ECSTUFF4U for Electronics Engineer

What is the full form of PSK?

Answer :

Phase Shift Keying

What does PSK mean?

PSK is the simplest form of phase shift keying, sometimes it called as BPSK or 2PSK. It can be used phases which are separated by 180 degrees and so can also be termed 2 PSK.

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PAM full form

What is the full form of PAM?

Answer :

Pulse Amplitude Modulation

What does PAM mean?

PAM is a form of a modulation called as signal modulation, it is part of signal communication where the message information is encoded in the amplitude of a series of signal pulses. PAM is an analog pulse modulation scheme in which the amplitudes of a train of carrier pulses are varied according to the sample value of the message signal is transmitted.

Advantages and disadvantages of AC over DC

We all are aware of the basic concept of AC as well as DC. This article gives information about the advantages and disadvantages or drawback of AC over DC to know more details about this topic.

Advantages of AC over DC :

The generation of A.C is much more cheaper than that of D.C
AC can easily be converted into DC with the use an of rectifier
A.C machines are simple
The variation of AC can easily be done using transformer either using a step up or step down
They are robust and also do not require much attention for their repair and maintenance during their use
In while using AC the loss of energy during transmission is negligible
The AC can be easily converted into DC
The AC generator have higher efficiency compare to DC
The value or magnitude of AC can be decreased easily without loss of an excess of energy this can be done by only using a device the choke coil
The AC is easy to generate than DC easily converted into DC
It is cheaper to generate AC compare DC
A wide range of voltages are obtained by use of a transformer device
In AC the magnitude of current can be reduced by using an a conductor or inductance without any appreciable loss of energy
When AC is supplied at higher voltages in long-distance transmission, the line loss is small compared to a DC transmission side

Disadvantages of AC over DC :

The peak value of AC is high and it dangerous to use so too much better insulation required
An AC is transmitted from the surface of the conductor hence need several strands of thin wires insulated from each other
It attracts a person who touches it unlike DC which gives a repelling shock

Difference between pin photodiode and avalanche photodiode

Before we learn about this article first let we check it out PIN diode and avalanche photodiode (APD), so we have to better understand this article. This article gives information about the difference between a PIN diode and APD to know more details about it.

PIN diode :

PIN photodiode does not have a high-intensity electric field region.
Sensitivity is very low in PIN photodiode.
The responsibility of a PIN diode is limited.
Cost is low.
S/N ratio is very poor.
Conversion efficiency is 0.5 to 1.0 amps/watt.
The response time of PIN is half that of APD.
The detector circuit is very simple.

APD :

APD is a high-intensity electric field region.
Sensitivity is very high in APD.
The responsibility of APD can have much larger values,
Cost is high.
S/N ratio is better.
Conversion efficiency is 0.5 to 100 Amps/watt.
The response time of APD is almost double that of the PIN,
The detector circuit is more complex.

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Impulse invariant method example

Step 1 : Analog frequency transfer function H(s) will be given. If it not given then obtain expression of H(s) from the given specification

Step 2 : If required H(s) by using fraction expansion

Step 3 : Obtain Z transform of each PFE term using in-variance transformation equation

Step 4 : Obtain H(z) this is required digital IIR filter

Find out H(Z) using impulse in-variance method at 5 Hz sampling frequency from H(s) as given below :

H(s) = 2 / (s+1) (s+2)

Step 1 : Given analog transfer function is,

H(s) = 2 / (s+1) (s+2)

Step 2 : We will expand H(s) using partial fraction expansion as :

H(s) = A₁/s+1 + A₂/s+2

p₁= -1 and p₂ =-2

Step 3 :

A₁= s+1 * 2 / (s+1) (s+2) where s=-1

A₁= 2/-1+2

A₁= 2

Same way

A₂= s+2 * 2 / (s+1) (s+2) where s=-2

A₂= 2/-2+1

A₂= -2

H(s) = 2/s+1 - 2/s+2

Step 3 : Obtain Z transform of each PFE term using in-variance transformation equation

1 / s-p_k = 1/ 1-e ^p_k^T_s. Z^-1

^1/^F_s = 1/5 = 0.5 sec = ^T_s

_{1/ s+1 →}1/ 1-e ^-1(0.2) . Z^-1

_{1/ s+1 →}1/ 1-e ^-0.2 . Z^-1

_{1/ s+2 →}1/ 1-e ^-2(.2) . Z^-1

_{1/ s+2 →}1/ 1-e ^-0.4 . Z^-1

Step 4 : Obtain H(z) this is required digital IIR filter

H(Z) = A₁/ 1-e ^p₁^T_s. Z^{-1 +}A₂/ 1-e ^p₂^T_s. Z^-1

^{H(Z) =}2/ 1-e ^-0.2 . Z^{-1 -}2/1-e ^-0.4 . Z^-1

^{H(Z) =}^{2/ 1-0.818}Z^-1 - 2/ 1-0.67Z^-1

^{H(Z) = 2Z / Z-0.818 - 2Z/ Z-0.67}

H(Z) = 2Z(Z-.67-2Z (Z-0.818) / (Z-0.818)(Z-0.67)

^{H(Z) = 0.29 Z /}Z²-1.488Z+0.54

This require transfer function for digital IIR filter.

