The thesis explores the possibilities of implementing discrete current sources for powering general photoplethysmographic applications. The motivation for discrete implementation stems from the geopolitical consequences of the COVID-19 pandemic on the global semiconductor industry, leading to the unavailability of elements (so-called chips) commonly used in cost-effective current sources to ensure reliable operation of photoplethysmographs. The aim of the work is to develop a discrete topology with functionality, current accuracy, and energy efficiency comparable to general integrated implementations, which includes the development, implementation, and validation of the current source and other key elements of the photoplethysmographic signal analysis instrument. The first part of the thesis describes the theoretical foundations of photoplethysmography, current sources, and mappings, based on which criteria for the current source and validation methods are determined. The second part involves determining the topology of the discrete current source and conducting computer-aided analysis to mitigate the influence of component tolerances on the circuit's operational accuracy and to determine the characteristics of theoretical circuit responses. The implementation of current sources is described in the third part and includes the implementation of two versions of discrete current sources and a reference current source using commercially available integrated circuits. Special emphasis is placed on the development of algorithms for controlling light-emitting diodes, signal acquisition, and processing in discrete frequency space, implemented in the C programming language for the STM32 L series microcontroller. The final part of the thesis presents measurement procedures considering uncertainties, results, and their numerical and statistical analysis performed in the Matlab environment. Based on the analysis, two versions of circuits are implemented and characterized, which is particularly crucial for achieving energy efficiency, operational accuracy, and measurement precision in discrete implementation. The measurement results are summarized at the end in terms of achieving the criteria. For a clearer understanding of the results and determination of further improvements, the analysis of meeting the criteria is supplemented with characterization based on computer-aided analysis.
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