Details

Integrated Circuit Interface for SAW Biosensors Applications

by Aggour, Khaled, MS

Abstract (Summary)
This thesis explores the design and simulation of an Integrated Circuit to interface Surface Acoustic Wave (SAW) sensors in biological applications. The signal conditioning circuit also consists of an integrated temperature measurement and control mechanism to keep the SAW chip in a constant temperature. The design includes the SAW resonator modelling. The key issues in the design are the SAW resonant frequency translation accuracy and the precise temperature control without high power consumption. Cadence software tools were used for the design, modelling, simulation and layout stages. For digital simulation of the temperature control circuit; ALDEC Active-HDL software were used. The 2-port SAW resonator is modelled as a resonant circuit including motional capacitance, inductance and resistance and parallel IDT capacitance based on specifications. The designed SAW model takes in consideration the temperature effect. The model is general and can be utilised at further applications. The SAW resonator is positioned in an oscillator feedback loop as the frequency selection element. Current source inverting amplifier was chosen to compensate for the SAW attenuation losses to achieve an oscillator open loop gain more than unity. A trade-off was made to choose the optimum aspect ratio within the available 0.6µm technology between the gain and bandwidth due to parasitic effects. Two oscillators were used each consists of a SAW resonator, one as a reference without chemical perturbation and the other is sensitive to biological stimulus. The two oscillators’ outputs are buffered and applied to the inputs of a mixer. The mixer output is low pass filtered through a two-section RC filter to provide the frequency difference of the two oscillators’ outputs. The filtered signal is converted to a square wave by applying it with its delayed version to a comparator. The comparator output supplies a digital counter’s clock for a constant counting period (10 ms). The counter output is proportional to the frequency change and consequently the sensed quantity and is ready for digital processing. The time resolution is 10ms. The circuit has the ability to measure up to 6.5MHz. The SAW temperature behaviour was tested, analysed, and modelled. The relationship between heating power and temperature was experimentally tested and the results were applied to the temperature control logic mechanism. The temperature measurement of the SAW is done via a gold resistive heater. The heater resistance is placed in series with a temperature invariant poly silicon resistance in order to measure the current. The voltage drop and flowing current across the heater are used to calculate the heater resistance. The voltage across the heater is converted to digital by an Analogue to Digital Converter (ADC). A digital logic calculates the resistance and consequently the temperature. The logic compares the current temperature with the required temperature and feeds a suitable control voltage to realize the required temperature via a Digital to Analogue Converter. The temperature operating range is between 20°C and 50°C with maximum 200 mW power consumption.
Full Text Links

Main Document: View

10-page Sections: 1 2 3 4 5 6 7 8 9 10 11 12 13 Next >

Bibliographical Information:

Advisor:Prof Julian Gardner

School:University of Warwick

School Location:United Kingdom

Source Type:Master's Thesis

Keywords:CMOS, Surface acoustic wave (SAW), sensor interface circuit,Bio sensor, microelectronics, mixer, oscillator

ISBN:

Date of Publication:07/05/2010

Document Text (Pages 1-10)

i

Integrated Circuit Interface for

SAW Biosensors Applications

By

Khaled Aggour

School of Engineering
University of Warwick

A thesis submitted to the University of Warwick
for the degree of Master of Science by Research
February 2010


Page 2

ii

Contents

List of Figures.......................................................................................................... 6

Acknowledgment ..................................................................................................... 8

Declaration .............................................................................................................. 9

Abstract ................................................................................................................. 10

List of Abbreviations ............................................................................................. 12

Chapter 1 ................................................................................................................. 1

1.1 Introduction .................................................................................................... 1

1.2 Technological aspects and State-of-the art ...................................................... 2

1.3 Scientific aspects and State-of- the art............................................................. 3

1.4 Pheromone Biosynthesis Pathways ................................................................. 4

1.5 Pheromone Detection Pathways...................................................................... 5

1.6 Aims of the thesis ........................................................................................... 6

1.7 Thesis Outline ................................................................................................ 6

1.8 References ...................................................................................................... 7

Chapter 2 ................................................................................................................. 8

2.1 Introduction .................................................................................................... 8

2.2 Sensors ........................................................................................................... 8

