ADCs shrink in size, power for portable-scanner sockets
By Graham Prophet, Editor, EDN Europe -- EDN, March 20, 2008
Texas Instruments’ analog-products group has introduced the ADS5281, ADS5282, and ADS5287 series of ADCs featuring 10- and 12-bit resolution and sampling speeds as high as 65M samples/sec. The units come in octal format—that is, eight per package—for compactness and low power consumption. The devices target use in medical imaging, such as ultrasound and MRI (magnetic-resonance imaging), wireless communications, military guidance, automatic-test equipment, and video.
At 65M samples/sec, the ADS5281 family uses 77 mW/channel. With dynamic scaling, at 30M samples/sec, the per-channel power drops to 48 mW. The chips interface directly with TI’s recently introduced VCA8500 octal-variable-gain amplifier, which exhibits 0.8-nV/
input noise for a 63-mW-per-channel power consumption. The ADC-and-octal- amplifier pairing constitutes a complete medical-signal-chain device with better noise performance and lower power than alternative offerings, TI claims. Both parts come in 64-pin, 9×9-mm QFN packages for high-density systems.
The family of parts features a low-frequency noise-suppression mode that eliminates flicker noise, improving SNR (signal-to-noise ratio) by as much as 4.2 dB over a 1-MHz band in baseband and time-domain applications. Overload-recovery circuitry allows each ADC to provide valid data within one clock cycle after an input overload as high as 6 dB, allowing for immediate signal recovery and processing. You can program the devices’ gain from 0 to 12 dB, driving full-scale outputs for input signals as low as 0.5V p-p.
TI also supplies the ADCs in an 80-pin TQFP that provides an easy transition to these next-generation devices, because it is pin-for-pin compatible with the previous-generation ADS527x family. Prices range from $40 to $68.60 (100), depending on speed and resolution. The octal amplifier costs $40.
