Wireless transceiver chip designed for excellent car remote control access control (RKE) system

RKE (Remote Keyless Entry) is the abbreviation of remote access control system / remote control door switch. The RKE system allows the user to use the transmitter on the key fob to lock the car door or unlock it. The transmitter transmits data to the car and the user presses the button switch on the key fob to trigger the system to work. In addition to the technology of opening the car brakes, RKE also has an anti-theft function.

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RKE system composition

It consists of a receiving controller mounted on the car and a transmitter carried by the user, ie the wireless remote control door key.

Figure 1: Composition of the RKE system

How RKE works

The RKE system allows the user to use the transmitter on the key fob to lock the car door or unlock it. The transmitter transmits data to the car and the user presses the button switch on the key fob to trigger the system to work. This will wake up the CPU inside the RKE key fob, and the CPU will send the data stream to the radio frequency (RF) transmitter. The data stream is typically 64 to 128 bits long and includes a preamble, a command code, and a rolling code. The data stream is typically transmitted at a rate of 2 kHz to 20 kHz. The modulation method is amplitude keying (ASK), the main purpose is to extend the battery life of the key fob.

Figure 2: Structure of the RKE key and base station

Especially suitable for transceivers of the RKE system

Melexis' low-power 425MHz to 445MHz transmitter, the MLX72013, is ideal for RKE systems in an 8-pin SCIC-8 package. Its 1.9V to 5.5V supply range allows the device to be powered from a single-cell Li-Ion battery and consumes only 5nA of supply current in standby mode.

Figure 3: Block diagram of the RF transmitter MLX72013

When transmitting Manchester encoded data, the MLX72103 supports data rates up to 40kbps, consumes 2.9mA and 5.5mA supply current, and delivers -10dBm to +10dBm output power to 50Ω loads. The crystal-based phase-locked loop produces an accurate carrier frequency that allows the receiver to use a narrower IF bandwidth to increase the transmission distance.

For RKE receivers, MELEXIS offers a 315MHz to 915MHz superheterodyne ASK receiver MLX71121. The MLX71121 is a highly integrated single-channel/dual-band RF receiver based on a double-conversion superheterodyne architecture. Can be used with the MLX72103.

Figure 4: Block diagram of the RF receiver MLX71121