Continuous and Discrete Time Signal & Analog and Digital Signal

Continuous And Discrete Time Signal 

A signal x(t) is a continuous-time signal if t is a continuous variable. If t is a discrete variable, that is, x(t) is defined at discrete times, then x(t) is a discrete-time signal.a discrete-time signal is often identified asa sequence of numbers, denoted by {x,) or x[n], where n = integer

Analog And Digital Signal 

• If a continuous-time signal x(l) can take on any value in the continuous interval (a, b),where a may be - 03 and b may be + m, then the continuous-time signal x(t) is called analog signal. 
• If a discrete-time signal x[n] can take on only a finite number of distinct values, then we call this signal a digital signal.

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Types of signals , Energy And Power Signal

Types Of Signals

A signal is a function representing a physical quantity or variable, and typically itcontains information about the behavior or nature of the phenomenon.

Signals are of following types-

• Continuous and Discrete time signal
• Analog and Digital signal
• Even and Odd signal 
• Perodic or Non Perodic Signal 
• Energy and Power Signal 
• Determinestic and Random Signal 

Difference Between Energy And Power signal 

For an arbitrary continuous-time signal x(t),

the normalized energy content E of x(t) is defined as

The normalized average power P of x(t) is defined as

for a discrete-time signal x[n],

the normalized energy content E of x[n] is defined as

The normalized average power P of x[n] is defined as

Note it -

1. x(t) (or x[n]) is said to be an energy signal (or sequence) if and only if 0 < E < m, and so P = 0.
2. x(t) (or x[n]) is said to be a power signal (or sequence) if and only if 0 < P < m, thus implying that E = m.

Signals that satisfy neither property are referred to as neither energy signals nor power signals.

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HALL EFFECT

HALL EFFECT

If a piece of metal or semiconductor carrying a current I is placed in a transverse magnetic field B then an electric field E is induced in the direction perpendicular to both I and B. This phenomenon is known as Hall effect.

Hall effect is normally used to determine whether a semi-conductor is n-type or p-type.

To find whether the semiconductor is n-type or p-type

• In the figure. above, If I is in the +ve X direction and B is in the +ve Z direction, then a force will be exerted on the charge carriers (holes and electrons) in the –ve Y direction.
• This force is independent of whether the charge carriers are electrons or holes.Due to this force the charge carriers ( holes and electrons) will be forced downward towards surface –1 as shown.
• If the semiconductor is N-type, then electrons will be the charge carriers and these electrons will accumulate on surface –1 making that surface –vely charged with respect to surface –2. Hence a potential called Hall voltage appears between the surfaces 1 and 2.
• Similarly when surface –1 is positively charged with respect to surface –2, Then the semiconductor is of P-type. In this way, by seeing the polarity of Hall voltage we can determine whether the semiconductor is of P-type or N-type.

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DIFFUSION CURRENT IN SEMICONDUCTORS

DIFFUSION   CURRENT

• The directional movement of charge carriers due to their concentration gradient produces a component of current known as Diffusion current.
• The mechanism of transport of charges in a semiconductor when no electric field is applied called diffusion. It is encountered only in semiconductors and is normally absent in conductors.

• With no applied voltage if the number of charge carriers (either holes or electrons) in one region of a semiconductor is less compared to the rest of the region then there exist a concentration gradient.

• Since the charge carriers are either all electrons or all holes they sine polarity of charge and thus there is a force of repulsion between them.
• As a result, the carriers tend to move gradually or diffuse from the region of higher concentration to the region of lower concentration. This process is called diffusion and electric current produced due to this process is called diffusion current.
• This process continues until all the carriers are evenly distributed through the material. Hence when there is no applied voltage, the net diffusion current will be zero.

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DRIFT CURRENT IN SEMICONDUCTORS

DRIFT CURRENT 

• If an electron is subjected to an electric field in free space it will accelerate in a straight line form the –ve terminal to the + ve terminal of the applied voltage.
• However in the case of conductor or semiconductor at room temperature, a free electrons under the influence of electric field will move towards the +ve terminal of the applied voltage but will continuously collide with atoms all the ways as shown in figure.

