JP4298089B2 - Keyless entry receiver - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a keyless entry receiver, and more particularly to improvement of reception performance.
[0002]
[Prior art]
In general, locking / unlocking of vehicle doors, etc. is performed by inserting a mechanical key common to the ignition key into a key cylinder of the door. For example, a remote operation keyless entry control system that does not use mechanical keys has been adopted. This keyless entry control system transmits a code assigned to each vehicle from the transmitter by the driver's operation to the keyless entry receiver on the vehicle side, demodulates it, and collates it with the code stored on the vehicle side. Then, the operation of the electromagnetic actuator or the like unlocks the vehicle, which has the advantage that the door can be locked / unlocked at night.
[0003]
FIG. 5 shows an example of the configuration of such a keyless entry control system. The transmitter 4b is built in the handle portion of the key 4 held by the driver, and a switch (door lock, door unlock, trunk open, panic) 400 is provided. A storage unit 401 that stores an ID code corresponding to the switch 400, and a control unit 402 that reads the ID code from the storage unit 401 in response to the switch 400. When the driver presses one of the switches 400, The control unit 402 outputs a code signal corresponding to the switch 400 to the oscillation unit 403. The oscillation unit 403 includes a 314.35 MHz crystal oscillator 4032 for generating a carrier signal. A frequency modulation (FM) signal is generated using the code signal as a modulation signal and transmitted from the antenna 404. The transmitter 4b includes a battery 405 and a voltage control unit 406 for supplying power to these units.
[0004]
The keyless entry receiver 5 includes a receiving unit 5a and a control unit 5b. The receiving unit 5a receives a radio wave received by the antenna 500 as a first band pass filter (BPF) 501, a high frequency (RF) amplifier 502, a mixer. 503, a superheterodyne system including a local oscillator 504. The local oscillator 504 has a fixed oscillation frequency using a 313.895 MHz crystal oscillator 5041. The received wave signal is frequency-converted by the mixer 503 into an intermediate frequency signal from the oscillation signal of the local oscillator 504, and the center frequency is 455 kHz. The signal is input to the second band pass filter (BPF) 505, and an intermediate frequency (IF) signal of 455 kHz is passed through. The IF signal is amplified by an IF amplifier 506, and then the digitized code signal is demodulated by a detection circuit 507, a phase shifter 508, a low-pass filter (LPF) 509, and a waveform shaping circuit 510.
[0005]
The control unit 5b determines whether or not the received signal strength known from the received signal strength detection circuit (RSSI circuit) 511 is sufficient. If the received signal strength is sufficient, the control unit 5b outputs the code signal to the body computer 6 as it is. The determined code is determined and a control signal corresponding to the code is output to the drive circuit of the electromagnetic actuator.
[0006]
[Problems to be solved by the invention]
By the way, the stability of the keyless entry receiver depends on the stability of the transmission / reception frequency, and particularly depends on the performance of the oscillator used in the transmission / reception device. Therefore, it is necessary to use a resonator having a small frequency deviation and good stability, which increases the cost. On the other hand, if the bandwidth of the second BPF is widened, the radio wave from the transmitter can be picked up even if the frequency stability is somewhat poor, but the S / N deteriorates because noise is likely to enter, resulting in sensitivity. Becomes worse.
[0007]
Since this type of receiver uses a crystal oscillator that is sufficiently stable but is stable for the local oscillator, the inventors have covered the fluctuation range of the oscillation frequency of the local oscillator in Japanese Patent Application No. 10-359028. We propose a keyless entry receiver capable of accurate reception even when using an oscillator that is not very stable by sweeping the oscillation frequency within the range to be used and tuning based on the received signal strength at that time Yes. Among them, there has been proposed a technique for tuning by detecting the timing at which the RSSI signal peaks when the oscillation frequency is swept. In the case of tuning based on the peak timing of the RSSI signal, it is found that the received wave signal is not perceived due to the failure to read the code from the demodulated signal. That is, it is necessary to wait for a code reading operation to determine whether or not the signal is a correct received wave signal, and there are problems of shortening the time required to capture the correct received wave signal and reducing power consumption.
[0008]
The present invention has been made in view of the above circumstances, and even if an oscillator that does not necessarily have sufficient performance is used as the oscillator of the transmitter or the local oscillator of the receiver, it can be received with high sensitivity, and a correct received wave can be obtained. An object of the present invention is to provide a keyless entry receiver capable of shortening the time until a signal is captured and reducing power consumption.
