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1.6 Op-Amp Basics

Basic Op-Amp

Op-amp equivalent circuit

Practical (Ri = high , Ro = small) Ideal (Ri =∞ , Ro = 0)

2

1.6 Op-Amp Basics

Basic Operation of Op-Amp input voltage at minus (-) output voltage opposite in phase input voltage at plus (+) output voltage in phase

Basic Op-Amp - Constant-gain multiplier

Input signal is applied through resistor Ri to the minus input

Output is connected to the same minus input through resistor Rf

Resulting output: opposite in phase to input signalInverting constant gain multiplier

3

1.6 Op-Amp Basics

Op-amp ac equivalent circuit

Basic Op-Amp - Constant-gain multiplier

4

1.6 Op-Amp Basics

Ideal Op-amp equivalent circuit Redrawn equivalent circuit

(for circuit analysis)

Basic Op-Amp - Constant-gain multiplier

5

1.6 Op-Amp Basics

11

1 VRR

RV

f

fi

Using Superposition theorem

Basic Op-Amp - Constant-gain multiplier

i) V1 only (set –AvVi =0)

ii) –AvVi only (set V1 =0)

ivf

i VARR

RV

1

12

6

1.6 Op-Amp Basics

11

VRA

RV

v

fi

11)1(V

RAR

RV

vf

fi

Basic Op-Amp - Constant-gain multiplier

ivff

fiii VA

RR

RV

RR

RVVV

1

11

121

i

f

v

f

i

v

i

iv

i

o

V

V

R

R

RA

VR

V

A

V

VA

V

V 1

11

1

11 R

R

V

V fo

It is shown that the ratio i/o depends only on the value of Rf and R1

7

1.6 Op-Amp Basics

Basic Op-Amp - Unity Gain

111

R

R

V

V foIf Rf = R1

Gain with negative sign shows that the output voltage has undergone 180º phase inversion from input signal

Basic Op-Amp - Constant Gain

If Rf = 10R1 1011

R

R

V

V fo

If we select precise values for Rf and Ri, we can obtain a wide range of gains

Gain accuracy depends on resistors used

Gain is slightly affected by temperature & other circuit factors

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1.7 Practical Op Amp Circuits

Inverting Amplifier Non-inverting Amplifier

11

0 1R

R

V

V f11

0

R

R

V

V f

Inverting constant gain multiplier Non-inverting constant gain multiplier

9

1.7 Practical Op Amp Circuits

Non-inverting Amplifier

01

11 V

RR

RV

f

Equivalent circuit Non-inverting constant-gain multiplier

11

1

1

0 1R

R

R

RR

V

V ff

Which results in;Since Vi = 0, using voltage divider rule,

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1.8 Data Sheet LM741

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1.8 Data Sheet LM741

ABSOLUTE MAXIMUM RATINGS

Supply voltage = +22V

Internal power dissipation = 500mW

Differential input voltage = + 30V

Input voltage = + 15V

ELECTRICAL CHARACTERISTICS

Input offset voltage

Input offset current

Input bias current

Input resistance

12

1.8 Data Sheet LM741

ELECTRICAL CHARACTERISTICS

Large signal voltage gain

Output voltage swing

Output short circuit current

Supply voltage rejection ratio

Bandwidth

Slew rate

Supply current

Power consumption

13

1.8 Data Sheet LM741

14

1.8 Data Sheet LM741

15

1.8 Data Sheet LM741