IE980932A1

IE980932A1 - A low power receiver and a method for operating the receiver

Info

Publication number: IE980932A1
Application number: IE980932A
Authority: IE
Inventors: Patrick John Lyons; Joseph Oliver Mcbreen
Original assignee: Hi Key Ltd
Priority date: 1997-11-14
Filing date: 1998-11-12
Publication date: 1999-05-19
Also published as: GB9824978D0; GB2331389A; GB2331389B; IES980933A2

Abstract

A low power radio receiver (3) is for use in a remote keyless entry system for a motor vehicle having an electronic control unit (2) for controlling e.g. a car alarm (5), a vehicle immobiliser (6), and a central locking system (7), in response to transmitted signals comprising a preamble and security code. A power cycling circuit (15) operates in a first mode whereby power is intermittently supplied to a radio receiver circuit (8) and a data monitoring circuit (9) so that a preamble of the signal can be read and validated. On a signal with a valid preamble being received the power cycling circuit (15) operates in a second mode and continuously powers the radio receiver circuit (8), the data monitoring circuit (9) and an output circuit (10) for receiving a complete segment of the signal, the format of which is validated by the data monitoring circuit (9), and on the format being valid the signal is outputted to the electronic control unit (2) which wakes-up and validates it again.

Description

The present invention relates to a low power receiver, and in particular, though not limited to a low power receiver for use in a remote keyless entry system for a motor vehicle. The invention also relates to a method for operating the low power receiver, and additionally, the invention relates to a remote keyless entry system for a motor vehicle which incorporates the low power receiver. fie* »« · τ ACTION AWIC RULF 23 LU C C Sg -25J Remote keyless entry systems for motor vehicles typically consist of a transmitter, a receiver and an electronic control unit. The electronic control unit is mounted in the vehicle and typically, controls a vehicle immobiliser, central locking of the vehicle, and an alarm which is activated in the event of an unauthorised entry or an attempted unauthorised entry to the vehicle. The receiver, typically a radio receiver is controlled by the electronic control unit, and is also located in the vehicle for receiving a radio signal transmitted by the transmitter, typically a hand held keyfob transmitter. These three elements, namely, the electronic control unit, the receiver and the transmitter in general, make up a keyless entry system ror a Vfifllcle. The transmitter in the INT Cl IflUOUtU/lb form of a keyfob is powered by a battery, and is activated typically, by depressing a button. On being activated the transmitter transmits a radio frequency signal which comprises a plurality of identical complete segments which are transmitted in sequence. Each complete segment is modulated with a binary data message. In general, the binary message has two parts, a fixed preamble followed by a code which is unique for each electronic control unit. In general, the preamble is the same for all electronic control units of a similar type. The radio receiver receives the signal from the keyfob transmitter and extracts the binary message from one or more of the complete segments, the binary message is fed to the electronic control unit.

If the electronic control unit recognises the code in the message as being valid and unique to itself, the electronic control unit executes an appropriate function. If the components of the vehicle which are controlled by the electronic control unit are in one state, the electronic control unit causes them to revert to an alternate state, for example, an alarm system of the vehicle which is controlled by the electronic control unit would be armed if it were in the disarmed state, and disarmed if it were in the armed state. Similarly, a vehicle immobilizer controlled by the electronic control unit would be activated or deactivated depending on its state when a valid unique code is received. Similarly, the central locking of the vehicle would either be operated to lock or unlock the vehicle.

In order to minimize power consumption of the electronic control unit and the radio receiver, the electronic control unit is kept in a powered down state except for a small section of the electronic control unit which monitors the output from the radio receiver. When a data signal appears on the radio receiver output the electronic control unit becomes fully powered up to analyse the data signal and to verify if the data signal is a valid message from the associated keyfob transmitter. In the absence of a valid message the electronic control unit reverts to its powered down state after a short interval. If the data signal is a valid message, then the electronic control unit executes the appropriate function, and subsequently reverts to its powered down state.

In order to reduce the power consumption of the radio receiver a process generally referred to as power cycling is used. This requires the radio receiver being repeatedly switched on and off under the control of the electronic control unit monitoring section. In general, the on time durations are less than the off time durations, and accordingly, the average power consumed by the radio receiver is significantly reduced. During on time periods, should a data signal appear on the output of the radio receiver the electronic control unit as well as powering itself up retains the radio receiver in a continuous on state for a predetermined period of time sufficient to allow a complete data message to be received.

