What is the principle of patch miniature FM radio?

Last Update Time: 2019-01-12 13:42:13

The core of the chip micro FM radio circuit is the monolithic radio integrated circuit CD9088, which uses the special low if frequency 70 kHz technology peripheral circuit to eliminate if transformer and ceramic filter to make the circuit simple, reliable and easy to debug.

 

The same type of radio uses integrated circuits, such as SC1088, SL1088, TDA7088 D7088 and other manufacturers of products, circuit performance and leads are exactly the same, can be used instead of each other.

 

CD9088 is encapsulated with SOT16 leadand the miniature FM radio composed of CD9088 is mainly composed of FM signal input circuit, local oscillator tuning circuit, if amplifier limiting circuit and frequency discriminating circuit and power amplifier circuit.

 

1) FM signal input loop

FM signals are fed by headphone wires into the input circuits  into the 11 and 12-pin mixed-frequency circuits of the integrated chip IC. The FM signal here has no tuned FM signal, that is, all FM signals are available to get in.

 

2) Local oscillator tuning circuit

The key component in the local oscillator tuning circuit is the varactor, which is related to bias by using the junction capacitance of the PN junction characteristic made of "variable capacitance".

 

3) Amplifier limiter and detector circuit

The active devices and resistors of the intermediate frequency amplification and limiting circuit and the proximity circuit are all in the IC of the integrated chip. FM broadcast signal and local oscillator circuit signal are mixed in IC of integrated chip to produce if signal of 70 kHz in mixer. After internal 1dB amplifier and intermediate frequency limiter, it is sent to discriminator to detect audio signal. After the internal loop filter, the audio signal is outputted by the integrated chip 2 feet.

 

4) Power amplifier circuit

Because of the small power required for earphone listening, the audio signal output from a simple transistor amplifier circuit with two feet is adjusted by the potentiometer RP, and then the transistor is composed of a type A amplifier. R, and C constitute audio output load, coil L and L are RF and audio isolation coil.


This article is from Allicdata Electronics Limited.