERRUPT INTERRUPT OFF LOAD CHANNEL CONTINUE SWEEP NOT USED LOAD CHANNEL STOP SWEEP
DO4 0 0 0 0 . . . 1 1 1
R2E1 0 1
RAMP 2 ENABLE DISABLED ENABLED
DO3 0 0 0 0 . . . 1 1 1
DO2 0 0 1 1 . . . 0 1 1
DO1 0 1 0 1 . . . 1 0 1
4-BIT DEV OFFSET WORD 0 1 2 3
13 14 15
07828-116
Figure 27. Deviation Register (R5) Map
Rev. 0 | Page 21 of 36
ADF4158
STEP REGISTER (R6) MAP
With Register R6 DB[2:0] set to [1, 1, 0], the on-chip step register is programmed as shown in Figure 28.
Step SEL
Setting DB23 to 0 chooses Step Word 1. Setting DB23 to 1 chooses Step Word 2.
Reserved Bits
All reserved bits should be set to 0 for normal operation.
20-Bit Step Word
DB[22:3] determine the step word. Step word is a number of steps in the ramp.
DEL START EN
RAMP DEL FL
DEL CLK SEL
RAMP DEL
RESERVED
12-BIT DELAY START WORD
CONTROL BITS
DB31 DB30 DB29 DB28 DB27 DB26 DB25 DB24 DB23 DB22 DB21 DB20 DB19 DB18 DB17 DB16 DB15 DB14 DB13 DB12 DB11 DB10 DB9 DB8 DB7 DB6 DB5 DB4 DB3 DB2 DB1 DB0 0 0 0 0 0 0 0 0 0 0 0 0 0 RDF1 RD1 DC1 DSE1 DS12 DS11 DS10 DS9 DS8 DS7 DS6 DS5 DS4 DS3 DS2 DS1 C3(1) C2(1) C1(1)
RDF1 0 1
RAMP DELAY FAST LOCK DISABLED ENABLED RD1 0 1 RAMP DELAY DISABLED ENABLED DC1 0 1
DSE1 0 1
DEL START ENABLE DISABLE ENABLE
DS12 DS11 .......... DS2 DS1
0 0 0 0 . . . 1 1 1 1 0 0 0 0 . . . 1 1 1 1 .......... 0 .......... 0 .......... 1 .......... 1 .......... . .......... . .......... . .......... 0 .......... 0 .......... 1 .......... 1 0 1 0 1 . . . 0 1 0 1
12-BIT DELAY START WORD 0 1 2 3 . . . 4092 4093 4094 4095
DEL CLK SEL PFD CLK PFD x MOD_DIV CLK
Figure 28. Step Register (R6) Map
Rev. 0 | Page 22 of 36
08728-118
ADF4158
DELAY REGISTER (R7) MAP
With Register R7 DB[2:0] set to [1, 1, 1], the on-chip delay register is programmed as shown in Figure 29.
Delay Clock Select
Setting DB16 to 0 selects the PFD clock as the delay clock. Setting DB16 to 1 selects PFD x MOD_DIV (MOD_DIV set by DB[14:3] in Register R2) as delay clock.
Reserved Bits
All reserved bits should be set to 0 for normal operation.
Delayed Start Enable
Setting DB15 to 1 enables delayed start. Setting DB15 to 0 disables delayed start.
Ramp Delay Fast Lock
Setting DB18 to 1 enables the ramp delay fast-lock function. Setting DB18 to 0 disables this function.
12-Bit Delayed Start Word
DB[14:3] determine the delay start word. The delay start word affects the duration of the ramp start delay.
Ramp Delay
Setting DB17 to 1 enables the ramp delay function. Setting DB17 to 0 disables this function.
