ANALOG CIRCUITS – I

8/4/2019 ANALOG CIRCUITS I

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DEEPAK.P

ECE

SNGCE

ANALOG CIRCUITS I


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RC circuits

Diode circuits

Voltage regulators

UNIT I


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Basics of circuit analysis

Calculate the ID,VR

Answer-----7.3V,3.32 mA

0.7V

8 V

2.2 K

VD

VR

ID


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Calculate the ID,VR

0.7V

8 V

2.2 K

VD

VR

ID


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Calculate the ID,VR,VD

Assume that RD is Germanium Diode

8 V

2.2 K

RD

VR

ID

Low R


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Calculate the ID,VR,VD

Assume that RD is Silicon Diode

8 V

2.2 K

RD

VR

ID

High R


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Diode

Diodes allow electricity to flow in only one direction.

The arrow of the circuit symbol shows the direction in which the current can

flow.

Diodes are the electrical version of a valve and early diodes were actually called

valves.


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Diode


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Diode


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Diode Biasing

Forward Voltage DropElectricity uses up a little energy pushing its

way through the diode, rather like a personpushing through a door with a spring.This means that there is a small voltage

across a conducting diode, it is called theforward voltage dropand is about 0.7V forall normal diodes which are made from silicon.The forward voltage drop of a diode is almost

constant whatever the current passingthrough the diode so they have a very steepcharacteristic (current-voltage graph).


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Diode


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Diode

Reverse Voltage

When a reverse voltage is applied a perfectdiode does not conduct, but all real diodesleak a very tiny current of a few A or less.

This can be ignored in most circuitsbecause it will be very much smaller thanthe current flowing in the forward direction.

However, all diodes have a maximum

reverse voltage (usually 50V or more)and if this is exceeded the diode will failand pass a large current in the reversedirection, this is called breakdown.


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Diode characteristics


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IdealDiodeForward bias

Reverse bias

R is Low

R is High


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RealDiodeForward bias

Reverse bias

Cell


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Different Diode Bias

Determine the bias condition of the diodein the following cases0V5V

5V0V

5V 0V

3V5V

5.1V5V

-3V-5V

-6V-2V


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Diode application

It is useful in non linear wave shaping circuits.

Commonly used circuits areClippers

Clampers.

Rectifiers

In electronics, a clipper is a device designed to prevent

the output of a circuit from exceeding a

predetermined voltage level without distorting theremaining part of the applied waveform.


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CLIPPING

A clipping circuit consists of linear elements likeresistors and non-linear elements like junction diodes

or transistor.

Clipping circuits are also called asSlicers, amplitude

selectors or limiters.

One of the most basic clipping circuit is thehalf-wave rectifier.

A half-wave rectifier clips either thenegative half cycle or the positive half cycleof an alternating waveform, and allows topass only one half cycle.


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Application of Clipping Such a circuit has great applications in

radars, digital computers and otherelectronic systems for removing unwantedportions of the input signal voltages aboveor below a specified level.

Another application is in radio-receivers forcommunication circuits where noise pulsesthat rise well above the signal amplitudeare clipped down to the desired level.


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Clipper Circuits

The basic components required for aclipping circuit are an ideal diode and aresistor.

In order to fix the clipping level to thedesired amount, a dc battery must also beincluded.

Different levels of clipping can be obtainedby varying the amount of voltage of the

battery and also interchanging thepositions of the diode and resistor.

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Classification of CLIPPING

Classifications Of ClippersAccording to non-linear devices used,

clippers may be classified asDiode clippers andTransistor clippers.

According to biasing, the clippers may beclassified as

Unbiased clippers andBiased clippers.


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According to configuration used theclippers may be

Series diode clippersA series combination of diode, resistor and reference supply

Parallel or shunt diode clippers

Multi-diode clippers/Combinational clippers

It consisting of several diodes, resistors and reference voltages.


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According to level of clipping the clippersmay bePositive clippers

Negative clippers

Biased clippers and

Combination clippers


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There are two types of clipper circuitsSeries clipping

Parallel clipping

Series clipping

In these types of circuits, the diode is connected

between the input and output voltage terminals.

Parallel clipping

In these types of circuits, the diode is connected inparallel.


