1Leonid B. Goldgeisser, et al. DAC 2007

Modeling Safe Operating Area in Hardware Description Languages

Leonid Goldgeisserleonidg@synopsys.com

Ernst Christenchristen@synopsys.com

Zhichao Dengzhichao@synopsys.com

Synopsys Inc2025 NW Cornelius Pass Rd.

Hillsboro, OR, USA, 971241.503.547-6118

Predictable Success© 2006 Synopsys, Inc. (1)

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Outline

• Safe Operating Area (SOA) concept Design reliability vs. Stress

• Requirements for modeling SOA Ratings De-rating Measurements

• Simulation tools are used for functional verification. We demonstrate that extending simulation tools capabilities to measure the stress can improve the robustness of a design. Using MAST and VHDL-AMS HDLs

• Conclusions

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Safe Operating Areas

• SOA describes the Operating Conditions of the device operating without self-damage

• SOA often combines various limitations (Constraints) of a device

1.SOA Curves for MJL4281A/4302A

Duration of

the current

Junction Temper

ature

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SOA for Semiconductors

• Limits the voltage, current and temperature.

• Maximum voltage, above which a mechanism such as avalanche breaks down, will lead to loss of electrical control.

• Maximum power dissipation, above which the active part becomes too hot to function correctly.

• Maximum current, above which the interconnect terminal such as wire contact region can be heated to damage.

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SOA in Automotive and Aerospace designs

• Limits the pressure, speed, and torque.

• Maximum speed, above which the moving part can be damaged.

• Maximum torque, above which the part can suffer due to the internal forces.

• Maximum pressure, above which the containing part will be damaged.

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Need for modeling SOA

Failure to measure and model stress adequately

Reliability suffers

Performance drops:

•Design is too conservative

•Incorporating defense techniques

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Outline

• Safe Operating Area (SOA) concept Design reliability vs. Stress

• Requirements for modeling SOA Ratings De-rating Measurements

• Simulation tools are used for functional verification. We demonstrate that extending simulation tools capabilities to measure the stress can improve the robustness of a design. Using MAST and VHDL-AMS HDLs

• Conclusions

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Requirements for modeling SOA

• Operating under significant stress levels shortens the component life.

Components are tested for allowable stress; the results usually are reported as rating.

• Ratings are the attributes of the component. (HDL has to support it).

• The rating represents a boundary of the SOA for a given device.

For a reliable design, common sense is to use components operating sufficiently lower their ratings, hence the concept of de-rating.

• De-rating is the attribute of the design (The tool has to support it).

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Requirements for modeling SOA (Cont’d)

• Robust design implies that no component operates near or outside of its rated limits.

All components breaking this rule must be identified.• A measurement must be taken between the actual value and the

de-rated value.• The measurement could be performed for all possible types of

analysis -> measuring waveform, values, etc.

• HDL must provide the capability to describe the measurement.

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Example

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Circuit Example, Cont’d

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Circuit Example, Results

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SOA Modeling Requirements Digest

1. SOA boundary is associated with a waveform.

2. Should have a name, so a user can select it.

3. Should include a description string to be included in the stress report.

4. Should provide a way to specify a variety of waveform measurements.

5. Should include the rating from the manufacturer.

6. Should provide a way to specify a de-rating by the user.

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Measuring capabilities

•Peak (the maximum deviation from a reference).

•Minimum allowable value.

•Maximum allowable value.

•Minimum and maximum for a time interval, integrated over the interval.

•Average over time.

•RMS for periodic signals.

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Modeling SOA With MAST® HDL

• The considerations listed above were the basis for the design of the stress_measure specification.

