Micro-Cap v7.1.6 / RM

Diode

SPICE format

Syntax

D<name> <anode> <cathode> <model name> [area] [OFF] + [IC=<vd>]

Example

D1 7 8 1N914 1.0 OFF IC=.001

Schematic format

PART attribute <name>

Example

D1

VALUE attribute

[area] [OFF] [IC=<vd>]

Example

10.0 OFF IC=0.65

MODEL attribute <model name>

Example 1N914

Both formats

[area] multiplies or divides model parameters as shown in the model parameters table. The presence of the OFF keyword forces the diode off during the first iteration of the DC operating point. The initial condition, [IC=<vd>], assigns an initial voltage to the junction in transient analysis if no operating point is done (or if the UIC flag is set).

Model statement form

.MODEL <model name> D ([model parameters])

Example

.MODEL 1N4434 D (IS=1E-16 RS=0.55 TT=5N)

387

Function sources

Schematic format

PART attribute

<name>

Example

F1

VALUE attribute for formula (NFV and NFI) type <formula>

Example of formula type 10*Sin(2*PI*1E6*T)*V(3)*I(L1)*EXP(-V(IN)/100NS)

FREQ attribute [<fexpr>]

Example 1200*(1+sqrt(F/1e6))

NOISE EXPRESSION attribute for NFI only [<noise_expr>]

Example 1200*(1+sqrt(F/1e6))

TABLE attribute for table (NTIOFI, NTIOFV, NTVOFV, NTVOFI) types (<x1,y1>) (<x2,y2>) ... ([(xk,yk)])

Braces are required for expressions and optional for variables.

Examples of table type (-1m,25) (1m,25) (2m,30)

({start - 1m}, {25*level} ) (end,level) ({end+3m}, level2)

FREQ usage

If <fexpr> is used, it replaces the ordinary small-signal AC incremental value determined during the operating point. <fexpr> may be a simple number or an expression involving frequency domain variables. The expression is evaluated during AC analysis as the frequency changes. For example, suppose the <fexpr> attribute is this:

391

1+V(3)*(1+1e6/F)

In this expression, F refers to the AC analysis frequency variable and V(3) refers to the AC small-signal voltage from node 3 to ground. There is no time-domain equivalent to <fexpr>. Even if <fexpr> is present, only <value> will be used in transient analysis.

NOISE_EXPRESSIONusage

If noise_expr is used, it generates a noise current equal to the expression. For example to simulate shot noise you might use an expression like this:

1E-16 * pow(6.5ma,1.1) / F

Note that the expression should contain only frequency (F) dependent variables. The feature is available only in the NFI source.

Function sources provide the principle time domain Analog Behavioral Modeling capability. The two basic types are distinguished by the way the value of the output variable (current or voltage) is calculated.

Formula type

The Formula type, which is similar to the SPICE3 B device, uses an algebraic formula, or expression, to compute the value of the output variable as a function of any set of valid time-domain variables. There are two versions of this source:

Here is an example of an expression that models a vacuum triode:

K* pow((V(Plate)-V(Cathode)+Mu*(V(Grid)-V(Cathode))),1.5)

Table type

The Table type, which is similar to the SPICE3 A device, uses a table of ordered data pairs which describe the output variable as a function solely of the input variable. The table describes a time-domain transfer function.

The input variable for a Table source may be either:

Current flowing into the positive input lead.

Voltage between the positive input lead and the negative input lead.

392 Chapter 22: Analog Devices

There are four basic types of Table source:

There are two rules for constructing the data pairs in the TABLE attribute.

1.The x,y pairs are separated by commas, pairs are enclosed in parentheses and are separated by spaces. The x,y values may be replaced by expressions containing constants or symbolic variables created with a .define statement.

Expressions are evaluated only once, in the setup phase of the analysis, so they must not contain variables that vary during an analysis run, like V(1) or T, or even simulation control variables like tmin that are unknown when the expressions are evaluated.

2.Data pairs must be arranged in input ascending order.

x1<x2<...xk

Output is calculated from the input value as follows:

1.The output value is constant at y1 for input values below x1.

2.The output value is constant at yk for input values above xk.

3.Output values are interpolated for input values between table values.

For example:

(-.010,-10) (.010,10)

For an NTVOFV source, this describes an ideal amplifier having a gain of 1000 and with the output clipped to +-10 volts. The output value when the input is greater than .010 is limited to +10.0. Similarly, the output value when the input is less than -.010 is limited to -10.0.

See the sample circuit T1 for an example of table sources, and the sample circuits F1, F2, F3, and F4 for examples of formula sources.

393

GaAsFET

SPICE format

Syntax

B<name> <drain> <gate> <source> <model name> + [area] [OFF] [IC=<vds>[,vgs]]

Example

B1 5 7 9 2N3531 1 OFF IC=1.0,2.5

Schematic format

PART attribute <name>

Example

B1

VALUE attribute

[area] [OFF] [IC=vds[,vgs]]

Example

1.5 OFF IC=0.05,1.00

MODEL attribute <model name>

Example

GFX_01

The device is an n-channel device. There is no p-channel version. Level 1 specifies the Curtice model, level 2 specifies the Raytheon or Statz model, and level 3 specifies the Triquint model. The [OFF] keyword forces the device off for the first iteration of the operating point. The initial condition, [IC=vds[,vgs]], assigns initial voltages to the drain-source and gate-source terms. Additional information on the model can be found in references (14) and (15).

Model statement form

.MODEL <model name> GASFET ([model parameters])

Example

.MODEL B1 GASFET (VTO=-2 ALPHA=2 BETA=1E-4 LAMBDA=1E-3)

394 Chapter 22: Analog Devices

GaAsFET model equations

Figure 22-5 The GaAsFET model

Notes and Definitions

The model parameters BETA, CGS, CGD, and CDS are multiplied by [area] and the model parameters RG, RD, and RS are divided by [area] prior to their use in the equations below.

T is the device operating temperature and Tnom is the temperature at which the model parameters are measured. Both are expressed in degrees Kelvin. T is set to the analysis temperature from the Analysis Limits dialog box. TNOM is determined by the Global Settings TNOM value, which can be overridden with a .OPTIONS statement. T and Tnom may both be customized for each model by specifying the parameters T_MEASURED, T_ABS, T_REL_GLOBAL, and T_REL_LOCAL. See the .MODEL section of Chapter 20, "Command Statements", for more information on how device operating temperatures and Tnom temperatures are calculated.

Vgs = Internal gate to source voltage

Vds = Internal drain to source voltage

Id = Drain current

VT= k • T / q = 1.38E-23 •T / 1.602E-19

In general, X(T) = Temperature adjusted value of parameter X

Temperature Dependence

BETA(T) = BETA•1.01BETATCE•(T- Tnom)

EG(T) = 1.16-.000702•T2/(T+1108)

VTO(T) = VTO + VTOTC•(T - Tnom)

396 Chapter 22: Analog Devices