Advantages and disadvantages of digital communication

Digital communication is a system that any message pass through digital devices. It is the ability to create communication in different media. It transmits any information by digitally. Now let us check it out a lot of advantages, so we have to know more about digital communication.

Advantages of digital communication :

It can be done over large distances through internet devices and other things
Digital communication technology is easy to mix signals and also have data using digital techniques
Greater dynamic range is possible
More option and flexibility in terms of recording and also a reviewing data
Used in military application
The inexpensive circuit may be used
Digital communication gives facilities like video conferencing which save a lot of time, money as well as effort
Digital communication is done over a large distance through the Internet and is spread almost in every cities and town. So in the compatibility of digital communication systems with the internet has opened a new area of applications
Using data encryption, it is very useful for in a military application
High-speed computers and powerful software design tools are available, so a digital communication system flexible
It can be tolerated the noise interference
The digital communication is fast, easier and cheaper
Digital communication has excellent processing techniques are available for digital signals processing such as processing methods like image processing, video processing, data compression, channel coding and equalization etc
Much less bulky than analog equivalent
The error may offer to be corrected with the use of coding
Much more options being able to share media called both socially and for business

Disadvantages of digital communication :

High power consumption
It has a sampling error
Nongraceful degradation
Bit error rate or probability of error
Require A/D conversion at a high rate
It requires more bandwidth as compared to an analog system
It needs synchronization in synchronous modulation
As the square wave is more affected by noise, that's what while communicating through channel we send sine wave but while operating on a device we use squire pulses
Complex circuit, more sophisticated device making is also disadvantages of a digital system
More expensive to fix when it does wrong
It was harder to fix when it does go wrong
Miss-communication is possible if a user doesn't understand something

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Application of DFT

Before we learn about application of DFT, first let we check it out the DFT stands for Discrete Fourier transform, it is a finite duration frequency sequence which is obtained by sampling one period of Fourier transform. So in sampling is done at 'N' equally spaced points, over the period extending from o to 2π.

Signal analysis
Sound filtering
Data compression
Partial differentiation equation
Multiplication of large integer
Cross correlation
Matched filtering
System identification
Power spectrum estimation
Coherence function measurement
Display signal and spectrum

DFT example

Before we fine DFT first let we check it out the what is DFT.

Find the DFT of the following finite equation sequence of length L.

x(n) = A for 0≤ n ≤ L-1

= 0 otherwise

We have

N-1

X(K) = ∑ x(n) . e ^–j2πkn/N

n=0

N-1

X(K) = ∑ A . e ^–j2πkn/N

n=0

N-1

X(K) = ∑ x(n) .( e ^–j2πk/N) ⁿ

n=0

We have standard summation formula

X(K) = ∑ a ^K= a ^N1- a ^N2+1/ 1- a

K=N1

here N1=0, N2 = L-1 and a = e ^–j2πk/N

N-1

X(K) = ∑ A [ ( e ^–j2πk/N)⁰ - .( e ^–j2πk/N)^L-1+1/1- e ^{–j2πk/N ]}

n=0

N-1

X(K) = ∑ A [ ( 1 - .( e ^–j2πkL/N)/ 1- e ^–j2πk/N

n=0

Butterworth low pass filters

There are so many digital filters like FIR and IIR filter, here this article gives one more analog type batter-worth filter. To shown in figure typical characteristics of batter-worth low pass filter.

This type of response is called a butter-worth response because its main characteristics are that the pass-band maximally flat. It means there are no variations in the pass-band device.

Now the magnitude squared response of low pass butter-worth filters is given by,

│H(Ω)²│ = 1 / 1 + (Ω/Ω_c)^2N

Where;

H(Ω) = Magnitude of analog low pass filter

N = Order of the filter

Ω_c= Cut of frequency

Silent features of low pass butter-worth filter :

Since the magnitude response is nearly constant at lower frequencies. That means passband and are maximally flat.
There are no ripples in the passband and also for stopband.
The maximum gain occurs at the value at Ω = 0 and it is │H(0)│= 1
The magnitude response is monotonically decreasing.

