A low noise differential charge amplifier with input buffer stage for toroidal gyroscope

Abstract The low-noise charge detection circuit is crucial for the precision of a gyroscope system. Traditional three-op-amp differential charge amplifier suffer from high noise and power consumption, whereas single-op-amp charge amplifier exhibit limited common-mode rejection performance. To improve the noise performance and common mode rejection ratio (CMRR) of differential charge amplifiers, an enhanced differential charge amplifier has been recently introduced. This paper presents an enhanced single-op-amp differential charge amplifier featuring a fully differential common-source structure as the input buffer stage. The input buffer stage is engineered to minimize input noise, maintain a high input impedance, and enhance the CMRR of the circuit. Utilizing the architecture of the enhanced differential charge amplifier, this study develops an equivalent noise model and meticulously analyzes the noise sources, thereby substantiating the efficacy of the structure in diminishing input noise. The designed charge amplifier is experimentally verified to have demonstrated an overall charge gain of 9 V/pC and an input-referred RMS charge noise of 142.2 aC, with a −3 dB passband width of 18 Hz–810 kHz. The CMRR consistently achieves a maximum of 54.5 dB, thereby effectively suppressing the common-mode noise. The enhanced circuit proposed herein possesses an ultra-low noise floor and a high signal-to-noise ratio and exhibits rapid response characteristics, thereby markedly attenuating system noise and precisely tracking the dynamically varying charge signals. This enhancement leads to a substantial improvement in the measurement precision of toroidal gyroscope test systems. The findings of this study also offer a novel approach to the design of low-noise, high-gain, and high-precision differential charge amplifiers.