Electric vehicles are definitely one of the most complex network electronic systems today, with the physical interconnection network becoming highly complex. This vast network connects numerous new safety devices and sensors to each other and to new higher-level control layers.
For bidirectional communication, automotive network architecture has introduced automotive Ethernet, and for unidirectional communication, LVDS has also been introduced. LVDS，Low voltage differential signal is a low-power, low bit error rate, low crosstalk, and low radiation differential signal transmission technology that can achieve high transmission rates and suppress EMI as much as possible. It is commonly used in systems such as car cameras. In LVDS transmission, in order to reduce the weight of the wiring harness, PoC (Coaxial Cable Power) technology, which uses a coaxial cable to achieve signal transmission and power supply, is widely used.
PoC and LVDS
Simultaneously supplying DC power and transmitting AC signals on a single cable is a power supply scheme commonly used by many car camera modules and other similar remote devices, known as PoC coaxial cable power supply. It utilizes power superposition technology to simultaneously process DC power supply and AC signals through a coaxial cable without interfering with each other.
PoC is a single wire transmission method that only uses a two core coaxial cable architecture. The architecture is relatively simple, but PoC requires single ended long-distance transmission of high-frequency analog video signals, which is technically difficult.
Especially in systems such as car cameras that transmit signals through LVDS, the number of car interfaces is constantly increasing, and the required data capacity is constantly expanding, requiring higher transmission rates and higher transmission power. LVDS-PoC continuously improves transmission speed and power to meet the transmission needs of more sensors.
In PoC applications, the problem of signal interference on power lines is already quite serious and needs to be solved through appropriate EMC filtering. In LVDS-PoC, with faster rates and higher frequencies, the interference encountered will be more severe. At this point, inductance will play an important role in the circuit, improving signal quality and power supply efficiency.
For the communication signal path, the AC signal in coaxial cable is generally in a high-frequency state. At this time, the higher the impedance of the inductor, the better, which can prevent high-frequency signals from being lost in this link and causing signal attenuation, seriously affecting communication quality. At the DC end, it is necessary to minimize the internal resistance of the inductor and the cable to reduce losses in DC power supply and improve power supply efficiency.
Application of Inductors in LVDS-PoC
With the rapid development of high-speed interfaces in vehicles, the usage of high-speed interfaces in vehicles is also constantly increasing. In systems such as car cameras that transmit signals through LVDS, PoC coaxial cable power supply technology plays an important role. In order to solve various interference problems in PoC transmission, isolate wideband signals and power sources, and ensure high impedance in wideband, the application of inductors is crucial.
In terms of inductance performance, firstly, it needs to have a wide bandwidth and high impedance. Secondly, with the upgrading of transmission requirements in the car, high current capability is also necessary. While meeting these performance requirements, the size should be as small as possible, otherwise it will affect the DC internal resistance. A large DC internal resistance will increase the loss of DC power supply and reduce power supply efficiency.
Broadband and high impedance are the two most basic requirements, and the common 2nd and 3rd order filtering schemes on the market are also aimed at building high impedance schemes with sufficient bandwidth. These performances mainly depend on the optimization of coil structure design and material preparation. A dedicated PoC filter inductor will avoid the expansion of parasitic capacitance on the coil structure, thereby obtaining a larger resonance frequency and filtering bandwidth.
The higher the impedance of the inductor, the better, to prevent high-frequency signals from being lost in this link and causing signal attenuation, in order to effectively avoid the impact of high-speed signals and interference with communication quality.
At the same time, high current capability is also an essential ability applied in vehicle systems. It must have a sufficiently high saturation current to support the current passing through at full load, in order to reduce impedance changes in current applications and improve the performance of the entire PoC system.
Smaller size is also more friendly to the limited space of in car sensor modules, and the lightweight development of onboard devices requires PoC systems to be implemented with fewer components and smaller dimensions.
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