JP2013205101A - Radio terminal distance measuring system, and distance measuring system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a radio terminal distance measuring system capable of narrowing a bandwidth and simplifying the configuration of a radio terminal while maintaining a high measurement accuracy.SOLUTION: A radio terminal distance measuring system includes: a reference oscillator 10 for oscillating a reference signal which is the signal of a reference frequency; a mixed signal in which first and second signals of a reference frequency which is a frequency difference between thereof are transmitted from a distance measuring device and received in a radio terminal and then mixed together; a first phase comparator 21 for performing a phase comparison with the reference signal; a VCO 23 for controlling the phase and the frequency of an output signal so as to make a phase difference zero; first and second phase synchronization circuits 30, 40 for multiplying the frequency to the output signal and generating the first and second signals, respectively; and a second phase comparator 60 for performing the phase comparison with the phase of the reference signal oscillated by the reference oscillator 10, and measures a distance with the radio terminal based on the phase difference outputted by the second phase comparator 60.

Description

  The present invention relates to a system and apparatus for measuring a distance to a wireless terminal, and more particularly to a technique for improving distance measurement accuracy.

  A technique for measuring a distance to a measurement object using radio waves is widely known, for example, called radar. As a technique for measuring a distance with high accuracy in a radar, a pulse radar is known. In the pulse radar, it is known that the distance measurement accuracy is improved by widening the band (for example, Patent Document 1).

JP 2012-32161 A

  Patent Document 1 discloses that the distance measurement accuracy is improved by widening the band. However, in order to effectively use radio resources, it is desirable to narrow the band while realizing high distance measurement accuracy. It is.

  Further, when considering a wireless terminal distance measurement system in which a distance measuring device measures the distance to a wireless terminal carried by a person by communicating with the wireless terminal, the portability of the wireless terminal is not impaired as much as possible. Therefore, it is desirable that the configuration mounted on the wireless terminal for distance measurement is as simple as possible.

  The present invention has been made based on this situation, and the object of the present invention is to provide a wireless terminal distance capable of narrowing the band and simplifying the configuration of the wireless terminal while maintaining high distance measurement accuracy. An object of the present invention is to provide a measurement system and a distance measurement device used in the system.

The present invention for achieving the object is a wireless terminal distance measuring system comprising a wireless terminal and a distance measuring device, wherein the distance measuring device measures the distance from the distance measuring device to the wireless terminal,
The distance measuring device includes:
A reference oscillator that oscillates a reference signal that is a reference frequency signal;
A first signal for comparing the phase of the mixed signal after the first and second signals having a frequency difference of the reference frequency are transmitted from the distance measuring device and received by the wireless terminal is compared with the reference signal. A phase comparator;
An output signal oscillation circuit for controlling the phase and frequency of the output signal so that the phase difference compared with the reference signal by the first phase comparator becomes zero;
First and second phases for generating the first and second signals by multiplying the frequency of the output signal while synchronizing the phase with the output signal based on the output signal output from the output signal oscillation circuit. A synchronization circuit;
A second phase comparator for performing a phase comparison between the phase of the output signal output from the output signal oscillation circuit and the phase of the reference signal oscillated by the reference oscillator;
The distance from the distance measuring device to the wireless terminal is measured based on the phase difference output from the second phase comparator.

  According to the present invention, the phase comparison between the reference signal and the mixed signal is performed by the first phase comparator, and the output signal oscillation circuit outputs the output signal so that the phase difference compared by the first phase comparator becomes zero. Is output. Although this output signal is once divided into a first signal and a second signal, the phases of the first signal and the second signal are synchronized with the output signal, and the mixed signal input to the first phase comparator is: The first signal and the second signal are signals mixed after being received by the wireless terminal. Therefore, the configuration including the first phase comparator and the output signal oscillation circuit constitutes a phase synchronization circuit that returns from the distance measurement device to the distance measurement device via the wireless terminal.

  Therefore, the phase of the reference signal and the phase of the output signal should match if there is no time delay for the signal to propagate between the distance measuring device and the wireless terminal. In other words, the phase difference between the reference signal and the output signal indicates the time that the signal propagates between the distance measuring device and the wireless terminal. Therefore, in the second phase comparator, the phase of the output signal and the phase of the reference signal can be compared, and the distance from the wireless terminal can be measured using the phase difference output from the second phase comparator. It is.

