Library Characterization Tidbits: Understanding the Liberate AMS Command-Line Flow

11 Jun 2020 • 3 minute read

Hello Readers,

Characterizing mixed-signal macros to create instance-specific models for timing, power, and noise can be a challenging task. The Cadence characterization portfolio offers Liberate AMS, a mixed-signal characterization solution that enables you to take care of your characterization needs.

You can perform characterization with Liberate AMS either from the command line or the Virtuoso GUI as talked about in the Exploring Intuitive Means to Characterize Large Mixed-Signal Blocks blog. This blog covers the Liberate AMS command-line flow and a related Rapid Adoption Kit (RAK) that helps you understand this flow.

The following diagram depicts the Liberate AMS command-line flow:

Liberate AMS Flow

As shown in this diagram, the Liberate AMS control files amschar.tcl and template.tcl, along with the netlist and model files, are passed to the tool. Using these inputs, Liberate AMS has two methods for characterizing a block:

Static flow: The default method (shown in the green block)
Dynamic flow: The backup method (shown in the purple block)

In both the flows, the tool operates in a server-client model. The server decides which arcs must be characterized and then passes these arcs to the clients for characterization by Spectre APS. After the characterization is complete, the server gathers the results from the clients and places them in a database called the LDB (Liberate DataBase), from which different Liberty file formats (NLDM, CCS, and so on) can be written.

Liberate AMS: Command Line Flow (RAK)

This RAK demonstrates the capabilities of Liberate AMS using various examples. Characterization flow of six different IP blocks is covered in the following sections of this RAK:

amsDAC: Covers the characterization of an 8-bit current steering digital-to-analog converter.
amsADC: Describes the characterization of an 8-bit successive approximation analog-to-digital converter.
amsRegInv: Explains the use of regulators when used as part of logic circuits.
amsPLL: Covers the characterization of an integer phased-lock loop with both feedback and output dividers.
Serializer: Covers the characterization of an 8:1 serializer.
DeSerializer: Explains the characterization of a 1:8 deserializer.

Each section provides detailed information on the operation of the IP blocks using top-level Virtuoso testbenches and the simulation requirements to verify if the design is working as expected. Which all arcs must be characterized and the required Liberate AMS setup is also explained. Then the steps to run the characterization and analysis of the output files is also well covered.

In addition to demonstrating the use of the command-line flow for IP blocks, the RAK also includes an appendix covering the following information:

Using the existing .lib file to generate template.tcl
Understanding observation windows in dynamic mode
Overview of characterization for those new to the field
Overview of the various sections of a Liberty (.lib) file

This is just a summary of the information covered in the RAK; for detailed information check out the RAK on the Cadence Support portal .

Jommy Thomas

Related Resources

For more information about working with the Liberate Variety statistical characterization solution, see the following documents:

About Library Characterization Tidbits

Library Characterization Tidbits is a blog series aimed at providing insight into the useful software and documentation enhancements in the LIBERATE release. In addition, this series would broadcast the voices of different bloggers and experts, who would share their knowledge and experience about all the tools in Liberate Characterization Portfolio. To receive notifications about the new blogs in this series, click Subscribe and submit your email ID in the Subscriptions box.