Mixed Signal Modelling Comp

8/6/2019 Mixed Signal Modelling Comp

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VHDL AMS DESIGN FOR AN

EMBEDDED CONTROLLER


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Agenda

Introduction

Need for mixed signal modeling

VHDL AMS

Features ,Advantages and applications

Digital flight controller

QFT

QFT design

References


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Introduction

Mixed signal system modeling

HDL programming language used for modeling.

3 types of HDL

1. analog ( spectre HDL)

2.digital (VHDL, Verilog)

3. mixed signal (VHDL AMS, Verilog AMS)


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Introduction to VHDL AMS

IEEE Std. 1076-1993

description and simulation of event-driven systems.

IEEE Std. 1076.1-1999

support the description and simulation ofanalog and

mixed-signal circuits and systems.

IEEE Std. 1076.1-1999 together with IEEE Std. 1076-1993 is VHDL-AMS.


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Extension of VHDL standard

Adds support for DAEs and conservative quantities

Supports description and simulation of analog, digital,mixed signal, multi-physics devices

Encourages device modeling at various architecturelevels (ideal, non-linear, transistor)


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Features

It has a well-defined simulation cycle

It can model continuous and discontinuous behaviour

Equations are solved using conservation laws

Represents complex models directly.

High efficiency.

Describes non electrical physical phenomenon.

Easy to model.


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VHDL AMS language architecture


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Basic concepts

A VHDL-AMS model consists of an entity and one or

more architectures.

The entity specifies the interface of the model to theoutside world.

The architecture contains the implementation of the

model.

Packages define collections of re-usable declarations

and dfinitions, types, constants, functions etc.


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Advantages

Readable documentation of discontinuous behavior

Facilitates model exchange

Facilitates model reuse

Facilitates tool substitution

Competition will strengthen capabilities of the tools and

will reduce tool cost

Modeling concepts have proper semantics


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VHDL Vs VHDL AMS

VHDL

IEEE 1076-1993

digital domain

model only electrical

parameters

single domain simulation

Time discrete system

VHDL AMS

IEEE 1076.1-1999+1076-

1993

Mixed domain

model electrical and non

electrical parameters

Multi domain simulation

Time continous system

Conservative and non

conservative systems


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Digital flight controller

Digital control system transfers all pilot commands to the

control surface actuators through electrical wires


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Robust control

Fundamental issues in the design, analysis andevaluation of control systems.

Stability

Performance Stability

In the absence of external excitation, all signals inthe system decay to zero.

It is an absolute requirement.

Its absence causes signals to grow without bound,eventually destroying and breaking down the plant.


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Performance

Ability to track reference signals closely

Reject disturbances.

Robust Control system

Should preserve stability in the presence ofvarious classes of uncertainties.

Should be capable of tracking all reference

signals belonging to a class of signals, withoutexcessive error, despite various types ofuncertainties.


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QFT

Developed by Horowitz and Houpis in 1960

QFT is an extension of frequency domain

approaches.

QFT is a method for practical design of feedbackcontrol systems.

controller can be obtained to satisfy performanceand stability specifications over a range of plant

uncertainty.


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Main objectives of QFT

Get simple low order controllers

Get minimum bandwidth controllers To avoid noise amplification

To avoid resonance

To avoid high frequency dynamics


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Characteristics of QFT

Amount of feedback depends on

Amount of plant

Magnitude of disturbance

Level of performance specifications

QFT offers direct tradeoff between

Stability and performance specifications

plant uncertainity and disturbance uncertainity

controller complexity

controller bandwidth


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Feedback Design with QFT

Define frequencies

Create frequency response data

Define sampling time

Define nominal response

Define controller type

Define phase array for bounds.

Compute bounds

Loop shaping

Compare design to

specifications

End

Define

problem data

Compute and

manipulate

bounds.

Design

Analysis


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QFT CONTROLER STRUCTURE

y(t) is required to track the input r(t) and reject

disturbances.

controller is designed so that variations are within

tolerance range

Filter is the input filter transfer function


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Plant as a second order system

Actuators and flight control surface are modelled as

second order systems

F=PA

FA - Fp = Mps2Xp+BpsXp Torque due to hydraulic force imbalance is

Tr= kh/Rh (xp-xL)

torque on actuator is

TR - TL = J Ls2L +BLsL


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Final transfer function is


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Future work

Digital flight controller is converted in to VHDL AMS

hardware description language.

The design technique is to control transmission aroundthe feedback loop within certain specifications.


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Expected simulation result


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[l] Peter J Ashended,Gregory D Peterson and Darell A Teegarden, SYSTEMDESIGNERSGUIDETO VHDL AMS2nd edition Morgan Kaufmann

Publishers September 2002.

[2] Robert L. Ewing, John W. Hines, Greg D. Peterson, & Maya Rubeiz,VHDLAMS design for flight control system IEEE proceedings,Aerospace

conference,vol 1;pp 223-229;march 1998.

[3] Alex Doboli,Ranga Vemuri,Behavioural modeling of high level synthesis

of analoge and mixed signal system from VHDL AMS IEEE transactions

on computer aided design of integrated circuits and

systems,vol.22,No:11,nov 2003.

[4] VHDL-AMSA hardware description language for analog and

mixed-signal applications, IEEETrans. Circuits Syst. II, vol. 46, pp.

12631272, Oct. 1999.

[5] The Institute of Electrical and Electronics Engineer, IEEE Standard 1076.1-

1999,IEEE, 1999.


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[6] Isaac M. Horowitz. Quantitative Feedback Design Theory (QFT),volume 1.

QFT Publications, 1993.

[7I C.H. Houpis and R.L. Ewing. TOTAL-PC Users Manual.Air Force Institute

of Technology, 1997.

[8] Constantine H. Houpis and Gary B. Lamont. Digital ControlSystems.

McGraw-Hill Book Company, 2nd edition, 1992.

[9] KI- Ho Kang. Electro-hydrostatic actuator controller design using

quantitative feedback theory. Masters thesis, Air Force Institute ofTechnology, December 1994.

[10] Giovanni De Micheli. Synthesis andOptimization ofDigital Circuits.

McGraw-Hill Book Company, 1994.[11] A lain V achoux. Analog and mixed-signal extensions to VHDL. Analog

Integrated Circuits and Signal Processing, 1998.


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Mixed Signal Modelling Comp