Review of Linear Op-Amp Circuits

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
Summing
Amplifier

Node

Input

Output

Error 0



-

K

• 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

4
Non-inverting Amplifier
Remember the rules for negative feedback
5
Example
To design a non-inverting amplifier with a
voltage gain of 10
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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
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
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 arent really true
• more about practical op-amps next time