lecture 09.pdf
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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.