Study On Synchronous Multi-beam Detecting System Based On PSD Using Phase Detection And Digital Signal Processing Technology

PSD (Position Sensitive Detector) is a kind of semiconductor device based on lateral photoelectric effect offering many advantages such as high resolution, fast response, simple signal processing circuit and good acclimatization, and it is well suited for measuring displacement, distance, angle and the like physical quantity which can be transformed to the displacement or location of a light spot on PSD. A light spot can be located by the PSD by two different ways—by using magnitude detection or by phase, and the later has some unparalleled advantages such as light-intensity independent position information, more suited for multi-beam detection and simplified processing circuit compared with the former. However, the research of phase detection has been far from perfect, which is practically under the stage of theory-exploring and still need a great deal of work to apply it in engineering practice. For the above-mentioned reasons, a multi-beam detecting system based on PSD and digital signal processor has been designed after analyzing and studying the present technology closely.First, the history and research of PSD is introduced and the scheme of a multi-beam detecting system based on PSD and digital signal processing technology proposed as well. Then the derivative processes of the principle of multi-beam detecting based on PSD using phase detection and digital signal processing technology are given, which mainly includes phase detection principle based on RC transmission line model and its realization based on FFT algorithm. On the basis of research above, the scheme of multi-beam detecting system based on TMS320F2812 is proposed, and the hardware and software of which is designed further. After that, the calibration experiments of the system have been done and some important conclusions obtained. And the error classification and distribution of the system are analyzed and the method and suggestion for reducing it are given finally.The experimental results reveal that the phase difference of the output signals of PSD radiated by the sinusoidal modulation lights has obvious linear relationship with the light spot position and the sensitivity of PSD increases with the increasing frequency, which is coincident with the phase detection theory. Meanwhile, a considerable amount of error sources result in a large nonlinear error to the fitting line and data distortion can be found in some detecting areas, so that the further improvement and development are awaited in subsequent research. A novel and effective solution for multi-beam detecting based on PSD using phase detection is provided in this thesis and some important conclusions, which can offer valuable reference for the follow-up research, are obtained.