AD8031ARTZ datasheet(18/32 Pages) AD

18 / 32 page

UG-609

EVAL-AD7903SDZ User Guide

Rev. 0 | Page 18 of 32

GENERATING A FAST FOURIER TRANSFORM

OF AC CHARACTERISTICS

Figure 24 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 FFT test,

1. Apply a differential sinusoidal signal with low distortion

(better than 100 dB) to the evaluation board at the J6/J7 or

J10/J15 input SMA connector pair. To attain the requisite

low distortion, which is necessary to allow true evaluation

of the part, one option is to

a. Filter the input signal from the ac source. A band-pass

filter can be used; its center frequency must match the

test frequency of interest.

b. If a low frequency band-pass filter is used when the full-

scale input range is more than a few volts peak-to-peak,

use the on-board amplifiers to amplify the signal, thus

preventing the filter from distorting the input signal.

2. Click the FFT tab from the main window.

3. Click Sample.

As in the histogram test, raw data is then captured and passed

to the PC, which performs the FFT and displays the resulting

SNR, SINAD, THD, and SFDR.

The FFT Analysis area displays the results of the captured data.

•

The area labeled 1 in Figure 24 shows the spectrum

information.

•

The area labeled 2 in Figure 24 displays the fundamental

frequency and amplitude. You can also click Show

Harmonic Content to view information about the second

to fifth harmonics.

•

The area labeled 3 in Figure 24 displays the performance

data, including the SNR, dynamic range, THD, SINAD,

and noise performance.

Figure 24. FFT Tab

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