JP2000087609A - Electronic key system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To restrain a misjudgment of a received-signal judging means due to the variation in the voltage of a battery in relation to an electronic key system in which a portable unit having both a received-signal judging means for judging the appropriateness of the request code transmitted from a fixed station and a transmitting means for transmitting a return signal on the basis of the result of the judgment is used. SOLUTION: A portable unit 24 is provided with a comparator 30 for repeatedly signalizing a request code from a received request signal, a judging part 32 for judging the conformity/inconformity of the repeatedly signalized request code with a prestored judging code, and a transmitting part 34 for transmitting a prescribed return signal when the judging part 32 judges the conformity. A voltage regulator converts the battery voltage into a stable regulator voltage Vreg. The reference voltage to the comparator 30 is produced by dividing the regulator voltage Vreg. During the transmission by means of the transmitting part 34, and for a prescribed period after completion of transmission, the input signal to the judging part 32 is invalidated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electronic key system, and more particularly, to a portable device having a function of receiving a request code transmitted from a vehicle and transmitting a return signal according to the received request code. For example, the present invention relates to an electronic key system suitable for controlling, for example, a door lock of a vehicle.

[0002]

2. Description of the Related Art Conventionally, Japanese Patent Application Laid-Open No.
A keyless entry device for a vehicle is known as disclosed in Japanese Patent No. This keyless entry device includes a portable transmitter carried by a user and a receiving device provided on a vehicle side. The portable transmitter transmits a predetermined ID code intermittently. If the received ID code matches the code stored in advance, the receiving device determines that the user is near the vehicle and releases the door lock. If the received ID code does not match the code stored in advance, the receiving device determines that the user has left the vehicle and locks the door of the vehicle. Therefore, according to the conventional keyless entry device, the door can be unlocked and locked simply by the user carrying the portable transmitter approaching or leaving the vehicle.

[0003] By the way, as a system having the same function as the above-mentioned keyless entry device, a portable device side includes:
A receiving determination unit that receives a request code transmitted from the vehicle side and determines whether the received request code matches a previously stored determination code; and a predetermined ID when the request code matches the determination code. There is known an electronic key system including a transmission unit for returning a code. In such an electronic key system, control such as unlocking of a door is performed only when the ID code returned from the portable device is received by the vehicle and the ID code matches the judgment code stored in advance.

[0004]

In the above-mentioned electronic key system, the reception judgment means decodes the request code using, for example, a comparator, and judges a match / mismatch with the judgment code based on the decoding result. by the way,
The portable device is driven by a battery as a power source because the portable device is carried by a user. For this reason, when the ID code is returned, the transmitting unit consumes a large amount of power, and the battery voltage decreases. Therefore, if the battery voltage is used as it is as the power source of the reception determining means, the decoding operation or the like by the above-described comparator will not be performed properly, and there is a possibility that the reception determining means may make an erroneous determination.

[0005] The present invention has been made in view of the above points, and has as its object to provide an electronic key system capable of suppressing the occurrence of erroneous determination due to a change in battery voltage.

[0006]

The above object is achieved by the present invention.
As described in, has a mobile station that operates with a battery as a power supply, the mobile station receives a request code transmitted from a fixed station, and reception determination means for determining the validity of the received request code, A transmission means for transmitting a predetermined return signal when the reception determination means determines that the mobile station is valid, wherein the mobile station includes at least a power supply path from the battery to the reception determination means. This is achieved by an electronic key system with voltage stabilization means.

In the invention according to claim 1, the mobile station comprises:
At least a voltage stabilizing unit is provided in a power supply path from the battery to the reception determining unit. Therefore, even if the battery voltage fluctuates, the stabilized power supply voltage is supplied to the reception determining means. As a result, a decrease in the accuracy of the determination by the reception determination unit is suppressed. Further, as described in claim 2,
2. The electronic key system according to claim 1, wherein the mobile station is an electronic key system that does not include the voltage stabilizing unit on a power supply path from the battery to the transmitting unit, and is effective in suppressing a decrease in transmission output. is there.

