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Integrated Circuit Interface for SAW Biosensors Applications

by Aggour, Khaled, MS

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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 200mW
power consumption.


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List of Abbreviations
Abbreviation Definition
AC Alternating Current
ADC Analogue to Digital Converter
AlN Aluminum Nitride
ASIC Application Specific Integrated Circuit
BAW Bulk Acoustic Wave
BCD Binary Coded Decimal
BJT Bipolar Junction Transistor
CMOS Complementary Metal Oxide Semiconductor
DAC Digital to Analogue Converter
DC Direct Current
DSP Digital Signal Processor
FAS Fatty Acid Synthetase
FPGA Field Programmable Gate Array
FRET Fluorescence Resonance Energy Transfer
HDL Hardware Description Language
IC Integrated Circuit
iCHEM Infochemical Communication
IDT Inter-Digital Transducer
IF Intermediate Frequency
LiTaO3 Lithium Tantalate
LO Local Oscillator
MCU Micro-Controller Unit
MEMS Micro Electrical Mechanical Systems
MFC Mass Flow Control
MOS Metal Oxide Semiconductor
MOSFET Metal Oxide Semiconductor Field Effect Transistor
PSS Periodic Steady State
O/PBP Odorant / Pheromone Binding Proteins
OR Olfactory Receptor
QCM Quartz Crystal Microbalance
RF Radio Frequency
SAW Surface Acoustic Wave
SAWR Surface Acoustic Wave Resonator
SH-SAW Shear Horizontal Surface Acoustic Wave
SiO2 Silicon Dioxide
TC Temperature Coefficient
TCD Temperature Coefficient of Delay
TCF Temperature Coefficient of Frequency
TD Trans-membrane Domain
UHF Ultra High Frequency

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VHSIC Hardware Description Language
Very High Frequency
Very large Scale Integration
Zinc Oxide

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Chapter 1: iCHEM Project Overview 1

Chapter 1

Introduction and iCHEM Project

1.1 Introduction

Pheromone biosynthesis pathways are comprehensible by modern biological science.
Understanding the way pheromone molecules (a key category in infochemical
communications (iCHEM)) are detected and decoded can help developing the field
of infochemical communications. The iCHEM project aim is to emulate the
molecular, sub-cellular and cellular machinery of the biosynthesis pathways of
pheromone infochemical production in the moth Spodoptera littoralis.

The bio-synthesis and detection pathways implemented in this project form a
novel type of device technology for chemical communication over space and time.
The info chemical communication can be used in automatic identification and data
capture (AIDC), product labelling, search and rescue, air silent communication,
unmanned space exploration, medical diagnosis and treatment, therapeutic agents
and environmental control.

The moth is a suitable model for chemical communication because of its
ability to use a blend of infochemicals in a precisely controlled mix (Löfstedt et al.,
1988). Both the moth infochemicals and biosynthesis steps are well characterised
(Linn et al., 1995). Moreover, the moth antenna is very sensitive to a few molecules
of the infochemical blend over distances of several hundreds of metres.

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Chapter 1: iCHEM Project Overview 2

The emulation system will be composed of two main entities: The first unit is
the chemo-emitter which is responsible for producing an accurate blend of
synthesized composites in programmable ratios of concentration. The other entity is
the chemo-receiver. Its main function is to decode the ratio metric information
received based on the molecular decoding of receptor and antennal lobe neurons of
the moth.

1.2 Technological aspects and State-of-the art

Figure 1- 1 Schematics of the infochemical system of the project

Source: European Community, 2006. Biosynthetic infochemical communication, URL:, Accessed 18th June, 2010.

Figure 1-1 shows a schematic diagram of one possible configuration of biosynthetic
modules forming an infochemical communication system. The joint biosynthesis
subsystem constructs the chemo-emitter, which is defined as a micro system that can
produce an exact mix of predefined volatile compounds in controllable concentration
ratios. “The chemoemitter exploits three types of biosynthetic modules for the
production of infochemicals based upon known enzymatic activity within the
exocrine system of the moth – chain shortening (-2C), desaturase (Δn), and
functional group modification (functional group is indicated by alcohol (OH), aldehyde
(Ald), hydrocarbon (Hc), acetate ester (OAc) or epoxide (Epox)). A
piezoelectric actuator (Q) can deposit an infochemical blend onto a surface or
produce a fine aerosol.” European Community, Biosynthetic infochemical
communication, 2006. The chemo-receiver is the detection system which is a
combination of Trans-membrane domain (TD) transduction and neuronal processing.
Microreactors for chain restriction, de-saturation, and operational adjustment are
designed to be exchangeable, acting upon a common precursor fatty acid.

