JP2012182703A - Gain adjusting device and receiver unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a gain adjusting device which can send an amplification signal subjected to gain adjustment to the post-stage side by performing optimum gain adjustment while leaving the amplitude information superimposed on an input signal even when a signal absence state is provided after a signal presence state, and to provide a receiver unit, or the like.SOLUTION: A reception gain adjustment unit 314 which adjusts the gain of a received signal, i.e. an input signal, comprises: an amplifier 400 which amplifies the received signal; a comparison circuit 412 which compares an amplification signal by the amplifier 400 with a reference signal; a gain adjustment circuit 414 which adjusts the gain by using the comparison results from the comparison circuit 412; and a time constant setting circuit 416 which sets a time constant corresponding to the speed for adjusting the gain. The gain adjustment circuit 414 adjusts the gain of the input signal at a speed corresponding to the time constant set by the time constant setting circuit 416.

Description

  The present invention relates to a gain adjusting device and a receiving device including the same, and more particularly to a gain adjusting device that adjusts the gain of an input signal and a receiving device including the same.

  2. Description of the Related Art Conventionally, an electronic key system has been put to practical use in which key data transmitted by an electronic key is authenticated to perform control for permitting locking and releasing of a door of a vehicle such as an automobile and starting and stopping of an engine. This type of electronic key is equipped with a transmission circuit and a reception circuit. The reception circuit having high frequency selectivity correctly receives signals from the vehicle even in the presence of disturbance noise, and responds to the vehicle by the transmission circuit. Send a signal.

  Generally, a transmission signal (received signal of an electronic key) from a vehicle is an amplitude shift keying (ASK) signal (amplitude modulation signal in a broad sense), and transmission data is included in the amplitude component of the signal. Is a signal superimposed. Since the electronic key leaves this amplitude component and sends it to the demodulation side, it is necessary to amplify the received signal without saturating the output of the amplifier, and gain adjustment of the received signal is important.

FIG. 16 is a block diagram showing a configuration example of a general receiving circuit included in the electronic key.
FIG. 17 shows an operation explanatory diagram of the receiving circuit of FIG. In FIG. 17, the envelope of the received signal is schematically represented by a rectangular wave.

  The receiving circuit 10 included in the electronic key includes an amplifier 12, a gain adjusting circuit 14 that adjusts the gain of the amplifier 12 based on the signal amplified by the amplifier 12, and an attenuation that attenuates the received signal under the control of the gain adjusting circuit 14. Circuit 16. In the receiving circuit 10, the gain adjustment circuit 14 generates a control signal Cont for controlling the attenuation degree of the attenuation circuit 16 based on the amplitude of the amplified signal amplified by the amplifier 12. In FIG. 17, the gain of the receiving circuit 10 decreases as the potential of the control signal Cont increases. The attenuation circuit 16 that has received the control signal Cont from the gain adjustment circuit 14 adjusts the attenuation of the received signal based on the control signal Cont. The received signal attenuated by the attenuation circuit 16 with the attenuation according to the control signal Cont is input to the amplifier 12. In this way, the gain of the received signal received by the receiving circuit 10 is adjusted, and the amplitude of the amplified signal is controlled to be a desired amplitude.

  In such a receiving circuit 10, the gain of the received signal is determined in a period in which the burst signal B1 is received as the received signal. Thereafter, communication data C1 to be demodulated is sent. The communication data C1 represents data “0” or data “1” corresponding to the length between the edges. In the reception period of the communication data C1, by amplifying the reception signal by fixing (locking) the gain determined using the burst signal B1, an amplified signal having substantially the same amplitude can be obtained regardless of the intensity of the transmission signal from the vehicle. Can be passed to the demodulator side. As described above, the reception circuit 10 adjusts the gain of the reception signal by determining the gain of the reception signal during reception of the burst signal at the beginning of communication.

  For example, Patent Literature 1 to Patent Literature 5 disclose gain adjustment of a received signal in an electronic key constituting such an electronic key system.

  In Patent Document 1, an adjustment voltage is generated so that the level output from the received signal strength indicator that receives the amplified intermediate frequency signal is maximized, and the adjustment voltage is supplied to the matching circuit unit. A remote keyless entry system is disclosed. Patent Document 2 discloses a vehicular electronic key device in which the reception sensitivity is reduced based on the result of collation of the electronic key and the reception sensitivity is restored when the engine is stopped. Patent Document 3 discloses a vehicle electronic key system in which the reception sensitivity of a reception circuit is switched based on an operation of a reception sensitivity switching switch on the portable device side. Patent Document 4 discloses a keyless entry device including a receiving unit that switches between a high-sensitivity circuit and an anti-jamming circuit. Patent Document 5 discloses a passive entry system in which reception sensitivity is lowered when background noise is detected.

JP 2003-18664 A Japanese Patent Laying-Open No. 2005-207083 JP 2006-306161 A JP 2007-39989 A JP 2010-216142 A

  In this type of electronic key system, in order to reduce power consumption, it is required to transmit a signal including the burst signal of FIG. 17 in as short a period as possible. Therefore, the electronic key is required to converge the gain adjustment of the received signal including the burst signal as quickly as possible.

  On the other hand, the transmission side may send communication data after setting a non-signal state called a space after a burst signal. In this case, if the gain adjustment of the received signal is converged as quickly as possible, even if the gain adjustment of the received signal is performed based on the burst signal, the gain before the adjustment is restored immediately after detecting the no-signal state.

  In this regard, in the techniques disclosed in Patent Documents 1 to 5, gain adjustment of the received signal is performed during reception regardless of a signaled state and a no-signal state. Therefore, in the techniques disclosed in Patent Documents 1 to 5, adjustment is performed to lower the gain in a signaled state and increase the gain in a no-signal state. Therefore, in the techniques disclosed in Patent Documents 1 to 5, there is a problem that even if the gain adjustment of the received signal is performed based on the burst signal, the gain before the adjustment is restored immediately after detecting the no-signal state. Remain. As a result, it becomes difficult to extract information superimposed on the amplitude component, and the demodulation side may not be able to demodulate.

  As described above, in the techniques disclosed in Patent Documents 1 to 5, even when a no-signal state is provided after a signaled state, optimal gain adjustment is performed while leaving amplitude information superimposed on the input signal. In some cases, the amplified signal after gain adjustment cannot be sent to the subsequent stage.

  The present invention has been made in view of the above technical problems. According to some aspects of the present invention, even when a no-signal state is provided after a presence / absence state, an optimum gain adjustment is performed while the amplitude information superimposed on the input signal remains, and a gain is obtained on the subsequent stage side. It is possible to provide a gain adjusting device, a receiving device, and the like that can send the amplified signal after adjustment.

  (1) According to a first aspect of the present invention, there is provided a gain adjusting device that adjusts the gain of an input signal, an amplifier circuit that amplifies the input signal, a comparison circuit that compares an amplified signal by the amplifier circuit and a reference signal, A gain adjustment circuit for adjusting the gain using a comparison result of the comparison circuit, and a time constant setting circuit for setting a time constant corresponding to a speed for adjusting the gain, wherein the gain adjustment circuit includes the time adjustment circuit. The gain is adjusted at a speed corresponding to the time constant set by the constant setting circuit.

