The extended use of microelectromechanical systems (MEMS) in the development of new microinstrumentation for aerospatial applications, which combine extreme sensitivity, accuracy and compactness, introduced the need to simplify their design process in order to reduce the design time and cost. The recent apparition of analogue and mixed signal extensions of hardware descriptions languages (VHDL-AMS, Verilog-AMS and SystemC-AMS) permits to co-simulate the HDL (VHDL and Verilog) design models for the digital signal processing and communication circuitry with behavioral models for the non digital parts (analog and mixed signal processing, RF circuitry and MEMS components). Since the beginning of the microinstrumentation design process the modeling and simulation could help to define better the specifications and in the architecture selection and in the SoC design process in a more realistic environment. We will present our experience in the application of these languages in the design of microinstruments by using behavioral modeling of MEMS.
Proc. SPIE. 5836, Smart Sensors, Actuators, and MEMS II
KEYWORDS: Mathematical modeling, Microelectromechanical systems, Oscillators, Sensors, Linear filtering, Signal processing, Analog electronics, Integrated circuit design, Smart sensors, Systems modeling
The objective of this work is to develop a modeling of a complete smart sensor to be used in a distributed architecture, with the new modeling language, VHDL-AMS. This smart sensor is composed by a sensor or actuator, for example we have used a piezoresistive accelerometer, its signal conditioning module, with both analogue and digital elements, and a bus driver that allows communication with the instrument control device and other sensors. In that way, it is also possible to introduce these microsensors in a distributed architecture that permits communication between microinstruments. This example of modeling through VHDL-AMS shows how this language allows a multitechnological description of a microsystem, including not only electrical signals, but also thermical, kinematic, fluidic, etc. signals. This language also permits to describe systems in different levels of complexity and abstraction, giving the possibility of covering several models from a physical model until a behavioral model, which can be used to obtain a design methodology for MEMS, analogous to the existent design methodology for integrated circuits. The combination of smart sensors models at behavioral level with the microinstrument control circuit models is a first step in the development of a complete design methodology.
A microelectromechanical system (MEMS) merges integrated sensors, microactuators, and low-power electronics. These systems normally have a local sensor communication bus managed by a master node. The purpose of this work is to implement a communication interface that permit connect the integrated MEMS local bus (through the master node) with on a high level microinstrument communication bus. The basic philosophy of this development has been to create an IP model with VHDL for the bus module interface. This interface can be added easily to a microsystem and from of point of view of microinstrument design methodology, MEMS based in this interface module could be easily plugged with the other microsystems on microinstrument architecture. The IP developed is based on the concept of Interface File System (IFS) that contains all relevant information of the microsystem. The use of the IFS in integrated microsystems design permits to insulate its particular characteristics from the whole of microinstrument. Also, this IFS has associated a communication model that allows different views of the system, such as, real-time or command service view, configuration and diagnostic service view. Implementation experiences presented in this paper show that the IFS reduces the complexity of microinstrument applications and make easy the MEMS reuse in other microinstruments. The communication module based on IFS was successfully tested between microsystems based on local sensor bus namely IBIS (Interconnection Bus for Integrated Sensors) and a generic real time microinstrument bus.
Our main objective in this work has been to develop a comunication system applicable between sensors and actuators and the data processing circuitry inside the microsystem in order to develop a flexible and modular architecture. This communication system is based on the use of a dedicated sensor bus composed by only two wires (a bidirectional data line and a clock line for sincronization). The basic philosophy of this development has been to create an IP model with VHDL for the bus driver that can be added to the sensor or the actuator to create an smart device that could be easily plugged with the other componets of the microsystem architecture. This methodology can be applied to a high integrated microsystem based on an extensively use of microelectronics technologies (ASICs, SoCs & MCMs). The reduced number of wires is an extraordinary advatage because produce a minimal interconnection between all the components and as a consequence the size of the microinstrument becomes smaller. The second aspect that we have considered in this development has been to reach a communication protocol that permits to built-up a very simple but robust bus driver interface that minimize the circuit overhead. This interconnection system has been applied to biomedical and aerospatial microsystems applications.