# Phase sensitive demodulation circuit

1. May 9, 2007

### LM741

hello all,

really stugglin with this one - need to build/design a phase sensitive demodulator - i.e a circuit that can recover my orginal signal....

don't suppose anyone has any idea how to go about this or some circuit diagram i could work with?

thanks

John

2. May 9, 2007

### chroot

Staff Emeritus
I think you'll need to explain what a "phase-sensitive demodulator" is in a lot more detail before we could begin to help you.

- Warren

3. May 9, 2007

4. May 9, 2007

### LM741

ok - so im using a linear variable diff transformer to measure vibrations. Such a device takes in an excitation voltage at specified frequency, lets say 10kHz. Now lets say the core is moving with a frequencey of 100Hz - my ouput will now be a modulated signal that will have frequnceies of about 10.1kHz and10.9kHz. The phase sensitive demodulater is meant to separate the the core frequency from the excitation frequency (carrier frequency). I am only interested in the frequency of the core. All i know is that the phase sensitive demodulator uses the frequency from the oscillator (that i use to generate the AC excitation voltage) to recover the orignal signal. Just stugglin to find a circuit that can do this. there are many chips that have cover all signal conditioning issues for an LVDT but this is no ood to me - i just want the phase sensitive demodulator - also called synchronous demodulator.

Thans very much

5. May 9, 2007

### waht

That's like a SSB receiver. Just mix the carrier frequency with the modulated signal (derived from the same carrier), that will produce the sum and difference frequencies, with appropriate filters, filter out the unwanted frequencies.

6. May 9, 2007

### LM741

ok?? what is a SSB receiver?? is it easy to build? ill google it - then talk tomorro
thanks

7. May 9, 2007

### Averagesupernova

So are there 3 signals coming out of this device? Both the upper and lower sidebands and the carrier or does this device act like a double balanced mixer with just the sidebands coming out?

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