ADS7040EVM-PDK Kit Operation
6.4
FFT Analysis
The
Performance Analysis
page in the GUI performs the fast Fourier transform (FFT) of the captured data
and displays the resulting frequency domain plot. This page also calculates key ADC dynamic
performance parameters, such as signal-to-noise ratio (SNR), total harmonic distortion (THD), signal-to-
noise and distortion ratio (SINAD), and spurious-free dynamic range (SFDR).
shows the FFT
performance analysis display. The FFT calculated parameters are shown on the bottom right side of the
display.
Figure 16. FFT Performance Analysis Page
6.4.1
FFT Analysis Settings and Controls
The SCLK, Sampling Rate and Sample Count fields are the same as described in
.
Fi Required:
Enter the frequency of the largest amplitude analog input signal here.
Optimal Fi to set:
Adjust your input frequency from the signal source to this value computed by the GUI
based on the
Fi Required
value entered. A minor difference from
Fi Required
will be seen here to enable a
system to be coherent in nature.
Window:
The window function is a mathematical function that reduces the signal to zero at the end points
of the data block. In applications where coherent sampling cannot be achieved, a window-weighting
function can be applied to the data to minimize spectral leakage. The following options are available:
•
No windowing (no window weighting function applied; use for coherent data)
•
Windowing. In this case the 7-Term Blackman-Harris window is applied by default. For a more
thorough discussion of windowing, refer to
•
# Harmonics: This field sets the number of harmonics to be included in the calculations of the harmonic
distortion. Any harmonic signal greater than this number is treated as noise in the performance
calculations. The typical value used in this analysis is 9 as per the ADS7040 datasheet (
14
ADS7040EVM-PDK
SBAU240 – November 2014
Copyright © 2014, Texas Instruments Incorporated