[0009]
[Means for Solving the Problems]
According to the first aspect of the present invention, there is provided a superheterodyne receiver that inputs an intermediate frequency signal between the received wave signal and the local oscillator signal of the local oscillator to the intermediate frequency filter, modulated by the code signal, and transmitted from the transmitter. In a keyless entry receiver that receives a received radio wave, demodulates the code signal, and outputs a control signal corresponding to the code signal to the vehicle control unit, a local oscillator of the receiving unit is provided with an oscillator that is less stable than a crystal oscillator. Use. Further, the reception unit is provided with reception signal strength detection means for detecting reception signal strength, sweep means for controlling the local oscillator to sweep the oscillation frequency of the local oscillator, and sweep control means for controlling the sweep means. . When the sweep control means sweeps the oscillation frequency within a predetermined range set in advance, the sweep control means includes timing detection means for detecting a timing at which the received signal intensity takes a maximum value. The oscillation frequency of the local oscillator is fixed based on the timing at which the signal intensity takes a peak value. In addition, an sensation determination unit that compares the received signal strength with a preset lower limit value and determines that there is no sensation when the received signal strength falls below the lower limit value in the entire predetermined range is provided.
[0010]
Since the received wave signal is tuned by sweeping the oscillation frequency of the local oscillator, even if the frequency deviation of the oscillation frequency of the transmitter oscillator or the receiver local oscillator is large and the stability is not good, High sensitivity can be received.
[0011]
In addition, when the received signal strength is lower than the predetermined value, it is known that there is no feeling without waiting for the time to read the code from the demodulated signal, so the time until the correct received wave signal is captured can be shortened. And power consumption can be reduced.
[0012]
According to a second aspect of the present invention, there is provided intermittent operation control means for intermittently operating the receiving unit so as to alternately repeat an operation period in which the receiving unit operates and a sleep period in which the receiving unit stops operating. The intermittent operation control means is set to stop the operation of the receiving unit and switch to the sleep period when the feeling determination means determines that there is no feeling.
[0013]
As long as there is no sensation, the operation of the receiving unit is suspended, so that power consumption can be further suppressed.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 shows a configuration of a keyless entry control system to which a keyless entry receiver (hereinafter simply referred to as a receiver) of the present invention is applied. The transmitter 4a built in the ignition key 4 is substantially the same as that described in the prior art except that the oscillator of the oscillation unit 403 uses a SAW 4031 which is inexpensive but slightly less stable in place of the crystal oscillator. Therefore, the description is omitted, and the receiver 1 will be mainly described.
[0015]
The receiver 1 includes a receiver 1a and a controller 1b, and is mounted on the vehicle together with the body computer 3. The receiving unit 1 a has a superheterodyne configuration, and a received wave signal received from the antenna 100 is input to the mixer 103 via the first BPF 101 and the RF amplifier 102. The pass band of the BPF 101 is set so that the transmission radio wave can be felt even if the transmission frequency of the transmitter 4a varies due to drift of the oscillation unit 401 or the like. The mixer 103 constitutes a frequency conversion circuit with a voltage controlled oscillator (VCO) 104 serving as a local oscillator, and generates an intermediate frequency signal between the received wave signal and the oscillation signal of the VCO 104. The second BPF 105, which is an intermediate frequency filter, has a center frequency of 455 kHz, and is composed of a ceramic filter or the like.
[0016]
The intermediate frequency (IF) signal that has passed through the second BPF 105 is amplified by the IF amplifier 106 and input to the detector 107 and the phase shifter 108. The detector 107 and the phase shifter 108 constitute a frequency discriminating circuit, and converts a frequency change into an amplitude change. The received wave signal output from the detector 107 further passes through the LPF 109 and the waveform shaping circuit 110 that remove high frequency components, and the code signal is demodulated, and the code signal is input to the control unit 1b.
[0017]
The receiving unit 1a includes an RSSI circuit 111 serving as received signal strength detecting means, and outputs an RSSI voltage VRSSI. The RSSI voltage VRSSI increases as the input to the IF amplifier 106 increases, and the received signal strength can be detected.
