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acquisitionZONE Products for the week of January 28, 2008
Texas Instruments Says…
ADS5281/82: Low Power Data Converters Enable Compact Medical Imaging and Wireless Systems
Octal ADCs Cut Power Consumption by 30%
A new family of 10- and 12-bit, eight-channel (octal) analog-to-digital converters (ADCs) introduced by Texas Instruments Incorporated (TI) features the industry's lowest power consumption and smallest size. The new data converters enable smaller and more energy-efficient medical imaging, wireless communications, military guidance, automatic test equipment and video equipment. The ADS5281 family offers high resolution and sampling speeds of up to 65 million samples per second (MSPS), low noise performance and advanced digital features, which are critical in sensitive imaging applications like portable ultrasound and MRI equipment.
"As medical imaging systems become more portable and compact, TI is committed to solving challenges manufacturers face when designing these increasingly complex systems," said Art George, senior vice president of TI's high-performance analog business unit. "The ADS5281 ADC family and TI's octal amplifier provide the ultra-low power and high density these systems require, without sacrificing performance and image quality."
Industry's Lowest Power Consumption Critical to High-Density Systems
The ADS5281, ADS5282 and ADS5287 ADCs feature market-leading power consumption, 30 percent less than competing solutions. At the highest sample rate of 65 MSPS, the ADS5281 family consumes as little as 77 milliwatts (mW) per channel. With dynamic scaling, at a 30 MSPS sample rate, the per-channel power consumption is as low as 48 mW per channel.
The ADS5281 family is designed to interface with TI's new octal variable gain amplifier, the VCA8500, which features 0.8 nV/square root Hz input noise at only 63 mW per channel power consumption. When combined, the ADC and octal amplifier offer a complete medical signal chain solution with better noise performance and a combined power of less than 130 mW per channel at 50 MSPS, less than any competing solution on the market today.
EN-Genius Says…
Today, January 28, 2008, there is expected to be an announcement from National Semiconductor of the first production continuous-time delta-sigma ADC resulting from their acquisition of Xignal Technologies. CT∆∑ has been a bit of an academic fad over the last years, frequently raising its head at conferences with most of the research coming from Germany. The architecture removes the switched-capacitor loop filter and replaces it instead with a high-order op amp integration filter. The input is simpler because there is then no need to filter the switching glitches. Its benefits have always been touted as reducing power at any given speed. However, there have been clock jitter issues that have delayed implementation.
National’s ADC12EU050 50 Msample/s 12 bit ADC overcomes that problem by including the clock on chip. At that speed it beats this new family from TI by about 25% in power consumption. However, the part’s clock does not appear scalable, but the data sheet is months short of representing a real part at all, let alone being informative.
This TI family has flexible speed going for it from the get-go, and the characterizations in the data sheet are a real indication that the parts will be on time, and as advertised.
The ADS5281 is an octal 12-bit pipeline ADC (multi-bit and single bit internal stages) that can be clocked up to 50 Msample/s. The ADS5282 extends that capability to 65 Msample/s. The inputs are differential switched-capacitor sample-and-hold stages, while the serialized outputs and clocks are LVDS. The analog input full-scale range is 2 Vpp and the input bandwidth is 520 MHz. The inputs will recover from a 6 dB overload within one clock cycle.
Dissipation per channel is 48 mW at 30 Msample/s, 55 mW at 40 Msample/s, 64 mW at 50 Msample/s, and 77 mW at 65 Msample/s. An external source of differential clock is required which, after buffering, drives the 8 ADCs. The clock is also fed to a PLL which produces 12x clock for the LVDS serializers and also outputs, through buffers, both 6x clock and 1x clock.
There is a lot of programming possible in the chains, including up to 10 dB of digital gain at the outputs of the ADCs, all stored in on-chip registers. There is also power-down control and an internal trimmed reference that can be overdriven externally. The analog circuits require a nominal 3.3 V supply and the digital ones use 1.8 V.
Inter-channel crosstalk (7 channels driven FS, with the 8th channel measured) is -90 dBc and the two tone (9.5 MHz and 10.2 MHz at -7 dBFS) third-order intermod is -92 dBFS. The DNL has a worst case possibility of ±0.75 LSB with ±1.5 LSB for INL. At 50 Msample/s and with a 30 MHz input, SFDR is 80 dBc and SINAD is 69.5 dBFS.
The VCA8500 variable gain amplifier is the device designed to interface with this family of converters. It has a calculated input voltage noise of 0.75 nV/rtHz, way down there with the lowest numbers around. The input amplifier has a fixed gain of 20 dB so that input noise dominates the noise of the chain. The combination of this VGA with the new ADCs is a perfect solution for medical equipment.
The medical imaging market is huge and getting bigger. By offering real solutions with future path performance laid out by pin-compatible parts a user can be reassured that basic designs can be improved on in performance quickly, and with little fuss. Price in this market is not an obstacle, considering the tens of thousands of dollars that the end result costs. Customers who already use the ADS527x family will stick with TI as supplier, using the same HTQFP-80. New customers will recognize the known quality and come on board using the QFN-64. The new family will be a huge moneymaker for TI. Put together with the remarkable VCA8500 – which will come back to when it is closer to release – TI is offering a complete solution. Now, if the company put the octal ADCs and the octal VGAs in the same package…
The ADS5281 and ADS5282 are in both QFN-64 and HTQFP-80 (for existing customers upgrading performance) with the former priced at $60.00 and the latter at $68.00, both in 100-piece lots. The ADS5281 is sampling now and evaluation modules are available. The VCA8500 is sampling, also in QFN-64, and will be priced at $40 in 100-piece lots.
Data Sheet ADS5281
Data Sheet VCA8500
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