LeCroy ZS1000, Инструкция по эксплуатации

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ZS1000 High Impedance Active Probe
5–2
ZS1000-OM-E Rev C
The resonant frequency of a series LC circuit can be raised by decreas-
ing the inductance, capacitance or both.
Since the input capacitance is already very low and cannot be reduced,
you can only try to reduce the inductance. This can be accomplished by
using the shortest possible input lead as well as the shortest possible
ground lead.
For example, to obtain the shortest possible ground lead when measur-
ing IC related signals, attach a small piece of copper clad material to the
top of the IC package and connect this to the package grounding wires.
Using the shortest ground lead and input lead available makes probing
signals on the package easier and makes for the shortest lead length for
the best signal fidelity.
To illustrate how dramatic this effect is, we will work a simple example.
Assuming an input capacitance of 0.9 pF and a total lead length (input
and ground) of 2 inches (inductance of
≈
25 nH/inch) such a setup may
cause ringing with a resonant frequency (f
0
) of:
This frequency is well within the passband of the probe and will there-
fore show up as part of the measured signal at faster time/div settings.
To determine how fast a waveform to be measured can be without caus-
ing ringing on a probe like this, divide the BW (ringing frequency) of the
probe into 0.35:
Any input signal with a rise time faster than 0.47 ns can cause ringing.
CAPACITIVE LOADING
Capacitive loading is usually the most troublesome of the three loading
effects.
It can affect the rise time, bandwidth and delay time measurements.
f
0
1
2
π
50 10
9 –
0.9 10
12 –
× × ×
-------------------------------------------------------------------
750 MHz = =
t
rise
0.35
BW
----------
0.35
750 MHz
---------------------
0.47 ns = = =