  According to the present invention, the first and second phase synchronization circuits generate two first and second signals whose frequency difference is the reference frequency while synchronizing the phase with the output signal. The mixed signal is a signal mixed after the first and second signals are transmitted to the wireless terminal. This mixed signal rises when the phases of the first signal and the second signal coincide with each other, but since the frequency difference between the first signal and the second signal is the reference frequency, the first signal and the second signal The period in which the phases match is the same length as the period of the reference signal.

  When the phase coincidence of the first signal and the second signal is multiple times within one cycle of the reference signal, that is, when there are multiple rising edges of the mixed signal within one cycle of the reference signal, the multiple rising times Either of these may coincide with the rising edge of the reference signal. However, if the wrong rising edge of the mixed signal is matched with the rising edge of the reference signal, it leads to a distance measurement error. On the other hand, in the present invention, since the period of the mixed signal is the same as the period of the reference signal, there is only one rise of the mixed signal within one period of the reference signal. It is theoretically impossible to match the rising edge of the reference signal. Therefore, since the phase difference between the phase of the mixed signal and the phase of the reference signal accurately reflects the distance to the wireless terminal, the distance to the wireless terminal can be measured with high accuracy.

  In the present invention, the first signal and the second signal transmitted from the distance measuring device are each a single frequency obtained by multiplying the reference frequency, so that the used frequency band can be narrowed.

  Further, according to the present invention, the mixed signal for comparing the phase difference with the reference signal is a signal obtained by mixing the first signal and the second signal, and the first signal and the second signal are generated by the distance measuring device. Yes. Further, the mixed signal itself is not synchronized with other signals. Therefore, since it is not necessary to perform phase synchronization in the wireless terminal, it is not necessary to mount a complicated circuit in the wireless terminal for distance measurement, and the configuration of the wireless terminal can be simplified.

In the invention of claim 2, the wireless terminal is
A local oscillator,
A terminal receiving unit that receives the first signal and the second signal transmitted from the distance measuring device, and a first signal and a second signal received by the terminal receiving unit are respectively mixed with a signal oscillated by the local oscillator. A mixer,
A terminal transmitter for transmitting the first signal and the second signal after frequency conversion by the mixer,
The distance measuring device includes:
A first receiver and a second receiver for receiving the first signal and the second signal transmitted by the terminal transmitter, respectively;
And a mixed signal generator for mixing the first signal and the second signal received by the first receiver and the second receiver to generate a mixed signal to be input to the first phase comparator.

  In this way, the wireless terminal only includes a receiving unit and a transmitting unit, a local oscillator, and a mixer as a configuration for distance measurement, and the local oscillator outputs a signal synchronized with the signal on the distance measuring device side. Since it is not necessary to oscillate, a circuit for synchronizing the signals is also unnecessary. Therefore, the configuration of the wireless terminal can be simplified and reduced in size. In addition, since a passive mixer can be used, the power consumption of the wireless terminal can be reduced.

  The invention of claim 3 is an invention of a distance measuring device in the wireless terminal distance measuring system of claim 2.

It is the figure which showed the radio | wireless terminal distance measuring apparatus 1 of this invention notionally. It is a figure which shows the signal shown in FIG. 1 on the same time axis. 1 is a configuration diagram of a wireless tag distance measuring system 100 as an embodiment of a wireless terminal distance measuring system. FIG. It is a conceptual lineblock diagram of radio terminal distance measurement system 400 of a comparative example. It is a figure which shows the signal in the radio | wireless terminal distance measurement system of FIG. 4 on the same time axis.

  Hereinafter, the present invention will be described with reference to the drawings. First, the concept of the present invention will be described with reference to FIG. FIG. 1 is a diagram conceptually showing the configuration of a distance measuring device 1 in the wireless terminal distance measuring system of the present invention. The wireless terminal distance measuring system according to the present invention includes a distance measuring device 1 and a wireless terminal not shown in FIG.

The distance measuring device 1 includes a reference oscillator 10. The reference oscillator 10 oscillates a signal having a reference frequency (here, 10 MHz). The phase of the reference signal oscillated by the reference oscillator 10 is “ω _10M t + θ _ref ”.

  The reference signal is input to the first phase comparator 21 and the second phase comparator 60. The first phase comparator 21 receives the reference signal and a mixed signal described later, and detects the phase difference between the reference signal and the mixed signal. For example, the phase difference is detected by detecting the time difference between the rising edges of both signals, and an error signal pulse proportional to the phase difference is output as a phase comparison result.