According to the second aspect of the present invention, no voltage stabilizing means is provided in a power supply path from the battery to the transmitting means. For this reason, since the battery voltage is directly supplied to the transmitting unit, a decrease in the transmission output by the transmitting unit is suppressed. In addition, the above object has a mobile station that operates using a battery as a power source, the mobile station receives a request code transmitted from a fixed station, and receives the request code transmitted from the fixed station. In an electronic key system comprising: reception determination means for determining validity; and transmission means for transmitting a predetermined return signal when the reception determination means determines that the mobile station is valid. The present invention is also achieved by an electronic key system including a determination invalidating unit that invalidates a determination operation of the reception determining unit in a voltage reduction expected state where a voltage reduction is expected.

In the present invention, the judgment operation of the reception judging means is invalidated in a voltage drop assumption state in which a battery voltage drop is assumed. For this reason, when there is a possibility that the reception determination unit makes an erroneous determination due to a voltage drop, the determination result of the reception determination unit is not used. Therefore, according to the present invention, the return signal is prevented from being erroneously transmitted based on the erroneous determination by the reception determination unit.

In this case, a large current is consumed at the time of transmission by the transmission means, so that the voltage of the battery tends to decrease. Therefore, as described in claim 4, claim 3
In the electronic key system described above, the voltage drop assumption state may be when the predetermined return signal is transmitted by the transmission unit.

After the battery voltage drops, it may take a certain period of time to recover. Therefore, as described in claim 5, in the electronic key system according to claim 3 or 4, the determination invalidating means performs the determination operation of the reception determining means for a predetermined time after the end of the voltage drop prediction state. The prohibited or invalidated state may be maintained.

[0012]

FIG. 1 is a block diagram showing an electronic key system according to an embodiment of the present invention. As shown in FIG. 1, the electronic key system includes a body multiplex ECU 10 provided in a vehicle. The ECU 10 is a control device that performs various controls related to the vehicle body such as control of automatic lighting of headlights and meters of a vehicle, control of an air conditioner, and door lock control. The body multiplex ECU 10 includes an illuminance sensor (not shown), a temperature sensor (not shown), an operation panel 11 for performing various settings, an occupant sensor 12, and a switch 13 operated by the occupant when the operation of the electronic key system is prohibited. Is connected.

The ECU 10 is also connected to door lock motors 14a to 14c, a steering lock device (not shown), and an immobilizer (not shown). The door lock motors 14a to 14c are respectively E
The door of the vehicle is locked / unlocked according to a control signal supplied from the CU 10. Further, the steering lock device sets / releases a steering lock state according to a control signal supplied from the ECU 10. Similarly, the immobilizer sets / cancels the engine start prohibition state according to the control signal supplied from the ECU 10.

A transmitter 16 and a receiver 20 are connected to the ECU 10. Transmitter 16 and receiver 20
Are both provided on the vehicle. The transmitter 16 is the ECU 1
On / off according to a control signal supplied from 0, a request signal is generated at the time of on, and the antennas 18a to 18c
Send from. The request signal is generated by encoding a predetermined request code for identifying a vehicle by, for example, an ASK (amplitude shift keying) method using a high-frequency signal of a predetermined frequency (for example, 134 KHz) as a carrier. Further, the receiver 20 receives an ID signal returned from a portable device 24 described later with the antenna 22, and
The ID code included in the signal is decoded and supplied to the ECU 10.

The portable device 24 receives and decodes the request signal from the transmitter 16 with the antenna 26, and when the decoded request code matches a predetermined judgment code or when the switch 27 is turned on, A return signal is transmitted from the transmission unit. Hereinafter, the configuration and operation of the portable device 24 will be described in detail with reference to FIG. FIG. 2 is a system circuit diagram showing a configuration of the portable device 24. As shown in FIG. 2, the portable device 24 includes an antenna 26. A filter 28 is connected to the antenna 26. Filter 2
Reference numeral 8 denotes a high-frequency filter such as a band-pass filter or a low-pass filter, which has a characteristic of passing a carrier band of a request signal transmitted from the transmitter 16. The output side of the filter 28 is connected to the anode of the diode D3. The cathode of the diode D3 is connected to the positive input terminal 30a of the comparator 30 via the resistor R2.
It is connected to the. The cathode of the diode D4 is connected to the connection between the filter 28 and the diode D3. The anode of the diode D4 is connected to the constant voltage power line 36.
It is connected to the. As described later, the constant voltage power supply line 3
6 is supplied with a positive regulator pressure Vreg. The anode of the diode D4 is connected to the ground line via the capacitor C2. The capacitor C2 bypasses the carrier of the request signal mixed in the constant voltage line 36 to the ground line. Diode D3 and resistor R2
A resistor R1 and a capacitor C1 are connected in parallel between the connection portion of the first and second and the ground line.

