Octal A/Ds target medical, instrumentation sweet spot

Dallas, Tex.–So many A/D converters (ADC), so many application niches: vendors must carefully tailor converter specs to meet the subtle tradeoffs among user priorities for a given application, as demonstrated by the ADS5281 family of 10- and 12-bit eight-channel devices from Texas Instruments. Their ADS5281, ADS5282, and ADS5287 span sampling rates and resolution pairings of 50 MSPS/12 bit, 65 MSPS/12 bits, and 65 MSPS/10 bits, respectively, with per-channel power dissipation of 64 to 77 mW, which they claim is 30% less than competitive devices.

The primary application areas for these converters are medical devices with moderate to high channel count, such as portable ultrasound and MRI equipment, as well as wireless base stations, test and measurement, and other instrumentation designs. To better match the unique needs of these applications, the converters incorporate two extra features. First, there is a user-selectable low-frequency noise-suppression mode which greatly reduces 1/f (flicker) noise, and improves SNR by as much as 4.2 dB over a 1-MHz band (useful in baseband and time-domain applications. Second, each ADC has overload-recovery circuitry so that the converter's output will be again be valid within one clock cycle of an overload as high as 6 dB; this is needed, for example, when the ultrasound head front end is ramping up “gain versus time” (typically done to compensate for signal attenuation versus tissue depth) and the signal hits a solid object such as a pin or staple under the skin. Full-scale input range is 2 Vp-p , and full-scale output is available for inputs signals down to 0.5 Vp-p due to digitally programmable gain range of 12 dB.

Power consumption of the A/Ds scales down dramatically as sampling rate is decreased, so the OEM end product can go into a lower-performance mode to save power. Output format is serial LVDS compatible. The converters, which use a 3.3 V supply for the analog side and a 1.8 V supply for the digital side, and are housed in pin-compatible 64-pin, 9×9 mm QFN packages. TI also offers a complementary octal, variable gain amplifier, the VCA8500, which yields very tight and effective PCB layout.

More product information, including a demo video, is available at

Pricing: between $40 and $68.60 (100 pieces) depending on model.
Availability: immediate

Texas Instruments Incorporated , www.ti.coms

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