Start Your Engines: Speed Up your Analog Mixed-Signal Verification

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 your simulation performance and accelerate down the road to productivity.

Bonjour!

Today's complex analog mixed-signal SoCs and memory design verifications need high accuracy and fast simulation.
In this post, I will cover how you can speed up your analog mixed-signal verification by leveraging the Spectre FX simulator. Your complex SoC designs or analog IPs may include several thousands or millions of transistors, resistors, capacitors and inductors. Some blocks could even operate at very high frequencies, for example, in the range of 50 gigahertz. Some other analog or digital blocks could operate at lower frequencies with a long time constant.

For such large and complex designs, a scalable and high capacity mixed-signal FastSPICE simulation engine is necessary, compared to a pure SPICE-level mixed-signal simulator, to boost productivity and reduce verification time.
Through this blog, I am going to explain how you can achieve that.

What is Spectre FX?

Cadence Spectre FX is a next-generation FastSPICE simulator. Its architecture offers a performance boost up to 3X or more than the latest FastSPICE simulators, in addition to equal or better accuracy.

The engineer can select between the global accuracy presets for Spectre FX or, in future, a special sub-circuit that applies local scope presets for very limited use.

Figure: Possible values for preset option

Analog Mixed-Signal Languages

Using the Spectre AMS Designer simulator with the Spectre FX supports all 10 of the following languages for mixed-signal verification:
1. VerilogHDL, IEEE Standard
2. SystemC
3. SystemVerilog
4. VHDL
5. Verilog-A, the analog subset of Verilog-AMS
6. Verilog-AMS, Accelera Standard
7. SystemVerilog-AMS (Cadence implementation)
8. VHDL-AMS, IEEE Standard
9. Spectre language for structural netlist
10. SPICE for structural netlist

In addition, the power intent of the Design Under Test (DUT) could be described either using LP1801 (UPF) or CPF standards.
The Spectre FX analog solver has been designed and optimized to quickly resolve non-linear differential equations created by transistors and passive component, as well as the analog context of the mixed-signal behavioral model instances. Spectre FX can partition the analog circuits to compute smaller matrices with different time steps. For circuits with parasitics, Spectre FX can automatically apply accurate and optimized RC reduction.

Analog Mixed-Signal Simulation

During a time domain simulation, the Spectre AMS Designer simulator automatically synchronizes both Spectre FX and Xcelium event solvers. The designer does not have to worry about this. The Interface Elements (IE) that are automatically inserted translate the signals from logic to electrical, electrical to logic, real to electrical, or real to electrical.
The goal of this analog mixed-signal simulation is to predict how the test bench and DUT will behave when different voltages, currents, or digital signals are applied to them. The engineer can test and explore different modes of the DUT operations, identify potential problems in advance, and optimize the performance of the SoC before tapeout.

Usage

To enable Spectre FX for AMS Designer simulations:
1. Choose Setup – High-Performance Simulation.
The High-Performance Simulation Options form is displayed.
2. Select Spectre FX as the simulation performance mode.

The engineer can then select an accuracy preset from the following:

• Vx: Fastest mode for functionality checks
• Lx: Appropriate for timing, voltage and accurate avg current checks
• Mx: High-accuracy timing checks and peak current checks
• Ax: For accurate reference with FastSPICE capacity

Alternatively, use the xrun command -spectre_args +fx to enable Spectre FX as the figure below shows:

For running faster simulations with Spectre FX mode, use the option +preset=vx as follows:
-spectre_args "+fx +preset=vx"

The resulting signals can be plotted either in SimVision as the figure below shows, or, in Virtuoso Visualization and Analysis XL.

Key Benefits

• Ease of use: Out-of-the-box, intuitive use model that requires minimal tuning
• Accuracy: Designers can easily specify accuracy with the preset option
• Scalability: Up to 32 cores with multi-threading to parallelize transient simulations
• Automation: Spectre FX simulator automatically analyzes the analog context of the TC/DUT and intelligently optimizes the analog solver's detailed setting operation for pre- and post-layout test cases by default
• Efficiency: To achieve good simulator accuracy and speed compromise, the designer does not need to spend days on manual setup research
• Productivity: Engineers will notice a decrease in simulation time
• Integrated in the Virtuoso platform and other command-line flows
• Works for simple to complex designs instantiating Verilog-AMS, Verilog-A modules, SystemVerilog-AMS connect modules, and VHDL-AMS entities or architectures with large number of transistors sub-circuits for the latest foundries processes in the world

Conclusion

Using Spectre AMS Designer with Spectre FX is very simple and intuitive. The solution helps speed-up your analog mixed-signal verification.
We have been receiving excellent feedback from the designers and CAD engineers that have enabled it for their simulations. At the last EMEA CadenceLive conference, an AMS designer presented the results to hundreds of attendees and explained how he successfully verified multiple designs in a complex SoC. Spectre AMS Designer with Spectre FX solution was faster than any other simulator. He finished with this message:
“I advise all the conference attendees to immediately use Spectre AMS Designer with Spectre FX. It will reduce your verification time. In addition, the setup is simple and so intuitive.”

Hope you are now excited to try it out yourself! If you need more details, contact your Cadence Support team.

Related Resources

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

About Start Your Engines

The Start Your Engines series will bring to you blog posts from several analog/mixed-signal subject matter experts on a variety of topics, such as introduction to the new features in AMS Designer, tips for enhanced working with 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.

- Andre Baguenier