According to the above configuration, the request signal received by the antenna 26 and filtered by the filter 28 is detected by the voltage doubler rectifier circuit composed of the diodes D3 and D4, and is further subjected to the carrier component by the capacitor C1 and the resistor R2. Is removed, the signal is input to the positive input terminal 30a of the comparator 30. As described above, the request signal is
The request code is a signal in which a request code is encoded by an ASK method using a high-frequency signal as a carrier wave. Therefore, a signal is input to the positive input terminal 30a of the comparator 30a such that the signal goes high in response to the request code "1" and goes low (substantially 0 volt) in response to "0".

In the above configuration, the constant voltage power line 3
A predetermined bias current is always supplied to the diodes D3 and D4 by forming a series circuit including the diode D4, the diode D3, and the resistor R1 between the diode 6 and the ground line. With such a bias current, a change in characteristics due to a temperature change in the diodes D3 and D4 is suppressed to a small level. However, the anode side of the diode D4 may be grounded so that no bias current is supplied.

In the configuration shown in FIG. 2, the diode D
Although the detection is performed by voltage doubler rectification using D3 and D4, the diode D4 may be omitted and the detection may be performed by half-wave rectification using only the diode D3.
A resistor R is connected between the constant voltage power line 36 and the ground line.
3 and R4 are connected in series. Resistance R3 and R4
Is connected to the negative input terminal 30b of the comparator 30. Therefore, the regulator voltage Vreg is applied to the negative input terminal 30b of the comparator 30 by the resistors R3 and R3.
4 (= Vreg · R4 / (R3
+ R4)) is input. Hereinafter, the voltage input to the negative input terminal 30b of the comparator 30 is referred to as a reference voltage Vref.

A constant voltage power supply line 36 is connected to a power supply terminal of the comparator 30. Therefore, the comparator 30 is driven using the regulator voltage Vreg as the power supply voltage. When the positive input terminal 30a has a lower potential than the reference voltage Vref, the comparator 30
0c is output, and when the positive input terminal 30a is at a higher potential than the reference voltage Vref, the regulator voltage V is applied to the output terminal 30c.
A high level voltage VH substantially equal to reg is output. Therefore, the output terminal 30a of the comparator 30 outputs a signal that takes the high-level voltage VH for the logical value “1” of the request code included in the received request signal and the low-level voltage VL for the logical value “0”, that is, , A decoded signal obtained by decoding the request code is output.

The judging section 32 is connected to the output terminal 30c of the comparator 30. The determination unit 32 has an input invalid terminal (not shown in FIG. 2). The determination unit 32 validates the decoded signal input from the comparator 30 when the input invalid terminal is maintained at a low level, and when the voltage of the input invalid terminal becomes high, the comparator 30
Invalidates or ignores the decoded signal supplied from.

When the decoded signal input from the comparator 30 is valid, the judging section 32 decodes the request code based on the decoded signal. Judgment unit 3
2, a predetermined determination code is stored in advance. Then, the determination unit 32 supplies an ON signal (high-level voltage) to the transmission unit 34 when the decoded request code matches the determination code, and transmits the transmission signal when the received code does not match the determination code. An off signal (0
Volts).

In the present embodiment, the judgment section 32 having the above function is realized by hardware by an integrated circuit. However, the determination unit 32 may be realized by software using, for example, a microcomputer or the like. When the ON signal is supplied from the determination unit 32, the transmission unit 34 transmits a return signal including a predetermined ID code from the antenna 35. Therefore, according to the portable device 24, the return signal is transmitted only when the received request code matches the judgment code stored in advance. The above ID code is used to identify the portable device 24 that has transmitted the return signal.
The code is set so as to be unique to each portable device 24.

