Limiter circuit before FM demodulator

Hi,

Can a differential amplifier can be used as a limiter circuit for FM demodulation ? Can anybody explain the circuit, if it exixt !!
Thanks

abhijitrc said:

Hi,

Can a differential amplifier can be used as a limiter circuit for FM demodulation ? Can anybody explain the circuit, if it exixt !!
Thanks

Click to expand...

Yes if you adjust it to limit the signal. In fact all ICs for FM demodulation utilize differential limiters before the quadrature demodulator.

You can use any amplifier configuration as a limiter. All it has to do is clip the signal beyond a certain voltage (limit it's range). The idea of a limiter in FM systems is to eliminate as much variation in amplitude as possible so the classic methods are to use a voltage clipping circuit (two diodes in anti-parallel) or an amplifier with such high gain that the signal tries to exceed it's output capability and hence loses it's peaks.

Brian.

jiripolivka said:

Yes if you adjust it to limit the signal. In fact all ICs for FM demodulation utilize differential limiters before the quadrature demodulator.

Click to expand...

Sir,
What i feel differential amplifier can suppress the noise in a better way so we can put differential amplifier before fooster seeley discriminator also?

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jiripolivka said:

Yes if you adjust it to limit the signal. In fact all ICs for FM demodulation utilize differential limiters before the quadrature demodulator.

Click to expand...

Can a circuit diagram be provided so that i could be better understood!!!

abhijitrc said:

Sir,
What i feel differential amplifier can suppress the noise in a better way so we can put differential amplifier before fooster seeley discriminator also?

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Can a circuit diagram be provided so that i could be better understood!!!

Click to expand...

LImiters suppress not the noise but the amplitude variations due to signal propagation, interference spikes etc. Noise is determined by receiver thermal noise and FM signal modulation has a "FM gain" above threshold, typically 12...16 dB of S/N. FM gain is a function of deviation, ~18 dB in satellite TV FM transmission.
Foster-Seeley discriminator is a nice device but now all FM demodulator ICs use a quadrature detector with better results.
For IC schematics try the old TDA series, there were several FM demodulator ICs with limiting IF amplifiers. I do not remember their numbers.

Thank u sir, for nice guidance