Hey guys. I had a question regarding using Op-amps in a signal conditional amp circuit. Assuming I have some input to the cct, and I need to reduce that signal by a gain factor of 0.555 or so, is this doable without any reprocussions?

I ask this because the input span of SCA is around 143mV and the output of my circuit needs to be around 80mV. I've really only dealth with "amplifying" using op amps and SCA's. By amplifying I mean making a signal larger.

Thanks guys. Let me know if theres more info needed to answer this question.

*Edit*

Also these are DC signals only. No AC involved

Ive also attached the circuit i will be using. The operation equation for my circuit is Vout = 0.55613 (V(+)-V2(-)) + Bias

Im just wondering if its okay to have a gain of less than 1 in this case.

 

What's an SCA?

 

Hello,

You could take a look at a voltage divider.
In the eBook there is this page with the theory about them:
http://www.allaboutcircuits.com/vol_1/chpt_6/1.html

Bertus

 

Thanks. An SCA is a signal condition amplifier circuit. Using opamps to "amplify" or condition a signal. For instance I am using a RTD (Resistive Temperature Device) that will measure temperature. At 0 Degrees it will give me some voltage, and at 80 degrees C it will give me a different voltage (e.g 400mV to 543mV) in my case. I need to take this signal and "condition it" so that I can input a smaller signal into a digital display. The display requires the signal range from 0 to 80 mV.

 

Yes, you can use an opamp to attentuate a signal -- although the stability of an opamp goes down as the gain goes down. Since you are only talking about ~0.5, you should be okay as long as your opamp is "unity gain stable".

 

Hey guys. I had a question regarding using Op-amps in a signal conditional amp circuit. Assuming I have some input to the cct, and I need to reduce that signal by a gain factor of 0.555 or so, is this doable without any reprocussions?

I ask this because the input span of SCA is around 143mV and the output of my circuit needs to be around 80mV. I've really only dealth with "amplifying" using op amps and SCA's. By amplifying I mean making a signal larger.

Thanks guys. Let me know if theres more info needed to answer this question.

*Edit*

Also these are DC signals only. No AC involved

Ive also attached the circuit i will be using. The operation equation for my circuit is Vout = 0.55613 (V(+)-V2(-)) + Bias

Im just wondering if its okay to have a gain of less than 1 in this case.

I don't get it.
Your first amplifier has a gain of 50. The second amplifier has a gain range of -2.45 to -3.6. Why do you say your gain is 0.55613?

 

Yes, you can use an opamp to attentuate a signal -- although the stability of an opamp goes down as the gain goes down. Since you are only talking about ~0.5, you should be okay as long as your opamp is "unity gain stable".

Just as an aside, an inverting amp can have a gain of zero, and it will still be stable, as long as the op amp is unity gain stable.

 

Just as an aside, an inverting amp can have a gain of zero, and it will still be stable, as long as the op amp is unity gain stable.

Ah. I wasn't sure if that was the case or not. Good to know.

 

Ah. I wasn't sure if that was the case or not. Good to know.

A zero gain inverting amp has Rf=0 when Rs is finite. Rf/Rs=0. This has the same loop gain as a unity gain noninverting amplifier.

 

Makes sense.

All of the opamp designs I've done haven't required me to get into looking at loop gain and so I just don't think in those terms off the bat.