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New Cirrus ADCs Combine SAR and Delta-Sigma Strengths

June 25, 2007

Cirrus Logic ADCs offer high throughput of SAR converters with high resolution and low-noise performance of delta sigma converters; deliver superior accuracy for industrial, scientific instrumentation applications.


AUSTIN, TX -- With the introduction of the CS556x/7x/8x family of 16- and 24-bit analog-to-digital converters (ADCs), Cirrus Logic (Nasdaq: CRUS) has rewritten the rule book for high-performance Delta-Sigma industrial analog converters.

Cirrus' new family of high-precision analog converters combines the higher-bandwidth, low-distortion performance of a SAR converter with high-resolution, low-noise performance that is the hallmark of Delta-Sigma ADCs. The breakthrough 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.

"This breakthrough performance means that various industrial applications will be able to obtain an extremely accurate measurement of data," said John Paulos, vice president and general manager, Industrial Products Division, Cirrus Logic. "Greater measurement accuracy leads to a wealth of benefits for industrial systems such as systems for achieving tighter production yields, higher-precision machine tools, improved temperature control, valve control and speed of flow, just to name a few."

The CS556x family overcomes many of the critical performance issues associated with SAR and Delta-Sigma converters. SAR converters are typically very sensitive to noise, whether the source of noise is in the converter itself or in the system that the SAR converter operates. Virtually any noise present can—and often will—propagate directly to the output of the converter. The CS556x provides 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.

The CS556x also offers exceptional differential non-linearity (DNL) error, which measures the accuracy of the ADC and is of critical importance in control applications. 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. The CS556x's high throughput precision performance stands out among high-resolution Delta Sigma converters. 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. 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 utilize Sinc filters, which attenuate the signal at specific frequencies. Other additional key features of the CS556x 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 superior 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 and Availability
The CS5560 offer 24-bit resolution, a conversion rate of 50 Ksps and is priced at $8.45 in 1000 quantities. The CS5570 offers 16-bit resolution, a conversion rate of 100 Ksps and is priced at $10.95 in quantities of 1000. The CS5580/81 offer 14-bit resolution, conversion rate of 200 Ksps and is priced at $7.95 in quantities of 1000. The ICs, which are currently in volume production, are available in a 24-lead SSOP package.

Cirrus Logic Inc.
Cirrus Logic develops high-precision analog and mixed-signal integrated circuits for a broad range of consumer and industrial markets. Building on its diverse analog mixed-signal patent portfolio, Cirrus Logic delivers highly optimized products for consumer and commercial audio, automotive entertainment and industrial applications. The company operates from headquarters in Austin, Texas, with offices in Europe, Japan and Asia.

Cirrus Logic and Cirrus are trademarks of Cirrus Logic Inc. All other product names noted herein may be trademarks of their respective holders.


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