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Current Source, Piecewise Linear

Current Source, Piecewise Linear

Piecewise Linear Current Source Netlist Format

The netlist format for a piecewise linear current source is:

Ixxxx n+ n- [DC=val] PWL (t1 v1 [t2 v2... tN vN]
[R[=repeattime]] [TD=delay]) [M=val] [AC acmag acphase]
[TONE=tone_val] [PWL_FILE=file_reference]
[NOISEVEC=[f1,psd1, ... fn,psdn]]

n+ and n- are the positive and negative nodes. The parentheses around the parameters after the PWL keyword are required. The first time-value pair (t1 v1) is required, while subsequent pairs are optional.

Note

The time points t1 ... tN must be given in STRICTLY INCREASING order. Two points may not refer to the same time.

**Piecewise Linear Current Source Parameters**
Parameter	Description	Unit	Default
acmag	Magnitude for AC analysis	Amp	1.0
acphase	Phase for AC analysis	Degree	0.0
DC	DC current	Amp	0.0
M	Multiplier for simulating multiple parallel current sources	None	1.0
NOISEVEC	List of shot noise frequencies (f1...fn) and corresponding noise power spectral densities (psd1...psdn), in pairs. The sequence of frequencies must be monotonically non-decreasing.	Hertz, Volt²/Hertz	None
t1 ... tN	Timepoints	Second	0.0
v1 ... vN	Current values at corresponding timepoints	Amp	0.0
PWL_FILE	Reference to file containing the timepoint and current values	None	None
R	Repeat the segment of the waveform that begins at repeattime and ends at timeN. Repeattime must be less than timeN. If R is entered with no repeattime, repeats from 0.0 seconds to timeN.	Second	None
TD	Time delay to start of first PWL waveform, and to start of first repeat	Second	0.0
TONE	Frequency to use for harmonic balance analysis, should be a submultiple of or equal to the driving frequency and should also be included in the HB solution setup	Hertz	0.0

Piecewise Linear Current Source Netlist Example

Ipwl 23 53 PWL (0 0 10ns 0.05 15ns 1.5e-2 20ns 1.0e-2 30ns 0
+ R TD=5ns)

Notes

1. The time delay specified by TD=delay is applied to the start of the PWL waveform, so that the wave starts at (time1 + delay).

2. The repeat specified by R=repeattime repeats the portion of the PWL waveform that lies between repeattime and timeN. The repeattime must be greater than or equal to 0.0 seconds, and less than timeN. The repeat begins at time tN , subject to any delay. The delay is applied to the repeattime as well as to the PWL waveform, so that the repeating segment is the portion of the PWL waveform between (repeattime + delay) and (timeN + delay). The repeating wave starts at the PWL value that occurred at repeattime in the original wave, interpolated if necessary.

Note

The transition from the PWL value vN at time tN to the (possibly interpolated) value at the start of the repeat can create a discontinuity in the output, especially if the transition is “instantaneous,” that is, occurring with no time difference between the two values. Care should be taken to avoid such a discontinuity, or to ensure that it is very small if it cannot be avoided. Discontinuous current or voltage jumps larger than a minimum value can create a timestep problem for transient analysis.

3. Here is an example using eight time points plus a time delay, with a repeat time (R) that occurs between timepoints, so that interpolation is required.

I2 1 0 PWL(

+ 0.0 1.0e-3 $ t1 v1

+ 1.0e-3 2.0e-3 $ t2 v2

+ 2.6e-3 1.6e-3 $ t3 v3

+ 3.3e-3 2.7e-3 $ t4 v4

+ 4.1e-3 1.6e-3 $ t5 v5

+ 4.7e-3 1.6e-3 $ t6 v6

+ 5.2e-3 1.0e-3 $ t7 v7

+ 5.3e-3 0.4e-3 $ t8 v8

+ ) R=0.4e-3 TD=1.0e-3

Note the use of timepoint t8 to avoid an “instantaneous” jump in output where the repeat begins. If t8 were omitted, the output would change from the level at t7 to the (interpolated) value at the start of the repeat with no time difference between the two values. Such a sudden discontinuity can cause a timestep-too-small failure in transient analysis. The diagram below illustrates this example, showing one repeat:

4. The AC parameter specifies the AC magnitude and phase to be applied during a small-signal AC analysis. The default for acmag is 1 Amp, the default for acphase is 0 degrees.

5. For harmonic balance (HB) analysis, the test tones must be submultiples or equal to the frequencies of the actual voltage or current inputs to the circuit. To ensure that the desired HB frequency is used with a SIN, PWL, or PULSE source, qualify the source by adding a TONE=tone_val entry at the end of the instance statement. The tone_val is then used in a subsequent HB statement.

6. The TONE entry is required with any PWL or PULSE source. For example, to analyze a mixer driven by sources at 1 MHz and 27 kHz over the first four harmonics of a PWL source and the first two harmonics of a PULSE source, the netlist syntax would be:

I23 20 0 PWL(0 0 0.1e-6 2.0 0.5e-6 5.0 1.0e-6 0 R) TONE=1.0e6

I1 1 0 PULSE (0 5 0 5e-3 5e-3 27e-3 27.0e3) TONE=27.0e3

.HB TONES=(1.0e+6, 27.0e+3) MAXK=(4, 2)

7. The parameter PWL_FILE =file_reference refers to an external file containing the PWL data. See File References in the Nexxim Netlist File Format topic for details.

The format of the PWL data file is:

t1 v1 [t2 v2 ...]

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