EP1986135A1

EP1986135A1 - Device, in particular key, using a battery as part of a transmitting antenna

Info

Publication number: EP1986135A1
Application number: EP07008684A
Authority: EP
Inventors: Loic Trocme
Original assignee: Continental Automotive Technologies GmbH
Current assignee: Aumovio Germany GmbH
Priority date: 2007-04-27
Filing date: 2007-04-27
Publication date: 2008-10-29

Abstract

The device for transmitting information by radio, comprises a transmit antenna (An), processing components (1, 2, 3) for processing a signal to be transmitted by the antenna (An), and a battery (Ba) feeding the processing components. There is a connection between the battery (Ba) and the antenna (An) such that the battery (Ba) functions as part of the antenna.

Description

The present invention relates to a device for transmitting information by radio.
Electronic access control systems have undergone a rapid and widespread distribution in various areas. These systems comprise a mobile device having a transmit or transmit and receive antenna, which is carried around by the user, and a control unit with a receive or receive and transmit antenna on the side of the entity to be accessed. The functionality and usage of such systems are being continuously extended and, concurrently therewith, the requirements regarding e.g. the size and performance of the mobile device rise.
In the automotive industry, radio-controlled locking systems have become common practice. In many cases, not only is access gained to the interior of a vehicle through the electronic access control system, but different vehicle functions can be controlled.
Along with automotive systems, building engineering systems represent a further focal point for the use of radio access systems. In addition to garage door controls, which have been in use for some time, access control systems in company offices and public buildings are being increasingly used.
Besides access control systems, there are other kinds of systems necessitating the use of devices having a transmit antenna. They have in common with each other the presence of a transmit antenna and a battery supplying electronic parts needed for the operation of the antenna. It is desirable to reduce the size of the devices comprising the antenna, while on the other hand the performance of the radio communication should not be impaired.
An object of the present invention is to provide an advantageous device having an antenna and a battery.
The object is achieved by a device according to the independent claim. Further developments and advantageous embodiments of the invention are the subject-matter of dependent claims.
The device for transmitting information by radio comprises a transmit antenna, processing components for processing a signal to be transmitted by the antenna, and a battery feeding the processing components. Between the battery and the antenna, there is a connection so that the battery functions as part of the antenna.
The device is capable of emitting radiation, e.g. RF radiation. For this purpose, the processing components work on information which is to be transmitted and activate the antenna accordingly, so that the antenna emits a signal corresponding to the information. The energy needed for the operation of the processing components is provided by the battery. For this purpose, there is a suitable connection between the battery and the processing components.
The function of emitting radiation is not only fulfilled by the antenna, but also by the battery. For this, the antenna is connected to the battery. This means that the alternating current which is causing the emission of radiation does not only flow through the antenna, but also through at least parts of the battery, in particular through the housing of the battery. This results in the battery at least not completely shielding the radiation emitted by the antenna, because the battery itself emits radiation.
According to an embodiment of the invention, the device is part of a key. The key can be part of an electronic access control system, e.g. for a vehicle. Alternatively, the key can be part of a wheel's pressure monitoring system. In this conjuncture, the antenna can transmit information regarding measured pressure values and where applicable regarding other parameters.
According to an embodiment, the device comprises at least one coil separating the antenna's alternating current from a direct current supplied by the battery. The coil performs the task of not letting through alternating currents, while direct currents can flow through it. Preferably the device comprises a coil next to the first electrode of the battery and a coil next to the second electrode of the battery. The latter embodiment brings about that in the antenna and battery, alternating current can flow, while outside the border of the battery which is marked by the coils, the alternating current cannot flow.
According to a further embodiment, the device comprises a capacitor connected in parallel to the battery for providing current to the processing components. The capacitor can e.g. be used for providing higher currents than the battery with faster transitions.
It is possible that the antenna is a transmit and receive antenna. In this case, the processing components are designed accordingly, i.e. they can process a signal to be transmitted as well as a signal received.
The present invention will become more apparent from the description given herein below and from the accompanying drawings which are given by way of illustration only, and thus are not limitative of the present invention, and wherein:

Fig. 1: depicts a first circuit,
Fig. 2: depicts a second circuit.

