UTP Video Transport with Common Mode Sync and Delay Compensation
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Solution Overview
Problem
Existing technologies are inadequate for transmitting audio and video signals over extended lengths of unshielded twisted pair cable, particularly in maintaining synchronization between signals, which is crucial for producing an acceptable display.
Innovation Solution
A system that transmits first and second synchronization signals as differentials across the common modes of four twisted wire pairs, allowing for the transportation of video and digital audio signals over extended lengths of unshielded twisted pair cable, with a transmitter unit processing input signals and a receiver unit recovering these signals for video and audio devices.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of stationary object
If synchronization signals are transmitted as differentials across the common modes of twisted wire pairs, then signal transmission over extended cable lengths is enabled, but timing skew and synchronization errors occur due to unequal electrical lengths of the pairs
Solution Approach 1:
A delay compensation circuit is introduced as an intermediary element between the received synchronization signals and the video signal processing. This circuit actively measures and compensates for timing skew caused by unequal cable pair lengths, restoring synchronization without requiring perfect cable manufacturing precision.
Solution Approach 2:
The system dynamically adjusts the delay parameter of the synchronization signals based on the measured timing skew. By changing the delay parameter compensatorily, the system maintains proper synchronization even when cable pair lengths vary, effectively decoupling synchronization quality from manufacturing precision constraints.
2Device complexity
If synchronization signals are superimposed onto video signals, then transmission complexity is reduced, but signal integrity and synchronization precision deteriorate
Solution Approach 1:
The transmission system is segmented into separate channels: video signals are transmitted on three twisted pairs while synchronization signals are transmitted as differentials across the common modes of the same pairs. This segmentation allows independent optimization and processing of each signal type, maintaining both low complexity and high reliability.
Solution Approach 2:
The same four twisted wire pairs serve multiple functions: they transmit both video component signals and synchronization signals simultaneously. The transmitter and receiver units are designed to handle both signal types through different processing paths, achieving multi-functionality without compromising signal integrity.
3Reliability
If common mode differential signaling is used for synchronization, then immunity to electromagnetic interference is improved, but signal transmission speed decreases
Solution Approach 1:
The system applies partial differential signaling only to the synchronization signals that require noise immunity, while video signals use standard differential transmission. This partial application of common mode differential signaling achieves the necessary noise immunity for synchronization without excessively slowing down the overall system performance.
Data Source
AI summary
A video and digital audio transport system transports high resolution computer, video, computer video graphics and other video signals, as well as multiple channels of high quality audio, over extended lengths of unshielded twisted pair (UTP) cabling. Frequency compensation techniques are employed to extend the bandwidth of the UTP cables, and differential signaling over the common mode of a first two of the four twisted pairs comprising the UTP cable is used to transmit horizontal sync and differential signaling over the common mode of a second two of the four twisted pairs is used to transmit vertical sync. In addition, a unique digital encoding technique is applied to a standard digital audio encoding protocol to augment the number of available audio channels. A digitally controlled delay line is incorporated to compensate for the different lengths of each twisted pair.