VSFFM - Frequency Modulated Sinusoidal Voltage Source Model

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Modified by Phil Loughhead on Mar 4, 2014

Model Kind

Voltage 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 Volts). (Default = 2.5).
Amplitude	the peak amplitude of the output voltage (in Volts). (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 below shows an example waveform produced by an FM voltage 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:

V(t) = V_O + V_A sin[2πF_Ct + MI sin(2πF_St)]

where,

t is an instance of time
V_O is the DC offset of the signal generator
V_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 voltage source component (VSFFM) can be found in the Simulation Sources integrated library (\Library\Simulation\Simulation Sources.IntLib).

Examples

Consider the frequency modulated sinusoidal voltage source in the above image, with the following characteristics:

Pin1 (positive) is connected to net IN
Pin2 (negative) is connected to net GND
Designator is V1
Offset = 0
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: V1 IN 0 DC 0 SFFM(0 1 10k 5 1k) AC 1 0