enhancing the performance of piezoelectric mems · pdf file · 2017-04-04enhancing...

Enhancing the Performance of Piezoelectric MEMS Accelerometer

For

Professor D. Prescott Associate Professor

American University of Sharjah Sharjah, UAE

by Saeed Nusri Walid Diab

Shaikha Al Kendi Basel Zam

January 13, 2011

PiezoelectricMEMSAccelerometer 2

Executive Summary

This report examines the drawbacks of a conventional Piezoelectric MEMS

Accelerometer and proposes ideas about how its design can be improved to increase its

efficiency and broaden its potential range of applications. The report also covers a brief

background about accelerometer, including its operation and applications.

The current accelerometer contains certain problems that have been discussed in this

report. These problems include the current spring design, the weakness of the piezoelectric signal

and the noise incurrence due to temperature variations and vibrations.

Correspondingly, five solutions have been proposed that will enhance the performance of

the Piezoelectric MEMS Accelerometer. Four of these include the choice of piezoelectric

ceramics, a new spring design called the fold spring, the use of rubber coated ceramics as

housing, the addition of a Whetstone Bridge and a filter to reduce temperature and vibration

effects and the use of amplifiers to amplify the piezoelectric charge. Additionally, the

implementation of software programming called Very Long Instruction Word (VLIW) that aims

to reduce the response time has been discussed.

The proposed solutions are evaluated, while paying close attention to cost effectiveness.

This evaluation is included as a separate section of this report. The report concludes with

recommendation that will enhance the performance of the Piezoelectric MEMS Accelerometer in

an approach that is practical and cost effective.


TableofContents

ExecutiveSummary......................................................................................................................................2

ListofFigures...............................................................................................................................................4

ListofTables.................................................................................................................................................4

1.0 Introduction......................................................................................................................................5

1.1 Purpose of the Report.........................................................................................................................5

1.2 General Introduction...........................................................................................................................5

1.3 Situation.............................................................................................................................................7

2.0 Problem Statements and Solutions...................................................................................................7

2.1 Piezoelectric Material.........................................................................................................................7

2.2Theuseofsprings...............................................................................................................................8

2.3 Environmental Factors.....................................................................................................................12

2.4NoiseSegregation.............................................................................................................................14

2.5 Application of Amplifiers.................................................................................................................16

2.6 Software Implementation.................................................................................................................17

3.0 Evaluation.......................................................................................................................................20

4.0 Conclusion......................................................................................................................................21

5.0 Recommendations.........................................................................................................................22

6.0 References......................................................................................................................................23

7.0 Appendices.....................................................................................................................................25


List of Figures

Figure Name Page 1 Bending Spring 8 2 Torsion Spring 8 3 Tensile Spring 8 4 Bending Spring Equation 9 5 Torsion Spring Equation 10 6 Tensile Spring Equation 10 7 Fold Spring 11 8 Fold Spring Equation 11 9 Natural Frequency Equation 12 10 Wheatstone Bridge 13 11 Active filter output voltage 14 12 Amplifier 15 13 DAC 16 14 Processing using VLIW 17

List of Tables

Table Name Page

1 Modulus of Elasticity 9

2 Equation Notations 10


1.0 Introduction

1.1 Purpose of the Report

This report examines the basic problems of a conventional Piezoelectric MEMS

accelerometer and how its design can be improved to increase its efficiency and broaden its

potential range of applications. The problems discussed in this report relate to the current spring

design, the weakness of the piezoelectric signal and noise incurrence that occurs due to

temperature variation and vibration.

Correspondingly, the proposed solutions are; the choice of piezoelectric ceramics, the

new spring design called the fold spring, the use of rubber coated ceramic for the housing, the

Whetstone Bridge and filter addition to reduce the temperature and vibration effect, the use of

amplifier to amplify the piezoelectric charge and the software implementation of Very Long

Instruction Word programming technique to reduce the response time.

