1. Design
The solution described in this article proposes as the physical environment the use of a simple twisted pair cable; in addition to its lower price (compared to the shielded coaxial cable) it also features a much smaller weight, which sometimes can be a critical design criteria, especially for instance, in automotive environments, where cable weight account for the most percentage of the mass of a car.
Usually the regular configuration of a video transmitting system consists of an output amplifier (which either amplifies or acts as a simple repeater) mounted in the part of the system which generates video signal, connected via a shielded coax cable to the receiver part of the system. At the receiver, the signal is filtered, then amplified again, and fed to the display or perhaps to a video processing unit.
As stated above, using this configuration has a significant impact on both the price and the weight of the system. A much more advantageous solution, from these points of view, may be achieved through the use of a differential amplifier at the transmitting side, which would thus be able to confer a good degree of immunity to the video signal with respect to outside influences. The Video Driver is shown in Figure 2. It converts a single-ended input signal from a camera or DVD player into a differential signal that drives the twisted-pair line. The input receives an NTSC composite video signal with 1VPP amplitude, and the output drives the twisted-pair with a 2VPP differential signal. A 50Ω source resistor is in series with the outputs of both op-amps, matching the Video Driver output resistance to the twisted-pair characteristic impedance.
Read More: Increasing cable length in precision video applications