QUANTUN QP-750, Service Manual

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QP-750 Service Manual
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86 P00/D0 FK2 I Side Key2
87 P107/AN7 BATTSEL I Battery Type detect (NC)
88 P106/AN6 BATT I Battery voltage detect
89 P105/AN5 VOX I MIC signal input
90 P104/AN4 NC
91 P103/AN3 SELF I Reset mode control
92 P102/AN2 RSSI I RSSI detect pin
93 P101/AN1 SQL I Squelch level input
94 AVSS GND I A/D conversion power supply input.
95 P100/AN0 TI I CTC/CDC input
96 VREF VCC I A/D conversion reference voltage
97 AVCC VCC I Power supply input.
98 P97 NC
99 P96 NC
100 P95 NC
6.3 Audio Circuitry
6.3.1 Transmit and Receive Audio Circuitry
The majority of RX and TX audio processing is performed by IC1408, the Audio processing IC ,
which provides the following functions:
• Tone CTC/CDCSS rejection filter in RX audio path
• TX and RX audio amplifier
• Pre/De-emphasis circuit
•Compressor and Expander with no external components
• Scrambler and De-scrambler in frequency inversion type
•Limiter with level adjuster
• Splatter filter for wide and narrow band
• Digital controlled amplifier for microphone, modulator and demodulator sensitivity
The parameters of IC1408 that are programmable are selected by the microprocessor.