# Instrumentational Amplifier

T

#### tuurbo46

Jan 1, 1970
0
Hi

Im currently trying to alter the input impedance of an operational
amplifier, but cant find the right page on google. I think impedance
means, there must be an RC circuit in series with the amplifier? Does
anybody have any ideas?

K

#### Kevin Aylward

Jan 1, 1970
0
tuurbo46 said:
Hi

Im currently trying to alter the input impedance of an operational
amplifier,
Why?

but cant find the right page on google. I think impedance
means, there must be an RC circuit in series with the amplifier?

Impedance is the net impediment to current. It can be a function of many
things. It is not exclusively the result of R's and C's.
Does
anybody have any ideas?

Yes. Explain what problem you are trying to solve, don't ask questions
on your preconceived solution to the problem. From your post it is clear
that you don't understand impedance at all, i.e. what it even is. Since
this is the case, how do you know that you want to "alter the input
impedance of an operational amplifier" at all? Incidentally, this
statement makes no sense. You cant alter the input impedance of an
op-amp at all. You can only alter the impendence at a node that the
op-amp is connected to. The input impedance of an op-amp, is whatever it
is, usually Mohms.

Kevin Aylward
[email protected]
http://www.anasoft.co.uk
SuperSpice, a very affordable Mixed-Mode
Windows Simulator with Schematic Capture,
Waveform Display, FFT's and Filter Design.

T

#### tuurbo46

Jan 1, 1970
0
Kevin Aylward said:
Impedance is the net impediment to current. It can be a function of many
things. It is not exclusively the result of R's and C's.

Yes. Explain what problem you are trying to solve, don't ask questions
on your preconceived solution to the problem. From your post it is clear
that you don't understand impedance at all, i.e. what it even is. Since
this is the case, how do you know that you want to "alter the input
impedance of an operational amplifier" at all? Incidentally, this
statement makes no sense. You cant alter the input impedance of an
op-amp at all. You can only alter the impendence at a node that the
op-amp is connected to. The input impedance of an op-amp, is whatever it
is, usually Mohms.

Kevin Aylward
[email protected]
http://www.anasoft.co.uk
SuperSpice, a very affordable Mixed-Mode
Windows Simulator with Schematic Capture,
Waveform Display, FFT's and Filter Design.

Hi

i will read my uni assignment again and i will get back to you with
the correct question!

Cheers Turbo46

T

#### tuurbo46

Jan 1, 1970
0
Hi

Im currently trying to alter the input impedance of an operational
amplifier, but cant find the right page on google. I think impedance
means, there must be an RC circuit in series with the amplifier? Does
anybody have any ideas?

The above question was in relation to one of my recent uni
assignments. The assignment was to design an Audio premaplifier
question. The part i didnt understand and still dont is how you
change the input impedance to an operational amplifier? I have
enclosed the question below:

Input 1: Design a low inpedance source(1.2k) balanced(i.e.
differential i/p plus ground).

At this point i choose the operational amplifier, but i was lost on
the input impedance part. My misusderstand was that impedance was AC
resistance, but i was wrong.

R

#### Rich Grise

Jan 1, 1970
0
tuurbo46 said:
[email protected] (tuurbo46) wrote in message

The above question was in relation to one of my recent uni
assignments. The assignment was to design an Audio premaplifier
question. The part i didnt understand and still dont is how you
change the input impedance to an operational amplifier?

Howcome you can't ask your teacher? Isn't that what they're there for?

Good Luck,
Rich

J

#### JeffM

Jan 1, 1970
0
Input 1: Design a low inpedance source(1.2k)
balanced(i.e. differential i/p plus ground).

My misusderstand was that impedance was AC resistance,
tuurbo46
You're getting warm.
but i was wrong.
Cold again.

It appears you slept thru several semesters of basic electricity
(ELC 102 AC Circuits, ELC 103 Applied AC Circuits).

R
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