Generalized Circuit Techniques for Low-Voltage High-Speed Reset- and Switched-Opamps

Abstract

This paper presents several comprehensive and novel circuit techniques that can be efficiently applied to low-voltage (LV) high-speed reset-opamp (RO) and switched-opamp (SO) in LV switched-capacitor circuits. The first, designated as virtual-ground common-mode (CM) feedback with output CM error correction, allows the design of fully differential RO circuits that could only be traditionally implemented before in pseudo-differential mode, and it leads to considerable savings of half of the opamps' power. The second, uses a crossed-coupled passive sampling interface to avoid the extra track-and-reset stages as required in both RO and SO circuits, further saving one front-end opamp's power. The third, employs a voltage-controlled level-shifting (LS) technique that utilizes the charge redistribution property to process the CM LS in an LV environment, avoiding the degradation of the feedback factor by the use of extra LS circuits. Finally, the fourth, the LV finite-gain compensation technique allows the use of low-gain high-speed single-stage amplifier in contrast to the conventional high-gain, low-speed two-stage opamp to achieve a high-speed operation in both RO and SO circuits. Without any clock boosting or bootstrap circuits, all of the above techniques can be applied in LV applications without any floating switches limitations. Measurement results of a 1.2-V 10-bit 60 MS/s pipelined analog-digital converter in 0.18- mum CMOS with RO are presented to verify the effectiveness of the proposed techniques, achieving a signal-to-noise distortion ratio of 55.2 dB with 85-mW power consumption.