An ultra-low noise capacitance to voltage converter for sensor applications in 0.35  µm CMOS

Abstract

Abstract. In this paper we present a readout circuit for capacitive micro-electro-mechanical system (MEMS) sensors such as accelerometers, gyroscopes or pressure sensors. A flexible interface allows connection of a wide range of types of sensing elements. The ASIC (application-specific integrated circuit) was designed with a focus on ultra-low noise operation and high analog measurement performance. Theoretical considerations on system noise are presented which lead to design requirements affecting the reachable overall measurement performance. Special emphasis is put on the design of the fully differential operational amplifiers, as these have the dominant influence on the achievable overall performance. The measured input referred noise is below 50 zF/ √Hz within a bandwidth of 10 Hz to 10 kHz. Four adjustable gain settings allow the adaption to measurement ranges from ±750 fF to ±3 pF. This ensures compatibility with a wide range of sensor applications. The full input signal bandwidth ranges from 0 Hz to more than 50 kHz. A high-precision accelerometer system was built from the described ASIC and a high-sensitivity, low-noise sensor MEMS. The design of the MEMS is outlined and the overall system performance, which yields a combined noise floor of 200 ng/ √ Hz, is demonstrated. Finally, we show an application using the ASIC together with a CMOS integrated capacitive pressure sensor, which yields a measurement signal-to-noise ratio (SNR) of more than 100 dB.

Python-Based Open-Source Electro-Mechanical Co-Optimization System for MEMS Inertial Sensors

“…A capacitance-to-voltage converter was implemented in the code, to calculate a voltage output from the acceleration induced capacitance change. The converter is based on the converting block designed by Utz et al [20], as shown in Figure 2 with a governing equation stated in Equation ( 6), in which V DD is considered 5 V and V CM is considered 2.5 V.…”

A MEMS Accelerometer for Sub-mG Sensing

“…(23) The total noise of a capacitive accelerometer consists of B N and electrical noise. (26) In this study, we assume that the electrical noise is negligibly small, which can be achieved by considering the sensing circuit technology (27) and large sensitivity, typically on the order of several pF/G.…”

“…The sensitivity was experimentally obtained to be 3.3 pF/G, which showed the potential of sub-mG sensing with capacitance-to-voltage converter circuits. (27)…”

Low Noise Interface ASIC of Micro Gyroscope with Ball-disc Rotor

“…And the circuit noise includes electrical-thermal noise (Johnson noise), shot noise, flicker noise (1/f noise), demodulation phase noise, and so on. To reduce this noise, low-noise readout circuits have been reported [10][11][12][13][14][15][16]. But, the published papers mostly focus on vibratory micro gyroscope, and the noise analysis of rotor-type micro gyroscope is rarely mentioned.…”