Improved Chopping in Continuous-Time Delta–Sigma Converters Using FIR Feedback and <inline-formula> <tex-math notation="LaTeX">${N}$ </tex-math> </inline-formula>-Path Techniques

Abstract

Chopping the operational transconductance amplifier (OTA) of the input integrator in a continuous-time delta–sigma modulator is an effective way of addressing ${1/f}$ noise. This, however, causes shaped noise to alias into the signal band. A solution to this problem is to chop at the sampling rate of the modulator. High-speed chopping reduces the OTA’s dc gain, and degrades its linearity. Alternatively, the OTA can be chopped at a low rate, and FIR feedback can be used to introduce spectral nulls in the feedback waveform, so that the components that alias into the signal band are attenuated. This brief combines chopping and FIR feedback with ${N}$ -path techniques, enabling a much lower chopping frequency than would otherwise be possible with a given number of FIR DAC taps. Simulation results confirming the theory are given.