JP2005309670A - Detection circuit and vehicle-mounted device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To detect presence or absence of a radio wave transmitted from a unit on a road without having to install a PLL synthesizer. <P>SOLUTION: A radio wave detecting circuit 12 comprises an antenna 12a for receiving a radio wave of a first receiving frequency F1 and a radio wave of a second receiving frequency F2 transmitted from the unit on a road, a local oscillator 12c for outputting a signal of a local oscillation frequency FL, and a mixing device 12d for converting the signal of the first receiving frequency F1 and the signal of the second receiving frequency F2 that are received by the antenna, to an intermediate frequency FIF in correspondence with the local oscillation frequency FL from the local oscillator, and sets the local oscillation frequency FL of the signal outputted from the local oscillator to (F1+F2)/2. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a detection circuit that detects a radio wave transmitted from a roadside device, and an in-vehicle device including the detection circuit.

  Conventionally, ETC (Electronic Toll Collection: Non-stop automatic fare) that communicates with on-road machines at entrance gates and exit gates of toll roads and enters, exits, and pays charges while passing through the entrance gates and exit gates non-stop Payment system) has been put into practical use.

  In addition, with the widespread use of ETC in-vehicle devices, there is an increasing number of events where the ETC lane stops without opening and closing bars due to forgetting to insert an IC card into the ETC in-vehicle devices or poor insertion.

Therefore, a navigation device is provided. Based on the travel route set by the navigation device, it is estimated whether or not the vehicle passes through the toll gate. Before the vehicle passes through the toll gate, the IC to the ETC in-vehicle device is installed. Some of them detect and warn of forgetting to insert a card or a defective insertion (see, for example, Patent Document 1).
Japanese Patent No. 3314238

  However, in the invention described in Patent Document 1, for example, when an ETC gate is newly installed and the information about the newly installed ETC gate is not added to the map data of the navigation device, the IC card to the ETC in-vehicle device is added. Forgetting to insert or poor insertion is not warned.

  Therefore, when the vehicle passes through the toll gate by detecting the presence of radio waves transmitted from the ETC roadside equipment provided at the toll gate without providing a navigation device, the IC card to the ETC in-vehicle device in advance is detected. It may be possible to warn of forgetting to insert or poor insertion.

  By the way, two frequencies of 5795 MHz and 5805 MHz are defined as frequencies of radio waves transmitted from the ETC roadside equipment installed on the roadside. As a result, for example, when an ETC roadside equipment is installed adjacent to a toll gate, it is possible to avoid interference by changing the transmission frequency of each other, but depending on the operation mode, one wave is sufficient In that case, one of the waves is used.

  Therefore, in order for the ETC in-vehicle device to detect the presence or absence of radio waves transmitted from the ETC roadside device, it is necessary to include a circuit that receives both signals of two frequencies. A PLL synthesizer is widely used as a circuit for receiving signals of such a plurality of frequencies.

  When receiving a plurality of frequencies using a PLL synthesizer, for example, in FIG. 8, the PLL synthesizer has an intermediate frequency in which the difference between the received carrier frequency f0 and the local oscillation frequency fl (f0−fl) is constant. The local oscillation frequency fl is controlled according to the carrier frequency f0 so as to be fif. Thereby, it becomes possible to receive signals of a plurality of frequencies.

  However, since the PLL synthesizer has a complicated configuration, there are problems that the area occupied by the circuit is large and the power consumption is large. In addition, when two carrier frequencies are switched and received using a PLL synthesizer, there is a problem that a dead time during which the presence or absence of a radio wave transmitted from a roadside device cannot be detected occurs.

  The present invention has been made in view of the above problems, and an object of the present invention is to detect the presence or absence of radio waves transmitted from a road device without providing a PLL synthesizer. In addition, based on the presence or absence of radio waves transmitted from the ETC roadside equipment provided at the toll booth, when the vehicle passes the toll booth, a warning is given in advance about forgetting to insert the IC card into the ETC in-vehicle device or a defective insertion. For other purposes.

  In order to achieve the above object, according to the first aspect of the present invention, there is provided a detection circuit for detecting presence / absence of at least one of a radio wave having a first reception frequency and a radio wave having a second reception frequency transmitted from a road device. , An antenna (12a) that receives the radio wave of the first reception frequency and the radio wave of the second reception frequency, a local oscillator (12c) that outputs a signal of the local oscillation frequency, and the local oscillation frequency from the local oscillator And a mixer (12d) that converts the signal of the first reception frequency and the signal of the second reception frequency received by the antenna into an intermediate frequency, and the signal output from the local oscillator The local oscillation frequency is characterized by being set to (F1 + F2) / 2 where F1 is the first reception frequency and F2 is the second reception frequency.

