无钥匙门禁系统(Passive Keyless Entry，简称PKE)作为新一代汽车防盗技术正在逐步发展壮大，目前已经从高档车市场逐步进入中档车市场。现在不仅奔驰、宝马等高端汽车制造商广泛采用了PKE，本土车厂华晨、奇瑞、比亚迪等也都开始配装该类产品。

　　无钥匙门禁系统的核心技术可以分为两大类：智能感应和无线遥控。该系统除了能够支持远程遥控开门、寻车之外，当驾驶员距离车门一定范围时，其能智能感应车门钥匙，如果判断是车主则进行自动遥控开门，并实现一键启动的功能。那么，如何实现PKE的智能感应和远程遥控技术?世强将为你带来合适的解决方案，下面介绍世强提供的PKE方案实现原理。

　　简单地说，PKE的工作原理就是无线射频技术进行信号交换与认证的过程。车身基站包含125kHz低频(LF)发射模块和高频(UHF)接收模块，由 Melexis公司的MLX74190+MLX73290来实现;而钥匙端应答器由MLX73290来集成125kHz低频(LF)接收模块和高频(UHF)发射模块以及三相天线。通常情况下主MCU应处于低功耗模式以节省电量，因此，可选择瑞萨车规级RL78/F12系列R5F1096E芯片，其特有的低功耗功能可将功耗降至0.57uA。

【MLX74190】

The MLX74190 is a low-frequency (LF) initiator composed of two high power LF drivers and built-in immobilizers.

The main application for the MLX74190 is automotive passive start, where the IC transmits a high power LF telegram to wake-up the key inside the car. The key then returns the authorization identification to the car through ultra high frequency (UHF) to enable the engine start.

The MLX74190 also features two built-in immobilizers (for both ASK and FSK communications), used when the battery of the key is depleted. In this case, the key is placed in a specific zone close to the initiator and a full passive RFID communication is initiated. The load modulation signal returns by the key is received and demodulated by the MLX74190.

The MLX74190 is also suitable for tire pressure monitoring system (TPMS) initiator or non-automotive applications such as: dead man switch for 2-wheeler and off-road vehicles like all-terrain vehicles (ATVs), jet skis, snowmobiles ..., LF door opener or active RFID initiator.

The MLX74190 can also serve for a similar purpose with other vehicles such as motorcycles, scooters, ATV, jet skis, snowmobiles and motorboats, where the key holder can be detected when approaching the engine and will be able to activate it from a “start” button or as a dead man switch, so that if the driver falls off then the engine is automatically cut. In addition it may be incorporated into building access systems, TPMS initiators and pet identification system.

Both LF drivers are independently programmable to generate sine (max. 1 Ap) or square (max. 2.5 Ap) waves with a frequency from 109 kHz to 140 kHz and an output amplitude from 0.25 to 32 Vpp. The two drivers can be used in full or half bridge configuration and are protected against overload (overcurrent and overtemperature). A built-in diagnosis function allows detecting any wrong connection with the LF antenna (short to GND, short to Vbat, open load or wrong resonance frequency).

The MLX74190 is supplied by an external VS voltage from 6-40 V and VDD voltage of typically 5 V. The VS voltage can be generated by an external DC-DC converter or by DC voltage from vehicle supply.

The MLX74190 is controlled through a standard SPI interface (SDI, SDO, SCK and NCS) and an interrupt pin is generated on-purpose by the IC. The MLX74190 is clocked either with a 2 MHz clock frequency signal coming from the MCU or by an on-chip oscillator connected to an external 4 MHz crystal or ceramic resonator.

