Spectre Tech Tips: Using Spectre X for RF Analyses

We released Spectre® X-RF  in the SPECTRE 20.1 base release at the end of September 2020. The Spectre X-RF technology integrates the Spectre X engine into the RF analyses of Spectre . In this blog, we  introduce the Spectre X-RF technology.

Spectre X-RF Overview

Spectre X-RF targets the most challenging RF simulation problems, including advanced node designs with complex FinFET (and other) device models and challenging RC-dominated post-layout designs. It includes the following two technologies:

• Single-machine multi-core Spectre X-RF simulations (+preset mode)
• Highly distributed multi-machine multi-core HB simulations (+xdp mode)

In this blog, we'll focus on the single-machine multi-core Spectre X-RF simulation. The distributed harmonic balance (HB) analysis will be discussed in later blogs.

The Spectre X engine was released in SPECTRE 19.1. It has already proven itself for non-RF applications at many customer tapeouts. Starting with SPECTRE 20.1, the Spectre X engine is also available in Spectre RF analyses, where it provides improved RF analyses performance and capacity compared to Spectre APS. Spectre X-RF is based on the same and simple usage model as Spectre with the addition of only the +preset values CX, AX, and MX. LX and VX are usually considered as too aggressive settings for RF analysis. The +preset use model applies to both Spectre X-RF shooting newton and harmonic balance methods. 

Spectre X-RF: Single Option Speed/Accuracy Tradeoff

Spectre X-RF Performance

As known from non-RF applications, the Spectre X engine provides the most performance gains for large, post-layout advanced node designs. The average Spectre X-RF performance gain over Spectre APS is around 2-3x for these designs. The following figure shows the performance gains for a few representative, large, post-layout advanced node designs. A few of these designs used the shooting newton method, while others used the harmonic balance analysis method. 16 cores were used for all simulations. The Spectre X-RF accuracy was confirmed to match the Spectre APS RF accuracy.

Spectre X-RF Performance Gain

In conclusion, Spectre X provides a performance gain in RF analyses, however, the performance gain is typically less compared to a Spectre X transient simulation of the same design.

Spectre X-RF may also provide performance gains for other designs, but the smaller a design is, the more pre-layout character it has; and the more legacy technology it uses, the less performance gain will be observed.

Experience shows that Spectre X provides most performance gains on transient-like simulations. It therefore provides best performance on the PSS shooting and the TSTAB simulation portion, while the gain in other large and small-signal RF analyses may be less.

Note that a performance gain from Spectre X-RF can only be observed on a simulation-intensive RF analysis. If the RF simulation finishes in seconds to minutes, there may not be any performance gain from Spectre X because the time isn’t spent in RF analysis but rather in pre- and postprocessing.

Spectre X-RF Memory Consumption

One challenge for the RF simulation of large, post-layout advanced node designs is the high memory consumption. Spectre X significantly reduces the memory consumption for such designs. The following figure illustrates the memory reduction for the same representative post-layout designs.

Spectre X-RF Memory Reduction

Summary

In this blog, we introduced Spectre X-RF and observed the performance and memory consumption improvements it provides compared to Spectre APS RF. In one of the upcoming blogs, we'll discuss the Spectre X-RF distributed harmonic balance technology.

Related Resources

• Spectre Classic Simulator, Spectre APS, Spectre X, and Spectre XPS User Guide
• Introducing Spectre X
• Spectre ISR What's New release presentations on the Spectre product web page

 You may also contact your Cadence support AE for guidance.

 For more information on Cadence products and services, visit www.cadence.com.

 About Spectre Tech Tips

Spectre Tech Tips is a blog series aimed at exploring the capabilities and potential of Spectre®. In addition to providing insight into the useful features and enhancements in Spectre, this series broadcasts the voice of different bloggers and experts, who share their knowledge and experience on all things related to Spectre. Enter your email address in the Subscriptions box and click SUBSCRIBE NOW to receive notifications about our latest Spectre Tech Tips posts.