Convert CMRR db in ppm error

[nickagian]

Hi to all!

I would like some quick help here... Since yesterday, I'm trying to figure out how to compute the error caused by the non-ideal CMRR in an instrumentation amplifier. For example check this link:

https://www.electro-tech-online.com/custompdfs/2011/01/AN-539.pdf

Down to page 4, at table II, it says that CMR in dB is 105dB and this is translated in 5.6ppm error. How is this number extracted? I couldn't find the way to do it...

Nikos

 

[MrAl]

Hello,

First translate the db into a gain, then invert it, then multiply by 1 million.

For your example, 105db is a gain of 177827.94, which inverted (the db is negative) equals 5.6e-6, multiplied by 1 million equals 5.6ppm.

 

[nickagian]

Hello,

First translate the db into a gain, then invert it, then multiply by 1 million.

For your example, 105db is a gain of 177827.94, which inverted (the db is negative) equals 5.6e-6, multiplied by 1 million equals 5.6ppm.

Hi!

Well, my mistake was that I overlooked that the CMRR is actually negative and didn't invert the gain..

Thanks a lot MrAl!