AMC3330EVM: Noise

Ken Henderson

Part Number: AMC3330EVM
Other Parts Discussed in Thread: AMC3330

Hello,

I am testing then AMC3330EVM with the inputs INN & INP shorted and get quite a bit of output noise, approx 10mVrms on OUTP & OUTN.

Taking the spectrum, the main energy is at 620kHz:

The data sheet says output noise is 220uVrms at 100kHz BW.

Two questions:

1. Is this 620kHz content normal for the AMC3330?

2. Do I need to add more filtering to the EVM to achieve the 200uVrms? or how should noise be tested?

Thanks for any suggestions.

Ken

over 3 years ago

0 Ken Henderson over 3 years ago

Intellectual 670 points

Sorry, the images did not attach properly. Here they are:

Noise on time domain:

And spectrum:

0 kai klaas69 over 3 years ago in reply to Ken Henderson

Guru 140200 points

Hi Ken,

the recommended noise filtering is usually done in the differential amplifier connected to the output of AMC3330. See figure 9 of datasheet.

Kai

0 Ken Henderson over 3 years ago in reply to kai klaas69

Intellectual 670 points

Thanks Kai, I will try some filtering.

But it would still be good to know if the 620kHz content is normal, and how the 220uV noise is measured in the data sheet.

0 Alexander Smith over 3 years ago in reply to Ken Henderson

TI__Mastermind 47575 points

Hi Ken,

The 620kHz content is normal.

You could try changing the differential capacitor on the output, C2, from 33pF to 3.9nF and see if this helps. It would change the cutoff frequency to 408kHz, which should attenuate some of the 620kHz content. If you are only interested in DC measurements, you could further increase the capacitor size to further decrease the cutoff frequency.

As you've pointed out, the 220uV noise measured in the DS was done only looking from 0-100kHz.

0 Ken Henderson over 3 years ago in reply to Alexander Smith

Intellectual 670 points

Hi Alex,

Thanks for the reply. I changed R1 & R3 to 1k and C1, C2, C7 to 1nF to get approx 100kHz cutoff and now the noise is reduced to 1mVrms. It seems that the 620kHz is in phase on each output, so should be rejected in the differential measurement, which is helpful:

Thanks for the confirmation that the 620kHz is normal, at least I know it is not something wrong with my measurement setup.

Best regards, Ken

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AMC3330EVM: Noise