Texas Instruments ADS1299, User Manual

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ADS1299EEG-FE Analysis Tools
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Figure 32. Analysis : FFT Graph of Input Short Test
Coherent Frequency Calculator: 1
Coherent sampling in an FFT is defined as F
AIN
/F
SAMPLE
= N
WINDOW
/N
TOTAL
, where:
• F
AIN
is the input frequency
•
FSAMPLE
is the sampling frequency of the ADS1299
• N
WINDOW
is the number of odd integer cycles during a given sampling period
• N
TOTAL
is the number of data points (in powers of 2) that is used to create the FFT If the conditions for
coherent sampling can be met, the FFT results for a periodic signal will be optimized. The Ideal A
IN
Frequency is a value that is calculated based on the sampling rate, such that the coherent sampling
criteria can be met.
AC Analysis Parameters: 2
This section of the tool allows the user to dictate the number of harmonics, dc leakage bins, harmonic
leakage bins, and fundamental leakage bins that are used in the creation of various histograms. Pressing
the Windowing button, illustrated in
Figure 33 , allows the user to evaluate the FFT graph under a variety
of different windows. Note that pressing the Reference button toggles between dBFS (decibels, full-scale)
and dBc (decibels to carrier).
30 EEG Front-End Performance Demonstration Kit SLAU443 – May 2012
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