Design Of High-Speed Optocoupler Chip Based On CMOS Process

As one of the most important devices in the field of optoelectronics,optocoupler plays an irreplaceable role in medical,military and communication fields due to its good electrical isolation characteristics.In order to achieve the goal of high integration,low development cost and easy packaging of optocoupler,this thesis uses CMOS technology for the monolithic integration of silicon-based photodetectors and CMOS optical receiving circuits.Photodetector is a core in the optocoupler design.It's necessary to achieve both high responsibility and wide bandwidth as for performance.Beginning with the analysis of basic photodetectors structures in CMOS process,three kinds of photodiodes are designed on the basis of corresponding theory in this thesis designs.The performance of photodiodes including DNW/P-Sub photodiode,double photodiode and triple photodiode is analysed.The bandwidth of photodiodes with different structures are optimized and the method of improving bandwidth by comparing a pair of structures are put forward..Finally,DNW/P-Sub photodiode is chosen as the most appropriate photoelectric detector in optocoupler according to the predicted index of the optocoupler and testing results.The simulation results show that when V_cathode=5V,?=850nm,the photocurrent I_p=6.38?A,responsibility R=0.17A/W,-3dB bandwidth f_-3dB=70MHz.In photodiode,there is slow diffusion photocurrent,which affects the bandwidth of the device and leads to the pulse width distortion of the output of optical receiving circuit.The relationship between frequency and pulse width distortion is studied in this thesis.To solve this problem,a peak-sampling circuit is added to the traditional optical receiving circuit.The whole optical receiving circuit module includes transimpedance amplifier,peak-sampling circuit,comparator and D flip-flop.This thesis shed light on the function of the peak signal sampled by the peak-sampling circuit in the optical receiving circuit,and the effect of the novel optical receiving circuit on improving the pulse width distortion.Three basic structures and parameters of transimpedance amplifier are introduced.Based on common source transimpedance amplifier,a structure with internal negative feedback is designed.The simulation results of the optical receiving circuit show that the bandwidth of the transimpedance amplifier is 62.5MHz,the transimpedance gain is 100k?,the delay of the comparator is 0.18ns,the bandwidth of the analog part of the whole circuit achieves 20MHz,the duty cycle of the final output waveform is 66%,the pulse width distortion is 3.5ns,and the improvement of the duty cycle of the waveform of the optical receiving circuit in the traditional mode is up to 30%.