Lecture notes Electronics and Communication

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BASIC ELECTRONICS UNIT-1 (10 Hours) Introduction to Electronics: Signals, frequency Spectrum of Signals, Analog and Digital Signals, Linear Wave Shaping Circuits: RC LPF, Integrator, RC HPF, Differentiator. Properties of Semiconductors: Intrinsic, Extrinsic Semiconductors, Current Flow in Semiconductors, Diodes: p-n junction theory, Current-Voltage characteristics, Analysis of Diode circuits, Rectifiers, Clippers, Clampers, Special diodes UNIT-II (14 Hours) Bipolar junction Transistor (BJTs): Physical Structures & Modes of Operation, Transistor Characteristics, DC analysis, Introduction to Small Signal Analysis, Transistor as an amplifier, The RC coupled amplifier, Introduction to Power Amplifiers, Transistor as switch. Field Effect Transistors (FETs): Physical Structures & Modes of Operation of MOSFETs, MOSFET Characteristics, DC Analysis. Feedback Amplifiers & Oscillators: General Principles, Different types of feedback amplifier (block diagram only), Properties of Negative Feedback, Barkhausen criteria for Oscillation. Operational Amplifiers (OP-Amps): Ideal OP-AMP, Inverting Amplifier, Non-Inverting Amplifier. Adder, Subtractor, Integrator, Differentiator. UNIT-III (10 Hours) Digital Fundamentals: Binary Numbers, Signed-binary numbers, Decimal-to-Binary & Binary-to- Decimal Conversion, Binary Addition, Subtraction, Multiplication and Division, Hexadecimal Number Systems, Logic Gates, Boolean Algebra, De Morgan s Theorems, Laws of Boolean Algebra, Basics of Flip flops, Shift Resistors, Counters. UNIT-IV (10 Hours) Introduction to Electronic Instruments: CRO, Multimeter, Signal Generators. Principles of Communication: Fundamentals of AM & FM, Transmitters & Receivers TEXT BOOKS: 1. Microelectronics Circuits, A.S Sedra, K.C. Smith, Oxford University Press. Selected portions from chapters 1to 5, 8, 13. 2. Electronics Fundamentals and Applications, D Chattopadhyay and P.C. Rakshit, NewAge International Publications. Selected portions from chapters 4 to 14, 16 to 20. REFERENCE BOOKS: 1. Integrated Electronics, Millman and Halkias, Mc.Graw Hill Publications. 2. Electronic Devices & Circuit Theory, R.L Boylestad and L. Nashelsky, Pearson Education MODULE-I INTRODUCTION TO ELECTRONICS: Electronics is the branch of science and engineering dealing with the theoty and use of a class of devices in which electrons are transported through a vacuum, gas or semiconductor. Signals: It contains information about a variety of things and activities. Example - Voice of the radio announcer, weather information Analog Signal: The signal magnitude can be represented at any instant of time by a sequence of numbers. Discrete Signal: It is a sequence of numbers that represent the magnitudes of the successive signal samples. Digital Signal: Signal is in the form of 0 and 1. Frequency Spectrum of Signal: Any arbitrary signal is characterized by its frequency spectrum. The signal is represented in frequency domain. Fourier series: It is an expansion of periodic signal as a linear combination of sine and cosine with different frequencies and amplitudes. It is applied to periodic signals. Fourier transform: Fourier transform can be applied to aperiodic signals to find the frequency spectrum. Low Pass Filter: · Filter that passes low frequency components of a signal but rejects the high frequency components of a signal is called as low pass filter. · Filters designed with passive components (Resistor, capacitor, inductor) are called as passive filters. Behaviour of capacitor to frequency can be described as follows V 1 For f=0 (Low frequency) capacitive reactance of capacitor X = = =, So it c I 2pfC acts as a open circuit V 1 For f= (High Frequency) capacitive reactance of capacitor X = =0So it = c I 2pfC acts as a short circuit Operation For low frequency since capacitor is open circuited, current flowing in the circuit is zero. So the output voltage v v out= in For high frequency since capacitor is short circuited, the output voltage across a short is zero So the output voltage v 0 out= The frequency response curve can be shown as below Calculation of cutoff frequency: XC v = v out in R + XC XC vout = vin R2 + XC2 If R=X c 1 V = v 0.707 v out in= in 2 At the frequency of which R=X , the output will be 70.7% of the input. c 1 X =R= c 2pfC 1 Cutoff frequency f = c 2pRC LPF as Integrator: · Output voltage (current) is directly proportional