Wavecrest SIA-3000, Руководство пользователя

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High Frequency
Modulation
1-sigma view
To Measure:
For more
information on this
tool, refer to:
High Frequency
Modulation—Quick
Reference Guide
available at
www.wavecrest.com
Find the causes of DJ; Identify Periodic Jitter (PJ), crosstalk and
modulation
The High Frequency modulation tool shows accumulation of jitter over many cycles and
the frequency and amplitude. First, look at the 1-sigma view to see jitter accumulation.
This is important because this is the record that will be used for an FFT calculation
showing the PJ components.
•
From the main menu, press Clock, then High Frequency Modulation to open the tool.
•
Press the SINGLE/STOP button on the front panel or the top menu.
This will make a measurement from the “HPF -3db freq” up to ½ the clock rate. The HPF
corner frequency is set in Acquire Options menu. This determines the low frequency end
of the acquisition. The High-end maximum frequency is always ½ the clock frequency or
less.
Figure 4 - 1-Sigma values vs. number of periods skipped. Analysis of 2GHz
clock from Figure 2. Note that this is a zoomed view to show
details every couple of edges.
Each point on this plot is the 1-sigma from a histogram. Each histogram encompasses
an increasing number of edges, up to 82 in Figure 4. A histogram is made from rising
edge to rising edge; the 1-sigma value is plotted on the y-axis at Period 1 on the x-axis.
Then a histogram is made from a rising edge to the second rising edge (skipping an
edge and thus measuring two periods). This 1-sigma value now corresponds to Period 2
on the x-axis. This process is repeated until enough edges are skipped to encompass
the frequency set in “HPF –3dB freq”.
When modulation is present, these 1-sigma values change periodically, as in Figure 4.
The example shows alternating high and low values every other edge. Other periodicities
are apparent. From these measurements we can determine the periodic jitter
frequencies and magnitudes.
Clock Tools Overview Page 5 of 13