A two-layer library-based approach to synthesis of analog systems from VHDL-AMS specifications

Abstract

This paper presents a synthesis methodology for analog systems described using VHDL-AMS language. Synthesis produces net-lists of analog components that are selected from a library, and sized so that specified objectives (like AC response, signal to noise ratio, dynamic range, area) are optimized. The gap between abstract specifications and implementations is bridged using a two-layered methodology. The first layer is architecture generation. The second layer is component synthesis and constraint transformation. Architecture generation employs the branch-and-bound algorithm to create architectural alternatives for a system. Component synthesis and constraint transformation use a directed interval based genetic algorithm that operates on parameter ranges. The performance estimation engine embeds technology process parameters, SPICE models for basic circuits, and symbolic composition equations for basic structural configurations. The paper discusses the VHDL-AMS subset for synthesis. The subset offers the composition semantics. As a result, specifications offer sufficient insight into the system structure to allow automated architecture generation. To justify the flexibility of the methodology, the paper presents results for three case studies, a signal conditioning system, a filter, and an analog to digital converter. Experiments show that constraint-satisfying designs can be synthesized in a short time, at a low cost, and without requesting broad knowledge on analog circuits.