ISFFM - Frequency Modulated Sinusoidal Current Source Model

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Modified by Phil Loughhead on Mar 4, 2014

Model Kind

Current Source

Model Sub-Kind

Single-Frequency FM

SPICE Prefix

SPICE Netlist Template Format

@DESIGNATOR %1 %2 ?"DC MAGNITUDE"|DC @"DC MAGNITUDE"| SFFM(@OFFSET @AMPLITUDE @"CARRIER FREQUENCY" @"MODULATION INDEX" @"SIGNAL FREQUENCY") #"AC MAGNITUDE"|AC @"AC MAGNITUDE"| @"AC PHASE"

Parameters (definable at component level)

The following component-level parameters are definable for this model type and are listed on the Parameters tab of the Sim Model dialog. To access this dialog, simply double-click on the entry for the simulation model link in the Models region of the Component Properties dialog.

DC Magnitude	DC offset used in an Operating Point Analysis. (Default = 0).
AC Magnitude	the magnitude of the source when used in an AC Small Signal Analysis. (Default = 1).
AC Phase	the phase of the source when used in an AC Small Signal Analysis. (Default = 0).
Offset	the DC offset of the signal generator (in Amps). (Default = 2.5).
Amplitude	the peak amplitude of the output current (in Amps). (Default = 1).
Carrier Frequency	the carrier frequency (in Hz). (Default = 100k).
Modulation Index	the modulation index (Default = 5).
Signal Frequency	the signal (message) frequency (in Hz). (Default = 10k).

Notes

The image above shows an example waveform produced by an FM current source (connected to a 1Ohm load) with the parameters set to their default values. The shape of the waveform is described by the following formula:

I(t) = I_O + I_A sin[2πF_Ct + MI sin(2πF_St)]

where:

t is an instance of time
I_O is the DC offset of the signal generator
I_A is the maximum amplitude of the output swing (excluding the DC offset)
F_C is the Carrier frequency
MI is the Modulation Index and
F_S is the Signal frequency.

The simulation-ready frequency modulated sinusoidal current source component (ISFFM) can be found in the Simulation Sources integrated library (\Library\Simulation\Simulation Sources.IntLib).

Examples

Consider the frequency modulated sinusoidal current source in the previous image, with the following characteristics:

Pin1 (positive) is connected to net IN
Pin2 (negative) is connected to net GND
Designator is I1
Offset = 0
Amplitude = 1m
Carrier Frequency = 10k
Signal Frequency = 1k
All other parameters for the model are left at their default values.

The entry in the SPICE netlist would be:

*Schematic Netlist:

I1 IN 0 DC 0 SFFM(0 1m 10k 5 1k) AC 1 0