Inverting amplifier for signal biased at 2.5V.

Thread Starter

Bod

Joined Sep 18, 2016
301
I don't really want to bring attention to that post of mine, because it's a bit of an embarrassing one on my part, but a good learning experience nonetheless.

In that post, I basically asked for a circuit that would take an audio signal and centre it at 2.5V (clamped between 0V and 5V). Although I wanted to use it for LED strips, I didn't actually have any led strips to control.

Months later I do! I came back to the post looking for a circuit knowing there's lots there. I ended up settling on BobTPH's circuit because that was exactly what I wanted - and it worked (honestly not sure how it didn't work when I tried it back then)
However, the output of this circuit, and others I have tried, all seem to be inverted, like below (what's the reason for this?):
4FG7G.png
Anyway, for the sake of continuity, I want the input to be the same as the output, not flipped upside down. Normally I could use an inverting amplifier but I believe because of the way the audio signal is (entered @ 2.5V), a normal inverting amplifier will not work:

Screen Shot 2020-01-28 at 19.40.48.png
(blue line is output of inverting amp)
Screen Shot 2020-01-28 at 19.39.59.png
Is there a simple way to invert the output signal?
(I just though - about three seconds before posting - maybe I can put the inverting amp on the very input, so the audio going into the first LT1366 is inverted, meaning the output is the right way up)
 

TeeKay6

Joined Apr 20, 2019
572
I don't really want to bring attention to that post of mine, because it's a bit of an embarrassing one on my part, but a good learning experience nonetheless.

In that post, I basically asked for a circuit that would take an audio signal and centre it at 2.5V (clamped between 0V and 5V). Although I wanted to use it for LED strips, I didn't actually have any led strips to control.

Months later I do! I came back to the post looking for a circuit knowing there's lots there. I ended up settling on BobTPH's circuit because that was exactly what I wanted - and it worked (honestly not sure how it didn't work when I tried it back then)
However, the output of this circuit, and others I have tried, all seem to be inverted, like below (what's the reason for this?):
View attachment 197763
Anyway, for the sake of continuity, I want the input to be the same as the output, not flipped upside down. Normally I could use an inverting amplifier but I believe because of the way the audio signal is (entered @ 2.5V), a normal inverting amplifier will not work:

View attachment 197764
(blue line is output of inverting amp)
View attachment 197765
Is there a simple way to invert the output signal?
(I just though - about three seconds before posting - maybe I can put the inverting amp on the very input, so the audio going into the first LT1366 is inverted, meaning the output is the right way up)
Use a non-inv amp configuration:
Non-inv amp999.JPG
 

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crutschow

Joined Mar 14, 2008
25,686
the output of this circuit, and others I have tried, all seem to be inverted, like below
The output you show cannot be from the circuit you show, as it has two inverters in series so the output would be in phase tihe the input.
Also the DC offset from the first stage would cause the second stage to be clamped at 0V.

Here's the simulation with the output op amp (+) input connected the to the input amps offset voltage.

1580254428723.png
 

Wolframore

Joined Jan 21, 2019
1,990
I believe the dual inverting circuit at the end was TS’s solution which he proposed before posting.

i would go with a non-inverting circuit which has the advantage of higher input impedance.
 

Thread Starter

Bod

Joined Sep 18, 2016
301
Use a non-inv amp configuration:
View attachment 197771
It works perfectly, thank you!

The output you show cannot be from the circuit you show, as it has two inverters in series so the output would be in phase tihe the input.
The top output I showed (the sine wave) was not from my circuit. It was an just an image from online to represent my problem (didn't have access to LTSpice at the time).
Here's the simulation with the output op amp (+) input connected the to the input amps offset voltage.
This also work very well. Thanks!
 
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