Hello, I am looking for help designing a charge amplifier that has very low input impedance. My basic circuit design looks like this:
Here, R1 is a many-turn coil with resistance from 3 ohm to 130 ohm. I am looking to measure the charge that flows through the coil due to changing magnetic fields -- I expect around 0.5 to 3 nC. However, the magnetic field takes about 1 s to change, so I have been using C1 = 30 nF and R2 = 30 Mohm. That combination of R1 and R2 produces a lot of noise when there is no signal in the coil, and other charge amplifiers (like the AD8488) seem to be made only for pulses. Is there anything that would work for my application?