Radio signal receiver device

A radio signal detector includes first and second detector circuits. The first detector circuit has a higher detection sensitivity to detect a radio signal earlier than the second detector circuit. The second detector circuit has a lower detection sensitivity to detect the radio signal accurately. When the second detector circuit detects the radio signal, it starts up a microcomputer. When the first detector circuit detects the radio signal, a time counter starts to count time. After being started up, the microcomputer acquires a time difference between the radio signal detection by the first detector circuit and the start-up. The microcomputer determines time of radio signal transmission by a radio signal transmitter device based on the determined time difference, and outputs control information after an elapse of a predetermined time.

CROSS REFERENCE TO RELATED APPLICATION

This application is based on and incorporates herein by reference Japanese Patent Application No. 2008-172422 filed on Jul. 1, 2008.

FIELD OF THE INVENTION

The present invention relates to a radio signal receiver device, which starts up a control circuit in response to detection of a radio signal transmitted from a radio signal transmitter device based on a signal level of a received signal.

A conventional radio signal receiver device includes a demodulator circuit and a control circuit such as a microcomputer having a central processing unit (CPU). The demodulator circuit demodulates data transmitted in a radio signal transmitted from a transmitter device and received by a receiver antenna. The CPU executes predetermined control processing based on demodulated data.

It is proposed in the following patent document 1 to provide a detector circuit in a radio signal receiver device for reducing electric power consumption. Specifically, the detector circuit is configured to detect a signal level (electric field strength) of a radio signal received by a receiver antenna, and detects reception of a radio signal when the signal level of the received signal exceeds a predetermined threshold level. This detector circuit starts up or activates the control circuit when the reception of the radio signal is detected. The control circuit is controlled to a sleep state after the control circuit completes the control processing.

The detector circuit charges a capacitor by wave-detecting and rectifying the received signal by semiconductor elements such as diodes, and compares a charge voltage of the capacitor with a threshold voltage by a comparator. The detector circuit thus checks whether a radio signal is received.

This detector circuit however takes some time to detect the reception of the radio signal from the start of reception of the radio signal by the receiver antenna, because the capacitor need be charged to attain the threshold voltage. This period of time (detection delay time) varies with a distance up to the radio signal transmitter device, multi-path fading and the like.

If the detection delay time varies, a period of time from the start of transmission of the radio signal of the radio signal transmitter device to the start-up of the control circuit for executing the control processing based on the received data also varies. As a result, it often becomes impossible to execute the control processing, which includes processing of transmission of response data in correspondence to the received data for example.

It is possible to suppress variation in the detection delay time by shortening the detection delay time. To shorten the detection delay time, the following patent document 2 proposes to switch over, in a device having a band-pass filter in an input path of a received signal, bandwidths of the band-pass filter between received signal level detection time and data demodulation time. The bandwidth of the band-pass filter is widened in the received signal level detection time than in the received data demodulation time.Patent document 1: JP 2007-186065APatent document 2: JP 2780725 (JP 4-286228A)

This proposed device, which switches over the bandwidths to shorten the detection delay time, however, is required to have a plurality of band-pass filters having different bandwidths and select one of the band-pass filters. This results in increase of circuit size and cost.

It is also proposed to increase radio signal detection sensitivity of the detector circuit by decreasing the size of the capacitor or the threshold voltage of the comparator, which are provided in the detector circuit, for shortening the detection delay time without switchover of the bandwidths of the band-pass filter.

If the radio signal detection sensitivity of the detector circuit is increased, reception of a radio signal is detected not only when the radio signal is properly received by the receiver antenna but also when external noise is superimposed on the received signal from the receiver antenna. If the external noise is detected as a part of a received radio signal, the control circuit will be started up unnecessarily.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide a radio signal receiver device, which protects a control circuit from being started up by erroneous detection of a radio signal and enables execution of control processing of the control circuit at proper time corresponding to start of transmission of the radio signal from a radio signal transmitter device.

