I am designing a low-pass filter for a charge output transducer. The filter must be passive and provide a 2nd order Butterworth response, no more than 0.01dB of ripple in the passband is acceptable.
I have a filter available that does not meet my cutoff frequency requirements, but, as it operates on charge I am not sure how to approach analyzing or redesigning it.
The attached image shows a model that I built to simulate the filter. The design shown gives an approximately 3 kHz cutoff.
- The transducer is simulated by the voltage source, transformer and series capacitor.
- An example of the lowpass filter topology is shown at the output of the simulated charge source.
- A textbook charge amplifier has been included at the filter output (the choice of op-amp might not be ideal here).
Can anyone offer insight into the design and analysis of the filter topology shown? Specifically, I would like to understand what method could be used to select the components to achieve a Butterworth response.
EDIT: The ripple and filter type requirements could be modified. The biggest challenge( for me at least) is designing a filter for charge signals. I am not sure how to use any standard technique to design such a filter.