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Nexxim Simulator >
Nexxim Component Models >
S-Parameter Elements >
S Frequency Dependent Data Model

S Frequency Dependent Data Model

The S model provides frequency-dependent data in the Touchstone^Ò format. Touchstone is a registered trademark of Agilent Technologies. Refer to the Touchstone File Format Specification for information on this format.

The S model has the following netlist syntax.

.MODEL modelname S TSTONEFILE=”[pathname]filename”

[INTERPOLATION=LINEAR|STEP] [INTDATTYP=MA|RI|DBA]

[HIGHPASS=val] [LOWPASS=val]

[CONVOLUTION=0|1|2] [RELTOL=val] [MOR=val] [MAX_STATES=val]

[CACHE_STATE_SPACE=val] [BY_ENTRY=val]

[G_TO_GND=val] [Q_LIMIT=val]

[DELAYHANDLE=0|1]

The file_reference specifies the directory and filename for the Touchstone file.

Note

If the reference normalization impedance is not specified in the Touchstone file, 50 ohms is the default.

A W-element can be described by S-parameter data from a Touchstone file. Additional S-model parameters for W-elements are listed below. When Nexxim encounters one of these parameters in an S-Model definition, it looks in the circuit for the corresponding W-element. If the W-element is found, the S-model calculates the W model. If no W-element is found, these parameters are ignored.

XLINELENGTH=val

[ER=val]

[MAX_ER=val]

The XLINELENGTH parameter on the S-Model specifies a unit length (default 1 meter). Nexxim computes the equivalent RLGC or TABLE model for that unit length from the S-parameter data. The parameter L on the W-Element specifies the actual length of transmission line to simulate using the calculated model.

The parameter ER is the dielectric constant of the substrate for the W-element. If ER is not known, or if there are multiple substrates, use MAX_ER to provide an estimate that is greater than the probable maximum value. If both ER and MAX_ER are given, the larger of the two values is used. If neither parameter is supplied, a dielectric constant of 15 is used. An accurate RLGC or TABLE model will always be produced as long as no actual dielectric constant is larger than the one used in the calculation.

Note

Parameters ER and MAX_ER are Nexxim-specific. The XLINELENGTH parameter is HSPICE-compatible.

**S Model Parameters**
Parameter	Description	Unit	Default
BY_ENTRY	Error tolerance method 0=absolute 1=relative	None	0
CACHE_STATE_SPACE	0= do not cache 1 = cache	None	1
CONVOLUTION	Transient analysis method 0: state space 1: convolution using PWL waveform 2: Convolution using reverse FFT 3: Convolution using linear interpolation of reverse FFT.	None	0
DELAYHANDLE	Transient analysis method 0: state space, 1: convolution NOTE: DELAYHANDLE is supported as a model parameter for HSPICE compatibility only. Use the CONVOLUTION model parameter instead. DELAYHANDLE=1 is the same as CONVOLUTION=1. When convolution=1, 2, or 3 is in effect (either by global option or by model parameter), any DELAYHANDLE=0 model parameters are ignored.	None	0
G-TO-GND	Conductance between all terminal nodes and ground	Siemens	0.0
INTERPOLATION	Interpolation method LINEAR: Piecewise linear STEP: Take value from the closest table entry that is lower in frequency	None	LINEAR
INTDATTYP	Complex data type for linear interpolation MA: Magnitude-phase RI: Real-imaginary DBA: Decibel-phase	None	MA
HIGHPASS	Extrapolation method for points above the given frequency range 0: Forced to zero 1: Forced to highest frequency point in the table 2: Linear extrapolation 10: Hold the highest magnitude, linearly extrapolate the phase	None	10
LOWPASS	How a DC point is generated if none exists in the input data (always real) 0: Set to zero 1: Magnitude and sign equal to those of the lowest given point 2: Real part of linear extrapolation to DC 10: Magnitude equal to the lowest given point, phase linearly extrapolated and forced to be a multiple of pi 11: All signal lines open circuited (S-parameter matrix is identity matrix) 12: All signal lines shorted together 13: All signal lines shorted to ground (S-parameter matrix is negative identity matrix)	None	10
MAX_STATES	Maximum number of states per entry in the state space formulation	None	128
MOR	Model-order reduction 0=none 1=entire matrix 2=MOR of rows individually, plus final MOR for combination 3=MOR of rows individually, no final MOR 4=MOR of columns individually, plus final MOR for combination 5=MOR of columns individually, no final MOR	None	0
Q-LIMIT	Limit of quality factor of poles in rational fit	None	1e4

**S Model Parameters for W-Elements**
Parameter	Description	Unit	Default
XLINELENGTH	Unit length for computing RLGC or Table model for W element	Meter	1
ER	Exact dielectric constant.	None	None
MAX_ER	Maximum dielectric constant	None	15

S Model Netlist Examples

Here is an example of an S model netlist statement:

.MODEL S_2port S TSTONEFILE=”C:/fdata/tsdata.s2p”

Here is an example of a two-port S-parameter file with three frequency points, in real-imaginary format, adapted from the Touchstone File Format Specification:

!2-port S-parameter file, three frequency points

# GHZ S RI R 50.0

!freq ReS11 ImS11 ReS21 ImS21 ReS12 ImS12 ReS22 ImS22

1.000 0.393 -0.121 -0.001 -0.002 -0.001 -0.002 0.393 -0.121

2.000 0.352 -0.305 -0.010 -0.030 -0.010 -0.030 0.352 -0.305

10.000 0.342 -0.334 -0.013 -0.038 -0.013 -0.038 0.342 -0.334

Here is an example of a four-port S-parameter file with three frequency points, in magnitude-angle format, adapted from the Touchstone File Format Specification:

! 4-port S-parameter data, three frequency points

# GHZ S MA R 50

!freq MS11 AS11 MS12 AS12 MS13 AS13 MS14 AS14
! MS21 AS21 MS22 AS22 MS23 AS23 MS24 AS24
! MS31 AS31 MS32 AS32 MS33 AS33 MS34 AS34
! MS41 AS41 MS42 AS42 MS43 AS43 MS44 AS44

5.000 0.60 161.24 0.40 -42.20 0.42 -66.58 0.53 -79.34
0.40 -42.20 0.60 161.20 0.53 -79.34 0.42 -66.58
0.42 -66.58 0.53 -79.34 0.60 161.24 0.40 -42.20
0.53 -79.34 0.42 -66.58 0.53 -79.34 0.60 161.24

6.000 0.57 150.37 0.40 -44.34 0.41 -81.24 0.57 -95.77
0.40 -44.34 0.57 150.37 0.40 -44.34 0.41 -81.24
0.41 -81.24 0.57 -95.77 0.57 150.37 0.40 -44.34
0.57 -95.77 0.41 -81.24 0.57 -95.77 0.57 150.37

7.000 0.50 136.69 0.45 -46.41 0.37 -99.09 0.62 -114.19
0.45 -46.41 0.50 136.69 0.62 -114.19 0.37 -99.09
0.37 -99.09 0.62 -114.19 0.50 136.69 0.45 -46.41
0.62 -114.19 0.37 -99.09 0.45 -46.41 0.50 136.69

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