2.3 Smart Sensors................................................................................................. 9

2.4 Biosensors .................................................................................................... 11

2.5 Surface Acoustic Wave (SAW) sensors ........................................................ 12

2.5.1 Introduction ........................................................................................... 12

2.5.2 Acoustic Wave sensors:.......................................................................... 14

2.5.2.1 Rayleigh Surface Acoustic Waves: .................................................. 14

2.5.2.2 Shear Horizontal Surface Acoustic Waves (SH-SAW) ..................... 15

2.5.2.3 Love Surface Acoustic Waves ......................................................... 15

2.6 SAW Devices as Biosensors ......................................................................... 15

2.6.1 SAW Biosensor Applications ................................................................. 16

2.6.2 SAW Delay-Line Biosensor ................................................................... 17


Page 3

iii

2.6.3 SAW Resonator Biosensor ..................................................................... 18

2.6.4 Smart SAW Resonator Biosensor........................................................... 18

2.7 SAW Resonator Modelling ........................................................................... 19

2.8 Conclusion ................................................................................................... 22

2.9 References .................................................................................................... 23

Chapter 3 ............................................................................................................... 26

3.1 Introduction .................................................................................................. 26

3.2 SAW Oscillator ............................................................................................ 26

3.3 Mixer............................................................................................................ 28

3.4 Temperature Control..................................................................................... 31

3.5 System Integration........................................................................................ 32

3.6 Conclusion ................................................................................................... 32

3.7 References .................................................................................................... 33

Chapter 4 ............................................................................................................... 35

4.1 System Design.............................................................................................. 35

4.2 Oscillator...................................................................................................... 36

4.3 Mixer............................................................................................................ 46

4.4 Frequency to Digital Conversion .................................................................. 48

4.5 Temperature Control..................................................................................... 51

4.5.1 Temperature effect and control circuit .................................................... 51

4.5.2 Temperature Control logic ..................................................................... 55

4.6 Layout .......................................................................................................... 58

4.6.1 Oscillator layout..................................................................................... 59

4.6.2 Mixer Layout ......................................................................................... 61

4.6.3 Sine to square converter Layout ............................................................. 62

4.6.4 Analogue layout ..................................................................................... 63

4.6.5 Digital layout ......................................................................................... 63

4.6.6 Chip layout ............................................................................................ 65

4.7 Conclusion ................................................................................................... 65

4.8 References .................................................................................................... 66

Chapter 5 ............................................................................................................... 67

5.1 Introduction .................................................................................................. 67


Page 4

iv

5.2 Oscillator...................................................................................................... 67

5.3 Mixer............................................................................................................ 71

5.4 Digital Conversion........................................................................................ 76

5.5 Power consumption ...................................................................................... 80

5.6 Temperature effect........................................................................................ 81

5.7 Temperature Control..................................................................................... 84

5.8 Conclusion ................................................................................................... 88

5.9 Reference ..................................................................................................... 89

Chapter 6 ............................................................................................................... 90

6.1 Objectives Revision...................................................................................... 90

6.2 Achievements ............................................................................................... 91

6.2.1 SAW Modelling ..................................................................................... 91

6.2.2 Interfacing Circuit .................................................................................. 91

6.2.3 Temperature Effect................................................................................. 92

6.3 Specifications ............................................................................................... 93

6.4 Further Work................................................................................................ 93

6.5 References .................................................................................................... 95

APPENDIX A ....................................................................................................... 96

A.1 Basic Design Rules ...................................................................................... 96

A.2 Device Parameters ....................................................................................... 97

A2.1 MOS Transistors .................................................................................... 97

A2.2 Sheet Resistances ................................................................................... 97

A2.3 Gate Capacitance.................................................................................... 98

A2.4 Parasitic Capacitances ............................................................................ 98

A.3 Analogue Cells ............................................................................................ 99

A.3.1 Band gap ............................................................................................... 99

A.3.2 Bias Cell ............................................................................................. 100

A.3.3 Comparator ......................................................................................... 100

A.3.4 Oscillator (Clock)................................................................................ 101

A.3.5 Power On Reset ( ................................................................................ 101

A.3.6 Analogue to Digital Converter............................................................. 102

A.3.7 Digital to Analogue Converter............................................................. 103


Page 5

v

APPENDIX B...................................................................................................... 104

B.1 16-bit Counter............................................................................................ 104

B.2 Clock Divider by 215 ................................................................................. 105

B.3 System Temperature control ...................................................................... 105

B.4 Clock Divider by 100,000 .......................................................................... 116


Page 6

vi

List of Figures

Figure 1- 1 Schematics of the infochemical system of the project........................................ 2
Figure 1- 2 The moth pheromone communication................................................................ 4

Figure 2- 1 Smart Sensing system...................................................................................... 10
Figure 2- 2 General block diagram of biosensors ............................................................... 11
Figure 2- 3 Piezoelectric effect .......................................................................................... 13
Figure 2- 4 The main two Interdigital Transducers (IDT) structures ................................... 13
Figure 2- 5 Surface acoustic wave generation in Quartz by IDTs ....................................... 14
Figure 2- 6 Schematic of a Love wave propagation region and relevant layers ................... 15
Figure 2- 7 Basic SAW biosensor setup exemplified by a SAW immunosensor ................. 16
Figure 2- 8 Schematic of a delay-line arrangement with inter-digitated transducers............ 17
Figure 2- 9 SAW resonator oscillator block diagram.......................................................... 18
Figure 2- 10 Sensing system block diagram....................................................................... 19
Figure 2- 11 SAW resonators ........................................................................................... 20
Figure 2- 12 One-Port SAW resonator electrical circuit model........................................... 20
Figure 2- 13 Two-port SAW resonator electrical circuit model .......................................... 21

