Analog Layout Automation Research Articles

Hierarchical Analog and Mixed-Signal Circuit Placement Considering System Signal Flow

Placement is a critical step in layout automation for analog and mixed-signal (AMS) integrated circuits (IC). It determines the proximity of devices and influences the wiring topology, significantly impacting post-routing parasitics and coupling capacitance. Existing analog placement techniques mainly focus on geometric constraints in analog building blocks. However, there yet lacks an effective way to consider the system-level signal flow for sensitive AMS circuits. Leveraging prior knowledge from schematics, we propose considering the critical signal paths in automatic AMS placement. A multilevel analog layout automation flow is further developed to reduce manual efforts in synthesizing hierarchical AMS circuits. Experimental results demonstrate the efficiency and effectiveness of our proposed framework with a 22.8% reduction in routed wirelength compared to state-of-theart AMS placer and a 10 dB improvement in the signal-to-noiseand-distortion ratio (SNDR) for an ADC.

Generating the Generator: A User-Driven and Template-Based Approach towards Analog Layout Automation

Various analog design automation attempts have addressed the shortcomings of the still largely manual and, thus, inefficient and risky analog design approach. These methods can roughly be divided into synthesis and procedural generation. An important key aspect has, however, rarely been considered: usability. While synthesis requires sophisticated constraints, procedural generators require expert programmers. Both prevent users from adopting the respective method. Thus, we propose a new approach to automatically create procedural generators in a user-driven way. First, analog generators, which also create symbols and layouts, are utilized during schematic entry to encapsulate common analog building blocks. Second, automatic code creation builds a hierarchical generator for all views with the schematic as input. Third, the approach links the building block generators with the layout through an object-oriented template library that is accessible through generator parameters, allowing the user to control the arrangement. No programming is required to reach this state. We believe that our approach will significantly ease the transition of analog designers to procedural generation. At the same time, the templates allow for a “bridge” to open frameworks and synthesis approaches so that the methodologies can be both better spread and combined. This way, comprehensive frameworks of both synthesis-based and procedural-based analog automation methods can be built in a user-driven way, and designers are enabled to gain early layout insight and ease IP reusability.

Analog layout retargeting using geometric programming

To satisfy the requirements of complex and special analog layout constraints, a new analog layout retargeting method is presented in this article. Our approach uses geometric programming (GP) to achieve new technology design rules, implement device symmetry and matching constraints, and manage parasitics optimization. The GP, a class of nonlinear optimization problem, can be transferred or fitted into a convex optimization problem. Therefore, a global optimum solution can be achieved. Moreover, the GP can address problems with large-scale variables and constraints without setting an initialization variable range. To meet the prerequisites of the GP methodology for analog layout automation, we propose three kinds of mathematical transformations, including negative coefficient transformation, fraction transformation, and maximum of posynomial transformation. The efficiency and effectiveness of the proposed algorithm, as compared with the other existing methods, are demonstrated by a basic case-study example: a two-stage Miller-compensated operational amplifier and a single-ended folded cascode operational amplifier.

Multilevel symmetry-constraint generation for retargeting large analog layouts

The strong impact of layout intricacies on analog-circuit performance poses great challenges to analog layout automation. Recently, template-based methods have been shown to be effective in reuse-centric layout automation for CMOS analog blocks such as operational amplifiers. The layout-retargeting method first creates a template by extracting a set of constraints from an existing layout representation. From this template, new layouts are then generated corresponding to new technology processes and new device specifications. For large analog layouts, however, this method results in an unmanageable template due to a tremendous increase in the number of constraints, especially those emerging from layout symmetries. In this paper, we present a new method of multilevel symmetry-constraint generation by utilizing the inherent circuit structure and hierarchy information from the extracted netlist. The method has been implemented in a layout-retargeting system called Intellectual Property Reuse-based Analog IC Layout (IPRAIL) and demonstrated 18 times reduction in the number of symmetry constraints required for retargeting an analog-to-digital converter layout. This enables our retargeting engine to successfully handle the complexities associated with large analog layouts. While manual relayout is known to take weeks, our layout-retargeting tool generates the target layout in hours and achieves comparable electrical performance