Shawn Luke recently had a "Let's Talk Technical" conversation about simulation for RF design with Mike Engelhardt, renowned physicist and analog engineer for Qorvo. Mike is well known for his contributions to circuit simulation software, including LTspice and QSPICE.
Let's Talk Technical with Qorvo: Advancing RF Circuit Simulation
Shawn Luke, Technical Marketing Engineer | DigiKey
Radio frequency (RF) technology lies at the heart of modern communication, enabling the wireless systems that connect our devices, homes and industries. From high-speed 5G networks and satellite communications to IoT devices and automotive radar systems, RF systems power the invisible networks shaping our world. For engineers, understanding RF design and its challenges is essential to pushing the boundaries of what’s possible in electronics.
RF design is a unique and complex field, demanding a blend of theoretical knowledge, practical expertise and creative problem-solving. Unlike digital systems, where signals are binary and predictable, RF operates in a dynamic analog domain, where even minor adjustments can have significant effects on performance.
There have been significant changes in RF design over the last 50 years. As we usher in a new generation of RF designers, we’re seeing modern designs focus more on simulation to optimize performance, model parasitics, and ultimately reduce development times. At DigiKey, our origins in ham radio have evolved into helping engineers working with RF systems consider factors like signal integrity, power management and noise reduction while navigating real-world constraints such as size, cost and regulatory compliance. DigiKey’s support of the RF community continues by providing excellent hardware components, including chips, antennas and RF connectors.
I recently had a “Let’s Talk Technical” conversation about simulation for RF design with Mike Engelhardt, renowned physicist and analog engineer for Qorvo. Mike is well known for his contributions to circuit simulation software, including LTspice and QSPICE. The below Q&A adapted from our conversation includes discussion of Qorvo’s QSPICE development and how it transforms simulation for RF engineers and mixed-signal designers.
RF engineers have traditionally preferred frequency-domain simulators over SPICE. What drove the need for a new approach?
Traditionally, RF engineers have leaned heavily on frequency-domain or harmonic balance simulators, largely because SPICE tools struggled to simulate spurious harmonic generation and low-level nonlinearities accurately. QSPICE changes the game by enabling precise time-domain simulations, which offer a more complete and realistic view of circuit behavior.
Time-domain simulations allow designers to work directly with the physical bias point and full circuit nonlinearity, capturing real power dissipation and avoiding the assumptions inherent in frequency-domain analysis. While frequency behavior remains central to RF design, QSPICE handles it from first principles—linearizing the actual circuit at its true bias point—making the design flow more accurate and less error-prone.
How does QSPICE manage the challenge of visualizing large amounts of simulation data?
Visualization is often a bottleneck in simulation tools, as traditional SPICE programs generate more data than can be efficiently plotted. QSPICE solves this by leveraging GPU-based graphics technology, the same used in video games. This allows it to render massive amounts of data—up to 100,000 times faster than older tools—without compression or loss of fidelity.
The graphics engine uses triangle tessellation (a technique borrowed from gaming) to plot data with incredible speed and clarity. With this technique, users can view real, uncompressed simulation results and perform accurate FFTs to identify spurious signals and harmonics with ease.
What specific benefits do these bring to RF engineers working on modern designs?
At its core, the value of simulation is about deepening understanding. Simulation helps designers build intuition, explore behavior and refine their designs in ways that are often impossible at the physical bench. For RF circuits, this is especially critical.
Unlike baseband designs, RF circuits are susceptible to PCB parasitics, which are the unintended reactive elements introduced by the physical layout of the printed circuit board. In simulation, designers can turn off these parasitics to isolate and study the core circuit behavior. This ability to decouple parasitic effects allows for a clearer understanding of which elements truly impact performance.
On the bench, this kind of analysis is nearly impossible. You can't "turn off" parasitics in a physical PCB, nor can you easily reroute or modify components embedded in multilayer boards. Simulation offers a clean, flexible environment to test, iterate and learn.
As technology pushes into the gigahertz range, what are the biggest challenges in simulating high-frequency phenomena?
The most significant challenge is accurately identifying parasitics—those unintended inductive, capacitive, or resistive elements that emerge from physical layout. At high frequencies, even small parasitics can dramatically affect circuit behavior. While basic formulas for wire or trace inductance can get you far, the real difficulty arises when lumped element models break down. QSPICE includes built-in models for solenoids, strip lines and straight wires
Due to dispersion, component behavior changes with frequency. Materials like dielectrics and magnetics exhibit frequency-dependent properties at the atomic level, making it nearly impossible to create a broadband lumped model. In such cases, designers must shift their approach from trying to eliminate parasitics to designing defensively, accounting for their inevitable influence.
What has QSPICE done to improve the user experience for RF designers?
Most electronic CAD tools lag in modern user interface design. QSPICE breaks through by focusing on ergonomic, intuitive interaction. For example, instead of modal pop-up dialogs that interrupt workflow, QSPICE uses in-place text editing so users can stay visually and mentally connected to their schematic. Additionally, QSPICE replaces traditional toolbar navigation with context-sensitive right-click menus, minimizing mouse movement and keeping users focused. This design philosophy prioritizes flow and efficiency, helping engineers stay immersed in their design process without unnecessary distractions.
What does QSPICE change for mixed-signal designers?
QSPICE offers exceptional mixed-mode simulation performance, enabling advanced features for all designers. It allows native compilation of C++ and Verilog directly into executable object code, which runs during simulation. This results in digital logic being evaluated faster than real hardware—except when simulating a high-frequency signal (like 5 GHz) on a processor running less than 5 GHz.
The process is simple: drag a box onto the schematic, type your code and run. QSPICE includes all necessary compilers out of the box, streamlining the experience and empowering designers to simulate complex analog-digital interactions with ease and speed.
Conclusion
For RF engineers tackling GHz-level challenges and mixed-signal designers needing integrated logic simulation, QSPICE represents a major step forward in circuit simulation technology.
At DigiKey, we recognize the unique challenges engineers face in the RF domain. Designing high-performance systems requires access to the right components, tools and resources, as well as a strong grasp of the principles that govern RF behavior. By bringing together innovative products and expert support, we aim to help engineers overcome these challenges and develop solutions that meet the demands of today’s connected world. For more information on simulation for RF design, check out the episode of Let's Talk Technical to hear more from Mike Engelhardt of Qorvo, along with e-magazines, articles and other resources on DigiKey.com.
Shawn Luke is a technical marketing engineer at DigiKey. DigiKey is recognized as the global leader and continuous innovator in the cutting-edge commerce distribution of electronic components and automation products worldwide, providing more than 17 million components from over 3,000 quality name-brand manufacturers.
The content & opinions in this article are the author’s and do not necessarily represent the views of ManufacturingTomorrow
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