professional audio systems. The technology is based on enhanced dual-bit ΔΣ scheme, thus offering a high accuracy and a low cost.
4.
The transmission of audio and video signals using the developed modules has been demonstrated experimen-tally. The experimental setup is shown in Figure 9. A DVD player is used to generate both the audio and video signals. The white and red light sources are used for transmission of audio and video signals, respectively. At the receiver, LCD TV and speakers are used to monitor the quality of the video and audio signals following post-photodetection processing. As shown in Figure 9, transmitters and receivers were placed in a directed diffuse link configuration [3], with 10-cm spacing between the
two transmitter modules. The transmission span was set at 50 cm with no lenses. The link distance can be extended by using appropriate optics both at the source and the receiver or increasing the transmit power within the eye safety limit.
Figure 10 shows the digital audio signal S/PDIF wave-forms at the input (upper trace) and output of the S/PDIF module (lower trace) stages. Due to the response time of the used devices, the total transmission delay achieved is 200 ns, which is sufficiently small and therefore does not affect the audio and video signals quality. Figure 11 illustrates the PWM video signal wave-forms at the input (upper trace) and output (lower trace) stages.
In order to assess the transmission quality of the video signal, we used two test signals: (1) the NTSC composite video time domain waveform (see Figure 12) with the upper and lower traces showing the input and recovered analog video signals and (2) the video test cards (i.e., SMPTE color bars [16] and a modified version of the PM5544 Philips test card) as shown in Figure 13. As shown in Figure 13, the slight difference in the con-trast between received and transmitted video images might be due to contribution (leak) from the audio signal. However, this can be improved by using an optical band pass filter and higher carrier frequency for PWM