Abstract
This paper presents a low-power second-order sigma-delta modulator (SDM) for micro-electromechanical systems (MEMS) digital geophones (DGPs). The proposed SDM optimizes the performance of the first stage integrator and uses an adaptive class-AB current recycling operational transconductance amplifier (OTA) to improve the current efficiency. In addition, gain-enhancing circuits are applied in the OTA to increase the DC gain, and the chopper technique is used in the first stage integrator to reduce the flicker noise. The proposed SDM was implemented in the SMIC 0.18 μm CMOS technology and occupies an area of 0.82 mm2. The simulation results reveal the signal-to-noise ratio (SNR) was 76.46 dB and the effective number of bit (ENOB) was 12.4 bits. Measurements show that the SNR was 57.5 dB and the ENOB was 9.26 bits with a sampling rate of 256 kHz, an oversampling ratio 128, and a signal bandwidth of 1 kHz. The proposed SDM has a supply voltage of 1.8 V and a power consumption of 193.5 μW, which is suitable for the low-power MEMS DGPs applications.
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