As driving assistance and automation in automobiles advance, cameras, radars, LiDAR, and other devices are increasingly being installed in vehicles. These devices need to transmit both power and signals via the Serializer/Deserializer (SerDes) interface between the device and the Electronic Control Unit (ECU). Connecting these separately requires a corresponding number of harnesses. Accordingly, as the number of devices increases, the resulting increase in weight and cost can no longer be ignored.
Therefore, Power over Coax (PoC) systems, which combine power and signal transmission into a coaxial cable, are increasingly being used for the SerDes interface. In PoC systems, it is necessary to combine power and signals on the transmitting side and then separate them on the receiving side. A circuit called "Bias-T" is used for this combination and separation process. Capacitors are used to ensure the DC power does not flow into the signal side while inductors are primarily used to prevent high-frequency signals flowing into the power side.
When handling high-speed digital signals, failing to appropriately mount the inductor can degrade the PoC signal integrity. In this article, we explain the key considerations for mounting inductors in PoC systems. These considerations include the need for caution because the characteristic impedance changes depending on the pattern design around the inductor and the need for careful planning because crosstalk may affect the signal integrity depending on the placement of the inductor.