The infochemical component ratios may be programmed in the chemo-emitter
through mass flow control (MFC) and recovered in the receiver using a large set of

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Chapter 1: iCHEM Project Overview 3

proteins whose original natures were altered during mixing. This change is detected
by using Fluorescence Resonance Energy Transfer (FRET) optical measurement,
Hoffmann et al. and Kenakin (2005 cited European Community, Biosynthetic
infochemical communication, 2006).

It is possible to create almost unlimited diversity of ligands and
complementary detectors using a hierarchy of biosynthetic modules. By controlling
the volatility of the predefined infochemical compounds, it is possible to transmit
time-sensitive and time-registered information. The volatility of the ligand may also
determine over which distances communication may occur.

1.3 Scientific aspects and State-of- the art

In animals in general and insects in particular, olfaction plays a dominant role in
everyday routines. Enemy avoidance, food hunting, and sex partner communications
are clear examples of the importance of the insect olfactory system. This
communication is carried out using infochemicals (Pearce et al., 2005).

Pheromones are the means of chemical communications between individuals
from the same species. This is the essential information exchange shape between
individuals. Neuro-endocrine function provides the chemical signals due to the
relevant behavioural action. Pheromone communications in insects is very complex;
the information usually is composed of different compounds to provide diversity. In
order to reproduce an insect behaviour; an exact set of pheromone cues and a
specific concentrations ratios set should exist simultaneously.

The compound shape of infochemical communication of insects through
chemicals has not been employed so far. The project focuses on understanding the
details of the biosynthesis of pheromones pathways and detection and decoding
mechanism to provide a starting point to expand new emulated biological
subsystems covering acid synthesis, chain shortening, functional group adaptation,
receptor protein signalling, and neuronal sensory handling out. Gathering these
elements will produce mixtures of infochemicals, deployed in varying mediations to
communicate information over space and time. This will be done by exploring the
pheromone biosynthesis concerned biological processes and detection pathways and
deploy these in supporting MEMS technology including micro-reactors and microfluidics,
nano-biotechnology and by constructing biologically constrained neuron
models. Convergence of expertise in diverging fields is a challenging task for
achieving the project goals. Pheromone biochemistry, genetics, biophysics,
materials, neuroscience and engineering are all utilised in the project.

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Chapter 1: iCHEM Project Overview 4

It is required have a single biological model that has the required chemical
transmission specifications in pheromones and the necessary chemical reception in
biosynthesis and detection pathways. The moth is a suitable choice for this study
because its sexual pheromone behaviour has been widely studied. In addition, its
behaviour depends solely on chemical signals.

Figure 1- 2 The moth pheromone communication

a. Pheromone compounds used by ermine moths and Spodoptera littoralis
b. The schematic of the biosynthetic pathways in Lepidoptera
Source: European Community, 2006. Biosynthetic infochemical communication / URL:, Accessed 18th June, 2010.

The moth pheromone communication is illustrated in figures 1-2.a and 1-2.b.
The filled circles are known pheromone components; open circles are gland
constituents. It can be seen that the moth develops up to nine distinctive pheromones
in different ratios to identify himself to his mate. The shown compounds are only a
small fraction of hydrocarbon chain based molecules composed by insects’ species.
The moth Spodoptera littoralis provides an ideal biological model for pheromone
communications, accordingly, it was chosen as the modelled insect in this project. In
this moth, at least two distinctive and well-studied pheromone components exist: Z9,
E11-14: OAc and Z9, E12-14: OAc. The animal detection pathways have been
extensively defined which makes this moth a highly favourable choice for the project

1.4 Pheromone Biosynthesis Pathways

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Chapter 1: iCHEM Project Overview 5

The moth nervous system controls the mechanism of the biosynthesis and pathway
detection and accordingly the chemical communications. A key factor is to know
whether the pheromone components are produced dietary forerunners or synthesised
from the start. The moth female synthesise the components from the beginning. This
indicates the association with complex biosynthesis.

The pheromone compounds are mostly simple structure constituted from
hydrocarbon chains and oxygenated functional groups. The process of producing the
pheromones can be summarized as follows:

• Acid synthesis: Fatty acid Synthetase (FAS) on acetyl-CoA carboxylase
constructs saturated fattcy acids.
• De-Saturases: Provides double bonds to the fatty acid chain.
• Chain shortening
• Reduction/functional group modification.