While this arrangement does to some extent reduce the power consumption of both the electronic control unit and the radio receiver, it is not an ideal solution.

Since by virtue of the fact that the control of the radio receiver in the power cycling mode and the data evaluation are both carried out by the electronic control unit, this to some extent increases the power requirement. Additionally, because of the fact that the radio receiver is operated under the control of the electronic control unit an additional control wire is required between the electronic control unit and the radio receiver.

There is therefore a need for a remote keyless entry system in which the power consumption of the system in the powered down state is minimized. There is also a need for a low power receiver for use in the remote keyless entry system, and indeed, for use in other systems, as well as a method for operating the low power receiver which overcomes the problems of known receivers .

The present invention is directed towards providing such a remote keyless entry system, a low power receiver and a method for operating such a low power receiver.

According to the invention there is provided a low power receiver for receiving a transmitted signal and for outputting at least a part of the received signal to an electronic control unit in response to the received signal being a valid type signal, the low power receiver comprising: a signal receiving means for receiving transmitted signals, a signal analysing means for analysing the received signals, a signal output means for outputting at least a part of a received signal to the electronic control unit in response to the signal analysing means determining that the received signal is a valid type signal, and a power supply control means for controlling the supply of power to the receiving means, to the analysing means and to the signal output means, the power supply control means being alternately operable in a first mode and in a second mode, in the first mode power being intermittently supplied to the receiving means and to the analysing means for first predetermined time periods at intervals of time of predetermined duration, so that in the first mode the receiving means can receive a portion of a transmitted valid type signal and the analysing means can determine if the received portion of the signal is of a valid type signal, and in the second mode power is continuously supplied to the receiving means, to the analysing means and to the signal output means for a second period of time so that a complete segment of the signal can be received by the receiving means and the complete segment can be analysed by the analysing means for further determining if the received signal is a valid type signal, and in the second mode the signal output means is responsive to the analysing means for outputting at least a part of the complete segment of the received signal to the electronic control unit, the power supply control means being responsive to the analysing means determining that a received portion of a signal is of a valid type signal for operating in the second mode, the duration of the intervals between the first predetermined periods of time being such as to permit the receiving means to receive at least a portion of a valid type transmitted signal for analysing thereof.

In one embodiment of the invention the low power receiver is adapted for receiving a transmitted signal of the type of which a complete segment comprises a preamble and a security code sequentially arranged in the signal, the preamble being common to a large number of transmitted signals for transmission to other similar type electronic control units, and the security code being unique to one specific electronic control unit.

Preferably, the predetermined time duration of the intervals between the first predetermined time periods is less than the time duration of the preamble of the transmitted signals.

Advantageously, the first predetermined time periods are each of duration sufficient to receive a portion of the preamble of the transmitted signal for permitting analysis of the preamble of the received signal.

Ideally, each second time period is of duration sufficient for reception of a complete segment of a transmitted signal.

In one embodiment of the invention the analysing means analyses the format of the received signal during each second time period for ascertaining if the received signal is a valid type signal.

In a further embodiment of the invention the signal output means outputs at least the security code to the electronic control unit.

In another embodiment of the invention the signal output means outputs at least one complete segment of a valid type received signal to the electronic control unit.

In a further embodiment of the invention the analysing 10 means comprises a comparing means for comparing the received portion of the preamble of the signal with a reference preamble signal for determining if the received portion of the signal is of a valid type signal.

In a further embodiment of the invention the analysing means compares the format of a complete segment of the received signal with a reference format for determining if the signal is a valid type signal.

In one embodiment of the invention the power supply control means operates in the first mode continuously until a received portion of a signal is determined as being of a valid type signal.

Preferably, each second time period is of predetermined duration.

In another embodiment of the invention the receiving means comprises a radio receiver.

