UG-450
EVAL-AD7276SDZ User Guide
Rev. 0 | Page 18 of 20
GENERATING A FAST FOURIER TRANSFORM OF
AC CHARACTERISTICS
Figure 20 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 sinusoidal signal with low distortion (better than
115 dB) to the evaluation board at the selected analog input.
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. Choose an
appropriate band-pass filter based on the sinusoidal
signal applied.
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.
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, THD, and SINAD.
The Spectrum Analysis box displays the results of the cap-
tured data.
•
The area labeled 1 in Figure 20 shows the input signal
information.
•
The area labeled 2 in Figure 20 displays the fundamental
frequency and amplitude in addition to the second to fifth
harmonics.
•
The area labeled 3 in Figure 20 displays the performance
data, including the SNR, THD, and SINAD.
Figure 20. FFT Tab
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