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Op Amps. Introduction. Op Amp is short for operational amplifier. An operational amplifier is modeled as a voltage controlled voltage source. An operational amplifier has a very high input impedance and a very high gain. Use of Op Amps.

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op amps

Op Amps

Lecture 30

introduction
Introduction
  • Op Amp is short for operational amplifier.
  • An operational amplifier is modeled as a voltage controlled voltage source.
  • An operational amplifier has a very high input impedance and a very high gain.

Lecture 30

use of op amps
Use of Op Amps
  • Op amps can be configured in many different ways using resistors and other components.
  • Most configurations use feedback.

Lecture 30

applications of op amps
Applications of Op Amps
  • Amplifiers provide gains in voltage or current.
  • Op amps can convert current to voltage.
  • Op amps can provide a buffer between two circuits.
  • Op amps can be used to implement integrators and differentiators.

Lecture 30

more applications
More Applications
  • Lowpass and bandpass filters.

Lecture 30

the op amp symbol

+

-

The Op Amp Symbol

High Supply

Non-inverting input

Output

Inverting input

Ground

Low Supply

Lecture 30

the op amp model

+

-

The Op Amp Model

v+

Non-inverting input

+

vo

Rin

v-

Inverting input

-

A(v+ -v- )

Lecture 30

typical op amp
Typical Op Amp
  • The input resistance Rin is very large (practically infinite).
  • The voltage gain A is very large (practically infinite).

Lecture 30

ideal op amp
“Ideal” Op Amp
  • The input resistance is infinite.
  • The gain is infinite.
  • The op amp is in a negative feedback configuration.

Lecture 30

the basic inverting amplifier

R2

R1

-

+

+

+

Vin

Vout

-

-

The Basic Inverting Amplifier

Lecture 30

consequences of the ideal
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

Lecture 30

solving the amplifier circuit
Solving the Amplifier Circuit

Apply KCL at the inverting input:

i1 + i2 + i-=0

R2

i2

R1

-

i1

i-

Lecture 30

slide13
KCL

Lecture 30

solve for v out
Solve for vout

Amplifier gain:

Lecture 30

recap
Recap
  • The ideal op amp model leads to the following conditions:

i- = 0

v+ = v-

  • These conditions are used, along with KCL and other analysis techniques, to solve for the output voltage in terms of the input(s).

Lecture 30

where is the feedback

R2

R1

-

+

+

+

Vin

Vout

-

-

Where is the Feedback?

Lecture 30

review
Review
  • To solve an op amp circuit, we usually apply KCL at one or both of the inputs.
  • We then invoke the consequences of the ideal model.
    • The op amp will provide whatever output voltage is necessary to make both input voltages equal.
  • We solve for the op amp output voltage.

Lecture 30

the non inverting amplifier

+

+

-

+

vin

-

vout

R2

R1

-

The Non-Inverting Amplifier

Lecture 30

kcl at the inverting input
KCL at the Inverting Input

+

+

-

+

i-

vin

-

vout

i1

i2

R2

R1

-

Lecture 30

slide20
KCL

Lecture 30

solve for v out21
Solve for Vout

Lecture 30

a mixer circuit

R1

Rf

R2

-

+

+

+

+

v2

v1

vout

-

-

-

A Mixer Circuit

Lecture 30

kcl at the inverting input23

+

v2

-

KCL at the Inverting Input

R1

Rf

i1

if

+

R2

v1

i2

-

-

i-

+

+

vout

-

Lecture 30

slide24
KCL

Lecture 30

slide25
KCL

Lecture 30

solve for v out26
Solve for Vout

Lecture 30