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Delay lines deliver clear images for KVM apps

Posted: 07 Aug 2009     Print Version  Bookmark and Share

Keywords:analogue  delay line  video transmission 

Intersil Corp. is offering four new triple analogue delay lines for video signals that provide sharp, clear images for keyboard-video-mouse (KVM) applications or any video carried over long distances of inexpensive twisted-pair cable.

The ISL59920, ISL59921, ISL59922, and ISL59923 are triple analogue delay lines that provide skew compensation between three high-speed signals. These parts are suitable for compensating for the skew introduced by a typical CAT-5, CAT-6 or CAT-7 cable (with differing electrical lengths on each twisted pair) when transmitting analogue video.

Intersil's triple analogue video delay lines enable users to meet a variety of bandwidth and transmission-length requirements using a single cost-effective design solution.

The whole family is footprint-compatible with Intersil's EL9115, which was the first-ever silicon delay line product. Now users have a choice of bandwidths, ranging from 150MHz up to 230MHz, which increases the range of video resolutions that can be handled up to UXGA and 1080p. The new family also has a greatly reduced offset of just ±25mV.

The ISL59920 features up to 62ns of delay compensation in 2ns steps, with a bandwidth of 153MHz. This is usually sufficient to compensate for the skew encountered in 300m of CAT 5/6/7 cable.

Users needing higher-bandwidth solutions over shorter distances may opt for the ISL59921 or ISL59922, which feature 200MHz or 230MHz -3dB bandwidth (typ), respectively.

The ISL59923 has bandwidth of 153MHz and with 30ns of total delay and is therefore ideally suited for shorter reach, lower resolution installations.

Using a simple serial interface, the ISL59920, ISL59921, ISL59922 and ISL59923's delays are programmable in steps of 2-, 1.5-, 1- or 2ns (respectively) for up to a total delay of 62-, 46.5-, 31- or 30ns (respectively) on each channel. The gain of the video amplifiers can be set to x1 (0dB) or x2 (6dB) for back-termination.

Delay lines solve the skew problem encountered when RGB video (often from a VGA source, such as a computer) is sent over twisted pair cables. CAT-5 (also CAT-6, or 7). Cables contain 4 pairs of wires, which are twisted together at different rates. This means that they are actually different physical lengths. When a red-green-blue (RGB) signal travels down a CAT-5 cable, each colour is carried on a different pair. Because the pairs are different lengths, the colours that make up a single pixel arrive at different times, so the images are not on top of one another. The triple delay line enables the designer to slow down the fastest two colours so that all three colours arrive simultaneously. The result is a sharp, clear image.

These products are available in 20-lead 5mm x 5mm QFN packages. The ISL59920 is priced at Rs.982.34 ($20.11) in 1,000-unit quantities. The ISL59921 is priced at Rs.1,074.66 ($22); the ISL59922 is priced at Rs.1,221.20 ($25) and the ISL59923 is priced at Rs.802.57 ($16.43).

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