Electronic Design

Monolithic Ultrasound AFEs Usurp Multiple Chips In New Designs

There are now two sources of analog front ends (AFEs) for ultrasound applications. Texas Instruments is sampling the AFE5805, the first member of a future family for portable to high-end ultrasound diagnostic equipment. Last year, Analog Devices introduced the AD9271 for the same market. Functionally similar, both are octal devices that incorporate a lownoise amplifier, variable gain amplifier (VGA), anti-aliasing filter, and 12-bit analog-to-digital converter (ADC).

The TI chip beats the ADI chip in terms of input-referred noise (1.1 versus 1.3 nV/vHz in CW/Doppler mode, 0.85 versus 1.2 nV/vHz in time-gain control/ imaging mode), VGA gain-control range (46 versus 30 dB), and power consumption per channel (122 versus 149 mW). These values are typical for parts rated for 40-Msample/s ADC conversion rates. ADI currently has a version that goes to 50 Msamples/s. The TI datasheet mentions 50 Msamples/s, but contains no specs for that speed.

That puts TI ahead in the specification race, but there’s more to the story. The subtext is about a change in the way medical- imaging systems are being designed. Engineers at ultrasound OEMs have until now used separate boards for analog and digital subsystems. The presence of two competitors with mixed-signal devices points to a market that no longer feels it needs to roll its own to achieve optimum performance in the system elements ahead of the number-crunching circuitry.

The demand for AFEs indicates that ultrasound OEMs think the IC makers can do it monolithically as well as or better than they can with separate chips. This indicates that the chip makers have been doing their homework, which in turn means that medical imaging is a market worthy of large investments. And medical imaging is significant because its end markets are particularly diverse.

Chinese OEMs concentrate on inexpensive portable units to spread 21st century diagnostics to an awakening population. European OEMs focus on high-end equipment for the most subtle kinds of diagnostics. Japanese and North American companies straddle both worlds, trying to push ever-greater imaging resolutions and blood-flow measurements into evershrinking ultrasound boxes for private clinics and even ambulances.

TI’s AFE5805 comes in a 15- by 9-mm, 135-pin, ball-grid-array package. Suggested retail price is $75 each in 100s. Samples and evaluation modules are available now, with volume production slated for June.



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