Contents

Coaxial Cable power supply (PoC) technology simultaneously transmits data and power through a single coaxial cable, significantly reducing the number of wiring required for on-board systems such as cameras and high-definition displays, and lowering the overall weight and complexity of the vehicle. This technology plays a crucial role in meeting fuel efficiency standards, supporting an increasing number of camera configurations, and enhancing the display size and resolution of vehicles.

 

Simplified wiring makes vehicles easier to produce and maintain. The adoption of coaxial cables can also effectively alleviate the common electromagnetic interference (EMI) problems in the communication and control systems of high-speed automobiles, thereby enhancing the reliability and consistency of critical signal transmission.

With the wide application of high-resolution radars, lidars and cameras in advanced driver assistance systems (ADAS) and autonomous driving, the demand for high-speed connectivity in vehicles continues to grow. The new generation of PoC technology can also support standards such as FDD-Link, meeting the high bandwidth requirements of real-time driving interfaces.

As a mature and reliable technology, PoC has been incorporated into various standards, including proprietary solutions of chip manufacturers and open-source implementations of standard organizations. Different solutions offer different signal transmission speeds and power supply capabilities to meet diverse application requirements.

Some standards already existed before the popularization of PoC technology. For example, FDD-Link III and subsequent versions are compatible with PoC; The Gigabit Multimedia Serial Link (GMSL) standard also integrates PoC functionality in its new generation specification. GMSL1 itself does not support PoC, but GMSL2 and GMSL3 have implemented support for it.

 

 

SerDes and PoC

SerDes are the core components in PoC implementation, capable of superimposing high-frequency digital signals and DC power supplies on the same coaxial cable for transmission. SerDes convert high-speed parallel signals from devices such as cameras and lidars into serial data streams that can be transmitted over a single line, while PoC further integrates power transmission to achieve data and power supply sharing cables. Many PoC systems also support bidirectional communication through Frequency Division multiplexing (FDM).

 

The advantages of two-way communication

In a PoC system, the forward channel (downlink) and the backward channel (uplink) transmit data in different frequency bands within the same cable through FDM technology. The forward channel typically operates above 50 MHz to 1 GHz and is used to transmit sensor data to the central ADAS system. The backward channel is mostly used for control signals, with a frequency range typically ranging from 1 to 40 MHz. The filter circuits at both ends of the cable are responsible for separating the DC power supply from the bidirectional data signal.

 

The key role of the filter circuit

The bias three-way inductor in the PoC filter is the core component for effectively separating the DC power supply from high-frequency signals. It can prevent AC signals from interfering with the power supply and suppress the impact of power supply noise on data quality. This inductor exhibits low impedance to direct current and high impedance to alternating current, thereby maintaining signal integrity while injecting power.

To ensure signal quality, the PoC filtering scheme needs to be capable of carrying the supply current while maintaining a high impedance (typically >1 kΩ, compared to the 50 Ω characteristic impedance of coaxial cables) and preventing inductance saturation. The multi-level LC filtering structure can maintain high impedance throughout the entire frequency band, ensuring the signal-to-noise ratio and stability of communication.

 

 

Summary

PoC has multiple standards and implementation methods in the automotive field, which helps to reduce system weight, enhance performance, and support two-way data communication among devices such as cameras and radars. Its key technologies include SerDes interfaces and multi-level filter circuits, which jointly promote the progress of vehicles in terms of fuel economy, connection reliability and system integration.