High-gain, high-bandwidth, rail-to-rail, constant-gm CMOS operational amplifier

This study presents a high-gain, high-bandwidth, constant-gm , rail-to-rail operational amplifier (op-amp). The constant transconductance is improved with a source-to-bulk bias control of an input pair. A source degeneration scheme is also adapted to the output stage for receiving wide input range without degradation of the gain. Additionally, several compensation schemes are employed to enhance the stability. A test chip is fabricated in a 0.18?mu m complementary metal-oxide semiconductor process. The active area of the op-amp is 181?X?173?mu m2 and it consumes a power of 2.41?mW at a supply voltage of 1.8?V. The op-amp achieves a dc gain of 94.3?dB and a bandwidth of 45?MHz when the output capacitive load is connected to an effective load of 42.5?pF. A class-AB output stage combining a slew rate (SR) boost circuit provides a sinking current of 6?mA and an SR of 17?V/mu s.