| With the rapid development and wide application of the MEMS micro-sensors, the requirements for sensor performance have become higher and higher, as well as the requirements for the front processing circuits which support the sensors. Meanwhile, the general trend of development is towards the direction of small size, low voltage, low power consumption, high precision, high stability and digitization.This paper focuses on the problems such as poor transmission quality, low stability, large volume and high energy consumption that are caused by the existing logarithmic conversion circuit of the bionic polarization sensor for navigation, and takes the basic principles and key technologies of DC logarithmic and operational amplifiers as its foundation to design a dedicated logarithmic amplifier which is based on the bipolar process.The main contents include the following aspects:Firstly, analyzed the basic structure and key features of the integrated logarithmic amplifiers and operational amplifiers and determined to take the DC logarithmic amplifier as the design principles. The effect of changed performance parameters of the logarithmic transistors and operational amplifiers on the accuracy of the overall logarithmic amplifier circuit was also analyzed. Secondly, employed double logarithmic transistors and operational amplifiers as the main structure of the logarithmic amplifier, in which the logarithmic transistors has higher βand relatively lower RB and RE according to the results of analysis. The operational amplifier uses multi-level structure to increase the Gain, and in the input stage, the bias current cancellation circuits were used to reduce the input bias current. Thirdly, the simulation analysis of the operational amplifier and the logarithmic amplifier circuits was made by using HSPICE software. The representation for the accuracy of the logarithmic amplifier was analyzed and the deviation of the logarithmic amplifier circuits was calculated. The overall circuit layout was designed by using CADENCE software.The circuit simulation results indicate that, in the case of the±15V DC power, the main characteristics of the circuit are performed as follows. The logarithmic amplifier has double lμA-lmA current input and single-5V～+5V voltage output, and the error of the logarithmic amplifier is less than2%. For the operational amplifier, the input bias current is5.5nA, differential mode DC open gain is96.8dB and Common mode rejection ratio is116.7dB. The simulation results show that the structural design is reasonable, parameters of the circuits meet the design requirements and the further study needs of the subject. |
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