  In this aspect, when the gain is adjusted using the comparison result of the comparison circuit that compares the amplified signal by the amplifier circuit that amplifies the input signal and the reference signal, the time constant set by the time constant setting circuit is set. The gain of the input signal is adjusted by the speed. In this way, when amplitude information is superimposed on the input signal, a no-signal state is provided after the presence / absence of signal, the gain adjusted in the presence / absence of signal returns to the pre-adjustment gain, and the amplitude information is lost. Can be avoided. In other words, even when a no-signal state is provided after the presence of a signal, the gain adjustment is performed by performing optimum gain adjustment while leaving the amplitude information superimposed on the input signal, and sending the amplified signal after gain adjustment to the subsequent stage side. An apparatus can be provided.

  (2) In the gain adjustment device according to the second aspect of the present invention, in the first aspect, the gain adjustment circuit charges and discharges the predetermined node, and a potential holding circuit that holds the potential of the predetermined node. And a charge / discharge circuit that controls a current value using a comparison result of the comparison circuit, and adjusts the gain according to the potential of the predetermined node.

  In this aspect, the gain adjustment circuit includes a potential holding circuit and a charge / discharge circuit that controls a current value for charging / discharging a predetermined node of the potential holding circuit, and adjusts the gain according to the potential of the node. I have to. As a result, the gain can be adjusted with a very simple configuration at a speed corresponding to the time constant corresponding to the charge / discharge characteristics of the charge of the node.

  (3) In the gain adjustment device according to the third aspect of the present invention, in the second aspect, the charge / discharge circuit includes a charge current source and a discharge current source, and the gain adjustment circuit includes the The adjustment speed of gain control based on the comparison result of the comparison circuit is adjusted to a current value for charging / discharging the predetermined node by the charging current source and the discharging current source.

  In this embodiment, a predetermined node is charged and discharged by the charging current source and the discharging current source. This avoids a situation where, for example, the node potential rises when an input signal is input while discharging the node charge, and the gain adjustment cannot be continued due to, for example, the attenuation becoming too large. Can do.

  (4) In the gain adjusting apparatus according to the fourth aspect of the present invention, in the third aspect, the current value of the charging current source is larger than the current value of the discharging current source.

  According to this aspect, in addition to the above-described effect, the gain can be reliably adjusted by charging the charge of a predetermined node.

  (5) In the gain adjusting apparatus according to the fifth aspect of the present invention, in the second aspect, the charge / discharge circuit corresponds to one or a plurality of charging current sources, each corresponding to a charging current source circuit. One or a plurality of discharge current sources provided, and the gain adjustment circuit is configured to select the predetermined current by a set of the charge current source and the discharge current source selected using a comparison result of the comparison circuit. The current value for charging / discharging the node is adjusted.

  According to this aspect, by switching the pair of the discharge current source and the charge current source, the time constant can be switched with a very simple configuration.

  (6) In the gain adjusting apparatus according to the sixth aspect of the present invention, in the fifth aspect, the current value of each charging current source is larger than the current value of the corresponding discharging current source.

  According to this aspect, in addition to the above-described effect, the gain can be reliably adjusted by charging the charge of a predetermined node.

  (7) A gain adjustment apparatus according to a seventh aspect of the present invention includes the attenuation circuit for attenuating the input signal in any one of the first to sixth aspects, and the amplification circuit includes a fixed gain amplifier. The attenuation circuit attenuates the input signal at a speed corresponding to the time constant set by the time constant setting circuit.

  According to this aspect, since the attenuation circuit is provided on the input side of the amplification circuit configured by the fixed gain amplifier, the input signal is transmitted by the attenuation circuit at a speed corresponding to the time constant set by the time constant setting circuit. The gain can be adjusted by the attenuation. Therefore, even when a no-signal state is provided after a signal-present state, an optimum gain adjustment is performed while leaving the amplitude information superimposed on the input signal, and a gain adjustment for sending an amplified signal after gain adjustment to the subsequent stage side The configuration of the apparatus can be simplified.

  (8) In the gain adjusting apparatus according to the eighth aspect of the present invention, in any one of the first to sixth aspects, the amplifier circuit is a variable gain amplifier and is adjusted by the time constant setting circuit. The gain of the amplifier circuit is changed at a speed corresponding to the time constant.

  According to this aspect, since the amplifier circuit is configured by the variable gain amplifier, the gain of the gain adjusting device is adjusted by changing the gain of the amplifier circuit at a speed corresponding to the time constant set by the time constant setting circuit. Will be able to. Therefore, even when a no-signal state is provided after a signal-present state, an optimum gain adjustment is performed while leaving the amplitude information superimposed on the input signal, and a gain adjustment for sending an amplified signal after gain adjustment to the subsequent stage side The configuration of the apparatus can be simplified.

  (9) In the gain adjusting apparatus according to the ninth aspect of the present invention, in any one of the first to eighth aspects, the input signal is an amplitude modulation signal, and the time constant setting circuit is The time constant is adjusted according to the demodulation result of the amplified signal.

Here, the amplitude modulation signal is a signal obtained by superimposing transmission data on an amplitude component. An example of such an amplitude modulation signal is an ASK signal.
According to this aspect, even when the no-signal state is provided after the presence / absence signal state, the optimum gain adjustment is performed while leaving the amplitude information superimposed on the amplitude-modulated signal, and the demodulator provided on the rear stage side It becomes possible to provide a gain adjusting device that sends an amplified signal after gain adjustment. This makes it possible to adjust the reception gain so that amplitude information that can be demodulated is maintained even when the signaled state provided before the no-signal state is a short period.

  (10) In the gain adjustment device according to the tenth aspect of the present invention, in any one of the first to ninth aspects, the time constant setting circuit is configured to be in a signaled state during the gain adjustment. The first time constant is switched to the second time constant in the no-signal state, and after the gain adjustment, the third time constant is switched.

  In this aspect, during the gain adjustment, the time constant is switched according to the signaled state or the received signal state, and the time constant is switched even after the gain is adjusted. As a result, an optimum gain adjustment can be performed while leaving the amplitude information superimposed on the input signal, and the gain-adjusted amplified signal can be sent to the subsequent stage side.

  (11) In the gain adjusting apparatus according to the eleventh aspect of the present invention, in the tenth aspect, the first time constant is larger than the second time constant and larger than the third time constant. .

  In this mode, the gain of the input signal is adjusted at a speed corresponding to the first time constant in the signal-carrying state, and the gain is adjusted at a speed corresponding to the second time constant in the no-signal state following the signal-carrying state. Like to do. Since the second time constant is larger than the first time constant, the gain adjusted in the signaled state slowly returns to the original in the no-signal state. For this reason, it is possible to avoid a situation where the gain adjusted in the signaled state returns to the original state when the reception gain adjustment in the signaled state after the no-signal state is started. Similarly, after the gain adjustment, the gain is adjusted at a speed corresponding to the third time constant that is larger than the first time constant, so that the gain adjusted in the signaled state is the signal after the no-signal state. It is possible to avoid the situation of returning to the original state at the start of the reception gain adjustment in the state.

  (12) In the gain adjusting apparatus according to the twelfth aspect of the present invention, in the tenth aspect or the eleventh aspect, the time constant setting circuit has an infinite second time constant and the third time constant. Adjust the time constant to be large.

  According to this aspect, since the gain is fixed in the no-signal state and the gain is also fixed after the gain adjustment, the gain adjusted in the signal-added state is received in the signal-added state after the no-signal state. It is possible to surely avoid the situation where the gain adjustment starts at the start of gain adjustment.

  (13) According to a thirteenth aspect of the present invention, in the receiver, the receiver receives the amplitude modulation signal, and adjusts the reception gain of the amplitude modulation signal received by the receiver. A gain adjustment device; and a demodulator that demodulates the signal based on the signal amplified with the reception gain adjusted by the gain adjustment device.

