Any independent source can be assigned a time-dependent value for transient analysis. The general form of frequency-modulated waveform is:



You must specify a value for the parameters VO and VA. the remaining parameters, if not specified, assume a default value.

Parameter Description Units Default
VO DC offset voltage or current. Used to adjust the DC bias of the signal generator with respect to the negative terminal (usually ground). V o A  
VA Peak amplitude. V o A  
FC Carrier frequency. Hz 1/TSTOP
MDI Modulation index. Value corresponding to a function of amplitude of the modulating signal indicating the level of modulation. MDI=(frequency deviation)/FS.   0
FS Signal frequency. Hz 1/TSTOP
PHASEC Carrier phase. degree 0
PHASES Signal phase. degree 0

TSTOP is the final time (see the .TRAN control line for explanation).

The waveform value generated by the SFFM option is as follows:

VO + VA * sin((2∏*FC*t+PHC)+MDI*sin(2∏*FS*t+PHS))

PHC = PHASEC in radiants; PHS = PHASES in radiants.


V1 12 0 SFFM(0 1M 20K 5 1K) 

See also

Independent voltage source
Independent current source