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Compensation Methods Electronic Engineering © University of Wales Newport 2009 This work is licensed under a  Creative Com...
<ul><li>The following presentation is a part of the level 5 module  -- Electronic Engineering. This resources is a part of...
<ul><li>For our amplifier we are going to apply negative feedback to reduce the gain to 55dB. </li></ul><ul><li>Comment on...
Gain Curve f C1 f C2 Phase Curve -40dB/dec
<ul><li>For our amplifier we are going to apply negative feedback to reduce the gain to 55dB. </li></ul><ul><li>Comment on...
Compensation Methods <ul><li>There are three methods which we will examine. </li></ul><ul><li>Dominant Pole compensation <...
Dominant Pole Compensation <ul><li>In this method the Manufacturer introduces an artificial break frequency (pole) which c...
<ul><li>Try this out on our plot and answer the following questions: </li></ul><ul><li>At what frequency does the dominant...
Gain Curve f C1 f C2 Phase Curve x 9.5dB – 5.1kHz 29.5dB – 510Hz 89.5dB – 0.51Hz 15dB – 2.8kHz 35dB – 280Hz 55dB – 28Hz
<ul><li>Try this out on our plot and answer the following questions: </li></ul><ul><li>At what frequency does the dominant...
Notes <ul><li>This method is stable for all applications. </li></ul><ul><li>The user does not need to carry out the compen...
Frequency Compensation <ul><li>This method is similar to the first in that a dominant pole is introduced. This time its po...
<ul><li>A table supplied by the amplifier manufacturer allows the user to convert the new pole frequency measured from the...
<ul><li>Try this out on our plot and answer the following questions: </li></ul><ul><li>At what frequency does the dominant...
Gain Curve f C1 f C2 Phase Curve x 69.5dB – 3kHz 89.5dB – 300Hz f C1  – 15kHz
<ul><li>Try this out on our plot and answer the following questions: </li></ul><ul><li>At what frequency does the dominant...
Notes <ul><li>The user must compensate each amplifier according to its use. </li></ul><ul><li>The Bandwidth, using this me...
Lead Lag Compensation. <ul><li>Let us examine the problem we have with our amplifier. </li></ul>f C1 f C2 Unstable Origina...
<ul><li>We cannot move the two break frequencies as they are inherent parameters of the amplifier. </li></ul><ul><li>BUT <...
<ul><li>Series combination of R2 and C </li></ul><ul><li>Now we can generate an equation for V OUT  in terms of V IN </li>...
Quantative Analysis At low frequencies  ω  parts << 1 so  the gain = 1 phase will be 0 ° At high frequencies  ω  parts >> ...
 
Frequency Gain Gain dB Phase 100 0.99764 -0.0205249 -1.99651 200 0.990659 -0.0815145 -3.97231 400 0.964149 -0.3171164 -7.7...
Compensation Methods
<ul><li>Referring to our equation for the network, we will have two break frequencies, one for the top line and one for th...
x x f 1 f 2 -20dB/dec Compensation Methods
Note <ul><li>The phase is not a concern as it returns to a low value by the time the gain curve stops reducing. </li></ul>...
f C1 f C2 Unstable Original Curve gain frequency Desired gain Introduce a lead lag network which starts before f C1  and s...
<ul><li>Try this out on our plot and answer the following questions: </li></ul><ul><li>What component values do we need – ...
<ul><li>Firstly f 2  must equal f C1 </li></ul><ul><li>Secondly what drop in gain is required </li></ul>Compensation Methods
Gain Curve f C1 f C2 Phase Curve Required drop in gain = -10dB
<ul><li>Firstly f 2  must equal f C1 </li></ul><ul><li>Secondly what drop in gain is required </li></ul><ul><li>Finally, w...
Gain Curve f C1 f C2 Phase Curve x x f 1 f 2 Bandwidth f C2
<ul><li>Try this out on our plot and answer the following questions: </li></ul><ul><li>What component values do we need – ...
