I'm currently laying out a PCB, and I'm thinking that I don't need to shiel d my 16-bit ADC because it has a differential analog input with a CMRR of 8 0 dB. I'm wondering if the CMRR will desensitize the input to any expected EMI, which will be common mode because the E-field across the input pin spa cing of 0.5mm should be predominantly uniform at expected frequencies. I do n't expect any EMI to exceed -60 dBm so 80 dB of CMRR should bury the EMI i nto the ADC noise floor. Any thoughts? I suppose one problem could be the f requency-dependent degrading of CMRR, though the ADC datasheet doesn't prov ide an CMRR vs frequency data. Darol Klawetter

That last point is highly relevant. If it were as amazing as you want it to be, they'd have trumpeted it to the skies. Unfortunately, now that datasheets are owned by the marketing department, you have to read them like Kremlin communiques. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 hobbs at electrooptical dot net

Shielding ADC with High CMRR?

Dec 18, 2013 23 Replies

Rate this thread:

miso 12 years ago

You are far better off measuring the CMRR at high frequency yourself if you actually care about it.

Vote

Phil Hobbs 12 years ago

Getting 22-23 bits stable requires averaging many samples. Since delta-sigmas are slow to begin with, the net bandwidth won't be very big.

Cheers

Phil Hobbs

Vote

krw 12 years ago

Sure, but it's assuming a lot to get from 17ish bits S/N to 23 bits without some extraordinary measures. He was talking about only having better than 1-2 LSBs of noise "inside a PC", so I guess I assumed this was a sound card sort of thing. I was asking for more information about the application. Seems incredible.

Vote

Phil Hobbs 12 years ago

Nah, you can probably do it by standing on one leg till your brain goes to sleep.

Cheers

Phil Hobbs

Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 hobbs at electrooptical dot net http://electrooptical.net

Vote

Join the Discussion

Have something to add? Share your thoughts — no account required.

Didn't find your answer?

Ask the community — no account required