Noise of piezoelectric accelerometer with integral FET amplifier

Since significant progress has been achieved in the development of low-noise piezoelectric (PE) accelerometers with integral FET amplifiers, detailed noise analysis of the system PE transducer-FET amplifier, and obtaining the engineering formula for its noise floor has become vital. As a result of this analysis, the formula for the noise floor of PE accelerometers in terms of acceleration spectral density is obtained at wide frequency band. Noise floor of the low-noise PE accelerometer comprising low-noise JFET charge amplifiers with some particular parameters of the PE transducer and the JFET amplifier was measured. The theoretical and experimental curves of the PE accelerometer's noise floor have a good correlation with each other at frequencies from 1 Hz; to 10 kHz. The contribution of the different noise sources to the overall noise floor is shown. Those noise sources include the mechanical-thermal noise and electrical-thermal noise of the PE transducer and all main noise sources of FET amplifiers: the thermal noise voltage of the FET biasing resistor, the thermal noise of the series resistor between the PE transducer and the gate of the FET, the channel thermal noise voltage, the 1/ f noise voltage, and the shot noise current in the gate circuit. At low frequencies, the f <= 50 Hz noise floor is determined mainly by the FET biasing resistor's thermal noise and the PE transducer's electrical-thermal noise. At frequencies from about 50 Hz; to about 1 kHz, the contribution of the PE transducer's electrical-thermal noise dominates over the amplifier's noise sources by a factor of less than 2. At frequencies above I kHz, noise floor is determined mainly by the JFET channel thermal noise and the PE transducer's electrical-thermal noise.