to the integration of the input voltage(current) · The time constant RC of the circuit should be very large as compared to the time period of the input wave. · The value of R should be 10 or more times larger than X . c For high frequencies the capacitor has insufficient to charge up, its voltage is small. So the voltage across the resistor is approximately equal to the input voltage. v =V in R VR vin i= = R R The charge q on the capacitor at any instant is q= idt ò idt q 1 ò output voltage v = v = = = vindt out c ò C C RC High Pass Filter: · Filter that blocks low frequency components of a signal but passes the high frequency components of a signal is called as high pass filter. · Filters designed with passive components (resistor, capacitor, inductor) are called as passive filters. Operation For low frequency Since capacitor is open circuited, current flowing in the circuit is zero. So the output voltage v V =0 out= R For high frequency since capacitor is short circuited, So the output voltage v V = v out= R in The frequency response curve can be shown as below Calculation of cutoff frequency: R v = v out in R + XC XC vout = vin R2 + XC2 If R=X c 1 V = v 0.707 v out in= in 2 At the frequency of which R=X , the output will be 70.7% of the input. c 1 X =R= c 2pfC 1 Cutoff frequency f = c 2pRC HPF as Differentiator: · Output voltage (current) is directly proportional to the differentiation of the input voltage(current) · The time constant RC of the circuit should be very small as compared to the time period of the input wave. · The value of R should be 10 or more times smaller than X . c For high frequencies the capacitor has enough time to charge up. So the voltage across the capacitor is approximately equal to the input voltage. v = v in c The charge q on the capacitor at any instant is q=C v c dq dvC dvi output voltage v iR= R=CR = CR out= dt dt dt Semiconductor: · Conductivity lies between conductor and insulator. · Forbidden energy gap 0.2-2.5eV. · At 0K a pure semiconductor behaves as an insulator. · Semiconductor materials show a reduction in resistance with increase in temperature. So said to have a negative temperature coefficient. Intrinsic Semiconductor: · Semiconductor refined to reduce the number of impurities to a very low level. e.g : Semiconductor in pure form · Group-IV elements. Si, Ge, Extrinsic Semiconductor: · To increase the conductivity, impurities also called dopant (Group III or V) are added to the pure semiconductor material and is called extrinsic Semiconductor (n-type or p-type). The process is called doping. · N-type Semiconductor- Pentavalent (As,Sb,P) atom is added to pure semiconductor. Diffused impurities with five valence electrons are called donor atoms. · P-type Semiconductor- Trivalent (Al,B,Ga) atom is added to pure semiconductor. Diffused impurities with three valence electrons are called acceptor atoms. · Holes are the majority carrier in p-type semiconductor and electrons are minority carrier. In n-type semiconductor electrons are the majority carrier and holes are the minority carrier. Diode: · Solid state device created by joining the p-type and n-type material is called as semiconductor diode. No Bias (V=0) · Absence of external voltage across the p-n junction is called the unbiased diode. Because of the density gradient electrons and holes diffuse and they combine leaving the ions unneutralised and are called uncovered charges. · The uncovered charges generate an electric field directed from n-side to p-side called as barrier field which opposes the diffusion process further. · Since the vicinity of the junction is depleted of mobile charges. Hence called a as depletion region. Reverse Bias (V 0V) D · Positive polarity of the external bias V is connected to n-type and D negative terminal is connected to p-type. · The number of uncovered positive and negative ions will increase in the depletion region causing widening the depletion region which creates a great barrier for the majority carrier to overcome, effectively reducing the majority carrier flow to zero and hence the current due to majority carrier I =0 majority · The minority carriers which travels down the potential barrier remain unaffected and give a small current called the reverse saturation current denoted as I . s Forward Bias (V 0V) D · Positive polarity of the external bias V is connected to p-type and negative D terminal is connected to n-type. · External bias V exerts a force on the mobile carriers