SCREENS Project
Digital video transfer research
The major research of high frequency video transmission was made by VTT. The DVI standard is based on very fast differential, serial channels for red, green, blue and clock signals. The bit speed can be even 1.6 Gbit/s.
When a signal propagates in a cable, it suffers from transmission losses, specially losses of high-frequency content in long cables. Techniques to compensate high-frequency signal attenuation in a cable was examined including signal equaliser techniques, which are used in a Gigabit level signal transmission. Adaptive signal equaliser techniques seems to be the most appropriate to this application.
Several cable types were tested. The most appropriate cables were high quality DVI cables, which have controlled propagation delays in a each pair keeping the jitter minimal.
Using high quality DVI cables and adaptive equaliser techniques the required 20 meters cable length was achieved. The most important measures have been so called eye-diagram measures (see picture 4), which shows typical attenuation as well as the jitter of the high frequency signal. For detailed signal waveform measurements an 20 GSamples/second scope was used.
Picture 4: Eye diagram of the DVI transmitter circuit