Transfer Function Analysis

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Modified by Phil Loughhead on Mar 4, 2014

Description

The Transfer Function analysis (DC small signal analysis) calculates the DC input resistance, DC output resistance and DC gain, at each voltage node in the circuit.

Setup

Transfer Function analysis is set up on the Transfer Function Analysis Setup page of the Analyses Setup dialog (after the dialog appears, click the Transfer Function Analysis entry in the Analyses/Options list). An example setup for this analysis type is shown in the image below:

Parameters

Source Name - the small signal input source used as the input reference for the calculations.
Reference Node - the node in the circuit used as a reference for the calculations at each specified voltage node. By default, this parameter is set to 0 (GND).

Notes

Data is saved for all voltage nodes in the circuit only.

The three small signal calculations are:

Gain (Transfer Function) - the ration of the voltage at the specific Voltage Node in the circuit to the input source defined by the Source Name parameter.
Input resistance - measured at the input source defined Source Name parameter.
Output resistance - measured across the specific Voltage Node in the circuit and the node defined by the Reference Node parameter.

The simulation results are displayed on the Transfer Function tab of the Waveform Analysis window.

Examples

Consider the circuit in the image above, where a Transfer Function analysis is defined with the following parameter values:

Source Name = Vin
Reference Node = 0 (GND)

The entry in the SPICE netlist will be:

*Selected Circuit Analyses: .TF V(INPUT) Vin .TF V(INV) Vin .TF V(OUTPUT) Vin .TF V(VCC) Vin .TF V(VEE) Vin

If the nodes INPUT and OUTPUT are taken into the Active Signals list on the General Setup page of the Analyses Setup dialog, then the following data will be obtained upon running the simulation: