The decoder's serial input information is supplied by the IR receiver after the received signal is amplified, filtered and demodulated. The receiver processing circuitry (Figure 8) consists of an amplifier, limiter, band pass filter, demodulator, integrator, and comparator. It is contained in the compact sized GP1U52X module (Archer), a hybrid IC/infrared detector circuit. Its operating voltage starts from 5 V, therefore allowing direct connection to TTL or CMOS components. The coil-free design provides total immunity from external noise induced by magnetic fields and the built-in low-pass filter on the power supply helps isolate the circuitry from power supply noise. The detector uses a pin photo diode that has its peak sensitivity in the near infrared range. The built-in filter blocks visible light to reduce or eliminate false operation caused by other light sources. The IR passband is 980 nm +/- 100 nm and the bandwidth (-3dB, 40 kHz) is 4 kHz. The output of the photo diode feeds into a preamplifier/limiter to provide a clean signal to the rest of the circuit. The band pass filter then rejects all signals outside the pass band and the resulting signal is fed to the demodulator, integrator and wave-shaper circuit. The output is a clean waveform without the carrier. The interface circuit between the GP1U52X module and the decoder's input consists of 2 general purpose transistors in an amplifying configuration.