• Stress_measure(uid, gid, descr, wave, measure, rating, ref_rat)

UniqueIdentifier

GroupIdentifier

Descript.String

MeasuredWaveform

MeasureType

Allowablerating

ReferenceRating

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Example of Specifying SOA Boundaries using the MAST Language

template resistor p m = r, vmax, pmax

electrical p, m

number r

number vmax = undef

number pmax = undef

{

val i i

val v v

val p pwrd

v = v(p,m)

i = v / r

pwrd = v * i

i(p->m) += i

control_section {

stress_measure(pavg, power,

“Average power dissipation”,

pwrd, average, pmax)

stress_measure(pmax, power,

“Maximum power dissipation”,

pwrd, winmax, pmax)

stress_measure(vmax, voltage,

“Maximum voltage“,

abs(v), max, vmax)

}

}

Name GroupDescr.

Measure

rating

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SOA Modeling in VHDL-AMS

• No Predefined Language Semantics to capture SOA.

• VHDL provides constructs to capture the SOA in a model – attributes.

• Since waveforms are represented by quantities in VHDL-AMS, a SOA boundary is represented by an (user defined) attribute on a quantity.

• The a value of the user defined attribute combines the remaining aspects of the SOA boundary.

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SOA Modeling with VHDL-AMS, example.

package soa is

-- Declare a record type to hold all aspects

-- of an SOA boundary

type soa_boundary is record

description: string(1 to 32);

rating: real;

reference_rating: real;

end record;

-- Declare the attributes, one for each

-- measurement method, that compares the

-- value of the quantity with the rating

attribute stress_minimum: soa_boundary;

attribute stress_maximum: soa_boundary;

attribute stress_peak: soa_boundary;

attribute stress_average: soa_boundary;

attribute stress_rms: soa_boundary;

attribute stress_winmin: soa_boundary;

attribute stress_winmax: soa_boundary;

-- Declare another set of attributes that

-- compares the absolute value of the quantity

-- with the rating

attribute stress_abs_minimum: soa_boundary;

attribute stress_abs_maximum: soa_boundary;

attribute stress_abs_peak: soa_boundary;

attribute stress_abs_average: soa_boundary;

attribute stress_abs_rms: soa_boundary;

attribute stress_abs_winmin: soa_boundary;

attribute stress_abs_winmax: soa_boundary;

-- Declare a function to help defining an

-- SOA boundary

function soa_value(description: string;

rating: real;

reference_rating: real := 0.0)

return soa_boundary;

end package soa;

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SOA Modeling with VHDL-AMS

library ieee;

use ieee.electrical_systems.all;

use work.soa.all;

entity resistor is

generic (r: real; -- resistance value

vmax: real := real’high; -- max. voltage

pmax: real := real’high);-- max. power

port (terminal p, m: electrical);

end entity resistor;

architecture simple of resistor is

quantity v across i through p to m;

quantity pwrd: real;

attribute stress_average of pwrd: quantity is

soa_value(“Average power dissipation”, pmax);

attribute stress_winmax of pwrd: quantity is

soa_value(“Maximum power dissipation”, pmax);

attribute stress_abs_maximum of v: quantity is

soa_value(“Maximum voltage”, vmax);

begin

i == v / r;

pwrd == i * v;

end architecture simple;

Observations: It is possible to have more than

one SOA boundary associated with a quantity.

Using stress_abs_maximum instead of stress_maximum makes the monitoring of the voltage boundary independent of the polarity of the voltage without having to declare an extra quantity.

Since the reference rating is 0 for all three SOA boundaries, there is no need to specify it.

stress related

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Conclusions

• We have demonstrated how measuring the stress by the circuit simulator can be related to the Safe Operating Area.

• Such measurements facilitate the creation of a robust design.

• We analyzed the requirements for measuring the stress.

• We have shown how those requirements can be translated into features of a behavioral modeling language and gave examples for the MAST and VHDL-AMS.

• We have demonstrated how stress analysis can be used to identify components operating under excessive amount of stress.

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Conclusions

• Realization that: Ratings:

• Are attributes of the part; must be provided by the manufacturer. De-rating:

• Are attributes of the design; must be chosen by the system designer based on the application of the design.

SOA modeling:• Must be either incorporated into or facilitated by the modeling

language. Stress Measurement:

• Must be supported by the tool (Simulator).

• Propose a SOA modeling standard for 1076.1 VHDL-AMS committee.