UG-409
AD7091R User Guide
Rev. 0 | Page 12 of 20
Figure 17. FFT Capture Tab
AC TESTING—FFT CAPTURE
Figure 17 shows the FFT capture tab. This tests the traditional
ac characteristics of the converter and displays a fast Fourier
transform (FFT) of the results. As in the histogram test, raw
data is captured and passed to the PC where the FFT is performed,
displaying SNR, SINAD, THD, and SFDR. To perform an ac
test, apply a sinusoidal signal to the evaluation board at the
SMB input, J5 or J6. Low distortion, better than 115 dB, is
required to allow true evaluation of the part. One possibility is
to filter the input signal from the ac source. There is no sug-
gested band-pass filter but consideration should be taken in the
choice. Furthermore, if using a low frequency band-pass filter
when the full-scale input range is more than a few volts peak
to peak, it is recommended to use the on-board amplifiers to
amplify the signal, thus preventing the filter from distorting the
input signal.
Figure 17 displays the results of the captured data.
•
Section 1 shows the input signal information.
•
Section 2 displays the fundamental frequency and
amplitude in addition to the 2
nd
to 5
th
harmonics.
•
Section 3 displays the performance data: SNR, dynamic
range, THD, SINAD, and noise performance.
1
2
3
1. INPUT SIGNAL INFORMATION.
2. FUNDAMENTAL FREQUENCY AND AMPLITUDE.
3. PERFORMANCE DATA.
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017
