Tektronix P6249, Инструкция по эксплуатации

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Operating Basics
18
P6249 4 GHz 5X Active Probe Instruction Manual
Ground Lead Length
When you are probing a circuit, you should always use as short a
ground lead as possible between the probe head and circuit ground.
When you touch your probe tip to a circuit element, you are
introducing a new resistance, capacitance, and inductance into the
circuit. This represents the characteristics of your probe and ground
lead.
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 path. A portion of the ground lead
path is uncontrollable since it is hard-wired on the circuit board
under test.
Calculate the approximate resonant frequency (f
0
) at which this
parasitic circuit will resonate, using 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
at least 3 times
greater than the frequency of your measurements .
The low-inductance ground contacts described in Accessories on
page 3 can help you reduce the effects of ground lead inductance on
your measurements.