IEXP - Exponential Current Source Model

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Model Kind

Current Source

Model Sub-Kind

Exponential

SPICE Prefix

I

SPICE Netlist Template Format

@DESIGNATOR %1 %2 ?"DC MAGNITUDE"|DC @"DC MAGNITUDE"| EXP(?"INITIAL VALUE"/&"INITIAL VALUE"//0/ ?"PULSED VALUE"/&"PULSED VALUE"//5/ ?"RISE DELAY TIME"/&"RISE DELAY TIME"//1U/ ?"RISE TIME CONSTANT"/&"RISE TIME CONSTANT"//700N/ ?"FALL DELAY TIME"/&"FALL DELAY TIME"//2U/ &"FALL TIME CONSTANT") #"AC MAGNITUDE"|AC @"AC MAGNITUDE"| @"AC PHASE"

Parameters (definable at component level)

The following component-level parameters are definable for this model type and are listed on the Parameters tab of the Sim Model dialog. To access this dialog, simply double-click on the entry for the simulation model link in the Models region of the Component Properties dialog.

DC Magnitude

DC offset used in an Operating Point Analysis. (Default = 0).

AC Magnitude

the magnitude of the source when used in an AC Small Signal Analysis. (Default = 1).

AC Phase

the phase of the source when used in an AC Small Signal Analysis. (Default = 0).

Initial Value

current amplitude at time zero (in Amps). (Default = 0).

Pulsed Value

maximum amplitude of the output swing (in Amps). (Default = 5).

Rise Delay Time

the point in time, from t 0 , where the output begins to rise from the Initial Value to the Pulsed Value (in seconds). (Default = 1u).

Rise Time Constant

RC charging time constant (in seconds). (Default = 700n).

Fall Delay Time

the point in time, from t 0 , where the output begins to fall from the Pulsed Value back to the Initial Value (in seconds). Must be >0. (Default = 2u).

Fall Time Constant

RC discharging time constant (in seconds). (Default = 300n).

Notes

  1. Use this source to create a pulse current waveform with an exponential rising and/or falling edge.

The image above shows an example waveform produced by an exponential current source (connected to a 1Ohm load) with the parameters set to their default values.

  1. The shape of the waveform is described by the following formulae:

I(t0 to tRD) = IIV
I(tRD to tFD) = IIV + (IPV - IIV ) (1 - e-(t-tRD)/tRT)
I(tFD to tSTOP) = IIV + (IPV - IIV) (e-(t-tRD)/tRT) + (IIV - IPV) (1 - e-(t-tFD)/tFT)

where:

  • t is an instance of time
  • IIV is the initial value of the current
  • IPV is the pulsed value of the current
  • tRD is the Rise Delay
  • tRT is the Rise Time
  • tFD is the Fall Delay and
  • tFT is the Fall Time.
  1. The simulation-ready exponential current source component (IEXP) can be found in the Simulation Sources integrated library (\Library\Simulation\Simulation Sources.IntLib).

 

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