[0018]
The VCO 104 is configured using a SAW 1041 as an oscillator, and the receiving unit 1 a is provided with a scanning circuit 2 that outputs a control voltage for controlling the frequency of the VCO 104. The VCO 104 is configured such that the oscillation frequency is high when the control voltage input from the scanning circuit 2 is high, and the oscillation frequency is low when the control voltage is low.
[0019]
The scanning circuit 2 has a counter 202 and a DA converter 203 constituting the sweep means 2b. The counter value of the counter 202 is converted into an analog signal by the DA converter 203, and the oscillation frequency of the VCO 104 is swept as a control voltage. (Scanning). Here, the resolution of the DA converter 203, that is, the number of bits, is greater than the value obtained by dividing the variable range of the oscillation frequency of the VCO 104 by the frequency at which the oscillation frequency of the VCO 104 is desired to be adjusted. Note that the frequency at which the VCO 104 is desired to be adjusted is the minimum variable of the oscillation frequency, and the smaller the bandwidth of the second BPF 105 is, the smaller the frequency is required. The clock frequency of the counter 202 that defines the scanning speed of the VCO is preferably set to a value that is not an integral multiple of 455 kHz, which is the intermediate frequency, so that the clock signal is not mixed into the second BPF 105. For example, 455 kHz is multiplied by 8.5 and set to 3.9675 MHz.
[0020]
The counter 202 is controlled by the first control logic 201. The control logic 201 is composed of a logic operation circuit or the like that executes a control flow to be described later, and based on the output result of the peak timing detection circuit 200 that constitutes the sweep control means 2a together with the control logic 201, the count initial value and the count up / down A direction and a count speed are given to cause the counter 202 to perform a predetermined operation, and the oscillation frequency of the VCO 104 is fixed in a state where tuning is finally achieved.
[0021]
Here, a plurality of ranges in which the counter 202 counts up / down are prepared as will be described later. The maximum range is that the oscillation frequency of the VCO 104 varies in transmission frequency of the transmitter 4a (drift, etc.) and the stability of the SAW 1041. The variation range of the oscillation frequency (drift, etc.) of the VCO 104 caused by the characteristics can be followed. For example, when the transmission frequency of the transmitter 4a and its variation is 314.35 MHz ± 0.15 MHz and the variation of the oscillation frequency of the VCO 104 is ± 0.15 MHz, the mixer 103 can obtain an intermediate frequency signal of 455 kHz. The range of the oscillation frequency of the VCO 104 may be 313.895 MHz ± 0.3 MHz. Therefore, the maximum count up / down range of the counter 202 is determined so as to be variable within the frequency range.
[0022]
The peak timing detection circuit 200 is provided with the RSSI voltage VRSSI as an input. When the oscillation frequency of the VCO 104 is scanned within a predetermined range, the peak timing detection circuit 200 detects the timing at which the RSSI voltage VRSSI takes a peak value. The timing at which the RSSI voltage peaks, that is, the count value of the counter 202 is known.
[0023]
Further, a comparator 204 is provided with the RSSI voltage VRSSI and the reference voltage output from the reference voltage generator 205 as inputs, and outputs an “H” or “L” signal to the second control logic 206. The comparator 204, the reference voltage generator 205, and the control logic 206 constitute the feeling determination unit 2c. Here, the reference voltage is set based on the lower limit value of the RSSI voltage VRSSI of the received wave signal from which the code can be decoded from the demodulated signal, and the control logic 206 can determine whether or not there is a feeling of sensation.
[0024]
The control unit 1b compares the demodulated code signal input from the waveform shaping circuit 110 with a pre-stored ID code, and if it matches, the control signal corresponding to the operation of the switch 400 of the transmitter 4a is sent to the body computer 3 as the vehicle control unit. Is output. The body computer 3 opens and closes the door by driving an actuator for opening and closing the door, for example, according to the control signal.
[0025]
The control unit 1b, which is an intermittent operation control means, is configured to perform start-up control of the reception unit 1a and the like so that the reception unit 1a performs an intermittent operation in which the operation period and the sleep period are alternately repeated by timer control. To reduce the dark current.
[0026]
FIG. 2 is a control flow executed in the first control logic 201, and FIG. 3 is a timing chart showing the oscillation frequency of the VCO 104 and the control voltage output to the VCO 104. In step S001, the first scanning is performed. In the first scanning, the oscillation frequency of the VCO 104 is swept in the range of 313.895 MHz-0.3 MHz to 313.895 MHz + 0.3 MHz over a period of 4 msec (first sweep). This sweep range is a range that can follow variations in the transmission frequency of the transmitter 4a. The first control logic 201 stores a counter value Ca when the RSSI voltage VRSSI takes a peak in a register.
