An Enhanced Input Differential Pair for Low-Voltage Bulk-Driven Amplifiers

Abstract

This article presents a low-voltage high-transconductance input differential pair for bulk-driven amplifiers. The proposed structure employs two bulk-driven flipped voltage follower (FVF) cells as nonlinear tail current sources to enhance the slewing behavior. This method also increases the transconductance of the proposed amplifier two times against the conventional one. The enhanced topology is merged with a conventional bulk-driven input differential pair using cross-coupled connections to significantly increase the transconductance. These circuitry ideas lead to an improvement in the amplifier's specifications, such as dc gain, slew rate (SR), and input noise without any degeneration in other parameters. Moreover, thanks to the use of the bulk terminals as the input nodes and also a simple common-source structure as the second stage, rail-to-rail input, and output swings are achieved, respectively. The proposed amplifier was fabricated in TSMC 0.18- μm CMOS technology. Under a supply voltage of 0.5 V, the measurement results show that the proposed amplifier achieves a dc gain of 78 dB, a gain bandwidth of 7.5 kHz, and an SR of 8.6 V/ms with just 91-nA current dissipation.