video delay lines, Intersil, ISL59920
Triple analogue video delay lines offer highest bandwidth and video resolution with longest transmission distance using a single cost-effective design solution
News Release from:
29 July 2009
Intersil has introduced four triple analogue delay lines for video signals that provide crystal clear video images at distances up to 1000 feet (300 metres) for keyboard-video-mouse (KVM) applications such as in offices, banks, supermarkets or classrooms, 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 ideal 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 own EL9115, which was the industry’s 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 1000 feet (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 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 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.