Mixed-Signal Design Blogs

Cadence^® Spectre^® AMS Designer is a high-performance mixed-signal simulation system. The ability to use multiple engines and drive from a variety of platforms enables you to "rev up" your mixed-signal design verification and take the checkered flag in the race to the market. The Start Your Engines! blog series will provide you with tips and insights to help you tune up your simulation performance and accelerate down the road to productivity.

 

Bonjour!

In this post, I will explain how you could speed up your mixed-signal verification with the Spectre X simulator. I will also cover how Spectre X can be set up for use in the AMS Designer flows. The designers in charge of mixed-signal verification are always looking for methods to speed up the test bench simulation run rate for a SoC or block.

First, let me introduce you to the Spectre X simulator and then I will explain its usage with the Spectre AMS Designer simulator. Finally, I will summarize the usage and benefits.

Spectre X Simulator

The Spectre simulator has been there in the EDA industry for over 25 years. It is a powerful platform for computing accurate electrical simulations.

Spectre X was introduced in 2019 and it offers the best of both worlds: high capacity and better accuracy.

Designers can use Spectre X for pure electrical circuit as well as mixed-signal test benches.

The designers who have used Spectre with the Accelerated Parallel Simulator (APS, +aps) mode would remember the errpreset option. It controls the accuracy and speed. Errpreset selects a reasonable collection of parameters' settings. The possible values are liberal, moderate (default), and conservative. You could also specify additional settings for post-layout and enable the Fast APS (++aps) as well.

Spectre X is a multi-thread simulation mode.

The Spectre R&D team simplified the settings in Spectre X by keeping only one command-line option, +preset=value. The possible values for this option are cx, ax, mx, lx, and vx, with cx being the most accurate mode and vx the highest performing mode. Spectre X inherits the settings conservative, moderate, and liberal from APS, and also provides two additional modes:

• ax: to be used when you want a higher speed than cx but also require high-precision. This mode provides a good performance boost.
• vx: to be used when you want to compute a fast verification of a huge and complex design.
   

The following figure compares the different preset values for performance and accuracy.

 

Spectre X by itself detects if the circuit is a pre-layout or post-layout case and smartly applies the possible optimization.

Usage of the Spectre X Simulator with Spectre AMS Designer

Spectre X is valuable when we instantiate transistors with or without parasitics R or C instances in the Device Under Test (DUT).

Languages Supported with Spectre AMS Designer Simulator with Spectre X

You can also instantiate the test bench or DUT models written in the languages listed in the figure below. In addition, the SoC power intent can be described in LP1801 (UPF) or CPF.

 

Setting the Spectre X Simulator in ADE Explorer

In the ADE Explorer environment, Spectre X can be set up in two steps. First, select Enable AMSD flexible release matrix from ADE > Simulation > Netlist and Run Options form.

  Then, select Spectre X from ADE > Setup > High-Performance/Parasitic Reduction Options form.

 

Setting Spectre X in the Command-Line Flow

In the command-line flow, also named as the AXUM flow, you can enable Spectre X with the following command:

–spectre_args “+preset=cx | ax | mx | lx | vx (default mx)

For example:

xrun –spectre_args “+preset=lx  –mt=16” *.sv *.v *.vams *.svams amscf.scs probe.tcl …

With –mt=number_threads, we define the maximum number of threads Spectre can use.

Note: After the simulation is launched, to verify if Spectre X is enabled, check for the following message in the simulator xrun.log:

Notice from Spectre during initial setup.

  Spectre X preset=lx Enabled

Usage Summary

Spectre X is simple to set up, with the 5 smart presets that provide the right balance of accuracy and performance.

• Use cx when a golden reference is required.
• Use ax for high-precision analog applications.
• Use mx for most analog applications. This is the default mode.
• Use lx for power management and other relaxed analog application circuits.
• Use vx for custom IC verification.

Benefits Summary

• 2X to 10X performance improvements across a large spectrum of designs while maintaining the Spectre golden accuracy.
• Up to 5X increased capacity to overcome unaddressed simulation challenges.
• Scalable and massively parallel simulation for today’s cloud infrastructure.
• Supports highly distributed single or multi-machine multi-cores simulation. 

If you are interested in more details about Spectre X, you could read the Custom IC Design Blogs written by Stefan, Spectre Tech Tips: Spectre X Update.

I wish you a happy experience with Spectre X-enabled analog and mixed-signal fast simulations…

~ Andre Baguenier

 

Related Resources

• One-Stop Knowledge Resource for Mixed-Signal Verification
• Spectre AMS Designer Product Page

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

About Start Your Engines

The Start Your Engines! series brings you blog posts from several analog/mixed-signal subject matter experts on a variety of topics, such as introduction to the new features in Spectre AMS Designer, tips for enhanced understanding of existing features, and much more. To receive notifications about new blogs in this series, click Subscribe and submit your email ID in the Subscriptions box.