Tektronix P6245, Instruction Manual

Page: 29 / 214

Operating Basics
P6245 Instruction Manual
2- 3
R
source
V
source
Probe C
in
1 pF
Probe R
in
1 M
Ω
L
gl
(Ground Lead)
Figure 2- 2: Ground Lead Equivalent Circuit
Ringing and rise time degradation can be masked if the frequency
content of the signal degradation is beyond the bandwidth of the
oscilloscope.
You can determine if ground lead effects may be a problem in your
application if you know the self-inductance (L) and capacitance (C)
of your probe and ground lead. Calculate the approximate resonant
frequency (f
0
) at which this parasitic circuit will resonate with the
following formula:
f
0
=
1
2 π LC
The preceding equation shows that reducing the ground lead
inductance will raise the resonant frequency. If your measurements
are affected by ringing, your goal is to lower the inductance of your
ground path until the resulting resonant frequency is well above the
frequency of your measurements.
The low-inductance ground contacts described in Accessories can
help you reduce the effects of ground lead inductance on your
measurements.