## Noise Implementation

This section contains all stuff related to AC Noise calculation in Gnucap.

Currently (April 2011) noise is implemented in experimental branch and work as plugin. Please see Code-related Stuff for more details.

#### Noise calculations basics

Noise is claculated using adjacent system method [TBD GS - complete, explain ]

#### Noise Simulation Syntax

To run noise simulation - ad the following line to circuit file (spice format):

`.noise V(a,b) Dev stepmode points fromF toF`

• V(a,b) - output to measure noise at - nodes a to b; possible form:

V(a) is the same as V(a,0)

• Dev - device which is considered as input
• stepmode - [o{ctave}, d{ecade}, lin, ti{mes}, step, by, +, *]
• points - number of points (depends on stepmode)
• fromF - lowest frequency
• toF - highest frequency

It will calculate noise power density between output nodes “a” and “b” and equivalent power at input device “Dev” using “stepmode” making “points” in frequency range “fromF”-“toF”

Example:

` .noise v(3) V1 oct 5 10 10K `

- calcualate spectral noise density at node “3” and reduce it to input device V1 making 5 points per octave in frequency range from 10HZ to 10KHZ

` .noise V(10,12) I1 dec 2 10K 10MEG`

- calcualate spectral noise density between nodes 10 and 12 and reduce it to input device I1 making 2 points per decade in frequency range from 10KHZ to 10MHZ

##### Output

Usually simulators also support `.print noise` statement. Now it is not implemented yet. Currently output contains:

` Freq inoise_density onoise_density `

Also - at the end of the frequency range total power over the range s integrated:

` inoise_total onoise_total `

#### Code related stuff

Currently noise simulation is implemented as plugin which is available at github at the following link

It re-uses s_ac.cc file (ac simulation) to implement noise analysis.

At the present moment (April 2011) noise works with only gnucap-a branch of gnucap, but hopefully soon it will work with main trunk too.

[TBD - make description of the noise code]