Hello!
I am doing a project which involves frequency demodulation, I am using the CD 4046. I have connected it in frequency demodulation configuration. However my ouput and at any carrier frequency I am gettting a triangular waveform at less than 20mV and at about the 10 -
100 Khz frequency.Also my demodulated signal "rides" on that signal, therefore my signal is noisy.
Are there any troubleshooting techniques any of you guys can give me. THANKS!!!
Hi,
It help if you posted a schematic with circuit values, frequencies, etc.
-- Luhan Monat (luhanis 'at' yahoo 'dot' com) "The future is not what it used to be..." http://members.cox.net/berniekm
using
-signal
Sounds like your loop is unstable. That triangular waveform is a tell tale sign. I bet it just gets worse if you try to use a bigger loop filter capacitor! You need to do the loop design properly. There's a worked example in Art of Electronics.
Do you know how these work? There is a phase detector and a voltage controlled oscillator. The phase detector compares the incoming signal with the output of the VCO, and outputs a signal which feeds the voltage control input of the VCO to get the VCO on that frequency.
If the input signal is just a fixed frequency, the DC output of the phase detector will be relatively constant, minuse noise that needs to be filtered out.
Change the input frequency, and that DC output will vary after you get the noise filtered out.
Frequency modulate the input frequency, and that DC output will vary with the modulation, but it is that output from the phase detector that is the recovered modulating signal.
If the filter at the output of the phase detector is not right, you won't be able to recover the modulating signal from the 4046.
Michael
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