  The low-pass filter 22 removes harmonic components from the pulse signal output from the first phase comparator 21. The signal that has passed through the low-pass filter 22 is input to the voltage controlled oscillation circuit 23 as a control signal.

The voltage controlled oscillation circuit 23 corresponds to the output signal oscillation circuit of the claims, and controls the output frequency by the input voltage. Hereinafter, the voltage controlled oscillation circuit is referred to as a VCO (Voltage controlled oscillator). An output signal output from the VCO 23 is input to the phase comparator 31 of the first phase synchronization circuit 30, the phase comparator 41 of the second phase synchronization circuit 40, and the second phase comparator 60. The phase of the output signal output from the VCO 23 is “ω _10M t + θ ₁ ” as shown in FIG.

  The first synchronization circuit 30 includes a low-pass filter 32, a VCO 33, and a frequency divider 34 in addition to the phase comparator 31 described above. The phase comparator 31 receives the output signal output from the VCO 23 and the first signal output from the VCO 33 after being frequency-divided. The phase comparator 31 outputs a pulse signal indicating the phase difference between the two signals. The low pass filter 32 removes a high frequency component from the signal output from the phase comparator 31 and outputs it as a control signal to the VCO 33.

The VCO 33 outputs a signal having a frequency corresponding to the control signal input from the low pass filter 32. A signal output from the VCO 33 is referred to as a first signal. The first signal is frequency-divided by the frequency divider 34, and the frequency-divided signal is input to the phase comparator 31. With this configuration, the first phase synchronization circuit 30 functions as a frequency synthesizer. The frequency generated by the first phase-locked loop circuit 30 can be set as appropriate depending on the ratio of the frequency divider 34 that divides, but here it is assumed to be 300 MHz as an example. Of course, this first signal is synchronized in phase with the output signal output by the VCO 23. Therefore, the phase of the first signal can be expressed as “ω _300M t + 30θ ₁ ” as shown in FIG.

The second phase synchronization circuit 40 includes the same components as the first phase synchronization circuit 30. That is, the second phase synchronization circuit 40 includes a phase comparator 41, a low-pass filter 42, a VCO 43, and a frequency divider 44. The difference between the second phase synchronization circuit 40 and the first phase synchronization circuit 30 is only the frequency of the output signal (referred to as the second signal). The second signal output from the second phase synchronization circuit 40 is set so that the frequency differs from the first signal output from the first phase synchronization circuit 30 by the reference frequency. In the following description, the frequency of the second signal is 310 MHz. Of course, the phase of the second signal is synchronized with the output signal output from the VCO 23. Therefore, the phase of the second signal can be expressed as “ω _310M t + 31θ ₁ ” as shown in FIG.

  The first signal and the second signal output from the first phase synchronization circuit 30 and the second phase synchronization circuit 40 reach the mixer 50 in a space with a propagation time δt. Then, the mixer 50 generates a mixed signal by mixing the first signal and the second signal.

As shown in FIG. 1, the phases of the signals transmitted through the first signal and the second signal are “ω _300M (t−δt) + 30θ ₁ ” and “ω _310M (t−δt) + 31θ, respectively. ₁ ". Therefore, the phase of the mixed signal can be expressed as “ω _10M (t−δt) + θ ₁ ” as shown in FIG. The mixed signal generated by the mixer 50 is input to the first phase comparator 21.

If the propagation time δt is not taken into account, the phase of the mixed signal is synchronized with the phase of the output signal of the VCO 23, and the mixed signal is input to the first phase comparator 21, so that the first phase comparator 21, The phase synchronization circuit 20 is configured by the low-pass filter 22 and the VCO 23. Therefore, the phase difference between the phase of the output signal (ω _10M t + θ ₁ ) output from the VCO 23 of the phase synchronization circuit 20 and the phase of the reference signal, that is, the phase difference output from the second phase comparator 60 is the propagation time. It is proportional to δt.

