Use this component to model a linear voltage-controlled voltage source system by specifying only its frequency response, using an S-variable Laplace expression.

If you intend to perform a time domain simulation and the frequency response is in rational polynomial form, the Transfer Function Block component is more appropriate, as it calculates the result more accurately and more quickly. This is especially true for low bandwidth systems such as integrators. This is due to different internal implementations. While the Transfer Function Block component uses a system of integrators, relying on numerical integration techniques, to process the input, the Arbitrary Laplace Function component uses its impulse response and a convolution technique to process the input. Since the impulse response is obtained from the sampled frequency response (using an inverse Fourier Transform), the overall result may contain inaccuracies.

The Value tab in this component's properties dialog box contains the following:

  Parameter   Description
S-variable Laplace expression

Enter the desired frequency response in this field as a mathematical expression which uses the complex frequency variable "s". You can use standard mathematical operators and functions. Refer to the Mathematical Expressions section for more information.

Examples:

-exp(-20*sqrt((1m*s+47k)*(1.6u*s+0.003)))Or 250/(0.0008*s+3e-8*s^2+250)
Custom accuracy

Two parameters control the sampling: the maximum frequency sampled and the frequency sampling resolution. By default, Multisim automatically chooses these parameters based on the simulation settings (TSTOP and TMAX) and the frequency response characteristics (bandpass range).

Due to computational constraints, the following restriction exists:

Frequency Resolution > 2*Maximum Frequency / 65536

If the above constraint is not met, then the Frequency resolution is set to:

2*Maximum Frequency / 65536.

In addition, to prevent an unncessary truncation in accuracy, the following restriction exists:

Frequency Resolution < 2*Maximum Frequency / 512

If the above constraint is not met, then the Frequency resolution is set to:

2*Maximum Frequency / 512.

Multisim also makes a conservative adjustment to any specified Frequency resolution value such that the ratio of 2*Maximum Frequency and Frequency Resolution is a power of 2.

The sampling values which are actually used to calculate the impulse response are reported in the Simulation Error Log/Audit Trail.

Refer to the Simulation Error Log/Audit Trail section for more information.