DEL START EN
RAMP DEL FL
DEL CLK SEL
RAMP DEL
RESERVED
12-BIT DELAY START WORD
CONTROL BITS
DB31 DB30 DB29 DB28 DB27 DB26 DB25 DB24 DB23 DB22 DB21 DB20 DB19 DB18 DB17 DB16 DB15 DB14 DB13 DB12 DB11 DB10 DB9 DB8 DB7 DB6 DB5 DB4 DB3 DB2 DB1 DB0 0 0 0 0 0 0 0 0 0 0 0 0 0 RDF1 RD1 DC1 DSE1 DS12 DS11 DS10 DS9 DS8 DS7 DS6 DS5 DS4 DS3 DS2 DS1 C3(1) C2(1) C1(1)
RDF1 0 1
RAMP DELAY FAST LOCK OFF ON RD1 0 1 RAMP DELAY OFF ON DC1 0 1
DSE1 0 1
DEL START ENABLE DISABLE ENABLE
DS12 DS11 .......... DS2 DS1 0 0 0 0 . . . 1 1 1 1 0 0 0 0 . . . 1 1 1 1 .......... 0 .......... 0 .......... 1 .......... 1 .......... . .......... . .......... . .......... 0 .......... 0 .......... 1 .......... 1 0 1 0 1 . . . 0 1 0 1
12-BIT DELAY START WORD 0 1 2 3 . . . 4092 4093 4094 4095
DEL CLK SEL PFD CLK PFD x MOD_DIV CLK
Figure 29. Delay Register (R7) Map
Rev. 0 | Page 23 of 36
08728-118
ADF4158 APPLICATIONS INFORMATION
INITIALIZATION SEQUENCE
After powering up the part, administer the following programming sequence: 1. 2. 3. 4. 5. 6. 7. 8. Delay register (R7) Step register (R6)--load the step register (R6) twice, first with STEP SEL = 0 and then with STEP SEL = 1 Deviation register (R5)--load the deviation register (R5) twice, first with DEV SEL = 0 and then with DEV SEL = 1 Test register (R4) Function register (R3) R-divider register (R2) LSB FRAC register (R1) FRAC/INT register (R0)
REFERENCE DOUBLER AND REFERENCE DIVIDER
The reference doubler on chip allows the input reference signal to be doubled. This is useful for increasing the PFD comparison frequency. Making the PFD frequency higher improves the noise performance of the system. Doubling the PFD frequency usually improves noise performance by 3 dB. It is important to note that the PFD cannot be operated above 32 MHz due to a limitation in the speed of the - circuit of the N-divider.
CYCLE SLIP REDUCTION FOR FASTER LOCK TIMES
In fast-locking applications, a wide loop filter bandwidth is required for fast frequency acquisition, resulting in increased integrated phase noise and reduced spur attenuation. Using cycle slip reduction, the loop bandwidth can be kept narrow to reduce integrated phase noise and attenuate spurs while still realizing fast lock times.
RF SYNTHESIZER: A WORKED EXAMPLE
The following equation governs how the synthesizer should be programmed: RFOUT = [N + (FRAC/225)] x [fPFD] where: RFOUT is the RF frequency output. N is the integer division factor. FRAC is the fractionality. fPFD = REFIN x [(1 + D)/(R x (1 + T))] where: REFIN is the reference frequency input. D is the RF REFIN doubler bit. R is the RF reference division factor. T is the reference divide-by-2 bit (0 or 1). For example, in a system where a 5.8002 GHz RF frequency output (RFOUT) is required and a 10 MHz reference frequency input (REFIN) is available, the frequency resolution is fRES = REFIN/225 fRES = 10 MHz/2 = 0.298 Hz From Equation 5, fPFD = [10 MHz x (1 + 0)/1] = 10 MHz 5.8002 GHz = 10 MHz x (N + FRAC/225) Calculating N and FRAC values, N = int(RFOUT/fPFD) = 580 FRAC = FMSB x 213 + FLSB FMSB = int(((RFOUT/fPFD) - N) x 212) = 81 FLSB = int(((((RFOUT/fPFD) - N) x 212) - FMSB) x 213) = 7537 where: FMSB is the 12-bit MSB FRAC value in Register R0. FLSB is the 13-bit LSB FRAC value in Register R1. int() makes an integer of the argument in parentheses.
25
(4)
Cycle Slips
Cycle slips occur in integer-N/fractional-N synthesizers when the loop bandwidth is narrow compared with the PFD frequency. The phase error at the PFD inputs accumulates too fast for the PLL to correct, and the charge pump temporarily pumps in the wrong direction, slowing down the lock time dramatically. The ADF4158 contains a cycle slip reduction circuit to extend the linear range of the PFD, allowing faster lock times without loop filter changes. When the ADF4158 detects that a cycle slip is about to occur, it turns on an extra charge pump current cell. This outputs a constant current to the loop filter or removes a constant current from the loop filter (depending on whether the VCO tuning voltage needs to increase or decrease to acquire the new frequency). The effect is that the linear range of the PFD is increased. Stability is maintained because the current is constant and is not a pulsed current.
