ALD SPICE Macromodels - Advanced Linear Devices

ALD SPICE Macromodel Advanced Linear Devices

ALD SPICE Macromodels

The increasing power of computer hardware and simulation software has led to the widespread proliferation and use of analog

simulators. ALD recognizes this, and has designed a SPICE library containing models of ALD's linear elements such as

operational amplifiers to facilitate easier and more accurate simulation by our customers.

MACROMODEL DEFINITION

If any computer simulation, there is a trade-off between accuracy and convenience. A transistor level SPICE operational

amplifier model would require extremely long simulation times and be prone to convergence problems. A very simple model

would simulate quickly, but the results would be inaccurate. The macromodel is a good compromise, suitable for most

engineering applications. The macromodel uses transistors in the input stage and ideal SPICE elements in the rest of the

model. Ideal SPICE elements include voltage controlled voltage and current sources, resistors and capacitors. This

combination reduces the number of active devices while providing a reasonably accurate model.

USING ALD MACROMODELS

The macromodels were designed, written and tested on MicroSim's PSPICE, version 4.03. The instructions that follow are

specifically for PSPICE. Tailor your macromodel implementation to your software package. The ALD macromodels can be

used on any SPICE program that uses SPICE 2G.6 format. If your syntax should happen to be different, it should be easy to

modify the macromodels to suit your system.

Each of the different ALD macromodels is for a different amplifier. These macromodels should be implemented on your

computer system in different ways depending on your level of usage. If you are only going to use a model a few times, type

it directly into your circuit file. If you are going to use it more than a few times, you may want to set up a library system. To do

this, type each operational amplifier macromodel you will use into a single file with a .lib extension. (e.g.ALD.lib) then, in your

circuit file, access the macromodel you need with a subcircuit cell. For example, set up file ALD.LIB, then in your circuit file

use

* ckt simulation

•

• Lib ALD.Lib

•

x1 2 7 9 18 24 ALD1701(where ALD 1701 is the model name of the subcircuit).

Advanced Linear Devices ALD SPICE Macromodel

This statement matches the five nodes you specify to the five operational amplifier inputs shown below:

The only other thing you need is a statement telling SPICE where to look for the library file. To do this, use the following

statement in your circuit file.

.lib c:/path to the ALD library

(e.g. .lib c:/ PSPICE/ libraries/ ALD/ALD.lib)

This method allows use of the ALD models as subcircuits without having to put them in every file.

Finally, if you plan on heavy use of the ALD macromodels, all of the ALD models are available on diskette and are a part

of the ALD design kit.

1 2

M2 M1

10X10

-6

5X10

-6

5X10

-9

Gcm

1X10

rd2

15K rd1

15K rd3

15K

5X10

-6

15pF V

LIM

fb R

148K

225Ω

0.1V

Vdd

Vss

20K

SYSTEM GND

E gnd

Vert GND VLn = 1.0

DLn

DLp

VLp = 1.0

CURRENT

LIMIT CKT.

hLim

D13

D41

D23

D42

GATE PROTECTION

ALD 1701

ALD SPICE Macromodel Advanced Linear Devices

POTENTIAL PROBLEMS

With any computer models there are difficulties encountered that would not be present in the use of as actual physical device.

These difficulties can range from a missing period in the circuit file to limitations of the simulators ability to adequately simulate

complex systems. The ALD macromodels do represent typical device behavior and they do not model every op amp parameter.

Consequently care must be taken during simulation. Most problems that occur can be placed under one of three categories.

1. Hardware or software problems related to the user's system

Such problems would include improper SPICE configuration and errors in the circuit file.

2. Problems related to the simulation application

These problems are sometimes very complex. Such problems include: failure of simulation to converge,

simulation does not model a certain parameter or the simulation behaves incorrectly. These problems involve the

simulator, the model and the application of the model in a very interrelated way.

3. Problems with the model itself

It can be difficult to distinguish these problems from type 2. It includes only model errors, not slight model

inaccuracy or the failure of a model to model certain parameters.

Because ALD is in the business of supplying integrated circuits, not SPICE macromodels, we only provide limited support for

our models. Obviously ALD cannot be responsible for case 1 errors. Case 3 errors( should any exist) will be addressed by ALD

at our discretion. The most difficult errors to address are those which come under case 2 It is crucial that all customers isolate

the source of such errors before contacting ALD. Although the company believes the models will be more than adequate for

almost all simulation needs, they are supplied on an "as is" basis and we do not guarantee the models will model every possible

operational amplifier behavior with accuracy. We do guarantee the model to have been thoroughly tested by our engineering

staff and we have encountered no errors. If a model is not to your liking, it can be easily modified by the user. Of course,

simulation problems can be tricky and elusive. However, ALD recommends using the simulator and various system simulations

as guidelines for engineering evaluation prior to building a breadboard where the "true" system parametric and performance

can be verified.

DETAILS OF THE MACROMODEL

PSPICE contain a program called Parts. Parts can create a macromodel given operational amplifier parameters. Our

macromodels began with the Parts model, but were extensively modified to provide a more accurate model of the attributes

for each ALD op amp.

An example of the circuit ALD macromodel is shown on previous page.

The following parameter are modeled with ALD's macromodels:

VOM+, VOM-, AV, CMRR, IOSAT, slew rate, rise and fall times, overshoot, output resistance, bandwidth, phase margin,

common mode input voltage range, output voltage range, input diode clamping and input capacitance.

Some of the parameters not modeled include:

VOS, IOS, noise and PSRR.

CONCLUSION

For the designer interested in off-the -shelf parts, this provides a powerful design simulation tool. For those involved in ASIC

design with our Function-Specific program these macromodels add yet another level of power, flexibility and convenience.