Constant-gm rail-to-rail input/output Op-Amp for video applications

An operational amplifier (op-amp) with input output (I/O) rail-to-rail (r-t-r) capability suitable for video applications is presented. The input stage provides a constant transconductance value over the entire input common-mode range, whereas a class-AB output stage with an accurate control of the quiescent current ensures r-t-r output swing. 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. Experimental results from a 0.8-µm CMOS test chip are shown.