Digital Alias-free Signal Processing

6

Direct Randomization of Sampling

In an ideal case, the features of a digital signal obtained as a result of analogto-digital conversions would copy the features of the original analogue signal. The reality is different. The sampling and quantization operations of this kind of conversion impact on the characteristics of the obtained digital signals substantially. The characteristics of the analogue signal at the input of an ADC and of its digital output are representative rather than identical. The methods used for digitization and their implementation determine how large and significant are the differences between them. Once a signal is digitized, the features of the obtained digital signal, good as well as bad, are fixed and nothing can be done to change them. Therefore it makes sense to invest a great deal of time and effort to ensure that the quality of the signal sampling outcome is high enough.

Deliberate randomization of the signal sample value taking process is one of the most promising sampling improvement options. Although the randomization approach significantly complicates the sampling operation and processing of the digital signals obtained in this way, the resulting benefits justify these complications. For instance, application of the randomized sampling technique, as shown in Chapter 1, often leads to much better exploitation of the resources of the existing ADCs.

There are various techniques used for randomization of sampling. The discussions in this chapter focus ...