AN314

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 ...