According to one aspect of the present invention, a radio signal receiver device is configured to receive a radio signal transmitted from a radio signal transmitter device, to restore, by processing a received signal, data transmitted from the radio signal transmitter and included in the received signal, and to execute control processing in correspondence to transmitted data. The radio signal receiver device is configured to detect first reception of the radio signal based on a signal level of the received signal, to start up the control processing by detecting second reception of the radio signal based on a signal level of the received signal at a later time than the first reception. The radio signal receiver device is further configured to count a time difference between the first and the second reception of the radio signal, and to detect a reception start time of the radio signal by the receiver antenna based on the time difference, after being started up and execute the control processing based on the reception start time.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention will be described in detail with reference to one embodiment and its modifications.

Referring toFIG. 1, a radio signal receiver device includes a receiver antenna2, an amplifier3, a demodulator4and a control circuit, which is denoted as a CPU of a microcomputer6. The receiver antenna2is for receiving a radio signal transmitted from a radio signal transmitter device (not shown). The amplifier3is for amplifying a received signal, which is produced from the receiver antenna2. The demodulator4is for demodulating transmitted data from an amplified received signal of the amplifier3. The transmitted data is transmitted from the transmitter device, which modulates a carrier wave according to a predetermined signal modulation method. The microcomputer6, operating as a control circuit, executes predetermined processing based on demodulated data produced from the demodulator4.

The amplifier3is provided with a filter for filtering out unnecessary signal components from the received signal of the receiver antenna2in addition to an amplifier circuit for amplifying the received signal. This filter removes signal components (noise components, etc.) other than the radio signal transmitted from the radio signal transmitter device.

The radio signal receiver device further includes a radio signal detector circuit8and a time counter9. The radio signal detector circuit8is for detecting reception of the radio signal of the radio signal transmitter device by the receiver antenna2based on a signal level of the received signal produced from the receiver antenna2.

The radio signal detector circuit8includes two detector circuits, that is, a first detector circuit10and a second detector circuit20, which have different detection sensitivities. The detection sensitivity of the first detector circuit10is higher than that of the second detector circuit20. The first detector circuit10is configured to output a first detection signal to the time counter9upon detecting reception of the radio signal. The time counter9is configured to start counting time in response to the first detection signal. The time counter9outputs counted time, which elapses after the start of time-counting, upon request from the microcomputer6.

The second detector circuit20is configured to output a second detection signal as a start-up or activation signal to the microcomputer6upon detecting reception of the radio signal, so that the microcomputer6is started up to operate. The microcomputer6is configured to execute start time processing (FIG. 3) for acquiring the demodulated data of the demodulator4and then execute predetermined control processing based on the acquired demodulated data.

The microcomputer6is further configured to make transition from a normal operation state to a sleep state, when the demodulated data is not supplied from the demodulator4any more for a predetermined sleep determination time, that is, the radio signal of the radio signal transmitter device is not received any more for a predetermined time, after being started up. After the transition to the sleep state, the microcomputer6continues to be inoperative until the second detection signal (start-up signal) is applied from the second detector circuit20.

The radio signal detector circuit8is configured as shown inFIG. 2. Specifically, the first detector circuit10and the second detector circuit20include diodes11and21, capacitors12and22, resistors13,14and23,24, and comparators16and26, respectively. The diodes11and21are for wave-detecting and rectifying the received signals of the receiver antenna2. The capacitors12and22are for being charged by wave-detected and rectified signals of the diodes11and21, respectively. The resistors13,14and23,24are for dividing charged voltages (capacitor voltages) of the capacitors12and22, respectively. The comparators16and26are for comparing the divided capacitor voltages with predetermined threshold voltages V1and V2, respectively. The comparators16and26determine reception of the radio signal by the receiver antenna2, when the divided capacitor voltages exceed the threshold voltages V1and V2, respectively.

The first detector circuit10is provided as a pre-stage circuit in the signal input path between the receiver antenna2and the second detector circuit20. The capacitor12in the first detector circuit10has a smaller capacitance than the capacitor22of the second detector circuit20. The first detector circuit10and the second detector circuit20are in the same configuration except the capacitances of the capacitors12and22.

