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Passive Keyless Entry
General description
Following on from the success of remote keyless entry systems, passive entry systems were developed. These require no additional action by the user to unlock and enter their car, further increasing user convenience
Background information
Passive keyless entry systems provide the ultimate in user convenience, recognizing drivers and opening the car as they approach. Once the driver is in the drivers seat the engine is started by simply pressing a button ("Keyless Go"). Authorization, traditionally given by inserting the key into the lock, is granted automatically by a card or token carried by the driver.
Products
Based on our contactless identification transponder knowledge, we have developed a passive entry concept that avoids the problems facing existing systems, while featuring low power consumption and a high level of integration. The system employs a bi-directional LF/UHF communication link between the car and the driver's security tag, with an operating range of about 1.5 m. The antennas used on the car are of relatively small size and can be fitted into the outside mirror or door handle. The system is capable of determining the presence of several security tags within its operating range at the same time, by means of a unique anti-collision algorithm.
To meet the desired operating range and provide a bi-directional communication link, a battery powered security tag is required. Communication is established by a sensitive receiver circuit which detects the data signal emitted from the basestation and a power amplifier that, in return, transmits data from the tag. The use of a magnetic field from the basestation to the tag, combined with an UHF link from the tag to the car receiver unit, provides the advantage of a well defined range of operation, avoiding interference with other systems. Communication with the tag is triggered as soon as the door lever is pulled.
The low 125 kHz/UHF frequency combination enables low tag power consumption, guaranteeing long battery life. The tag also features a backup mode to allow the system to operate, even in the case of a battery low condition. However, in this case, the operating range is reduced to 10 cm.
The tag provides a high level of integration, and tags are available in the shape of a card or keyfob. First prototypes are available for system demonstration purposes.
Introducing passive entry immediately raises a lot of system issues. The key point is to detect the location of a tag outside or inside the vehicle, with sufficient accuracy to initiate vehicle locking. A number of basestation antennas have to be installed in the vehicle to detect and collect information about tags in the vicinity of the driver's door, passenger's door or trunk.
Our basestation concept relies on the active antennas being placed close to the antenna coil in the desired operating range. The active antennas are wired, via a serial link, to the main access controller, which collects information about tags present and initiates the proper vehicle body function.
For keyless ignition to comply with safety demands, the system needs to be able to detect the tag within a restricted area inside the vehicle. Detecting whether the tag is inside or outside the vehicle was a major challenge, but already solved by several system houses.
Customer Benefits
- Increased convenience for motorist
- Part of an effective anti-theft system
- Replaces a mechanical key