Help Needed with Small Signal Amplifier Design

Thread Starter

cmcox118

Joined Jan 26, 2021
4
Hello all! I am working on designing a small signal amplifier around the ADA4505-2ARMZ OP Amp. My input signal would be in the range of 5mv to 50mv and I would need an output within the range or 0-2.4v so my data acquisition unit could read.

I am asking for help because I am unsure how to approach designing something like this. The frequencies are not high, so the frequency response would not need to be perfect, I am mostly just worried about amplification. I had asked for help previously with a different op amp, but it was a different type so I don't think I can use this one the same way.

I have seen some complex circuits that I could model mine after:
However, I would like for it to be as simple as possible.

Thank you for your time, and any help or points in the right direction would be greatly appreciated!

-Chris C.
 

crutschow

Joined Mar 14, 2008
27,894
That op amp has a gain-bandwidth of 50kHz, so will have a -3dB frequency response of about 1kHz at your desired gain of 48 (2.4V / 50mV).
Is that frequency response sufficient for your needs?
 
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Thread Starter

cmcox118

Joined Jan 26, 2021
4
That op amp has a gain-bandwidth of 50kHz, so will have a -3dB frequency response of about 1kHz at a your desired gain of 48 (2.4V / 50mV).
Is that frequency response sufficient for your needs?
Yes, that is sufficient for what I would need, and thank you for clarifying that!
 

Ian0

Joined Aug 7, 2020
3,463
What is the signal that you are trying to amplify? What is its output impedance? What is the sampling rate of your data acquisition unit? How much of that bandwidth do you need?
 
Hello all! I am working on designing a small signal amplifier around the ADA4505-2ARMZ OP Amp. My input signal would be in the range of 5mv to 50mv and I would need an output within the range or 0-2.4v so my data acquisition unit could read.

I am asking for help because I am unsure how to approach designing something like this. The frequencies are not high, so the frequency response would not need to be perfect, I am mostly just worried about amplification. I had asked for help previously with a different op amp, but it was a different type so I don't think I can use this one the same way.

I have seen some complex circuits that I could model mine after:
However, I would like for it to be as simple as possible.

Thank you for your time, and any help or points in the right direction would be greatly appreciated!

-Chris C.
What you are trying to do, in my opinion, is fraught with difficulty.
I tried to build something similar using an instrumentation amplifier when I was new to electronics and tried to amplify a thermocouple voltage.
If you decide to do this then I suggest you study this subject online somewhere as there are many considerations that are "ignored" with traditional amplifier design, which are crucial in this realm, including physical layout. It's a big subject, but worth the effort as it will greatly increase your knowledge base.
Others may take a different view or have experience in small signal instrumentation amplification. Just trying to save you time and energy!
 

Thread Starter

cmcox118

Joined Jan 26, 2021
4
Well it sure seems as if I am approaching this all incorrectly, even from the op amp. Thank you for all the suggestions, I truly appreciate all the time everyone has taken to write to me. This showed me that I should spend some more time researching amplifier design before I begin to jump into all of this, so I am going to go back to the drawing board with all of this. Thank you again to everyone!

-Chris C.
 

Ian0

Joined Aug 7, 2020
3,463
If you tell us what you are going to amplify as per my post #4 and @DickCappels 's post #7, we'll point you in the right direction of what particular aspect of amplifier design you need to look at.
 

#12

Joined Nov 30, 2010
18,223
I remember when I wanted to use an op-amp any time I could, but I found that high input impedance and low noise with low current usage is available with a j-fet input stage. This is a circuit I used for a Rhodes piano preamplifier. It might not be right for your circuit. I'm just jogging your brain about the fact that op-amps aren't always the simplest right way to do this.
RhodesPianoPreamp.PNG
 

Ian0

Joined Aug 7, 2020
3,463
I remember when I wanted to use an op-amp any time I could, but I found that high input impedance and low noise with low current usage is available with a j-fet input stage. This is a circuit I used for a Rhodes piano preamplifier. It might not be right for your circuit. I'm just jogging your brain about the fact that op-amps aren't always the simplest right way to do this.
View attachment 245213
NTE458 seems like a good device - pity about the datasheet - how about a few graphs?
And do they really mean "Noise Figure" not "Noise Frequency"?
The low frequency noise just seems wrong - assuming a 1/f noise corner of about 100Hz, then possibly a noise figure of 6dB at 10Hz would be 128nV in a 1kHz bandwidth, not 15mV
On-Semi do some very nice JFETs with noise figures around 1dB.
https://www.onsemi.com/pdf/datasheet/2sk3557-d.pdf
Not expensive either.
 

MrSalts

Joined Apr 2, 2020
617
NTE used to repackage common parts and relabel them with their generic (less detailed) datasheet so NTE could buy a bucket full of similar parts from a different manufacturer next year and those parts would also, technically meet the spec on their own datasheet. NTE never made parts as far as I know. I think it was a spin-off of Sylvania electronics spare parts department - Back in the day when people would replace parts on their TVs and Radios (even semiconductor parts in the post-tube era).
 
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