Additionally, the invention provides a method for operating a low power receiver for outputting at least a part of a received valid type signal to an electronic control unit, wherein the low power receiver comprises a signal receiving means for receiving transmitted signals, a signal analysing means for analysing the received signals, a signal output means for outputting at least a part of a received signal to the electronic control unit in response to the analysing means determining that the received signal is a valid type signal, and a power supply control means for controlling the supply of power to the receiving means, to the analysing means and to the signal output means, the method comprising alternately operating the power supply control means in a first mode and in a second mode, in the first mode power is intermittently supplied to the receiving means and to the analysing means for first predetermined time periods at intervals of time of predetermined duration, so that in the first mode the receiving means can receive a portion of a transmitted valid type signal and the analysing means can determine if the received portion of the signal is of a valid type signal, and in the second mode power is continuously supplied to the receiving means, to the analysing means and to the signal output means for a second period of time so that a complete segment of the signal can be received by the receiving means and the complete segment can be analysed by the analysing means for further determining if the received signal is a valid type signal, and at least a part of the complete segment of the received signal can be outputted by the signal output means to the electronic control unit in response to the analysing means determining that the received signal is a valid type signal, the power supply control means being operated in the second mode in response to the analysing means determining that a received portion of a signal is of a valid type signal, and the duration of the intervals between the first predetermined periods of time being such as to permit the receiving means to receive at least a portion of a valid type transmitted signal for analysing thereof.

In one embodiment of the invention the low power receiver is operated for receiving a transmitted signal of the type of which a complete segment comprises a preamble and a security code sequentially arranged in the signal, the preamble being common to a large number of transmitted signals for transmission to other It y«U932 similar type electronic control units, and the security code being unique to one specific electronic control unit.

In another embodiment of the invention the 5 predetermined time duration of the intervals between the first predetermined time periods is less than the time duration of the preamble of the transmitted signals .

Preferably, the first predetermined time periods are each of duration sufficient to receive a portion of the preamble of the transmitted signal for permitting analysis of the preamble of the received signal.

Advantageously, each second time period is of duration sufficient for reception of a complete segment of a transmitted signal.

In one embodiment of the invention the analysing means is operated to analyse the format of the received signal during each second time period for ascertaining if the received signal is a valid type signal.

In another embodiment of the invention the signal output means is operated for outputting at least the security code to the electronic control unit. Έ 980932 In a further embodiment of the invention the signal output means is operated for outputting at least one complete segment of a valid type received signal to the electronic control unit.

In a still further embodiment of the invention the analysing means comprises a comparing means and the comparing means is operated for comparing the received portion of the preamble of the signal with a reference preamble signal for determining if the received portion of the signal is of a valid type signal.

In a further embodiment of the invention the analysing means is operated for comparing the format of a complete segment of a received signal with a reference format for determining if the signal is a valid type signal.

Preferably, each second time period is of predetermined duration.

In one embodiment of the invention the receiving means is operated for receiving radio signals.

Further the invention provides a remote keyless entry system comprising an electronic control unit for controlling the system, and a low power receiver according to the invention for receiving a transmitted signal and outputting at least a part of a received signal to the electronic control unit on the received signal being determined as being a valid type signal.

In one embodiment of the invention the low power receiver is operated according to the method according to the invention.

The invention will be more clearly understood from the following description of a preferred embodiment thereof which is given by way of example only with reference to the accompanying drawings in which: Fig. 1 is a block representation of a remote keyless entry system according to the invention, and Fig. 2 is a flow chart of a subroutine of control software which controls the operation of a low power receiver also according to the invention of the remote keyless entry system of Fig. 1.

Referring to the drawings and initially to Fig. 1 there is illustrated a remote keyless entry system according to the invention which is indicated generally by the reference in numeral 1. The remote keyless entry ic youy32 system 1 comprises an electronic control unit 2 which controls various components and functions in a motor vehicle. For example, the electronic control unit 2 may control arming and disarming of an alarm system 5 in a motor vehicle, an immobilizer unit 6 for immobilizing the motor vehicle, and a central locking system 7 for the motor vehicle. The control and operation of such alarm systems 5, immobilizer units 6 and central locking systems 7 by an electronic control unit will be well known to those skilled in the art, and it is not intended to describe the electronic control unit 2 in further detail, nor is it intended to describe the alarm system 5, the immobilizer unit 6 or the central locking system 7 in further detail. The electronic control unit 2 controls the alarm system 5, the immobilizer unit 6 and the central locking system 7 of the motor vehicle in response to reception of a valid transmitted signal which is unique to the electronic control unit 2. The transmitted signal is typically transmitted by a remote transmitter, such as a transmitter of the type commonly housed in a keyfob. Such keyfob transmitters will be well known to those skilled in the art, and it is not intended to describe the transmitter further.

