Engineer Electronics II
Engineer Electronics II ECE 3110
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This 2 page Class Notes was uploaded by Shyanne Lubowitz on Monday October 26, 2015. The Class Notes belongs to ECE 3110 at University of Utah taught by R. Harrison in Fall. Since its upload, it has received 8 views. For similar materials see /class/230004/ece-3110-university-of-utah in ELECTRICAL AND COMPUTER ENGINEERING at University of Utah.
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Date Created: 10/26/15
Compensation Notes Compensation is a very important requirement for ampli er design When feedback is applied to an ampli er the possibility for instability is inherently introduced Compensation is a means for controlling the location of poles by inserting a dominant pole and thus guaranteeing the stability of the ampli er Instability refers to the chance that the output changes sign so that the output actually adds to the input instead of subtracting This will cause the output to grow without bound and saturate the ampli er The problem occurs when the phase delay decreases too slowly relative to the gain The phase reaches a value ofil80 degrees before the gain drops to 0 dB or less lfthere is positive gain and 7180 degrees of phase the output will add to the input and since there is positive gain the output will continue to increase without bound To x this problem the circuit has a dominant pole added to guarantee that the gain will be 0 dB or less before the phase reaches 7180 degrees In practice to insure stability the gain should reach 0 dB before 7120 degrees leaving a conservative 60 degree margin This distance an ampli er s phase is from 7180 degrees at 0 dB gain is called thephase margm The procedure is best seen by looking at a bode plot of the unstable system rst To make the circuit stable a pole needs to be moved to a lower frequency so that the gain will drop below OdB before the unstable phase of 71 80 degrees is reached The calculation for moving the pole can be done graphically To do so the phase margin of 60 degrees is located and a line is drawn vertically from this point to the intercept with the 0 dB line on the magnitude curve A line with a slope of 720dBdecade one pole s worth of gain loss is drawn from this new 0 dB intercept until it reaches the original gain curve This new intercept is the new corner frequency of the stable system If an expression for the comer frequency is known andor the transfer function is known components can be adjusted to move the pole as desired to the lower frequency The ideas are summarized graphically see also pp 849850 in the textbook Note that not all systems will be compensated in this manner Many circuits don t have a dominant pole and one must be added such as a capacitor to ground or a capacito between input and output etc This will be covered in a later class This introduction is only meant to help you with Lab 3
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