Nanometer Circuit RF Verification Challenges

Migrating to smaller process geometries brings benefits such as lower power and higher performance. However, RF designers working in nanometer CMOS face mounting challenges, including reduced voltage headroom, increased circuit nonlinearity, and greater sensitivity to noise.

Design complexity is further exacerbated by rising parasitic resistance and capacitance. Simulating only the schematic design without layout effects creates significant risk, as the model no longer reflects real analog behavior. This makes accurate post-layout simulation increasingly difficult.

To address these issues, designers must incorporate layout effects early in the design phase and employ digital calibration and compensation techniques to optimize both performance and power consumption. A comprehensive verification strategy must also account for process variations, voltage and temperature effects, and exhaustive sweeps across power, frequency, and tuning parameters before final tape-out.

Time-Domain and Frequency-Domain Analysis Methods

Two analysis methods dominate modern RF verification. Shooting Newton, a time-domain approach, is well-suited for periodic circuits with sharp transitions. Harmonic Balance, a frequency-domain method, excels in circuits with linear to moderately nonlinear behavior, high dynamic range requirements, or reliance on frequency-domain models such as S-parameters.

Multi-tone simulations are essential in transceiver design (Figure 2), where circuits must process multiple unrelated signals simultaneously. Time-domain analysis struggles here, as the smallest time step must match the highest frequency, leading to prohibitive runtimes. By contrast, Harmonic Balance handles multi-tone scenarios efficiently, offering faster, more accurate results when frequency spectra are sparse.

However, simulation runtime grows rapidly with the number of tones. For example, moving from a single-tone to a three-tone simulation can increase runtime up to ninefold due to the additional intermodulation terms (IM2, IM3) required for accuracy. For advanced finFET designs, only state-of-the-art multi-threaded solvers can make such simulations practical.

AFS: A Nanometer-Scale RF Verification Platform

Analog FastSPICE (AFS) provides both Shooting Newton and Harmonic Balance engines, supporting single- and multi-tone analyses, as well as Noise (HBNOISE), AC (HBAC), Stability (HBSTB), Scattering Parameter (HBSP), and Transfer Function (HBXF) simulations.

For linear and near-linear circuits, AFS Harmonic Balance solvers deliver superior accuracy and convergence speed, enhanced by automated intelligence algorithms. Certified by leading foundries, the AFS Platform provides nanometer SPICE accuracy at over five times the speed of traditional SPICE, and more than twice that of parallel SPICE simulators. With its new eXTreme technology, AFS delivers up to a 10× performance boost for large post-layout designs.

The AFS Platform supports designs with over 50 million elements and enables the fastest mixed-signal simulations through Symphony. It also provides the industry’s most comprehensive full-spectrum noise analysis and integrates seamlessly with Solido Variation Designer for variation-aware coverage using far fewer simulations than brute-force methods—without compromising accuracy.

Nanometer RF verification requires extensive sweeps, corner cases, and Monte Carlo analyses. AFS HB leverages multi-threading for additional speedup and, combined with Solido Variation Designer, delivers efficient coverage across all environmental corners. In recent benchmarks, AFS HB consistently achieved stringent accuracy targets for critical RF metrics such as IP2, IP3, and P1dB. It delivered an average speedup of 2.6× for post-layout designs and 1.8× for pre-layout designs compared to other commercial solutions, while being the only tool to converge reliably on the most demanding multi-tone post-layout simulations (Figure 3).

Conclusion

As high-performance computing, communications, autonomous driving, and IoT continue to evolve, RF technology has become truly ubiquitous. To ensure silicon-accurate results in this increasingly complex landscape, advanced RF analyses are essential.

The Analog FastSPICE Platform delivers the industry’s most accurate, comprehensive, and high-performance verification capabilities in a single executable. Foundry-certified at the most advanced process nodes, AFS provides the scalability and accuracy needed for today’s nanometer RF and mixed-signal designs—ensuring reliable performance for the RF technology that powers our daily lives.

YuLing Lin is a solutions architect at Mentor, a Siemens business.