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U2538B
IR Receiver for Data Communication
Description
The IC U2538B is a complete IR receiver for data communication. The useful input signals are separated by a special input circuit and amplified by a gain-controlled amplifier. The bandpass filter suppresses the off-band signals. The signal detector, consisting of a demodulator, an integrator and a Schmitt Trigger, forms the input signal to an output pulse that can be interfaced to a microcomputer. The AGC and the ATC circuit control the receiver's sensitivity, making it insensitive to ambient light sources.
Features
D D D D
Few external components Low power consumption Microcomputer compatible Insensitive to ambient light and other continuous interference
Applications
D Keyless entry systems D Remote control D Wireless data transfer up to 4 kbit/s
Ordering Information
Extended Type Number U2538B-MFP U2538B-MFPG3 Package SO8 SO8 Remarks Tube Taped and reeled
VS
95 9837
U2538B Input Amplifier and filter Detector
mC
AGC / ATC
Modulated IR signal carrier frequency 20 to 60 kHz min. 6 pulses/burst
Figure 1.
Rev. A2, 15-Oct-98
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U2538B
Pin Description
n.c. 8 RF 7 AGND 6 IN 5 Pin 1 2 3 4 5 6 7 8 Symbol VS CAGC OUT DGND IN AGND RF n.c. Function Supply voltage AGC capacitor Data output GND - DEM/INT/ST Input pin diode GND amplifier Frequency determination Not connected
U2538B
94 9285
1 VS
2 CAGC
3 OUT
4 DGND
Figure 2. Pinning
Block Diagram
VS RF0
94 9286
RF
VS
BIAS IN BPF
+ -
Comp 1
100kW dt
OUT
Vth + -
&
Comp 2 INT ST
TIA
CGA
AGC
ATC
DEM
A GND
CAGC
CAGC
DGND
Figure 3. Block diagram
TIA CGA BPF AGC
Transimpedance amplifier Controlled gain amplifier Bandpass filter Automatic gain control
ATC DEM INT ST
Automatic threshold control Demodulator Integrator Schmitt trigger
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U2538B
Functional Description
Input Stage (TIA)
The input stage provides the necessary bias voltage for the photo diode and ensures decoupling of the useful signal. This involves processing the dc and ac portions in separate parts of the circuit: the bias voltage (BIAS) and the transimpedance amplifier circuit (TIA). The bias voltage circuit operates like a load resistor with respect to the photo diode, the value of which is low for dc and low-frequency signals (3 to 100 kW), but as high as possible for the operating frequency (100 kW to 1 MW) depending on the input current). The ac portion of the input signal feeds an inverted amplifier with a sufficiently low input resistance (Zi < 10 kW). If the input resistance were too high, the useful signal would be lost to the junction capacitance of the photo diode.
Grel 120 100 80 60 40 20 0 0.4
95 9851
0.6
0.8
1.0 f/fo
1.2
1.4
1.6
Figure 4. Characteristic of the bandpass filter
Automatic Threshold Control (ATC)
During the reception of an incoming telegram, the ATC reduces the sensitivity of the demodulator to establish the highest possible signal-to-noise ratio according to the signal strength. This prevents interferences which may arise during transmission from affecting the output. The advantage of the circuit is achieved, if its output voltage exceeds VTh (Comp 1). That is the case when the input signal strength is more than twice as much as the minimum detectable signal intensity.
Controlled Gain Amplifier (CGA)
The controlled gain amplifier accounts for the greatest part of the voltage gain and can be controlled via the voltage at CAGC (Pin 2). Gain control is needed to support the interference suppression of the detector. High-pass behaviour results from the capacitive coupling of the individual stages. The cut-off frequency is approximately 20 kHz.
Automatic Gain Control (AGC)
The automatic gain control improves the circuit's resistance to interference by adapting the amplification of the gain controlled amplifier to the relevant existing interference level. In order to prevent the circuit from responding to transmitted data signals, it gradually reduces the sensitivity but only if the duty cycle exceeds a specific value (see figure 5). When using telegrams with higher duty cycles than this value, the capacitor, CAGC, maintains the sensitivity for a certain time period. A higher cpacitance enables a longer transmission time. A capacitance of C1 = 22 nF is adequate for most known telegrams. A typical value for the maximum duty cycle (DC) can be calculated by the following formula: DC max
Bandpass Filter (BPF)
The bandpass filter basically consists of integrated components. An external resistor determines the midfrequency. The filter quality is about 7 and is practically independent of the selected mid-frequency (see figure 4). The following formula can be used for calculating the resistor, Rf0: R fO (kW)
+ f 8855 -13 (kHz)
0
where: 20 kHz < f0 < 60 kHz
+ 14.2 ) N1.1
N
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U2538B
Transmitted Burst (N cycles)
t p1
+N f
T
Figure 5.
