Investigating The Property Of Feedback A Multi Stage Amplifier

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AN INVESTIGATION OF FEEDBACK Zhexun Chen University College London 6th January 2015 ABSTRACT The purpose of this report is to investigate the property of feedback in a multi-stage amplifier. The report describes the frequency response and time of distortion occurrence of open and close loop in their linear operating region. In the method of contrast, the advantages and disadvantages of feedback can be easily summarized. Besides the things above, practical amplifier has some operating constrains. The report also illustrates the possible constrains that are current limit, slew rate and saturation of the output at supply rails. The final investigation of this report is the relationship between resonance and the time-domain response. AN INVESTIGATION OF FEEDBACK CONTENTS Page 1.INTRODUTION 3 2.THEORY 3 2.1 The general feedback structure 3 2.2 cross-over frequency 4 2.3 spontaneous oscillation in a feedback circuit 4 2.4 conditions for closed loop stability 5 3. EXPERIMENTAL PROCEDURE 5 3.1 Measurements of frequency response 5 3.2 Measurements of the linear operating region 6 3.3 Determination of the effects of the current limit 7 3.4 Observation of spontaneous oscillation 7 3.5 Relationship between resonance and the time-domain response 7 4.RESULTS 7 4.1 raw material 7 4.2 open and closed loop gain response 8 4.3 Open loop phase response 8 4.4 input voltage at point of distortion 9 4.5 current limits 9 4.6 investigation of critical value of β 10 4.7

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