ADCs combine best features of SAR converters and sigma-delta ADCs

Austin, Tex. — Cirrus Logic has introduced its CS556x/7x/8x family of 16- and 24-bit analog-to-digital converters (ADCs) that claim to deliver the higher-bandwidth, low-distortion performance of a SAR converter with the high-resolution, low-noise performance of Delta-Sigma ADCs. The combination of features provides designers of precision instrumentation, such as industrial process controllers, laboratory instrumentation, medical instrumentation and high-speed weighing systems, with a significantly higher level of measurement accuracy, lower noise and higher throughput, according to Cirrus Logic.

The CS556x is said to provide a much higher level of noise suppression than SAR converters, resulting in higher accuracy conversions and reduced post-conversion processing while adding to the robustness of the system. It also offers exceptional differential non-linearity (DNL) error, which measures the accuracy of the ADC and is critical in control applications, said Cirrus Logic. The family features DNL error as low as ±0.04 LSB typical (CS5571), compared to ±1 LSB typical within SAR converters.

In addition, the single-clock latency digital filter allows conversion-rate switching of the input with no loss in throughput. With near-flat digital FIR filter characteristics, the CS556x product line achieves unrestricted, wide-bandwidth signal throughput usually seen only in higher-speed SAR converters — at resolutions up to 24 bits, said Cirrus Logic. With this flat filter, output data is a 1:1 representation of the input signal across the entire frequency range, up to the sampling rate of the converter. In comparison, most delta-sigma converters use sinc filters, which attenuate the signal at specific frequencies, added the company.

Other features include high-impedance buffered inputs that simplify external circuitry; fully differential inputs that provide the best possible noise rejection and dynamic accuracy with the ability to measure bipolar signals; and self calibration to ensure measurement accuracy over variations in supply and temperature.

A flexible serial interface eases connections to a variety of microcontrollers without external components (includes slave and self-sequencing master modes).

Pricing: The CS5560 (24-bit resolution, 50 kSPS conversion rate) is priced at $8.95; the CS5571 (16-bit resolution, a conversion rate of 100 kSPS) is priced at $10.29; the CS5581 (16-bit resolution, a conversion rate of 200 kSPS) is priced at $8.45, in quantities of 1,000.
Availability: The CS5561/70/80 will be available in September. The ICs, which are currently in volume production, are available in a 24-lead SSOP package.
Product information: industrial A/D converters

Cirrus Logic Inc. , 1-512-851-4000,

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