Figure 3- 1 Pierce Oscillator Connections......................................................................... 27
Figure 3- 2 Colpitt Oscillator connections ......................................................................... 27
Figure 3- 3 Mixer block diagram ....................................................................................... 28
Figure 3- 4 Single balanced mixer schematics ................................................................... 30
Figure 3- 5 Unbalanced mixer schematics ......................................................................... 30

Figure 4- 1 Sensing system block diagram......................................................................... 36
Figure 4- 2 Oscillator open loop block diagram ................................................................. 36
Figure 4- 3 SAW circuit model.......................................................................................... 37
Figure 4- 4 Calculated SAW resonator circuit model ......................................................... 39
Figure 4- 5 SAW model simulated gain and phase response............................................... 39
Figure 4- 6 Current source inverter amplifier ..................................................................... 40
Figure 4- 7 Complete current inverter amplifier schematics ............................................... 41
Figure 4- 8 Amplifier transfer function .............................................................................. 44
Figure 4- 9 Buffer schematic diagram................................................................................ 45
Figure 4- 10 Oscillator block diagram ............................................................................... 45
Figure 4- 11 Square law mixer .......................................................................................... 46
Figure 4- 12 Mixer schematics .......................................................................................... 47
Figure 4- 13 Mixer output to square wave conversion........................................................ 48
Figure 4- 14 Comparator input signals (mixer output and its delayed version).................... 49
Figure 4- 15 Comparator input and output signals.............................................................. 49
Figure 4- 16 Square-wave to digital word conversion ........................................................ 50
Figure 4- 17 Functional diagram of 50Hz clock generation ................................................ 51
Figure 4- 18 SAW resonator and heater chip photo............................................................ 52
Figure 4- 19 Temperature control circuit ........................................................................... 52


Page 7

vii

Figure 4- 20 Experimental results for Resistance vs. Temperature ..................................... 53
Figure 4- 21 Experimental results for Temperature vs. Heating Power ............................... 54
Figure 4- 22 Temperature control logic flow chart ............................................................. 56
Figure 4- 23 Heater voltage vs. Control voltage................................................................. 58
Figure 4- 24 Current source inverting amplifier layout....................................................... 59
Figure 4- 25 Buffer amplifier layout .................................................................................. 60
Figure 4- 26 Layout of the oscillator.................................................................................. 61
Figure 4- 27 Mixer layout.................................................................................................. 61
Figure 4- 28 Sine-to-square wave converter layout ............................................................ 62
Figure 4- 29 Layout of the analogue circuit ....................................................................... 63
Figure 4- 30 Clock divider layout ...................................................................................... 64
Figure 4- 31 Digital counter layout .................................................................................... 64
Figure 4- 32 Full chip layout ............................................................................................. 65

Figure 5- 1 Test bed of the oscillator ................................................................................. 68
Figure 5- 2 Reference oscillator transient response ............................................................ 68
Figure 5- 3 Reference oscillator PSS simulation Vout versus frequency............................. 69
Figure 5- 4 Reference oscillator PSS simulation Vout versus frequency (dB)..................... 70
Figure 5- 5 Sensing oscillator PSS simulation Vout versus frequency ................................ 71
Figure 5- 6 Mixer simulation test bed ................................................................................ 71
Figure 5- 7 Mixer unfiltered output ................................................................................... 72
Figure 5- 8 Mixer output after Low-pass filter ................................................................... 73
Figure 5- 9 Mixer PSS fundamental voltage and harmonics ............................................... 74
Figure 5- 10 Mixer PSS Fundamental voltage and harmonics in dB ................................... 74
Figure 5- 11 Mixer output conversion to a square wave ..................................................... 75
Figure 5- 12 Comparator positive and negative inputs ....................................................... 75
Figure 5- 13 Comparator square wave output .................................................................... 76
Figure 5- 14 Counter transitions at clock rising edge ......................................................... 78
Figure 5- 15 Counter output at one complete Enable cycle................................................. 79
Figure 5- 16 Oscillator DC power...................................................................................... 80
Figure 5- 17 Mixer DC power ........................................................................................... 81
Figure 5- 18 The SAW oscillator frequency change versus temperature............................. 83
Figure 5- 19 Mixer output at temperature range from 20°C to 50°C ................................... 83
Figure 5- 20 Temperature control calibration process ........................................................ 85
Figure 5- 21 Temperature control logic status after asynchronous reset .............................. 86
Figure 5- 22 Temperature control logic voltage enabled .................................................... 87
Figure 5- 23 Temperature control voltage calculation ........................................................ 88

Figure 6- 1 A possible layout of integrated CMOS implementation for SAW and interface
circuit ............................................................................................................................... 94


Page 8

viii

Acknowledgment

Foremost, all the best thanks are due to God, the most merciful. God blessed me and
gave me all guidance and support during my study.