From the above steps, it is clear that the broad varieties of pheromone
compounds can be produced through simple chemicals via basic reactions using
hierarchical group of simple chemical operations. Using modular operations allows
the construction of various composites that can be used in many applications inside
and outside the project.

1.5 Pheromone Detection Pathways

The pheromone is sensed in the insect’s environment as a signal of mate location.
Odour molecules are absorbed by a surface when hitting the sensilla. They spread
through the cuticle to interact with special purpose proteins. The Odorant/Pheromone
Binding Proteins (O/PBP) transport the molecules to the receptors.

Ligand binding TD receptors are the main special purpose units in the
detection pathways systems. Olfactory Receptors (OR) genes encode a large group
of GPCRs to detect the diverse set of ligands.

The project uses a transcript factor Gal4 to locate the equivalent moth
pheromone binding receptors to be able to transduce the genes responsible for
encoding the protein receptors. Two approaches will be made to make the
transduction of the biosynthesis detections:

First, immobilizing the protein within a lipid bi-layer was made then the
related mass change to release of G-protein after GPCR activation was measured. In
the mean time, the measurement of conformational changes directly using FRET
measurements was carried out.

The project is a collaboration between five European universities. The
university of Warwick Sensors Research Laboratory (SRL) role is to integrate the

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Chapter 1: iCHEM Project Overview 6

micro-systems, chemo-sensor development, integrate the system using rapid
prototyping and micro-stereo lithography.

1.6 Aims of the thesis

The thesis objective is to develop an analogue front-end Integrated Circuit (IC) to
interface the biosensor to a digital VLSI implementation of the neuromorphic model
which is developed by another partner university (figure 1-3).

Figure 1- 3 System Block Diagram

A SAW resonator sensor Interface IC and an integrated temperature control
circuit were designed and simulated. The proposed circuit is capable of producing a
digital output depending on the biological sensed quantity. The specified frequency
resolution of the proposed interface circuit is 100Hz (10ms). The circuit maximum
accepted temperature tolerance is 0.1°C. The chip power supply is a 5V DC supply.

1.7 Thesis Outline

The thesis describes the design and simulation of a front-end integrated circuit
interface for Surface Acoustic Wave biosensors. The first chapter presents the
iCHEM project overview and the thesis objectives and its role in the project.

Chapter 2 covers the theoretical background related to the project including
smart sensors, biological sensors and SAW devices and using SAW devices as
biosensors. In addition, SAW resonator electrical modelling is presented with a
particular focus on 2-port resonators.

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Chapter 1: iCHEM Project Overview 7

Chapter 3 reviews state of the art technologies in SAW resonators signal
conditioning. Some SAW oscillator technologies are discussed. A brief literature
review of several mixers topologies is presented. Sensors temperature compensation
and control techniques are described. Previous reports on SAW device integration
with its interfacing circuit and temperature control are briefly shown.

Chapter 4 contains the design of the interface circuit including the system
design and detailed description of the oscillator and mixer design in addition to the
temperature control circuit. All the circuit blocks layout are shown indicating the
digital and analogue parts. The full chip layout is presented.

Chapter 5 shows the simulation results block by block. This includes the
oscillator and mixer simulation in time and frequency domains. The frequency to
digital circuit and digital simulations are illustrated. DC analysis and simulation
shows the circuit power consumption. Temperature effect and temperature control
simulation are performed.

Chapter 6 concludes the work and discussing the results and the objectives
realisation. Possible further improvements on the circuit and its integration on the
same chip with the SAW are proposed.

1.8 References

1. European Community, 2006. Biosynthetic infochemical communication/
Accessed 18th June, 2010.
2. Linn Jr, C. E., Roelofs, W. L., 1995. Pheromone communication in moths

and its role in the speciation process. In Speciation and the Recognition
Concept – Theory and Application. ed. Lambert, D.M. and Spencer, H.G.,
John Hopkins University Press, Baltimore, USA.
3. Lofstedt, C., Bengtsson, M., 1988. Sex pheromone biosynthesis in the

codling moth Cydia pomonella involves E9-desaturation. - J. Chem. Ecol.
vol. 14, pp. 903-915.
4. Pearce, T.C., Fulvi-Mari, C., Covington, J.A., Tan, F.S., Gardner, J.W.,

Koickal, T.J., Hamilton, A., 2005. Silicon based neuromorphic
implementation of the olfactory bulb. IEEE Neural Engineering Conference,
WA, USA, pp. 307-312.

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