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Review of Linear Op-Amp Circuits

Review of Linear Op-Amp Circuits. We will quickly review the analysis & design of linear op-amp circuits that use negative feedback : Non-inverting amplifier Inverting amplifier Summing amplifier Integrator Difference amplifier. Negative Feedback Recap.

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Review of Linear Op-Amp Circuits

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  1. Review of Linear Op-Amp Circuits • We will quickly review the analysis & design of linear op-amp circuits that use negative feedback: • Non-inverting amplifier • Inverting amplifier • Summing amplifier • Integrator • Difference amplifier

  2. Negative Feedback Recap • Negative feedback minimises the error signal. • If the amplifier gain is very high: • the error signal will reduce to zero • the output will equal the input

  3. Adding a Feedback Network • Negative feedback still minimises the error signal. • If the amplifier gain is very high: • the error signal will reduce to zero • the output will equal the input times K Summing Amplifier Node Input Output Error = 0 + - K ¸

  4. Non-inverting Amplifier Remember the rules for negative feedback:

  5. Example To design a non-inverting amplifier with a voltage gain of +10:

  6. Inverting Amplifier Use the same rules:

  7. Input Impedance • Unlike the non-inverting amplifier, the input current is non-zero therefore the input impedance is finite:

  8. Example To design an inverting amplifier with a voltage gain of –10 and an input impedance of 1 kW:

  9. Apply Kirchoff’s current law to the V- node: Like the inverting amp, V- = 0 Summing Amplifier

  10. Input Impedances • Input impedance seen by: • Input 1 = R1 • Input 2 = R2 • Input N = RN

  11. Non-Inverting Summing Amplifier

  12. But… • Input current depends on the level of all the other inputs. • The effective input impedance is not constant. • This can be undesirable. • Inverting configuration is usually preferred.

  13. Integrator Like the inverting amp:

  14. Difference Amplifier Using superposition: First, set V1 = 0

  15. So, Combining the results for arbitrary V1 and V2: Now set V2 = 0

  16. Uses of Linear Op-Amp Circuits • Amplifiers • Making signals bigger! • Summing Amp • Mixing (e.g. audio applications) • Analogue arithmetic • Integrator • Analogue computing • Active filter design • Difference Amp • Balanced line receivers

  17. Ideal Op-Amp Linear Circuit Analysis • When negative feedback is applied, the use of these assumptions makes design/analysis much easier (although not necessarily simple!). • Of course, they aren’t really true… • …more about practical op-amps next time

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