1.2 General Introduction

Micro electro mechanicals systems (MEMS) are devices that consist of components that

measure between 1 to 100 micrometers in size. These micro systems, which are produced using

state of the art technique of micro fabrication, consist of two basic components: an actuating or a

sensing element and a processing unit. According to Dr. Hsu [1] of Jan Jose University, the small

size of these micro systems not only reduces their cost of production but also makes them less

viable to problems caused by thermal distortion and vibration. Also, the effect of gravity and

inertia is no longer important because of their negligible mass. These features endlessly increase


the potential of MEMS technology and place them at the pinnacle of modern industrial

applications.

Piezoelectric MEMS accelerometer is a micro scale sensor that is used to measure

acceleration. In general, micro sensors are built to sense the existence and the intensity of a

certain physical, chemical or biological quantities such as temperature, pressure force, sound,

light, nuclear radiation, magnetic flux and chemical compositions [1]. In this case, the sensor is

designated to measure acceleration forces. These forces can either be static, like the gravitational

acceleration force, or dynamic such as the forces exerted by a moving or a vibrating body [2].

The accelerometer appears in daily commercial products. A common example would be

its use in smart phones where accelerometer measures the movement of the device relative to the

gravitational acceleration and rotate the display of the screen to the convenience of the user. It is

also used in still cameras for image stabilization and anti blur capturing. By detecting the

movement of the camera it prevents the CCD shutter from snapping to prevent blur. Another use

of accelerometer appears in a device called foot pod, which athletes use to measure their speed of

travel of the distance they have covered [3].

The core of a MEMS accelerometer consists of a central mass that moves in response to

its acceleration. This inertial mass is mounted on a cantilever spring that limits its movements

and returns to its central position when it is at rest. A single piezoelectric crystal, which

characteristically produces a voltage under pressure, is attached at the end of the cantilever

spring such that when the mass moves the crystal compresses producing the voltage accordingly.

The force caused by vibration or a change in motion causes the mass to compress the

piezoelectric material which produces an electrical charge that is proportional to the force


exerted upon it. Since the charge is proportional to the force, and the mass is constant, then the

charge is proportional to the acceleration. This charge is collected as a voltage by the

measurement instrument and the required output is generated [4].

The use of MEMS accelerometer in the deployment of airbags in modern vehicles can be

used to illustrate this entire operation. In a vehicle crash situation, there is a sudden change in the

acceleration of the vehicle. This unsafe deceleration is detected by the component of the

accelerometer and signal collected by measurement instrument is processed and the air bags are

deployed. The whole process takes only a fraction of second. Earlier systems needed many

mechanical and electrical components that had to be located throughout an automobile for

measuring same data. But MEMS accelerometer, which consists of only microscopic chips, has

efficiently and cost effectively replaced these systems [4].

1.3 Situation

Since Piezoelectric MEMS Accelerometer is a recent engineering innovation it has a

wide scope of improvement in its design for achieving optimum efficiency and broadening its

range of applications. This report discusses the issues of a conventional Piezoelectric MEMS

Accelerometer and how its design can be improved for optimum performance.

2.0 Problem Statements and Solutions

2.1 Piezoelectric Material

The choice of piezoelectric material is the most integral step in the design the

accelerometer because it is the core element that produces the input signal. There are two main

categories of piezoelectric material. The first is the single crystal material which is usually


quartz. These crystals have a long life span in terms of sensitivity, but they are generally less

sensitive than the other category, the piezoelectric ceramic. Piezoelectric ceramic have a high

sensitivity and are inexpensive to produce than the crystal derivatives. Compounds such barium

titinate, lead zirconate, lead titanate and lead metabionate are mixed in various compositions to

produce the piezoelectric ceramic [5].

The conventional accelerometer uses either of the two categories. But considering that

response time is one of the main factors that determine the efficiency of the accelerometer, using

piezoelectric ceramic would be more feasible, since they are more sensitive than piezoelectric

crystal. Moreover, due to their lower cost of production they are much more cost effective.

Piezoelectric ceramic materials can appear in a wide range of selections, based on the

composition of lead zirconate titinate (PZT) and barium titanate. By combining these compounds

in the right proportion, a piezoelectric ceramic material can be produced that would best suited

for its application in the accelerometer (See Appendix A for properties of different piezoelectric

ceramic materials).

