UG-581 Datasheet, PDF (14/28 Pages) Analog Devices – Full-featured evaluation board

EVAL-AD7961FMCZ
AC TESTING—FFT CAPTURE
Figure 22 shows the FFT 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 SMA inputs J1/J2. Very low distortion, better than
130 dB input signal source (such as audio precision) is required
to allow true evaluation of the part. One possibility is to filter
the input signal from the ac source. There is no suggested band-
pass filter, but carefully consider the choices.
Evaluation Board User Guide
Furthermore, if using a low frequency band-pass filter when
the full-scale input range is more than a few V p-p, it is
recommended to use the on-board amplifiers to amplify the
signal, thus preventing the filter from distorting the input signal.
Figure 22 displays the results of the captured data.
• Shows the input signal information (see Label 1)
• Displays the fundamental frequency and amplitude in
addition to the 2^nd to 5^th harmonics (see Label 2)
• Displays the performance data, including SNR, dynamic
range, THD, SINAD, and noise performance (see Label 3)
1
3
2
Figure 22. FFT Capture Tab
Rev. 0 | Page 14 of 28