Notes <ul><li>The user must compensate each amplifier according to its use. </li></ul><ul><li>The Bandwidth, using this me...
Summary <ul><li>No compensation – Unstable </li></ul><ul><li>Dominant Pole Compensation –  B.W. = 28Hz </li></ul><ul><li>F...
This resource was created by the University of Wales Newport and released as an open educational resource through the Open...
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Compensation Methods

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The following presentation is a part of the level 5 module -- Electronic Engineering. This resources is a part of the 2009/2010 Engineering (foundation degree, BEng and HN) courses from University of Wales Newport (course codes H101, H691, H620, HH37 and 001H). This resource is a part of the core modules for the full time 1st year undergraduate programme.

The BEng & Foundation Degrees and HNC/D in Engineering are designed to meet the needs of employers by placing the emphasis on the theoretical, practical and vocational aspects of engineering within the workplace and beyond. Engineering is becoming more high profile, and therefore more in demand as a skill set, in today’s high-tech world. This course has been designed to provide you with knowledge, skills and practical experience encountered in everyday engineering environments.

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  1. 1. Compensation Methods Electronic Engineering © University of Wales Newport 2009 This work is licensed under a Creative Commons Attribution 2.0 License .
  2. 2. <ul><li>The following presentation is a part of the level 5 module -- Electronic Engineering. This resources is a part of the 2009/2010 Engineering (foundation degree, BEng and HN) courses from University of Wales Newport (course codes H101, H691, H620, HH37 and 001H). This resource is a part of the core modules for the full time 1 st year undergraduate programme. </li></ul><ul><li>The BEng & Foundation Degrees and HNC/D in Engineering are designed to meet the needs of employers by placing the emphasis on the theoretical, practical and vocational aspects of engineering within the workplace and beyond. Engineering is becoming more high profile, and therefore more in demand as a skill set, in today’s high-tech world. This course has been designed to provide you with knowledge, skills and practical experience encountered in everyday engineering environments. </li></ul><ul><li>Contents </li></ul><ul><li>Instructions </li></ul><ul><li>Gain Curve </li></ul><ul><li>Compensation Methods </li></ul><ul><li>Dominant Pole Compensation </li></ul><ul><li>Frequency Compensation </li></ul><ul><li>Lead Lag Compensation. </li></ul><ul><li>Summary </li></ul><ul><li>Credits </li></ul><ul><li>In addition to the resource below, there are supporting documents which should be used in combination with this resource. Please see: </li></ul><ul><li>Clayton G, 2000, Operational Amplifiers 4th Ed, Newnes  </li></ul><ul><li>James M, 2004, Higher Electronics, Newnes </li></ul>Compensation Methods
  3. 3. <ul><li>For our amplifier we are going to apply negative feedback to reduce the gain to 55dB. </li></ul><ul><li>Comment on the amplifiers stability. </li></ul>Compensation Methods
  4. 4. Gain Curve f C1 f C2 Phase Curve -40dB/dec
  5. 5. <ul><li>For our amplifier we are going to apply negative feedback to reduce the gain to 55dB. </li></ul><ul><li>Comment on the amplifiers stability. </li></ul><ul><li>Unstable as it crosses the Gain Curve on the -40dB/dec line. </li></ul><ul><li>The amplifier is therefore unsuitable for this application. </li></ul><ul><li>Can we do anything about it? </li></ul>Compensation Methods
  6. 6. Compensation Methods <ul><li>There are three methods which we will examine. </li></ul><ul><li>Dominant Pole compensation </li></ul><ul><li>Frequency compensation </li></ul><ul><li>Lead Lag compensation. </li></ul>Compensation Methods
