Transfer Function calculates the DC small-signal transfer function between an input source and two output nodes (for voltage) or an output variable (for current) in a circuit. It also calculates input and output resistances. Any non-linear models are first linearized based on the DC operating point and then a small-signal analysis is performed. The output variable can be any node voltage, while the input must be an independent source defined somewhere in the circuit.

Sample files for use with analyses are installed at C:\Users\Public\Documents\National Instruments\Circuit Design Suite <version>\samples\Analyses\.

Analysis Parameters

The Analysis parameters tab contains the following:

  Parameter   Description
Input source Choose a voltage or current source.
Output nodes/source

Voltage—Enable and select an output node from the Output node drop-down list and an output reference node (usually ground or node 0) from the Output reference drop-down list.

Current—Enable and select a current from the Output source drop-down list.

The DC small signal gain is the derivative of the output with respect to the input at the DC bias-point (and zero frequency). The following is the expression for the gain:

The input and output resistance of a circuit refers to the “dynamic” or small-signal resistance at the input or output. Mathematically, small-signal DC resistance is the derivative of the input voltage with respect to the input current at the DC bias-point (and zero frequency). The following is the expression for input resistance:

In Multisim, the results of the Transfer Function Analysis produces a chart showing the ratio of the output to the input signal, the input resistance at the input source node and the output resistance across the output voltage nodes.

  This is a DC analysis and does not calculate either the time- or frequency-domain transfer function.