Since the first detector circuit10has higher sensitivity in detecting the radio signal than the second detector circuit20, the first detector circuit10detects the radio signal at earlier time than the second detector circuit20. Since the second detector circuit20has a lower sensitivity in detecting the radio signal than the first detector circuit10, it takes more time to detect the radio signal than the first detector circuit10but can detect the radio signal more stably than the first detector circuit10without being affected by external noises.

The start-time processing, which the microcomputer6executes immediately after being started up by the start-up signal of the second detector circuit20, is shown inFIG. 3. As shown inFIG. 3, the microcomputer6acquires at S110after the start-up acquires the counted time from the time counter9by outputting a request of supply of the counted time to the time counter9.

As shown in (a) and (b) ofFIG. 4, this counted time represents a time difference ΔT from a radio signal detection time t1, t1′ of the first detector circuit10to a radio signal detection time t2, t2′ of the second detector circuit20. This counted time acquired at S110is referred to as time difference information.

At S120, the microcomputer6sets an output time (time t3, t3′) of control information corresponding to the received data. Here, the microcomputer6calculates as a reception start time a first detection time (time t1, t1′) of the first detector circuit10based on the time difference information acquired at S110and the start-up time of the microcomputer6(time t2, t2′). The microcomputer6calculates the output time t3and t3′ by adding to the first reception time t1, t1′ a predetermined fixed wait time and a predetermined fixed processing time of the microcomputer6.

At S130, the microcomputer6acquires the demodulated data from the demodulator4and compares the acquired demodulated data with predetermined reference data thereby to check whether the data received this time is regular data provided for the subject radio signal receiver device.

At S140, the microcomputer6further checks whether the received data is normal based on a check result of S130. If the received data is not normal, the microcomputer6ends the start-time processing. If the received data is normal, the microcomputer6checks at S150whether it is the output time set at S120. If it is not the output time, S150is repeated and no control signal including control information is outputted. If it is the output time, the microcomputer6outputs at S160the control information calculated in correspondence to the received data to an external device (not shown), thus ending the start-time processing.

As described above, when the receiver antenna2receives no radio signal from the radio signal transmitter device for more than the predetermined time, the microcomputer6transitions to the sleep state. When the second detector circuit20thereafter detects the reception of the radio signal (time t2, t2′), the start-up signal is outputted to start up the microcomputer6.

The microcomputer6, after being started up, executes the start-time processing. In this start-time processing, the microcomputer6acquires the demodulated data (received data) from the demodulator4at S130, and outputs the control information corresponding to the received data at S160only when the received data is normal. The microcomputer6controls the output time of the control information to the time t3, t3′, which is a predetermined time (wait time plus processing time) later after the time t1, t1′ of detection of the radio signal by the first detector circuit10.

Therefore, the time t3, t3′ of the microcomputer6to output the control information to the external device is controlled to generally the same time, even if the interval of time from the start of transmission of the radio signal by the radio signal transmitter device to the start-up of the microcomputer6is varied due to variation in the electric field of the radio signal transmitted to the receiver antenna2. This variation is caused by distance of the propagation path of the radio signal from the transmitter device to the radio signal receiver device, multi-path fading in the propagation path and the like.

InFIG. 4, (a) shows a case in which the radio signal is detected at the earliest time by the first detector circuit10and the second detector circuit20due to strong electric field strength of the radio signal arriving at the receiver antenna2, and (b) shows a case in which the radio signal is detected at the latest time by the first detector circuit10and the second detector circuit20due to low electric field strength of the radio signal arriving at the receiver antenna2.

As understood fromFIG. 4, the difference Δt1in times t1and t1′ of detection of the radio signal by the first detector circuit10is minimized and small, because the time required to charge the capacitor12after the reception of the radio signal is small due to small capacitance of the capacitor12and the high radio signal detection sensitivity of the first detector circuit10.

The difference Δt2in times t2and t2′ of detection of the radio signal by the second detector circuit20is much larger than the difference Δt1, because the time required to charge the capacitor22after the reception of the radio signal is large due to large capacitance of the capacitor22and the low radio signal detection sensitivity of the second detector circuit20.

Therefore, the microcomputer6is prevented from being started up in response to erroneous detection of the radio signal, by starting up the microcomputer6in response to the detection of the radio signal by the second detector circuit20. Further, by setting the output time of the control information based on the detection time of the radio signal by the first detector circuit10, the control information is outputted after elapse of a generally uniform time from the start of transmission of the data from the transmitter device.

