Anritsu BERTWave Series, Operation Manual, Page: 257 / 466

6.4 Setting CRU
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How to Operate Sampling Scope
Setting CRU 6.4
The clock recovery unit (CRU) generates a clock signal from the signal
input to
CRU In
connector.
The waveform can be observed by using the generated clock signal.
The clock recovery unit sets the following.
 Operation Rate
 CRU Loop BW
Operation Rate sets frequency range.
CRU Loop BW is a loop filter bandwidth that is used in the frequency
control circuit of the clock recovery unit.
Figure 6.4-1 Block Diagram of Clock Recovery Unit
A wider frequency bandwidth can absorb more frequency fluctuations
that occur momentarily. The loop filter bands for the Jitter measurement
are defined in the communication standards.
CAUTION
● The impedance of the CRU In and CRU Out connectors
is 50 Ω. If you use a coaxial cable with impedance other
than 50

, or connect a device with impedance other
than 50

, the measurement may not be performed
properly.
● The CRU Out connector output voltage is 0.4 to 0.8 Vp-p.
Make sure that the voltage output to the connectors
does not exceed the input voltage range of a device to
be connected. The voltage amplitude to be output to the
CRU Out connector exceeds the input voltage range of
a device to be connected, install an attenuator to the
CRU Out connector.
●
The amplitude of the signal input to the CRU In
connector is 0.8 Vp-p max. This is equivalent to +2 dBm
for a sine-wave signal. Inputting a signal with a larger
voltage risks damaging the internal circuits.
Phase
Comparator
Input Signal
Loop Filter
Voltage-Controlled
Oscillator
Buffer Amplifier
CRU Out
CRU In