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TI Introduces Fastest 16-bit SAR Data Converter

Low-Price ADC provides 16-bit No Missing Code Performance at Record 1.25 MSPS

The manufacturer says . . .

ChipCenter's Paul O'Shea says . . .

Raising the performance level of SAR (successive approximation register) converters, Texas Instruments (TI) Incorporated (NYSE: TXN) today introduced the industryıs fastest 16-bit SAR analog-to-digital converter (ADC) from the companyıs Burr-Brown product line. Utilizing a proprietary, state-of-the-art architecture, the ADS8401 and ADS8402 feature an industry-record 1.25MSPS (mega samples per second), true 16-bits No Missing Code performance and 155mW power dissipation.. These high-speed, low-power devices target a wide range of advanced applications, including medical imaging, portable medical instrumentation, high-speed data acquisition, wired communications and optical networking. SAR converters, in contrast to pipeline and delta-sigma architectures, feature no latency. ıThere is absolutely no other ADC on the market that can offer such a range of performance attributes ı 16-bit no missing codes, 2LSB linearity, 0.25mV offset, 90dB signal-to-noise ratio and 155mW power dissipation ı all at 1.25MSPS,ı said Tony Chang, strategic marketing engineer for TIıs data acquisition products. ıBy starting these devices at $11.95 in 1,000s, the ADS8401 and ADS8402 give customers an excellent price/performance ratio for advanced systems requiring high speed and high resolution.ı The ADS8401 and ADS8402 offer designers a complete solution without the need for an external reference or reference buffer. DC performance, especially offset and offset drift, is far superior to other high-speed ADCs currently available. The ADS8401 offers a pseudo-differential, unipolar input range, while the ADS8402 uses unipolar differential inputs with a bipolar range, which are common to many high speed ADCs. Both devices offer a full 16-bit interface and an 8-bit option when data is read using two 8-bit cycles, if necessary. Texas Instruments Incorporated, Semiconductor Group, SC-03xxx, Literature Response Center, P.O. Box 954, Santa Clara, CA 91380. Tel: 800-477-8924, ext. 4500 Texas Instruments Web Site

The TI ADS8401 converter at 1.25 MHz is the fastest 16-bit SAR converter available. It provides an internal reference buffer and that means you don't need any components to support a conversion process. What is unique about this product (other than the higher speed) is its very low latency, as compared to pipeline or Delta Sigma converters. And it combines good performance, including very low noise and very good linearity, with a low offset of 1 mV over the full temperature range (-40 to +85°C). That 1 mV offset becomes impressive when compared to a higher-speed pipeline converter that has hundreds of millivolts of offset and is less stable over the working temperature range. The ADS8401 and 8402 are very unique because they provide 16 bits of no missing code and have good linearity. There are other companies that offer a 1 MSPS part but they don't use an internal reference or buffer. They use an op amp and a large capacitor. The biggest problem with using an external reference on these converters occurs when the reference output gets a glitch between the process of conversion and the output. The impedance of this reference has to be very low at high frequency. That's why TI put the reference buffer inside, this way the glitches would be eliminated by the buffer and you can use a very low-cost external reference without needing to buffer the signal separately. The other designs need a very high-speed op amp as an external reference and that can introduce noise, resulting from the high speed. It's a delicate situation because these designs need the high speed to enable the converter to settle within one clock cycle. The clock cycle in the ADS8401 converter is about 50 MHz so it has enough time to settle within one clock cycle. All it needs is a start command and about 610 ns later (the conversion time) you get the digitized representation of the sampled signal. Another important difference between the internal and external reference is the higher cost and power consumption for the external types. Other competitive parts draw more voltage compared to the TI part, which, at 1.25 MHz only draws 150 mV versus about 450 mV for other parts. You probably know that other companies have introduced 2 MHz, 16-bit converters. However, they are a mixture of Delta-Sigma and Pipeline converters, which makes them difficult to compare to this SAR converter. Additionally, you wouldn't use the Delta-Sigma designs for the same applications as this SAR converter because the Delta-Sigma converters have much more latency, about 6 - 8 clock cycles of latency. The offset drift is also much greater, as is the linear noise. What sets this converter apart is its 16-bit linearity, with 90 dB signal-to-noise, 110 dB spurious-free dynamic range at 100 kHz, less than 1 mV offset over the -40 to +85°C temperature range, and of course the 1.25 M samples/second with the extremely low latency. The ADS8401 and ADS8402 come in a TQFP-48 package, and are available now from TI and its authorized distributors. Suggested resale pricing starts at $11.95 in 1,000 piece quantities. Data sheets: ADS8401 ADS8402

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