Equaliser promises lossless video
22 July 2008
The industry’s first automatic adaptive equaliser for composite video adjusts gain for cable length.
The MAX7474 is claimed to be the industry’s first automatic adaptive equaliser for composite video over long, unshielded twisted pair (UTP) cables.
Maxim Integrated Products believes it solves the challenge of lossless transmission of video over long, unshielded twisted pair cables in security video systems by compensating for cable loss characteristics that occur when transmitting a composite video signal over UTP cable up to 300m.
It automatically compensates for cable loss in transmission with blanking and sync over UTP cable lengths and improves signal quality for cables up to 600m long, according to the company. It adapts to cable length and adjusts the video signal gain and automatically switches over to fixed equalisation for monochrome composite video with blanking and sync.
Differential UTP cables are becoming more popular, replacing coaxial or CAT2-7 UTP cable. However, they are susceptible to transmission losses. Most cameras use single-channel coax connectors and need single-ended-to-differential video conversion. Instead of multiple passive options, such as baluns or twisted pair drivers/receivers to drive the video signals through UTP cables, which are limited to fixed-length cable equalisation, the MAX7474 does not need manual gain adjustments and without additional passive components, save board space.
It brings the video signal back to its original amplitude after long-distance transmission has degraded signal quality. For monochrome signals, it detects the absence of burst on the input signal and applies a user-selectable fixed equalisation to the signal.
It monitors the sync and colour burst of the colour video signal at the output and adjusts the gains accordingly. For monochrome signals, it applies automatic gain compensation with user-selectable fixed equalisation to the signal to continuously adjust the low-frequency luminance band gain and the higher frequency chrominance band gain to correct cables losses.
It is compatible with NTSC and PAL, accepting differential video input signals and automatically sets the optimal level of equalisation for the cable length. There is also an output unity-gain video driver and adjustable back-porch DC level. Application areas, because of the length of cables involved, are security video systems, video switching systems and automotive rearview cameras.
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