Tektronix DC 5010 Anleitung Seite 43

Operating Instructions-DC 501 0
Risetime A, and Falltime A
The RISEYFALL A function allows the operator to auto-
_ ,
matically measure the 10% to 90% risetime (or falltime) of
the counter's specified input signal appearing on Channel A.
See Fig. 2-8a. Select the SLOPE (+
=
risetime;
-
=
falltime) before pressing the RISEIFALL A button. The input
signal size is automatically measured and the 10% and 90%
levels are automatically calculated and set. These levels are
available over the GPlB bus.
If- Risetime
I
I
START
I
I I
I I
- - ) I
Risetime
(inaccurate)
Fig. 2-8. Measurement example for risetime.
Internally, the A input is routed to both the A Channel
and B Channel. The A Channel input conditioning is auto-
matically duplicated (and indicated by the front panel lighted
buttons) on the B Channel when the RISEIFALL A button is
pressed. Although risetime measurements are simple to
make, some operator problems can develop (even when
using the automatic level setting capability of the counter).
The signal being measured must satisfy the instrument re-
quirements as detailed in the Specification section of this
manual. The input signal amplitude must be greater than
1.4 V (50 Q) or 700 mV (1 MQ), have a risetime not less than
4 nsec (5 nsec for 1 MQ), and not exceed 10% aberrations.
The DC 5010 uses a true peak detector circuit and de-
tects the highest signal peak, even if the peak is an aberra-
tion (see Fig. 2-8b). If this aberration is too severe (greater
than lo%), the instrument will not measure the correct
risetime. Before pressing the RISEIFALL A button, the front
panel FILTER (20 MHz) button can sometimes be selected
to limit the internal risetime (less than 18 nsec) of the input
signal to reduce these aberrations. Effective use of the filter
will depend on the signal width and aberrations. Press the
RISEIFALL A button. After the signal peak is measured and
the 10% to 90% levels are set, the filter would be removed
so the DC 5010 may display the actual unlimited risetime
(without filter).
The counter front panel pushbuttons remain active after
pressing the RISEIFALL A button, to enable the operator to
modify signal input conditioning and trigger levels. The
modified conditioning and levels must satisfy the instrument
requirements as detailed in the Specification section of this
manual.
For example, if the AUTO button is pressed (while in
RISEIFALL A) the Channel A and Channel B levels will
move from the 10% and 90% points to the 50% point. In the
DC 5010 if the 20% and 80% risetime points are desired,
MIN and MAX values (see the Programming notes in this
section) are available over the GPlB bus. These values can
be used to calculate these 20% and 80% risetime points and
program them into the Channel A and Channel B.
Other specific signal levels such as TTL High or TTL Low
can be programmed by the operator; however, consider-
ation must be given for the termination setting. In the 50 Q
termination, the displayed trigger level is one-half the true
trigger level due to the internal power splitter (not evident to
the instrument). In the 1 MQ termination the instrument does
not take into account any attached probes (see RiseIFall
specification for level information with the use of probes).