(5)
(6)
If the phase error increases again to a point where another cycle slip is likely, the ADF4158 turns on another charge pump cell. This continues until the ADF4158 detects that the VCO frequency has gone past the desired frequency. It then begins to turn off the extra charge pump cells one by one until they are all turned off and the frequency is settled. Up to seven extra charge pump cells can be turned on. In most applications, it is enough to eliminate cycle slips altogether, giving much faster lock times.
Rev. 0 | Page 24 of 36
ADF4158
Setting Bit DB28 in the R-divider register (Register R2) to 1 enables cycle slip reduction. Note that a 45% to 55% duty cycle is needed on the signal at the PFD in order for CSR to operate correctly. The reference divide-by-2 flip-flop can help to provide a 50% duty cycle at the PFD. For example, if a 100 MHz reference frequency is available and the user wants to run the PFD at 10 MHz, setting the R-divide factor to 10 results in a 10 MHz PFD signal that is not 50% duty cycle. By setting the R-divide factor to 5 and enabling the reference divide-by-2 bit, a 50% duty cycle 10 MHz signal can be achieved. Note that the cycle slip reduction feature can only be operated when the phase detector polarity setting is positive (DB6 in Register R3). It cannot be used if the phase detector polarity is negative.
WAVEFORM GENERATION
The ADF4158 is capable of generating four types of waveforms in the frequency domain: single ramp burst, single sawtooth burst, sawtooth ramp, and triangular ramp. Figure 30 through Figure 33 show the types of waveforms available.
FREQUENCY
TIME
Figure 30. Single Ramp Burst
MODULATION
FREQUENCY
The ADF4158 can operate in frequency shift keying (FSK) or phase shift keying (PSK) mode.
Frequency Shift Keying (FSK)
FSK is implemented by setting the ADF4158 N-divider up for the center frequency and then toggling the TXDATA pin. The deviation from the center frequency is set by fDEV = (fPFD/2 ) x (DEV x 2 where: DEV is a 16-bit word. DEV_OFFSET is a 4-bit word. fPFD is the PFD frequency. The ADF4158 implements this by incrementing or decrementing the set N-divide value by DEV x 2DEV_OFFSET.
25 DEV_OFFSET
TIME
)
(7)
Figure 31. Single Sawtooth Burst
FREQUENCY
Phase Shift Keying (PSK)
When the ADF4158 is set up in PSK mode, it is possible to toggle the output phase of the ADF4158 between 0 and 180. The TXDATA pin controls the phase.
TIME
Figure 32. Sawtooth Ramp
FSK Settings Worked Example
For example, take an FSK system operating at 5.8 GHz, with a 25 MHz PFD, 250 kHz deviation and DEV_OFFSET = 4. Rearrange Equation 4 as follows DEV = f DEV f PFD x 2 DEV _ OFFSET 2 25 (8)
TIME
FREQUENCY
Figure 33. Triangular Ramp
DEV =
250 kHz = 20,971.52 25 MHz x 24 2 25
The DEV value is rounded to 20,972. Toggling the TXDATA pin causes the frequency to hop between 250 kHz frequencies from the programmed center frequency.
Rev. 0 | Page 25 of 36
08728-020
08728-019
08728-021
08728-022
ADF4158
Waveform Deviations and Timing
Figure 34 shows a version of a burst or ramp. The key parameters that define a burst or ramp are * * * Frequency deviation Timeout interval Number of steps
TIMER
Single Sawtooth Burst
In the single sawtooth burst, the N-divide value is reset to its initial value on the next timeout interval after the number of steps has taken place. The ADF4158 retains this N-divide value.
Sawtooth Ramp
The sawtooth ramp is a repeated version of the single sawtooth burst. The waveform repeats until the ramp is disabled.
Triangular Ramp
FREQUENCY
fDEV
TIME
Figure 34. Waveform Timing
The triangular ramp is similar to the single ramp burst. However, when the steps have been completed, the ADF4158 begins to decrement the N-divide value by DEV x 2DEV_OFFSET on each timeout interval. When the number of steps has again been completed, it reverts to incrementing the N-divide value. Repeating this creates a triangular waveform. The waveform repeats until the ramp is disabled.
