This paper presents the complete design methodology of a very low-voltage /spl Delta//spl Sigma/ third-order modulator from high-level specifications down to layout. Behavioral models taking into account cell nonidealities are developed and used to map performance specifications to lower levels. Emphasis has been made on eventual design reuse through design plans and layout templates in a layout-oriented circuit design approach. The modulator has been designed for two different technologies demonstrating the suitability of the methodology for very high performance mixed-signal circuits. Moreover the same design knowledge has been successfully reused in another fourth-order modulator.