A low voltage operational transconductance amplifier using common mode feedforward for high frequency switched capacitor circuits

In this paper, a topology for high frequency low voltage operational transconductance amplifiers (OTAs) is reported. This topology makes use of a pseudo-differential input stage and common mode feedforward. This technique was originally proposed for the realization of high frequency continuous time filters. This work shows how the technique can be modified for two stage OTAs used in switched capacitor filters. Low voltage amplifiers with high output swings, common-mode rejection ratios and power supply rejection ratios can be designed using this technique. The simulated performance of such an OTA gives a DC gain of 75 dB, unity gain frequency of 562 MHz and a low frequency common mode rejection ratio of 90 dB without mismatch. Simulation results for a 10 MHz center frequency bandpass filter making use of this technique are presented. The OTAs in the filter operate on a 1.8 V supply. The filter has been fabricated in a 0.5 μm N-Well CMOS process. Preliminary experimental results indicate proper operation of the OTAs