Videophone system

Abstract

Abstract In a videophone system sound, video, synchronizing and signalling signals are to be transmitted through a single pair of telephone cables of existing telephone communications. In that case sound, synchronizing and signalling signals are transmitted in a digital form and video signals are transmitted in an analog form. It is then possible to achieve optimum picture quality at the given bandwidth of the existing telephone communications. If for the given bandwidth the video signal were also digitalized, then this would be at the expense of the picture quality. However, it is then necessary to transmit information regarding clock pulses for decoding at the receiver end. These clock pulses must be regenerated at the receiver end for which purpose a synchronizing circuit is provided. To enable this synchronizing circuit to run in or to come into an on-synchronizing state again, information regarding the clock pulses is also transmitted at the transmitter end during at least part of a line scan period namely the part commencing after the beginning of a field flyback period and ending when a field code word is transmitted. This period must be long enough to introduce the direct voltage component lost during transmission and it must be long enough to establish synchronisation because otherwise the field code word cannot be detected in the correct manner. Furthermore means are present at the receiver end (clamping circuit or highpass filter) so as to restore this direct voltage component during the said period of transmitting clockpulse information.

Inventors

• 👤 C Vos
• 👤 J Wilhelmus
• 👤 N Verhoeckx
• 👤 Der Hoff H Van

Bibliographic Details