When receiving the return signal from the portable device 24, the receiver 20 decodes the ID code contained in the signal and supplies it to the ECU 10. The ECU 10 executes door unlocking, steering lock release, immobilizer release, and the like only when the received ID code matches a code stored in advance. Therefore, according to the electronic key system of the present embodiment, when the user having the portable device 24 having the ID code corresponding to the vehicle enters a predetermined operation area where radio waves can reach, the user can unlock the door. Control is automatic.

FIG. 3 is a block diagram showing the configuration of the power supply unit of the portable device 24. As shown in FIG. 3, the portable device 24 includes a battery 38 as a power source. Battery 38
Is a small and large capacity battery such as a lithium ion battery. The negative electrode of the battery 38 is grounded. Also,
The anode of the battery 38 is directly connected to the power supply terminals of the determination unit 32 and the transmission unit 34, and is also connected to the input terminal of the voltage regulator 40. The voltage regulator 40 converts the battery voltage VB supplied from the battery 38 into a stable regulator voltage Vreg, and outputs it to its output terminal. The constant voltage power supply line 36 described above
Is connected to the output terminal of the voltage regulator 40.
Therefore, a stable regulator voltage Vreg is supplied to the constant voltage power supply line 36. A capacitor C3 having a relatively large capacitance is connected between the output terminal of the voltage regulator 40 and the ground line.

In the above configuration, the battery voltage VB is supplied to the determination unit 32. However, the regulator voltage Vreg may be supplied to the determination unit 32.
By the way, the battery such as a lithium ion battery constituting the battery 38 in the present embodiment has such a characteristic that the output voltage decreases as the current consumption increases. For example, antenna 2
When the request signal is not input to No. 6, no signal is input to the comparator 30 and the determination unit 32, and
Since the transmitting unit 34 is in the sleep state, the current consumption is suppressed to a small value, and the battery voltage VB is maintained at substantially the same level as when no load is applied. When the request signal is input to the antenna 26, the current is increased by inputting the signal to the comparator 30 and the determination unit 32, and the battery voltage VB is lower than when no load is applied. Further, when the transmitting unit 34 transmits a return signal when the received request code matches the determination code, the transmitting unit 34 consumes a large current, so that the amount of decrease in the battery voltage VB is maximized.

As described above, the battery voltage VB fluctuates according to the magnitude of the current consumption. Therefore, if the reference voltage Vref of the comparator 30 is directly generated from the battery voltage VB, the reference voltage Vref also fluctuates. . In this case, the comparison process by the comparator 30 is not properly executed, the request code is not correctly decoded, and the determination unit 32 determines whether the request code matches the determination code (hereinafter, simply referred to as “determination process”). May be erroneous.

On the other hand, in the present embodiment, as described above, the reference voltage Vref is generated by dividing the regulator voltage Vreg. Therefore, even if the battery voltage VB fluctuates, the change in the reference voltage Vref is suppressed to a small value. Therefore, according to the present embodiment, the comparator 30 can generate an error-free decoded signal regardless of the fluctuation of the battery voltage VB, and can appropriately perform the determination processing by the determination unit 32. Further, since the regulator voltage Vreg is also used as the power supply voltage of the comparator 30, a stable operation of the comparator 30 can be ensured. Also in this sense, the determination process by the determination unit 32 can be performed with high reliability.

By the way, the battery voltage VB in the no-load state decreases according to an increase in the total current consumption since the start of use of the battery 38 (that is, a decrease in the remaining capacity of the battery 38). FIG. 4 shows an example of the relationship between the total current consumption of the battery 38 and the battery voltage VB at no load. In FIG. 4, the horizontal axis represents the battery 38.
, The vertical axis represents the battery voltage VB.

As shown in FIG. 4, in the initial state of the battery 38, the battery voltage VB is equal to the standard voltage Vs (for example, 3V).
V). As the current is consumed, the battery voltage VB decreases and the voltage V1
(E.g., 2.5 V), it is then kept substantially constant. Eventually, when the total current consumption exceeds a certain value (K shown in FIG. 4), the battery voltage VB starts to decrease rapidly, and the life of the battery 38 is reached.

