Continuous time modulation with PWM pre-coding and binary gm blocks

Abstract

A very simple technique to implement the first integrator of a continuous-time delta sigma modulator (CT-DSM) is presented. In the approach, the CT-DSM is preceded by a pulse-width modulator to convert the input signal to a pseudo-digital continuous time waveform. As a result, the first integrator of the DSM can be implemented with a capacitor and a switched current source, with inherent linearity. To illustrate the concept, it has been applied to the design of a second-order CT-DSM in 65 nm CMOS technology.