JP2002250767A - Distance measuring instrument - Google Patents

Abstract

PROBLEM TO BE SOLVED: To simplify constitution for distance measurement. SOLUTION: A transmit wave having its frequency modulated by a voltage- controlled oscillator 10 with an input signal is radiated from a transmitting antenna 12. This radio wave is reflected by an object, received by a receiving antenna 14, and demodulated by an FM receiver 16. The demodulated signal is binarized by a voltage comparator, inverted by a logic inverter 20, delayed by a specific quantity by a digital delay circuit 22, and amplified by an amplitude adjuster 24 to a specific amplitude. After a voltage corresponding to the amplified carrier frequency from a power source 28 for signal transmission frequency setting is added, the resulting signal is supplied as an input signal to the voltage-controlled oscillator 10.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a distance measuring device for receiving a reflected wave from an object and measuring a distance to the object.

[0002]

2. Description of the Related Art Conventionally, various distance measuring devices are known. A transmitting wave is radiated from an antenna, a reflected wave from an object is received, and a distance to the object is measured based on the reflected wave. Radar-type distance measuring devices are widely used.

For example, Japanese Patent Application Laid-Open No. 4-52586 discloses that
An example of such a distance measuring device is described. In this device, a subcarrier which is an output of a subcarrier voltage control oscillator is input to a transmitter, a carrier is modulated by the subcarrier, and the modulated radio wave is emitted from an antenna to an object. The reflected wave from the object is received by the receiver and demodulated, and the subcarrier voltage controlled oscillator is controlled by the PLL circuit so that the phase difference between the demodulated signal and the subcarrier from the subcarrier voltage controlled oscillator becomes zero. Is controlled by

[0004] Thus, the distance R to the object is f
When 0 is the frequency of the subcarrier signal output from the subcarrier voltage controlled oscillator and c is the speed of light, R = c /
2f0, and the distance to the object can be obtained.

[0005]

However, such a conventional configuration requires a subcarrier oscillator and a PLL circuit, and has a problem that the circuit becomes large-scale and complicated.

SUMMARY OF THE INVENTION The present invention has been made in consideration of the above problems, and has as its object to provide a distance measuring device capable of reliably measuring a distance with a simple circuit.

[0007]

SUMMARY OF THE INVENTION The present invention provides a transmitter for outputting a transmission wave modulated according to an input signal, a transmission antenna for transmitting a transmission wave from the transmitter, and a transmission antenna for transmitting the transmission wave from the transmission antenna. A receiving antenna that receives a reflected wave of an object with respect to the transmitted wave, a receiver that demodulates the received wave received by the receiving antenna, and amplifies the output of the receiver, and supplies an amplified signal as an input signal to the oscillator. And an amplifier for supplying the closed circuit including a reciprocating path to the object, thereby operating the closed circuit as a resonance circuit, and detecting the resonance frequency of the resonance circuit to reach the object. Measure the distance.

As described above, according to the present invention, since the distance is measured using the oscillation of the closed circuit including the amplifier, a subcarrier oscillation circuit and a PLL circuit are not required, and the circuit is simplified. Can be.

It is preferable that the apparatus further comprises amplitude control means for controlling the amplitude of the amplified signal to a predetermined value. Thus, the oscillation can be maintained by maintaining the amplification factor at 1 or more, and the oscillation can be prevented from becoming too large.

Preferably, the transmitter is a voltage-controlled oscillator, and outputs a transmission wave frequency-modulated according to an input signal. The frequency modulation can be easily performed by the voltage controlled oscillator, and the attenuation of the reflected wave and the influence of noise can be reduced by the frequency modulation.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. The voltage controlled oscillator 10 functioning as an FM transmitter oscillates at a frequency according to the supplied input signal (voltage signal). The oscillation output (transmission wave) of the voltage-controlled oscillator 10 is, for example, a radio wave of several tens of GHz and is frequency-modulated by an input signal.
The oscillation output of the voltage controlled oscillator 10 is
2 is emitted toward the object. For example, when monitoring the front of the vehicle, the radiation is emitted toward the front of the vehicle.

The reflected wave reflected by the object is received by the receiving antenna 14, and the received wave is input to the FM receiver 16, where it is subjected to reception processing. In particular, in the FM receiver 16, FM demodulation is performed, a carrier component is removed, and a baseband signal is obtained. Then, this baseband signal is supplied to the voltage comparator 18, where it is binarized (digitized).

The output of the voltage comparator 18 is supplied to a logical inverter 20.
, Where it is logically inverted and the inverted signal is supplied to the digital delay circuit 22. The digital delay circuit 22
The signal is delayed by a predetermined time τ0. The delay signal from the digital delay circuit 22 is amplified and converted into an analog signal having an appropriate amplitude by an amplitude adjuster 24 functioning as an amplifier and amplitude control means.

