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Schedule…

Schedule…. Increase. Helaman 12:2

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  1. Schedule… Discussion #17 – Operational Amplifiers

  2. Increase Helaman 12:2   2 Yea, and we may see at the very time when he doth prosper his people, yea, in the increase of their fields, their flocks and their herds, and in gold, and in silver, and in all manner of precious things of every kind and art; sparing their lives, and delivering them out of the hands of their enemies; softening the hearts of their enemies that they should not declare wars against them; yea, and in fine, doing all things for the welfare and happiness of his people; yea, then is the time that they do harden their hearts, and do forget the Lord their God, and do trample under their feet the Holy One—yea, and this because of their ease, and their exceedingly great prosperity. Discussion #17 – Operational Amplifiers

  3. Lecture 17 – Operational Amplifiers Discussion #17 – Operational Amplifiers

  4. RS Gain A + vL – CD 0:21 + – RL vS(t) Load Source Amplifier Source Amplifier Load Ideal Amplifiers Amplifier: a device for increasing the power of a signal. • Power increase is called gain (A) Discussion #17 – Operational Amplifiers

  5. RS Rout RS Gain A + vL – + vL – + vin – Avin RL RL + – + – Rin vS(t) vS(t) + – Load Source Amplifier Ideal Amplifiers Simplified Amplifier Model: • The source “sees” and equivalent load (Rin) • The load “sees” and equivalent source (Avin) NB: Thévenin equivalent NB: equivalent resistance Discussion #17 – Operational Amplifiers

  6. Rout RS + vL – + vin – Avin RL + – Rin vS(t) + – Ideal Amplifiers The gain is dependent on the source and load (i.e. is different for different sources and loads) NB: expression for vL depends on the source (RS) and the load (RL) Discussion #17 – Operational Amplifiers

  7. Rout RS + vL – + vin – Avin RL + – Rin vS(t) + – Ideal Amplifiers The gain can be made to be almost independent of the source (RS) and the load (RL) • Let Rin→ ∞ • Let Rout → 0 • NB: it is desirable for an amplifier to have: • a very large input impedance • a very small output impedance Discussion #17 – Operational Amplifiers

  8. – + Op-Amps Operational Amplifier: originally designed (late 1960’s) to perform mathematical operations (analog computer) • Addition • Subtraction • Integration • differentiation Positive power supply (usually +15V) VS+ NB: the power supplies (VS+ and VS–) are often omitted in drawings – they are implicit Inverting Input Output Noninverting Input VS– Negative power supply (usually –15V) Discussion #17 – Operational Amplifiers

  9. i1 – – vin + io + v– – + + vo – + v+ – i2 + – Op-Amps – Open-Loop Mode Open-Loop Model: an ideal op-amp acts like a difference amplifier (a device that amplifies the difference between two input voltages) i1 v– – – vin + Rin Rout + vo – AOLvin + v+ i2 NB: op-amps have near-infinite input resistance (Rin) and very small output resistance (Rout) AOL – open-loop voltage gain Discussion #17 – Operational Amplifiers

  10. i1 – – vin + io + v– – + + vo – + v+ – i2 Op-Amps – Open-Loop Mode Open-Loop Model: an ideal op-amp acts like a difference amplifier (a device that amplifies the difference between two input voltages) Ideally i1 = i2 = 0 (since Rin → ∞) Discussion #17 – Operational Amplifiers

  11. Op-Amps – Open-Loop Mode Open-Loop Model: an ideal op-amp acts like a difference amplifier (a device that amplifies the difference between two input voltages) What? No input current?? In reality there is a small current Discussion #17 – Operational Amplifiers

  12. RF – iF RS v– + i1 iS + – vS(t) + vo – v+ Op-Amps – Closed-Loop Mode The Inverting Amplifier: the signal to be amplified is connected to the inverting terminal i2 Discussion #17 – Operational Amplifiers

  13. – + + – vS(t) Op-Amps – Closed-Loop Mode The Inverting Amplifier: the signal to be amplified is connected to the inverting terminal RF Feedback current: current from the output is fed back into the input of the op-amp Node a iF RS v– i1 iS + vo – v+ Discussion #17 – Operational Amplifiers

  14. – + + – vS(t) Op-Amps – Closed-Loop Mode The Inverting Amplifier: the signal to be amplified is connected to the inverting terminal RF iF RS v– i1 iS + vo – v+ Discussion #17 – Operational Amplifiers

  15. RF – iF RS v– + i1 iS + – vS(t) + vo – v+ Op-Amps – Closed-Loop Mode The Inverting Amplifier: the signal to be amplified is connected to the inverting terminal Discussion #17 – Operational Amplifiers

  16. RF – iF RS v– + i1 iS + – vS(t) + vo – v+ Op-Amps – Closed-Loop Mode The Inverting Amplifier: the signal to be amplified is connected to the inverting terminal NB: if AOL is very large these terms → 0 Discussion #17 – Operational Amplifiers

  17. RF – iF RS v– + i1 iS + – vS(t) + vo – v+ Op-Amps – Closed-Loop Mode The Inverting Amplifier: the signal to be amplified is connected to the inverting terminal NB: as AOL→ ∞ v–→ 0 Discussion #17 – Operational Amplifiers

