This paper presents a top-down design methodology to synthesize mixed-signal systems described at behavioral level. Our methodology is intended to automate the synthesis process of analog CMOS integrated circuits. Also, the method enables the circuit description at high level of abstraction where complex systems are easier to specify. The behavioral models are represented by a set of simultaneous differential and algebraic equations (DAEs), which are written in VHDL-AMS using simple simultaneous and procedural statements. We present an algorithm to perform the topology selection process. As an example, a Dual-Tone Multiple-Frequency decoder is synthesized from behavioral model to analog CMOS transistor level. 1 Introduction The emerging analog hardware description languages will speed up the analog verification process and enable the analog designer to describe circuits at higher levels of abstraction. Analog integrated circuits have been typically designed at circuit, component and ...