Analog Angle Article

Tiny quad-channel 14/16-bit, 100 MSPS ADC targets medical MRI, available without magnetic “personality”

Designed for use in magnetic resonance imaging (MRI) systems, the ADS5263 IC from Texas Instruments is a four-channel analog/digital converter (ADC) which delivers up to 100 Msamples/sec at user-selectable 14/16 bits. The dual resolution allows designers to trade between lower-power versus higher-speed/higher-resolution operation.

It is housed in a space-saving 9×9 mm QFN package, which the vendor maintains is about half the board space of competitive single- and dual-channel ICs—the converter dissipates 380 mW/channel in 16-bit mode.

Block diagram: ADS5263 ADC IC for MRI

Critical specifications at 16-bit/100 Msps operation is SNR of 84.6 dB full scale with a 10-MHz input (4 Vpp full-scale input) with dissipation is 380 mW/channel; in 14-bit mode, SNR is 73 dB FS while dissipation drops to 195 mW per channel (2 Vpp full-scale input).

Unique fabrications and packaging is also part of the story. Since MRI image quality is adversely affected by the presence of magnetic materials in the field of view, many designs strive to minimize as much of this material as possible, TI also offers this converter in a non-magnetic package as a standard catalog item. Based on evaluations they have performed with real MRIs, this image pair supplied by TI shows the improvement in image clarity with a non-magnetic versus magnetic package.

Left: scan of standard tissue target with regular BGA package;

right: same scan but with non-magnetic package

Pricing and support : The ADS5263 in standard magnetic package is $236.50 (1000 piece orders); in the non-magnetic package, it is $385.50. TI offers an evaluation module, the ADS5263EVM, for $299. IBIS models are also available, to assist in verifying PC board signal-integrity requirements.

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