A Rail-to-Rail Operational Amplifier with Low Offset Volltage

An input and output rail-to-rail operational amplifier with low offset was introduced. The input and output stages of the circuit adopt compound folded common emitter and base structure which can not only get the input amplitude near to power supply rails but attain a high gain. Class-AB output structure is utilized to accomplish rail-to-rail output. Based on Xiyue corporation's 6 μm 40 V standard bipolar process, simulation results of Cadence Spectre demonstrate that the low-frequency gain and unity-gain bandwidth of the proposed circuit are 160 dB and 6.07 MHz respectively. It also shows offset voltage can be reduced to 10% of the traditional circuit with the 20% change of pJFET's threshold voltage in modified middle stage.