Top Features

High power drivers (2.5 Ap in square mode)

Output power programmable from 0.25 to 32 Vpp

Output frequency programmable from 109 kHz to 140 kHz

Features and benefits

High power drivers (2.5 Ap in square mode)

Output power programmable from 0.25 to 32 Vpp

Output frequency programmable from 109 kHz to 140 kHz

Full or half bridge capabilities

Antenna fault detection

Protected power outputs (overcurrent and T°)

Built-in ASK/FSK immobilizers

SPI port for easy control

　　车身和钥匙这两部分之间采取双向通信的方式。车身端的MLX74190 LF驱动会不停地发送一条编码为125kHz的低频报文，以搜寻并唤醒一定范围内的钥匙应答器。当车钥匙端系统中的 MLX73290的3D低频天线在有效范围内接收到该报文，则唤醒车钥匙主MCU，钥匙端识别低频125kHz 报文成功并应答，即代表成功地实现了智能感应功能。此时，钥匙端主控MCU R5F1096E通过SPI控制MLX73290发送一条高频段报文来控制车门打开，车身端在收到该报文后对其进行解码，如果识别成功，将控制打开车门，从而完成了智能感应到远程遥控的过程。

【MLX73290】

MLX73290-A

The MLX73290-A combines a highly integrated RF transceiver for long range, high speed communication and a 3 dimensional low frequency interface (3DLF) for low power wake-up. This unique combination makes the MLX73290-A suitable for applications requiring a very low power wake-up function together with long range, high speed RF feedback.

The transceiver part allows for multi-channel operation including frequency hopping in the European bands (433 and 868 MHz) as well as in North America or Asia bands (315 or 915 MHz). The output power, frequency channel, modulation type and frequency deviation are programmable. Thanks to the high frequency resolution and phase noise performance of its fractional-N PLL, the MLX73290-A is fit for narrow-band operation. There are two selectable modulation schemes: binary on-off keying (OOK) and binary frequency shift keying (FSK) as well as their Gaussian filtered versions. The low-IF receiver part comprises fully digital demodulation and self-polling features together with channel scanning and built-in packet recognition.

The 3DLF interface features an automatic and programmable wake-up algorithm together with an integrated data decoder to receive the payload. Monitoring independently the RSSI information from the 3-axis LF front-ends allows precise monitoring of the received LF field. Thanks to its internal rectifier, power management and load modulator, the MLX73290-A is capable of battery-less LF RFID tag operation.

Top Features

On-chip combination of 3DLF and RF technologies

3DLF interface for low power wake-up (battery-less mode possible)

Multi-band (300 to 960 MHz) RF transceiver for long range, high speed communication

Features and benefits

On-chip combination of 3DLF and RF technologies

3DLF interface for low power wake-up (battery-less mode possible)

Multi-band (300 to 960 MHz) RF transceiver for long range, high speed communication

RSSI information for both LF and RF interfaces

Supply voltage range of 2.1 to 3.6 volt

32L QFN5x5 package

MLX73290-M

The MLX73290-M is a 300 to 930 MHz multi-channel transceiver chip. Its output power, frequency channels, modulation type frequency deviation and many other parameters are programmable via SPI. The low-IF receive part comprises fully digital demodulation and self-polling features together with channel scanning and packet recognition.

A flex RF front-end with two PAs and two LNAs allows various set-ups of the transmit/receive air interface, for example antenna diversity or frequency diversity configurations.

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Top Features

Flex TX/RX RF front-end for antenna and frequency diversity

Energy harvesting interface

Transmitter with power detectors

Features and benefits

Flex TX/RX RF front-end for antenna and frequency diversity

Energy harvesting interface

Transmitter with power detectors

Receiver with digital RSSI

Receiver self-polling with MCU wake-up

Multi-band frequency coverage from 300 up to 960 MHz

Modulation schemes supported: (G)FSK, (G)MSK, (G)OOK

Transmitter power of -20 to 13 dBm, 64 steps

Receiver sensitivity of -120 dBm (FSK, 433 MHz, 9 kHz CHBW)

Supply voltage range of 2.1 to 3.6 V

　　在这个PKE系统解决方案中，MLX74190 LF驱动和MLX73290能够完美地搭配，实现在钥匙端电池耗尽的情况下进行无源RFID的通信，即在一定范围内仍能够实现遥控车门的功能。此时，由于电池耗尽，钥匙端的主控MCU通过MLX73290接收到的MLX74190无线电供电，并快速驱动MLX73290发送电池耗尽的LF报文并传送给汽车端的MLX74190，MLX74190支持LF FSK和ASK解码，将信息解码给汽车端，此时高频UHF可不工作。

