capacitor - Converting variable capacitance value to variable DC voltage level

I need a simple method to convert a small variable capacitance value into considerable variable DC voltage.

• Capacitance value range = 0nF ~ 14nF


• DC value range needed = 0V ~ 6V

What I've tried is shown below. However final output should be a pure DC level without any ripples for a fixed Cx. But the following circuit seems to be still have ripples or noises.

1. Is there any improvements to be made for this circuit to get a pure DC output?


2. Are there any other methods/circuits to do this task?

• Ro=100k


• Oscillator frequency is about 71.78 Hz (t1=7mS, t2=6.93mS)


• Cx is the variable capacitor (Range 0nF~14nF)