Researches On The Key Technologies Of Synchronous Scan Circuit In Streak Camera

Synchronous scan streak camera using quasi linear part of sine signal to scan theinput photoelectrons repeatedly, and the weak signal is accumulated to be strongenough to be detected. The quasi linear part of the sine signal should be strictlysynchronous to the input light impulse in the whole process, and this makes phasejitter of the scanning signal very important to the system. If time jitter of the sine scansignal applied on deflection plate is large enough, displacement of the scanned signalwill be deviated from initial place in the direction of both horizontal and vertical, andthis will affect time and spatial resolution of streak camera greatly.This article proposes a new method using phase locked loop and direct digitsynthesizer to generate high frequency scan signal. In this method, PLL is used toachieve strict synchronization of sine signal and trigger laser impulse. PLL can alsoprovide reference input to DDS. DDS is used to generate sine scan signal andmodulate phase and amplitude of the scan signal. After a brief introduction ofresearches on streak camera and character of synchronous scan circuit, a detailpresentation of PLL and DDS technique is followed. Analysis of structure andoperating principle is discussed, which provide theory basis of synchronous scancircuit design. Detail design of the synchronous scan circuit is exhibited then, with athorough explanation of each circuit module in the circuit. At last, software design ofPLL and DDS is shown. Measurement of phase noise and frequency spectrum isshown after that. We analyzed the relationship between phase noise and time jitter indetail, and calculated time jitter according to the phase noise. Experiment results showthat frequency of the scan signal can be as high as250MHz, and time jitter is less than5ps, which is close to the world level.Synchronous scan circuit designed in this article is of great importance toimprove the performance of the streak camera.