  According to this aspect, even when the no signal state is provided after the presence signal state, the optimum gain adjustment is performed while leaving the amplitude information superimposed on the input signal, and the amplified signal after the gain adjustment is performed on the subsequent stage side. It is possible to provide a receiving device to which a gain adjusting device capable of transmitting the signal is applied.

The figure which shows the outline | summary of a structure of the electronic key system in 1st Embodiment. The figure which shows an example of the functional block of the electronic key of FIG. FIG. 3 is a block diagram of a configuration example of a reception gain adjustment unit in FIG. 2. FIG. 4 is a circuit diagram of a configuration example of a reception gain adjustment unit in FIG. 3. Explanatory drawing of the amplitude modulation signal sent from the vehicle in 1st Embodiment. FIG. 6 is a first explanatory diagram of a start pattern signal in FIG. 5. FIG. 6 is a second explanatory diagram of the start pattern signal of FIG. 5. FIG. 4 is a flowchart of an operation example of a reception gain adjustment unit in FIG. 3. The figure which shows the operation example of the reception gain adjustment part in 1st Embodiment. The circuit diagram of the example of composition of the gain adjustment circuit in the modification of a 1st embodiment. FIG. 17 is an explanatory diagram of an operation example when a start pattern signal is received by providing a space after a burst signal in the reception circuit of FIG. 16. FIG. 17 is an explanatory diagram of an operation example when noise is included in a reception signal in the reception circuit of FIG. 16. Explanatory drawing of the operation example in case noise is contained in a received signal in 1st Embodiment. The block diagram of the structural example of the reception gain adjustment part in 2nd Embodiment. The circuit diagram of the example of composition of the receiving gain adjustment part in a 2nd embodiment. The block diagram of the structural example of the general receiving circuit with which an electronic key is provided. FIG. 17 is an operation explanatory diagram of the receiving circuit of FIG. 16.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The embodiments described below do not unduly limit the contents of the present invention described in the claims. In addition, all of the configurations described below are not necessarily indispensable configuration requirements for solving the problems of the present invention.

  In the following embodiments, a reception gain adjustment device that adjusts the gain of a reception signal that is an amplitude modulation signal as an input signal and a reception device that includes the reception gain adjustment device will be described as an example. The present invention is not limited to a gain adjusting device or a receiving device, and can be applied to a device that adjusts the gain of an input signal.

[First Embodiment]
FIG. 1 shows an outline of the configuration of the electronic key system according to the first embodiment of the present invention. FIG. 1 illustrates an example in which the electronic key system includes a vehicle and an electronic key, but the components of the electronic key system in the first embodiment are not limited to those shown in FIG. .

  The electronic key system 100 includes a vehicle 200 such as an automobile and an electronic key (electronic device in a broad sense) 300 as a portable device. The vehicle 200 periodically transmits an amplitude modulation signal 202 having a first frequency on which data to be transmitted to the electronic key 300 is superimposed, and waits for a response from the electronic key 300. The amplitude modulation signal 202 is an ASK signal in which transmission data is superimposed on the amplitude component of the signal. When the electronic key 300 receives the amplitude modulation signal 202 from the vehicle 200, the electronic key 300 responds to the vehicle 200 with a signal 204 of the second frequency. Thereafter, a signal is exchanged between the vehicle 200 and the electronic key 300, and when the electronic key 300 is authenticated, predetermined control such as locking and releasing of the door of the vehicle 200, starting and stopping of the engine is permitted. It is like that.

  The electronic key 300 operates with a built-in battery, and needs to operate with low power consumption in order to respond to a call from the vehicle 200. Therefore, the first frequency of the amplitude modulation signal 202 received by the electronic key 300 is set to a low frequency. In addition, the electronic key 300 has high frequency selectivity when receiving a signal so as to minimize the influence on disturbance noise of an engine or other electronic components mounted on the vehicle 200 as much as possible. Accordingly, the electronic key 300 adjusts the gain of the received signal so that the distortion of the received signal increases and the amplitude information that can be demodulated is sent to the demodulation side.

  FIG. 2 shows an example of functional blocks of the electronic key 300 of FIG. In FIG. 2, the same parts as those in FIG.

  The electronic key 300 includes a receiving unit (receiving device) 310, a communication processing unit 320, and a transmitting unit 330. The reception unit 310 includes a tuning circuit (receiver in a broad sense) 312, a reception gain adjustment unit (a gain adjustment device, a reception gain adjustment device, an amplification unit in a broad sense) 314, and a demodulator 316. . The tuning circuit 312 includes a parallel resonant circuit in which a coil 340 and a capacitor 342 are connected in parallel. The reception gain adjustment unit 314 is supplied with the amplitude modulation signal received by the tuning circuit 312, the demodulation result of the demodulator 316, and the processing result performed by the communication processing unit 320 using the demodulation result. The communication processing unit 320 includes a gain adjustment processing unit 322. The transmission unit 330 includes a modulator 332, a transmitter 334, and a transmission antenna 336.

  The amplitude modulation signal 202 from the vehicle 200 is received by the receiving unit 310 by causing the tuning circuit 312 to resonate at the resonance frequency. The reception gain adjustment unit 314 is configured to be able to adjust the gain, and amplifies the amplitude modulation signal as the reception signal received by the tuning circuit 312 with the adjusted gain. As will be described later, reception gain adjustment section 314 adjusts the gain of the received signal at a switchable speed (adjustment speed) using the demodulation result of demodulator 316 and the processing result of communication processing section 320 as necessary. Can be done. The demodulator 316 performs a given demodulation process corresponding to the modulation process performed on the transmission side with respect to the amplified signal amplified by the reception gain adjustment unit 314, and the demodulation result is received by the reception gain adjustment unit 314 and the communication process. Supplied to the unit 320. The reception gain adjusting unit 314 can determine whether the signal is in the signaled state or the no-signal state by using the demodulation result of the demodulator 316.

  The communication processing unit 320 performs given communication processing on the demodulation result of the received signal by the reception unit 310 and performs processing of transmitting a response to the vehicle 200 via the transmission unit 330. The gain adjustment processing unit 322 of the communication processing unit 320 performs a given gain adjustment process using the demodulation result of the demodulator 316 so that the gain adjustment process result can be supplied to the reception gain adjustment unit 314. It has become. As this gain adjustment processing, there are detection processing of a start pattern signal corresponding to the head of communication data from the vehicle 200, detection processing of normal end or abnormal end of communication from the vehicle 200, and the like.

  Such a function of the communication processing unit 320 is realized by a hardware circuit or by software processing. When the functions of the communication processing unit 320 are realized by software processing, the communication processing unit 320 includes a central processing unit (hereinafter referred to as CPU) and a storage unit. Then, the CPU reads out the program stored in the storage unit, and the CPU executes processing corresponding to the program, thereby realizing software processing.

  The modulator 332 modulates the result of communication processing performed on the communication processing unit 320. The transmitter 334 transmits a transmission signal corresponding to the modulation result modulated by the modulator 332 via the transmission antenna 336.

  FIG. 3 shows a block diagram of a configuration example of the reception gain adjustment unit 314 in FIG. 3, the demodulator 316 and the gain adjustment processing unit 322 in FIG. 2 are shown together.

  The reception gain adjustment unit 314 includes an amplifier (amplifier circuit) 400, a gain control circuit 410, and an attenuation circuit 420. The gain control circuit 410 includes a comparison circuit 412, a gain adjustment circuit 414, and a time constant setting circuit 416. Note that the time constant setting circuit 416 may be provided outside the reception gain adjustment unit 314.

