What is FM demodulator. IC type FM demodulator explained. CA3089

What is FM demodulator. IC type FM demodulator explained. CA3089

Description of FM de-modulator CA3089

Here in this article we will explore the block diagram of IC CA3089 which is commonly used as FM demodulator. This diagram can be available from IC CA3089 datasheet. The block diagram shows that the incoming signal is passed through three amplifier stages. All three amplifier stages have its own lever detectors. The output of these three amplifiers are summed together and fed through pin 13. Here the signal level can be measured. When the signal level enters the limiting the current of the signal reaches its maximum value.

CA3089 FM demodulator IC block diagram


Output stage of FM demodulator

Output of the final amplifier is fed to quadrature detector stage which convert frequency deviation or frequency changes to the amplitude changes. This is there actual demodulation of FM signal into audio signal or base frequency information. How this demodulator works is shown in the bellow image.

FM demodulator function diagram


Here shown the RLC network which is formed of two capacitors, one inductor and two internal resistors. The capacitors and inductor are outside the chip or they are external components. This RLC network is providing a 90 degrees phase shift at intermediate frequency or IF. From here the 10.7Mhz signal and the original siganal are fed to the mixer stage where the phase of the signal is detected and voltage is produced which is proportional to the phase shift or phase difference.

FM demodulator output response on frequency band

The response of this demodulatior is nonlinear over the large frequency band. Anyhow on narrow band its frequency response is nearly linear. It provides very low signal distortion of 0.1%. The value of signal distortion is dependent of circuit design and circuit calibration. If realistically designed, the circuit performs very well with very low distortion. This type of circuit is very suiatable for such small applications as it is very stable and consuming very low power and providing great degree of simplicity. Also its price is low too.

Due to all these benefits and qualities the CA3089 is the better choice for many portable FM radio receivers.

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