Alternating Voltage Sensor

This circuit is first a difference amplifier that low-pass filters the signal, with one pole, and also attenuates the signal. Next in the path is a second order low pass filter, with Butterworth damping. Finally, a summing junction shifts the level of the AC signal into a positive signal that is centered at 1.2 V. All together this a fourth order linear system. It has -9 dB attenuation at the corner frequency of 950 Hz.