Hello,
I have designed a circuit for capacitance measurement where if Cx is varied with a constant Cref we detect the change in voltage at the output of the filter. However because of the delay in filter the output of the multiplier and the output of the filter are not in phase. I need both of them in phase. How do i rectify this? A constant DC output is also fine. I have attached all the relevant documents to this circuit below.

Thank you.

Blue waveform- output of multiplier
green waveform-output of filter

 

We went over this before.
Do you somehow expect a different answer?

 

We went over this before.
Do you somehow expect a different answer?

Yes because this is what my professor mailed me today-
"The filter as a circuit doesnt make any delay even if it makes delay : The delay in Time has nothing to do with the amplitude of the signal
The goal is to rectify the signal so if possible with changing a capacitor" and when i said what u told me the last time his reply was "
"There two options:
- either you make the output amplitude of the filter the same as the output of modulator.
or you find the transfer function of the filter so that we can explain why the output of the filter is higher or lower than the output of the modulator".

I told him i will get a constant DC but he says this "We should get a DC voltage but not by chance , just by changing the value of the circuit components!! WE MUST know the behavior of the circuit step by step and not just make it by chance working "
I really do not know how else to convince him.

 

The filter as a circuit doesnt make any delay even if it makes delay

That's a self-contradictory and nonsense statement.
All filters have a delay.

The goal is to rectify the signal so if possible with changing a capacitor

That also makes no sense to me. (?)

either you make the output amplitude of the filter the same as the output of modulator.
or you find the transfer function of the filter so that we can explain why the output of the filter is higher or lower than the output of the modulator

I don't understand the first option.
Does he mean the average output or the peak output?

The second option sounds like he wants you to show the output of the filter from the filter's transfer function.
Do you know how to do that?

If you want the peak output of the multiplier with no delay, then you could use a peak-hold circuit.
But such a circuit doesn't suppress any signal noise.

 

That's a self-contradictory and nonsense statement.
All filters have a delay.
That also makes no sense to me. (?)
I don't understand the first option.

Does he mean the average output or the peak output?

He means that the peak output of both the multiplier and the filter have to be in phase.

The second option sounds like he wants you to show the output of the filter from the filter's transfer function.
Do you know how to do that?[/QUOTE]

No sir. I do not know. So my only option is to get both the outputs in phase.

If you want the peak output of the multiplier with no delay, then you could use a peak-hold circuit.
But such a circuit doesn't suppress any signal noise.[/QUOTE]
I am getting delay in filter output. Because of this delay it looks out of phase with the multiplier output. But since all filters have delay i do not know how to rectify this situation.

 

That's a self-contradictory and nonsense statement.
All filters have a delay.
That also makes no sense to me. (?)
I don't understand the first option.
Does he mean the average output or the peak output?
He means that the peak output of both the multiplier and the filter have to be in phase.

The second option sounds like he wants you to show the output of the filter from the filter's transfer function.
Do you know how to do that?
No sir. I do not know. So my only option is to get both the outputs in phase.

If you want the peak output of the multiplier with no delay, then you could use a peak-hold circuit.
But such a circuit doesn't suppress any signal noise.

I am getting delay in filter output. Because of this delay it looks out of phase with the multiplier output. But since all filters have delay i do not know how to rectify this situation.