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Positive Clipper

04/21/12Deepak.P25


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+VE series CLIPPING


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Transfer Characteristics

04/21/12Deepak.P27

Vm


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Negative Diode Clipper

04/21/12Deepak.P28


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-VE series CLIPPING

Diodes will act as an "ON/OFF switch.


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-VE Parallel CLIPPING


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Clipper circuits

04/21/12Deepak.P31


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Negative& Positive Diode Clipper

04/21/12Deepak.P32


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Biased Negative Clipper

A biased clipper comes in handy when asmall portion of positive or negative halfcycles of the signal voltage is to beremoved.

When a small portion of the negative halfcycle is to be removed, it is called a biasednegative clipper.

04/21/12Deepak.P33


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Biased Positive Clipper

04/21/12Deepak.P34


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Biased Positive Clipper and Biased Negative Clippers

04/21/12Deepak.P35

Biased Positive Clipper and Biased Negative


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Biased Positive Clipper and Biased Negative

Clipper

04/21/12Deepak.P36


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Combination Clipper

When a portion of both positive andnegative of each half cycle of the inputvoltage is to be clipped (or removed),combination clipper is employed. The

circuit for such a clipper is given in thefigure below.

04/21/12Deepak.P37


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Transistor Clipper

Transistor can be used to clip the I/P waveform.

Positive clipper , negative clipper, Combinational

clipper can be designed using Transistor circuit.

The practical circuit for positive and negative clippingis Transistor switching circuit.

The practical circuit for obtain Double side clipping is

Transistor amplifier circuit.


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Function of a Simple Switch

An OFF type switch

Lamp does not glows

No current will flow in the circuit

Lamp


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Function of a Simple Switch

An ON type switch

Lamp glows

Some amount of current flows in the circuit according to

the resistance.

Lamp


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Transistor as a Switch

Bipolar transistors can be made to operate as an"ON/OFF switch.

Because a transistor's collector current is

proportionally limited by its base current, it can be

used as a current-controlled switch.

If the circuit uses the Transistor as a Switch, then the

biasing is arranged to operate the transistor in the

"Saturation" and "Cut-off" regions.


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Transistor as a Switch

If we are using PNP transistor, Battery should be reversed.

Lamp


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Transistor Act as an OFF type switch

Transistor is biased in cutoff, lamp OFF , No current flow


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Cut OFF Region

Cut-off" region

Both junctions are reverse-biased.

Here the operating conditions of the transistor are

Zero input base current (Ib),

Zero output collector current (Ic)Maximum collector voltage (Vce)

Here the transistor is switched fully "OFF".


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Transistor Act as an ON type switch

Transistor saturated, lamp ON, Current flows


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Saturation Region

Saturation" region

Both junctions are Forward-biased.

Here the transistor will be biased so that the maximum

amount of base current is applied, resulting in

Maximum collector current flowMinimum collector emitter voltage

Here the transistor is switched fully "ON".


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Transistor Switching Circuit

Transistor switching circuit can be divided in to two

Normally ON type

Normally OFF type

In normally OFF ,transistor will be in cutoff.In normally ON ,transistor will be in saturation.


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O/P Characteristics of CE configuration

Load Line

Soft Saturation Point

Hard

SaturationP

oint


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Simple Amplifier

VCC

O/PI/P

RB

RC


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Amplifier Operation

LOAD LINE

VCC

VCC/

(RC+RE)

Q POINT

VCEQ

ICQ


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Normally ON type Switch

VCC

O/PI/P

RBRC


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Normally ON type SwitchThe Q point of the transistor must fix in the hard

saturation/Soft Saturation point.For that ,fix VCEQ=0.2and

ICRC= VCC-VCEQ

DC Load Line

VCC

VCC/RC

Q POINT

VCEQ

ICQ


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Design of Normally ON type SwitchAssume VCC,IC,

O/P Loop equationVCC=VCE+ICRC VCE sat=0.2

RC=VCC VCE sat/ IC ;

I/P Loop equation

IC= IB

VCC=5 IB RB+VBE ;

RB=VCC -VBE / 5 IB ;


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O/P wave form when I/P is Square wave

INPUT

OUTPUT

0.2 V


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O/P when I/P is Sine wave

VCC

VCC/(RC)

Q POINT

VCEQ

0.2V


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Normally OFF type Switch

VCC

O/P

I/P

RB

RC


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Normally OFF type SwitchThe Q point of the transistor must fix in the cut-off

For that ,fix VCEQ=VCC andICQ=0; To fix ICQ=0 , IB =0, So No Dc bias is applied to the base.