08728-023
Frequency Deviation
The frequency deviation for each frequency hop is set by fDEV = (fPFD/225) x (DEV x 2DEV_OFFSET) where: DEV is a 16-bit word. DEV_OFFSET is a 4-bit word. (9)
FMCW Radar Ramp Settings Worked Example
Take as an example, an FMCW radar system requiring the RF LO to sawtooth ramp over a 50 MHz range every 2 ms. The PFD frequency is 25 MHz, and the RF output range is 5800 MHz to 5850 MHz. The frequency deviation for each hop in the ramp is set to ~250 kHz. The frequency resolution of ADF4158 is calculated as follows: fRES = fPFD/225 (10) Numerically: fRES = 25 MHz/225 = 0.745 Hz The DEV_OFFSET is calculated after rearranging Equation 9: DEV_OFFSET = log2(fDEV/(fRES x DEVMAX)) (12) Expressed in log10(x), Equation 10 can be transformed into the following equation: DEV_OFFSET = log10(fDEV/(fRES x DEVMAX))/log10(2) where: DEVMAX = 215 - Maximum of the Deviation Word. fDEV = frequency deviation. DEV_OFFSET = a 4-bit word. Using Equation 13, DEV_OFFSET is calculated as follows DEV_OFFSET = log10(250 kHz/(0.745 Hz x 215))/log10(2) = 3.356 After rounding, DEV_OFFSET = 4. From DEV_OFFSET, the resolution of frequency deviation can be calculated as follows fDEV_RES = fRES x 2DEV_OFFSET fDEV_RES = 0.745 Hz x 2 = 11.92 Hz
4
Timeout Interval
The time between each frequency hop is set by Timer = CLK1 x CLK2 x (1/fPFD) where: CLK1 and CLK2 are 12-bit clock values (12-bit MOD divider in R2, 12-bit clock divider in R4--CLK DIV set as RAMP DIV). fPFD is the PFD frequency.
(11)
Number of Steps
A 20-bit step value defines the number of frequency hops that take place. The INT value cannot be incremented by more than 28 from its starting value.
(13)
Single Ramp Burst
The most basic waveform is the single ramp burst. All other waveforms are slight variations on this. In the single ramp burst, the ADF4158 is locked to the frequency defined in the FRAC/INT register. When the ramp mode is enabled, the ADF4158 increments the N-divide value by DEV x 2DEV_OFSET, causing a frequency shift, fDEV, on each timer interval. This happens until the set number of steps has taken place. The ADF4158 then retains the final N-divide value.
(14)
Rev. 0 | Page 26 of 36
ADF4158
To calculate the DEV word, use Equation 12. DEV = fDEV/(fRES x 2DEV_OFFSET) (15)
DEV =
fDEV = (25 MHz/225) x (20,972 x 24) = 249.986 kHz The number of fDEV steps required to cover the 50 MHz range is 50 MHz/249.986 kHz = 200. To cover the 50 MHz range in 2 ms, the ADF4158 must hop every 2 ms/200 = 10 s. Rearrange Equation 10 to set the timer value (and fix CLK2 to 1): CLK1 = Timer x fPFD/CLK2 = 10 s x 25 MHz /1 = 250 To summarize the settings: DEV = 20,972, number of steps = 200, CLK1 = 250, CLK2 = 1. Using these settings, program the ADF4158 to a center frequency of 5800 MHz, and enable the sawtooth ramp to produce the required waveform. If a triangular ramp was used with the same settings, the ADF4158 would sweep from 5800 MHz to 5850 MHz and back down again. The entire sweep would take 4 ms.
TIME
Figure 35. Dual Sweep Rate
Ramp Mode with FSK Signal on Ramp
In traditional approaches a FMCW radars used either linear frequency modulation (LFM) or FSK modulation. These modulations used separately introduce ambiguity between measured distance and velocity, especially in multitarget situations. To overcome this issue and enable unambiguous (range - velocity) multitarget detection, use a ramp with FSK on it.
Example
For example, if
* * *
Activating the Ramp
After setting all of the previous parameters, the ramp must be activated. It is achieved by choosing the desired type of ramp (DB[11:10] in Register R3) and starting the ramp (DB31 = 1 in Register R0).
PLL is locked to 5790 MHz. There are 100 steps each of which lasts 10 s and has a deviation of 100 kHz. The FSK signal is 25 kHz.
Then, 1. Program the ramp as described in the FMCW Radar Ramp Settings Worked Example section. While doing that DB23 in Register R5 and DB23 in Register R6 should be set to 0. Set the bits in Register R5 as follows to program FSK on ramp to 25 kHz: DB[18:3] = 4194 (deviation word), DB[22:19] = 3 (deviation offset), DB23 = 1 (deviation select for FSK on ramp), and DB25 = 1 (ramp with FSK enabled).
ADDITIONAL FEATURES
Two Ramp Rates
This feature allows for two ramps with different step and deviation settings. It also allows the ramp rate to be reprogrammed while another ramp is running.
2.
