Multi-function digital radio circuit

Published:2011/4/26 8:06:00 Author:TaoXi | Keyword: Multi-function, digital radio | From:SeekIC

Circuit Principle The AM-FM switch is one kind of FM AM conversion circuit that is composed of the Q2, Q3, R5-R8 and c7, power switch SW3 turns on, Q2 conducts and 03 cuts off, the A/F port outputs the high-level voltage, the voltage from R107 to the pin-15 of u1, so pin-15 of u1 has the high-level voltage and automatically switch to FM band. The FM high frequency signal which is received by the rod antenna is also amplified by the c101 to the Q101, and then pass the bandpass filter (compose of c104, L101, c105, c106) to pin-12 of u1, and then the FM signal of pin-12 is amplified by the selected frequency amplifier and the frequency selection circuit (compose of PVC, C109, L103). The oscillator circuit is composed of PVC, c110, L104, the LO signal inputs from pin-7 and outputs from pin-14. The audio signal of u1's pin-23 is coupled by the c123 and outputs from pin-24. w1 is the electronic volume control potentiometer, it controls the level of u1's pin-4 to control the volume. The output audio signal of u1's pin-23 send to the internal power amplifier of u1's pin-24, then the amplified audio signal from pin-27 drives the speaker or headphone.



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