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Modeling Safe Operating Area in Hardware Description Languages Leonid Goldgeisser [email protected] Ernst Christen [email protected] Zhichao Deng [email protected] Synopsys Inc 2025 NW Cornelius Pass Rd. Hillsboro, OR, USA, 97124 1.503.547-6118 © 2006 Synopsys, Inc. (1) Leonid B. Goldgeisser, et al. DAC 2007 1 Predictable Success 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 2 Safe Operating Areas • SOA describes the Operating Conditions of the device operating without self-damage • SOA often combines various limitations (Constraints) of a device Duration of the current Junction Temper ature 1.SOA Curves for MJL4281A/4302A 3 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. 4 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. 5 Need for modeling SOA Failure to measure and model stress adequately Reliability suffers Performance drops: •Design is too conservative •Incorporating defense techniques 6 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 7 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). 8 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. 9 Example 10 Circuit Example, Cont’d 11 Circuit Example, Results 12 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. 13 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. 14 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) Unique Identifier Group Identifier Descript. String Measured Measure Waveform Type Allowable Reference Rating rating 15 Example of Specifying SOA Boundaries using the MAST Language template resistor p m = r, vmax, pmax control_section { Name Group Descr. stress_measure(pavg, power, electrical p, m number r “Average power dissipation”, number vmax = undef pwrd, average, pmax) number pmax = undef stress_measure(pmax, power, { rating Measure “Maximum power dissipation”, val i i pwrd, winmax, pmax) val v v stress_measure(vmax, voltage, val p pwrd “Maximum voltage“, abs(v), max, vmax) v = v(p,m) i=v/r pwrd = v * i } } i(p->m) += i 16 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. 17 SOA Modeling with VHDL-AMS, example. package soa is -- Declare another set of attributes that -- Declare a record type to hold all aspects -- compares the absolute value of the quantity -- of an SOA boundary -- with the rating type soa_boundary is record attribute stress_abs_minimum: soa_boundary; description: rating: string(1 to 32); real; attribute stress_abs_maximum: soa_boundary; attribute stress_abs_peak: reference_rating: real; soa_boundary; attribute stress_abs_average: soa_boundary; end record; attribute stress_abs_rms: -- Declare the attributes, one for each attribute stress_abs_winmin: soa_boundary; -- measurement method, that compares the attribute stress_abs_winmax: soa_boundary; -- value of the quantity with the rating -- Declare a function to help defining an attribute stress_minimum: soa_boundary; -- SOA boundary attribute stress_maximum: soa_boundary; function soa_value(description: string; attribute stress_peak: rating: real; soa_boundary; attribute stress_average: soa_boundary; attribute stress_rms: soa_boundary; attribute stress_winmin: soa_boundary; soa_boundary; reference_rating: real := 0.0) return soa_boundary; end package soa; attribute stress_winmax: soa_boundary; 18 SOA Modeling with VHDL-AMS library ieee; Observations: use ieee.electrical_systems.all; It is possible to have more than use work.soa.all; entity resistor is generic (r: real; -- resistance value vmax: real := real’high; -- max. voltage 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); stress related pmax: real := real’high);-- max. power 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. begin i == v / r; pwrd == i * v; end architecture simple; 19 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. 20 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. 21