Generators

General

There are 12 standard spice generators/sources i.e. 6 voltage and 6 current ones. They all allow specification of dc, ac, distortion and transient values. Distortion runs require the IMD fields to be given values. The generator type specific data is data that is used in TRANSient runs.

DC Value

1 DC generator - The dc value is a dc voltage or current that is used in all simulations runs.

AC Value

Typically, the AC value is kept at 1V so that plots directly read gain.

2 Sine, Pulse, PWL, Exp, SFFM generators - The dc value is a dc voltage that all simulations runs except transient runs. i.e. Its value is not added to the transient voltage. If it is required for the same dc level to be set in the transient run as in the dc and op run, either the source offset can be se set to the required value, or a separate dc source can be used such that the transient generators are set with a dc=0 value.

Noise Value

When performing noise analysis, to obtain the correct scaling of noise results, make sure that the ac value is 1V or 1A.

Often, ac current sources are set to a value other than 1A, which will cause the noise results to be reported incorrectly.

IMD Values - Distortion

The text fields for IMD are the ac signal levels to be used for the small signal distortion analysis. That is, the distortion values used are not those set by the normal small signal ac response.

For harmonic distortion, (2nd and 3rd harmonics) only the IMD F1 value is used. For intermodulation distortion (f1-f2, f1+f2), both values are used as the f1 and f2 values.

The run type, harmonic distortion or intermodulation distortion is set in the distortion setup dialogue tab of the simulation setup dialog.

Notes:

Do not put voltage sources in parallel (generates infinite current), or current sources in series (generates infinite voltage), as spice can not handle it. Do not put inductors directly across voltage sources, as this will also generate infinite currents.

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