to move them towards the D junction. At the boundary they recombine with the ions and reduce the width of the depletion region. · The depletion region will continue to decrease in width as the voltage is increased further and a heavy flood of electrons will move from n-side to p-side giving the I an exponential rise from p-side to n-side, majority · The minority carrier flow will not be affected by this because the conduction level is determined by the limited number of impurities in the material and the current is denoted by I . s The total current is given by I =I +I D Forward Reverse =I - I (Direction opposite) majority minority In terms of reverse saturation current, I can be written as D eV I =I exp( )-I is called the Shockley s equation. D s s hKT Where e- Charge of an electron K-Blotzman s Conatant T-Temperature in Kelvin · - Quality factor depends upon the diode material (· =2 for Si and 1 for Ge) V- Supplied voltage across the junction Breakdown Condition: (a) Zener Breakdown · Too much of reverse bias across a p-n junction exert a strong force on a bound electron to tear it out from the covalent bond. Thus a large number of electron and hole pair will be generated through a direct rupture of the covalent bonds and they increase the reverse current and gives sharp increase in the characteristics. It is called zener breakdown. Diode employing the unique portion of the characteristics of a p-n junction is called zener diode. · Maximum reverse voltage potential that can be applied before entering the zener region is called the peak inverse voltage (PIV) or peak reverse voltage (PRV). (b) Avalanche Breakdown: · With increasing reverse bias voltage, the electric field across the junction of a diode increases. At a certain value of the reverse voltage, the electric field imparts a sufficiently high energy to a thermally generated carrier. The carrier on colliding with an ion on its way disrupts a covalent bond and gives a new hole electron pair. This process is cumulative and gives an avalanche of carriers in a very short time. It is called avalanche multiplication. Diode equivalent Circuit: · Equivalent circuit is a combination of element properly chosen to best represent the actual terminal characteristics of a device or system in a particular operating point. Ideal diode in forward and reverse biased condition is as follows Diode Resistance levels: · According to the applied signal the resistance levels in a diode has following type 1. DC or Static (DC signal) 2. AC or Dynamic(Small AC signal) 3. Average ac( Large AC signal) CLIPPER It controls the shape of the output waveform by removing or clipping a portion of the applied wave. Half wave rectifier is the simplest example.It is also referred as voltage limiters/ amplitude selectors/ slicers. Applications: · In radio receivers for communication circuits. · In radars, digital computers and other electronic systems. · Generation for different waveforms such as trapezoidal, or squarewaves. Helps in processing the picture signals in television transmitters. · In television receivers for separating the synchronizing signals from composite picture signals Types of Clipper Circuit 1. Series- Diode is in series with the source 2. Parallel- Diode is in parallel with the source. · Clipper circuit which uses a DC battery is called a biased clipper. SERIES CLIPPER: Assumption- diode is ideal in characteristics Analysis +ve Half Cycle: Diode is on because of forward biasing condition. Since no voltage drop across the diode the output voltage becomes V V =V O= R i -ve Half Cycle: Diode is off because of reverse biasing condition. Since no current flows through the circuit the output voltage V 0. O= Figure shows the output waveform of a simple series clipper with input as square and triangular waveform. Since the negative half cycle is clipped off in the output it is called as a negative clipper circuit. Biased Series Clipper: Assumption- diode is ideal in characteristics Analysis Since the diode is on because of the 5v battery The transition of the diode from one state to another can be found out to be atV =-5v above i which the diode is ON and below which the diode is OFF. +ve Half Cycle: Since the diode is on the output voltage will be (Applying KVL) V +5=V i R V = V +5 O i -ve Half Cycle: Since the diode is off V =0. O Figure Shows the input and output waveform. Example of Other Series Clipper Circuits: PARALLEL CLIPPER: Assumption- diode is ideal in characteristics