Application of Butter-worth filter :

Butter-worth filter can be used as radar such as in designing the display of radar target track.
In high quality, an audio application,s these are used.
These are also used in the digital filter for motion analysis.
This type of filter most commonly used in anti-aliasing filter in data converter applications

Relationship between DFT and Z transform

We already learn about what is DFT and what is Z transform, So now here this article gives the information about the relationship between DFT and Z transform to know more details about DFT as well as Z transform.

The Z transform of sequence x(n) is,

∞

X(Z) = ∑ x(n) . Z ^–n

n=-∞

We know that at Z = e ^–jω

∞

X(Z) = ∑ x(n) . e ^–jωn

n = -∞

It means that X(Z) is evaluated on the unit circle.

Now suppose X(Z) is sampled at N equally spaced point on the unit circle, then we have

ω = 2πK / N

Now if X(Z) is evaluated at Z = e ^–jωk/n then by putting equation we get;

∞

X(Z) = ∑ x(n) . e^{-j2πKn / N}

n = -∞

At Z = e^j2πK/N

In the equation, if x(n) is a causal sequence and has N number of the sample then we can write an equation

N-1

X(K) = ∑ x(n) . e^{-j2πKn / N}

n = 0

At Z = e^j2πKn/N

^{X(K) = X(Z)}At Z = e^j2πKn/N

DFT full form

What is the full form of DFT?

Answer:

Discrete Fourier Transform

What does DFT mean?

In digital signal processing, the DFT as the name implies the discrete Fourier transform is purely discrete. The discrete-time data is a set that is converted into a discrete frequency representation. This is in exact contrast to the DTFT that uses discrete-time but converts to continuous frequency.

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DFT meaning

In the digital communication system, the DFT stands for Discrete Fourier transform, it is a finite duration frequency sequence which is obtained by sampling one period of Fourier transform. Sampling is done at 'N' equally spaced points, over the period extending from o to around range of 2π.

Mathematical equations :

The DFT of discrete sequence sequence is x(n) and is denoted by X(k). It is given by,

N-1

X(K) = ∑ x(n) . e ^–j2πkn/N

n=0

Here k = 0,1,2,3.......N-1

Since this summation is taken for N point, it is called as N point of discrete Fourier transform called DFT.

We can obtain a discrete sequence x(n) from its DFT. It is called an inverse discrete Fourier transform. It is given by,

N-1

X(n) =1/N ∑ x(k) . e ^–j2πkn/N

k=0

Here n = 0,1,2,3.......N-1

This is called as N point IDFT.

Properties of DFT

Before we learn about properties of DFT first we learn about the exact meaning terms of DFT. The Fourier transform can be used for the analysis of a signal. It used for transformation from the time domain to the frequency domain. Here this article gives information about properties of DFT to know more details or learn about DFT.

Linearity :

Periodic signals : A x(n) + B y(n)

Fourier series coefficients : A a_k + B b_k

Time shifting :

Periodic signals : x(n - n₀)
Fourier series coefficients: a_k e^-jk(2π/N)n

Frequency Shifting :

Periodic signals : x(n) e^jm(2π/N)n

Fourier series coefficients : X(k - m)

Conjugation :

Periodic signals : x*(n)

Fourier series coefficients : ^a*_-k

Time Reversal :

Periodic signals : x(-n)
Fourier series coefficients : ^a_-k

Thyristor chopper circuit

Actually, a chopper consists of a main power semiconductor types of device together with their turn on as well as turn off mechanisms. Here we have already learned about different types of chopper circuit like type A, type B, type C, type E etc. Now let us check it out the information about thyristor chopper circuit to know more details about chopper circuitry design.

In chopper definition, the low power chopper circuit; power transistors and also a GTOs terms. are being used widely. In high power level, however thyristor definition are in most commonly use. So here we have to learn the object of this section is to study the thyristor chopper circuit along with their commutation circuitry.

Forced commutation:

In the method of forced commutation called, the external elements L and C which do not carry the load current continuously, are used to turn off a conducting Thyristor. Forced commutation can be achieved in the following ways :

1. Voltage commutation :

In this scheme, a conducting thyristor is commutated by the application of a pulse of a large reverse type of voltage. This reverse voltage is applied by switching a previously charged capacitor of the circuit device.
The sudden application of the reverse voltage across the conducting Thyristor reduces the anode to zero rapidly.
Then the presence of a reverse voltage across the SCR stands aids in the completion of its turn off process.

2. Current commutation :

In this scheme, an external pulse of current greater than the load current is passed in the reversed direction through the conducting SCR. When the current pulse attains a value equal to the load current, net pulse current through thyristor becomes zero and the device turn off. So the current pulse is usually generated by an initially charged capacitor.
An important feature of current commutation is the connection of a diode in anti-parallel with the main thyrostor so that voltage drop across the diode reverse biases the main SCR. Since this voltage drop is of the order of is 1 volt only, the commutation time in current commutation is more as compared to that in voltage commutation.
In both voltage and current commutation schemes, commutation is initiated by gating an auxiliary SCR called thyristor.