The circuits of figures 1 and 2 are part of a mobile device using RF (radio frequency) communication. The wavelength of the RF communication can e.g. be 432 MHz or 868 Mhz. Therefore, both comprise a transmit antenna An and a battery Ba. Further components are the matching circuit 1, the RF transceiver 2 and electronic components 3.
The matching circuit 1 is a passive circuitry that performs an adaptation of the impedance between antenna An and RF transceiver 2 in order to transmit with high efficiency. The RF transceiver 2 is an active stage able to generate and modulate an RF signal having a certain power level, and/or to receive and demodulate an RF signal. The electronic components 3 include other parts of the device fed by the battery, e.g. micro controller, sensors, display.
Therefore, a signal to be transmitted by the mobile device is processed by the electronic components 3, afterwards by the RF transceiver 2, passed to the antenna via the matching circuit 1, and finally transmitted by the antenna An. It is understood that the order is reversed in case of a signal received by the antenna An.
The battery Ba is the energy supply for electronic components 3 and RF transceiver 2; therefore it provides direct current to the electronic components 3 and RF transceiver 2. The capacitor K can be used for providing high currents and/or high variations of current to electronic components 3 and RF transceiver if needed.
According to the circuit of figure 1, one electrode E2 of the battery Ba is directly connected to the electronic components 3 and RF transceiver 2, while the other electrode E1 is connected to the ground of the circuit.
In the alternative circuit of figure 2, the antenna An is connected to the electrode E1. Self-evidently, the coupling between antenna An and battery Ba could take place next to electrode E2 instead of next to electrode E1. The coils L1 and L2 function as separation between the alternating current of the antenna An and the direct current supplied by the battery Ba, as alternating currents of RF frequency cannot pass the coils L1 and L2. Therefore by using the decoupling coils L1 and L2, there is no flow of Radio Frequency current between the antenna An and the ground and between the antenna An and the electronic components 3 or RF transceiver 2. As the decoupling coils L1 and L2 enframe the battery Ba, the battery takes part in the functionality of the antenna An. The battery Ba thus functions not only as energy support unit but also as radiation emitting element.
The design of the connection between antenna An and battery Ba can be of different kind. In case a retainer is provided for holding the battery Ba, the antenna An can be connected to the retainer.
There are two main advantages of connecting the antenna An to the battery Ba as opposed to the circuitry of figure 1:

The performance of antenna An is increased. The latter is directly linked to the size of the antenna An. By connecting antenna An with battery Ba, its size and accordingly its performance is increased as the battery forms a part of the antenna. The increased performance of antenna An allows for less expensive RF transceiver 2.
The battery Ba does not mask the RF field of the antenna An. In the circuitry of figure 1, the battery Ba screens parts of the antenna's An radiation transmitted in the direction of the battery Ba. In the circuitry of figure 2 however, as antenna An is directly connected to battery Ba, the battery Ba functions as part of the antenna and therefore emits RF radiation itself.

The circuitry of figure 2 can be used in a key, especially a car key. The key can be part of a remote keyless system (RKS), which is a system for remotely locking / unlocking premises or automobiles. A remote keyless system of a car can include both a remote keyless entry system and a remote keyless ignition system. The mobile device sends pulses of radio frequency energy on a particular frequency; these pulses are interpreted by the receiver e.g. in the automobile, which, in turn, performs the appropriate function.
The circuitry of figure 2 can alternatively be part of a system termed "Keyless Go" or "Keyless Entry", e.g. systems like "PASE" (Passive Start Entry System), "Advanced Key", "Comfort Access", "PEPS" (Passive Entry Passive Start), "PEG" (Passive Entry Go), "PE/PG" (Passive Entry Passive Go), "CE/CG" (Comfort Entry Comfort Go). For use in these systems, the circuitry is part of a chip carried by the car holder.
An other possible application of the circuitry of figure 2 is in a wheel unit of a tire pressure monitoring system. In this case, measurement systems are arranged near a vehicle wheel which determine tire inflation pressure. The pressure data is transmitted wireless via antenna An to a central receiver.
Although the invention has been elucidated in terms of a preferred embodiment described herein, those skilled in the art will appreciate other embodiments and modifications which can be made without departing from the scope of the teachings of the invention. All such modifications are intended to be included within the scope of the claims appended hereto.

Claims

Device for transmitting information by radio, comprising
- a transmit antenna (An),

- processing components (1, 2, 3) for processing a signal to be transmitted by the antenna (An),

- a battery (Ba) feeding the processing components,
characterized by
- a connection between the battery (Ba) and the antenna (An) such that the battery (Ba) functions as part of the antenna.
Device according to claim 1, wherein the device is part of a key.
Device according to claim 2, wherein the key is part of an electronic access control system.
Device according to claim 2, wherein the key is part of an electronic access control system of a car.
Device according to claim 1, wherein the device is part of a wheel's pressure monitoring system.
Device according to any one of the previous claims 1 to 5, comprising at least one coil separating the antenna's (An) alternating current from a direct current supplied by the battery (Ba).
Device according to claim 6, comprising a coil next to the first electrode (E1) of the battery (Ba) and a coil next to the second electrode (E2) of the battery (Ba).
Device according to any one of the previous claims 1 to 7, comprising a capacitor (K) connected in parallel to the battery (Ba) for providing current to the processing components.
Device according to any one of the previous claims 1 to 8, wherein the antenna (An) is a transmit and receive antenna.