FPGA designers are familiar with HDL-based, requirements-driven design methodologies for digital electronics. But how can requirements be expressed for a system that, while it contains digital elements, is fundamentally non-digital? Fortunately, an executable HDL exists that extends the capabilities of the digital VHDL language with continuous time, differential and algebraic equations, multi-physics, transfer functions (both s and z domain), energy conserving analog circuit capabilities (like SPICE), statistical distributions for parametric variations, and functions expressed in software C code. This language is the IEEE Std. 1076.1 VHDL-AMS³ language. VHDL-AMS is the perfect language for providing continuity in design and verification at all levels: functional specifications; architectural partitions; and component implementations (see Figure 2).

Figure 2. Multi-Discipline design and verification with VHDL-AMS (click on image to enlarge).

The VHDL-AMS language standard was completed in 1999. The description of this language sounds ideal, so why aren't more designers using the language today? Simply put, implementing the standard has been very difficult technically. Now, however, after years of development, several different tool suppliers are providing simulators that can efficiently execute the VHDL-AMS language. The long-awaited promise of this language standard and the resultant methodology is now a reality.

Digital designers at major automotive suppliers, such as Magneti Marelli¹, have confirmed significant benefits by using the VHDL-AMS language. Since VHDL-AMS is a pure superset of the VHDL language, the designer starts with all of the well-known benefits of HDL design and verification. Then, using the extensions provided by VHDL-AMS, the design can be thoroughly analyzed by incorporating the impact of the neighboring engineering disciplines: analog electrical engineering (Kirchoff's current and voltage laws), ADC, and DSP circuits; control system transfer functions; mechanical engineering (Newton's and Bernoulli's laws); and extensibility any other desired engineering or physics discipline.