A Two-Stage Single-Ended OTA with Improved Composite Transistors

Abstract

This work presents a two-stage single-ended Operational Transconductance Amplifier (OTA) with very high voltage gain and rail-to-rail output voltage excursion. This is achieved by using Improved Composite Transistors (ICT) with safe forward-body-biasing, so the amplifier can be used with typical I/O supply voltages and high- VT thick-oxide transistors without significant parasitic substrate current. Two versions of the same OTA were designed and simulated using the TSMC 180 nm PDK. The first version, made of only Rectangular Transistor Arrays (RTA), achieved a 109 dB voltage gain, 195.8 kHz GBW, 59° phase margin for a 10 pF capacitive load, while 6.57 µW of power at 3.3 V power supply. The proposed ICT OTA version achieve about the same specifications, however, its voltage gain was 155 dB, a 41 dB increase.