  18. RF – iF RS v– + i1 iS + – vS(t) + vo – v+ Op-Amps – Closed-Loop Mode The Inverting Amplifier: the signal to be amplified is connected to the inverting terminal NB: two important results for an ideal op-amp with negative feedback i2 Discussion #17 – Operational Amplifiers

  19. RF – iF RS v– + i1 iS + – vS(t) + vo – v+ Op-Amps – Closed-Loop Mode Example1: determine AOL and vo RS = 1kΩ, RF = 10kΩ, vs(t) = Acos(ωt), A=0.015, ω = 50 rads/s Discussion #17 – Operational Amplifiers

  20. RF – iF RS v– + i1 iS + – vS(t) + vo – v+ Op-Amps – Closed-Loop Mode Example1: determine AOL and vo RS = 1kΩ, RF = 10kΩ, vs(t) = Acos(ωt), A=0.015, ω = 50 rads/s Discussion #17 – Operational Amplifiers

  21. RF – iF RS v– + i1 iS + – vS(t) + vo – v+ Op-Amps – Closed-Loop Mode Example1: determine AOL and vo RS = 1kΩ, RF = 10kΩ, vs(t) = Acos(ωt), A=0.015, ω = 50 rads/s Discussion #17 – Operational Amplifiers

  22. RF – iF RS v– + i1 iS + – vS(t) + vo – v+ Op-Amps – Closed-Loop Mode Example2: What is the min/max gain, and gain uncertainty if 5% tolerance resistors are used? RS = 1kΩ, RF = 10kΩ, vs(t) = Acos(ωt), A=0.015, ω = 50 rads/s NB: nominal gain Discussion #17 – Operational Amplifiers

  23. RF – iF RS v– + i1 iS + – vS(t) + vo – v+ Op-Amps – Closed-Loop Mode Example2: What is the min/max gain, and gain uncertainty if 5% tolerance resistors are used? RS = 1kΩ, RF = 10kΩ, vs(t) = Acos(ωt), A=0.015, ω = 50 rads/s Discussion #17 – Operational Amplifiers

  24. RF iF RS1 v– – i1 + + vo – v+ RS2 + – + – + – vSN(t) vS2(t) vS1(t) i2 RSN iN Op-Amps – Closed-Loop Mode The Summing Amplifier: sources are summed together independently of load and source impedances Discussion #17 – Operational Amplifiers

  25. RF iF RS1 v– – i1 + + vo – v+ RS2 + – + – + – vSN(t) vS2(t) vS1(t) i2 RSN iN Op-Amps – Closed-Loop Mode The Summing Amplifier: sources are summed together independently of load and source impedances Node a NB: v– = v+ = 0 Discussion #17 – Operational Amplifiers

  26. – + + – + – + – vSN(t) vS1(t) vS2(t) Op-Amps – Closed-Loop Mode The Summing Amplifier: sources are summed together independently of load and source impedances RF Node a iF RS1 v– i1 + vo – v+ RS2 i2 RSN iN Discussion #17 – Operational Amplifiers

  27. RF – iF v– RS + i1 + – iS vS(t) v+ + vo – i1 R Op-Amps – Closed-Loop Mode The Noninverting Amplifier: the signal to be amplified is connected to the noninverting terminal Discussion #17 – Operational Amplifiers

  28. RF – iF v– RS + i1 + – iS vS(t) v+ + vo – i1 R Op-Amps – Closed-Loop Mode The Noninverting Amplifier: the signal to be amplified is connected to the noninverting terminal Node a Discussion #17 – Operational Amplifiers

  29. RF – iF v– RS + i1 + – iS vS(t) v+ + vo – i1 R Op-Amps – Closed-Loop Mode The Noninverting Amplifier: the signal to be amplified is connected to the noninverting terminal Node a Discussion #17 – Operational Amplifiers

  30. RF – iF v– RS + i1 + – iS vS(t) v+ + vo – i1 R Op-Amps – Closed-Loop Mode The Noninverting Amplifier: the signal to be amplified is connected to the noninverting terminal Node a NB: always positive and greater than or equal to 1 Discussion #17 – Operational Amplifiers

  31. – v– + i1 + – vS(t) v+ + vo – i1 Op-Amps – Closed-Loop Mode Voltage Follower: the voltage on the output of the op-amp is equal to the source voltage Discussion #17 – Operational Amplifiers

  32. – + + – vS(t) Op-Amps – Closed-Loop Mode Voltage Follower: the voltage on the output of the op-amp is equal to the source voltage NB: an ideal op-amp with negative feedback has the property v– i1 v+ + vo – i1 Discussion #17 – Operational Amplifiers

  33. Circuit 1 Circuit 1 Circuit 2 Op-Amps – Closed-Loop Mode Voltage Follower: the voltage on the output of the op-amp is equal to the source voltage ib + vb – + va – If va ≠ vb ib is the load current Loading: changing the behaviour of one circuit by connecting another circuit to it Discussion #17 – Operational Amplifiers

  34. Circuit 1 Circuit 2 – + Op-Amps – Closed-Loop Mode Voltage Follower: the voltage on the output of the op-amp is equal to the source voltage Voltage follower can be used to prevent loading (ib = 0) Loading: changing the behaviour of one circuit by connecting another circuit to it Discussion #17 – Operational Amplifiers

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