FIG. 2 shows the signals shown in FIG. 1 on the same time axis. 2, (A) is a reference signal, the phase is ω _10M t + θ _ref , (B) is an output signal output from the VCO 23, the phase is ω _10M t + θ ₁ , and (C) is a first signal output from the VCO 33. The phase is ω _300M t + 30θ ₁ , (D) is the second signal output from the VCO 43, the phase is ω _310M t + 31θ ₁ , and (E) is the first signal received by the mixer 50, and the phase is ω _300M (t−δt ) + 30θ ₁ , (F) is the second signal received by the mixer 50, the phase is ω _310M (t−δt) + 31θ ₁ , (G) is the mixed signal output by the mixer 50, and the phase is ω _10M (t− δt) is + θ _1.

  The phases of the first signal and the second signal shown in FIGS. 2C and 2D coincide with each other only once in a cycle of the reciprocal of 10 MHz, which is a frequency difference (hereinafter simply referred to as a 10 MHz cycle). Accordingly, the phases of the first signal and the second signal reaching the mixer 50 shown in (E) and (F), respectively, match only once every 10 MHz. Therefore, the cycle of the mixed signal is also a 10 MHz signal, and the rising edge of the mixed signal is a time point when the phases of the first signal and the second signal reaching the mixer 50 coincide.

In the phase synchronization circuit 20, the phase “wt + θ _ref ” (FIG. 2A) of the reference signal matches the phase “ω _10M (t−δt) + θ ₁ ” (FIG. 2G) of the mixed signal. Control. That is, control is performed so that θ _ref = −ω _10M δt + θ ₁ . As a result, the phase “ω _10M t + θ ₁ ” (FIG. 2B) of the output signal of the phase synchronization circuit 20 advances with respect to the phase “wt + θ _ref ” of the reference signal. At this time, the phase difference between the reference signal and the output signal of the phase synchronization circuit 20 is δt. Therefore, the phase difference output from the phase comparator 60 is proportional to the propagation time δt. Since this phase difference is output as a distance measuring voltage, the distance can be measured based on the distance measuring voltage.

  Next, an embodiment of a wireless terminal distance measurement system will be described. FIG. 3 is a configuration diagram of a wireless tag distance measurement system 100 as an embodiment of the wireless terminal distance measurement system. The wireless tag distance measuring system 100 includes a tag reader 200 as a distance measuring device and a wireless tag 300 as a wireless terminal.

  The tag reader 200 includes a transmission unit 70, a first reception unit 80, a second reception unit 90, and a low-pass filter 61 in addition to the configuration described in FIG. In FIG. 3, the frequency dividers 34 and 44 are shown with frequency division ratios of 1 / M and 1 / N, but M and N are, for example, 30 and 31, as described above.

  The wireless tag 300 includes a reception antenna 310, a transmission antenna 320, a local oscillator 330, and a mixer 340.

  First, the configuration of the tag reader 200 will be described. The transmission unit 70 includes two band-pass filters 71 and 73, and a first transmission antenna 72 and a second transmission antenna 74 connected to the two band-pass filters 71 and 73, respectively. The bandpass filters 71 and 73 pass signals in predetermined frequency bands including frequencies “M” and “N”, respectively. The band-pass filter 71 and the first transmission antenna 72 constitute a first transmission unit, and the band-pass filter 73 and the second transmission antenna 74 constitute a second transmission unit.

  The first signal output from the VCO 33 of the first phase synchronization circuit 30 is transmitted from the first transmission unit to the wireless tag 300, and the second signal output from the VCO of the second phase synchronization circuit 40 is the second transmission unit. To the wireless tag 300.

  The reception antenna 310 of the wireless tag 300 receives the first signal and the second signal transmitted from the first transmission antenna 72 and the second transmission antenna 74 of the tag reader 200. An example of the received first signal and second signal is the signal of FIGS. 2E and 2F described above.

  The local oscillator 330 oscillates a local oscillation signal having a predetermined frequency different from the transmission frequency band of the tag reader 200. The mixer 340 mixes the first signal and the second signal received by the receiving antenna 310 and the local oscillation signal. As a result, both the first signal and the second signal are signals having different frequencies from when the wireless tag 300 receives the signals. For example, the frequency is 100 MHz and 400 MHz and 410 MHz, respectively. The mixer 340 converts the frequency for the purpose of avoiding interference between the transmission radio wave and the reception radio wave, and does not need to be synchronized with the first signal and the second signal received by the reception antenna 310. Therefore, the mixer 340 does not include a synchronization circuit. The first signal and the second signal after being mixed by the mixer 340 are transmitted from the transmission antenna 320 to the tag reader 200.