Practically a small negative voltage is applied to the Base.

VCC

VCC/RC

Q POINT


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Design of Normally OFF type SwitchAssume VCC,IC,

O/P Loop equationVCC=VCE+ICRC VCE sat=0.2

RC=VCC VCE sat/ IC ;

I/P Loop equation

IC= IB

VCC=5 IB RB+VBE ;

RB=VCC -VBE / 5 IB ;


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O/P wave form when I/P is Square wave

INPUT

OUTPUT

0.2V


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O/P when I/P is Sine wave

ICQ

VCC

VCC/(RC)

Q POINT

VCEQ

ICQ=0 VCEQ=VCC

CAPACITOR


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CAPACITOR

A capacitor is a device that can store electrical charge.The simplest type is a "parallel plate " Capacitor that

consists of two metal plates that are separated by an

insulating material.

Capacitor is a two-terminal device.

Capacitor has two active electrodes.Anode

Cathode

CAPACITOR


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CAPACITOR


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Charging of a Capacitor from a DC source

If we connect the two plates to each other with abattery, the free electrons is accumulated in one plate

of a capacitor. Similarly positive charges is

accumulated to the another plate.

Ch i f C it


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Charging of a Capacitor

If we quickly remove the wires without touching the

plates, the charge remains on the plates.Because the two plates have different charge, there is a

net electric field between the two plates.

The "capacitance" of a capacitor is stated in terms of

the amount of charge (Q) stored at a given voltage

drop (across the capacitor).

C = Q / V

C = A / d= 0 r


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Charging of a Capacitor from a AC source

Assume that, we connect the capacitor to an ACsource.

In the positive half cycle + ve charges were

accumulated in one plate.


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Charging of a Capacitor from a AC source

In the negative half cycle +ve charges wereaccumulated in the other plate.

It is similar to coupling of an AC signal.


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Charging wave form of a Capacitor

Clamping


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Clamping

The clamping circuit can shift the waveform to a

specified voltage level.

Clamping circuit actually introduces a dc level to an

AC signal.

It is also known as DC restorercircuit.

It is used in the television receiver to restore the

original dc reference voltage to the video signal.

In television system ,the dc reference levelcorresponding to thebrightness level of the picture is

not transmitted with video signal.

Clamping


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Clamping

A capacitorand a diode can be used to design

clamping circuits.