  The amplifier 400 is a fixed gain amplifier that amplifies an amplitude modulation signal as a reception signal with a predetermined gain and outputs the amplified signal to the demodulator 316. This amplified signal is also supplied to the gain control circuit 410. The gain control circuit 410 generates a control signal Cont based on the amplified signal from the amplifier 400, the demodulation result of the demodulator 316, and the processing result of the gain adjustment processing unit 322. The attenuation circuit 420 attenuates the amplitude modulation signal input to the amplifier 400 with an attenuation corresponding to the control signal Cont from the gain control circuit 410.

  In the gain control circuit 410, a reference voltage (reference signal in a broad sense) is input to the comparison circuit 412. The comparison circuit 412 compares the amplified signal with the reference voltage and outputs a comparison result signal to the gain adjustment circuit 414. The gain adjustment circuit 414 adjusts the gain of the reception gain adjustment unit 314 based on the comparison result signal from the comparison circuit 412. At this time, the gain adjustment circuit 414 adjusts the gain of the reception gain adjustment unit 314 at a speed according to the time constant set by the time constant setting circuit 416. The time constant setting circuit 416 sets a time constant corresponding to the speed for adjusting the gain by the gain adjustment circuit 414 based on the demodulation result of the demodulator 316 and the processing result of the gain adjustment processing unit 322. In this way, the gain adjustment circuit 414 can output the control signal Cont that changes at a speed corresponding to the switched time constant while switching the time constant. The control signal Cont output from the gain adjustment circuit 414 is output to the attenuation circuit 420.

  When the gain adjustment circuit 414 is switched to a time constant larger than the reference time constant, the attenuation of the attenuation circuit 420 is adjusted at a slower speed than the speed according to the reference time constant. Therefore, the gain of the reception gain adjustment unit 314 changes at a slow adjustment speed. On the other hand, when the time constant is switched to a smaller time constant than the reference time constant, the attenuation level of the attenuation circuit 420 is adjusted at a higher speed than the speed according to the reference time constant. Therefore, the gain of the reception gain adjustment unit 314 changes at a high adjustment speed.

  As described above, the gain adjustment circuit 414 adjusts the time constant using the comparison result of the comparison circuit 412. More specifically, the gain adjustment circuit 414 adjusts the reception gain of the reception gain adjustment unit 314 at a speed corresponding to the time constant adjusted by the time constant setting circuit 416.

  FIG. 4 shows a circuit diagram of a configuration example of the reception gain adjustment unit 314 in FIG. 4, parts that are the same as those in FIG. 3 are given the same reference numerals, and descriptions thereof will be omitted as appropriate. In FIG. 4, it is assumed that the gain adjustment circuit 414 adjusts the reception gain while switching any one of the three types of time constants.

  The attenuation circuit 420 includes a resistance element R1 and a variable resistance VR. The resistance element R1 is inserted between a terminal to which a reception signal is input and an input terminal of the amplifier 400. The variable resistor VR is inserted between the input terminal of the amplifier 400 and the ground terminal. A control signal Cont is input to the variable resistor VR. The resistance value can be changed based on the control signal Cont. In FIG. 4, it is assumed that as the potential of the control signal Cont increases, the resistance value of the variable resistor VR decreases and the attenuation increases. When the reception signal is input, the attenuation circuit 420 outputs a voltage obtained by resistance-dividing the reception signal by the resistance element R1 and the variable resistance VR. This voltage is input to the amplifier 400.

  The comparison circuit 412 has a comparator and outputs a comparison result between the output of the amplifier 400 and the reference voltage Vref1.

  The gain adjustment circuit 414 includes a potential holding circuit 450, a charge / discharge circuit 452, and a charge / discharge current control circuit 454. The potential holding circuit 450 holds the potential of a predetermined node ND. Such a potential holding circuit 450 includes a capacitor CA having a ground voltage supplied to one end and a node ND connected to the other end. The potential of the node ND is output as the control signal Cont. Therefore, the attenuation of the attenuation circuit 420 changes according to the potential of the node ND, and the gain of the reception gain adjustment unit 314 can be changed.

  The charging / discharging circuit 452 includes one or a plurality of charging current sources and discharging current sources corresponding to the time constant, and switches a current for charging / discharging the charge of the node ND. In each pair of charging current source and discharging current source, the current value of the charging current source is larger than the current value of the corresponding discharging current source. By doing so, the potential of the node ND rises when the reception signal is received while discharging the charge of the node ND, and the gain adjustment cannot be continued because the attenuation of the attenuation circuit 420 becomes too large. Can be avoided.

  In FIG. 4, the charging / discharging circuit 452 includes charging current sources Ic1 to Ic3 and discharging current source Id1 corresponding to each of the first time constant τ1, the second time constant τ2, and the third time constant τ3. To Id3. Here, the time constants have a relationship of τ1 <τ2 and τ1 <τ3. τ2 = τ3 may be sufficient.

  Specifically, the charging / discharging circuit 452 is provided with a charging current source Ic1, a discharging current source Id1, and switch elements SWp1 and SWn1 corresponding to the first time constant τ1. The switch element SWp1 is provided between the charging current source Ic1 and the node ND, and the switch element SWn1 is provided between the discharging current source Id1 and the node ND. The current value of the charging current source Ic1 is larger than the current value of the discharging current source Id1.

  The charging / discharging circuit 452 is provided with a charging current source Ic2, a discharging current source Id2, and switch elements SWp2 and SWn2 corresponding to the second time constant τ2. The switch element SWp2 is provided between the charging current source Ic2 and the node ND, and the switch element SWn2 is provided between the discharging current source Id2 and the node ND. The current value of the charging current source Ic2 is larger than the current value of the discharging current source Id2. Since the time constant is proportional to ((capacitance value of the capacitor CA) / current value), the current value of the charging current source Ic2 is smaller than the current value of the charging current source Ic1.

  Further, the charging / discharging circuit 452 is provided with a charging current source Ic3, a discharging current source Id3, and switch elements SWp3 and SWn3 corresponding to the third time constant τ3. The switch element SWp3 is provided between the charging current source Ic3 and the node ND, and the switch element SWn3 is provided between the discharging current source Id3 and the node ND. The current value of the charging current source Ic3 is larger than the current value of the discharging current source Id3. The current value of the charging current source Ic3 is smaller than the current value of the charging current source Ic2.

  The charge / discharge current control circuit 454 performs control to switch a current for charging / discharging the charge of the node ND by the charge / discharge circuit 452. Specifically, the charge / discharge current control circuit 454 generates a switch control signal for performing switch control of the switch elements SWp1 to SWp3 and SWn1 to SWn3 of the charge / discharge circuit 452. The charge / discharge current control circuit 454 determines a time constant to be switched based on the output of the time constant setting circuit 416, and sets a charging current source and a discharge current source corresponding to the determined time constant and the node ND. Control to turn on the switch element to be connected is performed. As a result, the potential of the node ND changes according to the time constant corresponding to the charge / discharge characteristics of the charge of the node ND, and the control signal Cont can be changed.

  As described above, the charge / discharge circuit 452 can control the current value for charging / discharging the predetermined node ND using the comparison result of the comparison circuit 412 under the control of the charge / discharge current control circuit 454. The gain adjustment circuit 414 having such a charge / discharge circuit 452 has a gain control adjustment speed based on the comparison result of the comparison circuit 412, and a current value for charging / discharging a predetermined node ND with the charge current source and the discharge current source. Can be adjusted. When a plurality of sets of charging current sources and discharging current sources are provided, the gain adjustment circuit 414 includes a comparison circuit using a set of charging current sources and discharging current sources selected according to the time constant to be switched. The adjustment speed of gain control based on the comparison result of 412 is adjusted.

