REV. 0
–7–
EVAL-AD9874EB
Parameters associated with the Complex FFT display can be
modified by the user. They are highlighted in
yellow
across the
top portion of the display window and include CLK rate, FFT
Window type, BW, and FFT averages. BW sets the measurement
bandwidth for which the following parameters are calculated:
signal power, in-band noise power, SNR, SFDR, and NBW.
The Complex FFT display highlights the signal power in
red
,
the in-band noise power in
blue,
and the out-of-band region in
black
. Note, the signal power, SNR, and SFDR results are only
applicable for unmodulated carriers located in FFT bins. The
power of modulated carriers can be measured using the in-band
noise power (
blue
) with the BW parameter set appropriately.
The display window also has the ability to data log the SPI register
settings, the raw I/Q data, and the performance parameters. A
left click over the appropriate Save button will prompt the user
to specify a file name and location for the new data file. The data
is saved into this file with a time stamp for further evaluation.
Lastly, the display window can be printed to a file (or printer) using
the PRINT PANEL button located in the upper left-hand corner.
Figure 5. Complex Output Signal Display with I/Q Constellation
Undecimated Modular Display Description
Figure 5 shows the display that will appear after clicking on the
Observe Undecimated Modulator Output Signal button of the
control panel. The displays show the FFT of the AD9874’s
-
ADC’s undecimated output data. The clock rate and FFT
window type can be specified in the top right corner of the window.
Note, the FFT display provides a clear demonstration of the
noise-shaping inherent in the band-pass
-
ADC’s output
spectrum. Also, the peak signal level reported in the top right
corner of the FFT display is useful in observing the amount of
out-of-band rejection to signals falling outside its pass band
prior to any digital filtering.
This display also provides the quantized output levels with the
ability to write the data to a file. Single SPI register write capa-
bilities are also included with the most current SPI register
settings displayed on the lower portion of the window. A
PRINT PANEL button is also provided on the display.