Example
For example, if
* * *
Then, 1. 2. DB24 in Register R5 should be set to 1, which activates Ramp 2 rates mode. Program Ramp 1 and Ramp 2 as follows to get two ramp rates: Ramp 1: Register R5 DB[18:3] = 16,777, DB[22:19] = 3 with DB23 = 0; Register R6 DB[22:3] = 100, DB23 = 0. Ramp 2: Register R5 DB[18:3] = 20,972, DB[22:19] = 3 with DB23 = 1; Register R6 DB[22:3] = 80, DB23 = 1.
FSK SHIFT
LFM STEP = FREQUENCY SWEEP/(N - 1)
FREQUENCY SWEEP
PLL is locked to 5790 MHz. Ramp 1 jumps 100 steps, each of which lasts 10 s and has a frequency deviation of 100 kHz. Ramp 2 jumps 80 steps, each of which lasts 10 s and has a frequency deviation of 125 kHz.
An example of ramp with FSK on the top of it is shown in Figure 36. Eventually, the ramp must be activated as described in Activating the Ramp section.
FREQUENCY
0 TIME
RAMP END
Figure 36. Combined FSK and LFM Waveform (N Corresponds to the Number of LFM Steps)
Rev. 0 | Page 27 of 36
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08728-024
Rounding this to 20,972 and recalculating using Equation 9 to get the actual deviation frequency, fDEV, thus produces the following:
FREQUENCY
250 kH z = 20,971.52 25 MHz 4 x2 2 25
The resulting ramp with two various rates is shown in Figure 35. Eventually, the ramp must be activated as described in Activating the Ramp section.
SWEEP RATE SET BY OTHER REGISTER
SWEEP RATE SET BY ONE REGISTER
ADF4158
Delayed Start
A delayed start can be used with two different parts to control the start time. The idea of delayed start is shown in Figure 37.
RAMP WITHOUT DELAYED START
Example
For example, to add a delay between bursts in a ramp, 1. 2. Set DB17 in Register R7 to 1 to enable delay between ramps option. Set Bit DB16 in Register R7 to 0 and the 12-bit delay start word (DB[14:3] in Register R7) to 125 to delay the ramp by 5 s. The delay is calculated as follows: Delay = tPFD x Delay Start Word = 40 ns x 125 = 5 s If a longer delay is needed, for example, 125 s, Bit DB16 in Register R7 should be set to 1 and the 12-bit delay start word (DB[14:3] in Register R7) should be set to 125. The delay is calculated as follows Delay = tPFD x MOD x Delay Start Word = 40 ns x 25 x 125 = 125 s There is also a possibility to activate fast-lock operation for the first period of delay. This is done by setting Bit DB18 in Register R7 to 1. This feature is useful for sawtooth ramps to mitigate the frequency overshoot on the transition from one sawtooth to the next. Eventually, the ramp must be activated as described in Activating the Ramp section.
FREQUENCY
TIME
Figure 37. Delayed Start of Sawtooth Ramp
Example
For example, to program a delayed start with two different parts to control the start time, 1. 2. Set DB15 in Register R7 to 1 to enable the delayed start of ramp option. Set Bit DB16 in Register R7 to 0 and the 12-bit delay start word (DB[14:3] in Register R7) to 125 to delay the ramp on the first part is delayed by 5 s. The delay is calculated as follows: Delay = TPFD x Delay Start Word = 40 ns x 125 = 5 s 3. Set Bit DB16 in Register R7 to 1 and the 12-bit delay start word (DB[14:3] in Register R7) to 125 to delay the ramp on the second part is delayed by 125 s. Use the following formula for calculating the delay: Delay = tPFD x MOD x Delay Start Word = 40 ns x 25 x 125 = 125 s Eventually, the ramp must be activated as described in Activating the Ramp section.
08728-126
RAMP WITH DELAYED START
Nonlinear Ramp Mode
The ADF4158 is capable of generating a parabolic ramp. The output frequency is generated according to the following equation: fOUT(n + 1) = fOUT(n) + n x fDEV where: fOUT is output frequency. fDEV is frequency deviation. n is step number. (16)
Delay Between Ramps
FREQUENCY
This feature adds a delay between bursts in ramp. Figure 38 shows a delay between ramps in sawtooth mode.
FREQUENCY
DELAY
TIME
08728-028
Figure 39. Parabolic Ramp
TIME
Figure 38. Delay Between Ramps for Sawtooth Mode
Rev. 0 | Page 28 of 36
08728-029
ADF4158
The following example explains how to set up and use this function.
