Brochure

16
Differential
broadband probes
High common mode rejection
Differential signals are used especially at high clock rates
to effectively suppress common mode interference and
to transmit broadband signals without errors. These sig-
nals can be measured accurately only by using differential
probes. Common mode rejection is an important quality
parameter. Rohde & Schwarz differential probes suppress
common mode interference over the entire probe
bandwidth.
Low loading at DC and high frequencies
In the case of DC voltage, a distinction must be made be-
tween the input impedance for differential and common
mode signals. This is particularly important when measur-
ing low voltage differential signaling (LVDS) lines, for ex-
ample. Although the differential input impedance of LVDS
receivers is typically 100Ω, the operating point is often set
at high impedance. Excessive loading on the signal line
can shift the operating point outside of the receiver's in-
put voltage range and impair the functioning of the circuit.
Almost all Rohde & Schwarz differential probes have a very
high differential input impedance of 1MΩ and a common
mode impedance of 250kΩ, ensuring that the loading re-
mains low.
Typical DC equivalent circuit in an LVDS receiver
Low DC loading is key when measuring LVDS signal lines with operating points set
at high impedance
Compact R&S®RT-ZD40 active broadband probe
A flat frequency response and a high input
impedance with low input capacitance permit
precise measurements on differential signals
while keeping the loading on the DUT low. The
high common mode rejection over the entire probe
bandwidth ensures high immunity to interference.
Special browser adapters allow flexible contacting
with high signal fidelity.
+1.2 V
500 k
LVDS driver
Probe
LVDS receiver
–30 V
60 k60 k
In–
500 k
In+
100
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