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Block Diagrams
Oscilloscope Tutorial

Read the page on Cathode Ray Tubes before reading this.


The signal to be observed is applied to the Y plates.

It is attenuated if it is too large in amplitude.

It is amplified if it is too small in amplitude.

The time base generates a saw tooth. (see page on waveforms).

The saw tooth is variable in frequency and amplitude.

As the saw tooth voltage rises, it causes the spot to sweep from left to right, across the face of the CRT.

When the saw tooth suddenly falls to zero, the spot flies back to the left of the screen ready for another sweep.

This sweep and fly back usually happens so quickly that that the display appears as a straight line.

So we have the spot being deflected horizontally by the time base, while the signal is deflecting it vertically, by means of the Y plates.

The combination of forces produces a display which represents the input signal.

To display one cycle, the time base and signal frequencies must be the same.

If the frequencies are slightly different, the display will drift sideways.

To avoid this , the input signal is sampled by the trigger circuit and used to ensure that the time base runs at exactly the same frequency as the input signal.

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