are depicted in different shades of gray in Fig. 1(b). (a). (b). Fig. 1 Gilbert mixer mask layout (a) and enhanced shape function with abstract module placement (b).
Plantage+, Fully Automated, Industrial Level Analog Layout Tool Martin Strasser, Helmut Graeb, and Ulf Schlichtmann {strasser, graeb, ulf.schlichtmann}@tum.de Institute for Electronic Design Automation, Technische Universit¨at M¨unchen, Munich, Germany www.eda.ei.tum.de
Abstract The presented tool “Plantage+” significantly speeds up the layout process of analog circuits. Integrated in an industrial IC design environment, the tool recognizes basic building blocks in the circuit. It automatically sets up constraints and generates layouts using a deterministic algorithm.
1 Introduction Due to the variety of constraints, designing the layout of an analog circuit is a complicated task. Compared to the degree of automation of digital circuits, analog circuits are a manual task for the designers. Therefore, the analog layout design process can be timeconsuming and error-prone. Plantage+ is focusing on the first part of the layout step, the placement of the components. During the last decades, different approaches were proposed for analog layout automation. Most of them use Simulated Annealing, considering a subset of common analog layout constraints. These approaches operate either on absolute coordinates of the modules, or on topological representations, like sequencepairs [3] and B∗ -trees [1]. Plantage+ is based on a completely deterministic approach [4], which uses B∗ -trees [1] to generate placements. It considers all common analog layout constraints, such as symmetry, alignment, matching, common centroid, and proximity constraints. In contrast to other approaches, Plantage+ is also capable of handling wells and guard rings.
2 Demonstration In our demonstration of Plantage+, we illustrate how to generate a placement for an analog circuit in a very fast way. As an industrial level analog layout tool, Plantage+ is fully integrated into the widely used R Cadence° Design Framework. As an example, a standard Gilbert mixer cell, designed using a 0.35µ technology, is shown in Fig. 1. For the differential pairs, which are used for mixing the two input frequencies, as well as for the load resistors, matching is ensured using a common centroid layout style [2]. The groups sharing a common centroid are depicted in different shades of gray in Fig. 1(b).
(a)
(b)
Fig. 1 Gilbert mixer mask layout (a) and enhanced shape function with abstract module placement (b) generated by Plantage+. The circuit is placed symmetrically to enable symmetric routing. These constraints are set up automatically, based on a structure recognition approach. To reduce substrate coupling, guard rings have been defined surrounding the block and for providing seperate bulk contacts for the different parts of the circuit. As shown in Fig. 1(b), Plantage+ generates an enhanced shape function for this circuit, consisting of 18 compact placements, with different aspect ratios. These placements were calculated in 3.6 seconds.
3 Conclusion In this demonstration, a fully automated layout tool, Plantage+, is presented. Its integration into a stateof-the-art IC design tool and the comprehensive constraint set enables industrial application. Its automatic constraint generation shortens the setup time. The run times of the algorithm allow for interactive use.
4 References [1] [2] [3] [4]
Y.-C. Chang, Y.-W. Chang, G.-M. Wu, and S.-W. Wu. B*-trees: A new representation for non-slicing floorplans. In ACM/IEEE Design Automation Conference (DAC), volume 37, pages 458–463, 2000. A. Hastings. The Art of Analog Layout. Prentice-Hall, 2001. H. Murata, K. Fujiyoshi, S. Nakatake, and Y. Kajitani. VLSI module placement based on rectangle-packing by the sequence-pair. IEEE Trans. on CAD of Int. Circuits and Systems, 15(12):1518–1524, 1996. M. Strasser, M. Eick, H. Graeb, U. Schlichtmann, and F. M. Johannes. Deterministic analog circuit placement using hierarchically bounded enumeration and enhanced shape functions. In IEEE/ACM Int. Conf. on Computer-Aided Design (ICCAD), pages 306–313, Nov. 2008.
