Circuit Simulation Shapes Up for Energy-Conscious Design

Author:
Jeff Strang, GM Power Management, and Surinder P. Singh, Sr. Manager, Customer Design Tools, Qorvo, Inc.

Date
04/23/2024

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Simulation and modeling tools have evolved from rudimentary beginnings

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Figure 1: Improved I-V curves

­SPICE (Simulation Program with Integrated Circuit Emphasis) was created at Berkeley in 1970 and has become the reference for integrated circuit simulators, receiving an IEEE Milestone in Electrical Engineering and Computing award in 2011. The ability to model components and simulate their behavior has empowered generations of engineers; not only chip designers but those developing all kinds of circuits and systems. They have been able to rapidly prototype and iterate their designs, quickly establish performance predictions under different operating conditions - optimizing before building the hardware, a costly and resource-intensive proposition - and generally analyze and optimize their designs more quickly and effectively to accelerate successful project completion.  Simulation allows designers to design and optimize before building the hardware, a more costly and resource-intensive proposition.

Tackling Design Complexity

Although simulation tools have evolved to offer numerous improvements, the demands placed on engineers continue to intensify. Today’s system designs are becoming increasingly complex as the world looks to the electronics and semiconductor innovators to solve today’s challenges. Performance expectations have increased, design margins have narrowed, and time-to-market pressure is perennially more critical.

In particular, today’s power designs are increasingly turning to more advanced architectures including high-efficiency topologies and digital power. Hence engineers are now looking to do larger amounts of digital simulation with AI driving increasingly complex designs alongside power and RF work.

Improvements in Simulation Tools

It is true that some of the improvements in simulator capabilities, which many engineers enjoy today, are enabled by the vastly greater computing power now sitting on their desktops. Key developments include solid-state drives that deliver high storage density and fast response, faster processors generally, and the adoption of GPUs in particular. This move toward heterogeneous processing is a widespread trend throughout the industry. In SPICE engines they offer a close to 100,000-fold speed-up in the time taken to render data and so enabling the tools to display the results quickly and accurately on screen. It’s now possible to display every data point in waveforms that would have been impossible to render at such a detailed level in the past.

On the other hand, there have been further enhancements intrinsic to the tools themselves, including Improvements to the SPICE modeling engine that ensure greater accuracy as well as increased power and analog capabilities.

In addition, there are notable bug fixes. Some commercial tools have contained implementation errors that can trace back to the original Berkeley SPICE code, allowing discontinuities in the I-V curves of semiconductor devices. Qorvo’s development of QSPICE™ circuit simulator provided an opportunity to correct these errors and unleash the real power of the SPICE engine for analog circuit simulation. With these discontinuities now eliminated, simulations can complete more accurately and more reliably -a significant step forward towards faster and more reliable simulation.

New Digital Capabilities

Also new is the ability to simulate massive amounts of digital, which makes it possible to handle schematic capture and compile and run digital code. This is not usually possible with easily accessible and affordably priced tools, much less free tools. Historically, SPICE tools have been aimed purely at analog circuit simulation. Now it is possible to click a button to compile Verilog or C++ code and quickly be running high-speed digital simulation along with analog simulation.

This can help overcome some of the challenges with developing applications leveraging AI (Artificial Intelligence) and ML (machine learning). An engineer can take the code base for, say, a RISC-V processor, which is open source, load it into a QSPICE code block, and compile it. They can then load in code for a TinyML algorithm that runs on RISC-V and simulate it next to their motor driver and their motor model to run the analog simulation together.

Another example involves developing systems to make batteries charge more effectively, or to maximize the number of charge cycles. It’s now possible to put the battery model in and quickly start running machine-learning algorithms. So, power design challenges can be solved without needing to build a physical test bench or handle the additional concerns that come with experimenting on large motors or batteries.

Moreover, the possibility for time-step control further enhances the scope for designers to tackle power design challenges. Timestep control helps accurately and efficiently simulate power electronic circuits, facilitating insights into fast-switching events, nonlinearities, and dynamic behavior.

With timestep control, the simulation can automatically adjust for smaller time intervals during critical events to capture dynamic response or noise and ripple effects. It can help analyze the system’s transient response or the fast rise and fall times of switching waveforms. While setting larger timesteps during slower variation periods can reduce computational costs, the flexibility to use smaller time steps during fast-switching events yields more accuracy.

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Fig 2a: Power Dissipation and timestep circuit

 

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Fig 2b. and 2c. Power dissipation and timestep

 

Meeting Demands for Accuracy

While the systems to be simulated are becoming increasingly complex, the demand for accurate analysis is also intensifying. Power analysis is a particularly pertinent example. Power consumption is critically important both from the product performance standpoint - influencing metrics such as EV (electric vehicle) range, runtime of cordless tools, renewable-energy cost per Watt - as well as sustainability. Consumption of many devices is now in the order of nanoamps. Hence, in addition to the accuracy, achieving suitable resolution is also extremely challenging.

Closer to Reality

While issues like complexity and accuracy continue to become more challenging, some demands remain the same. Users want the results to be as close to real life as possible, and tool developers have the perennial ambition to make it so.

And all this needs to be achieved without incurring excessive demand for system resources such as storage and simulation execution time. The QSPICE simulator can perform digital simulations at a high speed because the Verilog or C++ source code that describes the digital logic is compiled into native desktop processor object code.

Conclusion

Circuit simulation has come a long way but will always be chasing a target that is not only moving but also accelerating. The journey will never end and progress is self-fueling. As the tools enable technical development, the results of that development – especially faster and more efficient processors – can further improve the process of modeling. Now adding capabilities such as massive digital simulation, as well as enhancing accuracy and general improvements to the SPICE engine, tools like the QSPICE simulator are equipped to support state-of-the-art projects in fields such as power conversion, e-mobility, and AI.

 

Qorvo

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