Research On Synchronous Acquisition And Processing System Detecting Defocus Signal Based On DSP

The laser direct writing system is the key equipment used for making diffractive optical elements. The defocus detection system provides the focus error signal (FES) for the focus-servo system, which makes the writing spot precisely focusing on the resist. Therefore, the etching quality can be ensured. The defocusing detecting technique based on differential astigmatic method is selected to satisfy the defocus detection system.The defocus signal detection of laser direct writing system is established based on the differential astigmatism. Due to the former acquisition system has poor synchronization and real-time problem, a method of the DSP-based synchronous data acquisition is presented. The DSP control CPLD trigger four AD at the same time, then the relationship between defocus signal and output signals is given. Thus realizes the synchronous multi-channel, real time, high-precision data acquisition.The acquisition circuit is based on TMS320LF2407A chip to achieve software and hardware design. It was composed by the DSP, CPLD, photoelectric conversion and signal amplification, AD converters, memory and DA converter and other components. Focus on the hardware and software design of the acquisition circuit, the corresponding principle of hardware and software flow chart is given.According to these research works, the system was established. Experimental results show the influence by the instability of laser power can be eliminated.