An 81.5dB SNDR, 2.5 MHz Bandwidth Incremental Continuous-Time Delta-Sigma ADC in 180 nm CMOS

Abstract

Adapting a continuous time delta-sigma analog-to-digital converter (ADC) for incremental operation at high sampling rates degrades the noise and distortion due to potential overload of the modulator as it comes out of reset and nonlinear residue on the reset switch due to input current flowing through it in the reset phase. It is shown that the input and DAC currents must simultaneously begin to flow through the first integrating capacitor to minimize the possibility of overload. The first integrator reset has to be released just before the start of the DAC pulse. A feedforward path must be used to ensure that the DAC output is close to the input signal from the beginning. Blocking the input current from flowing through the reset switch in the reset phase eliminates the effect of the nonlinear residue. A 320 MS/s fourth-order incremental delta-sigma ADC prototype in an 180nm process using the above techniques has 90 dB dynamic range, 82 dB SNDR, and 84.5 dB SNR in a 2.5 MHz bandwidth. It consumes 46.3 mW from a 1.8V supply and occupies 0.7 mm2.