I cannot thank my wife Rodania for her unlimited support. She had a very tough year
with me and supported me all the time. She helped me in my study in many aspects
and supported me both financially and spiritually. Without her support, I would not
fulfil anything special. I would like to express my great appreciation to what she did.

I would like to thank my academic supervisors Prof. Julian Gardner and Dr. Marina
Cole for their supervision and guidance. They provided me with the chance to work
in such a large project in an important field. They helped me to overcome many
technical challenges during my degree. They deserve many thanks for their
continuous support during my study.

I am grateful to Dr. Zoltan Racz for assisting me in iCHEM project matters, SAW
modelling and lab experiments. The support of Dr. Prasanta Guha in using Cadence
tools was very powerful and I owe him special thanks. I am thankful to Mr. Frank
Courtney for helping me setting up experiments quickly and efficiently. I would like
to thank Dr. Foysol Chowdhury for his support in digital layout and is using tools. I
would like to express my thanks to all the staff of Sensors Research Laboratory for
their support and collaboration.

It is important to me to acknowledge the financial support I received from my
brother Hesham, my friends Ahmed Abdel-Alim, Tamer Nakhla, and Mostafa
Abdel-Azim. I show them all my gratitude. I would like to thank my mother, my
sister Mona, my parents-in-law, and my brothers Yasser and Wael.

Last but not least, I cannot forget my undergraduate professors Abdel Halim Zekry,
Mohamed El-Saba, and Mohamed Marzouk for their support to go towards research
study.


Page 9

ix

Declaration

This thesis is presented according to the regulations for the degree of Master by
Research.

The work described in this report is original and my own work except otherwise
indicated.

The thesis has not been submitted in any previous application for a degree at another
university.


Page 10

x

Abstract

This thesis explores the design and simulation of an Integrated Circuit to interface
Surface Acoustic Wave (SAW) sensors in biological applications. The signal
conditioning circuit also consists of an integrated temperature measurement and
control mechanism to keep the SAW chip at a constant temperature. The design
includes the SAW resonator modelling. The key issues in the design are the SAW
resonant frequency translation accuracy and the precise temperature control without
high power consumption.

Cadence software tools were used for the design, modelling, simulation and
layout stages. For digital simulation of the temperature control circuit; ALDEC
Active-HDL software were used.

The 2-port SAW resonator is modelled as a resonant circuit including motional
capacitance, inductance and resistance and parallel IDT capacitance based on
specifications. The designed SAW model takes into consideration the temperature
effect. The model is general and can be utilised for further applications.

The SAW resonator is positioned in an oscillator feedback loop as the
frequency selection element. A current source inverting amplifier was chosen to
compensate for the SAW attenuation losses to achieve an oscillator open loop gain
more than unity. A trade-off was made to choose the optimum aspect ratio within the
available 0.6µm technology between the gain and bandwidth due to parasitic effects.
Two oscillators were used each consisting of a SAW resonator, one as a reference
without chemical perturbation and the other is sensitive to biological stimulus. The
two oscillators’ outputs are buffered and applied to the inputs of a mixer. The mixer
output is low pass filtered through a two-section RC filter to provide the frequency
difference of the two oscillators’ outputs. The filtered signal is converted to a square
wave by applying it with its delayed version to a comparator. The comparator output
supplies a digital counter’s clock for a constant counting period (10 ms). The counter
output is proportional to the frequency change and consequently the sensed quantity
and is ready for digital processing. The time resolution is 10ms. The circuit has the
ability to measure up to 6.5MHz.

The SAW temperature behaviour was tested, analysed, and modelled. The
relationship between heating power and temperature was experimentally tested and
the results were applied to the temperature control logic mechanism. The
temperature measurement of the SAW is done via a gold resistive heater. The heater
resistance is placed in series with a relatively temperature invariant poly silicon
resistance in order to measure the current. The voltage drop and flowing current
across the heater are used to calculate the heater resistance. The voltage across the
heater is converted to digital by an Analogue to Digital Converter (ADC). A digital
logic calculates the resistance and consequently the temperature. The logic compares

© 2009 OpenThesis.org. All Rights Reserved.