What does the hold off control in an oscilloscope do?

In order to play with the hold off feature, I have a micro-controller output following pulses.

It is a repeating pattern of 5 pulses and an idle period; you, of course can create whatever pattern you want, for your demonstration.

Example digital signal

The problem with this kind of sequence is that, the oscilloscope would not know which pulse to trigger on. In my case I have my ‘scope set to trigger on rising edges, but which one, there are 5! The oscilloscope may trigger on any of the 5 rising edges; and so it does. The oscilloscope is not be able to lock on to the signal and produces a runny display on the screen.

Solution on a DSO, may be is to do just a Single capture, but there is another way – HOLD-OFF.

If we can tell the oscilloscope to just delay the next capture, after the first, we could be able to have a stable display. Let’s see how.

Let us say we tell the oscilloscope to delay the second capture by 10 μs. So after the first trigger, at point, it would wait for 10 μs and trigger only after point . It would trigger again at the next rising edge, which is at point . As and are same points in the sequence, the process continues and we get a stable, locked display on the screen.

This 10 μs is the hold-off duration.

The hold-off time for this signal can be anywhere from points to , or from 7 to 15.8 μs – The last rising edge occurs at and the first of the next sequence occurs at .

Now, hold-off is not only applies to digital signals, it also comes very handy in analog signals as well, for example AM or other complex signals.

This is a rather short entry, but please point out the mistkaes and have fun learning.


#electronics, #oscilloscope