Improved loop stability approach in fully differential operational transconductance amplifier with common‐mode feedback circuit

Abstract

This paper proposes a new approach to improve loop stability in a typical common‐mode feedback (CMFB) circuit of a differential operational transconductance amplifier (OTA). In this paper, a differential difference amplifier (DDA) with a current mirror load is employed as a CMFB circuit. The new approach is based on using two series diode‐connected transistors operating in subthreshold region in parallel with current mirror load. The proposed approach provides a reliable good function with no reduction in the OTA performance and dynamic operation of CMFB loop. The proposed scheme attains necessary high gain and large bandwidth with required phase margin for CMFB circuit. The proposed CMFB circuit is employed in a typical OTA structure. The post‐layout simulation results in TSMC 130‐nm CMOS technology show that the proposed approach leads to a better phase margin of 80°, a high unity gain bandwidth of 800 MHz, and a loop gain of 27 dB for the CMFB circuit.