Electronic Design

SDI Cable Equalizer Simplifies Hardware Design

The 3-Gbit/s LMH0384 serial digital interface (SDI) cable equalizer (EQ) from National Semiconductor simplifies the design of broadcast video routers, production switchers, distribution amplifiers, and editing and conversion equipment, according to the company. National Semiconductor also says that the device provides the industry’s lowest output alignment jitter along cable lengths, giving hardware designers more headroom for designing within system jitter budgets. Tighter jitter budgets translate to cleaner system design, fewer bit errors, and crisper images.

According to National, the LMH0384 is the only EQ to guarantee less than 0.3 unit intervals (UI) of output jitter from 0 to 110 m of Belden 1694A coaxial cable at 2.97 Gbits/s. It equalizes up to 140 m of cable at 3G rates, 200 m at high-definition (HD) rates, and 400 m at standard-definition (SD) rates. It adaptively adjusts equalization levels based on cable length to receive incoming signals and provide low-jitter transmission of 1080p HD broadcast video at up to 60 fps over a single coaxial cable.

The LMH0384 also supports two modes of operation: pin mode and register mode. In pin mode, it is fully backward-compatible with National’s other SDI equalizers. The register mode opens up a suite of advanced features, accessible via a serial peripheral interface (SPI) bus, that enable flexibility to change and diagnose product parameters without requiring a board re-spin. These include automatic power down (auto sleep), cable length indicator, low-voltage differential signaling (LVDS) drivers with programmable offset and amplitude, and programmable input launch amplitude to facilitate operation with external splitters.

The EQ’s 1.05- to 1.85-V adjustable output common-mode voltage eliminates the need for level-translation buffers by facilitating direct coupling to most FPGAs and signal conditioning devices. Its active sensing features minimize power consumption and reduce cooling requirements in customer systems. For example, in the event of a cable detachment or loss of signal, the LMH0384 enters a power-saving auto sleep mode to reduce power consumption by 85%. In active mode, it automatically shifts equalization stages at cable lengths less than 140 m to reduce power consumptipn by 20%. It typically consumers 230 mW from a single 3.3-V supply.

Offered in a 16-LLP package, the LMH0384 costs $21 each in 100-unit quantities. It sampling now, with production quantities scheduled for May 2009.

National Semiconductor


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