A low power radio receiver also according to the invention which is indicated generally by the reference numeral 3, receives transmitted signals on an antenna 4, and is provided for minimising power consumption by the electronic control unit 2. The electronic control unit 2 is operated in a sleep mode until a signal received by the low power receiver 3 is determined by the low power receiver 3 to be a valid type signal and to be of a valid type format and the received signal is outputted to the electronic control unit 2 by the low power receiver 3, thereby significantly reducing the power requirement of the electronic control unit 2. In the event of the electronic control unit 2 determining that the signal received from the low power receiver 3 is valid and is a signal unique to itself, the electronic control unit 2 changes the state of the alarm system 5, the immobilizer unit 6 and the central locking system 7. For example, in the case of the central locking system 7, receipt of a valid, unique signal by the electronic control unit 2 causes the electronic control unit 2 to change the state of the central locking system 7, for example, if the central locking system 7 is in a state where the vehicle is locked, reception of the valid unique signal unlocks the vehicle and vice versa. Similarly, in the case of the alarm system 5, the electronic control unit 2 on reception of the valid unique signal arms the alarm system 5 should the alarm system have been disarmed and vice versa. The same applies to the vehicle immobilizer unit 6.

Before describing the low power radio receiver 3 in more detail, the type of transmitted signal which causes the electronic control unit 2 to change the state of the alarm system 5, the immobilizer unit 6 and the central locking system 7 will first be described.

In this embodiment of the invention the transmitted signal is a radio frequency signal which is modulated with a binary message. One complete segment of the signal comprises the binary message which is in two parts, namely, an initial or fixed part which is referred to as a preamble and is similar for many remote keyless entry systems of the same general type. The preamble is followed by a security code or codes which is unique and specific to one specific electronic control unit. Typically, the keyfob transmitter transmits a plurality of complete segments in sequence. On the received signal having been received and outputted by the low power radio receiver 3 to the electronic control unit 2, the electronic control unit 2 compares one or more complete segments of the received signal with a reference signal, and on the preamble and the security code of one complete segment being identical to the reference signal, the control unit 2 changes the state of the components which it is controlling.

The low power radio receiver 3 comprises a radio signal receiving means, namely, a radio receiver circuit 8 which receives the transmitted signal from the antenna 4. The received signal is relayed to an analysing means, namely, a data monitoring circuit 9 which compares the received part of the preamble with a reference preamble signal as will be described below.

On the received preamble or part thereof being similar to the reference preamble a complete segment of the received signal is analysed by the data monitoring circuit 9, and if the format of the received signal is in a valid format the received signal is outputted to the electronic control unit 2 by a signal output means, namely, a data output circuit 10. A power supply circuit 12 of the low power radio receiver 3 powers the radio receiver circuit 8, the monitoring circuit 9 and the data output circuit 10 through a power supply control means, namely, a power cycling circuit 15.

The power cycling circuit 15 operates in two modes, namely, a first mode which is a powered down mode and a second mode which is a powered up mode. In the first mode the power cycling circuit 15 power cycles, in other words, it intermittently supplies power to the radio receiver circuit 8 and the monitoring circuit 9 from the power supply circuit 12. In the first mode the power is supplied to the radio receiver circuit 8 and the monitoring circuit 9 for first predetermined time periods at intervals of time of predetermined duration. The first predetermined periods of time are of sufficient duration for permitting the radio receiver circuit 8 to receive a part of the preamble of a complete segment of a signal, and for permitting the monitoring circuit 9 to compare the received part of the preamble with the reference preamble stored in the monitoring circuit 9. The duration of the intervals of predetermined time between the first predetermined periods of time is sufficiently short so that at least a part of the preamble of a transmitted signal is received by the radio receiver circuit 8. In other words, the length of each predetermined time interval between the first predetermined periods of time is shorter than the time period of the preamble of the signal. However to conserve power the first predetermined periods of time are shorter than the predetermined time intervals.

