Operating Basics
2
P6133 Instruction Manual
Inductive Effects of Probe Grounding
Ground lead inductance can significantly reduce the performance of a probe. As
shown in Figure 1, the ground lead inserts inductance into the signal path
forming a series-resonant circuit with the probe input capacitance C
in
and
R
source
as damping. This forms a resonant circuit with
f
0
+
1
B
(2
p
LC
Ǹ
)
.
Probe C
in
Typ. 10 pF
Probe R
in
10 M
W
Ground lead
inductance
R
source
V
source
Figure 1: Circuit model: test point and probe input
A six-inch ground lead has approximately 150 nH of inductance, which produces
an f
0
of approximately 130 MHz within the frequency response of the instru-
ment. This greatly degrades rise time, bandwidth, and transient accuracy as
shown in Figure 2.
Figure 2: Step response with six-inch ground lead
For best results, ensure that ground lead inductance is at a minimum.
