Modified Current-reuse OTA to Achieve High CMRR by utilizing Cross-coupled Load

Abstract

Since biomedical signals have very low amplitude and high common-mode like environmental noise, the amplifiers used with these signals should have high CMRR. The cross-coupled amplifier attenuates common-mode signal strongly because of its load behavior for differential and common-mode signal which leads to high CMRR. Since cross-coupled amplifier differential gain is low, its load is combined with current-reuse operational amplifier. The final CMRR of a fully differential current-reuse OTA with conventional common-mode feedback and modified load is simulated and compared in a 0.18 μm CMOS technology. Their CMRR is simulated for mismatch and process variation. According to the simulation, for the same power consumption, W and L, the modified current-reuse with cross-coupled load has the best performance. Its CMRR in the worst case was about 90 dB while the total power consumption was 18 μW at 1.8 V supply voltage. The Bandwidth is 4.8 kHz and the total input referred noise in this bandwidth is 1.04 μV rms and 0.43 μV rms from 0.5 to 100 Hz which is acceptable noise and bandwidth for the EEG application considered in this study.