A/D converters

Digital signal processing, as its name states, assumes that the signals to be processed are digital, i.e., they can be represented by a series of numbers. Nevertheless, the signals of the real world are continuous both in time and value. The conversion between the two representations is made by the analog-digital (A/D) converter, by which the incoming signal becomes sampled (i.e., discretized in time) and quantized (rounded, i.e., discretized in amplitude). The task of a D/A, digital-analog converter is to restore the analog signal from the series of numbers by interpolation.

The ability and efficiency of signal processing considerably depend on the properties of such converters. Improving the quality of the conversion on the digital side is a very hard task. Accordingly, important research area is (i) to search for higher quality A/D converter structures and (ii) to qualify the manufactured converters.

In our laboratory, research on delta-sigma (ΔΣ) or sigma-delta converters started in 2001. As a result of a fruitful foreign co-operation, internationally reknown results have been achieved. The practical outcome of the research is a commercial 22-bit A/D converter chip, which can be used primaliry in DC-measuring applications.

Research on A/D converter testing is lead by our college, Prof. István Kollár. Some of us are also involved in the research and development of the project, and most measurements and data acquisition required for testing are also carried out here. This project is also respected by the international professional community. Similarly to the previous project, the results achieved in this field are two-fold. On the one hand, theoretical derivations have been published on the achivable precision on the estimated parameters of a sine-wave fitted on quantized samples, on the other hand a software tool has been developed which implements most of the testing methods defined in the standard IEEE-STD-1241.

In the following, these research areas and results are discussed in details.