In order to maximize the capacity of the battery 38, the total current consumption reaches the above-mentioned constant value K until
That is, it is appropriate to continue using the battery 38 while the battery voltage VB is kept at least at the voltage V1. Therefore, it is necessary to configure the power supply unit of the portable device 24 on the assumption that the battery voltage VB at no load drops to V1. The above-described voltage regulator 40 cannot output a voltage higher than the battery voltage VB. For this reason, in the present embodiment, the regulator voltage Vreg is selected to be a specified value V0 (for example, 2 V) smaller than the voltage V1.

As described above, the regulator voltage Vreg is set to a lower voltage than the use lower limit value V1 of the battery voltage VB. Therefore, if the regulator voltage Vreg is used as the driving power source of the transmitter 34, the transmission of the transmitter 34 Power cannot be sufficiently secured. On the other hand, in the present embodiment, as shown in FIG. 3 described above, by directly supplying the battery voltage VB as the driving power source of the transmitting unit 34, it is possible to secure the maximum transmission power according to the battery voltage VB. It is possible.

Since the transmitting section 34 consumes a large current during the transmitting operation, noise may be superimposed on the regulator voltage Vreg when the transmitting section 34 is started. When this noise is transmitted to the reference voltage Vref, the comparator 30
Noise is also superimposed on the decoded signal output from the
Will cause an error in the determination process. On the other hand, in the present embodiment, since the capacitor C3 is connected between the output terminal of the voltage regulator 40 and the ground line, noise superimposed on the regulator voltage Vreg is suppressed to be small. Is prevented from being erroneous.

As described above, the battery voltage VB may decrease with V1 as the lower limit when the battery 38 is not loaded. When a lithium ion battery is used as the battery 38, the battery voltage VB decreases as the temperature decreases. On the other hand, as described above, during the transmission operation of the transmission unit 34, the battery voltage VB is lower than at the time of no load.

FIG. 5 shows an example of a temporal change of the battery voltage VB when the transmission operation of the transmission section 34 is turned on / off. 5A shows a time change of the battery voltage VB, and FIG. 5B shows a time change of an ON / OFF state of the transmission operation of the transmission unit 34. As shown in FIG. 5, at the same time when the transmission operation of the transmission unit 34 is turned on, the battery voltage VB is relatively significantly reduced. Therefore, the battery voltage V increases due to an increase in the total current consumption of the battery 38.
When the transmitting unit 34 performs a transmission operation in a state where B has decreased to V1 or in a state where the battery voltage VB has decreased due to a decrease in temperature, the battery voltage VB changes to the regulator pressure V
It is possible that reg falls below a prescribed value V0. As described above, the voltage regulator 40 cannot generate a voltage higher than the battery voltage VB. Therefore, the battery voltage VB becomes equal to the specified value V0 of the regulator pressure Vreg.
Is lower than the reference voltage Vreg, the reference voltage Vref of the comparator 30 changes because the regulator pressure Vreg decreases. Further, when the transmission operation of the transmission unit 34 is turned off, as shown in FIG. 5 (A), the battery voltage VB exhibits a characteristic of gradually recovering to a value at the time of no load. For this reason, even after the transmission operation is turned off, the regulator voltage V
There is a possibility that the state where reg is lower than the prescribed value V0 is maintained.

Therefore, in the present embodiment, when the transmission operation by the transmission unit 34 is started, thereafter, from the end of the transmission operation,
The time required for the battery voltage VB to recover (FIG. 5
Until the time T) shown in FIG.
Ignore the decoded data supplied from 0 to the determination unit 32 (that is, invalidate the determination operation by the determination unit 32)
I have to do that.

