AD608: FM detection

Document created by analog-archivist Employee on Feb 23, 2016
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In the past, I found AD608 which is working very well on 455kHz and 10,7MHz.
There is problem with demodulator. I was using XR215. This PLL demodulator had
good behavior only for 455kHz. On 10,7MHz it was unfit for low frequency
stability of the VCO.
I was thinking you developed an amazing AD608 but there is no suitable simple
demodulator or I am not able to find it.
Please, send me some info about recommended demodulator (PLL or quadrature) for


We do not make an FM demodulator which works with the AD608, but the circuit in
Fig 23 of the AD608 data sheet shows an FM
discriminator working at 455 KHz using a ceramic filter as a phase-shift
element. You could make much the same circuit at 10.7 MHz
but you would have to consult Murata, Toko or some other ceramicfilter
manufacturer about suitable ceramic resonators.

The transistor is necessary because the limiting output of the AD608 is only
400 mV pk-pk and a larger voltage is necessary to turn on the
diodes, even though the 1N60 is a germanium type.