An Ultra Low-Noise Vibration Monitoring System

This paper reports a piezoelectric accelerometer based vibration monitoring system. The used A1N accelerometers take advantage of a novel sensing structure to improving the charge sensitivity without increasing the sensing area using the approach of stress concentrations. Furthermore, the sensing structure is designed to have low off-axis sensitivity and to be reliable with symmetric balanced bars between sensing beams. Experimental results confirm the significantly improved sensitivity of the accelerometers obtained with the new sensing structures. The tested charge sensitivity is 5.2 pC/g and the measured total noise floor of sensor plus interface electronics is as low as 670 ng/ radicHz. The designed continuous-time sensor readout architecture is based on a CMOS charge amplifier with chopper stabilization to reduce the l/f noise, the dc offset, and the noise folding. The complete front-end readout system has been implemented in a 0.35 mum 4M2P CMOS process, and operates from a supply voltage of plusmn 1.65 V. The entire open-loop readout architecture was designed according to all relevant noise and error sources. The simulated DC gain, gain bandwidth product and phase margin are 90 dB, 15 MHz and 73 deg. respectively. The thermal noise floor is well below 400 ng/ radicHz (4 nV/radicHz) as periodic noise analysis reveal.