[0027]
Next, a second scanning is performed. A value Cb obtained by subtracting the offset value Oa from the counter value Ca is loaded (step S003), and a second sweep is performed using the counter value Cb as an initial value (step S004). In this sweep, 1/4 of the count range of the first sweep is performed over a period of 4 msec. That is, the sweep speed is 1/4 that of the first sweep. The offset value Oa is set to about ½ of the second sweep range, for example.
[0028]
The counter value Cc when the RSSI voltage VRSSI takes a peak is stored in the register (step S005).
[0029]
Next, the third scanning is performed. A value Cd obtained by subtracting the offset value Ob from the counter value Cc is loaded (step S006), and a third sweep is performed using the counter value Cd as an initial value (step S007). This sweep is performed 16 times in total by repeating step S007 and steps S008 and S009 described later. The sixteen sweeps are performed under the same conditions, and are described as the 3-kth (k = 1 to 16) in the order in which they are performed in the following description. Each sweep of the third sweep takes 1/16 of the count range of the first sweep, and thus 1/4 of the count range of the second sweep takes 0.5 msec.
[0030]
The counter value Ce1 when the RSSI voltage VRSSI takes a peak in this third sweep is stored in the register (step S008). Then, the counter value Cd is loaded again as an initial value (step S009), and steps S007 to S009 are repeated, and from the 3-1st sweep to the 3rd to 3-16th sweep in sequence. Thus, the counter value Cek (k = 1 to 16) when the RSSI voltage VRSSI takes a peak is obtained.
[0031]
When the sweep from the 3-1st to the 3-16th time is completed and the last counter value Ce16 is obtained, the process proceeds to step S010.
[0032]
In step S010, the average of the counter values Cek (k = 1 to 16) stored in the register is calculated and set as Cf. Although this average value Cf is a representative value of the counter value at the time of peak timing detection, since it includes a response delay of the RSSI circuit 111, etc., an offset value Oc corresponding to this response delay is subtracted from the average value Cf to obtain Cg. The counter value Cg is loaded to fix the oscillation frequency of the VCO 104.
[0033]
The slower the sweep speed, the smaller the peak frequency detection error. Since the receiver 1 performs the second sweep (step S004) in the low speed narrow range following the first sweep (step S001) in the high speed and wide range as described above, the following effect is obtained. In the first sweep, although the error is large, the peak frequency can be substantially specified (count value Cb) by scanning the first sweep range covering the transmission frequency deviation of the transmitter 4 in a short time. In the second sweep, since the peak frequency is substantially specified in the first sweep, the sweep range can be reduced as described above, and the tuning frequency can be further narrowed down by reducing the sweep speed.
[0034]
In this receiver, by performing the third sweep (step S007), it is possible to further suppress the variation in peak frequency (for example, the maximum value of the detected peak frequency—the range of 10 kHz at the minimum value).
[0035]
Therefore, the tuning accuracy can be improved by performing the third sweep as described above and fixing the oscillation frequency of the VCO 104 at the count value Cg. In addition, in this embodiment, the tuning frequency is specified to some extent by performing steps S001 to S005 before performing the third sweep, so that the sweep range is considerably narrowed in the third sweep, and a plurality of times in the third sweep. Even if the sweep is performed, it does not take a long time to complete the tuning.
[0036]
By performing such control, highly accurate scanning can be performed in a short time.
[0037]
When the first sweep (step S001) is completed, the first control logic 201 outputs a message to that effect to the second control logic 206, and the second control logic 206 is performing the first sweep in the widest range. If the signal indicating that the RSSI voltage VRSSI is higher than the reference voltage is not input from the comparator 204, it is determined that there is no feeling and the fact is transmitted to the controller 1b.
[0038]
When the control unit 1b receives a signal indicating that there is no sense of entry from the second control logic 206, the control unit 1b switches to the sleep mode. Thereby, the procedure after the second sweep (step S004) is not executed for the received wave signal whose RSSI voltage VRSSI does not exceed the reference voltage. Therefore, the code signal is not verified in the control unit 1b.