• Each time, when the electron strikes an atom, it rebounds in a random direction but the presence of electric field does not stop the collisions and random motion. As a result the electrons drift in a direction of the applied electric field.
• The current produced in this way is called as Drift current and it is the usual kind of current flow that occurs in a conductor.

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SEMICONDUCTOR : DEFINITION , TYPES

WHAT ARE SEMICONDUCTORS ?

• Semiconductors are those substances whose conductivity lies in between that of a conductor and Insulator.Example: Silicon, germanium, Cealenium, Gallium, arsenide etc.
• In terms of energy bands, semiconductors are those substances in which the forbidden gap is narrow.Thus valence and conduction bands are moderately separated .
• In semiconductors, the valence band is partially filled, the conduction band is also partially filled, and the energy gap between conduction band and valence band is narrow.
• Therefore, comparatively smaller electric field is required to push the electrons from valence band to conduction band . 
• At low temperatures the valence band is completely filled and conduction band is completely empty. Therefore, at very low temperature a semi-conductor actually behaves as an insulator.

TYPES OF SEMICONDUCTOR

a) Intrinsic semiconductors.

b) Extrinsic semiconductors.

a) Intrinsic semiconductors

• A semiconductor in an extremely pure form is known as Intrinsic semiconductor.
• Example: Silicon, germanium.

b) Extrinsic semiconductors

• When an impurity is added to an Intrinsic semiconductor its conductivity changes.
• This process of adding impurity to a semiconductor is called Doping and the impure semiconductor is called extrinsic semiconductor.
• Depending on the type of impurity added, extrinsic semiconductors are further classified as n-type and p-type semiconductor.

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Zener diodes

Zener diodes

The reverse voltage characteristics of a semiconductor diode including the breakdown region is shown below.

Zener diodes are the diodes which are designed to operate in the breakdown region. They are also called as Breakdown diode or Avalanche diodes.
The breakdown in the Zener diode at the voltage Vz may be due to any of the following mechanisms.

Avalanche breakdown

• We know that when the diode is reverse biased a small reverse saturation current I0 flows across the junction because of the minority cariers in the depletion region
• The velocity of the minority charge carriers is directly proportional to the applied voltage. Hence when the reverse bias voltage is increased, the velocity of minority charge carriers will also increase and consequently their energy content will also increase. 
• When these high energy charge carriers strikes the atom within the depletion region they cause other charge carriers to break away from their atoms and join the flow of current across the junction as shown above. The additional charge carriers generated in this way strikes other atoms and generate new carriers by making them to break away from their atoms.
• This cumulative process is referred to as avalanche multiplication which results in the flow of large reverse current and this breakdown of the diode is called avalanche breakdown.

Zener breakdown

                          electric field strength = Reverse voltage/Depletion region

• From the above relation we see that the reverse voltage is directly proportional to the  electric field hence, a small increase in reverse voltage produces a very high intensity electric field with ina narrow Depletion region.
• Therefore when the reverse voltage to a diode is increased, under the influence of high intensity electric filed large numbr of electrons within the depletion region break the covalent bonds with their atoms as shown above and thus a large reverse current flows through the diode. This breakdown is referred to as Zener breakdown.

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FILTER CIRCUIT : WHY WE USE ?

• We know that the output of the rectifier is pulsating d.c. ie the output obtained by the rectifier is not pure d.c. but it contains some ac components along with the dc o/p. 
• These ac components are called as Ripples, which are undesirable or unwanted. 
• To minimize the ripples in the rectifier output filter circuits are used. 
• These circuits are normally connected between the rectifier and load as shown below.

• Filter is a circuit which converts pulsating dc output from a rectifier to a steady dc output. In other words, filters are used to reduce the amplitudes of the unwanted ac components in the rectifier.

TYPES OF FILTER

1. Capacitor Filter (C-Filter)

2. Inductor Filter

3. Choke Input Filter (LC-filter)

4. Capacitor Input Filter (Π-filter)

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BIASING IN DIODE

BIASING IN DIODE 

Connecting a p-n junction to an external d.c. voltage source is called biasing.