The power cycling circuit 15 operates in the second mode in response to the monitoring circuit 9 determining that the received part of the transmitted signal comprises a valid preamble. As soon as the power cycling circuit 15 receives a signal from the monitoring circuit 9 confirming that the received part of the signal has a valid preamble, the power cycling circuit 15 commences to operate in the second mode. In the second mode the power cycling circuit 15 ceases power cycling and continuously powers the radio receiving circuit 8, the monitoring circuit 9 and the data output circuit 10 for a second predetermined time period which is of sufficient duration to allow a complete segment of a transmitted signal to be received and analysed. The received complete segment is analysed by the monitoring circuit 9. The preamble is again compared with the reference preamble, and the format of the complete segment is compared with a reference format stored in the monitoring circuit 9. On being confirmed as having a valid preamble and being in a valid format, the complete segment of the received signal is passed to the data output circuit 10, which in turn outputs the signal to the electronic control unit 2.

The electronic control unit 2 in a sleep mode monitors the output circuit 10, and on seeing a received signal on the output circuit 10, wakes up and reads the signal. Thereafter, the electronic control unit 2 analyses the received signal and compares the preamble and the security code with a stored reference preamble and a stored reference security code, and if the preamble and the security code of the received signal are identical to the stored reference preamble and security code, the electronic control unit 2 then changes the state of the components and functions of the vehicle which it is controlling to the alternate state as already described, and reverts to the sleep mode.

Immediately the second predetermined time period has timed out, the power cycling circuit 15 reverts to the first mode of operation and again commences to power cycle until the next time a transmitted signal received by the radio receiver circuit 8 is confirmed by the monitoring circuit 9 to comprise a valid preamble. At which stage, the power cycling circuit 15 ceases power cycling and commences to operate in the second mode as already described.

The durations of the first and second predetermined periods of time depend largely on the type of transmitted signal for which the remote keyless entry system is adapted to receive. However, typically, the preamble of such a transmitted signal is 25,000 microseconds, while the security data code is 100,000 microseconds long. In which case, the first predetermined period of time will be approximately 5,000 microseconds to allow sampling of a sufficient amount of the preamble of the signal to facilitate validation of the preamble of the signal, and the second predetermined period of time will be approximately 150,000 microseconds to allow one complete segment of the transmitted signal which includes a preamble and a security code to be received by the radio receiver circuit 8 and outputted to the electronic control unit 2 by the data output circuit . To ensure that a valid transmitted signal is received by the low power radio receiver 3, the duration of the predetermined intervals between the first predetermined time periods is approximately 15,000 microseconds.

Turning now to Fig. 2 a software subroutine for controlling a microprocessor (not shown) in the monitoring circuit 9 will now be described. The microprocessor (not shown) controls operation of the low power radio receiver 3. Block 20 starts the subroutine for controlling the power cycling circuit 15, and the subroutine moves to block 21 which operates the power cycling circuit 15 in the first mode, namely the power cycling mode, which has already been described. The subroutine then moves to block 22 which during each first predetermined period of time reads the output from the radio receiver circuit 8, and during each first predetermined period of time moves to block 23. Block 23 compares any signal on the output of the radio receiver circuit 8 with the stored it y#0932 reference preamble, and if block 23 determines that the output read from the output of the radio receiver circuit 8 is a signal with a valid preamble the subroutine moves to block 24. On the other hand, should block 23 determine that the signal on the output of the radio receiver circuit 8 does not have a valid preamble the subroutine returns to block 22 to await the commencement of the next first predetermined period of time. Block 24 causes the power cycling circuit 15 to operate in the second mode, and thereby pauses power cycling so that power is continuously supplied to the radio receiver circuit 8, the monitoring circuit 9 and the data output circuit 10 for the second predetermined period of time. The subroutine then moves to block 25 which reads a complete segment of the signal on the output of the radio receiver circuit 8, and then moves to block 26. Block 26 compares the format of the complete segment of the signal with the stored reference format, and if the received complete segment is of a valid format the subroutine moves to block 28. Block 28 passes the complete segment of the signal to the data output circuit 10 which in turn outputs the complete segment to the electronic control unit 2, and the subroutine moves to block 29 which causes the power cycling circuit 15 to operate in the first mode at the end of the second period of time, and in turn returns the subroutine to block 22. On the other hand, should block 26 determine that the complete segment of the signal read from the radio receiver circuit 8 is not of a valid format, the subroutine moves to block 29 which has already been described.

The advantages of the invention are many. A particularly important advantage of the invention is that by virtue of the fact that the preamble and format of received signals are validated by the low power radio receiver 3 the electronic control unit 2 remains in a sleep mode until a signal with a valid preamble and in a valid format is received. This, thus, allows the electronic control unit 2 to remain in the sleep mode for significantly longer time periods than known heretofore and thereby, significantly minimises the power requirement of the electronic control unit.