Table 7. Interrupt Modes
Mode DB[27:26] = 00 DB[27:26] = 01 DB[27:26] = 11 Action Interrupt is off Interrupt on TXDATA, sweep continues Interrupt on TXDATA, sweep stops
Example
fOUT = 5790 MHz fDEV = 100 kHz Number of steps = 50 Duration of a single step = 10 s Ramp mode must be either triangular (Register R3, DB[11:10] = 01) or single triangular (Register R3, DB[11:10] = 11). In the first case, the generated frequency range is calculated as follows: f = fDEV x (Number of Steps + 2) x (Number of Steps + 1)/2 = 132.6 MHz In the second case, the generated frequency range is calculated as follows: f = fDEV x (Number of Steps + 1) x Number of Steps/2 = 127.5 MHz The timer is set in the same way as for its linear ramps described in the Waveform Generation section. Activation of the parabolic ramp is achieved by setting Bit DB28 in Register R5 to 1. Next the counter reset (DB3 in Register R3) should be set first to 1 and then to 0. Eventually, the ramp must be activated as described in the Activating the Ramp section.
When an interrupt takes place, the data consisting of the INT and FRAC values can be read back via MUXOUT. The data is made up of 37 bits, 12 of which represent the INT value and 25 the FRAC value. The idea of frequency readback is shown in Figure 40.
FREQUENCY AT WHICH INTERRUPT TOOK PLACE
FREQUENCY
1
2
TIME TIME OF INTERRUPT 1. SWEEP CONTINUES MODE 2. SWEEP STOPS MODE
INTERRUPT SIGNAL
LOGIC LEVEL
LOGIC HIGH
TIME
Figure 40. Interrupt and Frequency Readback
Interrupt Modes and Frequency Readback
Interrupt modes are triggered from the rising edge of TXDATA. Depending on the settings of DB[27:26] in Register R5, the modes in Table 7 are activated.
Note that DB[22:21] in Register R4 should be set to 2 and DB[30:27] in Register R0 (MUXOUT control) should be set to 15 (1111). The mechanism of how single bits are read back is shown in Figure 41.
DATA CLOCKED OUT ON POSITIVE EDGE OF CLK AND READ ON NEGATIVE EDGE OF CLK READBACK WORD (37 BITS) 0 0001 1100 1111 0110 0010 0011 1010 0111 1000 (HEX01CF623A78) TXDATA LE CLK MUXOUT MSB 12-BIT INT WORD 0000 1110 0111 0E7 231 25-BIT FRAC WORD 1 0110 0010 0011 1010 0111 1000 1623A78 23214712 LSB
RF = fPFD x (231 + 23214712/2 25) = 1.7922963GHz = 1.846V V TUNE
Figure 41. Reading Back Single Bits to Determine the Output Frequency at the Moment of Interrupt
Rev. 0 | Page 29 of 36
08728-031
08728-030
LOGIC LOW
ADF4158
TXDATA 32 CLK PULSES CLK FREQUENCY READBACK MUXOUT R0 WRITE DATA R4 WRITE R4 WRITE FREQUENCY READBACK FREQUENCY READBACK 37 CLK PULSES 32 CLK PULSES 37 CLK PULSES 32 CLK PULSES 37 CLK PULSES
Figure 42. Continuous Frequency Readback
For continuous frequency readback the following sequence should be used: * * * * Register 0 write LE high Pulse on TXDATA Frequency readback (as described at the beginning of the Interrupt Modes and Frequency Readback section and Figure 41) Pulse on TXDATA Register R4 write Frequency readback (as described at the beginning of the Interrupt Modes and Frequency Readback section and Figure 41) Pulse on TXDATA ...
In addition, note that the fast-lock feature doesn't work in ramp mode.
FAST LOCK: AN EXAMPLE
If a PLL has a reference frequency of 13 MHz, that is, fPFD = 13 MHz, as well as MOD = 10 (12-bit MOD divider in Register R2) and a required lock time of 50 s, the PLL is set to wide bandwidth for 40 s. If the time period set for the wide bandwidth is 40 s, then Fast-Lock Timer Value = Time in Wide Bandwidth x fPFD/MOD Fast-Lock Timer Value = 40 s x 13 MHz /10 = 52. Therefore, 52 must be loaded into the clock divider value in Register R4 in Step 1 of the sequence described in the Fast-Lock Timer and Register Sequences section.
