STEP 10: Multi-Mode Multi-Corner (MMMC) STA
This step explains how Static Timing Analysis is extended to cover all realistic operating scenarios of a design. Modern digital designs do not operate in a single mode or under a single condition. MMMC STA ensures that timing is correct across all functional modes and across all process, voltage, and temperature variations.
What is Multi-Mode Multi-Corner STA
Multi-Mode Multi-Corner STA is a timing analysis methodology in which the design is analyzed across multiple operating modes and multiple PVT corners simultaneously. Each combination of mode and corner represents a unique timing scenario that must meet all timing requirements.
MMMC STA is the industry-standard approach for timing signoff in modern ASIC designs.
Modes in STA
Modes represent different functional states of the design. Each mode may have different active clocks, constraints, and timing behavior.
Functional Mode
Functional mode represents the normal operating condition of the design during real use. All functional logic is active, and clocks operate at their intended frequencies.
Timing analysis in functional mode ensures that the design meets performance requirements during normal operation.
Scan Shift Mode
Scan shift mode is used during manufacturing test. In this mode, scan chains are shifted using a scan clock, which is usually much slower than the functional clock.
Timing analysis in scan shift mode ensures that data shifts correctly through scan chains without setup or hold violations under the scan clock.
Scan Capture Mode
Scan capture mode occurs during test when scan data is captured into flip-flops using one or more functional clock pulses.
Timing analysis in scan capture mode ensures that the capture operation meets timing requirements under test conditions, which can differ from normal functional operation.
Corners and Modes Matrix
In MMMC STA, timing analysis is performed for every combination of mode and corner. This creates a matrix where each row represents a mode and each column represents a PVT corner.
For example, functional mode is analyzed at slow, typical, and fast corners. Scan shift and scan capture modes are also analyzed across relevant corners.
This matrix ensures that no timing scenario is missed and that the design is robust across all operating conditions.
Why MMMC STA is Necessary
A design may pass timing in functional mode but fail in scan mode. Similarly, a design may pass timing at one corner and fail at another. MMMC STA ensures that all such cases are detected and resolved.
Without MMMC analysis, timing closure would be incomplete and potentially unsafe for silicon manufacturing.
Tools Used for MMMC STA
PrimeTime and Tempus are industry-standard tools used for MMMC STA. These tools allow designers to define multiple modes, multiple corners, and analyze them efficiently in a single environment.
They support advanced features such as variation modeling, signal integrity analysis, and signoff-quality timing checks across the full MMMC space.
Goal of MMMC STA
The goal of this step is to develop the ability to clearly explain MMMC STA in interviews and technical discussions. Understanding MMMC means being able to explain why timing must be checked across multiple modes and corners and how modern STA tools ensure complete and reliable timing signoff.