EVAL-ADAQ7980SDZ User Guide
UG-1060
Rev. 0 | Page 19 of 30
Figure 25. FFT Tab
FFT TAB
The following contains information on the contents of the
FFT
tab
(see Figure 25).
FFT Plot
The FFT plot displays frequency analysis of the raw
ADAQ7980
results from the most recent capture burst. See the Generating
an FFT of AC Characteristics section for more information.
FFT Analysis
The
FFT Analysis
pane displays important ac analysis
parameters of the data in the FFT plot. The analysis items
reference the signal at the AMP_OUT pin of the
ADAQ7980
.
The parameters include the following:
•
Max Amplitude
displays the maximum value in the data
(displayed in
V
and
LSB
).
•
Min Amplitude
displays the minimum value in the data
(displayed in
V
and
LSB
).
•
Pk-pk Amplitude
displays the difference between the
maximum and minimum values in the data (displayed in
V
and
LSB
).
•
DC
displays the average value of the data (displayed in
V
and
LSB
).
•
Fund. Frequency
displays the frequency with the largest
amplitude in the FFT (displayed in
kHz
).
•
Fund. Amplitude
displays the amplitude of the
Fund.
Frequency
value (displayed in
dBFS
, which is dB relative to
the reference voltage).
•
Dynamic Range
displays the ratio of a full-scale signal
(which is the largest signal the
ADAQ7980
can accept with
amplitude equal to the reference voltage) to the noise floor
value (displayed in
dBFS
).
•
RMS Noise
displays the rms voltage of the noise floor in
the FFT plot. Specifically, this calculation includes all
frequency bins in the FFT plot that are not displayed in the
Show Harmonic Content
window. This value is used in
calculations for
Dynamic Range
,
SNR
,
SINAD
, and
SFDR
values.
•
SNR
displays the ratio of the
Fund. Amplitude
value to the
RMS Noise
value displayed in
dB
).
•
THD
displays the ratio of the energy in second through
fifth harmonic frequencies to that of the
Fund. Frequency
value (displayed in
dB
).
•
SINAD
displays the ratio of the
Fund. Amplitude
value to
the
RMS Noise
value and amplitude of the second through
fifth harmonic frequencies (displayed in
dB
).
•
Noise Floor
displays the ratio of the
RMS Noise
value and
the full-scale range of the
ADAQ7980
set by
Reference
Voltage
in the Configure tab (displayed in
dB
).
•
Bin Width
displays the range of frequencies included in
each point drawn on the FFT plot. A smaller
Bin Width
value corresponds with higher resolution in frequency
amplitude information in the FFT plot, affected by the
Sampling Freq
and
Num Samples
in the
Configure
tab
values. For example, increasing the
Num Samples
value
while leaving
Sampling Freq
constant results in a smaller
Bin Width
value.
•
SFDR
, the spurious-free dynamic range displays the ratio of
the
Fund. Amplitude
value to the largest spurious frequency
amplitude (displayed in
dB
).
•
The
Show Harmonic Content
button toggles a display
showing the
Fund. Frequency
value and the harmonics
amplitudes. Frequencies are displayed in
kHz
and
amplitudes in
dBFS
.
15065-
023
