Design Of The Weak Coherent Signal Processing Module Of Biometer Based On FPGA

The axial parameters of the eye are an important basis for the diagnosis and treatment of a variety of intraocular diseases.Accurate measurement of the axial parameters of the eye directly affects the diagnosis and treatment of intraocular diseases.Based on the principle of optical weak coherence interferometry,the biometer is an optical measuring instrument using non-contact technology,which can accurately measure the axial parameters of the patient’s eye at one time.During the measurement process,the interference signal returned from the human eye is very weak,and the interference signal is affected by the noise of the system’s working environment,optoelectronic devices,detection circuit,etc.,and the interference signal received by the detector is difficult to carry out subsequent processing.The thesis carried out the research and design of weak coherent signal processing in response to the above problems.In order to collect weakly coherent signals with high signal-to-noise ratio and improve the measurement accuracy of the biometer,the paper designs a weak coherent signal processing module based on FPGA.Based on the research on the principle of optical weak coherence interferometry,the overall scheme of the biometric system is constructed.A signal processing module circuit based on FPGA as the main control is designed,and the noise and bandwidth characteristics of the transimpedance photoelectric signal detection circuit are analyzed in detail.The signal detection circuit is designed according to the center frequency and bandwidth of the interference signal,and a balanced detector and The fully differential photoelectric detection circuit is combined to select and calculate the circuit device,and complete the design of the low-noise photoelectric signal detection circuit;design the A/D signal acquisition circuit,collect the interference signal on the FPGA,and complete the FPGA-based The main control signal processing circuit.The wavelet denoising algorithm for weakly coherent signals is studied,and the appropriate threshold and wavelet basis function are selected to complete the denoising and further improve the signal processing effect;the FIFO module is used to buffer the data,and the UART serial communication module is used to realize the communication between the computer and the signal processing module.Communication,transmitting the weakly coherent signal collected and processed by FPGA to the host computer.Combine the interference optical path and the designed FPGA signal processing module to build a prototype for actual text experiments.Using TINA simulation software to simulate and analyze the fully differential balanced detection circuit,the circuit’s-3d B bandwidth point frequency is 2.1MHz,which meets the bandwidth requirement for weakly coherent signal detection.Simulation and experimental results show that the designed FPGA signal processing module can detect weak coherent signals with high signal-to-noise ratio.The signal-to-noise ratio is as high as 87.61 d B,which can effectively suppress the influence of DC components and noise in weak coherent signals and meet the actual requirements of the system.