Noisy INA2332 or OPA2340

Hi Toma

Is the noise periodic with a frequency of 50/60Hz? If so it is pick-up from the AC mains and you will need to consider shielding.

regards

Steve

Noise. The Black Art.

You are also measuring 30mVpp at the junction of your voltage divider, but 3mVpp at the power supply node?

-Ken

Stephen,

The noise doesn't have a special frequency. I looked at the signal with a Dynamic signal analyzer and there is no particular frequency that is dominant.

Ken,

I know, I don't understand it either. Plus after the follower the two RefA, RefB signal only have 4mV Vpp. I realized I left the 3rd leg of the potentiometer floating so I thought it was it. But I tried to connect the 3rd leg to R6 and R8 and same thing: 30mV Vpp at the junction of the voltage divider. I even connected R8 straigth to ground (shorting the potentiometer) and nothing.

On the INA the noise seems to come up at the RGA, RGB pins.

I upload a more detailed version of the signals I have:

Thanks for your replies

Alrigth, it seems there is some parazite dominant high frequencies.

GND is fine:

5V isn't that great:

The output in B has foundamental at ~11kHz:

The output in A has foundamental at ~11kHz too:

Voltage divider junction R7 R8 has peaks every 2000Hz plus high 11kHz:

Voltage divider junction R5 R6 has peaks every 2000Hz plus high 11kHz:

What would you guys suggest?

Should I filter high frequency noise with a RC filter on the output of the INA?

or Should I filter the +5V?

Thanks for taking the time to read this post :)

Actually the 5V when it is not connected to the circuit looks like this:

I tried to add a 150uF electrolitic capacitor on the 5V. It make the 5V looks better but doesn't change anything to the output signals of the INA.

Also if I remove the jumper on the 3.3V line the noise on the ouput signals of the INA disappear and I get a clean signal (just not centered).

The 3.3V signal on the output of the LM3940 looks pretty good:

Any idea?

Hi Toma

Is C5 in backwards? It looks like it on your schematic.

Have you used decoupling capacitors on the various ICs?

I would suggest building up your circuit bit-by-bit. Try grounding the inputs of the INA2332, for example.

regards

Steve

Hi Steve,

Thanks for replying. I chose C5 as a ceramic capacitor. I don't have the decoupling capacitors on the various ICs but I feel that this wouldn't be it since the chips are pretty close to the .47uF.

I tried to ground the inputs B (Pin 5,6 of the INA) and the noise disappears on the output. I guess I shouldn't have accused the INA. Sounds like the APS00B is at fault in the end. I guess filtering is the only solution to the noise then.

Let me know if you think I am thinking correct.