ECE 201 Circuit Theory I 1

Introduction to the Operational Amplifier

μA 741 OP AMP

ECE 201 Circuit Theory I 2

Schematic -- 741 OP AMP

ECE 201 Circuit Theory I 3

741 OP AMP – Package & Pin Layout

•2 Inverting Input•3 Non-Inverting Input•6 Output•7 + Voltage Supply VCC

•4 – Voltage Supply VEE

•1 and 5 -- Offset Null

ECE 201 Circuit Theory I 4

Circuit Symbol for the OP AMP

Simplify to 3 terminals

ECE 201 Circuit Theory I 5

μA 741 OP AMP – Pin Identification

• 2 Inverting Input• 3 Non-Inverting Input• 6 Output

• 7 + Voltage Supply VCC

• 4 – Voltage Supply VEE

• 1 and 5 -- Offset Null

U1

741

3

2

4

7

6

51

For simplicity, use only pins 2, 3, and 6.

ECE 201 Circuit Theory I 6

Terminal Voltages

ECE 201 Circuit Theory I 7

Terminal Currents

ECE 201 Circuit Theory I 8

Voltage Transfer Characteristic

( )o p nv f v v

ECE 201 Circuit Theory I 9

( )o p nv A v v

A gain

10,000

20p n

A

v v mV

ECE 201 Circuit Theory I 10

Ideal OP AMP (Open Loop)

( )

0

o p n

in

p n

p n

v A v v

R

A

v v

i i

A

A = “open-loop” gain

ECE 201 Circuit Theory I 11

Connect Rf -- “Negative Feedback”

ECE 201 Circuit Theory I 12

Inverting Amplifier

ECE 201 Circuit Theory I 13

Analysis Using the Ideal OP AMP

0

i i is f n

v vn p

vsi

s Rsvoi

f Rf

“Virtual” ground

ECE 201 Circuit Theory I 14

Analysis continued

0n

f s

o s

f s

fo s

s

i

i i

v v

R R

Rv v

R

GND

ECE 201 Circuit Theory I 15

Non-Inverting Amplifier

ECE 201 Circuit Theory I 16

Analysis Using the Ideal OP AMP

1

p g

sn p g o

s f

s fo g

s

fo g

s

v v

Rv v v v

R R

R Rv v

R

Rv v

R

“Virtual Short