Zynq-7000 PCB Design Guide
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UG933 (v1.8) November 7, 2014
Chapter 3:
Power Distribution System
The measurement shown in
and
represents the peak-to-peak noise. If
the peak-to-peak noise is outside the specified acceptable voltage range, the decoupling
network is inadequate or a problem exists in the PCB layout.
3.0.1 Noise Spectrum Measurements
Having the necessary information to improve the decoupling network requires additional
measurements. To determine the frequencies where the noise resides, noise power
spectrum measurement is necessary. A spectrum analyzer or a high-bandwidth oscilloscope
coupled with FFT math functionality can accomplish this.
The FFT math function can be built into the oscilloscope, however, many of these functions
do not have resolution sufficient to give a clear picture of the noise spectrum. Alternatively,
a long sequence of time-domain data can be captured from an oscilloscope and converted
to frequency domain using MATLAB or other post-processing software supporting FFT. This
method has the advantage of showing as much resolution as the user is willing to process.
If neither math capacity is available, the noise frequency content can be approximated by
visually examining the time-domain waveform and estimating the individual periodicities
present in the noise.
A spectrum analyzer is a frequency-domain instrument, showing the frequency content of a
voltage signal at its inputs. Using a spectrum analyzer, the user sees the exact frequencies
where the PDS is inadequate.
X-Ref Target - Figure 3-9
Figure 3-9:
Infinite Persistence Measurement of Same Supply
UG933_c3_09_032811
