Study On A Low Power Rail-to-rail Input And Output Operational Amplifier

Operational amplifier is one of the most basic components in analog integrated circuits,and its performance affects the performance of the entire circuit system.With the gradual popularization of portable electronic products,low voltage and low power operational amplifiers have become a research hotspot in the field of analog circuits.Because the lower supply voltage and supply current will reduce the dynamic range and noise performance of the op amp,low voltage and low power systems put forward higher requirements for op amps.In order to obtain the maximum dynamic range,it is necessary to improve the structure of the traditional op amp,so that it can process the voltage signal from the negative supply rail to the positive supply rail.Therefore,it is of great significance to study a low power,rail-to-rail operational amplifier.This paper introduces the trade-off relationship between power and noise,stability,analyzes the advantages of bipolar process in low power design of op amps,and studies the basic principles of rail-to-rail input stage with constant transconductance and rail-to-rail output stage.Then combined with relevant theoretical knowledge,this paper designs a low power rail-to-rail operational amplifier based on the bipolar process.The bias circuit uses a peaking current source to provide the reference current.The input stage uses a current switch structure to achieve a constant transconductance and the method of switch transistor in series with a resistance is used to extend the transition range.Therefore,the common mode rejection ratio of the transition region is improved.The intermediate stage uses a folded cascode structure to increase the open-loop gain of the op amp.The output stage uses a class AB,common emitter structure to achieve rail-to-rail output voltage swing.The operational amplifier designed in this paper uses CSEC WC40 S bipolar process,the circuit is simulated and verified by Cadence Spectre simulation tool.The simulation results show that the common-mode input range and output voltage swing of the op amp achieve rail-to-rail input/output requirements.At room temperature,the quiescent supply current is 346?A,the open-loop gain is 115.9dB,the unit gain bandwidth is 3.08 MHz,the phase margin is 65.6°,the common mode rejection ratio is 131.8dB,the positive and negative power supply rejection ratios are 131.3dB and 136.7dB,the positive and negative slew rates are 1.02V/?s and 1.2V/?s.Finally,the layout design and tape-out test of the four-channel operational amplifier are completed,and the test results basically conforms to the simulation results.The offset voltage of the operational amplifier is between 100?V³00?V,and the equivalent input noise voltage density measured at 1kHz is between 20³0nV/Hz^1/2.The above results indicate that the operational amplifier designed in this paper achieves the expected requirements.