subject: The Digital Oscilloscope In The Real World [print this page] A digital oscilloscope often uses an analogue input, which is then converter into digital information using ADC. It samples voltages as a series of discrete waveforms, which are stored as digital information until there are enough of them to reassemble a true picture of whats going on in the sampling area. As a result, while practical for interrogation and review, digital oscilloscopes may be eschewed in favour of analogue for some applications.
The most important factor in the accuracy of the digital oscilloscope is the frequency at which the waveform is sampled. To gain an accurate reading, sampling should follow the Nyquist rate, which states that a minimum frequency of double the highest part of the signal being observed. Less than this and inaccurate or aliased results are obtained.
While the analogue needles (familiar to stereo buffs still) of a fully analogue oscilloscope are sensitive and capable of delivering absolute real time pictures of the sampled voltage, they cant be interrogated properly later, nor stored. The digital oscilloscope, on the other hand, lets the user replay samples as many times as he or she likes freezing them, rewinding them and slowing them down to more clearly see the possible location of a problem. A good digital oscilloscope also allows the user to amplify a part of a stored signal for more detailed scrutiny.
Clearly the more sophisticated or sensitive you want your digital oscilloscope to be, the better the display reaction must be. A fast acting digital display gives a true reading and lets the user pan and zoom through the stored traces. A slower screen, with a delay of 1 ms, can lead to false interpretation.
A digital phosphor oscilloscope has a different internal architecture to a standard digital oscilloscope which is set up like an analogue scope, but with the ADC to render results in digital format. A digital phosphor oscilloscope, on the other hand, uses a parallel processing setup to allow the user to look at very small signal events in real time. Where a digital oscilloscope captures waves in serial (and so has a holdoff time while it returns to step one and starts again) the digital phosphor version is continually registering the real-time version of what it sees by rasterizing the waveforms into pixelated dots on a screen.
The function of the oscilloscope, commonly, is to see a properly resolved graph of the wave shape of the signal you are interested in. Mainly they are used as diagnostic and interpretative instruments for example by electricians checking the health of a circuit ring, or by surgeons contemplating the beat of a heart. In general, if you can partition an event into a wave with peaks (the highest or strongest signal point) and troughs (the weakest), then you can render it as a measurement on an oscilloscope.
By including a SD card or similar storage medium with a digital oscilloscope it becomes possible to build whole libraries of signal events. This makes them ideal for signal interpretation.
