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Nexxim Simulator >
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Current Source, Exponential (Netlist Only)

Current Source, Exponential (Netlist Only)

Exponential Current Source Netlist Format

The format for specifying an exponential current source is:

Ixxxx n+ n- EXP (v1 v2 [td1 [td2 [t1 [t2]]]])

n+ is the positive node and n- is the negative node of the current source. Parameters in parentheses are positional. The first two (v1 and v2) are required. The remainder (td1, td2, t1, and t2) can be omitted, but the parameters must be entered in the order given. To guarantee that a given parameter is interpreted correctly, all parameters to the left of it must be present.

Note

The exponential current source is available for use in netlists, but is not supported in the Components window of the Designer Schematic Editor.

**Exponential Current Source Parameters**
Parameter	Description	Unit	Default
v1	Initial current value	Amp	0.0
v2	Maximum current value	Amp	0.0
td1	(Positive) delay time to start of exponential rise	Second	0.0
td2	Delay time to start of exponential fall	Second	td1+TSTEP (step argument on TRAN statement)
t1	Rise time constant	Second	TSTEP
t2	Fall time constant	Second	TSTEP

Exponential Current Source Netlist Example

.TITLE IEXP TEST

I1 1 0 EXP(-4 -1 5ns 30ns 80ns 40ns)

R1 1 0 1

.TRAN 0.5ns 200ns

.PRINT tran I(R1)

.END

Notes

1. From time = 0 to time = td1:

Output = v1

From time=td1 to time = td2:

Output = v1+(v2-v1)´(1.0-EXP[-(time-td1)/t1]

From time = td2 to time = tstop:

Output = v1+(v2-v1)´(1.0-EXP[-(time-td1)/t1])-
(v2-v1)´(1.0-EXP[-(time-td2)/t2])

2. The td2, t1, and t2 parameters take their default values from the step argument on the transient analysis TRAN statement (see Transient Analysis Netlist Format). Therefore, when a circuit containing an exponential current source is to be analyzed with a tool other than transient analysis, the td2, t1, and t2 parameters must be given explicit values.

3. The exponential current source exhibits an 'overshoot' when the first time period is small relative to the first decay constant.

Here is the resulting waveform:

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