Phase Sensitive demodulator

[fawad_hd97]

I need a Phase Sensitive detector(demodulator) that has two inputs i.e
a reference input " ASinwt" and a modulated input "kASinwt" and the output should be 'k'

where parameters are;

ASinwt has amp 2 Vrms and freq 60Hz

k is a varrying factor (-1<k<1) and may vary sinusoidally

 

[flatulent]

This is the phase-frequency detector used in a phase locked loop. You can use comparators to convert to logic levels and then use the detector portion of a 74HC4046.

 

[Kral]

fawad_hd97,
I mislead you in my previous reply. There should be no resistor between the non-inverting input and the analog switch.
.
R1, R2 must be equal.
R3 can be any value, but its resistance must be very large compared to the "On" resistance of the analog switch.
The comparator can be almost any type. All it does is square up the Asin(wt) sine wave to a square wave to actuate the analog switch. The comparator output must be compatible with the gate (logic) input voltage requirements of the analog switch.

Operation is as follows:
With the switch closed, the circuit behaves as in inverting (gain of -1) amplifier.
With the switch open, the circuit behaves as a unity gain (gain of +1) amplifier. This might not be obvious at first glance. With the switch open, the voltage at the NI input is equal to the input voltage of the circuit. The op-amp output is at steady-state only when the inverting input equals the non-inverting input. The only way this can happen is if the current thru R1, R2 is zero. This means that the output voltage must equal the input voltage of the circuit.

The polarity of the output depends on whether the analog switch is closed with a "0" or a "1" applied to its logic input. The circuit as shown is based on an analog switch that closes with a "1" logic input. In this case, the output will be negative. For a positive output, either reverse the comparator inputs, or use an analog switch that turns on with a "0" logic input.

As shown on the schematic, the output voltage is | kAsin(wt) | Cos (Theta), where (Theta) is the phase shift between the reference and the input. In your case, Theta = 0, and so the output = | kAsin(wt) |
Regards,
Kral