HBM GEN3i, Руководство пользователя, Страница: 142 / 1160

Additional information
The Nyquist frequency (f/2) is the maximum frequency that can be accurately
measured by a digitizer sampling at a rate of (f). Otherwise stated: a digitizer
sampling at a rate of (f) cannot measure an input signal with frequency
components exceeding f/2 without experiencing "aliasing" inaccuracies.
Nyquist's theorem determines the range of frequencies that can be measured.
They range from DC to one half the sampling rate at which the data was
captured. An FFT of a sweep of N points produces N/2 frequency domain data
points within the range of frequencies between DC and the Nyquist frequency.
So the frequency resolution is:
(EQ 2)
f =
samplerate / 2
N
/
2
For example, assuming that a frame has 8192 points (N=8192) and a sample
rate has 40.96 kHz. This will yield the following:
l
Frequency resolution Δf = (
½
* 40960) / (
½
* 8192) = 5 Hz
l
Number of frequency domain points: N/2 = 4096
l
The minimum frequency component that can be measured is equal to the
frequency resolution Δf = 5 Hz
l
The maximum frequency component that can be measured is 40.96 kHz /
2 = 20.48 kHz
The FFT X
-
scale (frequency) will start at 5 Hz, end at 20480 Hz, and has 4096
points.
GEN3i
142 I3763-3.1 en HBM: public