Chapter3-2011

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Welcome

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The Topics covered in this session

Isolation Amplifier

Isolation device technology

Programmable Gain Amplifier

Negative feedback amplifiers and controlled sources

Voltage controlled Voltage source or Voltage series feedback amplifier

Instrumentation amplifier

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Difference Amplifier

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An Instrumentation Amplifier

'

2

'

1

1

0 VVR

RV F

'

2

'

1

21

1

21

R2R

RV-VAlso V

V

2111

2

0 V-V

2

1Therefore R

R

R

R

V

F

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Symbol of Instrumentation Amplifier

)(2

1 210 VVa

V

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Isolation Amplifier

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Isolation Amplifier






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1. I need an amplifier with gain = 0.785, suggestme the type of the amplifier.

2. I want an amplifier with very high inputresistance and low output resistance. Namethe amplifier.

3. A point with zero voltage and zero currentsink is called..

4. Which parameter of an op-amp is used to findhighest operating frequency without anydistortion?

Quiz

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Isolation Amplifier

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Isolation Devices

An isolation Device passes a signal, either analog or digital,

from input to output across an isolation barrier.

An isolation barrier ensures that there is no galvanic or

ohmic connection between input and output

Isolation barrier must have high breakdown voltage

Low dc leakage current (HIGH BARRIER RESISTANCE)

Low ac leakage current (LOW BARRIER CAPACITANCE)

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Isolation Devices: Basic concepts

Where VISO: Isolation-mode voltage

IMRR: Isolation-mode rejection ratio

GAIN

IMRR

V

CMRR

VVV ISOCMSIGO

Fig 3.6 Equivalence of isolation barrier

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Isolation Amplifier






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Isolation Device Technology

Transformer isolation

Optical Isolation

Capacitor isolation

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Isolation Device Technology contd..

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Isolation Device Technology contd

Optical isolator or opto isolator or opto coupler or photo coupler or photo MOS

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Optical isolator or opto isolator or opto coupler or photo coupler or photo MOS

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Isolation Amplifier






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Programmable Gain Amplifier (PGA)

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Programmable Gain Amplifier (PGA)

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Isolation Amplifier






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Current Controlled Voltage Source or Voltage shunt feedback amplifier

Differential voltage-to-current converter

Constant high current source

Current Controlled Current Source or Current shunt feedback amplifier

Voltage Controlled Current Source or Current series feedback amplifier

Voltage-to-current converter for grounded load

Inductance Simulation

Voltage Controlled Voltage Source or Voltage series feedback amplifier


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Negative feedback Amplifiers and Controlled Sources

For an ideal Amplifier, the input drawn from thesignal source is zero and the output load poweris finite.

For the input power to be zero,

(i) Vi=0 and Ii finite (Zin 0)

(ii) Ii=0 and Vi finite (Zin

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The ideal voltage amplifiers are classified in four different ways:1. Voltage Controlled Voltage Source (VCVS) or

ideal voltage amplifier (Zin , Zout 0, A=Av)or Voltage series feedback amplifier

2. Current Controlled Voltage Source (CCVS) or

Ideal transresistance amplifier (Zin 0, Zout 0, A=Rm)or Voltage shunt feedback amplifier

3. Voltage Controlled Current Source (VCCS) orideal transconductance amplifier (Z

in

, Zout

, A=Gm

)or Current series feedback amplifier

4. Current Controlled Current Source (CCCS) orIdeal current amplifier (Zin 0, Zout , A=Ai)

or Current shunt feedback amplifier



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)ABW(1BWfeedbackwithBandwidth(iv)

)A(1ZZfeedback,currentfor

1Zfeedback,for

Zfeedback,withImpedanceOutput(iii)

1Zfeedback,shuntfor

)A(1ZZfeedback,seriesfor

feedbackwithImpedanceInput(ii)

feedback,withoutgain-A

1feedbackGain with(i)

f

outoutf

outf

outf

inf

ininf

inf

A

Zvoltage

A

Z

Z

V

Vwhere

A

AA

out

in

O

f

f


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Voltage-Controlled Voltage Source

The Ideal Voltage Amplifier

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Voltage-Controlled voltage Source- The Ideal Voltage Amplifier

Example: Non-inverting Amplifier

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2

1Oifin

21

2fini

1V

,VV0,Vsince

andVVVHere:GainVoltage(i)

