In keeping up with today’s demand for HDTV and high definition video, it’s desirable to be able to use inexpensive CAT5 cables that currently exist in most homes and offices to send signals from room to room. CAT5 cable is attractive because of its wide-spread use, low cost, and easy installation.
A low-cost solution using a National Semiconductor high-speed current feedback (CFB) amplifier makes CAT5 transmission of 1080i high definition component video easy. In this article we will examine how HD video transmission over CAT5 cable is possible with a CFB high-speed amplifier as a video driver, receiver, and equalizer for CAT5 cable lengths up to 500ft.
Standard CAT5 cable consists of 4 twisted-pairs of AWG-24 cables with characteristic impedance of 100Ω. The DC resistance is 10Ω/100m and capacitance of 4.6nF/100m. Attenuation within CAT5 cable increases exponentially with respect to cable length and is a concern that will be addressed with equalization for 500ft of cable. Figure 1 illustrates this loss at various cable lengths.
Figure 1 - CAT5 Cable Attenuation
The video transmission block diagram consisting of the video driver, receiver, and equalization circuit sections is shown in Figure 2. The LMH6733 can be used to perform the functions of each section and will be explained in detail. The LMH6733 is a triple operational amplifier with enable that has a slew rate of 1900 V/us and a 2Vpp output signal bandwidth of 480MHz.
Figure 2: Video Transmission Block diagram
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