A Delta-Sigma Modulator for Low-Power Analog Front Ends in Biomedical Instrumentation

Abstract

This paper presents a high-resolution dual-integrating delta-sigma modulator (DI-DSM) for low-power analog front-end (AFE) circuits in biomedical instrumentation. The AFE contains a preamplifier and a switched-capacitor DS analog-to-digital converter. The proposed DI-DSM adopts two kinds of clock frequencies: one is the same as the conventional frequency and the other is one-half of the conventional frequency, which provides sufficient settling time for critical blocks. The proposed structure reduces harmonic distortions at the output of the preamplifier, since the preamplifier is given sufficient time to charge the sampling capacitor in the DSM. The use of a lower switching frequency at the critical blocks results in a significant reduction in the power consumption of both the preamplifier and the modulator. The proposed AFE chip is fabricated in a 65-nm CMOS process. The measurement results of the modulator show a peak signal-to-noise ratio (SNR) of 81.4 dB and a peak signal-to-noise-plus-distortion ratio (SNDR) of 80.4 dB, with a power consumption of 24.8 mu W at a supply voltage of 1 V and a signal bandwidth of 10 kHz. The complete AFE chip [which includes a preamplifier, a DI-DSM, a low-dropout (LDO) regulator, and a bandgap reference circuit (BGR)] shows a measured peak SNR of 79.3 dB and a measured peak SNDR of 77.0 dB with a preamplifier power of only 46.8 mu W (and 22.3 mu W for LDO, and 36.3 mu W for BGR).