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AN314

Cirrus Logic
Part Number AN314
Manufacturer Cirrus Logic
Description Multiplexing the CS556x/7x/8x Delta-Sigma ADCx
Published Dec 4, 2008
Detailed Description AN314 Multiplexing the CS556x/7x/8x Delta-Sigma ADCs 1. INTRODUCTION The CS556x/7x/8x devices represent a new generation...
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AN314
AN314


Overview
AN314 Multiplexing the CS556x/7x/8x Delta-Sigma ADCs 1.
INTRODUCTION The CS556x/7x/8x devices represent a new generation of delta-sigma analog-to-digital converters that compete with SAR (successive approximation register) converters, with some distinct advantages.
The unique features of these over-sampling converters allow them to be multiplexed at high speed across many input channels, because every conversion produces a fully settled result.
In this application note the similarities and differences between SAR converters and the CS556x/7x/8x family of ADCs will be discussed as well as some design tips on choosing www.
DataSheet4U.
com the right multiplexer and input amplifiers to drive these ADCs.
2.
COMPARING THE CS556X/7X/8X WITH A SAR Typically SAR ADCs have been used in the past for any high-throughput multiplexed application.
This is because most delta-sigma converters require multiple conversions to fully settle.
In other words, a large step change on the input takes a considerable amount of time to be reflected accurately (settled) in the output of the digital filter.
Most delta-sigma converters use single-bit modulators and sample at kilohertz rates, and many samples are required as input to the digital filter to achieve the required accuracy.
The CS556x/7x/8x family of converters is unique in that the modulator output is multi-bit and the sample rate is 8 MSps (megasamples per second).
This, in combination with a specially designed FIR filter that only takes a few clock cycles to compute a result, produces a converter that can fully settle in a single conversion.
There are several distinct advantages of delta-sigma converters over SAR converters such as their superior DNL (differential non-linearity) performance and excellent noise immunity.
One of the main reasons for the increased noise immunity is that the digital filter attenuates the out-of-band noise.
However, a SAR ADC typically has a bandwidth much higher than Nyquist, and out-of-band noise can al...


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