Ultra-Low Noise Charge Sensitive Amplifier for MEMS Gyroscope

This paper describes a ultra-low noise charge sensitive amplifier for readout of micromechanical capacitive sensors. This CSA employs a band-pass amplifier with n-JFET mu-amp achieving high gain and a very low power. The noise due to resister establishing a stable dc bias at the sensing electrodes is minimized by the capacitance multiplier of the mu-amp. This work shows that the n-JFET CSA can achieve lower noise than other capacitive interface for sensing ultra-small capacitance changes. The CSA equivalent input noise is 5nV/rms(Hz). A measured resolution of 0.001 aF (rms) in capacitance change integrated over the signal band of 10kHz-20kHz is achieved in MEMS gyroscopes.