FIG. 6 is an example of a time chart showing the operation of the electronic key system of this embodiment. In FIG.
(A) Request signal on / off state in order from the top,
(B) ON / OFF state of the transmission operation of the transmission unit 34, (C)
The battery voltage VB and the (D) time change of the valid / invalid state of the input signal to the determination unit 32 are shown. As shown in FIG. 6, the reception of the request signal ends at time t1,
When the request code included therein matches the identification code, transmission of the return signal is started almost simultaneously with time t1. Therefore, after time t1, the battery voltage VB becomes low, and the input signal to the determination unit 32 is invalidated. At the time t2, when the transmission of the return signal ends, the battery voltage VB gradually recovers thereafter. Then, at time t3 when time T has elapsed from time t2 (that is, when the battery voltage has recovered to the original voltage), the input signal to the determination unit 32 is enabled again.

FIG. 7 shows an example of the invalidation circuit 42 for realizing the above operation. As shown in FIG. 7, the invalidation circuit is configured by an RC integration circuit including a resistor R5 and a capacitor C4 connected to the input invalidation terminal 32a of the determination unit 32. A drive signal (hereinafter, referred to as a transmission drive signal) supplied from the determination unit 32 to the transmission unit 34 is input to the RC integration circuit.

According to this configuration, while the transmitting section 34 is performing the transmitting operation (ie, while the transmission drive signal is maintained at the high level), the input invalid terminal 32a is connected to the high level via the resistor R5. Is input. As described above, when a high-level signal is input to the input invalidation terminal 32a, the determination unit 32 is configured to invalidate the input signal from the comparator 30. Therefore, the transmitting unit 34
During the transmission operation, the input signal to the determination unit 32 is invalidated, and the determination operation by the determination unit 32 is not performed. When the transmission operation of the transmission unit 34 is completed (ie, when the transmission drive signal changes from a high-level ON signal to a low-level OFF signal), the input invalid terminal 3
The signal level input to 2a gradually decreases according to the time constant determined by R5 and C4 of the RC integration circuit. Therefore, even after the transmission operation of the transmission unit 34 ends, the input signal to the determination unit 32 is invalidated until the input level to the input invalidation terminal 32a becomes low. Therefore, after the transmission drive signal changes to low level, the input invalid terminal 32a
The time until the input of the input terminal becomes the low level is the time T described above.
By setting the time constant of the RC integrator so that the operation shown in FIG. 6 can be realized.

According to the above-described configuration, the state in which the battery voltage VB has dropped due to the transmitting operation of the transmitting unit 34, and
In the process of recovering the battery VB after the end of the transmission operation, the input signal to the determination unit 32 is invalidated, so that the determination operation by the determination unit 32 in a situation where the reference voltage Vref of the comparator 30 may fluctuate. Is prevented from being performed.

The above-described invalidation circuit 42 may be provided externally to the determination unit 32 or may be incorporated in the determination unit 32. When the determination unit 32 is configured by a microcomputer, the internal clock is used to measure the elapsed time after the transmission drive signal is changed from ON to OFF. , The function similar to that of the invalidation circuit 42 may be realized by ignoring the signal input from the comparator 30.

As described above, according to this embodiment, the reference voltage Vref of the comparator 32 is set to the regulator voltage Vr.
EG is generated by dividing the
The fluctuation of the reference voltage Vref can be suppressed even when the battery voltage VB fluctuates due to the change of the current consumption. Therefore, according to the electronic key system of the present embodiment, it is possible to suppress the erroneous determination of the determination unit 32 due to the fluctuation of the battery voltage VB. Further, by directly supplying the battery voltage VB to the transmission unit 34 without passing through the voltage regulator 40, the transmission output by the transmission unit 34 can be secured to the maximum.

Further, as described above, according to the present embodiment, it is possible to prevent the determination processing by the determination unit 32 from being performed in a situation where the reference voltage Vref of the comparator 30 may fluctuate. It is possible to prevent the transmission unit 32 from erroneously transmitting the return signal due to the erroneous determination of the determination unit 32. Therefore, according to the electronic key system of the present embodiment, it is possible to suppress improper execution of control such as unlocking of the door on the vehicle side due to the return signal transmitted erroneously.

Next, a second embodiment of the present invention will be described. The electronic key system of the present embodiment is realized by using the portable device 100 instead of the portable device 24 of the first embodiment. FIG. 8 is a block circuit diagram illustrating the overall configuration of the portable device 100 according to the present embodiment. 8, the same components as those of the portable device 24 shown in FIG. 2 are denoted by the same reference numerals, and description thereof will be omitted.

