### Design of an Ultra-Low Power CT Sigma Delta A/D Modulator in 65 nm CMOS for Cardiac Pacemakers: From System Synthesis to Circuit Implementation

#### Abstract

A high performance, ultra-low power, fully differential 2nd-order continuous-time Sigma Delta analogue-to-digital modulator for cardiac pacemakers is presented in this paper. The entire design procedure is described in detail from the high-level system synthesis in both discrete and continuous-time domain, to the low-level circuit implementation of key functional blocks of the modulator. The power consumption of the designed modulator is rated at 182 nA from a 1.2V power supply, meeting the ultralow power requirement of the cardiac pacemaker applications. A 65 nm CMOS technology is employed to implement the Sigma Delta modulator. The modulator achieves a simulated SNR of 53.8 dB over a 400Hz signal bandwidth, with 32KHz sampling frequency and an oversampling ratio of 40. The active area of the modulator is 0.45 × 0.50mm2.

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