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P7225 2.5 GHz 10X Active Probe User Manua l
23
V
source
Probe C
in
≤0.8 pF
L
gl
(ground lead)
Figure 7: 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 host
instrument.
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
2π LC
Ꭹ
The preceding equation shows that reducing the ground lead
inductance will raise the resonant frequency. If your measurements
are affected by ringing, lower the inductance of your ground path
until the resulting resonant frequency is well above the frequency of
your measurements.
The low-inductance ground pogo pin described in Features and
Accessories starting on page 5 can help you reduce the effects of
ground lead inductance on your measurements.