Signal Equalizer for Balanced Transmission Line-Based Video Switching

Abstract

A method of equalizing signals from a plurality of balanced transmission line cables having different lengths includes providing a first cable having a first length and a second cable having a second length, the first cable coupled to a variable resistor. A first signal is transmitted along the first cable to the variable resistor such that the first signal is attenuated to assume a first frequency domain characteristic. A second signal is transmitted along the second cable such that the second signal is attenuated to assume a second frequency domain characteristic. A voltage of the first signal is divided in the variable resistor such that the first signal assumes substantially the second frequency domain characteristic. The first signal having the second frequency domain characteristic is outputted.

Description

BACKGROUND OF THE INVENTION[0001]1. Field of the Invention[0002]The present invention relates to video switching equipment, and in particular, to a signal equalizer device, system, and method for shielded and unshielded twisted pair-based video switching.[0003]2. Description of Related Art[0004]A video switch allows a user to route a plurality of video source inputs to a single or plurality of video displays. Video switching is typically performed by centralized equipment having input and output ports through which video signals interface. However, there are a number of obstacles in displaying video with high quality. Video switching devices are subject to signal arrival skew, which occurs when multiple channels of video are propagated through physically separate transmission lines. Also, when a video source and display are connected through transmission lines, video signal quality suffers as the length of the transmission line increases. In a video switching environment, input sign...

AI Technical Summary

Benefits of technology

[0010]In one embodiment of the invention, a method of equalizing signals from a plurality of balanced transmission line cables having different lengths includes providing a first cable having a first length and a second cable having a second length, the first cable coupled to a variable resistor. In the context of this description the “first” or “second” cable can be a single cable or a series of cables coupling electrical elements. A first signal is transmitted along the first cable to the variable resistor such that the first signal is attenuated to assume a first frequency domain characteristic. A second signal is transmitted along the second cable such that the second signal is attenuated to assume a second frequency domain characteristic. A volt

Problems solved by technology

However, there are a number of obstacles in displaying video with high quality.

Video switching devices are subject to signal arrival skew, which occurs when multiple channels of video are propagated through physically separate transmission lines.

Also, when a video source and display are connected through transmission lines, video signal quality suffers as the length of the transmission line increases.

Furthermore, undesirable variations in video quality will appear as the video switch selects different inputs to be displayed.

Transmission lines, such as coaxial cables, fiber optic cables, and unshielded twisted pair cables, impose losses that are manifested as attenuation and high frequency roll off, which are the combined result of ohmic, skin effect, dielectric and radiation losses.

High-resolution analog signals that contain a very broad spectrum of energy, often occupying 20 octaves or more per channel, are especially susceptible to attenuation and roll off even in moderately long cables.

Visually, cable losses are manifested as horizontal aperture distortion (smearing) and a loss of fine detail resolution.

However, these cables are both costly and cumbersome, often requiring the installation of as many as five individual fibers or coaxial cables.

Termination of coaxial cables is difficult and expensive in comparison to other cable types such as shielded and unshielded twisted pair (STP, UTP) cables.

However, video transmission using UTP cables presents problems that prevent widespread adoption over the more commonly used coaxial cables.

Improved crosstalk comes at the expense of varying propagation speeds between individual pairs within a given cable sheath.

UTP cables are also susceptible to signal arrival skew.

While UTP cables are inexpensive and easier to install and maintain than coaxial cables, current solutions have not provided comparable performance to coaxial cables for high-resolution video over moderate to long distances.

However, the conventional solutions are effective only for low bandwidth, low-resolution, NTSC type video sources and switches.

Utilizing only a single time constant, the resulting transfer functions obtained conventionally do not provide the accuracy and frequency response necessary for high resolution analog video signals.

The current solutions for providing positive EQ are inadequate for equalizing high-resolution video signals and video signals transported over long distances.

Images