  The signal transmitted by the wireless tag 300 is received by the first receiver 80 and the second receiver 90 of the tag reader 200, respectively. Although the frequency of the received signal is different from that at the time of transmission by the tag reader 300, the phase is synchronized once in the period of the reciprocal of the frequency difference, as shown in FIGS.

  The first receiving unit 80 and the second receiving unit 90 include antennas 81 and 91 and bandpass filters 82 and 92, respectively. The two band pass filters 82 are set so as to selectively pass either the first signal or the second signal after frequency conversion in the wireless tag 300.

  The signals that have passed through the bandpass filters 82 and 92 are mixed by the mixer 50. Thereby, as in the case of FIG. 1, the signal of FIG. 2G is generated.

  The reference signal (FIG. 2A) and the mixed signal (FIG. 2G) have a frequency of 10 MHz, that is, a wavelength of 30 m. In the case of the embodiment of FIG. 3, the delay time δt is proportional to the reciprocating distance between the tag reader 200 and the wireless tag 300. When this round-trip distance exceeds the wavelength (30 m) of the mixed signal, that is, when the distance to the wireless tag 300 exceeds 1/2 (15 m) of the wavelength of the mixed signal, one cycle (or more) with respect to the reference signal The phase difference is determined based on the rise of the delayed mixed signal. Therefore, the wavelengths of the reference signal and the mixed signal are preferably longer than twice the upper limit of the measurement distance.

  As described above, in the RFID tag distance measuring system 100 of the present embodiment described above, the first phase comparator 21 performs phase comparison between the reference signal and the mixed signal, and the phase difference compared by the first phase comparator 21 is the same. The VCO 23 outputs an output signal so that it becomes zero. Although this output signal is once divided into a first signal and a second signal, the phases of the first signal and the second signal are synchronized with the output signal, and the mixed signal input to the first phase comparator 21 is These signals are mixed after the first signal and the second signal are received by the wireless tag 300. Therefore, the phase synchronization circuit 20 that returns from the tag reader 200 to the tag reader 200 via the wireless tag 300 is configured by the configuration including the first phase comparator 21 and the VCO 23.

Therefore, the phase “ω _10M t + θ _ref ” of the reference signal and the phase “ω _10M t + θ ₁ ” of the output signal match if there is no signal delay time δt. In other words, the phase difference between the reference signal and the output signal indicates the signal delay time δt, that is, the time δt during which the signal propagates between the tag reader 200 and the wireless tag 300. Therefore, the distance to the wireless tag 300 is determined based on the phase difference output from the second phase comparator 60 that performs phase comparison between the phase “ω _10M t + θ ₁ ” of the output signal and the phase “ω _10M t + θ _ref ” of the reference signal. Can be measured.

(Comparative example)
Next, a wireless terminal distance measurement system of a comparative example is shown. The wireless terminal distance measurement system 400 of the comparative example shown in FIG. 4 is a conceptual configuration diagram as in FIG. The wireless terminal distance measurement system 400 in FIG. 4 includes the same reference oscillator 10, the phase synchronization circuit 20, the first phase synchronization circuit 30, and the second phase comparator 60 as those in FIG.

  In addition, the configuration on the wireless terminal side includes a mixer 410 and two phase synchronization circuits 420 and 430. The mixer 410 receives a 300 MHz signal transmitted from the first phase synchronization circuit 30 on the distance measuring device side and a 290 MHz signal output from the phase synchronization circuit 430 of the wireless terminal.

There is a space between the first phase locked loop 30 and the mixer 410, and it takes time δt for radio waves to propagate through this space. Therefore, as shown in FIG. 4, the phase of the 300 MHz signal input to the mixer 410 is “ω _300M (t−δt) + 30θ ₁ ”. In this comparative example, a 300 MHz signal input to the mixer 410 is a first signal, and a 290 MHz signal is a second signal.

The signal mixed by the mixer 410 is input to the phase synchronization circuit 420. This phase synchronization circuit 420 is a known phase synchronization circuit including a phase comparator 421, a low-pass filter 422, and a VCO 423. The output signal of the phase synchronization circuit 420 is input to the phase synchronization circuit 430 and also input to the phase comparator 21 which is the configuration on the distance measuring device side. Here, the phase of the output signal of the phase synchronization circuit 420 is assumed to be “ω _10M t + θ ₄ ”. When the output signal of the phase synchronization circuit 420 is input to the phase comparator 21 that is the configuration on the distance measuring device side, the phase “ω _10M t + θ ₄ ” and the phase “ω _10M t + θ _ref ” of the reference signal are synchronized. To do.

