AUTOMATIC SYMBOLIC ANALYSIS OF SWITCHED-CAPACITOR FILTERING NETWORKS USING SIGNAL FLOW-GRAPHS

Signal flow graphs (SFG's) are a powerful technique to analyze switche d-capacitor (SC) circuits in a way that provides in-depth information about their operation and direct access to the corresponding symbolic z-transfer functions. Due to lengthy and error-prone symbolic manipula tions this is manually manageable for simple first- or second-order ci rcuits, but becomes unpractical for manipulating higher-order circuits which can not be decomposed into first- and second-order ones, Hence, there is an important need to provide designers with a computer-aided tool for the SFG symbolic analysis of a broad class of SC filtering n etworks, as described in this paper. Rule-based techniques are employe d to capture from arbitrary circuit schematic and timing diagrams the corresponding symbolic SFG leading to the automatic generation of the associated z-transfer function. Symbols can then be instantiated to nu merical values to obtain measurable data on a variety of performance i ndicators such as total capacitor area and capacitance spread as well as the resulting nominal frequency response and its variability agains t component errors. This is illustrated considering a variety of examp les of SC filtering networks including, besides the more traditional f ilters, both finite and infinite impulse response decimators.