Cirrus Logic CapturePlus II - Manual (Page 18)

CapturePlus II
18 DS789UM2
attenuation of 125 dB.
Crystal 7 Term: The Hodie 5 Term Windowing Function is a proprietary 7-term digital filter optimized
for examining an FFT with spectral content. It has a processing loss of 4.203dB and side lobe
attenuation of 175dB.
– Grounded Input FFT: Click on this button to change the voltage reference value used to calculate
the dynamic performance values. When the button is a light green color, the performance
calculations are for a grounded input FFT and an artificially generated 0 dBFS signal number
(equivalent to a full-scale input voltage) is used to calculate noise and distortion. When the button is
a dark green color, the externally applied analog input signal peak amplitude displayed in the FFT is
the reference voltage used to calculate noise and distortion.
– Linear / Log Freq Scaling: Click on this button to change the data graph x-axis scaling between
linear and logarithmic. When the button is a dark green color, the data graph x-axis scaling will be
linear. When the button is a light green color, the data graph x-axis scaling will be logarithmic.
– Frequency @ Max Magnitude: The frequency value displayed is the input signal's fundamental
frequency as observed in the data graph (highest amplitude peak).
– Magnitude: The magnitude value displayed is the input signal's magnitude as observed in the data
graph. The magnitude value displayed will include the windowing loss value given in the Window
Type description. Calculate the actual signal peak by adding the window loss to the magnitude value.
– FFT Bin Count: The bin count value displayed is the number of bins used to generate the FFT. The
bin count is one-half the data set sample size.
– S/PN(SFDR): Signal-to-peak noise (spurious free dynamic range). Measurement provides
S/PN(SFDR) for the present data set and is in units of dBFS (voltage ratio). Measurement references
either the analog input signal magnitude (if the Grounded Input FFT switch is disabled) or 0 dBFS (if
the Grounded Input FFT switch is enabled and bright green).
– SINAD: Signal-to-Noise and distortion. Measurement provides SINAD data for the present data set
and is in units of dBFS (voltage ratio). The SINAD calculation's signal variable uses either the analog
input signal magnitude (if the Grounded Input FFT switch is disabled) or 0 dBFS (if the Grounded
Input FFT switch is enabled and bright green).
– S/D: Signal-to-Distortion. Measurement provides S/D data for the present data set and is in units of
dBFS (volts). The S/D calculation's signal variable uses the analog input signal magnitude (Grounded
Input FFT switch is disabled).
– SNR: Signal-to-noise ratio. Measurement provides SNR data for the present data set and is in units
of dBFS (volts). The SNR calculation's signal variable uses either the analog input signal magnitude
(if the Grounded Input FFT switch is disabled and dark green) or 0 dBFS (if the Grounded Input FFT
switch is enabled and bright green).
– Analyze FFT: After acquiring a single data set the software will pause and wait for the Analyze FFT
button to be activated before performing the analysis and displaying the results. Likewise, to update
the data graph after making changes to the Window Type, Grounded Input FFT, or Linear / Log Freq
Scaling controls, activate the Analyze FFT button. Alternately, when averaging multiple contiguous
data sets the software will automatically perform the analysis and display the results.
– Cursors: The Cursors sub-panel displays the frequency and magnitude value of the fundamental
frequency and the 2
nd
to 5
th
harmonic frequencies as determined by the software. It also displays the
frequency and magnitude values for the user-controlled cursor. The cursor magnitude values are
referenced to 0 dBFS.