Model 2520 Output Circuit Model - Keithley 2520 User Manual

Model 2520 User's Manual

Model 2520 output circuit model

Figure F-11 shows the Model 2520 pulse output circuit model. There are several unique
features of this pulse circuit. The most notable is that the CURRENT OUTPUT HI termi-
nal provides a path to analog ground while the CURRENT OUTPUT LO terminal sinks
the current during the pulse. The OUTPUT HI terminal also has a high-frequency path to
chassis ground. While the current flows from the HI to the LO terminal, the HI terminal is
at ground potential and would be used as the reference ground while connecting an oscil-
loscope to verify the forward voltage signal across the laser diode under test.
Figure F-11
Model 2520 output circuit model
Analog
Ground
Voltage
Clamp
3-10.5V
The voltage clamp circuit acts to limit maximum voltage as seen by the output of the pulse
circuit. Since the clamp circuit is not directly across the laser diode, the voltage drop
across the transmission line connected between the pulse source and the laser diode is not
seen by the clamp circuit and cannot be regulated by the clamp. As a result, care must be
taken to minimize the negative effects of the transmission line.
10µF
Reversing
Relays
Current
Source
0-500mA
0-5A
Measurement Considerations F-13
Current
Output HI
DUT
Current
Output LO