Biomedical Sensors

Parte 1

BIOMEDICAL SENSORS

CODE COURSE: 39168-ENG

CREDITI FORMATIVI: 6CFU

(Corso Integrato)

DOCENTI:

Valerio Re valerio.re@unibg.it

Massimo Manghisoni massimo.manghisoni@unibg.it

Matteo Pezzoli matteo.pezzoli@unibg.it

MATERIALE DEL CORSO:

Moodle course - “Biomedical sensors, smart sensors and electronic system”

PW:bis2122

On Teams Channel in section “File”

MODALITA’ D’ESAME:

Oral exam, covering the subjects discussed during the course.

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INTRODUCTION

Sensors and microelectronic systems, also known as electronic technologies, are

▶ considered as the key technology of our modern life. They can be recognized as

enablers of novel application, impacting on our society. It is possibile to assume that

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this kind of technology will become more and more important during the years thanks

to their progression. It is known that di erent elds of our life are e ected by sensors.

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Thanks to the use of this kind of technologies, di erent elds, starting from healthcare

to industrial production, are being revolutionized by interconnected microelectronic

systems. This one are able to acquire and process all the data that are reached by the

sensors. four elds,

It can be possible summary this kind of market in which are:

- Smart industries: presence of automated and intelligent industrial processing for the

de nition of nal products thanks to sensors and electronic systems (articulated arms,

robots, automatics probes).

- Smart thing: considering wearable, like smart watch, or not wearable, like phone,

device, which are able to monitor di erent kind of parameters of the person, like heart

rate, blood pressure, oxygen content. Smart thing s are able to monitor both people

and environment in which people are living. A bene t of this kind of technology is that

all of them can communicate each other, sending information to cloud or archive

system.

- Smart home & city: presence of sensors, whose role is to control the house, like anti-

theft sensors, or also optimize the consume of the energy and water.

- Smart driving: vehicles are full of sensors which permit to point out all the possible

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problems that the vehicle could have, giving an advertisement to the driver, like lights

on the ignition dial or parking sensors. Nowadays it is working on self-driving vehicles.

4 evolution trends of electronic technologies,

During the years there has been an which

had started in 1980 and it continues to improved, decreasing the sizes and increasing the

number of processors.

At rst there was the Moore theory in which object were use for processing, going to

de ne the information age; these era was characterized by the presence of personal

computer and laptops. Nowadays we are living in the More that Moore Theory, which is

something that goes over the Moore rst law. Also known as interaction age, it is based

on the concept of sensing due to the combinations of di erent technologies for data

processing device. After this phase it has been predicted the Beyond Moore Theory,

which will be considered as the enhancement age. This era will be characterized from

some hypothesis that we don0t know if will became true, like telekinesis and robotic

servants.

Enabler: abilitatore;

1 Field: campo, settore;

2 Point out: segnalare;

3 Light on the ignition dial: spie sul quadrante di accensione;

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The kind of architecture that we

will analyzed during the course

are composed by integrated

sensors and microelectronic

systems. Considering the

image on the right, it stats from

sensing front end, which is the

part that interface with the real

world (microphone, antenna,

gyroscope, radio signals). After

the acquisition of the real signal

by the sensor, this one convert it into digital form, expressing the real input in voltage or

current units.This is called signal processing. When this data is started we can store the

data in electronic device or send them in a remote site which work on speci c protocols.

Di erent kind of transmission to go to another electrical device called gateway, which

collect information coming from di erent devices in the same local environment. After that

the information goes to cloud where data can be store and analyzed.

The possible applications of kind of architecture can be on the four elds that have been

de ned before. For the industries is the idea is to monitor some industrial machineries to

see if there could be some anomalous behavior that require maintenance actions before

the onset of problematics thanks to the use of sensors which can detect some

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anomalous behaves that cannot detected by human. All the data that have

been collected have been send to electronic system, which can process

them and then o er some possible solutions to limit the damage.

As it has been seen before, the application of sensors on person can be

useful for monitoring they health conditions. In this case it is possibile to

talk about wearable sensors which can be use for detect the conditions of

both person and environment. An important thing is that the sensors can

augment the person’s perception, so they do not increase only the ve

senses. This special feature increases the possibility to de ne an

augmented human.

It has also seen how the new digital technologies are having a large impact

on buildings and infrastructures. It is possibile to control the performance of

the structures using sensors and algorithms. These make possible the

monitoring of aging and degradation, going to plan ordinary and extraordinary

maintenance. So protecting and monitoring the structure of building consists in:

- Use MEMS sensors for pressure and stability real-time monitoring;

- Consideration of chemical sensors for pH monitoring;

- Analysis of energy harvesting from structural vibrations for data transfer;

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- Big data analysis with massive numbers aggregation for better understanding and

structure collapse prevention.

