EVAL-AD7903SDZ Datasheet, PDF (18/32 Pages) Analog Devices – EVAL-AD7903SDZ User Guide UG-609

UG-609
GENERATING A FAST FOURIER TRANSFORM
OF AC CHARACTERISTICS
Figure 24 shows the FFT tab. This feature tests the traditional
ac characteristics of the converter and displays a fast Fourier
transform (FFT) of the results.
To perform an ac FFT test,
1. Apply a differential sinusoidal signal with low distortion
(better than 100 dB) to the evaluation board at the J6/J7 or
J10/J15 input SMA connector pair. To attain the requisite
low distortion, which is necessary to allow true evaluation
of the part, one option is to
a. Filter the input signal from the ac source. A band-pass
filter can be used; its center frequency must match the
test frequency of interest.
b. If a low frequency band-pass filter is used when the full-
scale input range is more than a few volts peak-to-peak,
use the on-board amplifiers to amplify the signal, thus
preventing the filter from distorting the input signal.
EVAL-AD7903SDZ User Guide
2. Click the FFT tab from the main window.
3. Click Sample.
As in the histogram test, raw data is then captured and passed
to the PC, which performs the FFT and displays the resulting
SNR, SINAD, THD, and SFDR.
The FFT Analysis area displays the results of the captured data.
• The area labeled 1 in Figure 24 shows the spectrum
information.
• The area labeled 2 in Figure 24 displays the fundamental
frequency and amplitude. You can also click Show
Harmonic Content to view information about the second
to fifth harmonics.
• The area labeled 3 in Figure 24 displays the performance
data, including the SNR, dynamic range, THD, SINAD,
and noise performance.
1
2
3
Figure 24. FFT Tab
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