Contracts for Correct Composition and System-Level Design of Analog and Mixed-Signal Circuits
چکیده
The increasing complexity of today's electronic systems and the higher nonrecurring engineering costs of integrated solutions call for an efficient system-level design methodology relying on hierarchical design-space exploration and compositional methods to manage complexity, shorten time-to-market, and leverage design re-use, while still achieving optimal performances. Analog, mixed-signal (AMS) and RF components are first-class citizens of many integrated systems-on-chip. However, in most cases, integration and verification of these blocks in the complete system is the bottleneck in terms of design time and required resources. One of the challenges stems from the fact that AMS circuit behaviors are so tightly dependent on their interface conditions that accurate system performance estimations based on characterizations of individual stand-alone circuits is a hard task. Since there is no general solution to this problem, analog system integration has traditionally used ad-hoc solutions heavily dependent on designers' experience and detailed knowledge of the target application. In this work, we focus on the problem of assembling analog integrated systems out of pre-designed IP components in a systematic way. We argue that the burden of hierarchical mixed-signal design can be alleviated by leveraging the principles of platform-based design [1] to devise proper abstraction levels, and contracts to enforce proper compositions of elements and correct constraint propagation across hierarchy levels. Contracts intuitively capture the thought process of a designer, who aims at guaranteeing circuit performance only under specific assumptions (e.g. loading and dynamic range) on the interface properties. We develop contracts in the context of analog platform-based design (APBD), introduced in [2]–[4] as a meet-in-the-middle approach to allow efficient and reliable design space exploration at the system level. Circuit components are first built and characterized bottom-up by exporting high-level behavioral and performance models. System functionalities are independently specified and propagated top-down as constraints on the library of pre-characterized component models. Systems are optimized leveraging global tradeoffs among all components, while ensuring implementation feasibility at the circuit level. In this context, horizontal contracts have been introduced in [5] to ensure predictable component behavior after integration into the system. A horizontal contract for an analog platform (AP) component is a set of assume/guarantee tuples {(a where a δ i is the set of circuit (input, output and internal) variables and configurations that satisfy a set of assumption constraints A, within certain margins δ; g i is the set of output and internal variables that guarantee feasible performances for the component only if …