2.2Theuseofsprings

Typically, the term conventional spring depicts the picture of a helical kind that is often

used in vehicles, as shock absorbers, and in mattresses. However, engineers have a much broader

definition of conventional springs which includes various types suited for different applications.

These types of springs, including the helical one, can be simply listed as the bending type, the

torsion type and the tensile type. All these categories follow the basic principle of a spring,

which is to store mechanical energy. However, the main difference between these springs comes


in the direction of their deformation that determines their function and application. For example,

in bending springs, the force applied at the far end of the fulcrum causes it to deform

perpendicularly to the longitudinal axis. In torsion springs, the applied force causes a rotational

deformation (twist) to the spring while in tensile springs it causes lateral deformation in the axial

direction [6].

Figures 1-3 illustrate the different types of springs and their direction of deformation.

F

F F

Figure 1: Bending Spring [7]

Figure 2: Torsion Spring [8]

Figure 3: Tensile Spring [9]


Several factors have to be considered while selecting the spring so that it is best suited for

the required application. One of these factors is the spring stiffness, which is symbolized by the

letter ‘K’. The spring stiffness correspondingly depends on other variables, such as the length,

the orientation, the geometry and the elasticity of the material. Another property, the modulus of

elasticity, represents the ability of the material to maintain its rigidity and structure without

permanent deformation. Modulus of elasticity is denoted by the letter ‘E’. The following table

illustrates the empirical values of modulus of elasticity for different metals.

Metal GPa Aluminum 69

Brass 97 Copper 110

Magnesium 45 Nickel 207 Steel 207

Titanium 107 Tungsten 407

Table 1: Modulus of Elasticity [10]

Figures 4-6 illustrate the equations that are used for calculating the spring stiffness for the

different types of springs previously mentioned. Respectively, Table 2 illustrates the notations

used in each equation.

K = 3 ∗ E ∗ IL!

Figure 4: Bending Spring Equation [6]


𝐾 = 𝐺 ∗ ℎ ∗ 𝑏!

𝐿 ∗ 13− 0.21 ∗

𝑏ℎ 1−

𝑏!

12 ∗ ℎ!

Figure 5: Torsion Spring Equation [6]

K = E ∗ b ∗ h

L

Figure 6: Tensile Spring Equation [6]

Table 2 - Equation notation [6]

The current design of the Piezoelectric MEMS Accelerometer uses a bending spring to

measure the acceleration of the system. However, using this type of spring induces errors,

causing the piezoelectric material to produce a false signal that does not correspond to the real

acceleration that takes place. Therefore, a new spring design has been proposed that uniquely

combines all three of the previously mentioned categories of springs. The new design will be

E = Modulus of Elasticity

I =

! ∗ !!

!"

G =

A material property that is related to the stress resulting from the applied force (Published in Tables) [1]

b = Geometrical Base

h

= Geometrical Height

L = Length

K = Spring Stiffness


able to efficiently measure the system’s actual acceleration and transfer it to the piezoelectric

material. [6]

The new spring design is called the fold spring. This spring, counter acts in the direction

in which the acceleration is applied, as illustrated in Figure 7.

Figure 7: Fold Spring [6]

in which the stiffness of elasticity is given by the equation in figure 8.

K = 12 ∗ E ∗ I

L!

Figure 8: Fold Spring Equation. [6]

2.3 Environmental Factors

The Piezoelectric MEMS Accelerometer experiences a number of environmental factors

that affect its performance and life span. The first factor is the variation in temperature from the

surrounding medium. The presence of this factor, affects both the functionality and sensitivity of

the piezoelectric material which causes it to produce redundant error in the output signal. This


can be misinterpreted by the integrated circuit as an actual acceleration, when, in reality, no

physical acceleration takes place [11].

Another factor is vibration. In practice, all mechanical systems have an identification

property that defines the system’s ability to withstand external forces such as vibrations. This

property is called the natural frequency and it is symbolized by “ωn”. The natural frequency is

defined as the number of cycles of force that the system can handle in one second. It varies

depending on two main components used within the Piezoelectric MEMS Accelerometer; the

mass of the system and the stiffness (K) of the spring [11].

