7.1.1 Reduced Test Time

In Chapter 6, we briefly touched on the advantages of DSP-based testing before beginning our review of sampling theory. In this chapter, we will take a more detailed look at digital signal processing and the power it gives us in testing mixed-signal devices. Although a full study of DSP is beyond the scope of this book, many good texts have been written on the subject. ^[1]- ^[3] In this chapter, we will review the basics of DSP, limiting our discussion to discrete (i.e., sampled) waveforms of finite length.

Coherent DSP-based testing gives us several advantages over traditional measurement techniques. The first advantage of DSP-based testing is reduced test time. Since we can create and measure signals with multiple frequencies at the same time, we can perform many parametric measurements in parallel. If we need to test the frequency response and phase response of a filter, for example, we can perform a series of gain and phase measurements at a dozen or so frequencies simultaneously.

DSP-based testing allows us to send all the filter test frequencies through the device under test (DUT) at the same time. Once we have collected the DUT's output response using a digitizer or capture memory, DSP allows us to separate each test tone in the output waveform from all the other test tones. We can then calculate a separate gain and phase measurement at each frequency without running many separate tests. We can also measure...