Electronic Design

Successive-Approximation Register ADCs Sample To 800 ksamples/s

Three additions to the PulSAR family of successive-approximation register (SAR) analog-to-digital converters (ADCs) offer sampling rates of 800 ksamples/s (AD7674), 100 ksamples/s (AD7678), and 570 ksamples/s (AD7679). These monolithic 18-bit SAR ADCs have no missing codes and guaranteed performance over the full temperature range. Each is specified at ±2.5-LSB INL, 100-dB signal-to-noise ratio (typical), and ­110-dB total harmonic distortion (THD) (typical).

Following the normal progression in ICs of faster and higher accuracy over time, the ADCs deliver at least 16 bits of actual accuracy coupled with 18-bit resolution. The higher speeds and bit resolution let users move from modules to monolithic converters in those applications that require the speed and resolution. Their low noise and THD should enable full converter resolution in-system, but only if the rest of the analog signal chain is at least as good as the ADCs—not necessarily a simple proposition.

The parts feature fully differential inputs, a conversion clock, and both serial and parallel outputs. They come in a 48-lead chip-scale package. These features provide enough flexibility for the parts to be incorporated into a wide range of designs. The ADCs are pin-compatible with other members of the PulSAR family.

Other features include 5-V operation with an input differential range of ±5 V. The AD7464 has three operating modes: warp (800 ksamples/s), normal (666 ksamples/s), and impulse (500 ksamples/s). Power dissipation scales with operating speed from 120 mW (typical) at warp to 83 mW at impulse. Each part has a 7-µW power-down mode, so the ADCs can go offline when not needed. They operate from ­40°C to 85°C. Samples are available now in 48-lead LQFP and LFCSP packages. The AD7674 costs $39, the AD7678 $24, and the AD7679 $32 in 1000-unit lots.

Analog Devices Inc., (800) 262-5643; www.analog.com/PulSAR.

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