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System Simulator >
System Component Models >
Probes >
Power Spectral Density Probe (PSDP)

Power Spectral Density Probe (PSDP)

Properties	Description	Units	Default	Range/Type
Name	Probe name	None	Required	String
FFTL	Number of input samples used for spectral estimation per invocation	None	256	[8, Inf)/Integer (must be a power of 2)
TYPE	0 for nonperiodic signals and 1 for periodic	None	0	[0, 1]/Integer
WINDOW _TYPE	0 for Bartlett, 1 for Hanning, 2 for rectangular, 3 for Hamming, 4 for Blackman, 5 for Blackman-Harris (3 term), 6 for Blackman-Harris (4 term) 7 for Gaussian (alpha=3), 8 for de la Valle-Poussin.	None	1	[0, 8]/Integer
INITSAMP	Number of initial samples removed from waveform	None	0	[0, Inf)/Integer
RIN	Input impedance	Ohm	Inf	(0, Inf]/Real
RL	Impedance used for Power Spectral Density (PSD) calculation	Ohm	50	(0, Inf]/Real
Ports
Input	Input signal (complex)

Notes

1. For a given random input signal

this model takes blocks of the incoming input samples ( each block of length FFTL samples), and computes the resulting power spectrum density S(w) for each block according to

where V_in(w) is the frequency spectrum of the input complex envelope ( A(t)e^j^q⁽^t⁾) computed using an FFT of length FFTL, and R_L is the impedance used to calculate the PSD.

2. The resulting power spectrum is then averaged out over the total number of available input blocks (each of length FFTL samples). The averaging process is done according to the Welch Method [1] for spectral estimation. The averaging process becomes more accurate as more input samples are used in the estimation process. The averaging process then yields an estimate of the power spectral density of the random input signal.

3. The user should set the TYPE parameter to 0 if the expected spectral estimate is continuous. Non-periodic signals always yield continuous power spectral densities. If, on the other hand, the spectral estimate is expected to be discrete (i.e., input is periodic), the user should set the TYPE parameter to 1.

4. It is important to note that from a software point of view, a periodic signal (e.g., a sinusoid) will not yield a discrete spectrum unless the frequency of the periodic signal, the simulation time step, and the number of samples representing the signal all meet a certain criterion.

Netlist Form

PSDP:Name n1 FFTL=val [TYPE=val] [WINDOW_TYPE=val][INITSAMP=val]
+ [RIN=val] [RL=val]

Netlist Example

PSDP:My_Psdp 1 FFTL=256 Window_type=2 TYPE=0

References

1. J. G. Proakis and D. G. Manolakis, “Introduction to Digital Signal Processing”, Macmillan

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