4.13  TANH: Hyperbolic tangent transfer function

4.13.1  Syntax

TANH gain limit
TANH args

4.13.2  Purpose

Defines a hyperbolic tangent, or soft limiting, transfer function.


There is no corresponding capability in any SPICE that I know of, but you can get close with POLY.

For capacitors, this function defines charge as a function of voltage. For inductors, it defines flux as a function of current.

For fixed sources, it defines voltage or current as a function of time, which is probably not useful.

This function describes a hyperbolic tangent transfer function similar to what you get with a single stage push-pull amplifier, or a simple CMOS inverter acting as an amplifier.

4.13.4  Parameters

GAIN = x
The small signal gain at 0 bias. (Required)

Maximum output value (soft clipping). (Required)

4.13.5  Example

E1 (2 0 1 0) tanh gain=-10 limit=2 ioffset=2.5 ooffset=2.5
This gain block has a small signal gain of -10. The input is centered around 2.5 volts. The output is also centered at 2.5 volts. It “clips” softly at 2 volts above and below the output center, or at .5 volts (2.5 − 2) and 4.5 volts (2.5 + 2).