GVIF Cable and Connector

The maximum serial data rate of a video interface based on a single twisted pair GVIF system is approximately 2 Gbps. At such high data rates, good engineering practices must be followed during the design to avoid performance degradations that might lead to an increased bit error rate, lower than desired maximum supportable data rates, EMI, etc. Avoidance of reflections due to impedance match issues is insured through the use of terminators at both the transmitter and receiver ends. Mitigation of transmission line frequency dependent losses is, as described previously, made possible by the use of a built-in cable equalizer. To minimize EMI, GVIF makes use of small amplitude differential transmission signals and a recommendation for the use of shielded twisted pair (STP) cabling. but the following provides a summary of the composite GVIF cable and connector requirements:

• Good impedance matching using 100 ohm shielded twisted pair, with an overall impedance profile matching that shown in Figure 4-6.
• Cable plus connector loss should be small and the loss curve should be smooth. Maximum cable-loss should be less than 15dB at 1GHz.
• Skew of differential serial data pair should be small: 24% or less of 1-bit time in SVGA or 30% or less of 1-bit time in WQVGA, VGA and WVGA is recommended. As an example, this would imply a limit on intra-pair skew of 400ps for VGA resolutions at 25MHz shift clock rates, and 200ps for SVGA resolutions at 40MHz shift clock rates.
• Good EMI characteristics, which can be insured with the use of shielded twisted pair (STP) cable

Figure 4-6: Recommended Differential Impedance Template

An application note is available describing these issues in more detail and the applicable integrated circuit data sheets should be examined for the most complete interface recommendations.