In 2003, NXP introduced a keyless system (PKE or PEPS), which completely changed the development prospects of automotive security applications, bringing users a new experience of comfort and convenience: the owner does not need to use the key during the entire driving process. Just carry it with you. When the owner enters the effective range near the car, the car will automatically detect the key and identify it. If the driver succeeds, the door or trunk will be opened accordingly. When the owner enters the car, he only needs to press the engine start button, and the car will automatically detect the key. Position, determine whether the key is in the car, whether it is in the main driving position, if successful, start the engine. Don't underestimate this seemingly inconspicuous change, it plays a major role in simplifying your life. The keyless system not only brings comfort and convenience, but also has an essential improvement in safety. Through two-way communication between low frequency and radio frequency, complex two-way identity authentication can be completed between the car and the key, in terms of security. Similar to engine burglar, it is much better than traditional remote control keys. Since the successful mass production of keyless systems for a small number of high-end models in 2003, the global market has spent two to three years promoting the technology. At present, almost every major car manufacturer in the world has NXP keyless products covering the high-end The models are even low-end models.
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Let's take a look at how this technology is implemented. The keyless system requires a total of three areas to be detected: a gray exterior area, a pale pink interior area, and a gray-white main driving position. The shaded area of ​​gray includes three parts, which respectively represent the effective area of ​​the main door, the auxiliary drive, and the door control of the trunk. When the owner enters this position with the key, the car and the key can establish effective communication through the low frequency signal. The field strength detection, the car can determine the corresponding position of the key, and thus decide to open the corresponding door. The light pink interior is a difficult point in the design of the entire PKE system. It is necessary to accurately determine whether the key is in the car to determine the state of the door and whether the engine can be started. In some high-end models, the gray-white main driving area will be detected, whether the key is valid, whether the main driving position is there, avoiding engine start-up caused by child misoperation, and may also include detection of the area inside the trunk to prevent the key. Was locked into the trunk. In summary, we can find that in the keyless system, the area detection is a very important technology that is different from the previous various automotive security products. Therefore, the accuracy of the area detection becomes an important parameter to measure the quality of a keyless system. At present, there are mainly two corresponding technologies on the market. One is to adjust the sensitivity of the low-frequency signal and then make fuzzy judgment according to whether the communication is stable. The accuracy is limited but convenient to implement. The second is based on the strength detection of the received low-frequency signal. RSSI (Received Signal Strength Indication), according to the size of the low-frequency signal to calculate the relative distance between the key and the low-frequency antenna in the car, through a plurality of low-frequency antenna cross-coverage coverage, accurately locate the specific location of the key. NXP products all use the second technology. To achieve the desired performance parameters, NXP provides a signal sensitivity of a minimum of 2.5 mV for a three-dimensional low-frequency receiver front end, while typical sensitivity values ​​can reach 1 mV. Unlike other solutions, the Successive Approximation ADC, NXP uses a 12-bit Sigma-Delta (Σ-Δ) ADC to eliminate noise interference through multi-point sampling averaging. The best in-car has been implemented. The external detection accuracy is up to 2cm. At present, the accuracy of the in-vehicle inspection required by the depot is usually 5 to 10 cm.
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