A novel design of current differencing transconductance amplifier with high transconductance gain and enhanced bandwidth

Abstract

In this paper, transconductance gain of current differencing transconductance amplifier (CDTA) has been boosted by using a novel approach. Transconductance is generally varied by two well-known techniques. In the first technique, bias current of differential pair MOSFETs is varied whereas in the second technique, aspect ratios of differential pair MOSFETs are changed. The drawbacks of first technique are limited range of transconductance and higher power dissipation whereas second technique restricts dynamic range, output swing and bandwidth of CDTA. To overcome these drawbacks, 2 new structures of CDTA, namely high transconductance gain CDTAs (HTG-CDTA-I & HTG-CDTA-II) have been proposed. HTG-CDTA-I utilizes partial positive feedback in the active loads of differential pair MOSFETs to increase the transconductance gain. The partial positive feedback reduces the linear range of HTG-CDTA-I that is counter balanced by employing source degeneration resistors. In addition, parallel MOSFETs are used in the structures of current mirrors to achieve higher value of transconductance. To enhance the bandwidth of proposed HTG-CDTA-I, another structure known as HTG-CDTA-II has also been proposed. In this structure, compensation resistors are connected at the gate terminals of driver MOSFETs of current mirrors. To prove the worthiness of proposed HTG-CDTA-II, KHN filter is realized and its advantages have been discussed.