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12bit, 50 MSPS ADCs use sigma-delta architecture

Posted: 31 Jan 2008     Print Version  Bookmark and Share

Keywords:National  ADC 12bit  Texas Instruments 

Following close behind the octal mid-speed ADC announcement from Texas Instruments Inc., National Semiconductor Corp. has announced the first of its own roughly similar converters, but with significant architectural and performance differences as well.

The ADC12EU050 is an eight-channel, 12bit, 50 MSPS ADC that uses a continuous-time, sigma-delta architecture, and provides alias-free sampling for input signals with up to 25MHz bandwidth. The 350mW IC (44mW/channel; claimed to be 30 per cent less than comparable pipelined architectures) also includes an integral "brick-wall", low-pass anti-aliasing filter, eliminating the need for external filtering. Primary applications for this converter are portable medical ultrasound instruments, industrial imaging equipment, and other test and measurement units.

The input stages of the channels look purely resistive, thus simplifying drive requirements (no sample-and-hold needed) and handle signals of 2.1Vp-p. This input range decreases to 1.6Vp-p if the user switches on the input-overload recovery (IOR) function, which ensures that circuitry recovers from saturation within one clock cycle, a concern in applications where an unexpected, highly reflective obstacle (such as a metal clip) is in the ultrasound imaging path.

The IC operates from a moderate-performance crystal, and then uses an internal PLL to develop a low-jitter, high precision, 800MHz clock using its PLL and VCO functions. SNR is 70dB full scale and SINAD (signal-to-noise and distortion) reaches 68dB. The serialised outputs of the 1.2V, 10 x 10 mm, 68pin LLP IC are compatible with LVDS and SLVS formats. Price is Rs.2,526.62 ($64) each in 1,000 piece quantities. The product is sampling now with volume production scheduled Q3.

- Bill Schweber
Planet Analog

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