FM Demodulator

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mbonus

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Joined 2005
Hello!
Can somebody explain me on which principle works this FM Demodulator?

Thanks!
 

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Mark Kelly

Member
Joined 2006
To make it work properly in FM you have to carefully control the input pulse height so as to get rid of the AM demodulation.

If you read the analysis posted above you will see that it is about 100 times more sensitive to AM than to FM, so its noise performance will be very poor.
 
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Mark Kelly

Member
Joined 2006
Just a thought - if you put the input through a limiter and then ran a dual differential diode charge pump (reversing the diodes in the second pump) you should be able to reduce the AM demodulation significantly.

Any AM which escapes the limiter could be made to excite both demodulators equally and so be eliminated if the differential stage has good CMRR. The trick would be to make one of the integrating resistors on the charge pumps variable as this is the major determinant of Vout/ Fin so it needs to be able to tune out the difference in the integrating capacitors.
 
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