Mathematical Expressions

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Edition Date: February 2017
Part Number: 375482B-01
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You can create arbitrary mathematical expressions consisting of various functions and operators and apply the results to device parameters. Expressions are very useful modeling tools when used within the Arbitrary Source devices. Refer to the Arbitrary Sources section for more information.

The functions and operators in the expression can operate on numerical constants, on circuit parameters, and, when used within the Arbitrary Source device, on live circuit variables. Refer to the Supported Mathematical Functions, Operators and Constants section for a list of supported mathematical functions, operators and pre-defined constants.

Within the Arbitrary Source device, special functions V(nodeabs), V(node+,node-), and I(deviceX) can be used to reference the circuit voltages and currents.

  • V(nodeabs) references the voltage at node nodeabs relative to ground.
  • V(node+,node-) references the difference between node+ and node-.
  • I(deviceX) references the current through the device with the instance name deviceX. Currently only the Independent Voltage source, dependent voltage sources, and inductor devices are supported.

Additional Notes

  • We recommend that expressions be enclosed in {} to avoid ambiguous syntax. However, this is not required for simulation.
  • Portions of expressions that are not enclosed in {} or () should not contain any spaces.

Examples

*High-level filter specification
.param pole=1k
.param res_val=1k
R1 in out {res_val}
C1 out 0 {1/(2*pi*res_val*pole)}

*A very simple diode modeled using an expression in an Arbitrary source
G1 A C value={1e-12*(e^(V(A,C)/0.025)-1 ) }

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