DC
+ tT N w 6; f = 20 kHz to 60 kHz
p1 94 9287
Detector
The output signal of the bandpass filter is compared to a fixed reference (Comp 1) and to a reference generated by the ATC circuit (Comp 2). The output of the comparator with the higher threshold voltage controls the integrator. Using the integrator keeps the output free of short-time interference. The integrator drives the output stage after being processed through a Schmitt Trigger. The internal pull-up resistor can replace an external resistor in some applications.
Absolute Maximum Ratings
Supply voltage Input voltages Input current Power dissipation Junction temperature Ambient temperature Storage temperature Parameters Pin 1 Pins 2, 3 and 5 Pin 7 Pin 7 Tamb = 105C Symbol VS VIN IIN Ptot Tj Tamb Tstg Value -0.3 to +6.0 -0.3 to VS -0.3 to +1.5 0 to 0.1 110 125 -40 to +105 -40 to +125 Unit V V mA mW C C C
Maximum Thermal Resistance
Parameters Junction ambient Symbol RthJA Maximum 180 Unit K/W
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U2538B
Electrical Characteristics
Tamb = 25C, Vs = 5 V Parameters Supply voltage Supply current Max. input current VIN = 0 Output voltage low: IOL = 2 mA Internal pull-up resistor Center frequency of bandpass RF = 240 k Q factor Freqency range AGC current source sink AGC slope Number of pulses required Sensitivity Switch-on delay, iIN = 0.7 nA (rms) Switch-off delay, iIN = 0.7 nA (rms) Pulse width, iIN = 0.7 nA (rms), 6 pulse bursts Test Conditions / Pins Pin 1 Pin 1 Pin 5 Pin 3 Pin 3 Symbol VS IS IIN VOL RL f0 Q f Pin 2 Pin 2 6 Pin 5 Pin 3 see figure 6 Pin 3 see figure 6 Pin 3 see figure 6 tpo 4.5 10 Period tdoff 5 10 Period tdon 3 0.7 7.5 nA(rms) Period Min. 4.5 0.35 0.6 Typ. Max. 5.5 0.65 0.2 75 33.3 100 35 7 20 90 70 120 100 20 60 155 140 kHz nA nA dB/V 125 36.7 Unit V mA mA V kW kHz
R fO (kW)
+ f 8855 -13 kW (kHz)
0
VIN
Burst, X pulses
Repetition rate = 10 ms
VOUT tpo tdon
Figure 6.
tdoff
94 9288
Rev. A2, 15-Oct-98
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U2538B
Application Circuit
R1 220 3 VBatt R2 >10k *) 2 OUT 470p*) 1 GND feedback reduction C4 *) 4 DGND IN 5 3 C1 10m 16 V C2 100n C3 10n 1 VS n.c. 8 RfO
2
CAGC
RF
7
U2538B
OUT AGND 6 D1 D2*) D3 *)
95 9838
*) optional Figure 7. Application circuit
Package Information
Package SO8
Dimensions in mm
5.00 4.85 1.4 0.4 1.27 3.81 8 5 0.25 0.10 0.2 3.8 6.15 5.85 5.2 4.8 3.7
technical drawings according to DIN specifications 13034
1
4
6 (7)
Rev. A2, 15-Oct-98
U2538B
Ozone Depleting Substances Policy Statement
It is the policy of TEMIC Semiconductor GmbH to 1. Meet all present and future national and international statutory requirements. 2. Regularly and continuously improve the performance of our products, processes, distribution and operating systems with respect to their impact on the health and safety of our employees and the public, as well as their impact on the environment. It is particular concern to control or eliminate releases of those substances into the atmosphere which are known as ozone depleting substances ( ODSs). The Montreal Protocol ( 1987) and its London Amendments ( 1990) intend to severely restrict the use of ODSs and forbid their use within the next ten years. Various national and international initiatives are pressing for an earlier ban on these substances. TEMIC Semiconductor GmbH has been able to use its policy of continuous improvements to eliminate the use of ODSs listed in the following documents. 1. Annex A, B and list of transitional substances of the Montreal Protocol and the London Amendments respectively 2 . Class I and II ozone depleting substances in the Clean Air Act Amendments of 1990 by the Environmental Protection Agency ( EPA) in the USA 3. Council Decision 88/540/EEC and 91/690/EEC Annex A, B and C ( transitional substances ) respectively. TEMIC Semiconductor GmbH can certify that our semiconductors are not manufactured with ozone depleting substances and do not contain such substances.
We reserve the right to make changes to improve technical design and may do so without further notice. Parameters can vary in different applications. All operating parameters must be validated for each customer application by the customer. Should the buyer use TEMIC Semiconductors products for any unintended or unauthorized application, the buyer shall indemnify TEMIC Semiconductors against all claims, costs, damages, and expenses, arising out of, directly or indirectly, any claim of personal damage, injury or death associated with such unintended or unauthorized use. TEMIC Semiconductor GmbH, P.O.B. 3535, D-74025 Heilbronn, Germany Telephone: 49 ( 0 ) 7131 67 2594, Fax number: 49 ( 0 ) 7131 67 2423
Rev. A2, 15-Oct-98
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