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Analog Serial Digital Interface (SDI) chipset provides lowest jitter for HD video

High-definition (HD) broadcast video is coming on fast, and the irony is that it takes a lot of analog circuitry to make this so-called digital TV work. National Semiconductor has introduced a three-IC chipset for the 3-Gbps (also known as 3G, not be confused with the 3G cellular standard) Serial Digital Interface (SDI), supporting 1080p video at up to 60 frames per second over a single coaxial cable. Targeted at studio and professional equipment, the chipset consists of the LMH0344 adaptive cable equalizer, the LMH0346 reclocker, and the LMH0302 cable driver. The chipset adheres to and exceeds the SMPTE (Society of Motion Picture and Television Engineers) 42M broadcast video standard, and yield alignment jitter guaranteed to be less than 0.3 unit interval (UI).



The LMH0344 adaptive cable equalizer automatically adapts and equalizes up to 2.97 Gpbs, and is certified with 100 meters of Belden 1694A coax cable, and equalizes 120 m of cable at 3G rates, extending to 350 m at the lower standard definition (SD) rate. The 3.3V IC dissipates 285 mW and is packaged in a 16-lead LLP package; more information is available at www.national.com/pf/LM/LMH0344.html.

The LMH0346 reclocker automatically detects and retimes the incoming signal to reduce high-frequency jitter. The 390 mW, 20-pin TSSOP does not have an input multiplexer, which reduces pin-count to one-third of competitive devices and the package size by one-half. The reclocker can be set up to share a single 27-MHz reference across multiple devices, unlike units which require one reference crystal for each individual reclocker. More information is available at www.national.com/pf/LM/LMH0346.html.

The LMH0302 HD/SD cable driver can drive 75-ohm transmission lines up to 2.97-Gbps. It provides two selectable slew rates, for compliance with SMPTE 259M and SMPTE 424M/292M. Power consumption at 3G and HD data rates, using a single 3.3V supply, is 162 mW; there is also a power-saving standby mode in which the output driver is diabled and power consumption is reduced to 76 mW. More information is available at www.national.com/pf/LM/LMH0302.html.

The three ICs in the chipset are sampling in second quarter 2007, and are priced (100 piece orders) at: LMH0344 adaptive cable equalizer, $31; LMH0346 reclocker, $35; LMH0302 cable driver, $11.

National Semiconductor Corp. , www.national.com

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