Analysis +ve Half Cycle: Diode is on because of forward biasing condition. Since no voltage drop across the diode the output voltage becomes V V =0 O= d -ve Half Cycle: Diode is off because of reverse biasing condition. Since no current flows through the circuit the output voltage V V . O= i Figure shows the output waveform of a simple parallel clipper with input as square and triangular waveform. Since the positive half cycle is clipped off in the output it is called as a positive clipper circuit. Biased parallel Clipper: Assumption- diode is ideal in characteristics Analysis The transition of the diode from one state to another can be found out to be atV =4v above i which the diode is OFFand below which the diode is ON. +ve Half Cycle: Since the diode is OFF (above 4v) the output voltage will be (Applying KVL) V = V i O -ve Half Cycle: Since the diode is ON (below 4v) V =4v. O Figure Shows the input and output waveform. Example of Other Parallel Clipper Circuits: CLAMPERS: · A diode and capacitor can be combined to  clamp an AC signal to a specific DC level. · It must have a capacitor, a diode and a resistive element. · For additional shift an independent DC supply can be introduced in the circuit. · The time constant Ä =RC must be large enough to ensure that the voltage across the capacitor does not discharge significantly during the diode is nonconducting. Procedure to analyze a clamper circuit 1. Consider the part of the input signal that will forward bias the diode. 2. During the On state assume that the capacitor will charge up instantaneously to a voltage level determined by the network. 3. Assume that during the diode is in OFF sate the capacitor will hold on to its established voltage level. 4. The polarity of V must be same throughout the analysis. o 5. Total swing of the total output must match the swing of the input signal. -ve clamper analysis: -Diode is ON(Short Circuit) in the positive half cycle. - Established voltage level on the capacitor V =V c -During negative half cycle the diode is OFF and the output voltage is V =V = -V -V = -2V o R i c -Total swing of output is -2V which is same as the total swing of the input. Biased Clamper Circuit: -ve half cycle: Diode is ON (S.C). So applying KVL around the input loop we have -20+Vc=5=0 V =25v and V =5v c o During +ve half cycle diode is OFF. Applying KVL around the outside loop we have 10+25-V =0 o V =35v o Summary of the Clamper Circuit: RECTIFIERS An important application of  regular diodes is in rectification circuits. These circuits are used to convert AC signals to DC in power supplies. A block diagram of this process in a DC power supply is shown below. Half-Wave Rectifier: The above circuit is called as a Half-wave rectifier since it will generate a waveform v that will have an average value of particular use in the ac-to-dc conversion process. o  During 0- (Positive Half Cycle) the diode is ON. Assuming an ideal diode with no  voltage drop across it the output voltage v will be o v = V =V o R m  During -T(Negative Half Cycle) the diode is OFF(Open Circuit). So the current flowing  through the circuit will be 0. The output voltage v will be o v = V =i x R = 0 o R Figure shows the input and output waveform with output V =0.318V . dc m Disadvantage: 1. The ac supply delivers power only half the time. 2. Pulsating current frequency is equal to the supply frequency. Full wave Rectifier: The full wave rectifier utilizes both the positive and negative portions of the input waveform. Types of full wave rectifier are (a) Centre tapped configuration (b) Bridge configuration Centre tapped configuration: · Current flows through the load resistance in the same direction during the full cycle of the input signal. · Centre tap transformer is used with the secondary winding. +ve Half Cycle: · Diode D is short circuited and D is open circuited. Current flows through the 1 2 upper half of the secondary winding. -ve Half Cycle: · Diode D is short circuited and D is open circuited. Current flows through 2 1 the lower half of the secondary winding. Complete input and output waveform can be shown as While this full-cycle rectifier is a big improvement over the half-cycle, there are some disadvantages. Disadvantages: · It is difficult to locate the centre tap on the secondary winging. · The diodes must have high PIV. BridgeRectifier: The bridge rectifier uses four diodes connected in bridge pattern.

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