If the radio signal receiver device is applied in a control system (not shown) to control a control object (not shown) in response to a control command from a transmitter device (not shown), a response time required for the control object to respond to the control command after the transmission of the control command can be controlled to generally the same time. This is advantageous to enhance precision of control.

If the radio signal receiver device is applied in a communications system (not shown) to transmit response data through an external device (not shown) in response to transmitted data of a radio signal transmitter device (not shown), time required from start of transmission of data by the radio signal transmitter device to reception of response data by the radio signal transmitter device can be controlled to generally the same. This is advantageous to simplify response data receiving operation of the transmitter device.

Further, since the microcomputer6is not started up unnecessarily by erroneous detection of the radio signal, electric power required for the microcomputer6to operate can be reduced.

In the foregoing embodiment, the demodulator4, the microcomputer6, the time counter9, the first detector circuit10and the second detector circuit20operate as restoring means, control means, time difference counting means, first detection means and second detection means, respectively.

The foregoing embodiment may be modified in the following ways.

As one modification, as shown inFIG. 5, the diode11and the capacitor12charged through the diode11may be shared by both of the first detector circuit10and the second detector circuit20, thereby eliminating the diode21and the capacitor22of the second detector circuit20shown inFIG. 2.

In this case, since the first detector circuit10and the second detector circuit20are configured with the dividing resistors13,14,23,24and the comparators16,26, the radio signal detector circuit8can be simplified in configuration.

To maintain the first detector circuit10to be more sensitive to the radio signal than the second detector circuit20, the threshold voltage V1provided by a first voltage source15for the comparator16may be set to be lower than the threshold voltage V2provided by a second voltage source25for the comparator26.

The radio signal receiver device may be incorporated as a radio signal receiver device52in a mobile device50for an electronic key system of a vehicle as shown inFIG. 6. In this system, when data is transmitted from an in-vehicle radio signal transmitter device30, the time of transmitting response data from the mobile device50is controlled to generally the same time so that the time required for an in-vehicle radio signal receiver device40to receive the response data may be shortened.

This electronic key system has a smart entry function and a remote keyless entry function. According to the smart entry function, when a user carrying the mobile device50as an authorized one enters or leaves a radio communications area of the vehicle, doors of the vehicle are automatically unlocked and locked, respectively, for example. According to the remote keyless entry function, doors of the vehicle are unlocked or locked in correspondence to manipulation of buttons of the mobile device50by a user.

The in-vehicle transmitter device30is for transmitting a radio signal in a low frequency band (LF) to the mobile device50. The in-vehicle radio signal receiver device40is for receiving a radio signal in a radio frequency band (RF) from the mobile device50. The mobile device50is configured to transmit the radio signal in the RF band by using a spread spectrum method.

The transmitter device30and the radio signal receiver device40are connected to a body ECU (not shown), which is configured to control lock/unlock of vehicle doors in a conventional manner.

The radio signal transmitter device30includes a microcomputer32, a modulator34, an amplifier36, a transmitter antenna38and the like. The microcomputer32is configured to output LF data including a synchronization signal. The modulator34is configured to modulate a carrier wave in the LF band by the LF data of the microcomputer32and generate a LF transmission signal.

The amplifier36includes an amplifier circuit, which amplifies the LF transmission signal to a predetermined transmission level, and a filter, which filters out unnecessary signal components (noise or the like) from the LF transmission signal. The LF transmission signal amplified and filtered is transmitted from the transmitter antenna38as a LF radio signal. The microcomputer32is configured to apply a synchronization signal to the radio signal receiver device40at the time of outputting the LF data to the modulator34.

The mobile device50includes, in addition to the radio signal receiver device52shown inFIG. 1, a microcomputer54, an exclusive-OR (XOR) operation circuit55, a modulator56, an amplifier57, a transmitter antenna58and the like.

The receiver antenna2of the radio signal receiver device52receives the LF radio signal transmitted from the radio signal transmitter device30of the vehicle, and the received signal is amplified by the amplifier3and demodulated by the demodulator4.