FIG. 5 is an explanatory diagram of the amplitude modulation signal 202 sent from the vehicle 200 in the first embodiment. FIG. 5 represents the envelope of the amplitude modulation signal 202 as a rectangular wave for convenience of explanation.
FIG. 6 shows a first explanatory diagram of the start pattern signal of FIG.
FIG. 7 shows a second explanatory diagram of the start pattern signal of FIG.

  Prior to transmission of communication data from vehicle 200 to electronic key 300, burst signal B2 is received as a reception signal. This reception signal is configured to include a predetermined start pattern signal TP after a space SP1 in a no-signal state is provided after the burst signal B2.

  As shown in FIG. 6, the start pattern signal TP can be a pattern corresponding to a combination of a signaled state and a no-signal state. Alternatively, the start pattern signal TP may be a pattern defined by the length of at least one of a signaled state and a no-signal state as shown in FIG. In FIG. 7, the start pattern signal TP represents an example defined by the length t1 of the signaled state. Such a start pattern signal TP is detected by a gain adjustment processing unit 322 that performs a start pattern signal detection process as a communication process on the demodulation result of the demodulator 316 that demodulates the amplified signal after the gain adjustment.

  The reception signal shown in FIG. 5 includes communication data C2 to be sent from the vehicle 200 to the electronic key 300 after a space SP2 in a no-signal state is provided after the start pattern signal TP. The communication data C2 includes data “0” or data “1” corresponding to the length between edges.

  The reception gain adjustment unit 314 that has received such a reception signal switches the time constant according to the burst signal or the start pattern signal. Specifically, by switching the time constant, the reception gain adjusting unit 314 adjusts the reception gain by the burst signal B2, and maintains the adjusted gain as much as possible in the subsequent space SP1. The reception gain adjustment unit 314 adjusts the reception gain to be fixed or maintained as much as possible on condition that the start pattern signal TP is detected. In this way, even when the gain of the received signal is adjusted based on the burst signal, a situation in which the gain before the adjustment is restored immediately after detecting the no-signal state is avoided.

  FIG. 8 shows a flowchart of an operation example of the reception gain adjustment unit 314 of FIG.

  First, in the reception gain adjustment unit 314, the first time constant τ1 is set as an initial value by the time constant setting circuit 416 in the gain adjustment circuit 414 (step S10). That is, the reception gain adjustment unit 314 adjusts the gain of the reception signal at a speed corresponding to the first time constant τ1 immediately after the operation starts.

  Next, the reception gain adjustment unit 314 monitors the presence or absence of a reception signal (step S12: N). The reception gain adjustment unit 314 can monitor the presence / absence of a reception signal by determining whether the signal is in a signaled state or no signal state using the demodulation result of the demodulator 316. When the received signal is detected, it is determined that the signal is a burst signal (first signal state).

  When a reception signal is detected in step S12 (step S12: Y), the reception gain adjustment unit 314 adjusts the gain of the reception signal as it is at a speed corresponding to the first time constant τ1 (step S14). That is, in step S14, as the first reception gain adjustment step, the reception signal input to the amplifier 400 is attenuated by changing the attenuation of the attenuation circuit 420 at a speed corresponding to the first time constant τ1. The gain of the reception gain adjustment unit 314 is changed.

  Subsequently, the reception gain adjusting unit 314 detects whether or not there is no signal (step S16). That is, in step S16, the reception gain adjustment unit 314 detects whether or not the space is after the burst signal. When it is detected that a space is provided (step S16: Y), the reception gain adjustment unit 314 switches the time constant by the time constant setting circuit 416 in the gain adjustment circuit 414, and the first time constant larger than the first time constant τ1. The gain of the received signal is adjusted at a speed corresponding to the time constant τ2 of 2 (step S18). That is, in step S18, as a second reception gain adjustment step, the reception signal input to the amplifier 400 is attenuated by changing the attenuation of the attenuation circuit 420 at a speed according to the second time constant τ2. The gain of the reception gain adjustment unit 314 is changed. Thereby, in step S18, the gain of the received signal is adjusted more slowly than in step S14.

  In step S18, it is desirable that the second time constant τ2 is infinite. When the second time constant τ2 is infinite, the reception gain of the reception gain adjustment unit 314 is fixed.

  On the other hand, when it is detected in step S16 that no space is provided (step S16: N), the reception gain adjustment unit 314 is based on the processing result from the communication processing unit 320 (gain adjustment processing unit 322). It is determined whether the communication is abnormally terminated (step S20). When it is determined that it is not abnormal termination (step S20: N), the reception gain adjustment unit 314 returns to step S14. When it is determined in step S20 that the operation has ended abnormally (step S20: Y), the reception gain adjustment unit 314 returns to step S10 (returns), and again waits for a burst signal sent at the beginning of communication from the vehicle 200. .

  Subsequent to step S18, the reception gain adjustment unit 314 detects whether or not there is a signal state (step S22). That is, in step S22, the presence or absence of the input of the start pattern signal after providing the space after the burst signal is detected. When it is detected that there is a signal state (step S22: Y), the reception gain adjustment unit 314 detects whether or not the signal in the signal state detected in step S22 matches the start pattern signal ( Step S24, start pattern signal detection step).

  On the other hand, when it is detected that the state is not a signal presence (step S22: N), the reception gain adjustment unit 314, for example, based on the processing result from the communication processing unit 320 (or gain adjustment processing unit 322), abnormal communication It is determined whether the process is finished (step S26). When it is determined that it is not abnormal termination (step S26: N), the reception gain adjustment unit 314 returns to step S18. When it is determined in step S26 that the operation has ended abnormally (step S26: Y), the reception gain adjustment unit 314 returns to step S10 (returns) and waits for a burst signal sent again at the head of communication from the vehicle 200. .

  In step S26, a period in which gain adjustment is performed at a speed corresponding to the second time constant τ2 may be monitored, and when the period is equal to or greater than a predetermined period, it may be determined as abnormal termination. At this time, the process returns to step S10, the state of the reception gain adjustment unit 314 is initialized, and it is possible to realize the return operation at the time of abnormality by waiting for the burst signal again.

  When it is detected that the detected signal state signal matches the start pattern signal (step S24: Y), the reception gain adjustment unit 314 switches the time constant by the time constant setting circuit 416 in the gain adjustment circuit 414. The gain of the received signal is adjusted at a speed corresponding to the third time constant τ3 (step S28). As a result, it can be seen that the timing at which the signal data is sent after the elapse of a predetermined time after the start pattern signal is recognized. In step S28, as a fourth reception gain adjustment step, the reception signal input to the amplifier 400 is attenuated by changing the degree of attenuation of the attenuation circuit 420 at a speed corresponding to the third time constant τ3. The gain of the gain adjusting unit 314 is changed.

  In step S28, the third time constant τ3 is larger than the first time constant τ1. Thereby, in step S28, the gain of the received signal is adjusted more slowly than in step S14. More specifically, it is desirable that the third time constant τ3 is equal to the second time constant τ2. The third time constant τ3 is desirably infinite. When the third time constant τ3 is infinite, the reception gain of the reception gain adjustment unit 314 is fixed.

