Definition

Even-mode impedance (Zeven) is the impedance seen by each individual trace in a coupled pair when both traces are driven with identical signals (common mode). The coupling between traces raises the effective impedance compared to an isolated trace because the like-polarity fields partially cancel. Even-mode impedance increases as trace spacing decreases. Common-mode impedance of the pair equals Zeven/2. While differential signals ideally see only odd-mode impedance, any common-mode noise or signal imbalance sees even-mode impedance, which affects common-mode rejection and EMI performance.