车载以太网：100BASE-T1的EMC对策和共模滤波器/扼流圈
目录
车载以太网
OPEN（One-Pair Ether-Net）Alliance Special Interest Group（SIG）推荐100BASE-T1及1000BASE-T1标准的车载以太网。本文介绍了使用符合OPEN Alliance的100BASE-T1标准的ACT1210L-201和不符合标准的ACT1210-110的共模滤波器/扼流圈的辐射EMI、传导EMI、BCI的结果。
S参数的比较
作为一个例子，图1对CAN-BUS用共模滤波器/扼流圈：ACT1210-110和车载以太网用共模滤波器/扼流圈：ACT1210L-201进行了比较。
与车载以太网用共模滤波器/扼流圈：ACT1210L-201比较，可以看到，CAN-BUS用共模滤波器/扼流圈：ACT1210-110不能满足OPEN Alliance的标准值。
辐射EMI的比较
使用共模滤波器/扼流圈，可以获得抑制噪声的效果。特别是，还能获得使30MHz以上超过标准线的部分衰减到噪声基底附近的效果。（图2）车载以太网用共模滤波器/扼流圈：ACT1210L-201在10MHz～40MHz附近，与CAN-BUS用共模滤波器/扼流圈：ACT1210-110比较，可以获得噪声抑制效果更好的结果。
Emission Test for 100BASE-T1 (Automotive Ethernet)
- Setup
- Status
- ・Class: CISPR25 Ed3 class 5
- ・Test site: Anechoic chamber (3m)
- ・DUT: 100BASE-T1 EVB
- ・Cable length: 1.5 m
传导EMI的比较
使用共模滤波器/扼流圈，可以获得抑制噪声的效果。特别是在40MHz～90MHz超过标准的部分也能抑制噪声。（图3）
在150kHz～70MHz的范围内，车载以太网用共模滤波器/扼流圈：ACT1210L-201更能发挥噪声抑制效果。
- Setup
- Status
- ・Class: CISPR25 Ed3 class 5
- ・Test site: Anechoic chamber (3m)
- ・DUT: 100BASE-T1 EVB
- ・Cable length: 1.5 m
Comparison of BCI Results
Through时，几乎在所有的频率都会Fail，但加入共模滤波器/扼流圈后可以大幅改善。
车载以太网用共模滤波器/扼流圈：ACT1210L-201全部Pass。（表1）
- Setup
- Status
- ・Frequency: 1 - 400 MHz (CW)
- ・Injection Current: 200 mA (closed-loop method)
- ・Decision: CRC Error
- ・Test site: Shield room
| Frequency MHz | Through | ACT1210-110 | ACT1210L-201 |
|---|---|---|---|
| 1.00 | Fail | Fail | Pass |
| 1.20 | Fail | Fail | Pass |
| 1.44 | Fail | Fail | Pass |
| 1.73 | Fail | Fail | Pass |
| 2.07 | Fail | Fail | Pass |
| 2.49 | Fail | Fail | Pass |
| 2.99 | Fail | Fail | Pass |
| 3.58 | Fail | Fail | Pass |
| 4.30 | Fail | Fail | Pass |
| 5.16 | Fail | Fail | Pass |
| 6.19 | Fail | Fail | Pass |
| 7.43 | Fail | Fail | Pass |
| 8.92 | Fail | Fail | Pass |
| 10.70 | Fail | Fail | Pass |
| 12.84 | Fail | Fail | Pass |
| 15.41 | Fail | Fail | Pass |
| 18.49 | Fail | Fail | Pass |
| 20.00 | Fail | Fail | Pass |
| 21.00 | Fail | Pass | Pass |
| 22.05 | Fail | Pass | Pass |
| 23.15 | Fail | Pass | Pass |
| 24.31 | Fail | Pass | Pass |
| 25.53 | Fail | Pass | Pass |
| 26.80 | Fail | Pass | Pass |
| 27.00 | Fail | Pass | Pass |
| 28.14 | Fail | Pass | Pass |
| 29.55 | Pass | Pass | Pass |
| 31.03 | Fail | Pass | Pass |
| 32.58 | Fail | Pass | Pass |
| 34.21 | Fail | Pass | Pass |
| Frequency MHz | Through | ACT1210-110 | ACT1210L-201 |
|---|---|---|---|
| 35.92 | Fail | Pass | Pass |
| 37.71 | Fail | Pass | Pass |