Figure 9 illustrates the relationship between the natural frequency, the stiffness and the mass.

ωn = Km

Figure 9: Natural Frequency Equation [11]

If the frequency, due to vibration, reaches a value that is greater than or equal to the

natural frequency (ωn) of the system then the device can get permanently damaged. [3]

To avoid the effect of temperature and vibration, a composite material can be used for

housing the entire unit. Hence, a rubber coated ceramic would be the most appropriate composite

material for casing the unit. The ceramic property of the composite would make the device

impervious to the changes in the external temperature and would, hence, protect the piezoelectric

material. Moreover, possessing the properties of rubber, the casing would absorb vibration and

prevent the accelerometer from reaching its natural frequency.


2.4NoiseSegregation

When the piezoelectric material compresses under the force of the mass, it produces a

charge or a voltage which is registered by the integrated circuit as a signal. Sometimes, this

signal can incur noise which can lead to a false response by the system. For instance,

accelerometers used in vehicles can deploy airbags without any accident actually occurring

because of noise. Hence, noise has to be eliminated.

Noise can be introduced in the signal by many external factors, like temperature variation

and vibration. The noise causes distortion in such a way that false harmonics get introduced and

eventually become part of the desired signal. This means that if the signal is altered due to noise,

the system will return a faulty response. Moreover, the noise incurred by the signal is inversely

proportional to its strength, such that weaker signal is more prone to carry noise than a stronger

one. To overcome this issue, a Wheatstone Bridge along with active filters can be used.

Wheatstone Bridge is widely used in monitoring sensing devices. In Piezoelectric

MEMS Accelerometer it can be used for eliminating temperature variation. The circuit

configuration of Wheatstone Bridge is

shown in Figure 10.

Figure 10: Wheatstone Bridge[12].


The Wheatstone Bridge consists of two parallel branches that have two resistors in series.

The output voltage is taken from two nodes in the middle of the two adjacent resistors in both

sides. Whereas the input signal is fed to the circuit from the top node, and the bottom one is

grounded. This diamond shape configuration allows the Wheatstone Bridge to change its internal

resistance according to a specific level of temperature. Therefore, it serves as a balancer and

minimizes the deviation of the input signal from the signal produced by the piezoelectric material

[13].

To prevent the noise caused by vibration, an active filter can be used to purify the desired

signal. A filter is a device that passes electric signals at a certain range of frequencies while

preventing the remaining frequencies to pass.

A typical output voltage signal from an active filter is shown in Figure11.

Figure 11: Active filter output voltage [14]


2.5 Application of Amplifiers

In principal, accelerometer is an inertial measurement device that senses any changes in

its environment and produces a signal by changing its material properties. In Piezoelectric

MEMS Accelerometer, it is the piezoelectric material that produces a signal under deformation.

As mentioned before, there are three basic components in the accelerometer. These are the mass,

spring and the piezoelectric crystal. As the mass applies force to the crystal, the crystal creates

charge that is proportional to the measured acceleration. However the piezoelectric charge

produced is only in the pico-coulomb per gravity force (pC/g) range, which is a very small range

in value to work with. Moreover, the charge is not a voltage signal which cannot be further

processed. To overcome this problem, an internal charge amplifier can be used in converting the

charge output into a voltage signal in the range of mille-volts [16]. Figure 12 shows how the

amplifier can be integrated in main circuit.

Figure 12: Amplifier [15]


2.6 Software Implementation

Execution of a large number of operations in the central processing requires more

performance and time.The time needed for the processor to complete executing its instructions

increases the response time for the output to be generated at the required time. This causes delay

in the entire system. Using a Digital Signal Processor (DSP) is a suitable solution when a set of

mathematical operations requires efficient execution. Usually the purpose of DSP is to filter and

calculate the analog signal. It receives an analog signal from the sensor and converts it into

digital signal using analog-to-digital convertor (ADC). The central processing unit will be able

then to process the digital data before converting it again into an analog signal using a digital to

analog convertor (DAC), as depicted by Figure 13. However, the DSP is not efficient in term of

executing large number of instructions because it executes them sequentially. As a result, the

processor will use its resources inefficiently leading to poor performance.

