Electronic Design

SDI Equaliser Offers Longest Cable Reach At Half The Power

With the emergence of 3D TV, which requires stereoscopic video to be captured with two independent cameras, broadcasters must migrate to higher data rates (up to 3Gb/s) to transport high-definition (HD) video signals between equipment. The increased data rates present signal integrity and power budget challenges at greater distances.

To address these challenges, National Semiconductor came up with the LMH0394 serial-digital-interface (SDI) cable equaliser. According to the company, the equalizer extends the reach of broadcast video signals by 40%— 200m at 3Gb/s (3G), 220m at HD, and 400m at standard definition (SD)—while delivering half the power (115mW typical) of comparable equalizers.

Until now, broadcasters have used either copper links with multiple distribution amplifiers (a type of signal repeater) or more expensive optical solutions to extend the reach of video equipment. By enabling reception of 3G-SDI across a single 200m link of coax cable, it’s claimed that the LMH0394 improves performance and reduces bill of materials cost and operating power. It also alleviates upgrades to costly fibre solutions for longer-reach outdoor installations (such as sporting events).

Thanks to the low power consumption, the power budget margin opens up to add functionality such as audio processing and reclocking on video input cards. The device also includes an automatic power-down mode that, in the absence of an input signal, reduces power consumption by 85%.

Typical jitter for the equaliser is less than 0.15 unit intervals (UI) up to 100m, 0.20 UI up to 140m, and 0.40 UI up to 180m at 3G data rates. The low output jitter also removes the need for input relocking of short-reach links, further saving power consumption.

Advanced features include power-efficient, low-voltage differential signalling (LVDS) drivers with programmable offset, amplitude, and output de-emphasis; a cable length indicator that can approximate cable lengths within 1m of accuracy; and support for passive external splitters. These enhanced features can be accessed through the device’s SPI programming interface. Offered in a 4mm by 4mm, 16-pin LLP package, the LMH0394 is backward-compatible with National’s SDI equaliser family.

 A dual-output version, the LMH0395, is also available. It offers very low operating power, consuming 145mW from a 2.5V supply. The chip’s dual outputs remove the need for an external 1:2 buffer, further reducing system power and cost. Each of the outputs can be independently enabled and programmed to drive downstream devices with different input requirements and trace lengths. The LMH0395 comes in a 4mm by 4mm, 24-pin LLP package.

The LMH0394 and LMH0395 cost $21.95 and $22.95 each, respectively, in 1000-unit quantities. Both devices are sampling now, with production quantities scheduled for October 2010.

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