convert output of demodulator to original modulating input of X input multiplier

Thread Starter

denison

Joined Oct 13, 2018
172
refer to schematic of ltspice. Can anybody add a circuit to the output of the demodulator to recover the original modulating signal of the first multiplier?
There is available a digital to analog converter ad5671r in lt spice which perhaps could be used.
I have no problems with a 1000hz modulating frequency and 10khz carrier wave sine waves. A simple passive low pass filter at the output of the demodulator recovers the 1000hz signal.
A digital carrier wave and modulating input is a different matter. A passive low pass filter does not work.
 

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crutschow

Joined Mar 14, 2008
26,775
A digital carrier wave and modulating input is a different matter. A passive low pass filter does not work.
Your apparent modulation is just gating the carrier on and off.
You don't need an analog multiplier for that.
A simple AND gate will do.

To demodulate the signal you can rectify and feed it into a low-pass filter.
You can square it up by feeding the filter output to a Schmidt-trigger gate.
 

Thread Starter

denison

Joined Oct 13, 2018
172
Your apparent modulation is just gating the carrier on and off.
You don't need an analog multiplier for that.
A simple AND gate will do.

To demodulate the signal you can rectify and feed it into a low-pass filter.
You can square it up by feeding the filter output to a Schmidt-trigger gate.
Mr Crutschow, would you be able to do this for me in a working schematic for ltspice? I would do it myself using the 'and' gate and schmidt trigger both of which are available in ltspice.
My problem would be how to use the pins on e.g. the ' behavioral and gate' in lt spice and the schmidt trigger model.
Despite an extensive search on the help index of ltspice and the internet I cannot find out how to use the pins on both these models. For instance there are 8 pins on the 'and' gate model. 3 pins are given; common, and inverting and non-inverting outputs but no indication is given of what the other 5 pins are. 2 must be for 'and' inputs for the modulation you are referring to.
 

Thread Starter

denison

Joined Oct 13, 2018
172
Mr Crutschow, would you be able to do this for me in a working schematic for ltspice? I would do it myself using the 'and' gate and schmidt trigger both of which are available in ltspice.
My problem would be how to use the pins on e.g. the ' behavioral and gate' in lt spice and the schmidt trigger model.
Despite an extensive search on the help index of ltspice and the internet I cannot find out how to use the pins on both these models. For instance there are 8 pins on the 'and' gate model. 3 pins are given; common, and inverting and non-inverting outputs but no indication is given of what the other 5 pins are. 2 must be for 'and' inputs for the modulation you are referring to.
 
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