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Low-power ADCs go beyond handhelds

Posted: 31 Mar 2010 ?? ?Print Version ?Bookmark and Share

Keywords:ADC? processor? analog? front-end?

It's simplistic to think there's just a single dominant trend associated with the complex and diverse analog world, but some trend lines are stronger than others. For ADCs, the adjective that cuts across nearly all resolutions and speeds is low power.

What's especially interesting is that applications for low power now extend beyond the obvious handheld, battery-powered instrumentation to high-channel-count designs such as X-ray machines and ultrasound and MRI scanners, where the power dissipated by the analog channels is dwarfed by the needs of the rest of the system.

If you're drawing tens of kilowatts from the power line, why should a few watts for the analog front-end matter? It has to do with both the cost of delivering those clean power rails to the ICs, as well as local heat dissipation on the circuit boards. When you reduce consumption, you simplify the design of the power delivery subsystem, while enabling higher channel counts due to reduced thermal load as a consequence of lower dissipation.

In addition, low power allows IC vendors to pack more channels into a single IC, further increasing front-end density.

Simplifying the BOM also weighs on designers' wish lists. Noted Steve Logan, business manager for signal processing and conversion at Maxim Integrated Products, designers want "a single ADC to meet as many of their needs as possible, [and] run the ADC at its maximum speed and do post processing to achieve better SNR through oversampling and averaging. Or for their lower speed applications, they'll slow down the sampling speed to achieve power savings."

Another tactic for reducing footprint is increased integration and functionality, such as for the reference function required for every ADC. Integrating a high-end reference is easier in theory than execution, said Alison Steer, mixed-signal product marketing manager at Linear Technology Corp., "Precision references with guaranteed performance over temperature are not so easy . . . this is where we add value to the industrial and automotive markets with guaranteed low drift specifications over wide temperature ranges."

Making one converter fit multiple signal types is another tactic for design simplification. James Caffrey, marketing and applications director for the precision ADC group at Analog Devices Inc., pointed out that, "breakthroughs in converter performance are allowing a single converter to process inputs of different magnitude and signal type, such as temperature, humidity and pressure with minimal preconditioning."

It's not just the analog side of the ADC that matters, of course. Getting converted data out and managing and monitoring the converter and subsystem are key requirements. According to Harold Joseph, senior marketing manager in the precision signal-path group at National Semiconductor Corp., "this has meant an increase in the need for I?C bus-compatible ADCs to measure more system functions, without requiring an increase in processor inputs."

But there are limits to how much IC designers can put into the package. Allan Evans, marketing VP at Samplify Systems, pointed out that "this data explosion is causing a strain on the integration of these devices into data acquisition systems. . . this trend will be addressed with the following technologies: signal compression to reduce the aggregate bit rate, high-speed serial interfaces to reduce the number of I/Os and port concentration to maximize the use of the available I/Os."

- Bill Schweber
EE Times

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