1. Forward biasing

2. Reverse biasing

 

1. Forward biasing

• When external voltage applied to the junction is in such a direction that it cancels the potential barrier, thus permitting current flow is called forward biasing.
• To apply forward bias, connect +ve terminal of the battery to p-type and –ve terminal to n-type as shown in figure below.
• The applied forward potential establishes the electric field which acts against the field due to potential barrier. Therefore the resultant field is weakened and the barrier height is reduced at the junction as shown in figure. 

• Since the potential barrier voltage is very small, a small forward voltage is sufficient to completely eliminate the barrier. Once the potential barrier is eliminated by the forward voltage, junction resistance becomes almost zero and a low resistance path is established for the entire circuit. Therefore current flows in the circuit. This is called forward current.

2. Reverse biasing

• When the external voltage applied to the junction is in such a direction the potential barrier is increased it is called reverse biasing.
• To apply reverse bias, connect –ve terminal of the battery to p-type and +ve terminal to n-type as shown in figure below.
• The applied reverse voltage establishes an electric field which acts in the same direction as the field due to potential barrier. Therefore the resultant field at the junction is strengthened and the barrier height is increased .

• The increased potential barrier prevents the flow of charge carriers across the junction. Thus a high resistance path is established for the entire circuit and hence current does not flow.

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SEMICONDUCTOR DIODE

When a p-type semiconductor material is suitably joined to n-type semiconductor the contact surface is called a p-n junction. The p-n junction is also called as semiconductor diode.

• The left side material is a p-type semiconductor having –ve acceptor ions and +vely charged holes. The right side material is n-type semiconductor having +ve donor ions and free electrons.
• Suppose the two pieces are suitably treated to form pn junction, then there is a tendency for the free electrons from n-type to diffuse over to the p-side and holes from p-type to the n-side . This process is called diffusion.
• As the free electrons move across the junction from n-type to p-type, +ve donor ions are uncovered. Hence a +ve charge is built on the n-side of the junction. At the same time, the free electrons cross the junction and uncover the –ve acceptor ions by filling in the holes. Therefore a net –ve charge is established on p-side of the junction.
• When a sufficient number of donor and acceptor ions is uncovered further diffusion is prevented.
• Thus a barrier is set up against further movement of charge carriers. This is called potential barrier or junction barrier Vo. The potential barrier is of the order of 0.1to 0.3V.

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SIGNAL & SYSTEM VIDEO LECTURES

HELLO ,
THIS TIME I AM POSTING THE NPTEL LECTURES OF SIGNAL & SYSTEM .

LECTURE 1

This  lecture is basic introduction towards subjects .....

 

 

LECTURE 2 

This Lecture consist of Domain & Range of Signals 

 (SEE ALSO: http://itsknowledgemenia.blogspot.in/2014/06/general-knowledge.html)

LECTURE 3 

IN THIS LECTURE THE SYSTEM IS INTRODUCED.

 

LECTURE 4 

This lecture defines the properties of different signals

 

LECTURE 5 

This defines the frequently  used continuous signals

 

LECTURE 6

This defines the frequently used discrete time signals 

 

LECTURE 7

This shows the Transformations on time & range

LECTURE 8

(SEE ALSO :http://itsknowledgemenia.blogspot.in/2014/06/some-basic-learning-videos-for-kids.html)

This defines the properties of system  

LECTURE 9

This defines the properties of system

LECTURE 10

In this Communication diagram is shown.... 

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Microcontroller

Micro -controller is the integrated circuit , which contains the following things:-
1.Processor

 2.Memory
3.Input-output peripherals .

In the micro-controller , For program memory we use the following :-
1.NOR FLASH
2. OTP ROM
3.Small amount of RAM

Micro-controllers are used in different control products such as
1.Automobile engine control system
2.Remote controls
3. Office systems
4.Appliances
5.Toys etc....

Now days micro-controllers are used in Home Automation systems & other Embedded  System.
A micro-controller is  self-contained system with a processor, Memory and Peripherals and can be used as Embedded system .Embedded systems are very sophisticated & minimal requirements for memory and program length, with no operating system, and low software complexity.

