High-gain High-performance Op Amp For Capacitive Sensors

Operational amplifier is widely used in all kinds of analog and mixed-signal circuit. There are many differences of focused performance because it is applied for differential circuit. Based upon basic principles of the analog integrated circuit and theories of system stability, this paper deals with fully differential CMOS Operational Amplifiers(opamp).Other than discussions about its performance evaluation and testing, a two-stage fully differential opamp for capacitor accelemeter has also been designed including its core cell and the overall layout.Firstly, a two-stage structure for the opamp is presented after comprehensive considerations on characteristics like open-loop DC gain, unity-gain bandwidth, phase margin and settling time. Then the input and output topologies have been decided by comparing different structure available for this purpose.During the process of designing the core cell, a trimming continuous time common-mode feedback structure has been proposed to trim DC offset and miller compensation has been used to trim phase margin to meet circuit demand.At last, using the advanced EDA tool Cadence and IBM 0.35μm Bicmos process model, the typical circuit cells are simulated by specture.The results show that the open-loop gain, unit-gain bandwidth, and phase margin are 121.8dB, 8.48MHz, 78.6°respectively, at the cost of a power dissipation of 4.365mW. The module applies IBM 0.35μm Bicmos process,The final chip area consumption of the OTA circuit is 220μm×180μm.The results demonstrate that the high open-loop gain fully differential opamp satisfies (even exceeds) the parameters set beforehand. After slight modification, this circuit has been successfully applied to capacitor accelemeter..