Control system for automated drift compensation of the stand-alone charge amplifier used for low-frequency measurement

Abstract

A charge amplifier is an electronic current integrator that is frequently employed for converting electrical charges or electrical currents into voltage signals. The charge amplifier is very sensitive to DC drift, since the DC component in the input signal leads to a steady accumulation of charge in the feedback capacitor until the output voltage saturates. Various solutions for automated drift reduction have been proposed, but they either (i) disable measurements of low-frequency signals (mHz range), (ii) non-deterministically reset the charge amplifier output voltage, (iii) cannot compensate for high value drifts (above V/s), or (iv) have a high closed-loop time constant, which decreases the disturbance rejection performance and increases settling time. In this paper, we present a control system for automated drift compensation of the charge amplifier periodic output voltage, which solves the aforementioned problems. The proposed solution (i) efficiently rejects disturbances, (ii) offers fast settling time without affecting the measurement accuracy, (iii) can compensate for drift in a large range (up to tens of V/s), and (iv) is low-cost. The presented solution was tested on a charge amplifier that is part of a custom-made dedicated measurement system for automated high-temperature and low-frequency polarization measurements of dielectric materials. The presented results indicate that the proposed automatic control system efficiently compensates for the drift component of the charge amplifier without affecting the measurement precision. Most importantly, with the modifications presented in this manuscript, this system can be easily adapted for other charge amplifier periodic measurement usage examples.