L t 9Lecture 9Op AmpsOp Amps

ELECTRICAL ENGINEERING: PRINCIPLES AND APPLICATIONS, Fourth Edition, by Allan R. Hambley, ©2008 Pearson Education, Inc.

AmplifiersAmplifiers

ELECTRICAL ENGINEERING: PRINCIPLES AND APPLICATIONS, Fourth Edition, by Allan R. Hambley, ©2008 Pearson Education, Inc.

Input & Output Impedance

ELECTRICAL ENGINEERING: PRINCIPLES AND APPLICATIONS, Fourth Edition, by Allan R. Hambley, ©2008 Pearson Education, Inc.

Inverting versus Non invertingInverting versus Non-inverting Amplifiersp

Inverting amplifiers have negative voltageInverting amplifiers have negative voltage gain, and the output waveform is an inverted version of the input waveforminverted version of the input waveform. Non-inverting amplifiers have positive voltage gainvoltage gain.

ELECTRICAL ENGINEERING: PRINCIPLES AND APPLICATIONS, Fourth Edition, by Allan R. Hambley, ©2008 Pearson Education, Inc.

ELECTRICAL ENGINEERING: PRINCIPLES AND APPLICATIONS, Fourth Edition, by Allan R. Hambley, ©2008 Pearson Education, Inc.

Negative FeedbackNegative Feedback

ELECTRICAL ENGINEERING: PRINCIPLES AND APPLICATIONS, Fourth Edition, by Allan R. Hambley, ©2008 Pearson Education, Inc.

Negative FeedbackNegative Feedback

ELECTRICAL ENGINEERING: PRINCIPLES AND APPLICATIONS, Fourth Edition, by Allan R. Hambley, ©2008 Pearson Education, Inc.

Chapter 14Chapter 14Operational Amplifiersp p

1. List the characteristics of ideal op amps.p p

2. Identify negative feedback in op-amp circ itscircuits.

3. Analyze ideal op-amp circuits that have 3 a y e dea op a p c cu s a a enegative feedback using the summing-point constraint.

ELECTRICAL ENGINEERING: PRINCIPLES AND APPLICATIONS, Fourth Edition, by Allan R. Hambley, ©2008 Pearson Education, Inc.

p

IDEAL OPERATIONAL AMPLIFIERSIDEAL OPERATIONAL AMPLIFIERS

ELECTRICAL ENGINEERING: PRINCIPLES AND APPLICATIONS, Fourth Edition, by Allan R. Hambley, ©2008 Pearson Education, Inc.

The input signal of a differential amplifier consists of a differential component and aconsists of a differential component and a common-mode component.

21 vvvid −=

1 ( )21cm 21 vvvi +=2

ELECTRICAL ENGINEERING: PRINCIPLES AND APPLICATIONS, Fourth Edition, by Allan R. Hambley, ©2008 Pearson Education, Inc.

Characteristics of Ideal Op pAmps

Infinite gain for the differential input signal

Zero gain for the common mode input signalZero gain for the common-mode input signal

Infinite input impedances

Zero output impedance

Infinite bandwidth

ELECTRICAL ENGINEERING: PRINCIPLES AND APPLICATIONS, Fourth Edition, by Allan R. Hambley, ©2008 Pearson Education, Inc.

ELECTRICAL ENGINEERING: PRINCIPLES AND APPLICATIONS, Fourth Edition, by Allan R. Hambley, ©2008 Pearson Education, Inc.

ELECTRICAL ENGINEERING: PRINCIPLES AND APPLICATIONS, Fourth Edition, by Allan R. Hambley, ©2008 Pearson Education, Inc.

SUMMING POINTSUMMING-POINT CONSTRAINT

Operational amplifiers are almost alwaysOperational amplifiers are almost always used with negative feedback, in which part of the output signal is returned to the input inthe output signal is returned to the input in opposition to the source signal.

ELECTRICAL ENGINEERING: PRINCIPLES AND APPLICATIONS, Fourth Edition, by Allan R. Hambley, ©2008 Pearson Education, Inc.

In a negative feedback system, the ideal op-amp output voltage attains the value neededamp output voltage attains the value needed to force the differential input voltage and input current to zero. We call this fact thecurrent to zero. We call this fact the summing-point constraint.

ELECTRICAL ENGINEERING: PRINCIPLES AND APPLICATIONS, Fourth Edition, by Allan R. Hambley, ©2008 Pearson Education, Inc.

Ideal op amp circuits areIdeal op-amp circuits are analyzed by the following steps:

1. Verify that negative feedback is present.

2. Assume that the differential input voltage and the input current of the op amp are forced to zero. (This is the summing-point constraint.)

ELECTRICAL ENGINEERING: PRINCIPLES AND APPLICATIONS, Fourth Edition, by Allan R. Hambley, ©2008 Pearson Education, Inc.

3 Apply standard circuit analysis principles3. Apply standard circuit-analysis principles, such as Kirchhoff’s laws and Ohm’s law, to solve for the quantities of interestsolve for the quantities of interest.

ELECTRICAL ENGINEERING: PRINCIPLES AND APPLICATIONS, Fourth Edition, by Allan R. Hambley, ©2008 Pearson Education, Inc.

The Basic Inverter

ELECTRICAL ENGINEERING: PRINCIPLES AND APPLICATIONS, Fourth Edition, by Allan R. Hambley, ©2008 Pearson Education, Inc.

Verify Negative Feedbacky g

00 <<→> vv0000

>>→<<<→>

i

outin

vvvv

ELECTRICAL ENGINEERING: PRINCIPLES AND APPLICATIONS, Fourth Edition, by Allan R. Hambley, ©2008 Pearson Education, Inc.

00 >>→< outin vv

Applying the Summing Point Constraint

ELECTRICAL ENGINEERING: PRINCIPLES AND APPLICATIONS, Fourth Edition, by Allan R. Hambley, ©2008 Pearson Education, Inc.

Applying the Summing Point Constraint

1Rv

i inin =

2

1

Rv

i

R

outout

−=

21

2

Rv

Rv

ii

R

outinoutin

−=→=iin iout

1

2

21

RR

vv

RR

i

out −=V = 0

VinVout

R1 R2

ELECTRICAL ENGINEERING: PRINCIPLES AND APPLICATIONS, Fourth Edition, by Allan R. Hambley, ©2008 Pearson Education, Inc.

1Rvin

Inverting Amplifierg

2

RR

vv

A ov −==

ELECTRICAL ENGINEERING: PRINCIPLES AND APPLICATIONS, Fourth Edition, by Allan R. Hambley, ©2008 Pearson Education, Inc.

1Rvin

Inverting Amplifierg

1RZRv

i inin

in =→=

ELECTRICAL ENGINEERING: PRINCIPLES AND APPLICATIONS, Fourth Edition, by Allan R. Hambley, ©2008 Pearson Education, Inc.

1R

Inverting Amplifierg

inout vRRv 2−= Independent of load resistance

R → output impedance Z = 0

ELECTRICAL ENGINEERING: PRINCIPLES AND APPLICATIONS, Fourth Edition, by Allan R. Hambley, ©2008 Pearson Education, Inc.

R 1 RL→ output impedance Zout= 0

ELECTRICAL ENGINEERING: PRINCIPLES AND APPLICATIONS, Fourth Edition, by Allan R. Hambley, ©2008 Pearson Education, Inc.