  7. 7. Dominant Pole Compensation <ul><li>In this method the Manufacturer introduces an artificial break frequency (pole) which causes the gain to drop to 0dB before the first natural one occurs. </li></ul>f C1 f C2 Unstable Stable New f C Original Curve New Curve gain frequency Desired gain
  8. 8. <ul><li>Try this out on our plot and answer the following questions: </li></ul><ul><li>At what frequency does the dominant pole need to be placed? </li></ul><ul><li>What is the Bandwidth of the compensated amplifier? </li></ul>Compensation Methods
  9. 9. Gain Curve f C1 f C2 Phase Curve x 9.5dB – 5.1kHz 29.5dB – 510Hz 89.5dB – 0.51Hz 15dB – 2.8kHz 35dB – 280Hz 55dB – 28Hz
  10. 10. <ul><li>Try this out on our plot and answer the following questions: </li></ul><ul><li>At what frequency does the dominant pole need to be placed? </li></ul><ul><li>What is the Bandwidth of the compensated amplifier? </li></ul>0.51 Hz 28 Hz Compensation Methods
  11. 11. Notes <ul><li>This method is stable for all applications. </li></ul><ul><li>The user does not need to carry out the compensation exercise. </li></ul><ul><li>Bandwidths are limited in size using this method. </li></ul>Compensation Methods
  12. 12. Frequency Compensation <ul><li>This method is similar to the first in that a dominant pole is introduced. This time its position is selected by the user and is positioned so that the gain drops to the desired gain at the point the first natural break frequency occurs. </li></ul>f C1 f C2 Unstable Stable New f C Original Curve New Curve gain frequency Desired gain Compensation Methods
  13. 13. <ul><li>A table supplied by the amplifier manufacturer allows the user to convert the new pole frequency measured from the plot into a capacitor value which is connected between two pins on the amplifier. </li></ul>Compensation Methods
  14. 14. <ul><li>Try this out on our plot and answer the following questions: </li></ul><ul><li>At what frequency does the dominant pole need to be placed? </li></ul><ul><li>What is the Bandwidth of the compensated amplifier? </li></ul>Compensation Methods
  15. 15. Gain Curve f C1 f C2 Phase Curve x 69.5dB – 3kHz 89.5dB – 300Hz f C1 – 15kHz
  16. 16. <ul><li>Try this out on our plot and answer the following questions: </li></ul><ul><li>At what frequency does the dominant pole need to be placed? </li></ul><ul><li>What is the Bandwidth of the compensated amplifier? </li></ul>300 Hz 15 kHz (f C1 ) Compensation Methods
  17. 17. Notes <ul><li>The user must compensate each amplifier according to its use. </li></ul><ul><li>The Bandwidth, using this method is always at the first break frequency. </li></ul><ul><li>Once compensated if the gain is reduced the amplifier will become unstable. </li></ul>Compensation Methods
  18. 18. Lead Lag Compensation. <ul><li>Let us examine the problem we have with our amplifier. </li></ul>f C1 f C2 Unstable Original Curve gain frequency Desired gain The amplifier would be stable if either f C1 occurred at a lower frequency or f C2 occurred at a higher frequency Compensation Methods
  19. 19. <ul><li>We cannot move the two break frequencies as they are inherent parameters of the amplifier. </li></ul><ul><li>BUT </li></ul><ul><li>We can make f C1 “look” as though it started at a lower frequency using the circuit below. </li></ul>Compensation Methods R1 R2 C V IN V OUT
  20. 20. <ul><li>Series combination of R2 and C </li></ul><ul><li>Now we can generate an equation for V OUT in terms of V IN </li></ul>Compensation Methods
  21. 21. Quantative Analysis At low frequencies ω parts << 1 so the gain = 1 phase will be 0 ° At high frequencies ω parts >> 1 so the gain = R2/(R1 + R2) phase will be 0 ° In between gain must roll off in some way. e.g. R1 = 10k  , R2 = 1k  , C = 10nF Plot over the range 100 Hz to 100 kHz
