The in-vehicle signal is transmitted to the associated USB control unit, such as the "main unit", via a shielded USB cable. This type of connection is tested by various automotive application specifications. In the case of complete shielding, this connector can also meet the USB high-speed transmission standard of 480MBit / s. This ensures the stability of the USB interface to the control unit impedance and good electromagnetic compatibility. The 4-bit connector connected to the "main unit" has the same principle as the MQS connector mentioned in this article. This convenient and economical alternative USB adapter design principle is also applicable on other interfaces, such as the mini USB interface.
Testing and identification
All referenced parts have been tested in accordance with SAE/USCAR-30 draft 08-2006 specifications. It is particularly worth mentioning that the connector is tested in combination with temperature cycling and environmental testing. The USCAR-30 specification requires comprehensive testing of these connectors. It can be said that both the "user" and the "vehicle" requirements must be met. Therefore, it is necessary to replace the USB adapter every 5,000 times, that is, every 5 years.
Electromagnetic compatibility is also critical to the quality of the connector technology. To demonstrate this performance, the USB interface in operation has been tested according to the corresponding EMC standards. Considering the data transmission rate, the corresponding USB high-speed data transmission system should be developed according to the high-frequency parameters.
Some of the main high frequency parameters described in the USB 2.0 revisions covered by the SAE/USCAR-30 draft 08-2006 specification are as follows:
1. Impedance range (90 ± 15%);
2. Propagation delay (<26ns);
3. Propagation delay difference (<100ps);
4. Attenuation rate (<5.8dB, f=400MHz);
5. Shielding range (minimum 20dB, 30MHz ~ 1GHz).
Impedance discontinuities in the propagation path will result in reflection losses and signal distortion. With the Time Domain Reflectometry (TDR), the impedance value can be displayed directly as a function of time (see Figure 2) to monitor whether the value meets the specified system tolerances of the USB system.
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