VHDL-AMS design for flight control systems

This paper investigates a method to address the present and future flight control system analog IC requirements. The explosive growth in the development of VHDL-AMS (Analog Mixed Signal) has initiated the need for commercial CAD products based on mixed-signal design methodologies. Several design methodologies exist for developing analog-digital interface circuits. These methodologies range from the use of commercial off the shelf parts (COTS) to custom analog Integrated Circuit (IC) components that meet performance specifications. The current VHDL-AMS language has potential problems in the design of custom analog IC components in terms of scaling the internal device dimensions and maintaining robust design performance. As an example, a digital controller is being used in flight control systems. The digital controller is an embedded processor, which, through a D/A, controls the actuators of the aircraft. Sensors from the actuators are fed back through an A/D, a low-pass Alter, and then to the embedded processor, completing the loop. In this example, the VHDL-AMS language is used to describe the electronic elements of the flight control system, and also, uniquely, the digital compensator. The digital compensator and filter are designed with the use of quantitative feedback theory (QFT)-theory that emphasizes the use of feedback to achieve the desired system performance tolerances despite plant uncertainty and disturbances. The QFT design technique uses the frequency domain, and has been developed for both linear and nonlinear, time-invariant and time-varying, continuous and sampled data, uncertain multiple-input signal-output (MISO) and multiple-input multiple-output (MIMO) plants, and distributed systems (partial differential equations). The Anal QFT VHDL-AMS design, is tuned for performance to the bounds of uncertainty, the parameter tolerances, and the sampling time of the A/D and D/A, and may be used for either COTS design or custom analog IC components.