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75T204 5V Low-Power Subscriber DTMF Receiver
April 2000
DESCRIPTION
The 75T204 is a complete Dual-Tone Multifrequency (DTMF) receiver that detects 16 standard digits. No front-end pre-filtering is needed. The only external components required are an inexpensive 3.58-MHz television "colorburst" crystal for frequency reference and a bias resistor. An Alternate Time Base (ATB) is provided to permit operation of up to 10 75T204's from a single crystal. The 75T204 employs state-ofthe-art "switched-capacitor" filter technology, resulting in approximately 40 poles of filtering, and digital circuitry on the same CMOS chip. The analog input signal is pre-processed by 60-Hz reject and band split filters and then zero-cross detected to provide AGC. Eight bandpass filters detect the individual tones. Digital processing is used to measure the tone and pause durations
(continued)
FEATURES
* * * * * * * * * Intended for applications with less requirements than the 75T202/75T203 14-pin plastic DIP or 16-pin SO package for high system density NO front-end band-splitting filters required Single low-tolerance 5-volt supply Detects all 16 standard DTMF digits. Uses an inexpensive 3.579545-MHz crystal Excellent speech immunity Output in 4-bit hexadecimal code Three-state outputs for microprocessor interface
BLOCK DIAGRAM
BANDPASS FILTERS 697 BAND SPLIT FILTERS BS1 ZERO CROSSING DETECTORS AMPLITUDE DETECTORS
770
PRE-PROCESSOR ANALOG 60 Hz REJECT PREEMP
852
941
TIMING CIRCUITRY
BS2
1209
1336 DV DV XEN 1633 /8 CLOCK GENERATOR DATA STROBE
ATB
1477
XIN
CHIP CLOCKS D1
1Mz XOUT D2 OUTPUT DECODER OUTPUT REGISTER D4
POWER REGULATOR
VOLTAGE REF
D8 DATA CLEAR EN
VP
GND
75T204 5V Low-Power Subscriber DTMF Receiver
DESCRIPTION (continued)
and to provide output timing and decoding. The outputs interface directly to standard CMOS circuitry and are three-state enabled to facilitate bus-oriented architectures. ANALOG IN This pin accepts the analog input. It is internally biased so that the input signal may be AC coupled. The input may be DC coupled as long as it does not exceed the positive supply. Proper input coupling is illustrated in Figure 1. The 75T204 is designed to accept sinusoidal input wave forms but will operate satisfactorily with any input that has the correct fundamental frequency with harmonics less then -20 dB below the fundamental. CRYSTAL OSCILLATOR The 75T204 contains an onboard inverter with sufficient gain to provide oscillation when connected to a low-cost television "colorburst" crystal. The crystal oscillator is enabled by tying XEN high. The crystal is connected between XIN and XOUT. A 1 Mz 10% resistor is also connected between these pins. In this mode, ATB is a clock frequency output. Other 75T204's (or 75T202's) may use the same frequency reference by tying their ATB pins to the ATB of a crystal connected device. XIN and XEN of the auxiliary devices must then be tied high and low respectively. Ten devices may run off a single crystal-connected 75T204 (or 75T202) as shown in Figure 2. OUTPUTS D1, D2, D4, D8 and EN Outputs D1, D2, D4, D8 are CMOS push-pull when enabled (EN high) and open circuited (high impedance) when disabled by pulling EN low. These digital outputs provide the hexadecimal code corresponding to the detected digit. The digital outputs become valid after a tone pair has been detected (DV is high) and they are then cleared when a valid pause is timed. The hexadecimal codes are described in Table 1. DV DV signals a detection by going high after a valid tone pair is sensed and decoded at the output pins D1, D2, D4, and D8. DV remains high until a valid pause occurs. N/C PINS These pins have no internal connection and may be left floating.
Output Code Digit 1 2 3 4 5 6 7 8 9 0 * # A B C D D8 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 0 D4 0 0 0 1 1 1 1 0 0 0 0 1 1 1 1 0 D2 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0 D1 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0
TABLE 1: Output Codes
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75T204 5V Low-Power Subscriber DTMF Receiver
VP
VP
VIN < VP
VIN > VP
(On Chip)
0.01 F 7 10 pF >100 k Analog In
7 Analog In
(On Chip)
10 pF >100 k GND
GND
FIGURE 1: Input Coupling
VP XIN 10 ATB 11 75T204 9 6 XEN XOUT
XIN Connected to V P 10 75T204 11 6 XEN
Up to 10 Devices
FIGURE 2: Crystal Connections
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75T204 5V Low-Power Subscriber DTMF Receiver
DTMF DIALING MATRIX See Figure 3. Please note that column 3 is for special applications and is not normally used in telephone dialing.
