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Abstract-Precise behavioral modeling of switched-capacitor16 modulators is presented. Considering noise (switches' and op-amps' thermal noise), clock jitter, nonidealities of integrators and op-amps including finite dc-gain (DCG) and unity gain bandwidth, slew-limiting, DCG nonlinearities and the input parasitic capacitance, quantizer hysteresis, switches' clock-feedthrough, and charge injection, exhaustive behavioral simulations that are close models of the transistor-level ones can be performed. The DCG nonlinearity of the integrators, which is not considered in many 16 modulators' modeling attempts, is analyzed, estimated, and modeled. It is shown that neglecting this parameter would lead to a significant underestimation of the modulators' behavior and increase the noise floor as well as the harmonic distortion at the output of the modulator. Evaluation and validation of the models were done via behavioral and transistor-level simulations for a second-order modulator using SIMULINK and HSPICE with a generic 0.35-m CMOS technology. The effects of the nonidealities and nonlinearities are clearly seen when compared to the ideal modulator in the behavioral and actual modulator in the circuit-level environment.

This paper presents an implantable bio-impedance measurement system for cardiac pacemakers. The fully integrated system features a low power analog front-end and pulse width modulated output. The bio-impedance readout benefits from voltage to time conversion to achieve a very low power consumption for wirelessly transmitting the data outside the body. The proposed IC is fabricated in a 0.18 μm CMOS process and is capable of measuring the bio-impedance at 2 kHz over a wide dynamic range from to with accuracy and maximum current injection while consuming just from a 1 V supply.

In this paper, we show that excess loop delay seriously degrades the performance of continuous-time deltasigma modulators (AZM's). It is then demonstrated in theory that the effect can be alleviated by tuning the feedback digital-to-analog converter pulse-shaping coefficients.

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