SAR High throughput, low distortion AND Delta-Sigma high resolution, low noise performance

24 or 16- bit High-throughput ΔΣ ADCs

This new family of High-Throughput Data Converters offers designers a new level of high-resolution measurement performance. Combining high conversion rates, high resolution, and low system latency, these devices offer a significant improvement over SAR-type converters.

Utilizing the proven expertise of Cirrus Logic in low noise, low-drift input buffer amplifiers, absolutely leading-edge multi-bit delta-sigma modulator architectures, and high-performance digital filters, these new products are the first to bring a combination of high resolution, high conversion rate, and low latency to the market, resulting in a real breakthrough in measurement accuracy in industrial and instrumentation applications:

• Low-Drift, Chopper-Stabilized Amplifiers
• Leading-edge, Low-Noise Multibit Modulator
• High-speed FIR Digital Filter
• First combination of technology to achieve High Throughput in a Delta-Sigma ADC

The Delta-Sigma conversion topology, while seemingly complex, utilizes a more careful conversion technique to achieve high measurement accuracy in a way which is easier to use than SAR converters. One of the keys to this leading-edge technology is the use of an advanced multi-bit modulator which makes it possible to resolve higher resolution and accuracy at a higher conversion rate than past single-bit modulators.

Basic operation: (click here to see block schematic).

A difference amplifier with high input impedance measures the difference between the output of a fast-changing D/A (Digital-to-Analog) converter and the input signal. The input amplifier samples the input multiple times during the conversion, meaning that samples which are degraded by noise at the input will have reduced impact on the overall accuracy of the final measurement obtained at the output. The remainder of the circuit processes the output to generate a stream of 4-bit digital words which both control the output D/A converter, and supply a digital filter which averages the data stream over a long period to calculate the high-resolution result. Since the D/A converter changes it's output to match the input at a relatively high rate, this amplifier generates a well-behaved output which does not disturb the remainder of the device. The remainder of the circuit also operates within well-controlled voltage levels and thus does not generate significant levels of internal noise, and provides identical measurement accuracy over the entire input signal range. The digital output filter, since it is performing only a numerical average over a long period, provides the same measurement accuracy over the entire input range. The frequency characteristics of this filter, since they are bound by arithmetic, also provide absolutely repeatable performance characteristics.
As a result, a Delta-Sigma A/D is much more forgiving and easier to use, providing much better measurement accuracy and repeatability over it's rated range without costly high-performance input circuitry compared to typical SAR devices.