Program

 Micro-controller programs fit in the available on-chip program memory, Compilers and assemblers are used to convert high-level language and assembler language codes into a compact machine code for storage in the micro-controller's memory.
According to the requirement ,the program memory may be
1.Permanent,
2.Read-only memory
3. Field-alterable flash or Erasable read-only memory.

Micro-controllers included E PROM versions that have a "window" on the top of the device through which program memory can be erased by Ultraviolet light, ready for re-programming after a
programming ("burn") and test cycle.

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Logic Gates

Logic gates are physical device which are used to perform logical function.logic gates perform logical operation. In logic gates we can give one or more input and we have one output . every operation is expressed in "1" or "0".
1 means  "high"
0 means "low"

Their are three basic logic gates:-
1.OR Gate
2.AND Gate
3.NOT Gate

1.OR Gate

In case of OR Gate their are following conditions for the Output:-

1. If one of the input is high the output also HIGH it means it gives "logic 1" at the output.

2.If the both the input are low then the output of OR Gate is low it means it gives "logic 0" at the output.

Boolean Expression in case of the OR Gate is 

Y(Output)= A + B

2.AND Gate

In case of AND Gate their are following conditions  for the Output:-

1.If both of the input are high then the output also be HIGH(Logic 1).

 2.If both the input are low then the output also LOW.(logic 0).

3.If 1 input is high(1), other is low(0) then the output also be LOW.

Boolean  Expression in case of the AND Gate is

Y(Output)= A * B

3.NOT Gate

NOT Gate is said as the "INVERTER". In case of the NOT Gate:-

1. If Input is HIGH(1) then Output is LOW(0).

2.If the input is LOW(0) then  Output is HIGH(1).

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Random Access Memory

                               Random-Access Memory         

Random-access memory (RAM) is a Device which allows data to read as well as write.RAM is a basically a  form of computer data storage.
In contrast, with other direct-access data storage media such as hard disks, CD-RWs, DVD-RWs and the older drum memory, the time required to read and write data items varies significantly depending on their physical locations on the recording medium, RAM is basically used in computer or electronic gadgets now days.

RAM are of two types:

1.SRAM(Static Read Only Memory)

2.DRAM (Dynamic Read Only Memory)

Random-access memory takes the form of integrated circuits. Modern types of DRAM are not random access, as data is read in bursts, although the name DRAM / RAM has stuck. However, many types of SRAM are still random access even in a strict sense. RAM is normally associated with volatile types of memory (such as DRAM memory modules), where stored information is lost if the power is removed, although many efforts have been made to develop non-volatile RAM chips.

Difference between SRAM & DRAM

1. DRAM requires the data to be refreshed periodically in order to retain the data. SRAM does not need to be refreshed as the transistors inside would continue to hold the data as long as the power supply is not cut off. 
2. The additional circuitry and timing needed to introduce the refresh creates some complications that makes DRAM memory slower and less desirable than SRAM .
3. SRAM needs a lot more transistors in order to store a certain amount of memory. A DRAM module only needs a transistor and a capacitor for every bit of data where SRAM needs 6 transistors .

 

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BASIC OF MATLAB

MATLAB

MATLAB is the basic the tool by which the different mathematical expression are solved easily as well as there we can plot the graph of these expressions. MATLAB is the  abbreviation of  the MATRIX LABOTERY. As name suggest matrix which is the part of mathematics is  also use in physics . Chemistry and Engineering streams.  MATLAB have following applications as below :

 1Image and Video Processing

       2.Control Systems 
       3.Test and Measurement 
           4.Computational Finance 
       5.Computational Biology
       6.Signal Processing and Communications

MATLAB ENVIRONMENT

When we Launch MATLAB development IDE from the icon created on desktop. The main desktop appears in its default layout:

SOFTWARE PROCESSING

Double click the MATLAB icon the following window will open

Then go to File >>New>>M-File option as shown

M-file will open in the form of a editor window the entire program is written here as shown

 To run the program go to Debug >> Run Program or press F5 key as shown

 Current status of program can be checked at command window as shown

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