Rail-to-rail constant-gm operational amplifier for video applications
This paper presents an operational amplifier (op-amp) with input/output rail-to-rail capability suitable for video applications. The input stage, which is based on two complementary differential pairs, provides a constant transconductance over the entire input common-mode voltage range, whereas a class-AB output stage with an accurate control of the quiescent current ensures rail-to-rail output swing even in the presence of a heavy load. Both the input stage transconductance and the output stage quiescent current are controlled by means of static loops, which allows high-frequency operation of the amplifier. In addition, the proposed constant-transconductance technique does not depend on the IV characteristics of the input transistorsit is therefore compatible with modern submicron CMOS devicesand does not rely on any accurate matching between the complementary input pairs. The op-amp was designed to operate with 3V of supply voltage and fabricated in 0.8-?m CMOS technology. The measured open-loop gain and unity gain-bandwidth for a 100-??100-pF load are 60dB and 32MHz, respectively, while the output swing with the same output load reaches 83% of the total supply voltage.
constant-gm operational amplifiers video applications rail-to-rail operation