Q. Who is ScopeDSP™ for?
A. ScopeDSP is designed for engineers, scientists, and advanced amateurs working in practical applications of Digital Signal Processing. Anybody can use ScopeDSP as a plotting program or for file conversion, but to use all its features effectively you should have an understanding of basic DSP concepts such as complex data, the Discrete Fourier Transform (DFT), data windowing, filtering, and modulation. Most introductory college courses on DSP cover these topics.
Q. What are typical applications of ScopeDSP?
A. ScopeDSP fundamentally is a software tool for analyzing sampled data
signals. It began life as a tool to analyze data captured from the A/D
(analog-to-digital) converters. Of course, the manufacturer's specifications
tell you how well the A/D will perform--if you happen to insert it into
the ideal circuit design as they did. Probably your design isn't
quite ideal. The process of implementing an A/D converter in a real circuit
design and achieving specified performance always involves some
iteration. Typically, you will make an initial design, test it, change
something in the grounding, shielding, or power supplies, re-test it, and then
test it again. To guide your path through this Mysterious High Art, you will
need to capture data samples from your A/D into a file and calculate basic some
performance specifications such as SINAD and SFDR. ScopeDSP doesn't do the
capture part, but it does do the calculation part. See the
A/D Performance Measurement tutorial for more details.
Likewise, as you design the rest of your DSP system you probably will simulate
it extensively (if you know what's good for you.) But alas, even inside
your own seemingly perfect digital Denmark, indeed, something smells
rotten. Maybe your software has a bug (say it isn't so!) Or maybe there are
spurs or distortion caused by fact that, unlike the textbooks, you chose
to implement your DSP system with finite-precision arithmetic. (Tisk,
tisk!) ScopeDSP can read and write many data file
formats, including the ones used by most of the DSP microprocessor
simulators currently available.
Q. How do I acquire a sample from my A/D converter?
A. This is a tough one: the problem of collecting samples from your A/D
converter always seems to be a problem. Since ScopeDSP takes its input from
files, you must somehow collect data from your A/D and then write it to a file.
We can't be of much real help in the capture process; we come in only
after you have captured the data as a file. But here are a few tips. One
of the handiest ways to capture data, if your A/D is the " parallel"
type, is via a Logic Analyzer. Unfortunately, Logic Analyzers are limited to
relatively small sample sizes. Some of the newer Logic Analyzers can save data
samples on their built-in disk drive (though a disk file format conversion may
be required.) Alternatively, you might use an IEEE-488 interface or some other
interface to transfer data from the Analyzer to a computer. Of course, if your
A/D is connected to a DSP microprocessor and you have an emulator running, you
can use that for data capture. Another approach is to buy a "data
capture" card that connects to the computer bus of your choice. In any
event, be prepared to suffer some aggravation.
Q. How does ScopeDSP handle "real" data (as opposed to
A. ScopeDSP does all operations internally using complex data. However, just as
in the textbooks, "real" data is treated as a special case of complex
data in which the "imaginary" signal is zero. For real signals,
ScopeDSP just fills the imaginary channel with zeroes.
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