Texas Instruments ADS7854EVM-PDK, Руководство пользователя, Страница: 22 / 35

ADSxx54EVM-PDK Kit Operation
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6.6.1 FFT Analysis Settings and Controls
Sample Rate (kHz)— This field indicates the sampling frequency of the ADC data (kHz).
Samples (#)— The FFT requires a time domain record with a number of samples that is a power of 2.
The Samples (#) drop-down menu provides a list of values that satisfy this requirement.
Fi Calculated— This field displays the frequency of the largest amplitude input signal computed from the
FFT data, typically the fundamental frequency.
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 opions are available:
• None (no window weighting function applied; use for coherent data)
• Hanning
• Hamming
• Blackman-Harris
• Exact Blackman
• Blackman
• Flat Top
• 4-Term Blackman-Harris
• 7-Term Blackman-Harris
• Low Sidelobe
For a more thorough discussion of windowing, refer to IEEE1241-2000.
Harmonics— This field sets the number of harmonics that are included in the FFT performance
calculations.
Leakage Bins— These fields provide for the removal of the unwanted frequency bins that may be the
result of noncoherent data sampling.
Set the Fundamental Leakage Bins and Harmonic Leakage Bins fields to the number of adjacent
bins on either side of the fundamental or harmonic frequencies to include the main frequency
power. The
DC Leakage Bins field allows the number of frequency bins that are a result of the dc
portion of the measurement to be excluded from the calculations.
22 ADS8354EVM-PDK and ADS7854EVM-PDK SBAU209 – April 2014
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