## Zxxxxxxx

Semiconductor MESFET Device: This device is translated as a nonlinear N-type GaAsFET device. For information on the GaAsFET model, refer to the Statz_Model:Statz (Raytheon) GaAsFET Model.

##### Example SPICE Command Line:

`z1 1 2 3 Zmodel 2 OFF IC=0.6, 5.0`

##### SPICE dialect and netlist syntax:

**Spice2/3:**

zidnd ng ns mname[area] [OFF] [IC=vds,vgs]

**PSpice:**

Does not exist.

**HSpice:**

Does not exist.

##### ADS Netlist Syntax:

mname:zid nd ng ndArea=areaRegion=0

##### ADS Schematic Symbol:

##### Instance Parameters:

**zid** = GaAsFET element name

**mname** = Model name

**nd** = Drain node

**ng** = Gate node

**ns** = Source node

**area** = Area factor

**OFF** = Indicates an initial condition on the device for dc analysis. Translates to Region=0.

**ic=vds, vgs** = The initial condition specification intended for use with the UIC option on the .TRAN control line. Not translated.

## Unsupported Devices

The following devices are not supported:

Axxxxxxx

Nxxxxxxx

Pxxxxxxx

Sxxxxxxx

Wxxxxxxx

Yxxxxxxx

The following additional information provides a suggested action for your translation, each of which requires using a Symbolically Defined Device (SDD). For information on SDD's, refer to Using a Symbolically Defined Device.

#### Non-Linear Dependent Source (SPICE 3 only):

`Bxxxxxxx N+ N- I=expression V=expression`

Suggested Action

Insert an SDD to replace the unmapped element. Assign the appropriate wire labels to the SDD so you can maintain connectivity of the circuit. Insert the equation I=expression or V=expression into the correct current or voltage port definition.

#### Voltage Controlled Switch (SPICE 3 only):

`Sxxxxxxx N+ N- NC+ NC- mname [ON] [OFF]`

Suggested Action

Insert an SDD to replace the unmapped element. Assign the appropriate wire labels to the SDD so you can maintain connectivity of the circuit.

#### Current Controlled Switch (SPICE 3 only):

`Wxxxxxxx N+ N- VNAM mname [ON] [OFF]`

Suggested Action

Insert an SDD to replace the unmapped element. Assign the appropriate wire labels to the SDD so you can maintain connectivity of the circuit.

## Using a Symbolically Defined Device

The symbolically-defined device (SDD) enables you to create equation based, user-defined, nonlinear components in ADS. The SDD is a multi-port device which is defined by specifying algebraic relationships that relate the port voltages, currents, and their derivatives, plus currents from certain other devices.

Controlled sources from SPICE are modeled in ADS using the symbolically-defined device. The SDD allows a voltage or current source to be constructed whose output can be described as an arbitrary combination of a number of controlling voltages or currents.

The voltage controlled sources have 2(n+1) nodes, where n is the number of controls. The controlling voltage nodes are listed first in pairs (nc1p nc1n) at ports 1 through n, then the output node pair (outp outn) at port n+1. The controlling voltages have symbolic names like _v1. Each controlling voltage must have a current equation written for it (I[1,0]=0) so that no current flows between the controlling nodes through the SDD.

The current controlled sources have only 2 output nodes at port 1, while the name of the sources used to measure the controlling currents are specified using C[1]="ivs1". The controlling currents have symbolic names like _c1.

Current sources are written as a simple expression for the current at the output port. This expression is in SI units and is written in terms of the controls:

I[3,0]=_v1*1e-3+_v2*2e-3

A voltage source must have an implicit expression for the voltage at the output port such that F[3,0]=_v3-vout, where vout is the desired output voltage:

F[3,0]=_v3-(_v1*2+_v1*v2)

Controlled sources in SPICE may be linear or nonlinear and there may be one or more controlling voltages or currents. The general form of a controlled source is:

?id node1 node2 [poly(dim)] [sourcename | nodecp nodecn]*

+ value [value]*

The source has two nodes with the same polarity convention as the dependent sources. The method of specifying controls depends on whether the source is voltage controlled or current controlled. Current-controlled sources give the name of a source through which the current is measured; voltage-controlled sources provide two nodes with which to measure a differential voltage. The simple linear form for all four types:

eid n+ n- nc+ nc- value ; vout = value * vcon

fid n+ n- vname value ; iout = value * icon

gid n+ n- nc+ nc- value ; iout = value * vcon

hid n+ n- vname value ; vout = value * icon

A nonlinear source may be created whose output is a polynomial function of its control:

eid n+ n- nc+ nc- v0 v1 v2 v3 ... [ic=]

The polynomial is interpreted as:

v_{out}=v0+v1*v_{con}+v2*v^{2}_{con}+...

unless only a single value is given, in which case it reverts to a linear behavior:

v_{out}=v0*v_{con}

SPICE allows controlled sources with more than one control. When there is more than one control. the poly keyword must be used to identify the number of controls. The dimension refers to the number of controlling sources, not the order of the polynomial.

eid n+ n- poly(dim) [ nc+ nc- ]* values ... [ic=]

Coefficients for a polynomial of dimension two are interpreted as:

*v*_{out} =v0

+v1**v*_{con1}+v2**v*_{con2}

+v3**v*^{2}_{con1}+v4**v*_{con1*}*v*_{con2}+v5**v*^{2}_{con2}

+v6*v_^{3}_{con1}+v7**v*^{2}_{con1}**v*_{con2}+v8**v*_{con1*}*v*^{2}_{con2}+v9**v*^{3}_{con2}

+...

Coefficients for a polynomial of dimension three are interpreted as:

*v*_{out}=v0

+v1**v*_{con1}+v2**v*_{con2}+v3**v*_{con3}

+v4**v*^{2}_{con1}+v5**v*_{con1*}*v*_{con2}+v6**v*_{con1}**v*_{con3}+v7**v*^{2}_{con2}+v8**v*_{con2*}*v*_{con3}+v9**v*^{2}_{con3}

+v10**v*^{3}_{con1}+v11**v*^{2}_{con1*}*v*_{con2}+v12**v*^{2}_{con1}**v*_{con3}+v13**v*_{con1}**v*^{2}_{con2}+v14**v*_{con1*}*v*_{con2}**v*_{con3}

+v15**v*_{con1}**v*^{2}_{con3}+v16**v*^{3}_{con2}+v17**v*^{2}_{con2}**v*_{con3}+v18**v*_{con2}**v*^{2}_{con3}+v19**v*^{3}_{con3*}

+v20**v*^{4}_{con1}+...

The SPICE syntax provides no simple way to specify just a couple of the individual terms. If only the `v14`

term is needed, `v0`

through `v13`

must still be specified with zeros.

Initial conditions here are used to provide a guess at what the controlling values will be so the output of the dependent source can be evaluated; the initial values do not actually influence the controlling values. Enough initial conditions must be provided to match the dimensionality of the source.

Several translation examples for SPICE are presented below.

##### Example1

**SPICE Netlist:**

**ADS Netlist:**

##### Example 2

**SPICE Netlist:**

**ADS Netlist:**

##### Example 3

**SPICE Netlist:**

**ADS Netlist:**

##### Example 4

**SPICE Netlist:**

**ADS Netlist:**

##### Example 5

**SPICE Netlist:**

**ADS Netlist:**

##### Example 6

**SPICE Netlist:**

**ADS Netlist:**

##### Example 7

**SPICE Netlist:**

**ADS Netlist:**

For more information, refer to Custom Modeling with Symbolically-Defined Devices in User-Defined Models.