Design and Analysis of a Continuous-Time Common-Mode Feedback Circuit Based on Differential-Difference Amplifier

The main purpose of this study is to introduce a new continuous-time Common-mode Feedback Circuit (CMFB) based on Differential-Difference Amplifier (DDA) in order to achieve high speed, high loopgain, and simultaneously low distortion characteristics. Two control voltages with opposite variations used in the proposed CMFB make the loop-gain and speed enhancement of the circuit. Additionally, reducing the dc level and input signal amplitude of the CMFB by using source follower circuits helps to increase the effective voltage of differential pairs and hence the linearity performance of the circuit. HSPICE simulation based on 0.35 :m CMOS process is done in order to evaluate the performance of the proposed CMFB circuit and the results indicate that the proposed CMFB is faster than the typical one and has lower odd and even harmonics in comparison with the conventional CMFB.

Common-mode feedback, differential-difference amplifier, high speed, low distortion, operational amplifier, transconductance