Almost all commercial analog-to-digital converters
Last week, at the International Conference on Sampling Theory and Applications, researchers from MIT and the Technical University of Munich presented a technique that they call unlimited sampling, which can accurately digitize signals whose voltage peaks are far beyond an ADC's voltage limit.
The consequence could be cameras that capture all the gradations of color visible to the human eye, audio that doesn't skip, and medical and environmental sensors that can handle both long periods of low activity and the sudden signal spikes that are often the events of interest.
The paper's chief result, however, is theoretical: The researchers establish a lower bound on the rate at which an analog signal with wide voltage fluctuations should be measured, or "sampled," in order to ensure that it can be accurately digitized. Their work thus extends one of the several seminal results from longtime MIT Professor Claude Shannon's groundbreaking 1948 paper "A Mathematical Theory of Communication," the so-called Nyquist-Shannon sampling theorem.
Ayush Bhandari, a graduate student in media arts and sciences at MIT, is the first author on the paper, and he's joined by his thesis advisor, Ramesh Raskar, an associate professor of media arts and sciences, and Felix Krahmer, an assistant professor of mathematics at the Technical University of Munich.
Wraparound
The researchers' work was inspired by a new type of experimental ADC that captures not the voltage of a signal but its "modulo." In the case of the new ADCs, the modulo is the remainder produced when the voltage of an analog signal is divided by the ADC's maximum voltage.
"The idea is very simple," Bhandari says. "If you have a number that is too big to store in your computer memory, you can take the modulo of the number. The act of taking the modulo is just to store the remainder."
Read more at: https://phys.org/news/2017-07-ultra-high-contrast-digital.html#jCp