Col 0 Row 0 1
Col 1 2
Col 2 3
Col 3 A
Row 1
4
5
6
B
Row 2
7
8
9
C
Row 3
*
0
#
D
FIGURE 3: DTMF Dialing Matrix
ton Analog Input Tone burst 1
toff Pause tR Tone burst 2
tD D1, D2, D4, D8
tS DV
tH
FIGURE 4: Timing Diagram
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75T204 5V Low-Power Subscriber DTMF Receiver
DETECTION FREQUENCY Low Group f0 Row 0 = 697 Hz Row 1 = 770 Hz Row 2 = 852 Hz Row 3 = 941 Hz High Group f0 Column 0 = 1209 Hz Column 1 = 1336 Hz Column 2 = 1477 Hz Column 3 = 1633 Hz
75T204 TIMING (Refer to Figure 4.) PARAMETER tON tOFF tD tR tSU tH Tone Time Pause Time Detect Time Release Time Data Setup Time Data Hold Time Output Enable Time Output Disable Time Output Rise Time Output Fall Time CL = 50pF, RL = 1k1/2 CL = 35pF, RL = 5001/2 CL = 50pF CL = 50pF CONDITIONS for detection for rejection for detection for rejection MIN 40 40 25 35 7 4.2 NOM MAX 20 20 46 50 5.0 200 200 200 200 UNITS ms ms ms ms ms ms s ms ns ns ns ns
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75T204 5V Low-Power Subscriber DTMF Receiver
APPLICATION INFORMATION The 75T204 will tolerate total input RMS noise up to 12dB below the lowest amplitude tone. For most telephone applications, the combination of the high frequency attenuation of the telephone line and internal band-limiting make special circuitry at the input to the 75T204 unnecessary. However, noise near the 56kHz internal sampling frequency will be aliased (folded back) into the audio spectrum, so if excessive noise is present above 28kHz, the simple RC filter shown in Figure 5 may be employed to band limit the incoming signal. Noise will also be reduced by placing a grounded trace around the XIN and XOUT pins on the circuit board layout when using a crystal. It is important to note that XOUT is not intended to drive an additional device. XIN may be driven externally; in this case leave XOUT floating.
2.4 k = 5% NOISY SIGNAL ANALOG IN 75T204
0.01 mF = 20%
FIGURE 5: RC Filter
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75T204 5V Low-Power Subscriber DTMF Receiver
ELECTRICAL SPECIFICATIONS
ABSOLUTE MAXIMUM RATINGS (Operation above absolute maximum ratings may damage the device. connected to VP or GND, as appropriate.) PARAMETER DC Supply Voltage - V P Operating Temperature Storage Temperature Power Dissipation (25C) Input Voltage (All inputs except ANALOG IN) ANALOG IN Voltage DC Current into any Input Lead Temperature - Soldering, 10 sec. ELECTRICAL CHARACTERISTICS (-40C TA +85C, V P = 5V 10%) PARAMETER Frequency Detect Bandwidth Amplitude for Detection Twist Tolerance 60-Hz Tolerance Dial Tone Tolerance Talk Off Digital Outputs (except XOUT) Digital Inputs Power Supply Noise Supply Current Noise Tolerance Input Impedance "precise" dial tone MITEL tape #CM 7290 "0" level, 400A load "1" level, 200A load "0" level "1" level wide band TA = 25C MITEL tape #CM 7290 VPV INV P-10 100K||15pF 10 0 VP-0.5 0 0.7V P 2 0.5 VP 0.3V P VP 10 16 -12 each tone CONDITIONS MIN (1.5+2Hz) -32 -10 TYP 2.3 MAX 3.5 -2 +10 0.8 0dB UNITS % of fO dBm ref. to 600 dB Vrms dB* hits V V V V mV p-p mA dB* RATING +7V -40C to +85C Ambient -65C to +150C 65mW (VP + 0.5V) to -0.5V (VP + .5V) to (V P - 10V) 1.0mA 300C All 75T204 unused inputs must be
Twist=
High Tone Low Tone
* dB referenced to lowest amplitude tone
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75T204 5V Low-Power Subscriber DTMF Receiver
MECHANICAL SPECIFICATIONS
14-Pin DIP
16-Pin SOL
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75T204 5V Low-Power Subscriber DTMF Receiver
PACKAGE PIN DESIGNATIONS
(Top View)
CAUTION: Use handling procedures necessary for a static sensitive component.
D2
D2 D1 EN VP N/C XEN ANALOG IN 1 2 3 4 5 6 7
14-Pin DIP
1 2 3 4 75T204 5 6 7 8
16 15 14 13 12 11 10 9
16-Pin SOL
D4 D8 DV N/C ATB XIN XOUT GND
14 13 12 75T204 11 10 9 8
D4 D8 DV ATB XIN XOUT GND
D1 EN VP N/C N/C XEN ANALOG IN
ORDERING INFORMATION
PART DESCRIPTION 75T204 14-Pin PDIP 75T204 16-SOL 75T204-IL 75T204-IL 75T204-IP 75T204-IP ORDER NUMBER PACKAGING MARK
No responsibility is assumed by TDK Semiconductor Corporation for use of this product nor for any infringements of patents and trademarks or other rights of third parties resulting from its use. No license is granted under any patents, patent rights or trademarks of TDK Semiconductor Corporation and the company reserves the right to make changes in specifications at any time without notice. Accordingly, the reader is cautioned to verify that the data sheet is current before placing orders. TDK Semiconductor Corporation, 2642 Michelle Drive, Tustin, CA 92780-7019, (714) 508-8800, FAX: (714) 508-8877 (c)1989 - 2000 TDK Semiconductor Corporation 04/24/00- rev. C
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