IEXP - Exponential Current Source Model

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Modified by Phil Loughhead on Mar 4, 2014

Model Kind

Current Source

Model Sub-Kind

Exponential

SPICE Prefix

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

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.

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

I(t₀ to t_RD) = I_IV
I(t_RD to t_FD) = I_IV + (I_PV - I_IV ) (1 - e^-(t-tRD^)/tRT)
I(t_FD to t_STOP) = I_IV + (I_PV - I_IV) (e^-(t-tRD^)/tRT) + (I_IV - I_PV) (1 - e^-(t-tFD^)/tFT)

where:

t is an instance of time
I_IV is the initial value of the current
I_PV is the pulsed value of the current
t_RD is the Rise Delay
t_RT is the Rise Time
t_FD is the Fall Delay and
t_FT is the Fall Time.

The simulation-ready exponential current source component (IEXP) can be found in the Simulation Sources integrated library (\Library\Simulation\Simulation Sources.IntLib).