  Thus, the local oscillation frequency of the signal output from the local oscillator is set to (F1 + F2) / 2 where F1 is the first reception frequency and F2 is the second reception frequency. The radio wave of the reception frequency and the radio wave of the second reception frequency are each converted to a fixed intermediate frequency, and the presence or absence of the radio wave transmitted from the roadside device can be detected without providing a PLL synthesizer.

  The invention according to claim 2 includes the detection circuit (12) according to claim 1, and based on the detection result of the detection circuit, the radio wave of the first reception frequency and the radio wave of the second reception frequency. Determining means for determining the presence / absence of at least one of the IC card and an IC card insertion state detecting means (13) for detecting the insertion state of the IC card when the determining means determines that there is a radio wave transmitted from the ETC roadside device. And a warning means (14) for warning the user when the insertion failure of the IC card is detected by the IC card insertion state detection means.

  Thus, since the determination means determines the presence / absence of at least one of the radio wave of the first reception frequency and the radio wave of the second reception frequency based on the detection result of the detection circuit 12 according to claim 1, the toll gate When the vehicle passes through the toll gate based on the presence or absence of the radio wave transmitted from the ETC roadside device provided in the vehicle, it is possible to warn of forgetting to insert the IC card into the ETC in-vehicle device or a defective insertion in advance.

  In addition, the code | symbol in the bracket | parenthesis of each said means shows the correspondence with the specific means as described in embodiment mentioned later.

  FIG. 1 shows a block configuration of an ETC in-vehicle apparatus according to an embodiment of the present invention. The ETC in-vehicle device is mounted on the vehicle and communicates with an ETC roadside device installed on the roadside. As shown in FIG. 1, the ETC in-vehicle device 1 includes a transmission / reception circuit 11, a radio wave detection circuit 12, an IC card state detection circuit 13, an audio output circuit 14, and a control circuit 15. The transmission / reception circuit 11, the IC card state detection circuit 13, the audio output circuit 14, and the control circuit 15 are provided in the main body of the ETC in-vehicle device 1, and the radio wave detection circuit 12 is provided separately from the main body. The radio wave detection circuit 12 is connected to the control circuit 15 of the main body by a connection cable.

  The transmission / reception circuit 11 includes a high elevation ETC antenna 11a that receives radio waves from an ETC roadside device, and performs processing such as amplification, frequency conversion, and demodulation on a signal received by the high elevation ETC antenna 11a. The baseband signal generated by the process is output to the control circuit 15.

  In addition, the transmission / reception circuit 11 performs processing such as D / A conversion, modulation, and amplification on the baseband signal input from the control circuit 15 and transmits the processed signal from the high elevation angle ETC antenna 11a.

  The radio wave detection circuit 12 includes a low elevation ETC antenna 12a that receives radio waves from an ETC roadside device, and detects the presence / absence of radio waves from the ETC roadside device based on a signal output from the low elevation ETC antenna 12a. A signal corresponding to the detection result is output to the control circuit 15. Details of the radio wave detection circuit 12 will be described later.

  As shown in FIG. 2, the ETC in-vehicle apparatus 1 includes an insertion port 13a for inserting the IC card 20, and the IC card 20 is inserted from the insertion port 13a.

  The IC card state detection circuit 13 detects whether or not the IC card 20 is inserted into the insertion port 13a, and outputs a signal corresponding to the detection result to the control circuit 15.

  The audio output circuit 14 is constituted by a speaker, and outputs the audio according to the audio signal input from the control circuit 15.

  The control circuit 15 is configured as a normal computer, and includes a CPU, a ROM, a RAM, a flash memory, an I / O, and a bus line for connecting these configurations. The control circuit 15 executes the program read from the ROM, and when executing the program, writes information to the ROM, RAM, and flash memory, and transmits / receives the transmission / reception circuit 11 and the radio wave detection circuit 12 via the I / O. The IC card state detection circuit 13 and the audio output circuit 14 exchange various signals.

  Next, the configuration of the radio wave detection circuit 12 will be described. FIG. 3 shows a block configuration of the radio wave detection circuit 12. The reception method of the radio wave detection circuit 12 shown in the figure is a superheterodyne method in which a high-frequency input signal received by a low elevation antenna 12a is converted into an intermediate frequency signal by a local oscillator 12c and a mixer 12d.

  As shown in the figure, the radio wave detection circuit 12 includes a low elevation ETC antenna 12a, a low noise amplifier 12b, a local oscillator 12c, a mixer 12d, a rectifier circuit 12e, and a peak hold circuit 12f.