Figure 13: DAC [17]

Before executing, the processor must check for independency of every instruction and

confirm that there are no independent instructions in the program. For example, an instruction’s

output is used as an input for the next instruction. Logically, these instructions cannot be

executed at the same time, and the first instruction must get executed first. The scheduling

hardware of the processor handles the determination of interdependencies and the arrangement of

instructions.


There are two main methods of scheduling. A sequential scheduler receives a list of

sequential instructions and then it makes the decision of which instruction can get executed in

the functional unit of the processor at any instant. Actually, this method works fine, but it

requires the processor to do huge scheduling work. As a sequence, the processor’s scheduler

will require more transistors to handle the scheduling task which goes against the purpose of

integrating the circuits of the processor to get higher speed.

The performance of the DSP can be improved by using a technique called Very Long

Instruction Word (VLIW) where the processor executes different sub-steps of sequential

instructions simultaneously rather than sequentially. In the A VLIW processor, the task of

instruction reordering and scheduling is assigned to the compiler, a software that translates a

program written in a high-level programming language, like C/C++, COBOL, into machine

language [18] . The processor will then execute instruction it receives from the compiler as fast

as possible (See Appendix B for examples of VLIW software architecture). In other words, a

VLIW compiler groups the instructions and sends them to the processor as fixed-length packets.

This process is illustrated by Figure 14.

Figure 14: Processing using VLIW [19]


The essential advantage of using VLIW is that the processor doesn't have to consume

its hardware power on instructions scheduling and arrangement. VLIW simply reduces the

complexity of the hardware and increases the complexity of software. Actually, this trade-off has

a significant benefit because the compiler can be rewritten instead of redesigning the chip

therefore; the complexity is paid for only once. One of the available advantages is having smaller

chips, which leads to higher profits for the producers and cheaper prices for the users. Dealing

with complexity in a software design is much easier than in a hardware design, therefore, the

chip costs less to design, is faster to design, and requires less debugging, checking for errors,

which make the design process cheaper. Also, the compiler can be improved after the chip has

been made-up [20]

However, the problem with this technique is that it can cause a significant code bloat, is the

production of code that is perceived as unnecessarily long, slow, or otherwise wasteful of

resources [18]. In a the VLIW structure, the instruction packets are a fixed size, therefore when

there is no enough instructions to fill up the packets, the compiler inserts NOPS, an assembly

language instruction, sequence of programming language statements, or computer protocol

command that does nothing at all [18], in the empty spots of the packet.

A solution of this problem is encoding fewer operations than the number of available

functional units in the processor. For example a VLIW machine with ten execution units but only

5 operations can described in these units. Each operation will have unit number to specify the

execution unit that the operation should be sent to. As a result, of that the processor will use its

resources efficiently. However, this solution prevent the processor from maximizing the number

the operation that the processor can execute. To prevent the problem of limiting performance, the


number of the operation allowed to be executed can be decided based on analysis of program

behavior [20]

3.0 Evaluation

The use of piezoelectric ceramic as previously proposed is a more feasible solution than

the piezoelectric crystal because the ceramic materials are more sensitive and cost effective.

However, their life span is much less than piezoelectric crystal which makes them ineffective in

applications which are long-lasting. For example, airbag deployment system that uses a

piezoelectric crystal in its accelerometer would be more dependable than the one that uses the

piezoelectric ceramic, provided that both the vehicles are of equally old.

The implementation of the new spring design, which was discussed earlier, is neither

time efficient nor cost effective. However, the fold spring does significantly increase the

performance of the system. The compromise between the performance enhancement and the

price of the device depends on the application. For example in aircrafts, high performance is

required to measure the acceleration precisely and this incurs high cost.

While considering the solutions proposed for noise segregation, it should be noted that

active filters are difficult to implement. Low noise segregation is a sensitive procedure and any

factor that affects the process cannot be excluded. Moreover, since it is time consuming to

determine the criteria that are desired for the choice of appropriate active filters, the solution is

likely to incur high implicit cost of time. However, the implementation is necessary to minimize

noise while maintaining the highest accuracy in the shortest response time. On the other hand,

the use of the Wheatstone Bridge and the amplifier, are both cost effective. Their cost might


increase depending on fabrication and size; the smaller the size of the accelerometer the higher

the cost.

