Review of Linear Op-Amp Circuits

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# Review of Linear Op-Amp Circuits - PowerPoint PPT Presentation

Review of Linear Op-Amp Circuits. We will quickly review the analysis &amp; 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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Presentation Transcript
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 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
• 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

Remember the rules for negative feedback:

Example

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

Inverting Amplifier

Use the same rules:

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

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

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

Like the inverting amp:

Difference Amplifier

Using superposition:

First, set V1 = 0

So,

Combining the results for arbitrary V1 and V2:

Now set V2 = 0

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
• 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