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Best op-amp selection for gain of <12 op amp design ideas

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pavjayt

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Hello All,

I am trying to design an op-amp circuit with the following specs and wonder if you guys have any recommendation of an op-amp that would perform better.

1) Supply voltage will be ±15V
2) Input voltage 0-1V Analog signal (not a video signal)
3) Bandwidth of the input signal <= 1KHz
4) Gain should be in the range of >=7 to <=11
5) Output offset adjustment so that 0.5V i/p = 0V o/p
6) Very low output noise

Any recommendations on which IC to use and a better design for better performance?

thanks
 
5) Output offset adjustment so that 0.5V i/p = 0V o/p

You will have to sum in an offset current yourself; no IC chip with an offset trim has enough range to do this directly. Note that offsetting requires a very stable voltage source. Sometimes the +_15V supplies are not stable enough...
 
Maybe you could AC couple your input then the offset wouldn't matter?
 
5) Output offset adjustment so that 0.5V i/p = 0V o/p

You will have to sum in an offset current yourself; no IC chip with an offset trim has enough range to do this directly. Note that offsetting requires a very stable voltage source. Sometimes the +_15V supplies are not stable enough...

We use Acopian linear supplies and they tend to be very stable for us over the years in our designs. But maybe its better to use offset current, but not sure how to implement it in this case.
 
Maybe you could AC couple your input then the offset wouldn't matter?

If you dont mind, could you please explain how to implement this. I have never done this myself. Also any good stable IC recommendation for these gains?

thanks
 
What impedance can your input drive? Can it drive 10K to ground? Does it need to be buffered with a voltage-follower?
 
The inputs are coming out from the DAC section of this FPGA. Not sure what the impedance is on their outputs, I can find it out by digging into their manual/user guide. But I always like to use it with a voltage buffer.
 
Most OP amps these days have very good offset specs. How much can you tolerate.

Can you use an Instrumentation amp? Although this https://www.ti.com/product/ina333 doen't have the specs you require, the IA usually has an input and an output referemce, thus it is very easy to offset the output.

Usually with any IA, you have to provide the reference with a low Z source, so it usually supplied with a buffered reference.
 
The inputs are coming out from the DAC section of this FPGA. Not sure what the impedance is on their outputs, I can find it out by digging into their manual/user guide. But I always like to use it with a voltage buffer.

Here is a single-opamp circuit which has the required gain (~10) and offset (-0.5V). It has a very high input impedance for the DAC signal. Requires 1% resistors. It uses the +15V supply to generate the offset. Disadvantage is that the gain setting resistor R3 and the offset resistor R2 interact, so you will have to solve a system of two equations in two unknowns if you independently want a different gain or different offset.

Plot shows the output voltage vs the DAC signal.
 

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If you dont mind, could you please explain how to implement this. I have never done this myself. Also any good stable IC recommendation for these gains?

If your signal is an AC signal like audio you can AC couple it with a capacitor, but if you need DC information it would need to be DC coupled. If it's audio have a look at the OPA134.
 
Here is a single-opamp circuit which has the required gain (~10) and offset (-0.5V). It has a very high input impedance for the DAC signal. Requires 1% resistors. It uses the +15V supply to generate the offset. Disadvantage is that the gain setting resistor R3 and the offset resistor R2 interact, so you will have to solve a system of two equations in two unknowns if you independently want a different gain or different offset.

Plot shows the output voltage vs the DAC signal.
Thanks for your schematic. The offset is always constant (i.e. 0.5V I/p ~ 0V o/p), once its fine tuned and as well as the gain too once its calibrated to the system. So, at first, can I try to use trimmers in place of R2 & R3 and fine tune them to get to the required specs and then replace them with 1% resistors?

Do you have any recommendation of a stable op-amp at these gains or any op-amp should be able to do this (like AD811/ LT1363/OPA827)?
 
If your signal is an AC signal like audio you can AC couple it with a capacitor, but if you need DC information it would need to be DC coupled. If it's audio have a look at the OPA134.
My signal is not audio signal, its a randomly generated signal based upon the motion of an object that is detected. Any good op-amps for non-audio/video signals that you could think of?
 
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The op-amp doesn't care what the signal is as long as it's bandwidth and input range is within the spec of the amp and the amp can operate in it's linear region.
 
My signal is not audio signal, its a randomly generated signal based upon the motion of an object that is detected. Any good op-amps for non-audio/video signals that you could think of?

There are about a 1000 OpAmps that will operate on +_15V supplies that could be used for this application. How about you spend some quality time with the on-line selection tables on Digi-Key, TI.com, Linear.com, etc yourself...
 
There are about a 1000 OpAmps that will operate on +_15V supplies that could be used for this application. How about you spend some quality time with the on-line selection tables on Digi-Key, TI.com, Linear.com, etc yourself...
Well I ended up selecting few op-amps that we widely use in our designs that I am gonna try and see which one performs best...(OPA627, LT1363, AD811 and LM6181), hopefully one of those should work fine.
 
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