VIDEO TELEPHONE EMPLOYING PULSE WIDTH MODULATION FOR DATA TRANSMISSION

摘要

A video telephone employing pulse width modulation (10) is implemented. Minimal components are employed and the entire circuit is comprised of digital components except for a few analog components including a comparator (98) for detecting transitions in a received pulse width modulation signal. The pulse width magnitude for each transmitted data is determined by the binary value of the data input (81). The video picture along with the synchronization signals from a video source (12) are digitized and stored in a memory (24). The video telephone (10) operates by sending and receiving via pulse width modulation both the video data and the synchronization signals. The inverse of the video is entered into a binary counter (82) in the modem (80) and the pulse width is the result of counting to a transition of a more significant bit of the counter to create a pulse width modulation transmission on the telephone lines. On receiving pulse width modulation video the binary counter (82) is loaded with all ones and counted up until a transition of a received state is detected. Then the binary counter (82) is read to recover the sent data. Provisions are included to adjust for received pulse widths longer or shorter than expected (84). The data from the video source or the received video can be displayed on a local monitor (32).