THE IMPACT OF MULTIPLEXING ON THE DYNAMIC REQUIREMENTS OF ANALOG-TO-DIGITAL CONVERTERS

In data acquisition applications where the signals being digitized are produced in a time-division multiplexed system, the required dynamic performance of the analog-to-digital converter (ADC) is no longer boun d by the conditions set forth in the Sampling Theorem, This results fr om the introduction of very high-frequency information by the multiple xing process which, while not necessarily containing information of in terest, must be processed by the input circuitry of the ADC, In this s ituation, signal bandwidths and slew rates can greatly exceed those pr oduced in a Nyquist limited system and can surpass the capability of t he ADC, thus degrading overall system performance, This paper will exa mine two common multiplexing schemes and their impact on ADC dynamic r equirements, First, we will examine a simple voltage multiplexing sche me typically found in state-of-health or data-logging applications and develop the necessary equations to show how the ADC dynamic requireme nts are affected, Then, the analysis will be extended to a multiplexed photodiode array readout to see how this application further challeng es the dynamic performance of the ADC, Finally, the issues associated with developing dynamic test methodologies for assessing ADC performan ce in multiplexed systems will be discussed.