 
Jitter Spectrum and DCD Measurements
The BERTScope™ CRJ Variable
Clock Recovery Jitter Analyzer is based on our BERTScope CR, the highest performance
instrumentation-grade adjustable clock recovery product available today. The
CRJ retains all of the functionality of the current BERTScope CR,
with additional Jitter Analysis capabilities:
 Jitter Spectrum Measurements
The jitter spectrum display
lets you quickly validate device compliance
to serial data standards, such as PCIe 2.0,
which specify a total jitter value over a band-limited
range of frequency. These
measurements are also very useful in isolating the
source of excessive jitter in a system.
Jitter Spectrum is
a unique tool, in the respect that it is extracted
from the signal in the clock recovery circuit. While
some sampling oscilloscopes can perform jitter spectrum
measurements on repetitive signals, they can not
measure jitter at frequencies below the band-pass
frequency of the clock recovery loop, as these components
are tracked and removed during the sampling process.
Duty Cycle Dependent Measurements
The
BERTScope CRJ also directly measures Duty Cycle Dependent Jitter
(DCD). The result appears in the BERTScope CRJ Display
with a table of values and a graphical Level
Histogram.
DCD Jitter is a required
measurement in some serial data standard compliance
tests. It is a useful tool in system
design, for identifying jitter sources.
 The BERTScope
CRJ can combine with a BERTScope Signal Integrity Analyzer to
directly measure jitter components from the serial input data while simultaneously
generating a recovered clock. A Jitter Spectrum View in the analyzer's user interface
measures spectral analysis of jitter components, along with a direct measure of duty
cycle dependent jitter. Results are displayed as a plot of jitter magnitude vs. frequency.
The Y-axis of the graph is scaled in %UI or time (ps). The X-axis measures frequency,
with a range of 200 Hz to 90 MHz and 100 Hz resolution.
In addition, the BERTScope CRJ
operates stand-alone, providing the same unmatched performance with sampling oscilloscopes
and other bit error rate test instruments. |
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