* * *
* *
FAST LOCK: LOOP FILTER TOPOLOGY
To use fast-lock mode, an extra connection from the PLL to the loop filter is needed. The damping resistor in the loop filter must be reduced to 1/4 of its value while in wide bandwidth mode. This is required because the charge pump current is increased by 16 while in wide bandwidth mode, and stability must be ensured. To further enhance stability and mitigate frequency overshoot while frequency change (in wide bandwidth mode), Register R3 is connected. During fast lock, the SW1 pin is shorted to ground and SW2 is connected to CP (it is done by setting Bits DB[20:19] in Register R4 to 01--fast lock divider). The following two topologies can be used: * * Divide the damping resistor (R1) into two values (R1 and R1A) that have a ratio of 1:3 (see Figure 43). Connect an extra resistor (R1A) directly from SW1, as shown in Figure 44. The extra resistor must be chosen such that the parallel combination of an extra resistor and the damping resistor (R1) is reduced to 1/4 of the original value of R1.
The sequence is also shown in Figure 42.
FAST-LOCK TIMER AND REGISTER SEQUENCES
If the fast-lock mode is used, a timer value needs to be loaded into the PLL to determine the time spent in wide bandwidth mode. When the DB[20:19] bits in Register 4 (R4) are set to 01 (fastlock divider), the timer value is loaded via the 12-bit clock divider value. To use fast lock, the PLL must be written to in the following sequence: 1. Initialization sequence (see the Initialization Sequence section). This should only be performed once after powering up the part. Load Register R4 DB[16:15] = 01 and the chosen fast-lock timer value (DB[18:7]). Load Register R2 with the chosen MOD divider value (DB[14:3]) if longer time in wide loop bandwidth is required.
2. 3.
Note that the duration that the PLL remains in wide bandwidth is equal to the MOD x fast-lock timer/fPFD, where MOD is the 12-bit MOD divider in Register R2.
For both of the topologies, the ratio R3:R2 should equal 1:4.
Rev. 0 | Page 30 of 36
08728-144
LE
ADF4158
ADF4158
SW2 CP C1 C2 R1 SW1 R1A
08728-032
R3 R2 C3 VCO
Reference Spurs
Reference spurs are generally not a problem in fractional-N synthesizers because the reference offset is far outside the loop bandwidth. However, any reference feedthrough mechanism that bypasses the loop can cause a problem. One such mechanism is the feedthrough of low levels of on-chip reference switching noise out through the RFIN pins back to the VCO, resulting in reference spur levels as high as -90 dBc. Take care in the PCB layout to ensure that the VCO is well separated from the input reference to avoid a possible feedthrough path on the board.
Figure 43. Fast-Lock Loop Filter Topology--Topology 1
ADF4158
SW2 CP C1 C2 R1 R1A SW1
LOW FREQUENCY APPLICATIONS
R3 R2 C3 VCO
08728-033
The specification on the RF input is 0.5 GHz minimum; however, RF frequencies lower than this can be used if the minimum slew rate specification of 400 V/s is met. An appropriate LVDS driver can be used to square up the RF signal before it is fed back to the ADF4158 RF input. The FIN1001 from Fairchild Semiconductor is one such LVDS driver.
FILTER DESIGN--ADIsimPLL
A filter design and analysis program is available to help the user implement PLL design. Visit www.analog.com/pll for a free download of the ADIsimPLLTM software. This software designs, simulates, and analyzes the entire PLL frequency domain and time domain response. Various passive and active filter architectures are allowed.
Figure 44. Fast-Lock Loop Filter Topology--Topology 2
SPUR MECHANISMS
The fractional interpolator in the ADF4158 is a third-order - modulator (SDM) with a 25-bit fixed modulus (MOD). The SDM is clocked at the PFD reference rate (fPFD) that allows PLL output frequencies to be synthesized at a channel step resolution of fPFD/MOD. The various spur mechanisms possible with fractional-N synthesizers and how they affect the ADF4158 are discussed in this section.
PCB DESIGN GUIDELINES FOR THE CHIP SCALE PACKAGE
The lands on the chip scale package (CP-24) are rectangular. The printed circuit board (PCB) pad for these should be 0.1 mm longer than the package land length and 0.05 mm wider than the package land width. Center the land on the pad. This ensures that the solder joint size is maximized. The bottom of the chip scale package has a central thermal pad. The thermal pad on the PCB should be at least as large as this exposed pad. On the PCB, there should be a clearance of at least 0.25 mm between the thermal pad and the inner edges of the pad pattern. This ensures that shorting is avoided. Thermal vias can be used on the PCB thermal pad to improve the thermal performance of the package. If vias are used, they should be incorporated into the thermal pad at 1.2 mm pitch grid. The via diameter should be between 0.3 mm and 0.33 mm, and the via barrel should be plated with 1 ounce of copper to plug the via. Connect the PCB thermal pad to AGND.
