The role of noise in analog-to-digital converters

Because of the widespread use of digital systems in radars, instrumentation, and communication systems, an understanding of the role played by noise at the input to the analog-to-digital (A/D) converter is important. When digital signal processing is performed on the output of the A/D, it is crucial that the A/D respond linearly to the signal. The noise level at the input of the A/D is a determining factor for the linearity of the system. Many texts discuss the operation and performance of analog-to-digital converters and, although the understanding of the role of noise is not new, it seems that few, if any, discuss noise from the point of view presented here. This omission appears to lead to a misunderstanding of the importance of noise in these analog-to-digital systems. Single- bit and multiple-bit analog-to-digital converters will be analyzed, and it will be shown, that with the appropriate noise level at the input, even the single-bit converter can behave as a linear device. An example will be described whereby a ``feature`` of a particular commercial instrumentation system was based on a misunderstanding of the role of noise, and the use of this ``feature`` caused serious degradation of the system linearity and performance