PWM-to-message signal decoder circuit system based on opto-electronic devices and their PPC characteristics

In this paper, we propose an opto-electronic device-based pulse width modulation (PWM)-to-message hardware decoder circuit system consisting of opto-electronic light-emitting (LE) and light-receiving (LR) parts using persistent photocurrent (PPC) characteristics of semiconductors. To investigate the PPC characteristics of the opto-electronic device, the photo response characteristics of the LR part were studied for variations in frequency and pulse width of the input photo signal, generated from the LE part. For the input photo signals of the LE part, the original messages were converted to encrypted PWM signals by several comparator frequencies. In general, the higher comparator frequency produces the denser PWM waveform (a faster sampling rate); in other words, it should have less data loss from the original message. The best reconstruction of the encoded PWM photo signals was observed at the high comparator frequency of 200 kHz for triangular, sawtooth, and even composite sinusoidal message signals.