High Transconductance Gain Current Differencing Transconductance Amplifiers Using a New Approach of gm Boosting

Abstract

Two new structures of current differencing transconductance amplifier (CDTA) for high transconductance gains are proposed. Usually, the transconductance gain of conventional CDTA is controlled by varying the bias current which limits the transconductance gain up to a certain extent and increases the power dissipation. These problems have been eliminated by introducing a technique in which common source amplifiers are connected between gate and source terminals of the differential pair metal oxide semiconductor field effect transistors (MOSFETs) of conventional CDTA. The common source amplifiers are used to increase the gate-to-source voltages of differential pair MOSFETs which increase the transconductance gain of the proposed CDTA-I. To further increase the transconductance gain of the proposed CDTA-I, another structure namely, CDTA-II is also proposed which uses an ‘N’ number of n-type MOSFETs connected in parallel instead of a single n-type MOSFET in each side of the differential pair. The gate-to-source voltages of all ‘N’ parallel MOSFETs remain the same as in the proposed CDTA-I and the total output current of operational transconductance amplifier is increased and therefore, transconductance gain is further increased. The proposed CDTA-I and CDTA-II have been designed using Mentor Graphics Eldo tool. The simulation results have been obtained using 0.18 µm complementary metal oxide semiconductor technology parameters. The simulation results demonstrate that the transconductance gains of proposed structures have been increased significantly while power dissipations are the same as that of the conventional CDTA. The high-frequency Kerwin–Huelsman–Newcomb filters using both the proposed structures have also been presented to show the effectiveness of the proposed CDTAs.