User manual

Acquisition and Setup
R&S
®
RTO
21User Manual 1316.0827.02 ─ 06
2.1.4.1 Voltage Probes
The following table provides an overview on common voltage probes and their usage.
Table 2-1: Voltage probes overview
Probe type Attenuation Typical bandwidth
range
Oscilloscope
input
Usage
Passive, high impe-
dance
1:1 10 MHz
1 MΩ
Low speed, low level
signals
Passive, high impe-
dance
10:1 500 MHz
1 MΩ
General purpose
Passive, low impe-
dance
10:1 up to 10 GHz
50 Ω
High frequency
Active, single-ended 10:1 up to 10 GHz
50 Ω
High speed
Active, differential 10:1
50 Ω
Floating
For a list of recommended probes refer to the R&S RTO product brochure.
Besides the possible input voltage range, two factors are very important when selecting
a voltage probe: Bandwidth and impedance over frequency.
●
Bandwidth:
The combination of probe and oscilloscope builds up a system. The resulting system
bandwidth is approximately determined with:
22
111


















scopeprobesystem
BWBWBW
To measure the signal with low measurement error, the system bandwidth should be
higher than the highest frequency component of the signal. The probe bandwidth
must be even higher than the system bandwidth.
●
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:
●
No active components inside
●
BNC connector for universal use
●
Compensation needs to be executed when the probe is connected to a scope input:
LF compensation matches the probe (mainly cable) capacitance to the oscilloscope
input capacitance.
●
With high impedance probes, the impedance varies significantly over frequency.
●
With low impedance probes, the impedance variation over frequency is low, but the
load on the source is high.
Basics