Op Amp Inverting/Non-inverting terminal nomenclature

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Discussion Overview

The discussion revolves around the nomenclature of the inverting and non-inverting terminals of operational amplifiers (op-amps) and the implications of these designations on the behavior of the amplifier. Participants explore the definitions and operational characteristics of these terminals in the context of amplifier design and signal processing.

Discussion Character

  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant questions the rationale behind the naming of the inverting terminal as the negative terminal and the non-inverting terminal as the positive terminal.
  • Another participant explains that the terms inverting and non-inverting refer to the amplifier as a whole, noting that inverting amplifiers will invert the sign of the applied voltage.
  • A different participant discusses the concept of supply rails and how the output voltage behavior is influenced by the relative voltages at the + and - terminals.
  • It is noted that increasing the voltage at the + input results in an increase in output, while increasing the voltage at the - input results in a decrease in output.
  • A later reply supports the previous explanation without adding new information.

Areas of Agreement / Disagreement

Participants express differing views on the clarity and implications of the terminal nomenclature, with some agreeing on the operational characteristics while others seek further clarification on the terminology used.

Contextual Notes

Some assumptions about the behavior of op-amps and the definitions of inverting and non-inverting terminals may not be fully articulated, leading to potential misunderstandings. The discussion does not resolve these ambiguities.

Who May Find This Useful

Individuals interested in operational amplifier design, electronics students, and those exploring signal processing concepts may find this discussion relevant.

gfd43tg
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Hello,

I am wondering why the inverting terminal is the negative terminal and the non-inverting terminal is the positive terminal by name?
 
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The terms inverting/non-inverting refers to the AMPLIFIER as a whole, not the op-amp by itself. Inverting amplfiers (regardless of how they are are made) will invert the sign of the applied voltage (or, equivalently, invert the phase) , i.e. the gain will e.g be -10 meaning 1V in will results in MINUS ten volts out.

Now, if you want to an inverting amplfier using an op-amp you will find that you will have to connect the input voltage to the negative terminal. Hence the name.
 
All pins must be kept at voltages that lie between the power supply "rails".
They're called "supply rails" because they are reminiscent of railroad tracks , ie rigid limits .
The amplifier can't go outside them. (well, there's newfangled specialty ones that can but let's stick to basics)

Driving the + terminal more positive than the - terminal causes the output terminal's voltage to move toward the positive supply rail.
Conversely,
Driving the - terminal more positive than the + terminal causes the output terminal's voltage to move toward the negative supply rail.

Do you notice the reversal of sign?

An AC signal that's had its sign reversed looks on an osciloscope (or graph paper ) to be upside down, ie inverted.

It's really that old-fashioned and simple.
 
Increasing the + input makes the output go up
Increasing the - input makes the output go down
 
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What meBigGuy said.
 

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