This is a sponsored article brought to you by Siemens.
Layout-versus-schematic (LVS) comparison is a critical step in integrated circuit (IC) design verification that ensures that the circuit’s physical layout matches its schematic representation. The primary goal of LVS is to verify the correctness and functionality of the design. Traditionally, LVS comparison is performed during checkout validation, where dedicated tools compare layout and schema data to identify any inconsistencies or errors. However, discovering errors at the sign-off stage leads to time-consuming iterations that delay design closure and time-to-market. Although an early-stage LVS comparison could alleviate these problems, it often generates millions of error results due to the incomplete state of the design.
To address these challenges, we developed a left-shift methodology that allows designers to perform LVS comparisons earlier in the design flow. By incorporating LVS checks at earlier stages, design teams can catch errors earlier and reduce the number of iterations required during sign-off. Let’s take a deeper look at how the left-shift LVS validation approach can increase designer productivity and speed up validation.
The Caliber nmLVS™ Recon Compare solution introduces an intelligent left-shifting process for fast and accurate LVS comparisons earlier in the design cycle. It automates the black boxing of incomplete blocks and facilitates automatic port mapping, enabling designers to achieve faster LVS iterations on early-stage designs.
Challenges of traditional LVS verification
In the traditional LVS verification process, designers must verify the layout against its schematic representation to ensure that the final product performs as intended. Since all design blocks must be completed and ready for final comparison, the validation teams wait to perform thorough checks until the signature stage. Any errors discovered during this last-stage LVS run can trigger further validation iterations, resulting in wasted time and resources. Designers are then caught in a cycle of restarting the LVS process each time a patch or update is implemented, resulting in a logout bottleneck.
Designers could have done the LVS comparison earlier, although in the early design stages many blocks are not yet finished, making a comprehensive LVS comparison impractical. Running LVS on incomplete designs can generate millions of error messages, many of which are unusable because they come from unfinished parts of the layout. This overwhelming number of outcomes makes it difficult to pinpoint real design issues, making traditional LVS methods impractical for early-stage validation.
As shown in Figure 1, the validation flow can be more complex when design blocks are completed at different times, resulting in multiple iterations of validation checks as each block is integrated into the overall layout.
fig. 1: Design verification cycle with blocks at different levels of completion.
Swipe left for early LVS verification
Implementing the shift-left methodology for LVS verification means performing a layout vs. schematic comparisons earlier in the design cycle, before all blocks are completed. To do this, the flow must support flexibility in dealing with incomplete designs and allow for more targeted validation of critical blocks and connections.
One way to do this is through automation techniques such as black box and port mapping. By abstracting the internal details of incomplete blocks while preserving their external connectivity information, the verification flow can be tailored to focus on the interactions between the completed and incomplete parts of the design. Automated port mapping, on the other hand, ensures that all external connections between the layout and the schematic are properly aligned for accurate comparisons at an early stage.
A new approach to early LVS verification
An advanced methodology for early stage LVS verification uses these automated processes to speed up the left turn verification process. For example, an intelligent black box of incomplete blocks can significantly reduce the number of error results generated, making it easier for verification teams to identify real connectivity issues between blocks.
The Shift-left flow also benefits from using a powerful comparison engine that can quickly and efficiently analyze layout and schema data, skipping unnecessary operations and calculations. This approach focuses on the most difficult problems early in the flow, resulting in fewer bugs discovered at the signature stage and ultimately speeding up proposal closure.
The flows shown in Figure 2 show how this left-shift methodology streamlines the verification process by reducing unnecessary steps and focusing on critical design issues.
fig. 2: Traditional full flow LVS with all steps (left) vs. caliber nmLVS Recon flow (right).
Advantages of early LVS cf
Adopting the Shift-left methodology for LVS verification offers several key benefits to semiconductor design teams:
Early detection of errors: By performing LVS benchmarking earlier in the design flow, errors can be identified and resolved before they are deeply embedded in the design. This proactive approach reduces the risk of costly rework and minimizes the number of iterations needed during signing.
Expedited design verification: Automating the comparison process simplifies design verification and allows designers to efficiently identify and resolve issues even when not all blocks are complete. This results in faster overall circuit verification and reduces the time and effort required for manual inspection.
Improved collaboration and tuning: With a centralized platform for design validation and feedback sharing, early stage LVS validation supports collaboration between design teams. Engineers can more effectively isolate problems and provide insights to their colleagues, improving overall design quality.
Increased design reliability: Ensuring alignment between layout and schematic representations from the early design stages increases confidence in the correctness of the final product. By the time a proposal is approved, most of the critical connectivity issues have already been resolved.
Real world applications
Caliber nmLVS Recon has demonstrated significant benefits in real-world design projects, including 10x runtime improvements and 3x lower memory requirements. For example, the verification team at Marvell improved their LVS flow throughout the design cycle with Caliber nmLVS SI, achieving faster verification times and better efficiency.
Conclusion
Moving LVS comparison tasks earlier in the design flow offers significant benefits to IC design teams. Our new top-level approach to early LVS comparison automates black boxing and port mapping so designers can perform comprehensive validation even when not all blocks are complete. This speeds design verification, improves collaboration, and increases design confidence in semiconductor design workflows.
For more information, download my recent white paper “Speed up design verification with Caliber nmLVS Recon Compare”.
