Feature: Automotive system design
Managing power delivery and data
bandwidth in automotive systems By Rolf Horn, Applications Engineer, DigiKey
I
n automotive design, there is an ongoing quest to reduce the weight of vehicles, to reduce their demand on power. Automotive system designers then work out various solutions to achieve this,
and nowadays this means turning to Power over Coax (PoC) architectures, a technology that transmits data and power over a single coaxial cable to reduce vehicle weight and wiring complexity for systems like cameras, advanced driver assistance systems (ADAS), infotainment and powertrains. However, since the coax cable runs
data and DC power, to prevent the high frequency signals from leaking into the power line, a bias-T circuit is used. This is a simple circuit, consisting of only an inductor and a capacitor. It is typically positioned at the receiving end of the
18 October 2025
www.electronicsworld.co.uk
coaxial cable, separating DC power from high-speed data signals.
The importance of bias-T circuit design Implementing a reliable bias-T circuit requires careful selection of the inductor to manage competing demands for power and data delivery. See Figure 1 for its use in an automotive PoC setup. The inductors block high-frequency signals to keep the power supply clean, whereas capacitors prevent DC voltage from reaching sensitive serialiser/ deserialiser (SerDes) modules. Designing the inductive portion of a
bias-T circuit requires careful attention to detail. To prevent signal leakage onto the power line, the inductor must maintain high impedance across a broad frequency range. If this impedance
is inadequate, residual signal energy can introduce power fluctuations that degrade system performance. In practice, a single inductor may not
provide sufficient signal blocking across all frequencies of interest. As a result, designers often use several induct ors, accompanied by resistors and capacitors, to suppress anti-resonances – the narrow frequency bands where impedance dips and filtering becomes ineffective. These effects arise from the interaction of multiple components with different frequency responses.
PoC bias-T circuit design challenges Although multi-inductor configurations can extend the blocking range of a bias-T circuit, they also introduce complexity, with each added inductor
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