A Compact Fully Passive Loop Filter-Based Continuous Time ΔΣ Modulator for Multi-Channel Biomedical Applications

摘要

For the first time, we present a generic, formal design and optimization method for a fully-passive loop filter based CTDSM. The presented method aims at the automatic design of compact, low energy and simple, fully passive CTDSM for multi-channel biomedical applications. The challenges involving high RC variations, low energy consumption and compactness for multi-channel applications necessitates automated design and optimization of the CTDSM. The proposed method uses a simple linear model to arrive at the loop filter transfer function and minimize the SNR degradation across RC corners while minimizing the area and power per channel. The method was implemented in Matlab and verified using Spectre simulations. For target ENOB of 9 bits and consumed energy of less than 60 fJ/conv a CTDSM was automatically designed using the proposed method and fabricated in standard 180 nm CMOS mixed mode technology. The CTDSM uses a fully passive second order modulator with the CIFF architecture eliminating active summer circuits. The measurement results show that the modulator achieves peak SNDR of 55.42 dB at 1V supply while consuming 61.2 fJ/conv and occupies an extremely small area of 0.068 mm(2) making it the most compact reported CTDSM modulator among the low energy moderate resolution CTDSM.