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AMC1301: Negative CMRR

Noam Bihmouten
Prodigy 10 points

Part Number: AMC1301
Other Parts Discussed in Thread: AMC3301, AMC0300D,

Hi TI Experts,

I am currently designing a current shunt sensor and was checking the capability of my circuit to reject common mode. As I understand, CMRR is defined by 20Log(AD/|ACM|) = 20Log(ΔVCM/|ΔVos|) so a negative CMRR means that the common mode voltage will be amplified by the amplifier. 

I tried to recalculate the ratio but only find positive results. 

Could you please explain to me where the negative CMRR comes from.

Best regards,

Noam B.

 
  • 0
    TI__Guru 59542 points

    Hi Noam, 

    Common-mode noise will be attenuated by the input of the amplifier, not amplified. I'm sure there are results from search engines that could explain more thoroughly than me.

    I recommend considering a newer device such as AMC3301 with integrated DC/DC or AMC0300D.  There have been many advances in technology since the AMC1301 was originally released.