The development of a new generation of diagnostic tools and medical information systems requires the use of the latest advances in the field of primary converters of physical quantities. These include photodetector devices (PDDs) made on the basis of photodiodes. The direction of this research is the identification and analysis of FPU structures that have increased accuracy in recording light fluxes. Identification of the structure of the PDA, in which errors are eliminated due to temperature and time drifts of input currents and bias voltages of the operational amplifiers included in the PDA. The structure of the original FPU, which provides increased accuracy of registration of light fluxes, is presented and analyzed. It is advisable to use the presented FPU in the development of medical diagnostic devices and information-measuring systems. A special place in their use is occupied by various kinds of optical analyzers for medical purposes, for example, a tooth color analyzer, systems for studying microcirculation of the blood flow, magnetotherapy units that use optical methods for recording the patient’s breathing process, etc. FPU will be of interest to scientists and engineers involved in the development of medical diagnostic equipment and information measurement systems.