  In step S24, when it is detected that the signal in the signal state detected in step S22 does not match the start pattern signal (step S24: N), the reception gain adjustment unit 314 returns to step S14. That is, in step S14, as a third reception gain adjustment step, the reception gain adjustment unit 314 switches the time constant by the time constant setting circuit 416 in the gain adjustment circuit 414, and receives the signal at a speed corresponding to the first time constant τ1. Adjust the gain of the signal.

  Subsequent to step S28, the reception gain adjustment unit 314 detects whether it is normal termination or abnormal termination based on the processing result from the communication processing unit 320 (step S30). When it is detected in step S30 that the end is not normal end or abnormal end (step S30: N), the reception gain adjustment unit 314 continues to adjust the gain of the reception signal at a speed corresponding to the third time constant τ3. .

  When it is detected in step S30 that the end is normal or abnormal (step S30: Y), the reception gain adjustment unit 314 returns to step S10 (return) and is sent again at the beginning of communication from the vehicle 200. Wait for burst signal.

  As described above, the reception gain adjustment unit 314 switches to the first time constant τ1 in the signal-present state and the second time constant τ2 in the no-signal state during the reception gain adjustment in the time constant setting circuit 416. After the reception gain is adjusted, the third time constant τ3 is switched. As a result, even when the no-signal state is provided after the presence / absence of the signal, the optimum gain adjustment is performed while the amplitude information superimposed on the input signal remains, and the amplified signal after gain adjustment is sent to the subsequent stage side. Will be able to.

  FIG. 9 shows an operation example of the reception gain adjustment unit 314 in the first embodiment. FIG. 9 shows a received signal (amplitude modulated signal) in which an envelope is represented by a rectangular wave, a received waveform, a control signal Cont, and a demodulated signal that is an output of the demodulator 316. Here, for convenience of explanation, it is assumed that the gain of the reception gain adjustment unit 314 decreases as the potential of the control signal Cont increases.

  Prior to communication with the vehicle 200, the reception gain adjustment unit 314 sets a first time constant τ1 that is an initial value as a time constant (T1). Thereafter, when the burst signal B3 that is in the first signal state is detected as the reception signal, the reception gain adjustment unit 314 continues to adjust the gain of the reception signal at a speed corresponding to the first time constant τ1.

  When the non-signal state space SP3 is detected following the burst signal B3, the reception gain adjustment unit 314 adjusts the gain of the reception signal at a speed corresponding to the second time constant τ2. Since the second time constant τ2 is larger than the first time constant τ1, it is possible to avoid a situation where the gain of the reception gain adjustment unit 314 adjusted by the burst signal B3 returns to the gain before adjustment. Thereby, at the start of reception of the start pattern signal TP1 after the space SP3, the reception gain of the start pattern signal TP1 can be adjusted with a gain adjusted by the burst signal B3.

  When the start pattern signal TP1 is detected, the reception gain adjustment unit 314 adjusts the gain of the reception signal at a speed corresponding to the first time constant τ1. As described above, when the start pattern signal TP2 after the space SP3 is detected, the reception gain adjustment unit 314 is switched again to the first time constant τ1, so that it is quickly optimal when receiving the start pattern signal TP1. The gain can be adjusted.

  When the predetermined start pattern signal TP1 is detected, the reception start timing of the communication data C3 can be specified. Therefore, when the space SP4 in the no-signal state is detected after the start pattern signal TP1, the reception gain adjustment unit 314 adjusts the gain of the reception signal at a speed corresponding to the second time constant τ2. At this time, since the second time constant τ2 is larger than the first time constant τ1, it is possible to avoid a situation where the gain of the reception gain adjustment unit 314 adjusted by the start pattern signal TP1 returns to the gain before adjustment. When the communication data C3 that is in the third signal state after the space SP4 is detected, the reception gain adjustment unit 314 adjusts the gain of the reception signal at a speed corresponding to the third time constant τ3.

  By setting the second time constant τ2 and the third time constant τ3 to infinity, the gain adjusted in the immediately preceding signal state can be maintained when receiving the spaces SP3 and SP4. As a result, the gain of the reception gain adjusting unit 314 does not return to the gain before adjustment regardless of the transmission state from the vehicle 200. Therefore, even if the burst signal or the like is shortened in order to communicate from the vehicle 200 to the electronic key 300 in the shortest possible period, the reception gain of the amplitude modulation signal can be adjusted while maintaining the demodulated amplitude information.

  The reception gain adjustment unit 314 that has received such a reception signal switches the time constant according to the burst signal or the start pattern signal. At this time, even in the case of a short burst signal, the time constant is switched even during the burst signal reception period so that the reception gain can be adjusted accurately. Specifically, the reception gain adjustment unit 314 changes the reception gain at high speed to the vicinity of the target value at the start of reception of the burst signal B2, and then changes the reception gain at low speed and with high accuracy. Switch constants. When the reception gain is adjusted by the burst signal B2, the reception gain adjustment unit 314 maintains the adjusted gain as much as possible in the subsequent space SP1. The reception gain adjustment unit 314 adjusts the reception gain while fixing or maintaining the reception gain as much as possible on condition that the start pattern signal TP is detected.

  In this way, even with a short burst signal, the reception gain can be adjusted at high speed and with high accuracy. Furthermore, even when the gain of the received signal is adjusted based on the burst signal, it is possible to avoid a situation where the gain before the adjustment is restored immediately after detecting the no-signal state.

  By the way, as described above, it is desirable that the second time constant τ2 and the third time constant τ3 are infinite. In this case, the gain adjustment circuit 414 in FIG. 4 can employ the following configuration.

  FIG. 10 shows a circuit diagram of a configuration example of a gain adjustment circuit in a modification of the first embodiment. 10, parts that are the same as those in FIG. 4 are given the same reference numerals, and descriptions thereof will be omitted as appropriate.

  The gain adjustment circuit 414a in the modification of the first embodiment can be provided in place of the gain adjustment circuit 414 in the reception gain adjustment unit 314 of FIG. The gain adjustment circuit 414a includes a potential holding circuit 450, a charge / discharge circuit 452a, and a charge / discharge current control circuit 454a. The gain adjustment circuit 414a is different from the gain adjustment circuit 414 of FIG. 4 in that the charging current sources Ic2 and Ic3 and the discharging current sources Id2 and Id3 of the charging / discharging circuit 452a are omitted, and the charging / discharging current control circuit 454a is a switching element. This is the point of performing on / off control of SWp1 and SWn1. That is, when switching to the second time constant τ2 or the third time constant τ3, the gain adjustment circuit 414a performs control to turn off the switch elements SWp1 and SWn1 to stop the charge and discharge of the node ND. The potential of the control signal Cont is fixed (locked).

  As described above, in the gain adjustment circuits 414 and 414a, the attenuation by the control signal Cont is changed by switching the current value for charging and discharging the charge of the node ND. The gain can be adjusted.

  Next, the effect of the reception gain adjustment unit in the first embodiment or its modification will be specifically described. Therefore, first, a description will be given of a case in which the start pattern signal is received by providing a space after the burst signal in the conventional receiving circuit 10 of FIG.

  FIG. 11 is an explanatory diagram of an operation example in the receiving circuit 10 of FIG. 16 when a start pattern signal is received with a space provided after the burst signal. FIG. 11 shows a reception signal (amplitude modulation signal) whose envelope is a rectangular wave, a control signal Cont, and an amplification signal.

