ICs enable analog video to give and receive

By Bill Schweber -- 7/7/2005

Despite the digital nature of many video signals, they often need to live in the analog RGB/YPbPr world, alongside the line drivers and receivers that make that world possible. The ISL59830 IC from Intersil facilitates this collaboration. The single-supply triple-video driver internally generates its requisite negative supply, thus eliminating the need for a negative-supply rail and dc-blocking capacitors.

Pay attention, you digital-system designers: In the arcane world of video architectures, circuits use either ac or dc interstage coupling. The ac approach needs relatively large external capacitors but no negative supply; the dc approach requires a bipolar supply but no capacitors. According to Sameer Vuyyuru, director for high-speed analog at the company, “The video driver is often the only product in a design that still requires a negative-supply rail where dc accuracy is required.”

The 3.3V IC has built-in fixed-gain-of-two (6-dB) buffers and three-state outputs, designed to drive 75Ω, double-terminated lines. Bandwidth is 50 MHz at 0.1-dB flatness and 300 MHz at 3 dB for the 16-lead devices, which are available for $1.88 each (1000).

Line driving alone is only part of the video-signal chain. Analog Devices’ AD8143 triple differential receiver lets designers use Category 5 unshielded twisted-pair cable rather than more expensive coaxial cabling for RGB signals with resolution as high as 1600×1200 pixels. Designers can also use the IC for general differential-analog or high-speed data signals. The IC converts differential signals to single-ended signals with a common-mode range of ±10V to maintain signal integrity despite large ground-potential difference. CMRR (common-mode-rejection ration) is 70 dB at 10 MHz (Picture).

In addition to the line receivers, the device contains two comparators, which can sense digital signals from the unused fourth pair in the cable. A typical use would be to handle keyboard and mouse signals in KVM (keyboard/video/mouse) applications. The AD8413, a 5×5-mm, 32-lead device, sells for $2.55 (1000) and is the complement to the AD8133 triple-differential line driver.

Intersil Corp, www.intersil.com.

Analog Devices Inc, www.analog.com.

 

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