Keep clocks in line with LVDS replicator

-- EDN, 1/6/2000

Intended for use in telecommunications and other high-speed data systems, National Semiconductor's DS-92CK16 chip (Picture) allows you to generate multiple copies of clock signals with a channel-to-channel skew of 50 psec. For use with low-voltage differential signaling (LVDS), the chip works at the "edge" of a daughtercard, taking a single clock line off the backplane and replicating six copies for use on the card. It also has the facility to perform the reverse operation: taking a clock signal from the card and broadcasting it to the backplane. Operating at 100 MHz, the chip uses a feature that National calls the gradual-turn-on-backplane-LVDS driver; by shaping the pulse waveform, you get a clock signal that better handles the nonideal impedance characteristics of typical clock networks. Power demand is 30 mW.

National has also revealed details of a CMOS image sensor it is developing for release this year. The VGA device will integrate analogue-to-digital conversion, control, and interface functions. Target power consumption is 175 mW at 5V, and National says it will offer a 110-dB dynamic range compared with the 65 dB of earlier CMOS sensors. This range yields better image quality than CMOS image sensors have delivered, and sensitivity is also high. National does not reveal how it achieved this extra range but says that the necessary corrections occur at the pixel level, using an active-pixel-sensor technique. The VGA sensor will be compatible with standard 0.25-in. optics.

National Semiconductor, +49 69 9508 6208, www.national.com.

-by Graham Prophet