1-GHz multiplexers handle high resolution signals

Milpitas, Calif. — Intersil Corp. claims to have broken the current bandwidth barrier with triple RGB or YPbPr multiplexers with 1 GHz of bandwidth for high-speed analog video-input switching applications.

These MUX-amps exhibit a fixed gain of 1 and also feature high-speed tri-state outputs to enable the outputs of multiple devices to be wired together. All logic inputs have pull-downs to ground and may be left floating. The enable (EN) pin, when pulled high, sets the ISL59424 and ISL59445 to low-current mode, consuming just 15 mW. An added feature in the ISL59424 is a latch enable (LE) function that allows independent logic control using a common logic bus. When LE is high, the last logic state is preserved.

“Intersil's ISL5944xx family extends the available bandwidth of RGB multiplexers on the market from 500 MHz (Intersil's EL4342) up to 1 GHz — the first time this barrier has been broken,” said Sameer Vuyyuru, director of high-speed analog for Intersil. “This family of ultra high-speed devices allows customers to not worry about the resolution of their source as these devices can handle all existing sources. When combined with Intersil's 1-GHz triple amplifier (EL5367) and QXGA-capable video digitizer (ISL98001-275), we provide a unique, solution that's unfettered by bandwidth constraints, for high-resolution displays.”

The devices also feature a power-down mode, ±5-V operation, and ±1200 V/us slew rate. Applications include HDTV/DTV analog inputs, video projectors, computer monitors, set-top boxes, security video and broadcast video equipment.

Intersil's ISL59424 is available in a 24-lead QFN package and is priced at $4.11, and the ISL59445 comes in a 32-lead QFN package and is priced at $5.20. Both prices are in 1,000-unit quantities. Click here for the ISL59424 and ISL59445 data sheets.

Intersil Corp. , 1-888-468-3374,

Functional Block Diagram ISL59445

Click here to explore amplifier solutions using Intersil's free iSim online design tool .

Intersil claims that while single-channel 2:1 and 4:1 multiplexers are plentiful, there are very few triple 2:1 multiplexers, and there are no other triple 4:1 multiplexers. Furthermore, there are no 2:1 and 4:1 triple multiplexers at this bandwidth (1 GHz), which is what really makes them special.

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The closest competing devices only operate at a 380 MHz bandwidth, said Kathryn Tucker, product marketing manager for Intersil's video products. “Ours are twice as fast as anyone else's,” she said. These multiplexers are aimed at very high resolution video applications (1600 x 1200 pixel).

In today's world of ever increasing demand for higher resolution graphics, whether it's a projector in a home theatre, a large screen LCD TV or routing computer graphics — demand for higher bandwidth components is rising.

In simple terms, when designing with a high speed signal, the bandwidth of the components it passes through must be sufficiently high so that they do not degrade the signal in any way; the 0.1 dB gain flatness is often used as a measure of this. One rule of thumb is to use an amplifier with a bandwidth of up to 10 times the pixel clock of the signal you are trying to pass.

A few years ago, for example, 640 x 400 pixel was a common display resolution, with a refresh rate of 60 Hz (VGA). “This has a pixel clock of about 30 MHz. Using the rule of thumb above means the amplifiers and muxes should have a bandwidth of around 300 MHz,” Tucker said.

Today, resolutions of 1280 x 1024 pixel are becoming common in high end applications (SXGA). “The pixel clock has increased to about 100 MHz, resulting in the need for amplifiers and multiplexers with a bandwidth of 1 GHz,” Tucker said.

Intersil's preceding multiplexers, the EL4340 and EL4342, also triple 2:1 and 4:1 devices, offer similar functionality but lower bandwidth. Key performance parameters of the older triple 4:1 muxes include 500 MHz , -3 dB bandwidth, 16 mA per channel supply current, and a slew rate of ±870 V/us. In addition, a 0.1-dB flat band of 60 MHz ensures that HDTV quality video is not degraded, according to Tucker.

Along with the increased bandwidth, the slew rate on the newer devices has increased to 1200 V/us. “More bandwidth always requires more current. We have managed to double the bandwidth, but only increase the current by a few mA,” Tucker said. Additionally, the 0.1 dB bandwidth has been increased to 130 MHz, she said.

Click here for more details on Intersil’s EL4340 and EL4342 device at eeProductCenter.

Intersil also shrunk the package size of the ISL59424 and ISL59445 multiplexers to a 24-pin QFN measuring only 4 x 6-mm, versus a 24-pin QSOP for the previous devices, which takes up about 9 x 4-mm board space.

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