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Electronic Devices and Circuit Theory 10th Edition Boylestad Louis Chapter 11 Op AMP Applications

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(1)
(2)

Op

Op--Amp Applications

Amp Applications

Constant

Constant--gain multiplier

gain multiplier

Voltage summing

Voltage summing

Voltage buffer

Voltage buffer

Controlled sources

Controlled sources

Instrumentation circuits

Instrumentation circuits

Active filters

Active filters

Active filters

Active filters

(3)

Constant

Constant--Gain Amplifier

Gain Amplifier

Inverting Version

Inverting Version

more…

more…

(4)

Constant

Constant--Gain Amplifier

Gain Amplifier

Noninverting Version

Noninverting Version

(5)

Multiple

Multiple--Stage Gains

Stage Gains

=

A

A

A

A

1

2

3

The total gain (3-stages) is given by:

or

 −

 −





+

=

R3

R

R2

R

R

R

1

A

f

f

1

f

or

(6)

Voltage Summing

Voltage Summing









++++

++++

−−−−

====

R

f

V

R

f

V

R

f

V

V

The output is the sum

of individual signals

times the gain:

[Formula 14.3]













++++

++++

−−−−

====

3

3

f

2

2

f

1

1

f

o

V

R

R

V

R

R

V

R

R

V

(7)

Voltage Buffer

Voltage Buffer

Any amplifier with no gain or loss is called a

unity gain

unity gain

amplifier

amplifier

.

The advantages of using a unity gain amplifier:

Very high input impedance

Very low output impedance

Realistically these circuits

are designed using equal

resistors (R

1

= R

f

) to avoid

problems with offset

(8)

Controlled Sources

Controlled Sources

Voltage

Voltage--controlled voltage source

controlled voltage source

Voltage

Voltage--controlled current source

controlled current source

Current

Current--controlled voltage source

controlled voltage source

Current

(9)

Voltage

Voltage--Controlled Voltage Source

Controlled Voltage Source

The output voltage

is the gain times the

input voltage. What

makes an op-amp

different from other

amplifiers is its

impedance

Noninverting Amplifier Version

Noninverting Amplifier Version

impedance

characteristics and

gain calculations

that depend solely

on external

resistors.

more…

more…

(10)

Voltage

Voltage--Controlled Voltage Source

Controlled Voltage Source

The output voltage

is the gain times the

input voltage. What

makes an op-amp

different from other

amplifiers is its

impedance

Inverting Amplifier Version

Inverting Amplifier Version

impedance

characteristics and

gain calculations

that depend solely

on external

(11)

Voltage

Voltage--Controlled Current Source

Controlled Current Source

The output current

is:

1

1

o

kV

R

V

I

====

====

1

1

o

kV

R

I

====

====

(12)

Current

Current--Controlled Voltage Source

Controlled Voltage Source

This is simply another way

of applying the op-amp

operation. Whether the

input is a current

determined by V

in

/R

1

or as

I

1

:

f

R

−−−−

==

or

in

1

f

out

V

R

R

V

====

−−−−

L

1

out

I

R

V

=

(13)

Current

Current--Controlled Current Source

Controlled Current Source

This circuit may appear

more complicated than

the others but it is really

the same thing.

R





V

in

in

f

out

2

1

in

f

out

in

in

f

out

R

V

R

V

R

||

R

V

R

V

V

R

R

V

−−−−

====

−−−−

====













−−−−

====

kI

R

R

1

I

I

R

R

R

R

V

I

R

R

R

R

V

I

R

||

R

V

I

2

1

o

2

2

1

1

in

o

2

1

2

1

in

o

2

1

in

o

====













++++

−−−−

====













++++

−−−−

====













××××

++++

−−−−

====

−−−−

====

(14)

Instrumentation Circuits

Instrumentation Circuits

Some examples of instrumentation circuits using

op-amps:

• Display driver

• Instrumentation amplifier

• Instrumentation amplifier

(15)

Display Driver

Display Driver

(16)

Instrumentation Amplifier

Instrumentation Amplifier

For all Rs at the same value (except R

p

):

((((

1

2

))))

((((

1

2

))))

P

o

V

V

k

V

V

R

2R

1

V



−−−−

====

−−−−











++++

====

(17)

Active Filters

Active Filters

Adding capacitors to op-amp circuits provides external control of the

cutoff frequencies. The op-amp active filter provides controllable

cutoff frequencies and controllable gain.

• Low-pass filter

• High-pass filter

• Bandpass filter

(18)

Low

Low--Pass Filter

Pass Filter—

—First

First--Order

Order

1

1

OH

C

R

π

2

1

f

====

1

f

v

R

R

1

A

====

++++

The upper cutoff frequency

and voltage gain are given

by:

(19)

Low

Low--Pass Filter

Pass Filter—

—Second

Second--Order

Order

(20)

High

High--Pass Filter

Pass Filter

1

1

OL

C

R

π

2

1

f

====

(21)

Bandpass

Bandpass Filter

Filter

There are two cutoff

frequencies: upper and

lower. They can be

calculated using the same

low-pass cutoff and

high-pass cutoff frequency

formulas in the

formulas in the

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