  The low noise amplifier 12b amplifies an RF frequency band signal input from the ETC antenna 12a having a low elevation angle with low noise. The signal of this RF frequency band is both a signal of the first frequency (5795 MHz) and a signal of the second frequency (5805 MHz).

  The local oscillator 12c outputs, to the mixer 12d, a local oscillation frequency signal (sine wave) for converting an RF frequency band signal into an IF frequency signal.

  The local oscillation frequency FL of the local oscillator 12c in the present embodiment is a value represented by Equation 1 where F1 is the first reception frequency input from the low noise amplifier 12b and F2 is the second reception frequency.

(Formula 1)
FL = (F1 + F2) / 2
Specifically, F1 = 5795 MHz, F2 = 5805 MHz, and FL = 5800 MHz.

  The mixer 12d includes input terminals for a signal of the local oscillation frequency FL from the local oscillator 12c and an RF frequency band (F1, F2) signal output from the low noise amplifier 12b, and the local oscillation frequency signal (sine wave) is used. The RF frequency band signal input to the RF frequency band input terminal is down-converted to an IF frequency band signal and output from the output terminal.

  FIG. 4 shows the input / output relationship of the mixer 12d.

  When a signal of the first reception frequency F1 is input from the RF frequency band signal input terminal, the mixer 12d is an intermediate frequency corresponding to the difference (FL−F1) between the local oscillation frequency FL and the first reception frequency F1. The FIF signal is output from the output terminal.

  Similarly, when the signal of the second reception frequency F2 is input from the input terminal of the RF frequency band, the mixer 12d is an intermediate corresponding to the difference (F2−FL) between the second reception frequency F2 and the local oscillation frequency FL. A frequency FIF signal is output from the output terminal.

  Note that the mixer 12d, when the signal of the first reception frequency F1 and the signal of the second reception frequency F2 are simultaneously input from the input terminal of the RF frequency band, the difference between the frequencies (FL−F1, F2-FL) is output from the output terminal in a mixed state.

  In this case, a logical sum of the first reception frequency F1 and the second reception frequency F2 is output from the output terminal of the mixer 12d, and two types of signals are mixed in the intermediate frequency FIF. Since it is only necessary to detect the radio wave transmitted from the ETC roadside device, there is no problem even if two types of signals are mixed in the intermediate frequency FIF.

  The relationship between the first frequency F1, the second frequency F2, the local oscillation frequency FL, and the local oscillation frequency FIF is shown in Equation 2.

(Formula 2)
FIF = (FL−F1) = (F2−FL)
Specifically, since F1 = 5795 MHz, F2 = 5805 MHz, and FL = 5800 MHz, FIF = 5 MHz.

  The rectifier circuit 12e is configured by a detection circuit that performs half-wave rectification using a diode, and outputs a DC signal corresponding to the signal input from the mixer 12d.

  The peak hold circuit 12 f holds the maximum value (maximum voltage value) of the signal input from the rectifier circuit 12 e and outputs the held value to the control circuit 15. The peak hold circuit 12f is reset by the reset signal periodically inputted from the control circuit 15.

  As described above, the radio wave transmitted from the ETC road device is received by the low elevation ETC antenna 12a, amplified by the low noise amplifier 12b, and down-converted to a signal in the IF frequency band by the mixer 12d. The down-converted signal is rectified by the rectifier circuit 12e, and the maximum value held by the peak hold circuit 12f is output. Then, the control circuit 15 determines whether or not there is a radio wave transmitted from the ETC roadside device based on whether or not the output of the peak hold circuit 12f is greater than or equal to a predetermined threshold value.

  Further, as described above, when the signal of the first reception frequency F1 and the signal of the second reception frequency F2 are simultaneously input to the input terminal of the RF frequency band, the mixer 12d has a difference between the frequencies ( (FL-F1, F2-FL) are output from the output terminal in a mixed state, but not only the signal but also the noise of the frequency component of the first reception frequency F1 and the frequency component of the second reception frequency F2. Similarly, the noise is output from the output terminal in a state where the noise of the frequency component corresponding to the difference between the frequencies (FL-F1, F2-FL) is mixed in the intermediate frequency FIF. In this case, the noise is output from the output terminal of the mixer 12d. Since the noise contained in the output signal is doubled, the reception sensitivity can be lowered.

