Research And Design On A Kind Of Low Voltage Rail-to-rail Operational Amplifier

Recently,portable devices and smart wearable products are overwhelming global electronic market with the development of microelectronics technology and computer science.Lowering supply voltage becomes the main method to prolong the working time of these electronic devices under this situation.However,the signal noise ratio(SNR)of analog circuit becomes lower and lower with the decreasing of supply voltage,which might make circuits lose their functions.So rail-to-rail operational amplifiers has been becoming a hot research in order to make full of lowering voltage and keep a high SNR.With a brief introduction of rail-to-rail operational amplifier research progress,an input and output rail to rail operational amplifier is designed in this paper on the basis of general op-amp designing method and the key techniques of implementing rail-to-rail op-amp.The amplifier proposed in this paper is based on bipolar progress realizing a constant transconductance.To realize rail to rail input voltage range,the input stage consists of paralleling complementary differential transistors which conduct at high and low voltage alternatively,and current switch and mirror serving as accessory circuit.Two kinds of way to solve the phase reversal problem are mentioned in the input stage on the basis of bipolar process.The middle stage adapts common emitter-common base structure to implement a high gain with active loads that can stabilize common voltage.A Class-AB op-amp structure is utilized as output stage to achieve rail-to-rail swing and offer a certain amount of voltage gain.Besides,the total circuit can work stably in the whole input voltage range with the Miller compensation circuit.The amplifier in this paper is designed in double aluminum bipolar process of Xiyue Corporation with the simulation of Cadence Spectre.In the condition of 3V supply voltage and paralleling 2kΩresistor and 100pF capacitance as load,the simulation turns out that this amplifier achieves as high as 99.6dB dc gain,more than 63~°phase margin over the entire common-mode voltage range,and 125dB CMRR and 113 dB PSRR at low frequency.In terms of responding time of the circuit,the positive and negative slew rate are respectively0.47V/μs and 0.5V/μs,besides,the settling time is 22/μs.The designed op-amp characterizes rail-to-rail ability with the fact of 0~3V input common-mode voltage range and 0.017~2.92V output range.