Design trade-offs of using SAR and Sigma Delta Converters for Multiplexed Data Acquisition Systems

Maithil Pachchigar, Analog Devices
EDN (November 17, 2015)

Multiplexed data acquisition systems (DAS) utilized in industrial process control, portable medical devices and optical transceivers need increased channel density, where the user wants to measure the signals from multiple sensors and monitor and scan many input channels in to a single or several ADCs. The overall benefit of multiplexing is fewer number of ADCs per channel required, saving print circuit board (PCB) space, power and cost. Some systems in automated test equipment and power-line monitoring applications demand dedicated track and hold amplifier and ADC on per channel basis for simultaneously sampling the inputs to obtain increased sampling rate per channel and to preserve the phase information at the expense of additional PCB area and power.

System designers make trade-offs based on performance, power, space, and cost requirements in their end application. They select one of the converter architectures and topologies and implement their signal chain using either discrete or integrated components available in the market. The figure 1 shows a simplified block diagram of multiplexed DAS that monitor and sequentially sample various sensor types. Sometimes signal chains utilize either buffer amplifier or programmable gain amplifier between the multiplexer and ADC.

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