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OPERATIONAL AMPLIFIERS

OPERATIONAL AMPLIFIERS. Why do we study them at this point???. 1. OpAmps are very useful electronic components. 2. We have already the tools to analyze practical circuits using OpAmps. 3. The linear models for OpAmps include dependent sources. COMMERCIAL PACKAGING OF TYPICAL OP-AMP.

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OPERATIONAL AMPLIFIERS

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  1. OPERATIONAL AMPLIFIERS Why do we study them at this point??? 1. OpAmps are very useful electronic components 2. We have already the tools to analyze practical circuits using OpAmps 3. The linear models for OpAmps include dependent sources COMMERCIAL PACKAGING OF TYPICAL OP-AMP

  2. LM324 DIP LMC6294 MAX4240 OP-AMP ASSEMBLED ON PRINTED CIRCUIT BOARD APEX PA03 DIMENSIONAL DIAGRAM LM 324 PIN OUT FOR LM324

  3. OUTPUT RESISTANCE INPUT RESISTANCE TYPICAL VALUES GAIN CIRCUIT SYMBOL FOR AN OP-AMP SHOWING POWER SUPPLIES LINEAR MODEL

  4. LOAD OP-AMP DRIVING CIRCUIT CIRCUIT WITH OPERATIONAL AMPLIFIER

  5. TRANSFER PLOTS FOR SOME COMERCIAL OP-AMPS SATURATION REGION LINEAR REGION IDENTIFY SATURATION REGIONS OP-AMP IN SATURATION

  6. PERFORMANCE OF REAL OP-AMPS CIRCUIT AND MODEL FOR UNITY GAIN BUFFER WHY UNIT GAIN BUFFER? BUFFER GAIN

  7. THE IDEAL OP-AMP

  8. USING LINEAR (NON-IDEAL) OP-AMP MODEL WE OBTAINED PERFORMANCE OF REAL OP-AMPS THE UNITY GAIN BUFFER – IDEAL OP-AMP ASSUMPTION IDEAL OP-AMP ASSUMPTION YIELDS EXCELLENT APPROXIMATION!

  9. CONNECTION WITHOUT BUFFER CONNECTION WITH BUFFER WHY USE THE VOLTAGE FOLLOWER OR UNITY GAIN BUFFER? THE VOLTAGE FOLLOWER ACTS AS BUFFER AMPLIFIER THE VOLTAGE FOLLOWER ISOLATES ONE CIRCUIT FROM ANOTHER ESPECIALLY USEFUL IF THE SOURCE HAS VERY LITTLE POWER THE SOURCE SUPPLIES NO POWER THE SOURCE SUPPLIES POWER

  10. LEARNING EXAMPLE FOR COMPARISON, NEXT WE EXAMINE THE SAME CIRCUIT WITHOUT THE ASSUMPTION OF IDEAL OP-AMP

  11. REPLACING OP-AMPS BY THEIR LINEAR MODEL WE USE THIS EXAMPLE TO DEVELOP A PROCEDURE TO DETERMINE OP-AMP CIRCUITS USING THE LINEAR MODELS

  12. 3. Draw components of linear OpAmp (on circuit of step 2) 4. Redraw as needed • Identify Op Amp nodes 2. Redraw the circuit cutting out the Op Amp

  13. INVERTING AMPLIFIER: ANALYSIS OF NON IDEAL CASE USE LINEAR ALGEBRA R2 NODE ANALYSIS CONTROLLING VARIABLE IN TERMS OF NODE VOLTAGES

  14. NON-IDEAL CASE REPLACE OP-AMP BY LINEAR MODEL SOLVE THE RESULTING CIRCUIT WITH DEPENDENT SOURCES GAIN FOR NON-IDEAL CASE SUMMARY COMPARISON: IDEAL OP-AMP AND NON-IDEAL CASE IDEAL OP-AMP ASSUMPTIONS KCL @ INVERTING TERMINAL THE IDEAL OP-AMP ASSUMPTION PROVIDES EXCELLENT APPROXIMATION. (UNLESS FORCED OTHERWISE WE WILL ALWAYS USE IT!)

  15. OUTPUT CURRENT IS NOT KNOWN THE OP-AMP IS DEFINED BY ITS 3 NODES. HENCE IT NEEDS 3 EQUATIONS KCL AT V_ AND V+ YIELD TWO EQUATIONS (INFINITE INPUT RESISTANCE IMPLIES THAT i-, i+ ARE KNOWN) DON’T USE KCL AT OUTPUT NODE. GET THIRD EQUATION FROM INFINITE GAIN ASSUMPTION (v+ = v-) LEARNING EXAMPLE: DIFFERENTIAL AMPLIFIER THINK NODES!

  16. IDEAL OP-AMP CONDITIONS LEARNING EXAMPLE: DIFFERENTIAL AMPLIFIER; IDEAL CASE NODES @ INVERTING TERMINAL NODES @ NON INVERTING TERMINAL

  17. LEARNING EXAMPLE: USE IDEAL OP-AMP USE REMAINING NODE EQUATIONS ONLY UNKWONS ARE OUTPUT NODE VOLTAGES FINISH WITH INPUT NODE EQUATIONS… USE INFINTE GAIN ASSUMPTION 6 NODE EQUATIONS + 2 IDEAL OP-AMP

  18. LEARNING EXTENSION

  19. SET VOLTAGE “inverse voltage divider” INFINITE GAIN ASSUMPTION INFINITE INPUT RESISTANCE LEARNING EXTENSION NONINVERTING AMPLIFIER - IDEAL OP-AMP, Find V0

  20. COMPLETE EQUIVALENT FOR MESH ANALYSIS MESH 1 MESH 2 CONTROLLNG VARIABLE IN TERMS OF LOOP CURRENTS FIND GAIN AND INPUT RESISTANCE - NON IDEAL OP-AMP DETERMINE EQUIVALENT CIRCUIT USING LINEAR MODEL FOR OP-AMP NOW RE-DRAW CIRCUIT TO ENHANCE CLARITY. THERE ARE ONLY TWO LOOPS

  21. THE SOLUTIONS MESH 1 MESH 2 CONTROLLNG VARIABLE IN TERMS OF LOOP CURRENTS GAIN INPUT RESISTANCE REPLACE AND PUT IN MATRIX FORM THE FORMAL SOLUTION MATHEMATICAL MODEL

  22. Non-inverting amplifier and semi-ideal model A SEMI-IDEAL OP-AMP MODEL This is an intermediate model, more accurate than the ideal op-amp model but simpler than the linear model used so far

  23. Sample Problem Set voltages? Use infinite gain assumption Use infinite input resistance assumption and apply KCL to inverting input Find the expression for Vo. Indicate where and how you are using the Ideal OpAmp assumptions

  24. MESH 1 MESH 2 CONTROLLING VARIABLE Sample Problem DRAW THE LINEAR EQUIVALENT CIRCUIT AND WRITE THE LOOP EQUATIONS 4. Redraw if necessary 1. Locate nodes 2. Erase Op-Amp TWO LOOPS. ONE CURRENT SOURCE. USE MESHES 3. Place linear model

  25. “INVERSE VOLTAGE DIVIDER” LEARNING EXTENSION

  26. EXAMPLE OF TRANSFER CURVE SHOWING SATURATION OUTPUT CANNOT EXCEED SUPPLY (10V) THIS SOURCE CREATES THE OFFSET THE TRANSFER CURVE KCL @ v_ IN LINEAR RANGE OFFSET

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