Protecting differential data lines with a common-mode filter

In the world of increasing data rates of differential data lines, getting the right balance between data pass through and protection is key. That’s where Nexperia’s Common Mode Filters with integrated ESD protection are ideal. Delivering the right balance for various protocols, including HDMI2.1 with up to 12G FRL per line pair.

Behaviour of a Common-Mode Filter

Common Mode Filters are popular devices to help avoid EMI issues with differential data lines. As a pair of magnetically coupled coils, their influence on differential data lines is minimized while Common Mode noise is attenuated. This is because the two magnetic fields cancel each other out making the line impedance significantly lower for differential signals. But result in a much higher line impedance for common-mode noise or single-ended transients.

First and 2nd peak of an IEC61000-4-2 ESD pulse

Supporting ESD protection

When considering single-ended transients, such as electrostatic discharge (ESD), the combination of Common Mode Filters with ESD protection offers an additional benefit. Due to their selective line inductance, they also offer effective suppression of fast single-ended transients such as ESD. An IEC61000-4-2 pulse has two distinctive elements, a very steep first peak with a steep rise time < 1ns can reach several thousand volts; it is followed by a slower pulse, which contains more energy having a duration in the 100 ns range.

For some transceiver ICs, the first peak of this ESD pulse is not fully suppressed by the on-chip ESD protection, such transceivers can be damaged even at moderate voltages, while the on-chip protection is still unharmed. Short-term voltage spikes can also cause system soft fails.

On-board vs. on-chip ESD protection
On-board vs. on-chip ESD protection

Protecting the latest standards

Today’s transfer rates continue to rise. For example, the bandwidth stated in the HDMI 2.0 standard is up to 18 Gbps, this has risen by more than 2.5x with HDMI 2.1 offering rates up to 48 Gbps. Nexperia’s PCMF series offers ESD protection integrated with Common Mode Filtering for very fast data lines with pass-bands up to 10 GHz. However, can such a fast PCMF device offer a significant suppression of the peak voltage of an ESD pulse under real life conditions? As we show in our white paper “Why Common Mode Filters support ESD protection – and how much benefit to expect in practice”, this is clearly the case.


Download the whitepaper