  In the receiving circuit 10 of FIG. 16, the gain adjusted when the burst signal B4 is received returns to the original during the space SP5, and the gain is adjusted again when the start pattern signal TP2 is received (FIG. 11). P0). Therefore, when receiving the start pattern signal TP2, the reception circuit 10 adjusts the reception gain again with respect to the start pattern signal TP2 from the state where the gain of the amplifier 12 is set to the maximum. Therefore, even if the start pattern signal TP2 is provided, reception is unstable in the receiving circuit 10 of FIG. In particular, when the burst signal B4 and the space SP5 have the same length, the adjusted gain is restored, and the adjustment of the reception gain starts again with the start pattern signal TP2, making it difficult to demodulate the start pattern signal TP2. . This means that at the same time, it becomes difficult to demodulate the communication data C4.

  On the other hand, in the first embodiment or its modification, as shown in FIG. 9, even if a space having the same length as the burst signal is provided after the burst signal, the reception gain adjusting unit 314 Adjust the gain later. Therefore, when the start pattern signal after the space is received, the gain is not adjusted again, and the start pattern signal can be demodulated.

  Further, according to the first embodiment or its modification, the following resistance to noise is also improved.

  FIG. 12 is an explanatory diagram of an operation example in the reception circuit 10 of FIG. 16 when the received signal includes noise. FIG. 12 shows a reception signal (amplitude modulation signal) in which an envelope is represented by a rectangular wave, a control signal Cont, and an amplification signal.

  When the burst signal is received, the reception circuit 10 in FIG. 16 starts reception of communication data next. For this reason, if there is noise N1 as shown in FIG. 12, for example, reception of communication data starts at timing P1. Then, even if the normal signal has a larger amplitude than the noise N1, the normal signal cannot be received. This is because the amplifier 12 of the receiving circuit 10 is fixed in a state where the gain is increased following the noise N1. For this reason, the amplifier 12 also saturates the output of the regular signal after the noise N1.

  FIG. 13 is an explanatory diagram of an operation example in the case where noise is included in the received signal in the first embodiment or its modification. FIG. 13 shows a reception signal (amplitude modulation signal) in which an envelope is represented by a rectangular wave, a control signal Cont, and an amplification signal.

  In the first embodiment or the modification thereof, since the start pattern signal is provided, even if the noise N2 is included in the reception signal, the gain of the amplifier is fixed as in the reception circuit 10 of FIG. Instead, after receiving the start pattern signal (P2 in FIG. 13), the gain can be maintained or fixed as much as possible. Therefore, the normal signal after the noise N2 can be correctly demodulated without saturating the output, and the resistance to noise can be enhanced.

  As described above, in the first embodiment or its modification, the start pattern signal is provided after the burst signal in the first signal state, and the reception gain of the amplitude modulation signal is increased by switching to a larger time constant. I try to adjust it. Thus, for example, the reception gain is fixed for the communication data after the start pattern signal without the reception gain returning to the gain before adjustment in the period of the no signal state between the first signal state and the start pattern signal. By doing so, stable reception can be realized.

[Second Embodiment]
In the first embodiment or the modification thereof, the reception gain adjustment unit 314 adjusts the gain of the reception gain adjustment unit 314 by controlling the attenuation of the input of the amplifier 400. The form is not limited to this.

  FIG. 14 shows a block diagram of a configuration example of the reception gain adjusting unit in the second embodiment according to the present invention. 14, parts similar to those in FIG. 3 are denoted by the same reference numerals, and description thereof will be omitted as appropriate. In FIG. 14, the demodulator 316 and the gain adjustment processing unit 322 in FIG. 2 are shown together.

  The reception gain adjustment unit (gain adjustment device, reception gain adjustment device. In a broad sense, the amplification unit) 314b according to the second embodiment is applied to the reception unit 310 of FIG. 2 instead of the reception gain adjustment unit 314 of FIG. can do.

  Such a reception gain adjusting unit 314b includes an amplifier (amplifying circuit) 400b and a gain control circuit 410b. The gain control circuit 410b includes a comparison circuit 412, a gain adjustment circuit 414b, and a time constant setting circuit 416.

  The amplifier 400b is a variable gain amplifier that amplifies an amplitude modulation signal as a reception signal, which is an input signal, with a variable gain, and outputs the amplified signal to the demodulator 316. This amplified signal is also supplied to the gain control circuit 410b. The gain control circuit 410b generates a control signal Cont based on the amplified signal from the amplifier 400b, the demodulation result of the demodulator 316, and the gain adjustment processing result of the gain adjustment processing unit 322.

  In the gain control circuit 410b, the reference voltage is input to the comparison circuit 412. The comparison circuit 412 compares the amplified signal with the reference voltage and outputs a comparison result signal to the gain adjustment circuit 414b. The gain adjustment circuit 414b adjusts the gain of the reception gain adjustment unit 314b based on the comparison result signal from the comparison circuit 412. At this time, the gain adjustment circuit 414b adjusts the gain of the reception gain adjustment unit 314b at a speed corresponding to the time constant set by the time constant setting circuit 416. That is, the gain adjustment circuit 414b outputs the control signal Cont corresponding to the comparison result of the comparison circuit 412 at a speed corresponding to the switched time constant while switching the time constant. The control signal Cont output from the gain adjustment circuit 414b is output to the amplifier 400b.

  When the gain adjustment circuit 414b is switched to a time constant larger than the reference time constant, the gain of the amplifier 400b is adjusted at a slower speed than the speed according to the reference time constant. Therefore, the gain of the reception gain adjustment unit 314b changes at a slow adjustment speed. On the other hand, when the time constant is switched to a smaller time constant than the reference time constant, the gain of the amplifier 400b is adjusted at a higher speed than the speed according to the reference time constant. Therefore, the gain of the reception gain adjustment unit 314b changes at a high adjustment speed.

  FIG. 15 shows a circuit diagram of a configuration example of the reception gain adjustment unit 314b in the second embodiment. 15, parts similar to those in FIG. 4 are denoted by the same reference numerals, and description thereof will be omitted as appropriate.

  The configuration of the reception gain adjustment unit 314b in the second embodiment is different from the configuration of the reception gain adjustment unit 314 shown in FIG. 4 in that the output of the potential holding circuit 450 is used for gain control of the amplifier 400b. In the second embodiment, it is assumed that the gain of the amplifier 400b decreases as the potential of the control signal Cont, which is the output of the potential holding circuit 450, increases.

  When the second time constant τ2 and the third time constant τ3 are infinite, the configuration shown in FIG. 10 can be adopted as the configuration of the gain adjustment circuit. That is, in the configuration shown in FIG. 15, the charging current sources Ic2 and Ic3 and the discharging current sources Id2 and Id3 are omitted, and the charging / discharging current control circuit performs on / off control of the switch elements SWp1 and SWn1. Therefore, when switching to the second time constant τ 2 or the third time constant τ 3, the gain adjustment circuit performs control to turn off the switch elements SWp 1 and SWn 1 to stop charging and discharging of the node ND. The potential of the signal Cont is fixed (locked).

  Since the operation of the reception gain adjustment unit 314b is the same as the operation of the reception gain adjustment unit 314 shown in FIG.

  As described above, in the second embodiment, similarly to the first embodiment or its modification, the reception gain is reduced in the period of the no signal state between the first signaled state and the start pattern signal. There is no return to the gain before adjustment. Therefore, for the communication data after the start pattern signal, stable reception can be realized by fixing the reception gain, for example.

  As described above, the gain adjusting device, the receiving device, and the like according to the present invention have been described based on any one of the above-described embodiments or modifications thereof, but the present invention is limited to any of the above-described embodiments or modifications thereof. It is not something. For example, the present invention can be implemented in various modes without departing from the gist thereof, and the following modifications are possible.

