Electronic Design

18-Bit SAR, 20-Bit Delta-Sigma ADCs Up The Ante On Converter Specs

A new 18-bit successive-approximation-register (SAR) converter and a 20-bit delta-sigma unit expand the speed and accuracy envelopes for analog-to-digital converters (ADCs). Made by Analog Devices, the 18-bit AD7641 SAR converter runs at a speedy 2 Msamples/s, with 2-LSB linearity and 93-dB signal-to-noise ratio (SNR). The company's 20-bit AD7760 delta-sigma converter operates at 2.5 Msamples/s with an SNR of 100 dB. Both chips support instrumentation, imaging, and vibration analysis in the industrial, medical, and communications markets.

The converters' wide input dynamic range removes some of the need for analog signal conditioning. For example, the AD7641 eliminates the requirement for a separate low-noise programmable-gain amplifier (PGA) ahead of the converter in most vibration-analysis and medical-imaging appplications.

This SAR ADC dissipates 100 mW at 2 Msamples/s. In "impulse" mode, its power dissipation decreases with throughput, so users can trade off throughput for reduced power consumption. It operates from a single 2.5-V supply, providing an internal conversion clock as well as a reference buffer, error correction, and serial and parallel system-interface ports.

The AD7760 is the first chip in a projected family of 20-bit delta-sigma converters. It contains an integrated buffer to drive the reference, a differential amplifier for signal buffering and level shifting, an over-range flag, internal gain and offset registers, and an adjustable low-pass digital finite-impulse-response filter.

In 1000-piece quantities, the AD7641 costs $32.95 each. It comes in a 48-lead LFCSP or LQFP. The AD7760, housed in 64-lead TQFP or 48-lead LFCSP, costs $34.95 apiece in sample quantities.

Analog Devices

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