　　因此，MLX74190和MLX73290能够完美搭配，应用在PKE系统，乃至TPMS等场合。车规级芯片保证产品的可靠性，提供一致的接口匹配。其低功耗特性以及电池耗尽模式下的无源通信，进一步保障产品的可靠性，提升了产品档次。

　　MLX74190的主要特性：

　　• 内部集成两个低频驱动器，且都可以用来编程产生正弦波电流(最大峰值1A)或方形波电流(最大峰值2.5A)

　　• 频率范围： 109kHz~140kHz

　　• 输出振幅强度：0.25V ~32V峰-峰值

　　• 允许支持多种编码模式

　　• 可以支持幅移键控(ASK)和频移键控调制(FSK)，以确保无源RFID进行通信

　　• MLX74190的诊断模式使其能够检测与LF天线各种形式的误接

　　• 采用紧凑的48引脚TQFP封装

　　• 车规级芯片，工作温度范围：-40℃~105℃

　　MLX73290的主要特性：

　　• RF支持300MHz至960MHz的sub-GHz频段

　　• 支持3D LF天线接口，具有自动和全可编程的扫描模式

　　• RF输出功率范围为-20dBm至13dBm，LF接收灵敏度可达到-120dBm

　　• 最大数据速率为250kbps，支持OOK、FSK、MSK、GMSK和GFSK等调制方案

　　• 睡眠模式下的电流仅为400Na，LF轮询电流仅4uA

　　相关元件供应

　　型号：R5F1096EJSP#V0                                    品牌： RENESAS

　　型号：MLX74190RPF-ABA-000-SP                   品牌：MELEXIS

　　型号：MLX73290RLQ-BBM-000-TU                 品牌：MELEXIS

　　型号：R5F1096EJSPQ#YE                                 品牌：RENESAS

　　型号：MLX73290KLQ-ABA-000-SP                 品牌： MELEXIS

　　无钥匙门禁系统，分为公开密钥和私人密钥

　　PKE (public-keyencryption) 公开密钥加密。

　　使用加密和两把密钥的安全方法，一个是公开密钥，另一个是私人密钥。RSA是公开密钥加密的例子。请注意密钥用于协商安全链接，不是用于加密数据。请参阅RSA;会话密钥。

　　无钥匙门禁系统(PKE，Passive Keyless Entry)在RKE基础之上发展起来，作为新一代防盗技术正在逐步发展壮大，目前已经从高档车市场逐步进入中档车市场，不仅奔驰、宝马等高端汽车制造商已经广泛采用了PKE，像福特蒙迪欧、日产的天籁和新型马自达等中型车型也纷纷采用这一技术。PKE不是传统的钥匙，而是一个智能钥匙，类似于智能卡。当驾驶者踏进指定范围时，该系统通过识别判断如果是合法授权的驾驶者则进行自动开门。上车之后，驾驶者只需要按一个按钮即可启动点火开关。

　　遥控钥匙是利用中控锁的无线遥控功能，不用把钥匙键插入锁孔中就可以远距离开门和锁门的钥匙。

　　工作原理

　　工作原理简单来说：先从钥匙发出微弱的电波，由汽车天线接收该电波信号，经电子控制单元(ECU, Electronic Control Unit)识别信号代码，再由该系统的执行器(电动机或电磁线圈)执行开/闭锁的动作。

　　基本组成

　　该系统主要由发射机和接收机两部分组成。

　　发射机：由发射开关、发射天线(键板)、集成电路等组成。内含识别代码存储回路和调幅调制回路，并在电路的相反一侧装有揿钮型的锂电池。发射频率按使用国的无线电标准进行选择，发射开关每按揿钮一次进行一次信号发送。

　　接收机：发射机利用短波调制发出识别代码后，通过汽车的短波天线进行接收，并利用分配器进入接收机电子控制单元的短波高频增幅处理器进行解调，与被解调器的识别代码进行比较;如果是正确的代码，就输入控制电路并使执行器工作。