I am designing an integrator circuit using op-amp. The circuit works very well for inputs greater than 7mVACRMS from 10Hz to 2KHz (error is inside 1%). The issue I am having now is when the AC input less than 5mV, the output the integrator has big error. About -15% error when the input is 1mVRMS sine wave. The following is the circuit I am using now. Does anyone have ideas about how to design an integrator for small input signal with high accuracy? Thanks in advanced!
The circuit is designed for time constant tau=0.0026. So at 61.45Hz, the output equals to the input value. The tau value in the following circuit is 5 times less than 0.0026, So at 61.45Hz, if the input is 1mVACRMS, the output should be 5mVACRMS. But I only measured 4.3mVACRMS. If the input is 30Hz, 1mVACRMS, the output should be 10mVACRMS, but only measured 8.6mVACRMS.
C30(0.022uf) is a 2% film cap and R16(23.7K) is 1% resistor. C33 coupling cap is 20% Tan or ceramic cap. The power for the amp is +-3.3V.