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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
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
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
adding a feedback network
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

¸

non inverting amplifier
Non-inverting Amplifier

Remember the rules for negative feedback:

example
Example

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

inverting amplifier
Inverting Amplifier

Use the same rules:

input impedance
Input Impedance
  • Unlike the non-inverting amplifier, the input current is non-zero therefore the input impedance is finite:
example1
Example

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

input impedances
Input Impedances
  • Input impedance seen by:
    • Input 1 = R1
    • Input 2 = R2
    • Input N = RN
slide12
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.
integrator
Integrator

Like the inverting amp:

difference amplifier
Difference Amplifier

Using superposition:

First, set V1 = 0

slide15

So,

Combining the results for arbitrary V1 and V2:

Now set V2 = 0

uses of linear op amp circuits
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
ideal op amp linear circuit analysis
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