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What is the meaning of an negative amplifier?

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Hero999 said:
Anyway we all know it isn't as simple as having a 180° or 0° phase shift, roll of frequency and unity gain phase shift are also important fro stability.
Sure it is simple. An amplifier either inverts the signal or it doesn't.
Nothing is negative unless the amplifier attenuates the signal, then it shouldn't be called an amplifier, it should be called what it is.
 
audioguru said:
Sure it is simple. An amplifier either inverts the signal or it doesn't.
Nothing is negative unless the amplifier attenuates the signal, then it shouldn't be called an amplifier, it should be called what it is.
I disagree - unless you are talking about the gain in dB.

For example, if you have a DC amp (with the off set nulled) with a gain of say -1 and you input 3 Volt the output will be -3 Volt.

Or if you input -2 Volt the output will be +2 Volt.
 
ljcox said:
I disagree - unless you are talking about the gain in dB.

For example, if you have a DC amp (with the off set nulled) with a gain of say -1 and you input 3 Volt the output will be -3 Volt.

Or if you input -2 Volt the output will be +2 Volt.
Len, I'm with you, but it's all just opinion. The anti-negative-gain group would, I think, prefer us to describe negative gain as "inverting gain".

Whatever. :D
 
The generic feedback formulae for amplifiers works regardless of whether Av is positive, negitive or fractional so for this reason I'm a pro-negitive gain man.
 
Hero999 said:
The generic feedback formulae for amplifiers works regardless of whether Av is positive, negitive or fractional so for this reason I'm a pro-negitive gain man.
Agreed. For those you don't know what Av means, it is the amplifier voltage gain.

In my example above Av = -1.

If Vo is the output voltage and Vi is the input voltage then

Vo = Av * Vi. or if it is a current amp then

Io = Ai * Ii. or for transconductance amp

Io = Gt * Vi. or for a transresistance amp

Vo = Rt * Ii

Av, Ai, Rt and Gt can be either positive or negative.
 
Math definitions supercede english definitions, therefore I am a pro negative-gain.

[Math definitions] = 1 :ltoet: [English definitions] therefore
[Math speak] > [English Speak]
 
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It's so much easier to skip the context wars and just say Inverting Amplifier, with a gain of X, anyone that studys electronics will find that easier to both look up and understand without familiarity with the mathmatical syntax. Regardless of how 'correct' Negative gain is in it's syntax it's not intuative.
Like using a double negative, it make's sense but it's poor grammar
 
So, it looks like most of us feel positively negative about negative gain.
I still think it's less awkward to say "the gain is minus 3", or "the gain is negative three", than "the gain is 3, inverting". To each his own.
Do you realize we have generated a 2 page thread (inverting) about this subject? :D
 
Sceadwian said:
It's so much easier to skip the context wars and just say Inverting Amplifier, with a gain of X, anyone that studys electronics will find that easier to both look up and understand without familiarity with the mathmatical syntax. Regardless of how 'correct' Negative gain is in it's syntax it's not intuative.
Like using a double negative, it make's sense but it's poor grammar

If you re-visit the original question, he asked
wakiki said:
What's the meaning of a negative gain for a voltage amplifier?

I and others have tried to explain what it is, but if you are more comfortable with "inverting amplifier" then so be it.

However, it is not an issue of syntax or context or like a double negative in English.

Some people also have a difficulty with the concept of negative voltage but that does not mean that it is wrong or an issue of syntax, context or a double negative.
 
"Negative Amplifier" means it is an inverting amplifier.
An inverting amplifier and a non-inverting amplifier (a positive amplifier?) can both have negative feedback.

Playing with the words, can a positive amplifier amplify a negative voltage?
Can a negative amplifier amplify a positive voltage?
Stupid words, aren't they?
 
You don't need to tune the amplifier, you need to tune the English language.

An amplifier doesn't have polarity. It either inverts or it doesn't.
It is like some morons who talk about a "NOT" gate which is a logic inverter.
 
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