Rohde & Schwarz RTE - Active Voltage Probes - General; Passive Voltage Probes

Acquisition and waveform setup
R&S
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RTE
174User Manual 1326.1032.02 ─ 20
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scopeprobesystem
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To measure the signal with low measurement error, the system bandwidth should
be higher than the highest frequency component of the signal. The probe band-
width must be even higher than the system bandwidth.
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Impedance:
A minimum impedance is required to keep the circuit loading low. Over frequency,
the impedance decreases, in particular with passive probes. The probe impedance
should be approximately 10 times the impedance of the circuit test point at the
highest signal frequency.
Passive voltage probes
Passive probes have the following qualities:
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No active components inside
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BNC connector for universal use
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Compensate the probe when it is connected to a scope input: LF compensation
matches the probe (mainly cable) capacitance to the oscilloscope input capaci-
tance.
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With high impedance probes, the impedance varies significantly over frequency.
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With low impedance probes, the impedance variation over frequency is low, but the
load on the source is high.
If you use passive probes, remember some recommendations:
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Use a probe recommended for your oscilloscope model.
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Use a ground lead as short as possible to minimize the effect of ground lead induc-
tance. The resonance frequency can be much lower than the system bandwidth
and thus can affect the measurement results, in particular, if you measure steep
edge rise times.
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Select a probe that has a bandwidth of 5 to 10 times the highest frequency being
measured. This bandwidth preserves the harmonics and thus the waveform integ-
rity.
Active voltage probes - general
Active probes require operating power from the instrument and have a proprietary
interface to the instrument. Their main qualities are:
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Low loading on signal source
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The probe is automatically recognized by the instrument, no adjustment is
required.
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Adjustable DC offset at probe tip allows for high resolution on small AC signals
which are superimposed on DC levels.
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Connections should be as short as possible to keep the usable bandwidth high.
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Observe the operating voltage range.
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The probe impedance depends on the signal frequency.
Basics