Microchip Technology AC164120 Manuel D’Utilisation
Using the PICkit™ 1 Signal Analysis PC Application
2004 Microchip Technology Inc.
DS51476A-page 19
Rectangular – Window is a rectangular shaped window. Every point of the time scale
is multiplied by a constant. This window provides the best frequency resolution with the
narrowest lobe width. Amplitude accuracy errors occur if frequency of observed signal
has a non-integer number of cycles in the FFT time record. Most typically, this window
is best used when viewing transients, impulses, pseudo-random noise and when the
input signal is correlated with the sampling frequency.
is multiplied by a constant. This window provides the best frequency resolution with the
narrowest lobe width. Amplitude accuracy errors occur if frequency of observed signal
has a non-integer number of cycles in the FFT time record. Most typically, this window
is best used when viewing transients, impulses, pseudo-random noise and when the
input signal is correlated with the sampling frequency.
When the FFT windows are implemented there is a certain amount of energy that is
spread across adjacent frequency bins. This spreading is a result of converting
non-coherent signals and the particular window. Consequently, there is not a direct
correlation between the amplitude of the analog input signal to the A/D converter and
the height of the spur in the FFT analysis.
spread across adjacent frequency bins. This spreading is a result of converting
non-coherent signals and the particular window. Consequently, there is not a direct
correlation between the amplitude of the analog input signal to the A/D converter and
the height of the spur in the FFT analysis.
2.6.1
Glossary of Terms
Fundamental Frequency – The lowest frequency component in the Fourier
representation of a periodic quantity.
representation of a periodic quantity.
Noise Floor – The noise level at a referenced location and bandwidth.
SNR (Signal-to-Noise Ratio) – The ratio of relative power of the usable signal to the
noise present, expressed in decibels.
noise present, expressed in decibels.
SINAD (Signal to (Noise + Distortion) Ratio) – S/(N+D) is the ratio of the rms value
of the actual input signal to the rms sum of all other spectral components or harmonics
below the Nyquist frequency, excluding DC. This software includes nine harmonics in
the calculation. Decibels is the unit of measure for S/(N+D).
of the actual input signal to the rms sum of all other spectral components or harmonics
below the Nyquist frequency, excluding DC. This software includes nine harmonics in
the calculation. Decibels is the unit of measure for S/(N+D).
THD (Total Harmonic Distortion) – The ratio in dB of the energy of a fundamental test
frequency to the energy of its harmonics appearing in the band of interest.
frequency to the energy of its harmonics appearing in the band of interest.
SFDR (Spurious Free Dynamic Range) – The difference in decibels between the
input signal and the next largest harmonic.
input signal and the next largest harmonic.