Keithley 2520, User Manual, Page: 85 / 329

Model 2520 User’s Manual Source-Measure Concepts 5-3
Delay phase
The programmable delay specifies the minimum time between two pulses (pulse off time)
in a sweep. Note that data processing is part of the delay phase (
Figure 5-1 ). The time
needed for data processing is directly related to the length of the pulse phase. As the pulse
width becomes large relative to the pulse delay, the actual time between pulses will depend
more on the processing time rather than the programmable delay period.
The delay time for the sweep and fixed mode is defined as follows:
• For the list and sweep modes, the actual delay time is the same as the programmed
delay period.
• For the fixed mode, the total delay is the sum of the programmed delay and the trig-
ger latency.
Pulse phase
During the pulse phase, the unit outputs one current pulse at the specified amplitude with
the programmed pulse width. Sampling on all three measurement channels (laser diode
voltage; detector 1 and detector 2 current) is also performed during this phase. In the DC
mode, the readings are taken during the pulse phase and then averaged. Pulse width there-
fore becomes the aperture or sample time of the system.
Duty cycle
The pulse duty cycle is defined as the ratio between the pulse on time (pulse phase) and
the pulse off time (delay phase) expressed as a percentage:
Where: DC = duty cycle (%)
PW = pulse width (s)
PD = pulse delay (s)
NOTE The Model 2520 will not output pulses at a duty cycle larger than 4% for cur-
rents more than 1A.
DC
PW
PW PD
+
-----------------------
100
×
=