Fractional Spurs
In most fractional synthesizers, fractional spurs can appear at the set channel spacing of the synthesizer. In the ADF4158, these spurs do not appear. The high value of the fixed modulus in the ADF4158 makes the SDM quantization error spectrum look like broadband noise, effectively spreading the fractional spurs into noise.
Integer Boundary Spurs
Interactions between the RF VCO frequency and the PFD frequency can lead to spurs known as integer boundary spurs. When these frequencies are not integer related (which is the purpose of the fractional-N synthesizer), spur sidebands appear on the VCO output spectrum at an offset frequency that corresponds to the beat note or difference frequency between an integer multiple of the PFD and the VCO frequency. These spurs are named integer boundary spurs because they are more noticeable on channels close to integer multiples of the PFD where the difference frequency can be inside the loop bandwidth. These spurs are attenuated by the loop filter.
Rev. 0 | Page 31 of 36
ADF4158 APPLICATION OF ADF4158 IN FMCW RADAR
The application of ADF4158 in FMCW radar is shown in Figure 45.
NO DDS REQUIRED WITH ADF4158 REFERENCE OSCILLATOR LINEAR FREQUENCY SWEEP 26MHz ADF4158 PLL 5.1GHz TO 5.1333GHz 76.5GHz TO 77.0GHz
x5 VCO
x3
PA Tx ANTENNA
MULTIPLY x15
ADSP-BF531 AD9235 MICROCONTROLLER 16B DSP 10B TO 12B ADC
AD9288
BASEBAND
MIXER MUX
The ADF4158 in FMCW radar is used for generating ramps (sawtooth or triangle) that are necessary for this type of radar to operate. Traditionally, the PLL was driven directly by a direct digital synthesizer (DDS) to generate the required type of waveform. Due to the implemented waveform generating mechanism on the ADF4158, a DDS is no longer needed, which reduces cost. In addition, the PLL solution has advantages over another method (the DAC driving the VCO directly) for generating FMCW ramps, which suffered from VCO tuning characteristics nonlinearities requiring compensation. The PLL method gives highly linear ramps without the need for calibration.
HPF
08728-034
RANGE COMPENSATION Rx ANTENNAS
BUS CAN/FLEXRAY
Figure 45. FMCW Radar with ADF4158
Rev. 0 | Page 32 of 36
ADF4158 OUTLINE DIMENSIONS
PIN 1 INDICATOR 4.10 4.00 SQ 3.90 0.50 BSC 0.30 0.25 0.18
19 18 EXPOSED PAD 24 1
PIN 1 INDICATOR
2.65 2.50 SQ 2.45
6 7
TOP VIEW 0.80 0.75 0.70 SEATING PLANE
0.50 0.40 0.30
13 12
0.25 MIN
BOTTOM VIEW FOR PROPER CONNECTION OF THE EXPOSED PAD, REFER TO THE PIN CONFIGURATION AND FUNCTION DESCRIPTIONS SECTION OF THIS DATA SHEET.
0.05 MAX 0.02 NOM COPLANARITY 0.08 0.20 REF
COMPLIANT TO JEDEC STANDARDS MO-220-WGGD.
Figure 46. 24-Lead Lead Frame Chip Scale Package [LFCSP_WQ] 4 mm x 4 mm Body, Very Very Thin Quad (CP-24-7) Dimensions shown in millimeters
ORDERING GUIDE
Model 1 ADF4158CCPZ ADF4158CCPZ-RL7 EVAL-ADF4158EB1Z
1
Temperature Range -40C to +125C -40C to +125C
Package Description 24-Lead Lead Frame Chip Scale Package [LFCSP_WQ] 24-Lead Lead Frame Chip Scale Package [LFCSP_WQ] Evaluation Board
112108-A
Package Option CP-24-7 CP-24-7
Z = RoHS Compliant Part.
Rev. 0 | Page 33 of 36
ADF4158 NOTES
Rev. 0 | Page 34 of 36
ADF4158 NOTES
Rev. 0 | Page 35 of 36
ADF4158 NOTES
I2C refers to a communications protocol originally developed by Philips Semiconductors (now NXP Semiconductors).
(c)2010 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the property of their respective owners. D08728-0-4/10(0)
Rev. 0 | Page 36 of 36

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