In light analysis circuits, light detectors are best implemented in a way, that enables linearity of the response, wide bandwidth, low noise and low effect of unwanted currents and voltages, that can affect the signal. In case of higher frequencies and higher gain of pulse driven light sources, the output signal can become inadequate, due to effect of parasitic capacitance or the component’s limitations. In this thesis, we start by implementing the detector in a transimpedance circuit, which improves all the mentioned characteristics. We construct and design a printed circuit, compare the response of a photodiode and a phototransistor, and start improving the photodiode circuit, which gives a better response, based on the requirements. The circuit is divided into three stages. The improvements mostly focus on optimising the speed at higher gain, lowering the effect of parasitic capacitance, caused by the added resistances, from which we are choosing based on the required gain and the realisation of the circuit with the least number of components as well as a low price of the final product. Finally, we also optimize the two remaining stages.
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