Design and Implementation of a Linear Transconductance Amplifier with a Digitally Controlled Current Source

Abstract

This paper presents a new configuration for balanced Operational Transconductance amplifies where digitally controlled current switch is designed to generate the different bias currents. To achieve better linearity, the source degeneration circuit for differential pair is used in the Balanced OTA [1]. The digitally controlled switch is nothing but MOSFETs with different width and lengths. This helps to have different bias currents just by turning on particular MOSFET in the switch module. Using the designed structure a variable resistor is designed [2]. Also as an application example, an electronically tunable phase shifter is implemented [3]. In this phase shifter using the designed OTA, by applying different bias currents generated through the digital switch we can obtain different phase shifts. The circuit performance of linear transconductance amplifier is measured in terms of the linearity, slew rate, CMRR, settling time, over shoot and undershoot. Here all the circuits are implemented Tanner EDA and simulated in 130nm using TSMC MOSIS Level-49 model in TSPICE simulator.