The employment of rubber coated ceramics that are used for housing the accelerometer,

is indeed a highly cost effective method of shedding the effect of temperature variations and

vibrations. However, it is not as efficient as the implementation of the Wheatstone Bridge and

the active filters. Hence, the utilization of rubber coated ceramics can be excluded from the

design for cost reduction.

Finally, according to Dr. Gad-el-Hak [21], a professor at the Virginia Commonwealth

University, “Three primary areas that are considered in micro machined devise applications

include packaged volume or size, system cost and performance often these three drivers cannot

be met in a single technology choice”. This highlights that tradeoffs would have to be made in

size and cost while decreasing the efficiency of the accelerometer.

4.0 Conclusion

Overall, this report covers brief background information on accelerometers that explains

its fundamental operation and how it is being extensively used in daily products. Next, the report

states the situation which stimulates the need for a better and a more efficient design of

accelerometers. Then, the problems and respective solutions have been discussed. These

solutions include the choice of piezoelectric ceramic, the new spring design, the design of the

casing, the method of noise segregation, the application of filters and software implementation.

Finally, the solutions have been evaluated based on their feasibility and cost effectiveness.


5.0 Recommendations

1. The new design of Piezoelectric MEMS Accelerometer should include piezoelectric

ceramic instead of a single crystal piezoelectric crystal. This recommendation is

supported by the assumption that most applications of accelerometers do not live

long enough to drastically affect the sensitivity of the ceramic.

2. Fold spring should be included in the new design because it significantly enhances

the efficiency of the accelerometer, which outweighs the additional implementation

cost.

3. Though active filters involve high implicit cost of time, they should be present in the

design because of their importance in the noise segregation process.

4. Wheatstone Bridge and amplifiers are necessary for noise reduction due to

temperature variations and vibrations and should be present in the design, especially

if the rubber coated ceramic housing is not being included for cost reduction.

5. A DSP should be designed with VLIW technique where encoded functions are less

than the number of available functional units in the processor. Also the number of the

operation allowed to be executed can be decided based on analysis of program

behavior.


6.0 References

[1] T. R. Hsu. MEMS & Microsystems: Design and Manufacture. Avenue of the Americas, NY: McGraw-Hill Companies Inc., 2002.

[2] Texas Instrument. Accelerometers And How They Work. [Presentation]. 2005, Available FTP: http://www2.usfirst.org/2005comp/Manuals/Acceler1.pdf

[3] Wikipedia, "Accelerometer," n.d., http://www.useit.com/papers/heuristic/heuristic_list.html.

[4] MEMS Industry Group, An Introduction To MEMS. [Documentary]. Available FTP: http://www.youtube.com/watch?v=CNmk-SeM0ZI

[5] A. Safari and K. Akdogan, Piezoelectric and Acoustic Materials for Transducer Application. Spring Street, NY: Springer Science + Business Media LLC., 2008. [E-book] Available: SpringerLink e-book.

[6] V. Kaajakari, Practical MEMS. Las Vegas, NV: Small Gear Publishing, 2009.

[7] S.Z. Elgun, “Modulus of Elasticity Experiment,”2000, http://info.lu.farmingdale.edu/depts/met/met206/modulus.html

[8] S. J. Record, “The Mechanical Properties of Wood,” 1914, http://chestofbooks.com/home-improvement/woodworking/Mechanical-Properties-of-Wood/Toughness-Torsion.html

[9] WEAVE, “Module 2: Tensile Test,” 2003, http://dolbow.cee.duke.edu/TENSILE/

[10] W.D. Callister.Jr, Materials Science and Engineering an Introduction. Third Avenue, NY: John Wiley & Sons, 2007.

[11] S. Beeby, G. Ensell, M. Kraft, N. White, MEMS Mechanical Sensor. Norwood, MA: Artech House Inc, 2004.


