Controlling common mode noise radiation through differential signalling IO buffer optimization

Non-ideal IO differential signaling from the silicon die or transmitter buffer propagating through the package, printed circuit board, connector, cable until to the external device, may cause undesirable common mode noise radiation. This common mode noise could be radiated effectively through the external cable causing the risk of EMI. Although controlling the common mode noise is critical, it is challenging to define a specification of the allowable common mode noise. This paper proposes an analytical method on estimating differential signal rise/fall time mismatch and timing skew allowable for the unintended common mode radiation on the cable that meet the regulatory requirements.