The phase synchronization circuit 430 includes a phase comparator 431, a low pass filter 432, a VCO 433, and a frequency divider 434. The frequency of the second signal generated by the phase synchronization circuit 430 is a frequency (290 MHz) that is lower than the frequency (300 MHz) of the signal transmitted by the distance measuring device by the frequency (10 MHz) of the reference signal. The phase of the second signal is “ω _290M t + 29θ ₄ ”.

When the first signal and the second signal are mixed by the mixer 410, a signal having a phase “ω _10M t + 30θ ₁ −29θ ₄ −ω _300M · δt” is obtained. The aforementioned phase “ω _10M t + θ ₄ ” is equivalent to this phase.

FIG. 5 is a diagram illustrating signals in the wireless terminal distance measurement system 400 of FIG. 4 on the same time axis. In the case of the configuration shown in FIG. 4, control is performed so that the phase of signal (A) and the phase of signal (E) shown in FIG. The signal (E) is a mixed signal of the first signal (FIG. 5C) and the second signal (FIG. 5D), and the phase of the signal (C) and the signal (D) coincides. Then the signal (E) rises. However, the phase of the signal (C) and the phase of the signal (D) match every 2nπ / ω _300M t. Therefore, in practice, it is difficult to correctly determine the edge of the frequency division reference, and there is a possibility that phase synchronization is performed based on the phase difference including the error 2nπ / ω _300M t. Therefore, even if the distance variation (relative distance) can be measured, the absolute distance cannot be measured.

  On the other hand, in the wireless terminal distance measurement system 1 (wireless tag distance measurement system 100) of the present invention, the first and second phase synchronization circuits 30 and 40 synchronize the phase with the output signal, and the reference frequency (10 MHz). ) To generate first and second signals having a frequency difference of. In the mixed signal whose phase is compared with the reference signal by the first phase comparator 21, the first and second signals are transmitted to the wireless tag 300, and the phase is not changed only by the frequency conversion in the wireless tag 300. This signal is mixed after being returned to the tag reader 200. This mixed signal rises when the phases of the first signal and the second signal coincide with each other, but since the frequency difference between the first signal and the second signal is the reference frequency (10 MHz), the first signal and the second signal The period in which the phases of the two signals are the same as the period of the reference signal.

  In the case of the comparative example, the phase match between the first signal (FIG. 5C) and the second signal (FIG. 5D) exists multiple times within one cycle of the reference signal (FIG. 5A). Therefore, as described with reference to FIG. 5, any of the plurality of rising edges may coincide with the rising edge of the reference signal, and it is difficult to correctly determine the division reference edge. If the edge is not correctly determined, a distance measurement error will occur.

  On the other hand, in the present invention, since the cycle of the mixed signal (FIG. 2 (G)) is the same as the cycle of the reference signal (FIG. 2 (A)), the rising of the mixed signal within one cycle of the reference signal. It is theoretically impossible that the erroneous rise of the mixed signal coincides with the rise of the reference signal. Therefore, since the phase difference between the phase of the mixed signal and the phase of the reference signal accurately reflects the distance to the wireless terminal (wireless tag 300), the distance to the wireless terminal (wireless tag 300) can be accurately determined. It can be measured.

  In the present invention, the first signal and the second signal transmitted from the distance measuring device 1 (tag reader 200) are each a single frequency multiplied by the reference frequency, and two signals transmitted by the wireless tag 300 are also included. The first signal and the second signal transmitted by the tag reader 200 are merely frequency-converted, and each has a single frequency. Therefore, the wireless terminal distance measurement system (wireless tag distance measurement system 100) of the present invention can narrow the use frequency band.

  Further, in the case of the comparative example, the wireless terminal requires two phase synchronization circuits 420 and 430 having a relatively large circuit scale, whereas in the present embodiment, the wireless tag 300 includes the transmission and reception antennas 310, 320, only the local oscillator 330 and the mixer 340 are provided, and the local oscillator 330 does not need to oscillate a signal synchronized with the signal on the tag reader 200 side, so that a circuit for synchronizing the signals is also unnecessary. Therefore, the wireless tag 300 can be simplified and downsized. In addition, since a passive type mixer 340 can be used, power consumption of the wireless tag 300 can be reduced.

