capacitive sensor interface circuit

[vsoumyavarma]

Hi,
I am trying to simulate an interface circuit for capacitive sensors which is based on switched capacitor technique.
My problem is that while varying the sensor capacitor, the frequency is not varying.It is constant.But when there is a feedback from the comparator output to the sensor input, then there is frequency variation. But then what is the use of this input voltage source?
Also, it is mentioned that there is a controlled current source.But I don't know which voltage/current controls the source.

 

[Prototyp_V1.0]

Mee to don't quite understand the design of the two opamps. I think that the current source will cause the capacitors to charge all the way up. Unless that, I tend to beleive that the current source isn't just a current simple source, but also have some hidden features not shown in the schematic.

What happens to the average voltage at the output on rightmost opamp? Does it vary when sensor value vary?

 

[vsoumyavarma]

The average voltage at the output is not varying.

The first opamp is an integrator and the second one is a comparator. These form a relaxation oscillator.