Design Of Optocoupler Chip For Intelligent Hardware Application

Due to its advantages of small size,good isolation performance and unidirectional signal transmission,optocoupler plays an irreplaceable role in medical,aerospace,industry,and communication fields.With the continuous advancement of optoelectronic technology,the application fields of optocoupler are becoming more and more abundant.In order to solve the problem of low working speed and low integration level of optocouplers composed of discrete devices,the research and design of the optocoupler chip are carried out in this paper.Based on the Bi CMOS process,a high-speed and high-integration optocoupler chip for intelligent hardware applications is realized.The traditional structure,basic working principle and important performance parameters of optocoupler is studied in this paper firstly.And then the basic structure diagram and design index of the designed optocoupler is given.The basic working principle and main characterization parameters of light-emitting diode are introduced,and suitable light-emitting diode is selected for the optocoupler chip designed in this paper.Aiming at the problem of low working speed,a photodetector based on the interdigitated structure is designed.By increasing the proportion of photogenerated fast carriers,the response speed of the photodetector is improved,and finally the overall working efficiency is achieved.The current signal converted from the optical signal by the photodetector is very weak and easily disturbed.Aiming at this problem,the research on the circuit design of the transimpedance amplifier is carried out.The performance parameters and typical structure of the transimpedance amplifier are analyzed,and the differential structure transimpedance amplifier is designed to suppress the internal common mode noise of the optocoupler.After the structure of the transimpedance amplifier,an amplifier is designed to prevent the problem that the voltage signal converted by the transimpedance amplifier is too small to drive the subsequent circuit.NPN transistors are used in transimpedance amplifier and amplifier as input transistors to achieve low noise and low offset.The design of the whole light receiving circuit module also includes:reference circuit,hysteresis comparator,logic circuit and output driving circuit.Darlington transistors and NMOS transistors are used as output drive circuit to achieve class AB drive capability and ensure a wide operating voltage range of the output stage of the optocoupler.According to the application requirements,the circuit design,layout drawing and simulation analysis based on Bi CMOS process are carried out in this paper.Simulation results show that the optocoupler can work in the supply voltage range of 15?30V,and the peak output current can reach 2.85(32).In a typical case,the structure of 10Wresistor and a10n F capacitor in series is used as the load of the output terminal to test the signal transmission characteristics of the optocoupler.The measured rise time t_r of the output signal is 60ns,the fall time ? is 67.3ns,the rise propagation delay time t _PLH is 118ns,and the fall propagation delay time t _PHL is 113.8ns.The layout area of the entire optocoupler chip is1.069mm×1.209mm.