  As mentioned above, although embodiment of this invention was described, this invention is not limited to the above-mentioned embodiment, It can implement in various changes within the range which does not deviate from a summary.

1: distance measuring device, 10: reference oscillator, 20: phase synchronization circuit, 21: first phase comparator, 22: low-pass filter, 23: voltage controlled oscillation circuit (VCO) (output signal oscillation circuit), 30: first Phase synchronization circuit 31: Phase comparator 32: Low-pass filter 33: VCO 34: Frequency divider 40: Second phase synchronization circuit 41: Phase comparator 42: Low-pass filter 43: VCO 44: Frequency divider, 50: mixer, 60: second phase comparator, 61: low-pass filter, 70: transmission unit, 71: band-pass filter, 72: first transmission antenna, 73: band-pass filter, 74: second transmission Antenna: 80: first receiving unit, 90: second receiving unit, 100: Line tag distance measuring system (wireless terminal distance measuring system), 200: tag reader (distance measuring device), 300: wireless tag (wireless terminal), 310: receiving antenna, 320: transmitting antenna (terminal transmitting unit), 330: local oscillator 340: mixer, 400: wireless terminal distance measurement system, 410: mixer, 420: phase synchronization circuit, 421: phase comparator, 422: low-pass filter, 423: VCO, 430: phase synchronization circuit, 431: phase comparator, 432: Low-pass filter, 433: VCO, 434: Frequency divider

Claims (3)

A wireless terminal distance measuring system comprising a wireless terminal and a distance measuring device, wherein the distance measuring device measures a distance from the distance measuring device to the wireless terminal,
The distance measuring device includes:
A reference oscillator that oscillates a reference signal that is a reference frequency signal;
A first signal for comparing the phase of the mixed signal after the first and second signals having a frequency difference of the reference frequency are transmitted from the distance measuring device and received by the wireless terminal is compared with the reference signal. A phase comparator;
An output signal oscillation circuit for controlling the phase and frequency of the output signal so that the phase difference compared with the reference signal by the first phase comparator becomes zero;
First and second phases for generating the first and second signals by multiplying the frequency of the output signal while synchronizing the phase with the output signal based on the output signal output from the output signal oscillation circuit. A synchronization circuit;
A second phase comparator for performing a phase comparison between the phase of the output signal output from the output signal oscillation circuit and the phase of the reference signal oscillated by the reference oscillator;
A wireless terminal distance measuring system for measuring a distance from a distance measuring device to a wireless terminal based on a phase difference output from the second phase comparator. In claim 1,
The wireless terminal is
A local oscillator,
A terminal receiver for receiving the first signal and the second signal transmitted by the distance measuring device;
A mixer that mixes each of the first signal and the second signal received by the terminal receiver with the signal oscillated by the local oscillator;
A terminal transmitter for transmitting the first signal and the second signal after frequency conversion by the mixer,
The distance measuring device includes:
A first receiver and a second receiver for receiving the first signal and the second signal transmitted by the terminal transmitter, respectively;
And a mixed signal generator for mixing the first signal and the second signal received by the first receiver and the second receiver to generate a mixed signal to be input to the first phase comparator. Wireless terminal distance measurement system. A distance measuring device for measuring a distance to a wireless terminal,
A reference oscillator that oscillates a reference signal that is a reference frequency signal;
A transmission unit that transmits first and second signals having a frequency difference from each other, the reference frequency;
After the first signal and the second signal are received by the wireless terminal, a first receiving unit and a second receiving unit that respectively receive the first signal and the second signal transmitted from the wireless terminal;
A mixed signal generator for mixing the first signal and the second signal received by the first receiver and the second receiver;
A first phase comparator that performs phase comparison between the mixed signal mixed by the mixed signal generator and the reference signal;
An output signal oscillation circuit for controlling the phase and frequency of the output signal so that the phase difference compared by the first phase comparator becomes zero;
Based on the output signal output from the output signal oscillation circuit, the first and second signals transmitted by the transmitter are generated by multiplying the frequency of the output signal by synchronizing the phase with the output signal, respectively. First and second phase synchronization circuits;
A second phase comparator for performing a phase comparison between the phase of the output signal output from the output signal oscillation circuit and the phase of the reference signal oscillated by the reference oscillator;
A distance measuring apparatus that measures a distance to the wireless terminal based on a phase difference output from the second phase comparator.

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