When the received signal of the receiver antenna2is detected by the first detector circuit10, the time counter9starts to count time. When the received signal of the receiver antenna2is detected by the second detector circuit20, the microcomputer6starts up to operate.

The microcomputer6sets a transmission time of response data in response to demodulated data (received data) inputted from the demodulator4as an output time of a transmission command by executing the start-time processing shown inFIG. 3. At this output time, the microcomputer6outputs the transmission command to the microcomputer54, so that the response data (RF data) corresponding to the received data is transmitted from the transmitter antenna58.

When the microcomputer6receives the transmission data (LF data) of the radio signal transmitter device30during operation, the microcomputer6sets the output time of the transmission command in correspondence to a synchronization signal transmitted with the LF data from the radio signal transmitter device30and outputs the transmission command of the response data to the microcomputer54. Thus, the response data (RF data) corresponding to the received data is outputted from the microcomputer54.

The microcomputer54starts to output the RF data, which is the response data to the received data, and a spread code, when the transmission command is received from the microcomputer6. The response data and the spread code outputted from the microcomputer54are inputted to the XOR operation circuit55. An output signal of the XOR operation circuit55is modulated by the modulator56, amplified by the amplifier57and applied to the transmitter antenna58. Thus, the transmitter antenna58transmits the RF radio signal by the spread spectrum method.

The microcomputer54also starts outputting an RF data and a spread code so that a RF radio signal is transmitted in the spread spectrum method from the transmitter antenna58, when a command signal for locking/unlocking the vehicle doors is inputted by the user's manipulation on the buttons provided on the mobile device50. In this case, the microcomputer54generates the RF data in correspondence to the command signal inputted by the button manipulation.

The radio signal receiver device40includes a receiver antenna42, an amplifier43, a demodulator44, a correlator45, a synchronization detector46, an XOR operation circuit47, a microcomputer48and the like. The RF radio signal transmitted from the mobile device50is received by the receiver antenna42, amplified by the amplifier43, demodulated by the demodulator44and inputted into the correlator45. The correlator45is formed of a sliding correlator, a matched filter or the like, for synchronous capture. The received data (RF data) demodulated by the demodulator44is captured synchronously by the correlator45and the synchronization detector46, and restored or decoded by the XOR operation circuit47.

The microcomputer48receives the restored RF data and outputs a control command corresponding to the restored RF data is outputted to the body ECU, which responsively locks or unlocks the vehicle doors or the like.

When the RF radio signal of the mobile device50is received by the radio signal receiver device40, the microcomputer48causes the correlator45to perform synchronous capture by using the same spread code as the spread code outputted from the microcomputer54of the mobile device50. When the synchronization signal of the transmitter device30is inputted at the time of transmission of the LF radio signal from the transmitter device30, the microcomputer48estimates the transmission start time of the RF radio signal from the mobile device50based on the synchronization signal, and sets a period of the spread code used for restoring the RF data.

According to this electronic key system, when the mobile device50transmits the response data (RF data) in response to the transmission data (LF data) transmitted from the transmitter device30, the output time of the RF data and the spread code is set based on the synchronization signal transmitted with the LF data from the transmitter device30. As a result, it is made possible for the radio signal receiver device40to accurately estimate the transmission start time of the RF radio signal of the mobile device50based on the synchronization signal inputted from the transmitter device30.

According to this electronic key system, therefore, the microcomputer48greatly reduces control amount of the correlator45. Particularly, since the correlator45need not be controlled if variation in the detection time of the first detector circuit10is very small, reception of the RF data can be started quickly or at the earlier time.

Further, the radio signal receiver device52is provided in the mobile device50, and the output time of the RF data and the spread code is determined by detecting the transmission start time of the LF radio signal of the transmitter device30at a time immediately after the microcomputer6of the radio signal receiver device52is started up. Therefore, even when the microcomputer6is in the sleep state and cannot detect the synchronization signal at the time of receiving the LF radio signal, the RF data can be received speedily by setting the output time of the RF data and the spread code of the microcomputer54to the same time as the output time of the spread code used to restore the RF data from the RF radio signal by the radio signal receiver device40.