[0039]
FIG. 4 shows reception of a receiver of the present keyless entry receiver (the present invention) having a configuration in which a sleep mode is entered when a correct received wave signal is not sensed, and a keyless entry receiver (comparative example) that is not equipped. This shows the energized state of the unit when the correct received wave signal is not sensed (when there is no input).
[0040]
In the comparative example, the oscillation frequency of the VCO 104 is locked (step S011) regardless of the level of the RSSI voltage VRSSI, that is, whether or not the received wave signal is sensed. In the present invention, the first sweep is performed. Since the sleep mode is entered when the magnitude of the RSSI voltage VRSSI does not reach the reference voltage in (Step S001), the energization time is shorter than that of the comparative example, and the power consumption can be kept small.
[0041]
In this embodiment, the oscillation frequency is swept twice step by step while narrowing the low-speed narrow range until the oscillation frequency of the VCO is fixed, but the number of times is not necessarily limited to this. Depending on the transmission frequency of the machine and the stability of the oscillation frequency of the VCO (drift amount, variation), it may be increased to 3 times or more, and conversely, it may be decreased to 1 time. Even in the case of one time, when the RSSI voltage VRSSI does not exceed the reference voltage during the sweep period, the mode is shifted to the sleep mode, so that time is not spent on decoding the code, so that the power consumption can be reduced.
[0042]
In this embodiment, the sweep speed of the third sweep is faster than the sweep speed of the second sweep, but may be slower. In this case, the variation in the peak frequency average value becomes smaller as the sweep speed is slower, so the average number of times can be reduced accordingly.
[0043]
In addition, although each said embodiment was applied to the keyless entry control system using FM radio wave, it can be applied to what used other radio wave formats, such as an amplitude modulation (AM) radio wave.
[Brief description of the drawings]
FIG. 1 is an overall configuration diagram of a keyless entry control system to which a keyless entry receiver of the present invention is applied.
FIG. 2 is a flowchart for explaining the operation of the keyless entry receiver.
FIG. 3 is a first time chart for explaining the operation of the keyless entry receiver.
FIG. 4 is a second time chart for explaining the operation of the keyless entry receiver.
FIG. 5 is an overall configuration diagram of a keyless entry control system having a conventional keyless entry receiver.
[Explanation of symbols]
1 Keyless Entry Receiver 1a Receiver 103 Mixer 104 VCO (Local Oscillator)
105 Second bandpass filter (intermediate frequency filter)
111 RSSI circuit (reception signal strength detection means)
1b Control unit (intermittent operation control means)
2 Scanning circuit 2a Sweep control means 200 Peak timing detection circuit 201 Control logic 2b Sweep means 202 Counter 203 DA converter 2c Sensation determination means 204 Comparator 205 Reference voltage generator 206 Control logic 3 Body computer (vehicle control section)
4 key 4a transmitter

Claims (2)

It has a superheterodyne receiver that inputs the intermediate frequency signal of the received wave signal and the local oscillator signal of the local oscillator to the intermediate frequency filter, receives the radio wave modulated by the code signal and transmitted from the transmitter, and the code signal In the keyless entry receiver that outputs a control signal corresponding to the code signal to the vehicle control unit, the local oscillator uses an oscillator that is less stable than the crystal oscillator, and the reception unit receives the received signal strength. Receiving signal strength detecting means for detecting the oscillation frequency, sweeping means for controlling the local oscillator to sweep the oscillation frequency of the local oscillator, and sweep control means for controlling the sweeping means. It is provided with timing detection means for detecting the timing at which the received signal intensity takes the maximum value when the frequency is swept within a predetermined range set in advance. The oscillation frequency of the local oscillator is fixed based on the timing at which the received signal strength detected by the signal strength detecting means takes a peak value, and the received signal strength is compared with a preset lower limit value and the predetermined range. A keyless entry receiver comprising an sensation determining means for determining that there is no sensation when the received signal strength falls below a lower limit in the entire area.   2. The keyless entry receiver according to claim 1, further comprising intermittent operation control means for intermittently operating the receiving unit so as to alternately repeat an operation period in which the receiving unit operates and a sleep period in which the receiving unit stops operating. The intermittent operation control means is a keyless entry receiver that is set so as to stop the operation of the receiving unit and switch to the sleep period when the feeling determination means determines that there is no feeling.

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