chapter_7 Operational-amplifier(IT Version)

8/7/2019 chapter_7 Operational-amplifier(IT Version)

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SJTU Zhou Lingling 1

Chapter 7

Operational-Amplifier

and its Applications


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Outline

Introduction

The 741 Op-Amp Circuit

The ideal Op Amp

The inverting configuration

The noninverting configuration

Integrator and differentiator

The antoniou Inductance-simulation Circuit

The Op Amp-RC Resonator Bistable Circuit

Application of the bistable circuit as a comparator


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Introduction

Analog ICs include operational amplifiers, analogmultipliers, A/D converters, D/A converters, PLL,etc.

A complete op amp is realized by combininganalog circuit building blocks.

The bipolar op-amp has the general purposevariety and is designed to fit a wide range of

specifications. The terminal characteristics is nearly ideal.


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The 741 Op-Amp Circuit

General description

The input stage

The intermediate stage

The output stage

The biasing circuits Device parameters


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General Description

24 transistors, few resistors and only one

capacitor

Two power supplies

Short-circuit protection


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The Input Stage

The input stage consists of transistors Q1 throughQ7.

Q1-Q4 is the differential version of CC and CB

configuration. High input resistance.

Current source (Q5-Q7) is the active load of inputstage. It not only provides a high-resistance load

but also converts the signal from differential tosingle-ended form with no loss in gain orcommon-mode rejection.


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The Intermediate Stage

The intermediate stage is composed ofQ16, Q17and Q13B.

Common-collector configuration forQ16gives this

stage a high input resistance as well as reduces theload effect on the input stage.

Common-emitter configuration forQ17provideshigh voltage gain because of the active load Q13B.

Capacitor Cc introduces the miller compensationto insure that the op amp has a very high unit-gainfrequency.


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The Output Stage

The output stage is the efficient circuit called class ABoutput stage.

Voltage source composed ofQ18 and Q19 supplies the DCvoltage forQ14 and Q20 in order to reduce the cross-over

distortion.

Q23 is the CC configuration to reduce the load effect onintermediate stage.

Short-circuit protection circuitry

Forward protection is implemented by R6and Q15.Reverse protection is implemented by R7, Q21, current

source(Q24, Q22) and intermediate stage.


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The Output Stage

(a) The emitter follower is a class A output stage. (b) Class B output stage.


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The Output Stage

Wave of a class B output stage fed

with an input sinusoid.

Positive and negative cycles are

unable to connect perfectly due to the

turn-on voltage of the transistors.

This wave form has the nonlinear

distortion called crossover distortion.

To reduce the crossover distortion can

be implemented by supplying theconstant DC voltage at the base

terminals.


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The Biasing Circuits

Reference current is generated by Q12, Q11 andR5.

Wilder current provides biasing current in theorder ofA.

Double-collector transistor is similar to the two-output current mirror. Q13Bprovides biasingcurrent for intermediate stage, Q13A for outputstage.

Q5, Q6and Q7is composed of the current source tobe an active load for input stage.


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Device Parameters

Fornpn transistors:

Forpnp transistors:

Nonstandard devices:

Q14 and Q20 each has an area three times that of a standarddevice.

VVAI As 125,200,1014 !!! F

VVAI As 50,50,1014 !!! F

AISA141025.0 v! AISA

141075.0

v!


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The Ideal Op Amplifier

symbol for the op amp


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The Ideal Op Amplifier

The op amp shown connected to dc power supplies.


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Characteristics of the Ideal Op

Amplifier

Differential input resistance is infinite.

Differential voltage gain is infinite.

CMRR is infinite.

Bandwidth is infinite. Output resistance is zero.

Offset voltage and current is zero.

a) No difference voltage between inverting

andnoninvertingterminals.b) No inputcurrents.


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Equivalent Circuit of the Ideal Op

Amp


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The Inverting Configuration

The inverting closed-loop configuration.

Virtual ground.


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Shunt-shunt negative feedback

Closed-loop gain depends entirely on passive

components and is independent of the op

amplifier.

Engineer can make the closed-loop gain as

accurate as he wants as long as the passive

components are accurate.