Load commutation :

In load commutation, a conducting thyristor is turned off when load current flowing through a thyristor either :

1. It becomes to zero due to the nature of load circuit parameters

2.Transferred to another device from the conducting thyrostor

Types of chopper circuits

before we learn about different types of chopper circuit first let we check it out what is a chopper and how it used in power electronics application.

Chopper definition :

A chopper device is one type of electronic circuit used to refer to numerous types of electronic switching devices and used in power control and signals applications.

In power electronics, the much industrial application requires power from dc voltage sources. Several of these types of applications, however, perform better in case these are fed variable dc voltage source.

In power electronic the conversion from fixed dc voltage to an adjustable dc type of output voltage, through the use of semiconductor devices, can be carried out by the two types of dc to dc converters are as listed below :

AC link chopper
DC chopper

Here this article gives information about the different types of chopper circuit, to how to convert the dc output voltage.

1. AC link chopper

shows in the circuit diagram of an ac link chopper to, dc are first converted to ac by an inverter. AC is then stepped down by a transformer which is then converted back to dc by a diode rectifier, As the conversion is in two stages, dc to ac to dc. So Ac link chopper is costly, bulky, and less efficient.

2. DC chopper

To show in the figure here DC chopper is a static device that converts fixed dc input voltage to a variable dc output voltage directly.

A chopper may be thought of as dc equivalent of an ac transformer so that it can behave like is an identical manner. As a state that the chopper involves that one stage conversion, these are more efficient for a circuit, so is the one of the most useful compared to AC link chopper.

Chopper is now being all over for rapid transits systems. Chopper systems offer too much fast response, smooth control, high efficiency, and also regeneration.

The power semiconductor devices are used for a chopper circuit can be force commutative thyristor, and also power BJT full form, IGBT full form, power MOSFET full form. As we stated above, a chopper is dc equivalent to an ac transformer having continuously variable turn ratio.

As an alike transformer, a chopper can be used to step up or step down for the fixed dc input voltage. As a step-down dc chopper are more common, then the term dc chopper would mean a step-down dc chopper.

What is chopper

First of all, we should check what chopper exactly means and after that where it mostly used.

What is a chopper?

As we know that a chopper is one type of electronic circuit used to refer numerous types of electronic switching devices and used in power control and signals applications.

A chopper is a static device and it converts fixed dc input voltage to a voltage to a variable dc output voltage directly.

A chopper is basically a DC to DC converter whose main function is to create an adjustable DC voltage from a fixed DC voltage source through the use of semiconductors.

A chopper is more efficient as they involved in only one stage conversion. The future electric automobiles are likely to use the chopper for their speed control and also braking.

A chopper is considered as a DC equivalent of an AC transformer since it behaves in an identical manner.

The chopper used in trolley cars, marine hoists, forklift trucks, and also a mine hauler. The chopper is the dc equivalent to an ac transformer having continuously variable to a turn ratio. Like a transformer, a chopper can be used to step up or step down with the fixed DC input voltage.

In power electronic system the conversion from fixed dc voltage to an adjustable dc output voltage, through the use of semiconductor devices, can be carried out by the two types of dc to dc converters like ac link chopper and also a dc chopper.

Chopper circuits are very widely used in power electronics as also numerous electronics circuits as given below.

SMPS terms
DC DC converters
Amplifiers
Filters
DC motor speed control
VFD drives motors

Applications of chopper :

Switched mode power supply
DC to DC converter
Class D electronic amplifier
Switched capacitor filter
Variable frequency drive
DC voltage boosting
Battery operated electric cars
Battery chargers
Railway traction

FIR filter block diagram

In the digital signal processing system, the use of FIR short form is one type of filter whose impulse response is of finite duration, the reason of it settles zero in finite time. This is a contrast to IIR filter design, which has internal feedback and may continue to respond indefinitely.

A discrete time FIR filter of N number of order and the top part is an N stage delay line with total N+1 taps to shown in the figure. Each of unit delay is a Z^-1 type of operator in the Z transform notation.

The output y of a linear time-invariant system is determined by conveying its input signal x with its impulse response b.

For a discrete-time FIR filter, the output is depend on a weighted sum of the current and finite number of previous values of the input signal.

The operation is described by the following equation, which defines the output sequence of y[n] in terms of its input sequence of x [n] given below.

Y[n] = b₀ x[n] + b₁ x[n-1] + b₂ x[n-2] …………b_n x[n-N]

Y[n] = ∑ b_ix[n-i]

I=0

Where,

x[n] = input signal

y[n] = output signal