Slide điện tử tương tự chapter 9 op amp

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CHAPTER 9:
OPERATIONAL AMPLIFIER

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Symbol
Example
Characteristics
Structure
Operation
Applications
μp 741

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Contents

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Symbol

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Example

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Characters of circuits depend on outside circuit
structure, not the opamp itself

Gain AV: very high, ideally ∞
Zin: very large, ideally ∞
Zout: very small, ideally 0
Current entering the amp at either terminal:
extremely small, ideally 0
Voltage out (when voltages into each other are
equal): small, ideally 0
Bandwidth: broad, ideally infinite

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Characteristics

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Characteristics
Input: 2 inputs (positive and negative)
Single-ended input: 1 input to signal source, 1 input to
ground
Double-ended input: 2 different signal sources or 1 signal
source apply between 2 inputs

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Differential-mode gain Adm - large

Common-mode gain Acm - small
Common-mode rejection ratio CMRR=G=Adm/Acm, usually
about 103-105

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Output: 1 or 2 outputs, typically 1 output
Mode gain:

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Requirement:
large
 Offset: small
 Currents: small
 Input impedance: large
 Output impedance: small
 Input: symmetric

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 Gain:

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Structure

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Structure

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Example: 741 – at the end of chapter

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Input stage
Intermediate stage

Level shifting stage
Output stage

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non-inverting amplifier
 Uni-gain circuit
 Addition and subtraction circuits
 Integration and differential circuits
 Multi-stages circuit

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 Inverting,

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Basic and advance applications
Basic applications:

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Applications

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Advance applications

voltage source
 Voltage-controlled current source
 DC voltmeter
 AC voltmeter
 Driver circuit
 Active filters
 NIC
 .etc.

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 Current-controlled

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Applications

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Non-inverting fixed-gain amplifier

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Prove:
 V- = V+ = V1
 I- = I+ = 0
=>IR1 = Irf = V1/R1
=>A = 1+Rf/R1

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Non-inverting fixed-gain amplifier

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A = 1+Rf/R1=101
Vo=101Vi

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Inverting fixed-gain amplifier

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Prove:
 V- = V+ = 0
 I- = I+ = 0
=>IR1 = Irf = V1/R1
=>A = -Rf/R1

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Voltage addition

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Vo = -V1Rf/R1-V2Rf/R2 –
V3Rf/R3
If V1=V2=V3 then:
A= -Rf/R1-Rf/R2 –Rf/R3

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Voltage subtraction

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Vout1 = -Rf/R1V1

Vout = -Rf/R2V2 - Rf/R2Vout1 = -Rf/R2V2 + Rf/R2V1

= -Rf/R2(V1 – V2)
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Voltage subtraction with 1 amp

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Prove:
 V-=V+=V1*R3/(R1+R3)
 I- = I+ = 0

=>IR2 = IR4 = (V2V1*R3/(R1+R3))/R2
=>Vo=V1*R3/(R1+R3)*
(R2+R4)/R2 – V2*R4/R2

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Uni-gain (buffer) amplifier

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Provide required input and output resistant stage

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Provide multiple identical output signals

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Voltage-controlled voltage source

Vo=(1+Rf/R1)V1

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Vo=(-Rf/R1)V1

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Voltage-controlled current source

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Io=V1/R1

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Current-controlled voltage source

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Vo=-I1RL

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Current-controlled current source

Io=I1(R2+R1)/R2

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Vo=(Vi/RC)0ƒTVi(t)dt+Vou

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Integration circuit

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t(t=0)

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Vo=-RC dVi/dt

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Differential circuit

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Low pass filter
High pass filter
Band pass filter

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Filter

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order low pass filter

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Cutoff frequency: fOH=1/(2πR1C1)
Voltage gain below cutoff freq: Av=1+Rf/RG
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