Research on Position Detection of PSD Based on Light Intensity Modulation and Digital Fit

Position sensitive detector (PSD) is influenced by the background light source when the weak light falls on its photo sensitive face. This paper applies the technique of sine light intensity modulation and band-pass filter which can overcome the background light to enhance the signal to noise ratio (S/N) of this position detection system greatly. The sum-intensity signal and the difference-intensity signal extracted from PSD are modulation frequency signals and the amplitude ratio and phase discrepancy are decided by the position of the light spot. Based on these characteristics, the approach of using simultaneous A/D and elliptical fitting algorithm to locate the light spot is adopted, and the related theoretical formulas are also carried out. This approach can conquer the defects of traditional signal processing methods. The experiment results show that: when the range of measured position is 9 mm, the measurement accuracy is up to 0.01 mm.