Since the only function of the low power radio receiver is to validate the preamble and the format of received signals, and since the format is only checked after a signal with a valid preamble has been received the power requirement of the low power radio receiver is relatively low, and significantly less than would be required by an electronic control unit operating in conventional manner.

A further advantage of the invention is that since the low power radio receiver is effectively a stand alone unit, only a data signal connection is required between the data output circuit 10 and the electronic control unit 2, thereby minimising the connections required between the low power radio receiver and the electronic control unit.

While the second time period has been described as being of predetermined duration, in other words, a second predetermined time period, it will be appreciated that the second time period may not necessarily be of predetermined duration. For example, the second time period may be terminated after the analysing means has determined that a signal is not in a valid format, and in cases where the analysing means determines that the signal is of a valid format the second time period may be terminated after the signal has been relayed to the electronic control unit.

Claims

1. A low power receiver for receiving a transmitted signal and for outputting at least a part of the received signal to an electronic control unit in response to the received signal being a valid type signal, the low power receiver comprising: a signal receiving means for receiving transmitted signals, a signal analysing means for analysing the received signals, a signal output means for outputting at least a part of a received signal to the electronic control unit in response to the signal analysing means determining that the received signal is a valid type signal, and a power supply control means for controlling the supply of power to the receiving means, to the analysing means and to the signal output means, the power supply control means being alternately operable in a first mode and in a second mode, in the first mode power being intermittently supplied to the receiving means and to the analysing means for first predetermined time periods at intervals of time of predetermined duration, so that in the first mode the receiving means can receive a portion of a transmitted valid type signal and the analysing means can determine if the received portion of the signal is of a valid type signal, and in the second mode power is continuously supplied to the receiving means, to the analysing means and to the signal output means for a second period of time so that a complete segment of the signal can be received by the receiving means and the complete segment can be analysed by the analysing means for further determining if the received signal is a valid type signal, and in the second mode the signal output means is responsive to the analysing means for outputting at least a part of the complete segment of the received signal to the electronic control unit, the power supply control means being responsive to the analysing means determining that a received portion of a signal is of a valid type signal for operating in the second mode, the duration of the intervals between the first predetermined periods of time being such as to permit the receiving means to receive at least a portion of a valid type transmitted signal for analysing thereof.

2. A low power receiver as claimed in Claim 1 in which the low power receiver is adapted for receiving a transmitted signal of the type of which a complete segment comprises a preamble and a security code sequentially arranged in the signal, the preamble being common to a large number of transmitted signals for transmission to other similar type electronic control units, and the security code being unique to one specific electronic control unit.

3. A low power receiver as claimed in Claim 2 in which the predetermined time duration of the intervals 5 between the first predetermined time periods is less than the time duration of the preamble of the transmitted signals.

4. A low power receiver as claimed in Claim 2 or 3 in which the first predetermined time periods are each of 10 duration sufficient to receive a portion of the preamble of the transmitted signal for permitting analysis of the preamble of the received signal.

5. A low power receiver as claimed in any of Claims 2 to 4 in which each second time period is of duration 15 sufficient for reception of a complete segment of a transmitted signal.

6. A low power receiver as claimed in Claim 5 in which the analysing means analyses the format of the received signal during each second time period for 20 ascertaining if the received signal is a valid type signal.

7. A low power receiver as claimed in any of Claims 2 to 6 in which the signal output means outputs at least the security code to the electronic control unit.

8. A low power receiver as claimed in Claim 7 in which the signal output means outputs at least one 5 complete segment of a valid type received signal to the electronic control unit.

9. A low power receiver as claimed in any of Claims 2 to 8 in which the analysing means comprises a comparing means for comparing the received portion of the 10. Preamble of the signal with a reference preamble signal for determining if the received portion of the signal is of a valid type signal.

10. A low power receiver as claimed in any of Claims 2 to 9 in which the analysing means compares the format 15 of a complete segment of the received signal with a reference format for determining if the signal is a valid type signal.

11. A low power receiver as claimed in any preceding claim in which the power supply control means operates 20 in the first mode continuously until a received portion of a signal is determined as being of a valid type signal.

12. A low power receiver as claimed in any preceding claim in which each second time period is of predetermined duration.

