Keithley 2520, Руководство пользователя, Страница: 287 / 329

Model 2520 User’s Manual Measurement Considerations F-3
Cable inductance
Under transient conditions, the voltage across the cable inductance is defined as follows:
Where: L = total cable inductance
V
L
= voltage across inductance
di/dt = rate of change of current
For example, the voltage with 100nH of inductance, a 5A current pulse, and 100ns rise
time is:
From the above relationship, it is obvious that with excessive inductance, the voltage
across the inductance may cause the current source to go into compliance and effectively
become a voltage source with a value equal to the compliance setting (10.5V maximum).
Under these conditions, voltages in the circuit are related as follows:
Current while the source is in compliance then rises according the following relationship:
From the above discussion, it is obvious that the rise time of the current pulse through the
laser diode can be affected by the cable (and other) inductance in the circuit. Thus, it is
important to keep cable lengths as short as possible, and use only cables with low induc-
tance such as the supplied CA-290 BNC cables, which have a nominal characteristic
impedance of 15
Ω
and an inductance of 27nH/ft.
V
L
L
di
dt
----- =
V
L
100nH
5A
100ns
---------------
5V
= =
V
C
L
di
dt
-----
IR
DUT
+ =
I t
( )
V
C
R
DUT
-----------------
1 e
t
–
L R
DUT
⁄
------------------------
–
 
 
 
 
 
=