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  LECTURE NOTES ON ELETRONIC CIRCUIT ANALTSIS (A40412) II B.Tech II semester (JNTUH-R13) Mrs. Deepthi.S, Mrs. Ajitha .G, Mrs.Shruthi ,L, Mr. K Ravi ELECTRONICS AND COMMUNICATION ENGINEERING  INSTITUTE OF AERONAUTICAL ENGINEERING  DUNDIGAL, HYDERABAD - 500043 1 | P a g e   INSTITUTE OF AERONAUTICAL ENGINEERING (AUTONOMUS) Dundigal, Hyderabad - 500 043 ELECTRONICS AND COMMUNICATION ENGINEERING SUBJECT: ELECTRONIC CIRCUIT ANALYSIS (R 13) YEAR & SEM: II/IV B.Tech 2 ND  SEM (A, B & C) BRANCH: ECE ------------------------------------------------------------------------------------------------------------------------------------------ Unit-1 SINGLE & MULTISTAGE AMPLIFIERS Introduction An electronic amplifier circuit is one, which modifies the characteristics of the input signal, when delivered the output side. The modification in the characteristics of the input signal can be with respect to voltage, current, power or phase. Anyone or all these characteristics power, or phase may be changed by the amplifier circuit. Classification of Amplifiers   There are many forms of electronic circuits classed as amplifiers, from Operational Amplifiers and Small Signal Amplifiers up to Large Signal and Power Amplifiers. The classification of an amplifier depends upon the size of the signal, large or small, its physical configuration and how it processes the input signal that is the relationship between input signal and current flowing in the load. The type or classification of an amplifier is given in the following table. Type of Signal Type of Configuration Classification Frequency of Operation Type of coupling Based on the output Number of stages Small Signal Common Emitter Class A Amplifier Direct Current (DC) a. RC coupled amplifiers a. Voltage amplifiers a. Single stage amplifiers   Large Signal Common Base Class B Amplifier Audio Frequencies (AF)  b. Inductive coupled amplifiers  b. Power amplifiers  b. Two stage amplifiers   Common Collector Class AB Amplifier Radio Frequencies (RF) c. Transformer coupled amplifiers and c. Multistage amplifiers.   Class C Amplifier VHF, UHF and SHF Frequencies d. Direct coupled amplifiers. the number of stages,   Characteristics of amplifiers:  Amplifiers can be thought of as a simple box or block containing the amplifying device, such as a  Transistor ,  Field Effect Transistor  or   Op-amp , which has two input terminals and two output terminals (ground being common) with the output signal being much greater than that of the input signal as it has been “Amplified”.  Generally, an ideal signal amplifier has three main properties, Input Resistance or ( Rin ), Output Resistance or ( Rout ) and of course amplification known commonly as Gain or ( A ). No matter how complicated an amplifier circuit is, a general amplifier model can still be used to show the relationship of these three properties.  INSTITUTE OF AERONAUTICAL ENGINEERING (AUTONOMUS) Dundigal, Hyderabad - 500 043 ELECTRONICS AND COMMUNICATION ENGINEERING SUBJECT: ELECTRONIC CIRCUIT ANALYSIS (R 13) YEAR & SEM: II/IV B.Tech 2 ND  SEM (A, B & C) BRANCH: ECE ------------------------------------------------------------------------------------------------------------------------------------------ To choose a right kind of amplifier for a purpose it is necessary to know the general characteristics of amplifiers. They are: Current gain, Voltage gain, Power gain, Input impedance, Output impedance, Bandwidth. 1. Voltage gain: Voltage gain of an amplifier is the ratio of the change in output voltage to the corresponding change in the input voltage.  A V  = ΔV 0 / ΔV I 2. Current gain: Current gain of an amplifier is the ratio of the change in output current to the corresponding change in the input current  A  I  = Δ I 0 / Δ I I 3. Power gain: Power gain of an amplifier is the ratio of the change in output power to the corresponding change in the input power. where po and pi are the output power and input power respectively. Since power p = v × i, The  power gain A  P  = P O  / P I  A  P  = A V  x A I  (Power amplification of the input signal takes place at the expense of the d.c. energy.) 4. Input impedance (Zi): Input impedance of an amplifier is the impedance offered by the amplifier circuit as seen through the input terminals and is given by the ratio of the input voltage to the input current Z I   = ΔV I / ΔI I 5. Output impedance (Z0): Output impedance of an amplifier is the impedance offered by the amplifier circuit as seen through the output terminals and is given by the ratio of the output Z O   = ΔV O / ΔI O (At V s =0) 6. Band width (BW): The range of frequencies over which the gain (voltage gain or current gain) of an amplifier is equal to and greater than 0.707 times the maximum gain is called the bandwidth. In figure shown, f  L  and f  H  are the lower and upper cutoff frequencies where the voltage or the current gain falls to 70.7% of the maximum gain. Bandwidth BW=( f  H - f  L ). Bandwidth is also defined as the range of frequencies over which the power gain of amplifier is equal to and greater than 50% of the maximum power gain. The cutoff frequencies are also defined as the frequencies where the power gain falls to 50% of the maximum gain. Therefore, the cutoff frequencies are also called as Half power frequencies.  INSTITUTE OF AERONAUTICAL ENGINEERING (AUTONOMUS) Dundigal, Hyderabad - 500 043 ELECTRONICS AND COMMUNICATION ENGINEERING SUBJECT: ELECTRONIC CIRCUIT ANALYSIS (R 13) YEAR & SEM: II/IV B.Tech 2 ND  SEM (A, B & C) BRANCH: ECE ------------------------------------------------------------------------------------------------------------------------------------------ Comparison of CB, CE and CC amplifiers:   Small signal analysis of transistor amplifier   Fig shows a basic amplifier circuit. It can be noticed that to form a transistor amplifier it is necessary to connect an external load and signal source, along with proper biasing. Fig represents a transistor in any one of the three possible configurations Replacing transistor circuit with its small signal model as shown then analyzing hybrid model to find the current gain, i/p resistance, the voltage gain and the o/p resistance.
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