This paper discusses aBlox - a specification notation that we defined for automated synthesis of mixed-signal systems. aBlox addresses two important aspects of mixed-signal system specification: (1) description of functionality and performance issues and (2) expression of analog-digital interactions. The semantics of aBlox embeds concepts and rules of a computational model that we developed for mixed-signal systems. Finally, the paper shows some mixed-signal specifications that we developed in aBlox.