In this embodiment, the antenna 26 is constituted by an LC parallel resonance circuit. Therefore, antenna 2
With the resonance characteristic of No. 6, selectivity for the carrier frequency of the request signal transmitted from the transmitter 16 can be ensured. Therefore, in the present embodiment, as shown in FIG. 8, a capacitor C5 is provided instead of the filter 28 of the first embodiment. However, for better selectivity,
As in the first embodiment, a filter 28 may be provided. The portable device 100 further includes a capacitor C6 instead of the resistor R2 of the first embodiment. Therefore, in the present embodiment, the rectifier circuit and the comparator 30
Are AC-coupled (AC-coupled) via a capacitor C6.

The negative input terminal 30b of the comparator 30
It is connected to a connection point between the resistors R3 and R4 via the resistor R6. Further, the positive input terminal 3 of the comparator 30
Oa is connected to a connection point between the resistors R3 and R4 via a resistor R7, and is grounded via a resistor R8. Accordingly, the reference voltage Vref obtained by dividing the regulator voltage Vreg by the resistors R3 and R4 is input to the negative input terminal 30b, and the positive input terminal 30a
The voltage Vi obtained by dividing the reference voltage Vref by the resistors R7 and R8 (= Vref.R8 / (R7 + R8)
<Vref) is input.

Therefore, in a state where the request signal is not received by the antenna 26 or a state where the request code included in the request signal is “0”, the positive input terminal 30
When the input voltage to a becomes Vi lower than the reference voltage Vref, the output voltage from the output terminal 30c becomes low level (0 volt). On the other hand, when the request signal is received by the antenna 26, the received signal is detected by the diodes D3 and D4. Therefore, the input voltage to the positive input terminal 30a increases in response to the request code “1” and exceeds the reference voltage Vref,
A high-level voltage is output from the output terminal 30c. Thus, a decoded signal of the request signal is output from the output terminal 30c of the comparator 30.

In the first embodiment, the rectifier circuit and the comparator 30 are DC-coupled via the resistor R2. Therefore, when the received request signal changes from “1” to “0”, the charge stored in the capacitor C1 is discharged via the resistor R1.
The input voltage to the positive input terminal 30a gradually decreases with a time constant determined by C1 and R1. Therefore, after the request signal changes from the high level to the low level, the positive input terminal 3
A time delay occurs until the input voltage to 0a falls below the reference voltage Vref, that is, until the decoded signal output to the output terminal 30a changes from the high-level voltage VH to the low-level voltage VL. Such time delay is caused by the reference voltage Vr
By setting ef to be high, it can be suppressed, but in this case, a similar time delay occurs when the request signal changes from the low level to the high level. As described above, in the case of the DC coupling, a phenomenon that the duty ratio of the decoded request code does not match the duty ratio of the original request code due to the delay of the change of the decoded signal with respect to the change of the request signal occurs. It cannot be completely prevented from occurring.

On the other hand, in the present embodiment, the rectifier circuit and the comparator 30 are AC-coupled as described above. For this reason, when the received request signal changes between “1” and “0”, there is no delay in the voltage change due to the discharge of the DC component as in the case of the DC coupling described above. The input voltage to the terminal 30a changes around the above-mentioned voltage Vi immediately following the change of the request signal. Therefore, by setting the voltage Vi so that the difference from the reference voltage Vref is sufficiently small, it is possible to obtain a decoded signal that faithfully reproduces the duty ratio of the request code included in the received request signal.

As described above, in this embodiment, the input to the comparator 30 is performed by AC coupling.
When the request signal continues to be at the high level ("1"), the input level to the comparator 30 gradually decreases to a low level at a speed corresponding to a time constant determined by each resistor and capacitor included in the circuit. . Therefore, by setting the resistance value and the capacitance of the request code so that the above time constant is sufficiently large with respect to the maximum value of the time during which the logical value “1” is maintained in the request code, the request code “1” is maintained. Also in this case, the decoding process by the comparator 30 can be properly performed.

