Design of Adaptive Biased Operational Transconductance Amplifier with Enhanced DC Gain

Abstract

As the transistors are continuously scaling down, it becomes necessary to reduce voltage supply and power requirements of the circuit to increase its performance and stability. For voltage-mode devices, the output impedance must be low to decrease loading effect and also these devices require large number of stages which results in increased parasitic capacitance and reduced frequency response. Whereas, current- mode devices require less number of stages with high output impedance results in improved performance and large bandwidth as compared to voltage-mode techniques. Operational transconductance amplifiers are current-mode device that takes voltage as input and produces current as output with high gain and large bandwidth. To reduce power dissipation of the circuit without affecting its performance, adaptive biasing technique has been used in proposed OTA. Also, partial positive feedback and frequency dependent current mirrors are employed to further enhance the gain and the bandwidth of the proposed circuit. The simulations of proposed adaptive biased OTA with enhanced dc gain have been performed using Cadance Virtuoso Analog Design Environment in 180nm process technology. It is observed that the proposed circuit has high gain and high common-mode rejection ratio. The response of the circuit settles very fast with high power supply rejection ratio. Due to adaptive biasing technique used, the proposed OTA becomes highly sensitive to even very small different input with reduced mismatched effects. The proposed OTA can be used for biomedical equipments, gm-C filters, oscillators, variable resistors, capacitors etc.