Electronic Design

SAR ADC Conversion Rates Jump To 4 Msamples/s

The hottest battleground today among analog-to-digital converter (ADC) suppliers is the successive-approximation register (SAR) arena. SARs serve the medical/industrial market with zero latency and high linearity at modest conversion rates. New SAR products seem to notch up improved performance specifications every three to four months.

The latest entry, Texas Instruments 16-bit ADS8422, raises the ante on speed by 33% (see the figure). It delivers 4-Msample/s conversion, with no limitation on time between conversions, while providing excellent ac and dc characteristics.

Datasheet "typical" values include 92-dB signal-to-noise ratio, –102-dB total harmonic distortion, 2-LSB integral nonlinearity, 1-LSB differential nonlinearity, 0.5-mV offset voltage over temperature with less than 0.1-ppm/°C offset drift, 0.05% gain error, and 3.3-ppm/°C gain drift. TI says the chip s performance is based partly on the company's proprietary process technologies and partly on circuit design, particularly its on-chip voltage reference and the accompanying reference buffer. Otherwise, the ADS8422 architecture is just like a classic switched-capacitor SAR, with that architecture's intrinsic sample-and-hold capability.

The ADC has a fully differential input with pseudo-bipolar input range (–4 to 4 V). It provides the option of a full 16-bit interface or two 8-bit modes that allow data to be read in cycles. Other features include single-supply operation and guaranteed operation from –40°C to 85°C.

TI provides evaluation modules to facilitate design-ins. The company also will supply Gerber files for pc-board layout if requested. The ADS8422 is sampling now, with volume production scheduled for the third quarter. The device is available in a 48-pin, 7-by-7 quad flat no-lead (QFN) package. It costs $23.95 in 1000-piece quantities.

Texas Instruments

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