Maxim Integrated Circuits ( offered an application note on designing Remote keyless entry (RKE) systems. This application note describes how RKE systems work and ways to meet the primary design challenges, which are low power consumption, long battery life, RKE transmitter-receiver range, and reliability. Maxim devices designed to address these concerns are also presented.

Remote keyless entry (RKE) systems allow a user to lock and unlock the car using a transmitter on the keychain, which transmits data to a receiver in the vehicle. Most of the newer vehicles today come with a remote keyless entry (RKE) system either standard or as an option. RKE systems are also a high volume after-market accessory. Most remote keyless entry systems alarm the vehicle against theft and lock and unlock the doors and trunk. Some include remote start and car finder functions.

Remote keyless systems consist of a key fob transmitter and a receiver inside the vehicle. They most commonly use a frequency of 315MHz in the the U.S. and Japan, and 433.92MHz in Europe. Europe has also opened up the 868MHz band to accommodate the growing demand for remote keyless entry systems.

The key challenges for most remote keyless entry designs are achieving low power consumption in both the RKE transmitter and receiver, while achieving good range and reliability for the RKE system

Designing Remote Keyless Entry (RKE) System Circuits

Designing Remote Keyless Entry (RKE) System. Courtesy: Maxim-IC

As can be seen in the Remote keyless entry (RKE) system block diagram, the user presses a pushbutton switch on his key fob to initiate an action. This wakes up the CPU inside the RKE key fob, which sends a data stream to the RF transmitter. The data stream is usually 64 to 128 bits long and includes a preamble, a command code and a rolling code. It is sent at a rate usually between 2kHz and 20kHz. The modulation scheme is amplitude shift keying (ASK), mainly to extend the key fob’s battery life.

The Remote keyless entry (RKE) system’s RF receiver in the vehicle captures the RF signal, demodulates it and sends the data stream to the CPU, which decodes it and sends commands to the command module.