  An example of the input / output reception level of the mixer 12d of the ETC in-vehicle device during the traveling of the vehicle is shown in FIG. As shown in FIG. 5, when the vehicle passes through the toll gate, each signal of the first reception frequency F1 (indicated by a one-dot chain line) and the second reception frequency F2 (indicated by a two-dot chain line) of the ETC in-vehicle device. The reception level changes with the passage of time due to the influence of multipath due to reflection and the like.

  However, since the mixer output (indicated by the solid line) is in a state where both the signal of the first reception frequency F1 and the signal of the second reception frequency F2 are mixed, a diversity effect is obtained and reception in an actual field environment is performed. Sensitivity is improved.

  For example, when a vehicle passes through a toll gate where both an ETC roadside device that transmits a radio wave of the first reception frequency and an ETC roadside device that transmits a radio wave of the second reception frequency is installed, the above-described diversity effect is substantially effective. The reception sensitivity can be improved.

  FIG. 6 shows the structure of a general tollgate on a toll road. The toll gate shown in the figure has one lane and one general lane at the entrance (entrance toll gate) and exit (exit toll gate). And the roadside antenna of the ETC roadside machine (not shown) is provided in the upper part of each ETC lane of an entrance and an exit. These roadside antennas are provided in front of the toll booth.

  Further, in the in-vehicle device 1 shown in FIG. 1, the directivity of the high elevation ETC antenna 11a of the transmission / reception circuit 11 receives the radio wave from the roadside antenna. It is installed in the room front. Further, the ETC antenna 12a having a low elevation angle of the radio wave detection circuit 12 receives radio waves from the roadside antenna in front of the ETC roadside device, and therefore has a higher directivity in the vertical direction than the ETC antenna 11a having a high elevation angle of the transmission / reception circuit 11. Is installed at a low elevation angle.

  In such a configuration, the control circuit 15 of the ETC in-vehicle apparatus 1 periodically monitors the signal input from the radio wave detection circuit 12 and determines whether or not the presence or absence of the radio wave transmitted from the ETC roadside device has been detected. To do. When the vehicle approaches the toll gate, it is determined that there is a radio wave transmitted from the ETC roadside machine based on the signal output from the radio wave detection circuit 12. Then, based on the signal input from the IC card state detection circuit 13, it is determined whether or not there is forgetting to insert the IC card 20 into the ETC in-vehicle device or insertion failure. When it is determined that there is no forgetting to insert the IC card 20 into the ETC in-vehicle device or there is no defective insertion, information for payment of the toll is stored in the IC card 20 and the toll of the toll stored in the IC card 20 is stored. Information for payment is read out and transmitted to the ETC roadside device via the transmission / reception circuit 11. Also, if it is determined that the IC card 20 has been forgotten to be inserted into the ETC in-vehicle device or if there is a defective insertion, an audio signal is output to the audio output circuit 14, and the IC card "No IC card is inserted." Alternatively, a warning such as “IC card cannot be recognized” is generated.

  As a result, the driver can change the course to the general lane before entering the ETC lane.

  As described above, the radio wave detection circuit 12 includes the low elevation angle antenna 12a that receives the radio wave of the first reception frequency F1 and the radio wave of the second reception frequency F2 transmitted from the road device, and the signal of the local oscillation frequency FL. And a mixer for converting the signal of the first reception frequency F1 and the signal of the second reception frequency F2 received by the antenna into an intermediate frequency FIF according to the local oscillation frequency FL from the local oscillator The local oscillation frequency FL of the signal output from the local oscillator is (FL) = (F1 + F2) / 2.

  Thus, since the local oscillation frequency FL of the signal output from the local oscillator is (FL) = (F1 + F2) / 2, the radio wave of the first reception frequency F1 and the radio wave of the second reception frequency F2 Is converted to a constant intermediate frequency, and the presence or absence of radio waves transmitted from the roadside device can be detected without providing a PLL synthesizer.

  Further, the ETC in-vehicle device 1 determines whether or not at least one of the radio wave of the first reception frequency F1 and the radio wave of the second reception frequency F2 is based on the detection result of the radio wave detection circuit 12, and is transmitted from the ETC roadside device. If the IC card insertion state detection circuit 13 detects an IC card insertion state, and the IC card insertion state detection circuit 13 detects an IC card insertion abnormality, the voice output circuit 14 Warn the user.

Thus, since the presence / absence of at least one of the radio wave of the first reception frequency F1 and the radio wave of the second reception frequency F2 is determined based on the detection result of the radio wave detection circuit 12, the ETC roadside device provided in the toll gate When the vehicle passes through the toll gate based on the presence / absence of the radio wave transmitted from the terminal, it is possible to warn of forgetting to insert the IC card into the ETC in-vehicle device or a defective insertion in advance.
In addition, this invention is not limited to the said embodiment, Based on the meaning of this invention, it can implement with a various form.

