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What is an Op Amp? Ideal Op Amps Applications Examples

Lecture 9. Op Amps I. What is an Op Amp? Ideal Op Amps Applications Examples. What is an Op Amp?. Op Amp is short for operational amplifier. An operational amplifier is modeled as a voltage controlled voltage source.

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What is an Op Amp? Ideal Op Amps Applications Examples

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  1. Lecture 9. Op Amps I • What is an Op Amp? • Ideal Op Amps • Applications • Examples

  2. What is an Op Amp? • Op Amp is short for operational amplifier. • An operational amplifier is modeled as a voltage controlled voltage source. • An operational amplifier has a very high input impedance and a very high gain. • It has usually differential inputs and a single output.

  3. Use of Op Amps • Op amps can be configured in many different ways using resistors and other components. • Amplifiers provide gains in voltage or current. • Op amps can convert current to voltage. • Op amps can provide a buffer between two circuits. • Op amps can be used to implement integrators and differentiators. • Lowpass and bandpass filters.

  4. Applications of Op Amps • Amplifiers provide gains in voltage or current. • Op amps can convert current to voltage. • Op amps can provide a buffer between two circuits. • Op amps can be used to implement integrators and differentiators.

  5. + - The Op Amp Symbol High Supply Non-inverting input Output Inverting input Ground Low Supply

  6. + - The Op Amp Model – Voltage Dependent Source v+ Non-inverting input + vo Rin v- Inverting input - A(v+ -v- )

  7. + - Typical Op Amp • The input resistance Rin is very large (practically infinite). • The voltage gain A is very large (practically infinite). v+ Non-inverting input + vo Rin v- Inverting input - A(v+ -v- )

  8. “Ideal” Op Amp • The input resistance is infinite. • The gain is infinite. • The op amp is in a negative feedback configuration. • Infinite input resistance means the current into the inverting input is zero: i- = 0 • Infinite gain means the difference between v+ and v- is zero: v+ - v- = 0

  9. R2 R1 - + + + Vin Vout - - The Basic Inverting Amplifier

  10. Solving the Amplifier Circuit Nodal Analysis: i1 + i2 + i-=0 R2 i2 R1 - i1 i-

  11. Solving the Amplifier Circuit i1 + i2 + i-=0

  12. Solving the Amplifier Circuit Amplifier gain: Solve for vout

  13. How to solve Op Amp Circuit? • Nodal analysis or other methods to solve for the output voltage in terms of the input(s). • Keep in mind that the ideal op amp model leads to the following conditions: i- = 0 v+ = v-

  14. R2 R1 - + + + Vin Vout - - Where is the Feedback?

  15. + + - + vin - vout R2 R1 - The Non-Inverting Amplifier

  16. Nodal Analysis: Finding the nodes + + - + i- vin - vout i1 i2 R2 R1 -

  17. Nodal Analysis: Apply KCL

  18. Nodal Analysis: Solve for Vout

  19. R1 Rf R2 - + + + + v2 v1 vout - - - A Mixer Circuit

  20. + v2 - Nodal Analysis: Finding the nodes R1 Rf i1 if + R2 v1 i2 - - i- + + vout -

  21. Nodal Analysis: Apply KCL

  22. Nodal Analysis: Solve for Vout

  23. Class Examples • Seeing atoms with STM 1 nA

  24. Class Examples • Solar cell 1 nA A circuit constructed for measuring current from the solar cell.  The first Op Amp is the current-to-voltage converter and the second op Amp inverts the voltage.

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