With the rapid development of automotive electronics, in order to ensure safety, the importance of noise countermeasures has become increasingly prominent. Affected by environmental regulations, low fuel consumption and driver assistance systems are constantly evolving. The number of ElectronicControlUnits (hereinafter ECUs) per vehicle is increasing, and the Internet of Vehicles is constantly requiring high speed. These cables of the in-vehicle LAN connected to the ECU are prone to interference electric waves and are susceptible to external noise, so noise suppression measures are indispensable. In order to adapt to this trend, Murata Manufacturing Co., Ltd. (hereinafter referred to as " Murata ") is constantly developing products for common mode choke coils (hereinafter referred to as CMCC) with excellent noise suppression and high reliability.
CMCC is a product that uses the difference between mode propagation characteristics to suppress common mode noise. Murata has developed the CMCC for vehicles by making full use of the existing magnetic material technology, magnetic circuit design technology and unique winding technology accumulated in the CMCC for the people's livelihood.
Figure 1. Example of noise suppression for BroadR-Reach?
In addition to ordinary cars, considering the car Ethernet installed on trucks and buses, the transmission cable length must be set to 15m. In addition, in order to improve the transmission speed of the uncompressed image transmission of the in-vehicle camera and to minimize the frequency of retransmission due to transmission errors, the response speed is increased and standardized.
The return loss (Sdd11) and insertion loss (Sdd21) on the currently popular CMCC have met the specification limit, but have not satisfied the balance (Sds21), which may cause a drop in transmission quality.
Figure 2. Transmission specifications for automotive Ethernet and popular CMCC features
In terms of the popularization of CMCC for Minsheng Ethernet, it is not very clear about the Ethernet transmission specifications.
(Dash line: specification limit value; solid line: CMCC-DLW21SN491XQ for people's livelihood)
Compared with general equipment specifications (CISPR22), the strict automotive noise specification (CISPR25) is not only suitable for Ethernet, but also suitable for vehicles with a large number of ECUs and information equipment in a narrow space. Special attention should be paid here to the effects of electromagnetic waves generated by radio waves (AM, FM, TV) and communication devices (GPS, 4G-LTE, etc.).
Figure 3: Comparison of noise limits for vehicle and live equipment (radiation noise)
※Because of the different measurement conditions, it is not possible to make a simple comparison. The limit value itself is more severe. The measurement distance is also shorter than the 1 m of the vehicle (CISPR25) and 3 meters of the CICR22.
The CMCC specification for the in-vehicle Ethernet specifies the limit value of the squelch characteristic (Scc21). Considering the noise specifications for automobiles, it is unsatisfactory to use the popular CMCC for Minsheng Ethernet. Therefore, from the perspective of both transmission characteristics and squelch characteristics, it is necessary to use a higher performance dedicated CMCC to solve the EMC problem.
Figure 4. Vehicle Ethernet squelch characteristics specifications and popular CMCC characteristics
In terms of the popular CMCC for Minsheng Ethernet, the Ethernet squelch characteristic specification is not well understood.
(Dash line: standard limit value, solid line: CMCC-DLW21SN491XQ for people's livelihood)
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