Detection and Measurement of Weak Ophthalmic Biological Signals

To address the issues of insufficient photodetector bandwidth, common-mode noise, and baseline noise affecting measurement accuracy in existing ophthalmic biometric instruments, this paper presents a low-noise balanced photodetector design. The system comprises a balanced detection circuit and a low-noise power supply. By cascading the ADA4817 and AD8065ARZ operational amplifiers, it converts differential photocurrent signals into high signal-to-noise ratio voltages, supporting gain optimisation based on centre frequency. Experimental results demonstrate that this design effectively extends system bandwidth, elevates the common-mode rejection ratio to over 37 dB, and suppresses output noise floor to below 20 mV. This significantly enhances the accuracy of ocular parameter measurements, providing an effective solution for precision medical IoT sensing.