Onset: insorgenza;

5 energy harvesting: raccolta di energia

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OPERATIONAL AMPLIFIER AND LAPLACE TRANSFORM

operational ampli er

An can be de ned as a di erential

ampli er, which structure is generally characterized by the

presence of two inputs and one output. In microelectronic

system, the main analog signal processing function are

performed by circuits based on operational ampli ers,

especially in negative feedback con gurations. It is possible

function:

to talk about two di erent

- The ampli cation of small signals generated by sensors;

- The attenuation/cancellation of disturbances and Schematic image of an operational

interferences with lters. ampli er.

As we can see in the image above, the operational ampli er is composed by two inputs;

these two are named non inverting input (V ) and inverting input (V ) in which it is possible

+ -

to applied two voltage signals. With regard the output signal, it is seen which is only one

and it can be named as V OUT.

Making mathematical consideration it is possibile to say

that:

- + −

V = A ⋅ (V − V )

V is the multiplication between the gain (A) and the

OUT OUT

di erence value between the non-inverting and inverting

input [1] [1] Equations of the value of V OUT.

- current (I).

Consideration about the At rst it can be seen

two current: I and I , which the rst is related to the non-

+ - + −

I = I = 0

inverted voltage while the second to the inverted voltage.

The basic mechanics of operational ampli ers considered

the value of the current equal to zero this because on of [2] Consideration of the value of the

[2] current.

them is linked to the ground. This can be considered as an

ideal condition, because it is possibile to have some

amount of current but its value is really small.

The majority of the operational ampli ers is designed to work

with a dual supply voltage, which role is to fed it to improve its

work. It is possibile to talk about the positive supply voltage

(+V ) and the negative supply voltage (-V ), which are

DD SS

symmetrical to the ground. The two supply voltages need not

necessarily have the same value and it is a characteristics of

the modern CMOS microelectronic systems . The versatility of

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these devices is such that there may be applications where

the negative voltage can be set to zero, that is, the

component is powered by a single voltage. In dual power

supply, the output signal level can range between the two Operational ampli er with supply

supply voltage values at less than a small margin, which can voltages

vary depending on the type of op amp adopted.

CMOS: kind of technology used in digital electronics for the de nition of integrated circuits,

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based on the use of the MOSFET transistor inverter.

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So, after this account, we can said that, in which

Considering the circuit, it is possible kind of circuit:

making some consideration. + −

I = I = 0

• V

In the equations [1] representing the OUT

+ − + −

V = A ⋅ (V − V ); (V − V ) = ;

• OUT

relation of V , it has spoken about A

OUT

the gain (A). This one is a very large considering A→∞, it is possible to say that

+ − + −

(V − V ) = 0; V = V

number, which in the ideal operational .

ampli ers corresponds to an in nite

value.

The yellow arrows represent the currents

which pass through the resistances (I

R1,

I ).

R2 inverting

This circuits represents the

ampli er, which uses the inverted input of

the operational ampli er as the main input

while the non inverted input is grounded. Negative feedback and operational ampli ers

So due to this characteristics it is possibile to make

some analysis:

+ −

V = V = 0

• , this because it is connected to the ground;

I = I , this is said considering the Kirchoh ’s law on knots.

• R1 R2

Considering also the Ohm’ laws it is possibile write the same thing in a di erent way:

V

V R

OUT

IN 2

V = − V

= − . So from this equation, it is know that: OUT IN

R

R R 1

1 2 transresistance ampli er

A circuits which presents a is used to convert a current signal

into a voltage signal. A possibile application is for the processing of signals from

photodiode, that is a junction did in a t reverse region, where the reverse current is

proportional to the intensity of the radiation

to which the did is exposed.

As it has said before, it is possibile

non-inverting

to talk also about

ampli ers, which uses the non-inverted

input of the operational ampli ers as the

main input while the inverted input is

grounded.

Also in this case it is possibile to make

some considerations. Positive feedback and operational ampli er

The equivalence between the currents and the

as it has been seen before,

voltages in the operational ampli er, can be written as:

V − V

V IN OUT

IN

I = I ; − = .

R1 R2

• R R

1 2 R

2

V = (1 + )V

This brings to: .

OUT IN

• R

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voltage

▶A variant of non-inverting ampli er is the

bu er. Considering the image alongside, the circuit

presents a connection from the negative input to the

output. Considering an idea ampli er with in nite

gain A and the ohm’s and Kirchho ’s laws, it is

possible make some mathematical consideration:

+ + − −

V = V V = V V = V Voltage Buffer

→ → .

in out

We can say that there is a unity going circuit (A=1) that works as an impedance adapter; it is placed

between a circuit that has an high output impedance and a circuit that has a low input impedance.

