Research On Timing Control And Nonuniformity Correction Of Multi-Channel Electronic Multiplication CCD

With the rapid development of EMCCD,it has become one of the core devices in the field of low-light imaging and is widely used in military,astronomy and other fields.EMCCD can achieve the effect of charge multiplication at the solid state level,and is especially suitable for working under low light conditions.Because of its high resolution,high frame rate,low readout noise and high quantum efficiency,it has important applications in the adaptive optical system of large-aperture telescopes.Indepth study of the imaging mechanism of the EMCCD sensor,the design of its driving timing generator is completed,and the problem of uneven imaging quality caused by multi-tap readout is solved,which is of great significance for the domestic research and development of the high-performance EMCCD camera.Firstly,this paper analyzes the basic working principle of EMCCD device,establishes the photoelectric conversion model of electron multiplying CCD,focuses on the physical model of the electron multiplying part,and obtains the channel transmission equation of EMCCD.By measuring the electronic multiplication gain of the actual camera,the measurement method of the electronic gain is determined,and it is verified that the photoelectric conversion model can coincide with the multiplication curve of the actual device.The correct construction of the photoelectric conversion model is of great significance to guide the follow-up multi-tap drive timing generator design and non-uniformity correction research.In order to ensure that the multi-tap EMCCD camera can work normally and steadily,its most critical is the generation of driving signals and the processing of output signals.Based on the 8-tap CCD220 sensor,a 2000 frame / second high-speed,highprecision,multi-channel synchronous timing generator is designed,and a variety of pixels are combined on the CCD device through timing control,further increasing the camera frame rate to 3500 frames / second(2 × 2 merge)and 5700 frames / second(4 × 4 merge).The stepping accuracy of the timing generator can reach 2.5ns,and the phase jitter of the output drive signals can reach less than 200 ps.Aiming at the timing requirements of the driving signal in the CCD220 chip manual,designing a multi-tap high-precision timing generator is the premise for the camera to work normally,and is also the basic work of the subsequent non-uniformity correction research.Since CCD220 is an image sensor with eight-channel readout,according to the established photoelectric conversion model,it can be seen that the parameter difference of each channel will cause output non-uniformity.By analyzing the source of nonuniformity,and comparing the existing non-uniformity It is proposed that the two-step correction method be used to correct the non-uniformity of the linear system and the non-uniformity of the electronic gain respectively.The experimental results show that the non-uniformity correction of the EMCCD camera using the two-step correction method has obvious improvement effect.The root mean square deviation of the gray value of the image before correction is 0.09%,and 0.01% after correction;the PRNU of the camera before correction is 0.99%,and the PRNU of the camera after correction is 0.45%.The correction algorithm can reduce the image non-uniformity by more than 50% under different exposure time and different gain conditions.From the perspective of imaging effect,the image segmentation before correction is obvious,and after correction is eliminated,a uniform and clear image can be obtained,and the result is satisfactory.Finally,the localized EMCCD camera is tested,a test platform is built,and its performance is evaluated as a whole,and compared with the OCAM2 camera at the highest level of the current adaptive optical system,and the parameters of the selfdeveloped EMCCD camera are obtained.Basically meet the needs of adaptive optical systems,and can be comparable to foreign high-level cameras.