Abstract:In this paper, a specific circuit to detect the differential photoelectric signal is given according to the requirements of the automatic confocal-focusing system. Using the high performance instrumental amplifier AD620BN, low noise precision FET Op amplifier AD795JRZ and ultralow offset voltage Op amplifier OP07, the pre-circuit for photoelectric conversion, the signal conditioning and differential circuit, Second-Order Low-Pass Filter and pseudo-zero elimination circuit are made. By the processing of program in MCU MSP430F149, a signal is generated for the system to focuse automatically. The experimental results verified the feasibility and effectiveness of the circuit, showing that the design meets the demands of confocal-focusing system.