PARALLEL FEEDFORWARD CLASS-AB CONTROL-CIRCUITS FOR LOW-VOLTAGE BIPOLAR RAIL-TO-RAIL OUTPUT STAGES OF OPERATIONAL-AMPLIFIERS

A new family of class-AB control circuits for bipolar rail-to-rail out put stages of operational amplifiers is presented. Step by step, we re port the development of five simple class-AB control circuits showing the advantages of using parallel feedforward. The circuits have been d esigned in such a way that temperature, supply voltage and process par ameters have little influence. To test the output stages, one of them has been implemented in a very simple two-stage operational amplifier on a semi-custom chip. Measurements show a bandwidth of 2.5 MHz, a gai n of 40 dB, a quiescent current of 23 mu A and a maximum output curren t of 250 mu A. Simulation results of three other simple operational am plifiers with the new class-AB control circuits are shown, which have a higher gain and maximum output current.