  (1) In any of the above-described embodiments or modifications thereof, the example in which the reception gain adjustment unit is built in the reception unit shown in FIG. 2 has been described, but the present invention is not limited to this.

  (2) In any of the above-described embodiments or modifications thereof, an example has been described in which the reception gain adjustment unit is built in the reception unit illustrated in FIG. 2 and the reception unit is mixed with the transmission unit. Is not limited to this. For example, the reception gain adjusting unit in any of the above-described embodiments or modifications thereof may be incorporated in the receiving device having the function of the receiving unit illustrated in FIG.

  (3) In any of the above embodiments or modifications thereof, an example has been described in which the reception gain adjustment unit is built in the reception unit shown in FIG. 2 and the reception unit is built in an electronic key as a portable device. However, the present invention is not limited to this. For example, the reception gain adjustment unit in any of the above-described embodiments or modifications thereof may be incorporated in another portable device (electronic device) other than the electronic key.

  (4) In any of the above-described embodiments or modifications thereof, the example in which the reception gain adjustment unit is applied to the electronic key system shown in FIG. 1 has been described, but the present invention is not limited to this. It can be applied to various communication systems.

  (5) In any of the above embodiments or modifications thereof, the ASK signal has been described as an example of the amplitude modulation signal. However, the present invention is not limited to the ASK signal, and the amplitude information is superimposed on the signal. Can be applied to.

  (6) In any of the above embodiments or modifications thereof, a counter may be provided to count the number of bits of the communication data pattern. When an abnormal pattern exceeding a predetermined count number is detected by this counter, the adjustment of the reception gain adjustment unit is initialized, and it is switched to the first time constant τ1 again to wait for reception of the burst signal. Good. Such a counter can be provided in the communication processing unit 320 (gain adjustment processing unit 322) or the reception unit 310. By doing so, it becomes possible to initialize the reception gain adjustment unit and wait for reception of the burst signal again when communication data is abnormal.

  (7) In the first embodiment or its modification, the attenuation circuit has been described by taking the configuration in which the resistor element R1 is inserted in series as an example, but the present invention is not limited to this. For example, a high-pass filter circuit may be configured by inserting a capacitor instead of the resistance element R1 in the attenuation circuit, and the received signal may be attenuated by shifting the cutoff frequency of the high-pass filter circuit.

  (8) In any of the above-described embodiments or modifications thereof, the present invention has been described as a gain adjusting device, a receiving device, and the like, but the present invention is not limited to this. For example, a program for realizing the reception gain adjustment method in any of the above-described embodiments or modifications thereof, or a recording medium on which the program is recorded may be used. In addition, for example, the receiving method of the receiving device in any one of the above embodiments or a modification thereof, a portable device (electronic device) including the receiving device in any of the above embodiments or the modification thereof may be used. .

DESCRIPTION OF SYMBOLS 10 ... Reception circuit 12 ... Amplifier 14,414,414a, 414b ... Gain adjustment circuit 16,420 ... Attenuation circuit 100 ... Electronic key system 200 ... Vehicle,
202 ... amplitude modulation signal, 204 ... signal, 300 ... electronic key,
310 ... receiving unit (receiving device), 312 ... tuning circuit (receiver),
314, 314b ... reception gain adjustment unit (reception gain adjustment device), 316 ... demodulator,
320 ... Communication processing unit, 322 ... Gain adjustment processing unit, 330 ... Transmission unit,
332 ... Modulator, 334 ... Transmitter, 336 ... Transmitting antenna, 340 ... Coil,
342 ... capacitor, 400, 400b ... amplifier (amplifier circuit),
410, 410b ... gain control circuit, 412 ... comparison circuit, 416 ... time constant setting circuit,
450 ... Potential holding circuit, 452, 452a ... Charging / discharging circuit,
454, 454a ... charge / discharge current control circuit,
B1, B2, B3, B4 ... burst signal (first signal state),
C1, C2, C3, C4 ... communication data, CA ... capacitor, Cont ... control signal,
Ic1 to Ic3 ... charging current source, Id1 to Id3 ... discharging current source, ND ... node,
R1... Resistance element, SP1, SP2, SP3, SP4, SP5... Space (no signal state), SWn1 to SWn3, SWp1 to SWp3.
TP, TP1, TP2 ... start pattern signal, VR ... variable resistance, τ1 ... first time constant,
τ2 ... second time constant, τ3 ... third time constant

Claims (13)

A gain adjusting device for adjusting the gain of an input signal,
An amplifier circuit for amplifying the input signal;
A comparison circuit for comparing the amplified signal by the amplifier circuit with a reference signal;
A gain adjustment circuit for adjusting the gain using a comparison result of the comparison circuit;
A time constant setting circuit for setting a time constant corresponding to the speed for adjusting the gain,
The gain adjustment circuit is
A gain adjusting apparatus that adjusts the gain at a speed corresponding to a time constant set by the time constant setting circuit. In claim 1,
The gain adjustment circuit includes:
A potential holding circuit for holding a potential of a predetermined node;
A charge / discharge circuit that controls a current value for charging / discharging the predetermined node using a comparison result of the comparison circuit;
A gain adjusting apparatus that adjusts the gain according to a potential of the predetermined node. In claim 2,
The charge / discharge circuit is
A current source for charging;
Including a discharge current source,
The gain adjustment circuit includes:
A gain adjusting apparatus, wherein an adjustment speed of gain control based on a comparison result of the comparison circuit is adjusted by a current value for charging and discharging the predetermined node by the charging current source and the discharging current source. In claim 3,
The gain adjusting apparatus according to claim 1, wherein a current value of the charging current source is larger than a current value of the discharging current source. In claim 2,
The charge / discharge circuit is
One or more current sources for charging;
Each including one or a plurality of discharging current sources provided corresponding to the charging current source circuit,
The gain adjustment circuit includes:
A gain adjusting apparatus that adjusts an adjustment speed of gain control based on a comparison result of the comparison circuit by a pair of charging current source and discharging current source selected in accordance with a time constant to be switched. In claim 5,
The gain adjusting device, wherein a current value of each charging current source is larger than a current value of a corresponding discharging current source. In any one of Claims 1 thru | or 6.
An attenuation circuit for attenuating the input signal;
The amplifier circuit is a fixed gain amplifier,
The attenuation circuit is
A gain adjusting apparatus, wherein the input signal is attenuated at a speed corresponding to a time constant set by the time constant setting circuit. In any one of Claims 1 thru | or 6.
The amplifier circuit is a variable gain amplifier,
A gain adjusting device that changes the gain of the amplifier circuit at a speed corresponding to the time constant set by the time constant setting circuit. In any one of Claims 1 thru | or 8.
The input signal is an amplitude modulation signal;
The time constant setting circuit is:
A gain adjusting apparatus that adjusts a time constant according to a demodulation result of the amplified signal. In any one of Claims 1 thru | or 9,
The time constant setting circuit is:
During the gain adjustment, the first time constant is switched in the signaled state and the second time constant is switched in the no-signal state, and the third time constant is switched after the gain adjustment. Gain adjustment device. In claim 10,
The gain adjusting device, wherein the first time constant is larger than the second time constant and larger than the third time constant. In claim 10 or 11,
The time constant setting circuit is:
A gain adjusting apparatus, wherein the time constant is set so that the second time constant and the third time constant are infinite. A receiver for receiving the amplitude modulated signal;
The gain adjusting apparatus according to any one of claims 1 to 12, wherein the gain of the amplitude modulated signal received by the receiver is adjusted.
And a demodulator that demodulates the signal based on the signal amplified by the reception gain adjusted by the gain adjustment device.

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