Total Noise

Frank QT

Hi,

I have built a transimpedance amplifier using OPS355. I am generally happy with the performance but I like to check with the masters here, if the total noise performance is acceptable.

According to TINA simulation I should see a worst case noise of 15mV. Please see the attached.

However when I look at the system noise, I see about 50mV white noise on my system. I use a special probe with a short ground loop so I assume it is pretty reasonable measurement. The overall gain of the system is 6M times. I brought this noise figure down from 200mV level in my previous board so I assume it is decent but again I like to confirm with the experts.

The schematic is also attached.

4382.AFE.zip

over 13 years ago

0 Bart Stiller over 13 years ago

TI__Expert 5400 points

Frank,

The discrepancy you're seeing between the TINA simulation and the real circuit is likely caused by the capacitors C1 and C2. The TINA noise analysis doesn't account for the physical size and material of those capacitors, which will significantly contribute to the the total noise simulated at the output, so the noise you actually measure can vary depending on your choice of capacitor.

0 Frank QT over 13 years ago in reply to Bart Stiller

Intellectual 350 points

Bart,

I am currently using ceramic, 10% caps.. What do you recommend? If you can provide an indication, I can get better caps and try.

Thx,

0 Bart Stiller over 13 years ago in reply to Frank QT

TI__Expert 5400 points

Frank,

For most common analog applications, Class 1 ceramic capacitors are usually appropriate (ex. C0G or NP0), and that should be the case for your application as well.

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Total Noise