Mini FM Receiver Circuit

Posted on Feb 5, 2014

There are currently several nice ICs available that contain a nearly complete receiver. This project is a complete FM receiver circuit with excellent receive and sound qualities. The only disadvantage of using this IC TDA7021T from ST-NXP Wireless, from the DIY enthusiast`s perspective, is the fact that it is only available in a 16-pin SMD package

Mini FM Receiver Circuit
Click here to download the full size of the above Circuit.

. This is a nearly complete integrated receiver circuit which has been specifically designed for portable radios and the like, requiring only a minimum of external components. As a result the final dimensions of the radio can be kept very small. The IC uses a frequency-locked-loop (FLL) system with an intermediate frequency of 76 kHz. The selectivity is obtained with the aid of active RC filters. The only calibration` adjustment in the circuit is the resonance frequency of the oscillator for the tuning. The RF signal enters at pin 12 and is amplified first, after which it is transformed down by the mixer and passes through two IF filters. It is subsequently limited in amplitude. The IF limiter also supplies a signal for the optional signal strength indicator (via pin 9). The limited FM signal then goes to the demodulator and the correlator which decides whether the signal is tuned in properly. The demodulated are entirely available. This is also the reason that it is not recommended to connect the audio output directly to the line input of an audio system. The complete circuit for the FM receiver is shown above. The design is virtually identical to the test circuit shown in the datasheet for the IC, because this is difficult to improve even a little without adding a lot of additional electronics. Now we only need a few resistors and capacitors plus a coil. The tuning circuit There is also a connection (K2) for a simple...

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