Electronic Devices and Circuits

Electronic Devices and Circuits

Project Type: Presentation (pptx)

Downloads: 0 - 10 Monday 27th March 2017 Report

Electronic Devices and Circuits - Overview

------------ PAGE 1 ------------ ELECTRONIC DEVICES and CIRCUITS ------------ PAGE 2 ------------ PRESENTED BY: 1- XYZ 2- ABC 3- ETC ------------ PAGE 3 ------------ Multistage Transistor Amplifier • The output from a single stage amplifier is usually insufficient to drive an output device. In other words, the gain of a single amplifier is inadequate for practical purposes. Consequently, additional amplification over two or three stages is necessary. To achieve this, the output of each amplifier stage is coupled in some way to the input of the next stage. The resulting system is referred to as multistage amplifier. It may be emphasized here that a practical amplifier is always a multistage amplifier. ------------ PAGE 4 ------------ Multistage Transistor Amplifier ( Ex) Fig 11.1 shows the block diagram of a 3- stage amplifier. Each stage consists of one transistor and associated circuitry and is coupled to the next stage through a coupling device. ------------ PAGE 5 ------------ Names Of Multistage Transistor Amplifier • 1- RC Coupling • 2- Transformer Coupling • 3- DC Coupling ------------ PAGE 6 ------------ Gain and Frequency Response • Gain : The ratio of the output electrical quantity to the input one of the amplifier is called its gain. • Frequency Response : The voltage gain of an amplifier varies with signal frequency. It is because reactance of the capacitors in the circuit changes with signal frequency and hence affects the output voltage. The curve between voltage gain and signal frequency of an amplifier is known as frequency response. ------------ PAGE 7 ------------ Decibel Gain and Band Width • Decibel Gain : Although the gain of an amplifier can be expressed as a number, yet it is of great practical importance to assign it a unit. The unit assigned is bel or decibel. • Band Width : The range of frequency over which the voltage gain is equal to or greater than 70.7% of the maximum gain is known as bandwidth. ------------ PAGE 8 ------------ RC Coupled Amplifier • An RC coupled amplifier is a part of a multistage amplifier wherein different stages of amplifiers are connected using a combination of resistor and a capacitor. An amplifier circuit is one of basic circuits in electronics. An amplifier which is completely based on transistor is basically known as transistor amplifier . ------------ PAGE 9 ------------ Why Transformer Coupling is Used? • A transformer is a " coupling transformer " if it is used to couple signals ( usually audio) instead of deliver power. Early audio amplifiers used transformers to connect the output of one amplifier stage to the input of the next amplifier stage. ------------ PAGE 10 ------------ Feedback • The processing part of a feedback system may be electrical or electronic, ranging from a very simple to a highly complex circuits . ... A feedback system is one in which the output signal is sampled and then fed back to the input to form an error signal that drives the system. ------------ PAGE 11 ------------ Positive Feedback and Negative Feedback • Positive Feedback : Positive feedback is a process that occurs in a feedback loop in which the effects of a small disturbance on a system include an increase in the magnitude of the perturbation. • Negative Feedback : Negative feedback occurs when some function of the output of a system, process, or mechanism is fed back in a manner that tends to reduce the fluctuations in the output, whether caused by changes in the input or by other disturbances. ------------ PAGE 12 ------------ Advantages of Negative Feedback • Stabilization of Voltage Gain • Increasing Input Impedance • Decreasing Output Impedance ------------ PAGE 13 ------------ Voltage Gain in Negative Feedback • One of the benefits of negative feedback is the stabilization of the voltage gain of an amplifier against changes in the components ( e. g., with temperature, frequency, etc. ). If you represent the gain without feedback ( the open loop gain) by A 0 , then the system gain with negative feedback is where B is the fraction of the output which feeds back as a negative voltage at the input. The extent of this stabilizing influence can be illustrated as follows: ------------ PAGE 14 ------------ THANK YOU
Back to top of page