Feedback  amplifiers
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Feedback amplifiers

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i made this feedback amplifiers presentation for engineering students who are pursuing 2nd year i hope it'll be helpful for them.

i made this feedback amplifiers presentation for engineering students who are pursuing 2nd year i hope it'll be helpful for them.

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Feedback  amplifiers Feedback amplifiers Presentation Transcript

  • FEEDBACK AMPLIFIERS Presented By Harit Mohan B-tech (CSE-CCVT) 3rd sem University of technology and Management Shillong
  • OUTLINE        Definition Classification of Basic Amplifiers Amplifier without Feedback or with Feedback Basic Concept of Feedback General characteristics of negative-feedback amplifiers Effect of negative feedback on input-output resistance Method of identifying Feedback
  • Definition Feedback is defined as the process in which a part of output signal (voltage or current) is returned back to the input. The amplifier that operates on the principle of feedback is known as feedback amplifier.
  • CLASSIFICATION OF AMPLIFIERS • • Voltage Amplifier- An amplifier provides a voltage output proportional to the voltage input and the proportionality factor does not depend on the magnitudes of the source and load resistance Current Amplifier- An amplifier which provides an output current proportional to the signal current . • Transconductance Amplifier- An amplifier in which, the output current is proportional to the signal voltage, independent of the magnitudes of source and load resistance. • Transresistance Amplifier- An amplifier in which output voltage is proportional to the signal current of the magnitudes of source and load resistance.
  • Amplifier Without Feedback • The most important thing to understand from Fig. is that the output and input terminals of this amplifier are not connected to each other in any way. • Therefore the amplifier of Fig. is an amplifier without any feedback, Gain without feedback.
  • Amplifier With Feedback • Refer to Fig. Here the same amplifier with a gain A is being used along with a mixer network, sampling network and a feedback network. • The voltage gain of the feedback amplifier is given by,
  • BASIC CONCEPT OF FEEDBACK
  • • In each one of these circuits we may sample the output voltage or current by means of a suitable sampling network and apply this signal to the input through feedback two-port network. • At the input the feedback signal is combined with the external (source) signal through a mixer network and is fed into the amplifier proper.
  • Types of feedback 1. Positive feedback 2. Negative feedback.  If the original input signal and the feedback signal are in phase, the feedback is called as positive feedback.  However if these two signals are out of phase then the feedback is called as negative feedback.
  • General characteristics of negative feedback amplifier Stabilization of voltage gain Decreasing output impedance Increasing input impedance Decreasing distortion
  • Effect of negative feedback on inputoutput resistance • Input resistancefeedback amplifiers ,series mixing at the input tends to increase the input resistance and shunt mixing tends to decrease the input resistance. • Output resistance feedback amplifiers, voltage sampling at the output tends to decrease the output resistance and current sampling tends to increase the output resistance.
  • Method od identifying feedback topology Step1 -To find the type of sampling network • By shorting the output if feedback signal becomes zero, then it is called “voltage sampling “ • By opening the output loop if feedback signal becomes zero, then it is called “current sampling”. Step 2- To find the type of mixing network • If the feedback signal is subtracted from the externally applied signal as a voltage in the input loop , it is called “series mixing”. • If the feedback signal is subtracted from the externally applied signal as a current in the loop it is called “shunt mixing”.
  • Thus by finding the type of sampling network and mixing network ,type of feedback amplifier can be determined.
  • Thank you…