WAVEVSN BRD 5.1/NOPB National Semiconductor, WAVEVSN BRD 5.1/NOPB Datasheet - Page 20

• Manufacturer Part Number: WAVEVSN BRD 5.1/NOPB
• Description: BOARD INTERFACE DIGITAL HI SPD
• Manufacturer: National Semiconductor
• Series: WaveVisionr

Specifications of WAVEVSN BRD 5.1/NOPB

• Main Purpose: Interface, Data Capture
• Embedded: Yes, ASIC
• Primary Attributes: ADC & DAC Evaluation
• Secondary Attributes: Graphical User Interface, USB Interface
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Utilized Ic / Part: -
• Other names: WAVEVSN BRD 5.1

9.3 FFT Options
FFT plots can be configured in many different ways. Clicking the “FFT Options” button at the top of the
plot will display a dialog showing the options for that particular plot. The software also maintains default
options for new FFT plots, which are editable. You can edit the default FFT options by choosing Default
FFT Options from the Settings menu. The options are:
Windowing: You may choose from one of five different window functions, one of which is the rectangular
window, which is often, but incorrectly, referred to as
parentheses in the list of functions. The window function is applied to the samples before executing the
FFT to compensate for the fact that the sample set may not be an integral number of cycles of the input
signal. In general, the Flat-Top window will give the best results for evaluating data converters, but it may
be easier to compare data with other systems when the windowing functions are the same.
dB Scale: You may select to represent power on the frequency domain plot in dBc (decibels relative to
carrier), in which 0 dB is taken to be the fundamental (carrier) power, or dBFS (decibels relative to full-
scale), in which 0 dB is taken to the be power contained in a signal which uses the entire dynamic range
of the ADC.
Harmonics: You may select the number of harmonics recognized (and labeled) by the software. You
may also select the number of FFT bins excluded around harmonics in, for example, SNR calculations.
The exclusion region around each harmonic will be shown in a different color than the rest of the data
points.
IMD Calculations: The WaveVision4 software is capable of performing Intermodulation Distortion (IMD)
calculations. When two fundamental frequencies within 3 dBFS of each other are present in the
waveform, the software will normally perform IMD calculations. You may inhibit this behavior by
deselecting the “Allow IMD calculation” checkbox. This can be useful in the unlikely event that a close-in
spur is nearly as large as the input signal without a second input frequency actually being applied, since it
is not really IMD that is being detected in that case. When IMD calculation is enabled, you may also
select whether the software will include only 2
9.4 Histogram Plots
Histogram plots are created by counting the number of times each ADC output code appears in a dataset.
A software histogram is computed from a dataset which is normally 128k samples or smaller. The
resulting histogram will show discontinuities between comparators, gain or offset errors, and other
common ADC system problems.
The Histogram plot also displays the number of codes that were never counted (missing codes), followed
by the first ten such missing codes.
N.B.:
N.B.:
The FFT algorithm can not determine whether any harmonics included are in the noise floor
The Histogram will indicate missing codes when an insufficient number of samples are
or not. To enhance the accuracy of your THD readout, set the number of harmonics to be
included in THD calculation to be those harmonics that are above the noise floor and set
the “bins excluded” to just include those bins that are within the harmonic frequency’s bin
width.
taken to represent every possible ADC output code. For example, a 12-bit ADC has 4096
possible output codes, but a histogram of 4k samples will show some codes missing in the
dataset because many of the codes in the dataset will be present more than once. The fact
that these codes are not present in the dataset does not necessarily mean that the
converter itself exhibits a missing code characteristic.
nd
order or both 2
20
“No
Windowing”. That is why it appears in
nd
and 3
rd
order terms.