Clamping can be classified in to

+ve clamping-ve clamping

Biased clamping circuits can be designed to clamp a

waveform at a desired level

Problem


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Problem

Vi=Vm Sint

VO

Draw the O/P/ wave form when the I/P is 20 Vpp

Answer


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Answer

-10 V

10 V

Problem


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Problem

Vi=Vm Sint

VO

Draw the O/P/ wave form when the I/P is 20 Vpp and it

contains a DC voltage of 2V

Answer


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Answer

2V

10 V

-10 V

Simple Clamping


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SimpleClamping

V

+-Vi=Vm Sint

VO

Battery

Answer


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Answer

V

Vm+V

Vm-V

Simple Clamping


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SimpleClamping

Vm

Vi=Vm Sint

VO

+-

Answer


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Answer

-V

Vm-V

-Vm-V

Simple Diode Clamping


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SimpleDiodeClamping

Vm

In negative half cycle ;Vo=vi+Vm=Vm Sint+Vm

+ -Vi=Vm Sint

VO

Capacitor



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SimpleDiodeClamping

Vm



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SimpleDiodeClamping

VmVm

O/P when I/P is square wave


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Vm+Vm



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SimpleDiode Clamping

Vm

+-

In the 2nd

positive half cycle;Vo=Vi-Vm=Vm Sint-Vm

Vi=Vm Sint

VO

Capacitor



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Vm+Vm



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Vm+Vm

Problem


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Problem

Vm

Vi=Vm Sint

VO

+

-

The I/p signal with 24 Vpp is applied to a clamper circuit. Sketch the O/P wave

form

Problem


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Problem

Vm

VO

+

-


form

Positive Clamping


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Positive Clamping

Vm

+

-

Draw the o/p wave form

VO



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Vm+Vm

Negative Clamping


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Negative Clamping

Vm

+

-

Draw the o/p wave form

VO

Biased Clamper


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Biased Clamper

Vm

Vi=Vm Sint

VO

+

-


form

-

+5V

Biased Clamper


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Biased Clamper

Biased Clamper


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Biased Clamper

Biased Clamper


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Biased Clamper

Biased Clamper


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Biased Clamper


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RC Circuits

An RC circuit is simply a circuit with avoltage source (battery) connected inseries with a resistor and a capacitor.

A resistor-capacitor circuit (RC circuit), or

RC filter or RC network, is an electric circuitcomposed of resistors and capacitorsdriven by a voltage or current source. The1st order RC circuit, composed of one

resistor and one capacitor, is the simplestexample of an RC circuit.

04/21/12Deepak.P95


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RC Circuits

04/21/12Deepak.P96


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RC Circuits

04/21/12Deepak.P97

As with circuits made up simply ofresistors, electrical currents can flow in thisRC circuit, with one modification. A batteryconnected in series with a resistor will

produce a constant current. The samebattery in series with a capacitor willproduce a time varying current, whichdecays gradually to zero. If the battery is

removed and the circuit reconnectedwithout the battery, a current will flow (fora short time) in the opposite direction asthe capacitor "discharges". A measure of

how long these transient currents last in a"


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RC Circuits

04/21/12Deepak.P98

Time ConstantThe time constant of an RC circuit is the

product of its resistance and capacitance.For R in ohms and C in farads, the time

constant tis in seconds.T = RC

The range of frequencies that the filterpasses is called its bandwidth. The point at

which the filter attenuates the signal to halfits unfiltered power is termed its cutofffrequency. This requires that the gain ofthe circuit be reduced to


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RC Circuits

04/21/12Deepak.P99


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RC Circuits

04/21/12Deepak.P100


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RC Circuits

High Pass FilterA High Pass Filter or HPF, is the exact opposite to that

of Low Pass filter circuit, as now the two components

have been interchanged with the output signal (Vout)

being taken from across the resistor.Where the low pass filter only allowed signals to pass

below its cut-off frequency point, c, the passive high

pass filter circuit as its name implies, only passes

signals above the selected cut-off point, c eliminatingany low frequency signals from the waveform.

04/21/12Deepak.P101

High Pass Filter


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04/21/12Deepak.P102

In this circuit arrangement, the reactance of the capacitor is very high at

low frequencies so the capacitor acts like an open circuit and blocks any

input signals at Vin until the cut-off frequency point (c) is reached. Above

this cut-off frequency point the reactance of the capacitor has reduced

sufficiently as to now act more like a short circuit allowing all of the input

signal to pass directly to the output as shown below in the High PassFrequency Response Curve.

High Pass Filter


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04/21/12Deepak.P103

High Pass Filter


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04/21/12Deepak.P104

The circuit gain, Av which is given as Vout/Vin (magnitude) and is

calculated as:

Cut-off Frequency and Phase Shift

High Pass Filter


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High pass filter stages can be cascadedtogether to form a second-order (two-pole)filter as shown.

04/21/12Deepak.P105

High Pass Filter


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A very common application of a passivehigh pass filter, is in audio amplifiers as acoupling capacitor between two audioamplifier stages and in speaker systems todirect the higher frequency signals to thesmaller "tweeter" type speakers whileblocking the lower bass signals or are alsoused as filters to reduce any low frequencynoise or "rumble" type distortion. Whenused like this in audio applications the highpass filter is sometimes called a "low-cut",or "bass cut" filter.

04/21/12Deepak.P106

High Pass Filter


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RC Differentiator

04/21/12Deepak.P107

RC Differentiator


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Each cycle of the square wave input waveformproduces two spikes at the output, one positive and one

negative and whose amplitude is equal to that of the

input. The rate of decay of the spikes depends upon the

time constant, (RC) value of both components, (t = R xC) and the value of the input frequency. The output

pulses resemble more and more the shape of the input

signal as the frequency increases.