This kind of structure t is common used some application where it is not necessary have

like when we have to drive a load.

a change between an input and output signal, So this

circuit gives the opportunity to don’t have e ect.

d i e re n t i a l

C i rc u i t s t h a t p re s e n t

ampli ers are really important due to their

function. In many cases, when we have to

acquire information from sensors, it is

necessary making a measure in a

d i e re n t i a l w a y l i k e a n a l y z e d t h e

di erence value between a quantity that

we are detecting and its reference value

i.g. measure of temperature.

for this value

The sensor provides two inputs: one is

related to the reference quantity and the

second one to the quantity that has Differential ampli er

change. In order to measure this

di erence, it can be possible use this kind

of ampli er, that will give an output signal proportional to the di erence of the inputs

signals with a gain factor.

Considering the Ohm’s and Kirchho ’s R = R3 R = R

If and ,

law, it is possible make some 1 2 4 R

considerations. 2

V = (V − V )

It is possible to say that out 1 2

R

It can be also possible to talk 1

instrumentation ampli er,

about the

which is an high-performance version of this i.e.

simple di erential ampli er thanks to the presence of three di erential ampli ers.

measurement of the ECG signal.

The logic conforms that ideal and real operational ampli ers have a di erent behavior. We

have seen that ideal condition supposes that everything is perfect but this terms cannot

i.e. The gain (A) in real ampli er cannot be equal to an in nite

be applied in real world.

value because it depends on frequency of the signal applied on circuit. Another i.e. can be

the value of the current: in ideal case it can be equal to zero but in reality is has always a

small value. Also the CMRR value: in ideal operational ampli ers the output has given by

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CMRR: parameter used to evaluate the performance od a circuit when it has to amplify the di erence between two signals.

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the gain multiple by the di erence between V and V According to this we aspect that

+ -.

V will be equal to zero but in reality internal circuits works even if the two input voltage

out

have the same value, de ning a V ’s value near to zero.

out

CMRR

It is possible deepen the In mathematical way it can be written as:

A

concept. Also know as a d

| |

CMR R =

Common Mode Rejection Ratio, it A

CM

v

is a parameter which de nes how out

A =

where: , which represents di erential gain

d

well te operational ampli er v

in v v

approximates its ideal behavior as in in

+ − + −

v = + v = − v − v = v

in which: , , with: in

an high-gain di erential ampli er. 2 2

v

out

Remember: the di erential A =

While: , which represents the common-

CM v

gain gives informations about the in + −

v = v = v

capability of the circuit to extend mode gain where: in

the di erence between two inputs

voltage signals. Instead, the

common mode gain can be calculated when the voltage input has the same value or the

same sign of the voltage output. In a good operational ampli er, the CMRR’s value can be

around 80-100dB. In addition it is possible to say that CMRR’s value can’t be equal to

zero: this because it is impossibile that two resistors can have the same value due to

factory feature.

The circuit that has been reported on the side can be

considered similar to the trans-resistance ampli er.

This because there is a presence of a negative

feedback operational ampli er but the feedback

element is a capacitor instead a resistor. In this case

relationship between the

we have to considered the

voltage current with the capacitor. Considering the

Kirchho ’s law, it is possible assume that the output

voltage is related to the input voltage. This one,

before arriving to the output section passes through

the capacitor and ideally the input currents, which ow in the capacitor, have to be equal

to the current that is absorbed to d V d V i

the generator that goes out of the out out in

i = C =

→ .

node. IN dt dt C

Considering the circuit and the integration current signals,

Considerino the it is

mathematical relation, it is possible writing:

t

1 ∫

possible to say that: V (t) = i (x)d x .

out in

So, this electric charge C 0

gives rise to a current signal, So it is possible to say that output voltage signal has

whose integral corresponds to the to be proportional to the integration of the input signal.

total charge generated in the

sensor. In this kind of circuit, a

voltage signal is generated at the output, whose amplitude is proportional to the charge

like in radiation sensors,

generated in the sensors. In some possible applications, the

relevant information is associated with the amount of electric charge generated in the

sensor, which is proportionate to the intensity of the radiation to which the sensors itself

The electric charge gives a measure of the intensity of radiation that

has been exposed.

hits the sensor. So due to the physical properties of the semiconductor material, whose

the sensor is made by, when the radiation hits the sensors, it releases energy and this

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generates an electric charge, which will give a current signal. We are talking about a

charge sensitive ampli er where the integral of the current correspond to the duration of

the current itself, that will be equal to the total charge delivered by the sensors when it is

expose to radiation.

Ina real contest, the structure is not achievable due to the non ideal behavior of the

operational ampli er, especially for the value of the current that we have already seen that

can’t be equal to zero. This because even if we considered o t