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SILICON CHIP is published 12 times
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ISSN 1030-2662
2
SILICON CHIP
The oscilloscope - the everyday time machine
This month, we have a feature article on oscilloscopes. This takes a look
at some of the features of current model scopes, both analog and digital. It
really only just touches on the subject, giving a glimpse of what these
remarkable measuring instruments can do.
When you think about it, we take the oscilloscope for granted. Want to
take a look at a signal? Simple, just grab a probe, connect it up, flick a few
switches and there it is on the screen. But what may be portrayed on the
screen is often happening so fast that it is impossible for the human brain to
really appreciate. Say you have a signal on the screen with a frequency of
100 megahertz. That's an absolutely routine frequency but you can display
it easily on many scopes these days so that you can see the actual waveform,
not just a signal envelope.
Think about that waveform. Each cycle of the waveform on the screen is
taking place in just ten nanoseconds. Such a time interval is so short that if
were to regard a nanosecond as a second, an hour of our lifetime would last
more than 100,000 years! And yet we look at those minute slices oftime as
though they were nothing more remarkable than a pencil sketch. Which in
a way is what they are; an accurate sketch sample produced automatically
by the flying electron beam behind the screen.
Think about how fast the electron beam has to move in order to accomplish that task. It is fairly easy to calculate how fast it is deflected up or down
the screen but think how much faster it is going as it hits the back of the
screen.
But a 100MHz scope is just routine these days and it is only scopes that
go up into the Gigahertz region that are regarded as really special. That's an
order of magnitude better - or more. Truly then, today's oscilloscope is a
veritable time machine - not one that allows us to travel forward or
backwards in time but one which allows us to divide time into portions so
small that time becomes meaningless.
Think about that the next time you hook up your scope for a routine
measurement.
Leo Simpson
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