Ac Testing - Fft Capture - Analog Devices EVAL-AD7656-1SDZ User Manual

Evaluation Board User
Guide

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 Low distortion, better than 115dB, 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
Figure 18. FFT Capture Tab
filter when the full-scale input range is more than a few Vpp, 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.
1. Shows the input signal information
2. Displays the fundamental frequency and amplitude in
addition to the 2
3. Displays the performance data. SNR, Dynamic Range,
THD, SINAD, Noise performance.
Rev. PrA | Page 21 of 32
UG-AD7656-1/57-1/58-1
nd th
to 5 harmonics.