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Operational Amplifiers

Operational Amplifiers. E80 Lecture Matthew Spencer 2016-02-02. Submitting Your Work on Time. Many snafus when submitting work at the last minute E.g.: Wrong naming convention for submitted files Think about administrative/IT stuff during prelab. How will I submit?.

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Operational Amplifiers

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  1. Operational Amplifiers E80 Lecture Matthew Spencer 2016-02-02

  2. Submitting Your Work on Time • Many snafus when submitting work at the last minute • E.g.: Wrong naming convention for submitted files • Think about administrative/IT stuff during prelab. How will I submit?

  3. Clarifying What is OK Outside of Lab • “Dry fits” which are dissembled by the time you enter lab • No Measurements. No working with “actual” data. • Don’t do the lab outside the lab • If you need a rule of thumb, any hardware you are allowed to take with you is fair game. Anything permanently in lab is not.

  4. Operational Amplifiers E80 Lecture Matthew Spencer 2016-02-02

  5. An Idea of Equivalent Importance http://www.stanleysupplyservices.com/search.aspx?f=2%3AVise+Grip

  6. What We Want to Know • What the heck is an operational amplifier (op-amp)? • How should I think about using it? • What are it’s many applications? • If time: What are it’s limitations?

  7. An Op-Amp is Used to Solve Analog Problems Circuit Model Physical Item Circuit Symbol

  8. The Big Input Resistance Isolates Circuits V+ R_in V_out = A*(V+-V-) V- Op-amp magic: R_in and A are both _very_ big

  9. An Example Where Input Isolation Helps V_measured R_sensor R_mv V_sensor Some Sensor A Multimeter R_sensor could be 100M-Ohm!

  10. Input Isolation Lets V+ Remain Large R_sensor V+ V_out = A*(V+-V-) R_in V_sensor V- R_in approx. infinity What’s V+? What’s I_Rin? Does this circuit work? What is the output?

  11. Negative Feedback Lets Us Use the Huge Gain R_sensor V+ V_out = A*(V+-V-) R_in V_sensor Description of negative feedback on board. This is a “Unity Gain Buffer”  Super good! V-

  12. The Two Cardinal Rules of Op Amp Analysis • I_in = 0 • In negative feedback, Vout is forced so V+=V- • Invoke these two rules to analyze any op-amp circuit • The rabbit hole goes significantly deeper

  13. Let’s Analyze a New Configuration R_f R_i V_in V_out Called an inverting amplifier configuration

  14. Now You Guys Try R_1 R_1 R_2 R_2

  15. Summing and Offset Amplifiers

  16. Impedance and Op-Amps • E59 big reveal: L and C can be treated as imaginary R for sine waves • Can put L and C into our existing op-amp model, which uses resistors.

  17. Example: Integrator https://en.wikipedia.org/wiki/Operational_amplifier_applications

  18. You Try https://en.wikipedia.org/wiki/Operational_amplifier_applications

  19. High Pass and Low Pass Filters https://en.wikipedia.org/wiki/Low-pass_filter https://en.wikipedia.org/wiki/High-pass_filter

  20. Sallen-Key Filter Topologies https://en.wikipedia.org/wiki/Sallen%E2%80%93Key_topology

  21. Don’t Forget About Power • So far, we’ve skipped V+ and V- connections. They are for power. • V+ and V- Set maximum and minimum in/out voltage. Voltage rails. • Use decoupling capacitors. Read all of the instructions!

  22. Single Supply vs. Dual Supply + GND Dual Supply + GND Symmetric + and – V, GND halfway between Single Supply Only GND and +V. Can’t generate negative voltage http://www.ti.com/lit/an/sloa030a/sloa030a.pdf

  23. Instrumentation Amplifiers https://en.wikipedia.org/wiki/Instrumentation_amplifier#/media/File:Op-Amp_Instrumentation_Amplifier.svg

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