| 39.60 | Fail | Pass | Pass |
| 41.58 | Fail | Pass | Pass |
| 43.66 | Fail | Pass | Pass |
| 45.00 | Fail | Pass | Pass |
| 45.84 | Fail | Pass | Pass |
| 48.13 | Fail | Pass | Pass |
| 50.54 | Fail | Fail | Pass |
| 53.07 | Fail | Fail | Pass |
| 55.72 | Fail | Pass | Pass |
| 58.51 | Fail | Fail | Pass |
| 61.43 | Fail | Pass | Pass |
| 64.50 | Fail | Pass | Pass |
| 67.73 | Fail | Pass | Pass |
| 69.81 | Fail | Pass | Pass |
| 71.11 | Fail | Pass | Pass |
| 74.67 | Fail | Pass | Pass |
| 78.40 | Fail | Pass | Pass |
| 82.32 | Fail | Pass | Pass |
| 86.44 | Fail | Pass | Pass |
| 90.00 | Fail | Pass | Pass |
| 90.76 | Fail | Pass | Pass |
| 95.30 | Fail | Pass | Pass |
| 100.06 | Fail | Pass | Pass |
| 105.07 | Fail | Pass | Pass |
| 110.32 | Fail | Pass | Pass |
| 115.84 | Fail | Pass | Pass |
| 120.00 | Fail | Pass | Pass |
| 121.63 | Fail | Pass | Pass |
| Frequency MHz | Through | ACT1210-110 | ACT1210L-201 |
|---|---|---|---|
| 127.71 | Fail | Pass | Pass |
| 134.10 | Fail | Pass | Pass |
| 140.80 | Fail | Pass | Pass |
| 147.84 | Fail | Pass | Pass |
| 155.23 | Fail | Pass | Pass |
| 162.99 | Fail | Pass | Pass |
| 171.14 | Fail | Pass | Pass |
| 179.70 | Fail | Pass | Pass |
| 188.69 | Fail | Pass | Pass |
| 190.00 | Fail | Pass | Pass |
| 198.12 | Fail | Pass | Pass |
| 198.12 | Fail | Pass | Pass |
| 208.03 | Fail | Pass | Pass |
| 218.43 | Fail | Pass | Pass |
| 229.35 | Fail | Pass | Pass |
| 240.82 | Fail | Pass | Pass |
| 252.86 | Fail | Pass | Pass |
| 265.50 | Fail | Pass | Pass |
| 278.77 | Fail | Pass | Pass |
| 280.00 | Fail | Pass | Pass |
| 292.71 | Fail | Pass | Pass |
| 307.35 | Fail | Pass | Pass |
| 322.72 | Fail | Pass | Pass |
| 338.85 | Fail | Pass | Pass |
| 355.79 | Fail | Pass | Pass |
| 373.58 | Fail | Pass | Pass |
| 380.00 | Fail | Pass | Pass |
| 392.26 | Fail | Pass | Pass |
| 400.00 | Pass | Pass | Pass |
支持TDK车载以太网的共模滤波器/扼流圈
作为支持车载以太网的共模滤波器/扼流圈，TDK准备了符合OPEN Alliance标准的100BASE-T1及1000BASE-T1用共模滤波器/扼流圈。
| 支持标准 | 产品名称 |
|---|---|
| 100BASE-T1 | ACT1210L-201-2P-TL00 |
| 1000BASE-T1 | ACT1210G-800-2P-TL10 |
总结
从EMC测试结果可以看出，使用了不是为车载以太网设计的共模滤波器/扼流圈时，EMI的噪声抑制效果和BCI的抗干扰性下降。因此，如果使用没有通过OPEN Alliance标准的共模滤波器/扼流圈，会辐射噪声，妨碍无线电等，也可能影响其他通信。另外，S参数的Sdd21特性是影响波形质量的参数，Sccc21特性是影响EMC抑制效果的参数，Ssd21（DCNR）特性是影响BCI耐性的参数。
因此，随着车载网络通信速度的提高，信号质量和EMC问题变得更加重要，所以应当选择在确保符合OPEN Alliance等S参数标准的高电感值的同时，也具备模式转换特性的DCMR（Ssd21）的共模过滤器/扼流圈。
