1. FM (FM) section
CD9088 is a dedicated monolithic FM radio chip, the external circuit is simple, the circuit built-in frequency of 70kHz phase-locked loop system, selectivity from the active RC filter to achieve, mute circuit can suppress non-IF signal and too weak IF signal The Features include the following: Mono radio from the RF input to the audio output of all functional circuits, silent circuit, including automatic frequency control system can be used for mechanical tuning, power polarity protection, the operating power supply voltage can be as low as 1.8V.
FM signal from the rod antenna by the C8.C10 and L1 input circuit into the IC1 11.12 feet mixed circuit, the local oscillator circuit is used in variable capacitor CA.L2 and other components, can be manually tuned. FM broadcast signal and the local oscillator circuit signal mixed in the IC1 70KHZ generated by the IF signal, the internal IF amplification, IF limiter, sent to the frequency detector detected audio signal, the internal loop filter by the 2 feet output audio signal. Circuit R2.C2 for the squelch circuit, 3 feet of C4 for the audio loop filter capacitor, 6.8 pin between the C13 is the IF feedback capacitor, 7 feet connected to the C14 is a low-pass capacitor, 8.9 feet indirectly C17 Is the IF coupling capacitor, 10 feet connected to the C12 is the limiting amplifier low-pass capacitance, 13 feet of C6 for the limiter offset voltage and capacitance. 2 feet output audio signal through R6. C18 coupled to the power amplifier IC TDA2822 input 7 feet, after IC3 (TDA2822) internal power amplified by its 1.3 feet after the output of the amplified audio signal to promote the speaker work, the circuit with a switch potentiometer VOL is used Control the power on and off, and control the size of the volume.
2, AM (AM) section
AM7642 integrated circuit TA7642 has 10 internal transistor composition, the appearance of the package is used in the form of TO-92, 1 feet ground, 2 feet input, 3 feet output. The audio signal output from 3 feet is coupled to the input of the power amplifier integrated circuit TDA2822 via R6.C18 for power amplification to drive the speaker.