  In the above embodiment, the radio wave detection circuit 12 shown in FIG. 3 detects the radio wave transmitted from the ETC roadside machine. However, the mixer 12d and the local oscillator 12c shown in FIG. A single side band type image suppression mixer may be used. This image suppression type mixer is composed of mixers 22c, 22d, 90 ° 3d hybrids 22e, 22g, and converts the received signal (high frequency input signal) into an intermediate frequency signal according to the local oscillation frequency of the local oscillator 22f. Each signal in the intermediate frequency band corresponding to the first reception frequency and the second reception frequency (the signal of the third reception frequency and the signal of the fourth reception frequency) is output separately. The switching circuit 22h can alternately output a signal of the third reception frequency and a signal of the fourth reception frequency.

  In the circuit shown in FIG. 7, the local oscillation frequency of the signal output from the local oscillator 22f is set to the value shown in Equation 1, and it is determined whether or not the signal level in the intermediate frequency band is equal to or higher than a predetermined threshold value. For example, the presence / absence of the signal of the first reception frequency and the signal of the second reception frequency can be detected without providing a PLL synthesizer. That is, the radio wave transmitted from the ETC roadside device can be detected. In this case, since the noise of the frequency component of the first reception frequency F1 and the noise of the frequency component of the second reception frequency F2 are not mixed and output from the output terminal, the noise does not double. . Therefore, the reception sensitivity does not decrease.

  Further, in the above embodiment, the mixer 12d of the radio wave detection circuit 12 outputs a signal of two types of frequencies mixed in a certain intermediate frequency band, and the in-vehicle device 1 is based on the signal level of this intermediate frequency band. In this example, the presence / absence of radio waves transmitted from an ETC road device is detected. In addition to the use of detecting the presence / absence of radio waves of two types of frequencies, for example, a plurality of frequencies such as spread spectrum communication are used. You may apply to the communication system which can be demodulated even if the signal of a component is mixed.

In the above embodiment, the example in which at least one of the radio waves of the first reception frequency and the radio waves of the second reception frequency is received with high sensitivity by the diversity effect shown in FIG. 5 has been described. In addition to detection of the presence / absence of radio waves transmitted from the network, the present invention is also effective when applied to frequency diversity and space diversity.

It is a figure which shows the block configuration of the ETC vehicle-mounted apparatus which concerns on one Embodiment of this invention. It is explanatory drawing of an ETC vehicle-mounted apparatus. It is a figure which shows the structure of a radio wave detection circuit. It is a figure which shows the input / output relationship of the mixer of an electromagnetic wave detection circuit. It is a figure which shows an example of the input / output reception level of the mixer of an ETC vehicle-mounted apparatus. It is a figure which shows the structure of the general toll booth of a toll road. It is explanatory drawing about other embodiment. It is a figure for demonstrating the control by a PLL synthesizer.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... ETC vehicle-mounted apparatus, 11 ... Transmission / reception circuit, 12 ... Radio wave detection circuit,
12a ... ETC antenna, 12b ... low noise amplifier, 12c ... local oscillator,
12d: mixer, 12e: rectifier circuit, 12f: peak hold circuit,
DESCRIPTION OF SYMBOLS 13 ... IC card state detection circuit, 14 ... Audio | voice output circuit, 15 ... Control circuit.

Claims (2)

A detection circuit for detecting the presence or absence of at least one of a radio wave having a first reception frequency and a radio wave having a second reception frequency transmitted from a road device,
An antenna (12a) for receiving the radio wave of the first reception frequency and the radio wave of the second reception frequency;
A local oscillator (12c) that outputs a signal of a local oscillation frequency;
A mixer (12d) that converts the signal of the first reception frequency and the signal of the second reception frequency received by the antenna into an intermediate frequency according to the local oscillation frequency from the local oscillator,
The detection circuit characterized in that the local oscillation frequency of the signal output from the local oscillator is set to (F1 + F2) / 2 where F1 is a first reception frequency and F2 is a second reception frequency. . A detection circuit (12) according to claim 1,
Determination means for determining the presence or absence of at least one of the radio wave of the first reception frequency and the radio wave of the second reception frequency based on the detection result of the detection circuit;
IC card insertion state detection means (13) for detecting the insertion state of the IC card when the determination means determines that there is a radio wave transmitted from the ETC roadside device;
An in-vehicle device, comprising: warning means (14) that warns a user when the IC card insertion state detecting means detects an abnormal insertion of the IC card.

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