High DC-Gain Two-Stage OTA Using Positive Feedback and Split-Length Transistor Techniques

Abstract

A fully differential and split-length transistors (SLT) CMOS two-stage operational transconductance amplifier (OTA) is presented. The proposed amplifier is designed in a CMOS 65 nm process with a 1.2 V supply voltage. The main advantage of this proposed amplifier is the use of both positive feedback technique and the split-length transistors to enhance its DC-gain without affecting the stability, unity-gain bandwidth (UGBW), output voltage swing and power dissipation of the conventional two-stage amplifier. The DC-gain is increased by about 40 dB. The two-stage OTA has been successfully verified and a comprehensive analysis has been provided for common mode gain, differential-mode gain, power supply rejection ratio, input-referred noise and the effect of using SLT on DC-gain sensitivity. The proposed two-stage OTA is used in a flip-around sample-and-hold amplifier (SHA) circuit. A total harmonic distortion of about 0.0018% is obtained for the output spectrum of the SHA circuit.