Level-crossing ADC design and evaluation methodology for normal and pathological electrocardiogram signals measurement

In this paper, the level-crossing analog-to-digital converter (LC-ADC) is employed for electrocardiogram signals measurement. A biosignal-dependent design methodology for the LC-ADC is proposed to avoid distortion, caused by slope changes, leading to an 8-bit LC-ADC topology with a 10-kHz and 12-bit time counter. To evaluate the proposed design, the LC-ADC is modeled then evaluated regarding systematic time-quantization error and analog components' non-idealities. A total number of 75 real electrocardiogram records from Physionet database with different waveforms and pathologies are used. LC-ADC evaluation results for time-quantization error show that 100% of the reconstructed signals have a signal-to-distortion ratio higher than 21 dB, which is the value of good quality. The evaluation of comparators' offset voltage impact is analyzed with different ranges of the signal-to-distortion ratio showing the robustness of the proposed design methodology. Internal digital-to-analog converters (DACs) non-linearity impacts are evaluated showing only 1-dB degradation for signal distortion.