In this embodiment, as in the first embodiment, the reference voltage Vref is generated based on the regulator voltage Vreg of the voltage regulator 40 shown in FIG. It is possible to suppress the determination. Also, by realizing the operation timing shown in FIG. 6 by the invalidation circuit 42 shown in FIG. 7, under the situation where the erroneous determination may be made by the determination unit 32, the return signal is transmitted based on the determination result. Can be prevented.

In the first and second embodiments, the comparator 30 and the judging section 32 correspond to the receiving judging means, the transmitting section 34 corresponds to the transmitting means, and the voltage regulator 40 corresponds to the transmitting means. The invalidating circuit 42 corresponds to the voltage stabilizing means described in the claims, and the invalidating circuit 42 corresponds to the determining invalidating means described in the claims.

[0052]

As described above, according to the first aspect of the present invention, even when the battery voltage fluctuates, it is possible to suppress a decrease in the accuracy of the determination by the reception determining means. Further, according to the second aspect of the invention, it is possible to suppress a decrease in the transmission output by the transmission unit.

Further, according to the third to fifth aspects of the present invention, it is possible to prevent the use of the determination result by the reception determining means when an erroneous determination by the reception determining means is assumed. Therefore, according to the present invention, erroneous transmission of a return signal based on an erroneous determination can be suppressed.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of an electronic key system according to an embodiment of the present invention.

FIG. 2 is a block circuit diagram showing a configuration of a portable device provided in the electronic key system of the embodiment.

FIG. 3 is a block diagram illustrating a power supply unit of the portable device.

FIG. 4 shows the total current consumption of the battery and the battery voltage V
FIG. 9 is a diagram illustrating an example of a relationship with B.

FIG. 5A is a diagram illustrating a time change of a battery voltage VB when a transmitting unit performs a transmitting operation. (B) is a diagram showing a time change of the on / off state of the transmission operation of the transmission unit.

FIGS. 6A and 6B are time charts showing an example of the operation of the electronic key system according to the present embodiment, wherein FIG. 6A shows an on / off state of a request signal, and FIG. (C) shows a change in battery voltage, and (D) shows a valid / invalid state of an input signal to the determination unit.

FIG. 7 is a diagram showing an invalidation circuit provided in the portable device.

FIG. 8 is a block circuit diagram showing a configuration of a portable device provided in an electronic key system according to a second embodiment of the present invention.

[Explanation of symbols]

 24, 100 Portable device 30 Comparator 32 Judgment unit 34 Transmission unit 38 Battery 40 Voltage regulator 42 Invalidation circuit

Continuation of the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (reference) H02J 7/00 302 H02J 7/00 302A F term (reference) 2E203 AA22 BB08 BB65 FF23 FF27 FF36 2E204 AA01 BB03 CC03 DD00 DD01 LL02 MM04 NN00 5G003 BA01 CA12 DA14 DA16 DA17 FA04 GC06 5G065 BA02 EA02 FA02 GA07 HA04 JA04 KA05 LA07 MA07 MA09

Claims (5)

[Claims] 1. A mobile station that operates using a battery as a power source. The mobile station receives a request code transmitted from a fixed station and determines the validity of the received request code. An electronic key system comprising: a transmission unit that transmits a predetermined return signal when the reception determination unit determines that the reception is appropriate. The mobile station includes a power supply path at least from the battery to the reception determination unit. An electronic key system comprising voltage stabilizing means. 2. The electronic key system according to claim 1, wherein the mobile station does not include the voltage stabilizing unit in a power supply path from the battery to the transmitting unit. 3. A mobile station that operates using a battery as a power supply, the mobile station receives a request code transmitted from a fixed station, and determines the validity of the received request code; An electronic key system comprising: a transmission unit that transmits a predetermined return signal when the reception determination unit determines that the voltage is appropriate. An electronic key system comprising: a determination invalidating means for invalidating a determination operation of the reception determining means. 4. The electronic key system according to claim 3, wherein the assumed voltage drop state is a time when the predetermined return signal is transmitted by the transmitting unit. 5. The electronic key system according to claim 3, wherein the determination invalidating unit maintains a state in which the determination operation of the reception determining unit is disabled for a predetermined time after the end of the voltage drop prediction state. An electronic key system characterized by: