Operational Amplifier

& aplikasinya

Elektronika(TKE 4012)

Eka Maulana

maulana.lecture.ub.ac.id

Op Amp

• Op Amp is short for operational amplifier

• Amplifiers provide gains in voltage or current

• Op amps can convert current to voltage

+

–

Non-inverting input

Inverting input

Ground

High Supply (+)

Low Supply (-)

Output

Simbol Op Amp

Applications of Op Amps

• Op amps can be configured in many different ways using resistors and other components

• Most configurations use feedback

• Op amps can provide a buffer between two circuits

• Op amps can be used to implement integrators and differentiators

• Lowpass and bandpass filters

Aplikasi Op-amp

• Komparator

• Penguat Non-inverting

• Penguat Inverting

• Penguat penjumlah

• Voltage follower

• Converter Tegangan ke Arus

• Integrator & Diferensiator

• Penguat diferensial

• Penguat instrumentasi

• Penguat histerisis

The Op Amp Model

+

–Inverting input

Non-inverting input

Rin

v+

v–

+

–

A(v+ – v– )

vo

• An operational amplifier is modeled as a

voltage-controlled voltage source.

Voltage controlled

voltage source

Typical vs. Ideal Op Amps

Typical Op Amp:

• The input resistance

(impedance) Rin is

very large (practically

infinite).

• The voltage gain A is

very large (practically

infinite).

Ideal Op Amp:

• The input resistance

is infinite.

• The gain is infinite.

• The op amp is in a

negative feedback

configuration.

Consequences of the Ideal

• Infinite input resistance means the current

into the inverting (–) input is zero:

i– = 0

• Infinite gain means the difference between

v+ and v– is zero:

v+ – v– = 0

Typical Op Amp Parameters

Parameter Variable Typical

Ranges

Ideal Values

Open-Loop

Voltage Gain

A 105 to 108

∞

Input

Resistance

Ri 105 to 1013 W ∞W

Output

Resistance

Ro 10 to 100 W 0 W

Supply

Voltage

Vcc/V+

-Vcc/V-

5 to 30 V

-30V to 0V

N/A

N/A

Symbols for Ideal and Real Op Amps

OpAmp uA741

LM324 LM111

Voltage Transfer Characteristic

Range where we

operate the op amp

as an amplifier.

vd

Vd = V1-V2

+

–

V1

V2

Vcc(+)

Vcc(-)

VO

+

–

V1

V2

Vcc(+)

Vcc(-)

When Vd is larger than 0V, Vo = Vcc(+).

When Vd is smaller than 0V, Vo = Vcc(-).

When Vd is equal to 0V, Vo = 0V.

Vo

Example #1: Voltage Comparator

Vd = V1-V2

Penguat Inverting Basic

–

+Vin

+

–

Vout

R1

R2

+

–

Solving the Amplifier Circuit

Apply KCL at the inverting (–) input:

i1 + i2 + i– =0

0i

111

R

V

R

VVi inin

222

R

V

R

VVi outout

–

R1

R2

i1 i–

i2

Vin

Vout

V–

Solve for Vout

• From KCL • Thus, the amplifier

gain is

21

21

21

00

0

R

V

R

V

R

V

R

V

iii

outin

outin

1

2

R

R

V

V

in

out

Lect8 EEE 202 15

Recap

• The ideal op-amp model leads to the

following conditions:

i– = 0 = i+

v+ = v–

• These conditions are used, along with KCL

and other analysis techniques (e.g.,

nodal), to solve for the output voltage in

terms of the input(s)

Penguat Non-inverting

+

–

vin

+

–

vout

R1

R2

+

–

KCL at the Inverting Input

+

–

vin

+

–

vout

R1

R2

i–

i1 i2

+

–

0i

11

1R

v

R

vi in

2

22

R

vv

R

vvi

inout

out

Solve for vout

1

2

21

21

1

0

0

R

Rvv

R

vv

R

v

iii

inout

inoutin

• Hence, the non-inverting amplifier has a gained output (> unity) relative to the resistance ratio

Rangkaian Penjumlah

–

+v2

+

–

vout

R2

RfR1

v1

+

–

+

–

KCL at the Inverting Input

1

1

1

11

R

v

R

vvi

2

2

2

22

R

v

R

vvi

0i

–

+v2

+

–

vout

R2

RfR1

v1

i1

i2

if

i–

+

–

+

–

f

out

f

out

fR

v

R

vvi

Solve for vout

• So, the mixer circuit output is a (negative)

combination of the input voltages

22

11

2

2

1

1

21

0

0

vR

Rv

R

Rv

R

v

R

v

R

v

iiii

ffout

f

out

f

ac coupled inverting amplifier

vout

vin

R1

R2

RL

C1

C2

AV =-R2

R1 R2

R1

+1

funityf2 =

fc1 = 2pR1C1

1fc2 = 2pRLC2

1

R2

Adjustable bandwidth

voutvin

R1

RA

f

-R2

R1

R1 R + R2

R1 RB =

f2 = Bfunity

R1

R2

ac coupled noninverting amplifier

C3

C2

C1

vout

R3

RL

vin

fc3 = 2pR1C3

1

Bdc = 1

R

JFET controlled inverter/noninverter

voutvinR

R

0 V

VGS(off)

R

Adjustable gain of ± 1

voutvin

R

R’

Phase shifter

vout

vin

R

R’

C

f

f = -2 arctan 2pRCf

t

R2

Differential amplifier

voutvin

R1’

R1

R2’

vin(CM)

vin(CM)

CMRR limiting factors

are the op amp itself and

the tolerance of the resistors.

AV =-R2

R1

±2 < ACM < ±4DR

RDR

R

Ideally:

R1 = R1’

R2 = R2’

R2

Wheatstone bridge

vout

R1

R4

R3

Transducer

+V

Wheatstone bridge

• The differential output signal is small.

• The common-mode output signal is large.

• Differential amplifiers are a good match.

• Transducers convert nonelectrical

quantities into an electrical quantity such

as resistance:

– examples: photoresistor, thermistor, strain

gage

Instrumentation amplifiers

• Differential amplifiers optimized for dc

performance

• Large differential voltage gain

• High CMRR

• Low input offsets

• Low temperature drift

• High input impedance

R

vout

vin

R

R

R

vin(CM)

vin(CM)

±2DR

RACM =AV =

-2R1

RG

+1

R1

R1

RG

Instrumentation amplifier

Monolithic instrumentation

amplifiers

• Use laser-trimmed resistors for high

performance.

• Resistor RG is external and is selected to

set the differential gain.

• Resistor RG can be split into two devices

for guard driving (bootstrapping the cable

shield to the common-mode potential).

RG

2

RG

2

vout

Guard driving

Guard voltage (common-mode voltage)

Instrumentation

amplifier

Summing amp with inverting

and noninverting inputs

vout

R1RF

R2

R3

R4

v1

v2

v3

v4

R5

D/A converter

vout

R R

2R

4R

8R

v3

v2

v1

v0

vout = -(v3 + 0.5v2 + 0.25v1 + 0.125v0)

Possible combinations = 2N = 24 = 16

N = 4

vin18

Unidirectional current booster

R2

R1 RL

vin

+VCC

vout

741

Imax = bdcISC = 100(25 mA) = 2.5 A

bdc = 100

Bidirectional current booster

R2

R1

RL

vin

+VCC

vout

-VEE

AGC circuit

vout

R1vin

R5

R6

R3

R4

R2

+VAGC

-VEE

As the signal level increases,

VAGC goes more positive.

As the JFET rds drops,

the input signal is attenuated.

Voltage-controlled

resistance

Single-supply inverting amplifier

vout

vin

R1

R2

RL

C1

C2

R

+VCC

RC3

+VCC

2