E.I. Chernov1

1 Ryazan State Radio Engineering University named after V.F. Utkina (Ryazan, Russia)

The development of a new generation of diagnostic tools and medical information systems requires the use of the latest achievements in the field of primary converters of physical quantities. These include position-sensitive photodetectors (PCHFPU), made on the basis of two and four-quadrant photodiodes, which allow recording the position and displacement of light beams along one or two coordinates.

In this article, two variants of the original position-sensitive photodetector with increased accuracy are considered and analyzed. It is shown that the described device excludes: one of the main errors of typical position-sensitive photodetector devices caused by a change in the difference in signal transmission coefficients from each photosensitive element of a two- or four-quadrant photodiode to the adder (difference circuit); errors due to input currents and offset voltages of the operational amplifiers of the PCHFPU and their temperature and time drifts; a change in the light the flow of the studied radiation beam. This is achieved by the fact that the photosensitive elements of the multi-quadrant photodiode of the PCHFPU are connected to the inputs of the input operational amplifiers through a signal switch. At the same time, the PCHFPU operates in push-pull mode. During the first clock cycle, one of the sensing elements is connected to the input of the first operational amplifier, and the other to the input of the second operational amplifier. During the second measure, they switch places. This leads to the fact that a variable signal is formed at the output of the PCHFPU adder, proportional to the sum of the transmission coefficients from the photosensitive elements of the photodiode to the output of the adder, proportional to the light flux of the radiation beam under study and does not depend on the input currents and bias voltages of the operational amplifiers and their temperature and time drifts. To eliminate the error caused by the change in the luminous flux of the light beam, the output signal of the PCHFPU is represented as the ratio of the amplitude of the variable signal from the output of the adder to the signal proportional to the sum of the signals from the used sensitive elements of the photodiode.

In the first version of the PCHFPU, the input operational amplifiers are covered by resistive negative feedback. In the second version, the outputs of the switch are connected to the inputs of logarithmic amplifiers.

According to the first embodiment, it is advisable to use the PCHFPU when changing the light fluxes of the studied light beams of radiation in the range of two to three orders of magnitude. With a larger range of changes in the light flux, the PCHFPU is made according to the second option.

The presented PCHFPU will be of interest to researchers and engineers involved in the development of medical diagnostic equipment and information measuring systems.

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