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Simple way to develop Spice macro models (Part 1)

25 May 2015  | Soufiane Bendaoud

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The current-controlled voltage source has two terms: a and b.

Set the "b" term to an arbitrary value of 1. The "a" term equals the "b" term divided by 1,000. This removes the DC bias voltage across the flicker-noise diode from feeding back at the EOS source as DC error.


VOLTAGE NOISE REFERENCE OF 15nV/rt(Hz)

*

VN1 80 98 0

RN1 80 98 16.45E-3

HN 81 98 VN1 15

RN2 81 98 1

*

* FLICKER NOISE CORNER

*

DFN 82 98 DNOISE

VFN 82 98 DC 0.6551

HFN 83 98 POLY(1) VFN 1.00E-03 1.00E+00

RFN 83 98 1


Supply current
You can model supply current with a voltage-controlled current source. The current is set with a polynomial written as:


GSY 99 50 POLY(1) (99,50) a b (19)


Set the "a" term equal to:


Is-Idq-I1-("b"*Vs) (20)


where Is is the supply current, I1, is the tail current (input stage) and Vs is the supply voltage.


Idq=kp*0.5*(W/L5)*Vdc5*2*(1+ ?*Vs/2) (21)


The idea is have the input pair driven from a supply internal to the model such that it doesn't draw external current for the model. The "b" term is simply the slope of the curve Is versus Vs from the datasheet.


* INTERNAL VOLTAGE REFERENCE

*

EREF 98 0 POLY(2) (99,0) (50,0) 0 0.5 0.5

GSY 99 50 POLY(1) (99,50) -11.2E-04 5.00E-07

EVP 97 98 (99,50) 0.5

EVN 51 98 (50,99) 0.5


Conclusion
The macro models created using this technique provide very accurate results and can be tested using the collection of test circuits provided in the reference section. You can tweak the formulas based on the datasheet parameters to quickly change the models to your liking and to fit your needs. In part 2, I will address a different topology with a similar approach.


Reference
Find the collection of test circuits here


About the author
Soufiane Bendaoud is Business Development Manager-Precision Analog at Texas Instruments.


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