High Frequency
Modulation
FFT N-clk view
To Measure:
For more
information on this
tool, refer to:
High Frequency
Modulation—Quick
Reference Guide
available at
www.wavecrest.com
Continue analysis of Periodic Jitter (PJ). Identify the Spectral
content of the jitter
To provide frequency and amplitude of jitter, we use Accumulated Time Analysis, a
patented
WAVECREST
algorithm that creates a frequency vs. jitter diagram.
•
While still in the High Frequency Modulation tool, you can now change views from the
1-sigma view to the FFT N-clk view.
•
Add a view by pressing ADD VIEW on the front panel or press
on the top menu
bar. Change this view to Summary.
Figure 5 - FFT shows jitter frequencies and amplitudes. Analysis of 2GHz
clock from Figure 3. Shows jitter at 866MHz
The cause of the bimodal histogram in Figure 3 is now apparent in this FFT. For the
purposes of this example, Periodic Jitter was added to the 2GHz clock. The summary
page shows the amplitude of this highest peak in the N-Clk (Pk-Pk) column as 7.6ps at
866MHz. Having identified the major contributor to jitter, the engineer can now work to
eliminate it. Usually, it is at a frequency that is familiar, such as some multiple of a
reference clock or crosstalk from another clock.
Clock Tools Overview
Page 6 of 13
