R.Vinoth Jeba Kumar said:
Hi
Mine is a simple qn. Please put up with my ignorance.
How are some "CRO"s able to display signals from two channels at the same time..? Are the signals time multiplexed? If so (or otherwise) how?
Thanx to anybody who replies
R.Vinoth
Very, very, old oscilloscopes used special dual beam tubes, but for many years they have simply multiplexed the display.
There are two basic modes, 'chop' and 'alternate'.
'Alternate' shows each beam in turn, so does a sweep of beam one, then a sweep of beam 2 - this only works at fairly high timebase speeds, otherwise you can see the individual sweeps.
'Chop' switches from beam to beam at a fairly high frequency, so as the single beam travels across the CRT it's rapidly switched from beam 1 to beam 2, beam1, beam 2 etc. This is done at a fairly high frequency, and as such is too high to be seen on the scope at low timebase speeds. If you try and use 'chop' at high timebase speeds you start to see the switching waveform.
Depending on the scope, you may have manual 'chop' or 'alternate' selection, but some scopes do this automatically via the timebase speed control. Usually the timebase control will be marked accordingly, showing the point where it changes from 'chop' to 'alternate'.
Other the years there have been a great many dual-beam addon units for scopes, they were always popular magazine articles. I'm sure a googel search will find plenty on the net.