13. A low power receiver as claimed in any preceding 5 claim in which the receiving means comprises a radio receiver.

14. A low power receiver substantially as described herein with reference to and as illustrated in the accompanying drawings . 10 15. A method for operating a low power receiver for outputting at least a part of a received valid type signal to an electronic control unit, wherein the low power receiver comprises a signal receiving means for receiving transmitted signals, a signal analysing means

15. For analysing the received signals, a signal output means for outputting at least a part of a received signal to the electronic control unit in response to the analysing means determining that the received signal is a valid type signal, and a power supply 20 control means for controlling the supply of power to the receiving means, to the analysing means and to the signal output means, the method comprising alternately operating the power supply control means in a first mode and in a second mode, in the first mode power is intermittently supplied to the receiving means and to the analysing means for first predetermined time periods at intervals of time of predetermined duration, so that in the first mode the receiving means can receive a portion of a transmitted valid type signal and the analysing means can determine if the received portion of the signal is of a valid type signal, and in the second mode power is continuously supplied to the receiving means, to the analysing means and to the signal output means for a second period of time so that a complete segment of the signal can be received by the receiving means and the complete segment can be analysed by the analysing means for further determining if the received signal is a valid type signal, and at least a part of the complete segment of the received signal can be outputed by the signal output means to the electronic control unit in response to the analysing means determining that the received signal is a valid type signal, the power supply control means being operated in the second mode in response to the analysing means determining that a received portion of a signal is of a valid type signal, and the duration of the intervals between the first predetermined periods of time being such as to permit the receiving means to receive at least a portion of a valid type transmitted signal for analysing thereof.

16. A method as claimed in Claim 15 in which the low power receiver is operated for receiving a transmitted signal of the type of which a complete segment comprises a preamble and a security code sequentially arranged in the signal, the preamble being common to a large number of transmitted signals for transmission to other similar type electronic control units, and the security code being unique to one specific electronic control unit.

17. A method as claimed in Claim 16 in which the predetermined time duration of the intervals between the first predetermined time periods is less than the time duration of the preamble of the transmitted signals.

18. A method as claimed in Claim 16 or 17 in which the first predetermined time periods are each of duration sufficient to receive a portion of the preamble of the transmitted signal for permitting analysis of the preamble of the received signal.

19. A method as claimed in any of Claims 16 to 18 in which each second time period is of duration sufficient for reception of a complete segment of a transmitted signal.

20. A method as claimed in Claim 19 in which the analysing means is operated to analyse the format of the received signal during each second time period for ascertaining if the received signal is a valid type 5 signal.

21. A method as claimed in any of Claims 16 to 20 in which the signal output means is operated for outputting at least the security code to the electronic control unit. 10

22. A method as claimed in Claim 21 in which the signal output means is operated for outputting at least one complete segment of a valid type received signal to the electronic control unit.

23. A method as claimed in any of Claims 16 to 22 in 15 which the analysing means comprises a comparing means and the comparing means is operated for comparing the received portion of the preamble of the signal with a reference preamble signal for determining if the received portion of the signal is of a valid type 20 signal.

24. A method as claimed in any of Claims 15 to 23 in which the analysing means is operated for comparing the format of a complete segment of a received signal with a reference format for determining if the signal is a valid type signal.

25. A method as claimed in any of Claims 15 to 24 in which the power supply control means is operated in the 5 first mode continuously until a received portion of a signal is determined as being of a valid type signal.

26. A method as claimed in any of Claims 15 to 25 in which each second time period is of predetermined duration. 10

27. A method as claimed in any of Claims 15 to 26 in which the receiving means is operated for receiving radio signals.

28. A method for operating a low power receiver, the method being substantially as described herein with 15 reference to and as illustrated in the accompanying drawings .

29. A remote keyless entry system for a motor vehicle, the remote keyless entry system comprising an electronic control unit for controlling the system, and 20 a low power receiver as claimed in any of Claims 1 to 14 for receiving a transmitted signal and outputting at least a part of a received signal to the electronic control unit on the received signal being determined as being a valid type signal.

30. A remote keyless entry system as claimed in Claim 29 in which the low power receiver is operated 5 according to the method as claimed in any of Claims 15 to 28 .

31. A remote keyless entry system substantially as described herein with reference to and as illustrated in the accompanying drawings.