Precision Photodiode Current Amplifier With Output Signal Scaling Capability

Abstract

A precision multi-range photodiode current amplifier with programmable gain scaling and compensation for both offset voltage and dark current is proposed. The relevance of the work lies in the need for accurate measurement of weak optical signals in photometric, spectroscopic, and other optoelectronic systems, where conventional fixed-gain amplifier circuits fail to provide a sufficient dynamic range. The introduction outlines the main limitations of traditional transimpedance amplifiers, particularly their sensitivity to temperature drift and limited adaptability to varying input signals. A literature review is conducted, covering modern solutions aimed at improving the accuracy of photodiode amplifier designs, including commercial systems with zero-adjustment and temperature compensation. The methodology section describes the structural and circuit design of the developed device, which consists of four functional blocks: an input transimpedance stage based on a low-bias-current operational amplifier; a programmable gain module implemented using switchable resistors that provide discrete gain scaling by orders of magnitude; an offset compensation circuit with a stable bias voltage generator; and an output buffer that ensures proper interfacing with a high-resolution analog-to-digital converter. Special attention is given to the implementation of thermally stable dark current compensation by introducing a negative voltage bias, which significantly reduces the drift of the zero-output level. Experimental results demonstrate a high level of precision and stability of the amplifier under varying photodiode current levels. The amplifier’s noise characteristics, linearity, and temperature dependence are evaluated. The functionality of the proposed solution is compared to existing commercial alternatives, highlighting advantages in versatility, scalability, and accuracy. Prospects for further development are discussed, including the implementation of automatic gain range control and the reduction of parasitic currents in electronic switches.