[12] Analog Devices, “Piezoresistive Sensing ICs in Portable Infusion Pumps,” 2007, http://www.analog.com/static/imported-files/solutions_bulletins/medical04-08/medical12.html

[13] T. Bartelt, “Wheatstone Bridge Application,” 2010, http://www.wisc-online.com/objects/ViewObject.aspx?ID=DCE4403

[14] Abyss Web Server, “noise2.gif,” 2000, http://lorien.ncl.ac.uk/ming/infer/noise2.gif

[15] Linear Technology Circuit Collection, “Shock Sensor Amplifier (Accelerometer),” 2010, http://circuits.linear.com/27

[16] P. A. Wlodkowski, K. Deng, M. Kahn, “The development of high-sensitivity, low-noise accelerometers utilizing single crystal piezoelectric materials” Sensors and Actuators A: Physical, pp. 125-131, May 2001. [Online]. Available: ScienceDirect, http://www.sciencedirect.com.ezproxy.aus.edu/. [Accessed November 10, 2010].

[17] Wikipedia, “Digital Signal Processor,” (n.d), http://en.wikipedia.org/wiki/Digital_signal_processor.

[18] PCMAG, “Definition of Compiler,”, 2008, http://www.pcmag.com/encyclopedia_term/0,2542,t=compiler&i=40105,00.asp.

[19] Berkeley Design Technology, “VLIW Architecture for DSP,”1999, http://www.bdti.com/MyBDTI/pubs/vliw_icspat99.pdf .

[20] Philips, “An Introduction to Very Long Instruction Word Computer Architecture,” 1995, http://www.nxp.com/acrobat_download2/other/vliw-wp.pdf

[21] M.Gad-el-Hak, The MEMS Handbook: MEMS Applications. Boca Raton, FL: Taylor & Francis Group, 2006


7.0 Appendices

AppendixA

Propertiesofdifferentpiezoelectricceramicmaterials


Reference:

Piezotechnology. Piezoelectric Ceramic Products. [Manual]. 2010, Available FTP: http://www.piceramic.com/pdf/KATALOG_english.pdf


AppendixB

ExampleofVLIWsoftwarearchitecture


ExampleofVLIWsoftwarearchitecturetakendirectlyfromSiliconIntelligence.com

This example demonstrates the execution model of the Defoe by computing the following set of expressions.

a = x + y - z

b = x + y - 2 * z

c = x + y - 3 * z

Register assignments: r1 = x, r2 = y, r3 = z, r32 = a, r33 = b, r34 = c Line # Code Comments

1. add r4 = r1, r2 // r4 = x + y

2. shl r5 = r3, 1 // r5 = z 1, i.e. z * 2

3. mul r6 = r3, 3 ; // r6 = z * 3. Stop bit.

4. sub r32 = r4, r3 // r5 = a = gets x + y - z

5. sub r33 = r4, r5 ; // r33 = b = x + y - 2 * z.

// Stop bit.

6. sub r34 = r4, r6 ; // r34 = c = x + y - 3 * z.

// Stop bit.

The first three lines are followed by a stop bit to indicate that those three operations constitute a MultiOp and that they should be executed in parallel. Unlike a super scalar processor where independent operations are detected by the processor, the programmer/compiler has indicated to the processor by means of the stop bit that these 3 operations are independent. The multiply operation will typically have a higher latency than the other instructions. In that case we have two different ways of scheduling this code. Since Defoe already uses score boarding to deal with variable load latencies, it is only natural for the scoreboard to stall issue till the multiply operation is done. In a traditional VLIW processor, the compiler will insert additional NOPs after the first MultiOp. Lines 4-6 show how structural hazards are handled in a VLIW system. The compiler is aware that Defoe has only two simple integer ALUs. Even though instruction


6 is independent of instructions 4 and 5, because of the unavailability of a suitable function unit, instruction 6 is issued as a separate MultiOp, one cycle after its two predecessors. In a super scalar processor, this decision will be handled at run-time by the hardware.

Reference: B. K. Mathew, “Very Long Instruction Word Architectures (VLIW Processors and Trace Scheduling),” 2006, http://www.siliconintelligence.com/people/binu/coursework/686_vliw/node12.html

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