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I have a doubt of a charge amplifier with a piezoelectric sensor

Cheolhwan Lim
Prodigy 10 points

Hello all,

I have a question about the charge amplifier with a piezoelectric sensor as shown above.

The first image shows a piezoelectric sensor and its equivalent circuit and the second one shows the charge amplifier with the sensor.

Since piezoelectric sensors have a very high impedance, Rp, the amplifier should have a very high input impedance in a voltage mode. Otherwise, the amplifier should have a very low input impedance in a charge mode to feed all the charge from the sensor to the feedback capacitor.

However, if I put a resistor, Ri, as shown above, is it fine?

I think the input signal to the amplifier will be dropped due to the Ri, but a TI application note (SLOA033A) shows the circuit.

I wonder how the circuit works with a piezoelectric sensor having very high impedance.