Rail‑to‑rail input/output bulk driven class AB operational amplifier with improved composite transistors

This work presents two-stage single-ended operational transconductance amplifiers (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-bodybiasing, 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 open-source Skywater 130 nm PDK. The first version, made of only trapezoidal transistor arrays, achieves an 84 dB voltage gain, 1.33 MHz GBW, and 60◦ phase margin for a 10 pF capacitive load while demanding 122μW of power at 3.0 V power supply. The proposed ICT OTA version attains about the same specifications, except for its voltage gain, which has increased by 33 dB, thus reaching 121 dB.