EVAL-AD7405FMCZ User Guide
UG-690
GENERATING A FAST FOURIER TRANSFORM OF
AC CHARACTERISTICS
Figure 18 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 test,
1.
Apply a bipolar sinusoidal signal with low distortion
(better than 115 dB) to the evaluation board at the VIN+
input. To attain the requisite low distortion, which is
necessary to allow true evaluation of the part, one option is
to filter the input signal from the ac source. Choose an
appropriate band-pass filter based on the sinusoidal signal
applied.
2.
Click the
FFT
tab from the main window.
3.
Click
Single Capture
or
Continuous Capture
.
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.
Figure 18 displays the spectral analysis results of the captured data.
•
The plot is the FFT image of the raw data.
•
The
FFT Analysis
box displays the performance data:
SNR, THD, SINAD, dynamic range, and noise
performance along with the input signal characteristics
(see label 1 in Figure 18).
•
Clicking
Show Harmonic Content (
labeled 2 in Figure 18
)
displays the frequency and amplitude of the fundamental
in addition to the second to fifth harmonics.
Figure 18. FFT Capture Tab
2
1
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