A fast-response reference voltage buffer for a sigma-delta modulator

Abstract

This paper presents a low-power reference voltage buffer with fast load transient response that can be used to drive capacitive loads. The circuit is based on an improved replica-biasing source follower structure that combines the high precision of the closed loop and the high bandwidth of the open loop, and it meets the requirements of high precision, fast load transient response for a sigma-delta modulator. The proposed circuit is implemented in 0.18 µm CMOS technology provided by Semiconductor Manufacturing International Corp. (SMIC). The reference voltage buffer is combined with a sigma-delta modulator. The result shows that when the load capacitor is 10 pF, the settle time is 134 ns, the quiescent current is 81.5 µA, and the chip area is 117 µm × 220 µm.