04/21/12Deepak.P108

RC Differentiator


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From theory we know that the voltageacross the resistor in an RC circuit is givenby:

Charging: vR = Vp e- tRC

Discharging: vR = - Vp e- tRC

04/21/12Deepak.P109

RC Integrator


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From theory we know that the voltageacross the capacitor in an RC circuit isgiven by:

Charging: vc = Vp (1 e-t/RC)Discharging: vc = Vp e- tRC

04/21/12Deepak.P110

RC Integrator


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04/21/12Deepak.P111

RECTIFIERS


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RECTIFIERS

A rectifier is an electrical device that convertsalternating current (AC) to direct current (DC).

Rectifiers have many uses including as components of

power supplies and as detectors of radio signals.

Rectifiers may be made of solid state diodes, vacuumtube diodes, mercury arc valves, and other

components.

RECTIFIERS(C td )


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RECTIFIERS(Contd..)

Rectifiers can be divided in to twoHalf wave Rectifiers

Full wave Rectifiers

In half wave rectification, either the positive or

negative half of the AC wave is passed, while the otherhalf is blocked.

Half-wave rectification can be achieved with a single

diode in a one phase supply, or with three diodes in a

three-phase supply.

HALF WAVE


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RECTIFIERS(Contd..)

Full WAVE RECTIFIERS


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A full-wave rectifier converts the whole ofthe input waveform to one of constantpolarity (positive or negative) at its output.Full-wave rectification converts both

polarities of the input waveform to DC(direct current), and is more efficient.However, in a circuit with a non-centertapped transformer, four diodes are

required instead of the one needed for half-wave rectification. Four rectifiers arrangedthis way are called a diode bridge or bridgerectifier.

Bridge RECTIFIERS


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g

Regulated Power Supply


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g pp y

There are many types of power supply.Most are designed to convert high voltageAC mains electricity to a suitable lowvoltage supply for electronics circuits and

other devices. A power supply can bybroken down into a series of blocks, each ofwhich performs a particular function.

Regulated Power Supply


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g pp y

Each of the blocks is described in more detail below:

Transformer - steps down high voltage AC mains to low voltage AC.

Rectifier - converts AC to DC, but the DC output is varying.

Smoothing - smoothes the DC from varying greatly to a small ripple.

Regulator - eliminates ripple by setting DC output to a fixed voltage.

Transformer only

Transformer + Rectifier

Transformer + Rectifier + Smoothing

Transformer + Rectifier + Smoothing + Regulator

Zener Diode


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Zener Diode

04/21/12Deepak.P121

A Zener diode is a type of diode that permits current not only in

the forward direction like a normal diode, but also in the reverse

direction if the voltage is larger than the breakdown voltage

known as "Zener knee voltage" or "Zener voltage". The device

was named after Clarence Zener, who discovered this electricalproperty.

Zener Regulator


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Zener Regulator

Zener diodes are widely used as voltagereferences and as shunt regulators toregulate the voltage across small circuits.When connected in parallel with a variable

voltage source so that it is reverse biased,a Zener diode conducts when the voltagereaches the diode's reverse breakdownvoltage. From that point on, the relatively

low impedance of the diode keeps thevoltage across the diode at that value.

04/21/12Deepak.P122

Zener Regulator


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Zener Regulator

A Zener diode is a PN junction that hasbeen specially made to have a reversevoltage

breakdown at a specific voltage. Its

characteristics are otherwise very similar tocommon

diodes. In breakdown the voltage acrossthe Zener diode is close to constant over a

widerange of currents thus making it useful as a

shunt voltage regulator.

04/21/12Deepak.P123

Zener characteristic


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Zener characteristic

04/21/12Deepak.P124

Zener Regulator


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Zener Regulator

04/21/12Deepak.P125

Zener Regulator


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Zener Regulator

04/21/12Deepak.P126

Fixed IC voltage Regulators


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Fixed IC voltage Regulators

Voltage Regulator (regulator), usuallyhaving three legs, converts varying inputvoltage and produces a constant regulatedoutput voltage. They are available in a

variety of outputs.The most common part numbers start with

the numbers 78 or 79 and finish with twodigits indicating the output voltage. The

number 78 represents positive voltage and79 negative one. The 78XX series ofvoltage regulators are designed for positive

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ANALOG CIRCUITS – I