Synthesis of PPG Waveform Using PSPICE and Simulink Model

Volumetric changes in the microvascular tissue can be studied by using an optically obtained plethysmogram; a photoplethysmogram (PPG). This has gained much intrigue in the modelling of PPG signal using appropriate Synthesis techniques. The obtained circuit is used to reconstruct PPG waveform. The current work is a proposal of a method for the development of an equivalent circuit to simulate the PPG waveform. Based on the amount of energy, the PPG signal was segregated into ‘complex’ and ‘plain’ zones. To construct that, the individual waves were modelled using Fourier analysis method by MATLAB Curve Fitting Tool Box. Then, after generating the Fourier series coefficients from MATLAB, we obtained the sine and cosine components of the data along with the DC component. The sine and cosine components along with the DC component are added via an adder circuit, followed by an inverter, which generates the final PPG waveform using PSPICE. The building blocks of the Simulink model have been developed using sine and cos function generator blocks, and adder blocks thereby generating an appropriate waveform. The errors between the actual normal PPG waveform and reconstructed PPG waveform using PSPICE for one cycle have been computed, which results in deviations within acceptable ranges of deviation.