| As a bridge between analog and digital signals,a digital to analog converter plays a very important role in the various equipment systems of the aerospace industry.As an important module in DAC,the performance of the operational amplifier is related to the performance of the DAC chip and even the function of the whole system.In order to ensure the stable work of the electronic system,it is essential to study the mechanism of all kinds of radiation effects which have different negative influences on the electronic equipment in the space environment.Profound theoretical learning of different radiation effects pave the way for future study.Designing an anti-irradiation operational amplifier circuit is very meaningful for the development progress of aviation industry,especially in the space environment.This paper designs and analyzes an amplifier with anti-irradiation capability that can operate in multi-voltage environment.The main research is as follow:Firstly,the mechanism of how the total ionizing does effects,and its negative effects on the electronic system have been analyzed in detail.Combined with the principle of damage and the requirements for the performance of the DAC for the operation of the amplifier under three power supply conditions(+15V,5V,0~5V),we use the LDMOS device with a thinner thickness of the gate oxygen layer(Eastern Dongbu HiTek BCD 0.18?m process)The device can effectively reduce the threshold voltage drift and the raising of leakage current caused by the total dose radiation,and because the drift region(high resistance zone)caused by the special doping of the LDMOS leakage end makes the device withstand high pressure,it can make the device meet the design requirements of anti-total ionizing does 100Krad and high pressure resistance(+15V).Secondly,a detailed study is carried out on the tradeoff relationship between the performance parameters of the operational amplifier and the common structure and characteristics of the operational amplifier,according to which,the design index of the operational amplifier is completed,combining with the operational principle and the requirement of the parameters of the amplifier.The first stage uses the PMOS transistor as the differential folded common source common gate structure to achieve a higher gain,so that the input common mode range is not limited in the negative power potential and has a better noise effect compared with the NMOS transistor.The second stage uses a common source amplification stage with the current source as the load.The structure further improves the gain on the input level,and compensates the frequency of the circuit with the Miller capacitance and the common leakage level structure in series with it.The third stage is the output stage that provides the driving power.The push-pull,complementary,and leaky AB structure is used to drive R_L=2K?C_L=100pF,a small load and large capacitance.To satisfy the requirement of output range and the input range,the level mobile structure is added before the output stage.Considering the overall area size,a bias source is used in the bias stage to provide the bias current for the whole circuit and to use the current mirror structure to make the amplifier biasing at a suitable static working point.Under the three different power supply conditions,the operational amplifier circuit has a suitable working condition.Combined with the rules of layout design,the layout design of operational amplifier circuit is completed.Finally,the Dongbu HiTek BCD 0.18?m process LDMOS device is used to simulate the circuit in the ADE simulation environment provided by Cadence software.After the circuit simulation,the total dose 100Krads radiation simulation of selected LDMOS devices in TCAD software is carried out.Based on the simulation and analysis of the results,the parameters such as the threshold voltage and other parameters of the LDMOS device N tube and the P tube are changed in the 100Krads irradiation environment,and the parameters of the irradiated device are simulated in the circuit simulation software to simulate the working condition of the whole circuit under the 100Krads irradiation environment.Compared with the circuit simulation results without radiation,it is proved that the circuit has the anti-irradiation performance of total dose irradiation.The simulation results show that under three kinds of power supply(+15V,+5V,0~5V)and parallel load with RL=2K?and CL=100pF,the gain of operation and amplifier under each process angle model is around 100dB,and the good minimum phase margin is 62°.The time and the pressure swing rate are fully conformed to the sampling frequency of the DAC chip100KHz,and the average co mode rejection ratio of around 130dB makes the amplifier have a good common mode suppression ability.The unbalanced voltage of each power supply is less than one LSB of DAC,which meets the precision requirement of the chip and realizes the requirement of supporting the normal work of the 12 bit high voltage anti irradiation DAC chip. |
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