## 4.11 `SFFM`: Frequency Modulation time dependent value

### 4.11.1 Syntax

`SFFM` *args*

`SFFM` *offset amplitude carrier modindex signal*
### 4.11.2 Purpose

The component value is a sinusoid, frequency modulated by another sinusoid.
### 4.11.3 Comments

For voltage and current sources, this is the same as the Spice `SFFM` function, with some extensions.

The shape of the waveform is described by the following equations:
mod = (_modindex * sin(2*PI*_signal*time));
ev = _offset + _amplitude
* sin(2*PI*_carrier*time + mod);

For other components, it gives a time dependent value.

As an extension beyond Spice, you may specify the parameters as
name=value pairs in any order.
### 4.11.4 Parameters

`Offset` = *x*- Output offset. (Default = 0.)

`Amplitude` = *x*- Amplitude. (Default = 1.)

`Carrier` = *x*- Carrier frequency, Hz. (required)

`Modindex` = *x*- Modulation index. (required)

`Signal` = *x*- Signal frequency. (required)