An Analog-to-Digital Converter with Frequency Dependent Effective Resolution

Abstract

A design method is described for a new analog-to-digital converter (ADC) which can vary its effective resolution depending on the input frequency. This is an important development, especially for video signal processing. Usually, 8 bits are sufficient for a video signal, however, when the video signal frequency is very low, 10-to 12-bit quantization becomes necessary.
The ADC is based on a subranging ADC, which consists of coarse and fine converters. The ADC can be contrasted with the conventional subranging ADC in which the fine conversion cycle follows the coarse conversion cycle. A prediction method is adopted to make both the fine and coarse conversions at the same time. The lower the input frequency is, the more accurate the prediction is. As a result, the effective resolution of the ADC depends on the input frequency.
To estimate the ADC performance, an experimental circuit has been implemented with discrete circuit components. The effective resolution change with change of input frequency was measured. Experimental results were in good agreement with the theory.