Design of Current Differencing Transconductance Amplifier using a Novel Approach of Transconductance Boosting for High Frequency Applications

Abstract

This paper introduces a novel approach of transconductance boosting for current differencing transconductance amplifier (CDTA). Generally, the variation in the transconductance is achieved by changing the bias current and/or by increasing the aspect ratios of differential pair MOSFETs. These techniques of transconductance variations suffer from several serious drawbacks which include higher power dissipation, limited range of transconductance gain and lower input/output swing. The proposed approach of transconductance boosting overcomes these drawbacks at certain extent and also provides a high value of transconductance gain with acceptable range of bandwidth and power dissipation. It includes two different techniques to make it more effective for transconductance boosting. In the first technique, common source amplifiers have been used between gate and source terminals of the differential pair MOSFETs whereas in the second technique the concept of partial positive feedback is utilized. Using this approach, a new structure of CDTA namely cross-coupled common source current differencing transconductance amplifier I (CCCS-CDTA I) is proposed. To further improve the transconductance gain of CCCS-CDTA I, another structure CCCS-CDTA II is also proposed, in which the differential pair MOSFETs are replaced by two networks of “n” parallel MOSFETs having same aspect ratios. The proposed CCCS-CDTAs are simulated in Mentor Graphics Eldo simulator using TSMC 0.18[Formula: see text][Formula: see text]m process parameters. To confirm the performance of CCCS-CDTA II, physical layout and post-layout simulation results have been presented using Mentor Graphics Calibre tool. The advantages of proposed CCCS-CDTAs have also been discussed by realizing KHN filters and oscillators.