Datasheet

Evaluation Board User Guide UG-408
Rev. A | Page 17 of 20
06704-018
Figure 18. FFT Capture Tab
AC TESTING–FFT CAPTURE
Figure 18 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 inputs J4/63. 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 suggested 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 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 18 displays the results of the captured data. Label 1
in Figure 18 shows the input signal information. The portions
of Figure 18 labeled 2 display the fundamental frequency and
amplitude in addition to the 2
nd
to 5
th
harmonics. See label 3
also which displays the performance data (SNR, dynamic range,
THD, SINAD, and noise performance.)