R

R

Vhavewe

RR

RVV

i

Of

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Voltage-Controlled voltage Source- The Ideal Voltage Amplifier

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feedback.withincreasesimpedanceinputThus.V

)1(

VfeedbackwithImpedanceInput(ii)

f

iinf

o

inin

f

inout

i

in

in

i

in

in

i

i

Vwhere

AZZA

AZ

AV

V

ZV

V

ZV

V

IZ

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Voltage-Controlled Voltage Source- The Ideal Voltage Amplifier

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A1

ZZ),(ansmaller t hmuchis

A1

Zsince

)(||A1

ZZThus

network.dividerpotentialofeffecttheincludewillimpedanceoutputtotalT he

RR

RV

)1(I,figurethefrom

Zfeedback,withImpedanceOutput(iii)

outoutf21

out

21out

outf

21

2fout

outf

RR

RR

VVZ

AV

Z

AVV

IV

outout

out

out

out

fout

out

out

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Current-Controlled Voltage Source (CCVS)- The

Transresistance Amplifier

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Current-Controlled Voltage Source (CCVS)- The

Transresistance Amplifier

RRwith

A

RZ

S

Sout

outfinf

R

A1

ZZand

1

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V l C ll d C S (VCCS)

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Voltage-Controlled Current Source (VCCS)-

The Ideal Transconductance Amplifier

Where Gm - transconductance

V lt C t ll d C t S (VCCS)

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V lt C t ll d C t S (VCCS)

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Here Ii

=0 and Vi

= Vf

= IO

R

imVGR

iO

VITherefore

LO RR

R

Vand f

V

)1( AZZ innfi

ARZisimpedanceoutputThe

.

R

VIequalsandRoftindependeniscurrentoutputThe

outf

i

OL

This circuit acts as perfect voltage-to-current converter with Zif ,Zout and Gm= 1/R.

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V lt t C t t f d d l d

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Voltage-to-Current converter for grounded load

V lt t C t t f d d l d

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Voltage-to-Current converter for grounded load

2

2

1

2ref

3

2

4

2O

R

V-Vand

R

V-VhaveweKCL,Applying

R

VVR

VI

O

L

2

1

2

2or RR

VVVV

ref

O

3

2

2

14

2

R

VIR

RR

VVL

ref

1

24

3

4

1

2

2

3

2

42

1

2Voror

R

VRIR

R

R

R

R

R

VIRR

R

VV refLL

ref

Choosing R1R4=R2R3, we have

341

2

R

V

RR

RVI

ref

refL

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Diff ti l lt t t t

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Diff ti l lt t t t

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Writing KCL equations

R

VV

R

VV OLL2

R

VVIand OLL

R

V-V L1

R

VVIor LL

2L1

R

V-V

R

V-V

IHence21

L

2O 2Vand VVL

Thus the load current is proportional to (V1-V2)

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C t t hi h t

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LE

S

Z IIR

V

Digitally controlled 4 20 mA current source

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Digitally controlled 4-20 mA current source

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Current Controlled Current Source (CCCS) The

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Current-Controlled Current Source (CCCS)- The

Ideal Current Amplifier

Current Controlled Current Source (CCCS) The

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Current-Controlled Current Source (CCCS)- The

Ideal Current Amplifier

Current-Controlled Current Source (CCCS)- The Ideal Current Amplifier

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( ) p

Here IO = If + Ii

Also If = Ii and Vf = - IsR2 = - If R1

2

111

R

RI

I

IIIII i

i

s

isio

2

1i

R1ATherefore

R

Example: If R1=99 k and R2=1k Then IO=100 Ii.

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2

)(

R

VVVVCjI oiii

VVand1 o

1

1

CjR

VRV i

Combining these equations and solving for Zi=Vi / Ii,

22

2

2

212

22

2

2

22

212

1

)(

1

)1(

CR

RRCRj

CR

CRRRZi xxii LjRZformtheofisZThus

1

)(

R

L

Qis,inductortheoffactor 2221

21

x

x

CRR

RRC

Q

21

2

1

2

1max

211

RRC

1atoccursitand

2

1Q

isQofvaluemaximumT heRRsuch t hatchosenisRNormally,

R

R

For C=0.1 F, R1= 100 k , R2= 100 , L= 1 H, Qmax= 15.8 at 505 Hz.

Measurement of L and Q

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Measurement of L and Q

f

Qand2

1 o

1fCL

fo

x

Documents

Chapter3-2011