What particular noise frequency band is of concern?? What sort of application is the amplifier intended for?? Or is this just a theoretical discussion??

 

Hi H,
I know very little about opamps, but somewhere rattling around my head is where two opamps were in parallel, but opposite, for cancelling out noise.
If this is all wrong, then just ignore it.
C.

Op-amps simply in parallel reduce the noise by the square root of the number of devices. Gain is increased by the number of devices but noise only increase by the square root of the number of devices, so SNR improves by the square root of the number of devices. It’s in Doug Self’s book. Unfortunately, you need resistors on the outputs to make sure that they share current, and that somewhat negates the improvement.

 

A noiseless resistor is not real, the term has been used in simulation programming, I think this term has caused some confusion.

With Low and ultra-low noise op amp along with a few circuit adjustments can lower noise,
But how does noise simulation help identify where noise density is? There are examples on this mitigating process.

In simulation the ability to turn off the current noise can be helpful in understanding how to optimize a circuit for noise reduction.
To flag a specific resistor and run simulation with and without the current noise we can identify where the biggest noise contributors are.
I found that if I run an op amp with very low voltage at minimum noise would compromise the range of adjustment. As I increased the voltage
I did find sufficient range and almost minimal noise. The supply noise and better voltage regulator further improved the noise but before it was more
difficult to separate the various causes without simulation. The last modification was adding bigger and better capacitors.