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The Noninverting Configuration

The noninverting configuration.

Series-shunt negative feedback.


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The Voltage follower

(a) The unity-gain buffer or follower amplifier.

(b) Its equivalent circuit model.


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The Weighted Summer


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The Weighted Summer

)()())(())((4

4

3

3

2

2

1

1R

RvR

RvR

R

R

RvR

R

R

Rvv cc

b

ca

b

cao !


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A Single Op-Amp Difference

Amplifier

Linear amplifier.

Theorem of linear

Superposition.


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Amplifier

Application of superposition

Inverting configuration

1

1

21 Io v

R

Rv !


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Amplifier

Application of superposition.

Noninverting configuration.

2

34

4

1

22 )(1( Io v

RR

R

R

Rv

!


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Integrators

The inverting configuration with general impedances in

the feedback and the feed-in paths.


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The Inverting Integrators

The Miller or inverting integrator.


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Frequency Response of the

integrator


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The op-amp Differentiator


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The op-amp Differentiator

Frequency response of a differentiator with a time-constant CR.


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The Antoniou Inductance-

Simulation Circuit


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The Antoniou Inductance-

Simulation Circuit


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The Op amp-RC Resonator

An LCR second order resonator.


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An op ampRC resonator obtained by replacing the inductorL in the LCR

resonator of a simulated inductance realized by the Antoniou circuit.


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Implementation of the buffer amplifierK.


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Pole frequency

Pole Q factor

25316460 11 RRRRCCLC !![

531

2

4

66660

RRRR

C

CRRCQ !![


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Bistable Circuit

The output signal only has two states: positive

saturation(L+) and negative saturation(L-).

The circuit can remain in either state indefinitely

and move to the other state only whenappropriate triggered.

A positive feedback loop capable of bistable

operation.


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Bistable Circuit

The bistable circuit (positive

feedback loop)

The negative input terminal of the opamp connected to an input signal vI.

Foo vRR

Rvv !

!

21

1


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Bistable Circuit

The transfer characteristic of

the circuit in (a) for increasing vI.Positive saturation L+ and

negative saturation L-

F!LVTH


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Bistable Circuit

The transfer characteristic

for decreasing vI.

F

!LVTL


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Bistable Circuit

The complete transfer characteristics.


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A Bistable Circuit with Noninverting

Transfer Characteristics

21

1

21

2

RR

Rv

RR

Rvv oI

!


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A Bistable Circuit with Noninverting

Transfer Characteristics

The transfer characteristic is

noninverting.

21

21

RRLV

RRLV

TL

TH

!

!


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Application of Bistable Circuit as a

Comparator

Comparator is an analog-circuit building block

used in a variety applications.

To detect the level of an input signal relative to a

preset threshold value.

To design A/D converter.

Include single threshold value and two threshold

values. Hysteresis comparator can reject the interference.


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Comparator

Block diagram representation and transfer characteristic for acomparator having a reference, or threshold, voltage VR.

Comparator characteristic with hysteresis.


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Comparator

Illustrating the use of

hysteresis in thecomparator

characteristics as a

means of rejecting

interference.


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Making the Output Level More

Precise

For this circuit L+ = VZ1+ VD and L= (VZ2

+ VD), where VD is the forward

diode drop.


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Making the Output Level More

Precise

For this circuit L+ = VZ+ VD1+ VD2

and L= (VZ+ VD3+ VD4

).


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Generation of Square Waveforms

Connecting a bistable multivibrator with inverting transfer characteristics in a

feedback loop with an RC circuit results in a square-wave generator.


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Generation of Square Waveforms

The circuit obtained when the bistable multivibrator is

implemented with the positive feedback loop circuit.


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Waveforms at various nodes of

the circuit in (b).

This circuit is called an astable

multivibrator.

Time period T = T1+T2

F

F

!

1

)1ln1

LLRCT

F

F

!

1

)1ln2

LLRCT

F

F

!

1

1ln2RT


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Generation of Triangle Waveforms


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Generation of Triangle Waveforms

chapter_7 Operational-amplifier(IT Version)

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