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ADCs provide high-precision measurements

Posted: 27 May 2008     Print Version  Bookmark and Share

Keywords:ADC  signal acquisition  multi-channel 

Texas Instruments Inc. (TI) has released two new multi-channel, 16-bit, delta-sigma analogue-to-digital converters that are said to combine excellent DC accuracy and AC performance with cost-effective integration. The 4-channel ADS1174 and 8-channel ADS1178 provide a simultaneous-sampling measurement system for signal acquisition applications such as power metering, defibrillators and ECG monitors, as well as pressure sensors, coriolis flow meters and vibration/modal analysis.

The ADS1174 and ADS1178 feature 25kHz bandwidth, 2 uV/C offset drift and up to 97 dB signal-to-noise ratio (SNR). Two operating modes allow for optimisation of speed (52 kSPS) or power dissipation (7 mW/channel).

Traditionally, industrial delta-sigma ADCs offering good drift performance use digital filters with large passband droop, resulting in limited signal bandwidth and mostly suited for DC measurements, TI said. High-resolution ADCs for audio applications offer larger usable bandwidths, but the offset and drift specifications are significantly worse (and often unspecified) than their industrial counterparts, added TI. The ADS1174 and ADS1178 combine these two types of converters, allowing for high-precision industrial measurements with excellent DC and AC specifications.

The high-order, chopper-stabilised modulator achieves very low drift and low noise over the signal bandwidth of DC up to the Nyquist frequency. The onboard decimation filter suppresses modulator and out-of-band noise, providing a usable signal bandwidth up to 90 per cent of the Nyquist rate with stopband attenuation of 100 dB.

A selectable SPI or frame sync serial interface allows for interfacing to DSPs, FPGAs and microcontrollers. Either interface supports daisy chaining to simplify readback of multiple ADS1174 or ADS1178 ADCs in high channel-count systems.

The ADCs are fully specified over the industrial temperature range of -40°C to +105°C. Available in identical packages, the ADCs are drop-in compatible with the high-performance, 24-bit ADS1274 and ADS1278 for convenient upgrades. The ADCs are available now in HTQFP-64 PowerPAD packages.

- Gina Roos

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