A Two-Channel Time-Interleaved Continuous-Time Third-Order CIFF-Based Delta-Sigma Modulator
Yue Hu, Yuekai Liu, Xinyu Qin, Yan Liu, Mingqiang Guo, Sai‐Weng Sin, Guoxing Wang, Yong Lian, Liang Qi
Abstract
This work introduces a two-channel time-interleaved (TI) continuous-time (CT) 3rd-order delta-sigma modulator (DSM). It uses the information from one complete channel to predict the other channel based on the extrapolation principle. Note that, Cascaded Integrator of Distributed Feedforward (CIFF) topology is selected for the loop filter for the following reasons: 1) it could reduce the number of required feedback DACs as much as possible; 2) it allows to implement the zero optimization for the TI DSM such that the performance could be further improved. Furthermore, we employ the technique of error correction to address the issue regarding the delay-free feedback path, which originates from the extrapolating TI DSM. We present the derivations of the target TI CT DSM starting from a single-channel discrete-time (DT) DSM, while the compensation for excess loop delay (ELD) is considered. Fabricated in 65nm CMOS process, this modulator achieves an equivalent output sampling rate of 800MS/s, while the analog channel operates at 400MHz. It exhibits a signal-to-noise and distortion ratio (SNDR) /spurious-free dynamic range (SFDR)/dynamic range (DR) of 75.5dB/89.7dB/79dB over a 10MHz bandwidth. The total power consumption is 33.73mW from 1.2v/1.8v power supplies. It results in a Schreier Figure of Merit (FoM) of 163.7dB based on DR.