Design of CMOS fully differential multipath two-stage OTA with boosted slew rate and power efficiency

Abstract

A CMOS fully differential multipath two-stage operational transconductance amplifier (OTA) with boosted slew rate and power efficiency is proposed in this paper. The new OTA consists of two gain stages. The basic structure of the proposed OTA is the recycling folded cascode (RFC) structure. By using the multipath technique in the first stage of the proposed OTA, it leads to an increase in gain and a decrease in power consumption. In addition, a high-speed current mirror is applied to increase the phase margin. The second stage with a class-AB amplifier is used to increase the transconductance and slew rate of the output. Moreover, the power efficiency of the proposed OTA is boosted compared to the recycling double-folded cascode (RDFC) OTA. This makes the proposed OTA more appropriate for applications that require low power consumption, such as neural amplifiers. Design and simulation of the proposed OTA is done in 0.18 μm standard CMOS technology with a 1 V supply voltage. Post-layout simulation results of the proposed OTA demonstrate that the OTA dissipates 180 nW of power, while showing a 136.7 dB voltage gain, and 127.1 kHz unity gain frequency for a capacitive load of 30 pF. Thus, compared to the RDFC OTA, the proposed OTA provides a 250 % increase in slew rate and a 20 % increase in PSRR and CMRR, while power consumption is reduced by 10 %. The proposed OTA is robust against process, voltage, and temperature (PVT) variations. The recommended OTA achieves a good figure of merit (FOM) over the previous OTAs.