  22. 23. Frequency Gain Gain dB Phase 100 0.99764 -0.0205249 -1.99651 200 0.990659 -0.0815145 -3.97231 400 0.964149 -0.3171164 -7.78572 700 0.901053 -0.9049962 -12.9442 1000 0.82426 -1.6787185 -17.2528 2000 0.590744 -4.572012 -26.0858 4000 0.350726 -9.1006474 -31.1146 7000 0.221129 -13.107079 -30.3226 10000 0.169115 -15.436358 -27.5696 20000 0.115878 -18.719977 -19.0967 40000 0.097777 -20.195268 -10.903 70000 0.093209 -20.610813 -6.45841 100000 0.092044 -20.720125 -4.5634
  23. 24. Compensation Methods
  24. 25. <ul><li>Referring to our equation for the network, we will have two break frequencies, one for the top line and one for the bottom. </li></ul><ul><li>Break frequency where roll off begins f 1 is given by: </li></ul><ul><li>Break frequency where roll off stops f 2 is given by: </li></ul><ul><li>Gain after roll-off is given by </li></ul>Compensation Methods
  25. 26. x x f 1 f 2 -20dB/dec Compensation Methods
  26. 27. Note <ul><li>The phase is not a concern as it returns to a low value by the time the gain curve stops reducing. </li></ul><ul><li>Let us return to our amplifier. </li></ul>Compensation Methods
  27. 28. f C1 f C2 Unstable Original Curve gain frequency Desired gain Introduce a lead lag network which starts before f C1 and stops at f C1 f 1 f 2 Stable f C1 now looks as though it starts at f 1 Compensation Methods
  28. 29. <ul><li>Try this out on our plot and answer the following questions: </li></ul><ul><li>What component values do we need – assume C has a value of 100pF </li></ul><ul><li>What is the Bandwidth of the compensated amplifier? </li></ul>Compensation Methods
  29. 30. <ul><li>Firstly f 2 must equal f C1 </li></ul><ul><li>Secondly what drop in gain is required </li></ul>Compensation Methods
  30. 31. Gain Curve f C1 f C2 Phase Curve Required drop in gain = -10dB
  31. 32. <ul><li>Firstly f 2 must equal f C1 </li></ul><ul><li>Secondly what drop in gain is required </li></ul><ul><li>Finally, what is f 1 </li></ul>Compensation Methods
  32. 33. Gain Curve f C1 f C2 Phase Curve x x f 1 f 2 Bandwidth f C2
  33. 34. <ul><li>Try this out on our plot and answer the following questions: </li></ul><ul><li>What component values do we need – assume C has a value of 100pF </li></ul><ul><li>What is the Bandwidth of the compensated amplifier? </li></ul>f C2 = 300kHz Compensation Methods 229k  106k  100pF V IN V OUT
  34. 35. Notes <ul><li>The user must compensate each amplifier according to its use. </li></ul><ul><li>The Bandwidth, using this method is always at the second break frequency. </li></ul><ul><li>Once compensated if the gain is reduced the amplifier will become unstable. </li></ul>Compensation Methods
  35. 36. Summary <ul><li>No compensation – Unstable </li></ul><ul><li>Dominant Pole Compensation – B.W. = 28Hz </li></ul><ul><li>Frequency Compensation – B.W. = 15kHz </li></ul><ul><li>Lead Lag Compensation - B.W. = 300kHz </li></ul>Compensation Methods
  36. 37. This resource was created by the University of Wales Newport and released as an open educational resource through the Open Engineering Resources project of the HE Academy Engineering Subject Centre. The Open Engineering Resources project was funded by HEFCE and part of the JISC/HE Academy UKOER programme. © 2009 University of Wales Newport This work is licensed under a Creative Commons Attribution 2.0 License . The JISC logo is licensed under the terms of the Creative Commons Attribution-Non-Commercial-No Derivative Works 2.0 UK: England & Wales Licence.  All reproductions must comply with the terms of that licence. The HEA logo is owned by the Higher Education Academy Limited may be freely distributed and copied for educational purposes only, provided that appropriate acknowledgement is given to the Higher Education Academy as the copyright holder and original publisher. The name and logo of University of Wales Newport is a trade mark and all rights in it are reserved. The name and logo should not be reproduced without the express authorisation of the University. Compensation Methods
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