ECE 488: RF Circuits and Systems Spring 2005
CORNELL UNIVERSITY © WES SWARTZ (03/8/2)
4
Whenever the display is crazy, try pushing this button before calling your TA.
Although the trigger signal determines when the trace is to be displayed, the neat thing
about these digital scopes is that this time does not need to correspond to the beginning of
the trace. The buffering of the input samples allows the trace on the display to begin
before the actual time of the triggering event. The time at which the trigger occurred is
marked by a downward-pointing arrow along the top edge of the display, as mentioned
earlier.
Manual triggering is initiated by the
FORCE TRIGGER
button.
The
LEVEL
knob serves another function called
HOLDOFF
which sets how much time
must elapse before another trigger can occur. The
SET LEVEL TO 50%
button causes the
trigger level to be set at the midpoint between the peaks and valleys of the triggering
signal.
Another important trigger item selected by the side-screen menu buttons is the source of
the triggering signal. Don’t select a source that is not connected!
5. Handy buttons
The cluster of three buttons in the top-right corner of the TDS 220 will prove to be quite
useful. The
AUTOSET
button has already been mentioned under Trigger Controls, but it
does much more. In fact, whenever you first connect it to a new point on your circuit,
you should push
AUTOSET
to have the scope automatically adjust the vertical and
horizontal settings as well as the trigger. Then you can optimize the display using the
separate vertical and horizontal controls. Since this function selects the lowest numbered
active channel for triggering, I recommend that channel 1 be used as the trigger source
whenever you are not using the external trigger port.
The
RUN/STOP
button toggles between freezing the display and allowing it to free-run.
The
HARDCOPY
button can send a copy of the display to a printer, if one is connected.
6. Automated measurements using digital readouts
The TDS 220 oscilloscope can produce digital readouts of most of the relevant input
signal parameters, including frequency, period, mean (average) voltage, and peak-to-peak
voltage. (Note that the “amplitude” of a sine wave is the zero-to-peak voltage, not the
peak-to-peak value.) The following steps give an example:
1. Push
the
MEASURE
button to see the Measure side-screen menu.
2. Push the top side-screen menu button to toggle the selection to
SOURCE
.
3. Select
CH1
for the sources in the next four menu boxes.