The output of the amplitude adjuster 24 is the voltage adder 2
6. The voltage signal from the transmission frequency setting power supply 28 is also supplied to the voltage adder 26, and the two are added to generate an analog voltage signal, which is supplied to the voltage controlled oscillator 10 as an input signal. In particular, the output voltage from the transmission frequency setting power supply 28 is a voltage corresponding to a carrier in a transmission wave from the voltage controlled oscillator 10. Basically low voltage. The transmission wave that is the output of the voltage controlled oscillator 10 is a signal obtained by subjecting a carrier having a frequency determined by the output of the transmission frequency setting power supply 28 to frequency modulation using the output of the amplitude adjuster 24 as a modulation signal. The output of the logic inverter 20 is also supplied to the frequency counter 30. This frequency counter 30 counts the cycle of the output of the logic inverter 20 and
And outputs the output frequency.

As described above, in the apparatus according to the present embodiment, a closed circuit including a reciprocating path to the object is formed. In particular,
The carrier wave voltage from the transmission frequency setting power supply 28 is input to the path by the voltage adder 26 and is removed by the FM receiver 16. Therefore, this signal is not a signal circulating in a closed circuit. On the other hand, the output of the FM receiver 16 is the voltage comparator 1
8. A closed circuit consisting of a logic inverter 20, a digital delay circuit 22, an amplitude adjuster 24, a voltage adder 26, a voltage controlled oscillator 10, a transmitting antenna 12, and a receiving antenna 14 is circulated. Therefore, this closed circuit operates as a resonance circuit for a signal having a frequency corresponding to the delay amount of the circuit, and a signal having the resonance frequency is obtained at the output of the logic inverter 20.

Here, in this circuit, the original signal is not input. However, the FM receiver 16 outputs some noise even when there is no received wave. Therefore,
A signal of a specific frequency of the noise is amplified in a closed circuit and resonates, and the frequency of the resonance signal is detected by the frequency counter 30.

Here, assuming that the distance from the transmitting antenna 12 or the receiving antenna 14 to the object is R, the reciprocating distance of this route is 2R, and the delay time τ caused by the radio wave reciprocating on this route is: 2R / c where c is the speed of light
(Τ = 2R / c).

The delay amount of the digital delay circuit 22 is τ0, and the total delay amount of the closed circuit is τ + τ0. And
Since the signal is inverted by the logic inverter 20, the signal whose delay amount becomes 180 ° in terms of phase becomes in-phase and resonates.

Therefore, the reciprocal of the period twice as long as the delay time τ + τ0 of the circuit is the resonance frequency f. That is, the resonance frequency f = 0.5 / (τ + τ0). Therefore, f = 0.
5 / (2R / c + τ0), and R = 0.5c (0.5
/ F−τ0), the distance R is calculated.

Therefore, the delay amount τ of the digital delay circuit 22
Since 0 is known, the distance R to the object is obtained based on the resonance frequency f detected by the frequency counter 30.

As described above, according to the distance measuring circuit of the present embodiment, the circuit is simply oscillated simply by taking into account noise and the like, and a subcarrier oscillating circuit and a PLL circuit are not required, and the circuit can be simplified.

Here, the digital delay circuit 22 is provided for easily counting the resonance frequency f by the frequency counter 30 and stabilizes the operation of the closed circuit, and may be omitted. Further, the amplitude adjuster 24 adjusts the amplitude so that the amplitude of the resonance signal becomes appropriate. When the amplification factor is less than 1, the signal is not amplified and resonance does not occur. On the other hand, when the amplification factor is too large, stable resonance cannot be performed. Therefore, it is necessary to adjust the amplitude with the amplitude adjuster 24. Furthermore, the logic inverter 20 can also be omitted, and without this logic inverter, the reciprocal is the resonance frequency f because the delay time τ + τ0 corresponds to 360 °. That is, f = 1 / (τ + τ0), and the distance R = 0.5c
(1 / f-τ0).

Further, in the present embodiment, a digital circuit is used, but all may be constituted by analog circuits. Further, the frequency modulation can be easily performed by the voltage-controlled oscillator, and the frequency modulation is performed by the voltage-controlled oscillator, so that the attenuation of the reflected wave and the influence of noise can be reduced. Note that the modulation can be AM modulation.

The occurrence of resonance in the circuit of this embodiment can be basically regarded as the configuration shown in FIG. That is, the output of the logic inverter 30 is supplied to the digital delay circuit 32, and the output of the digital delay circuit 32 is input to the logic inverter 30, thereby forming a closed circuit. And the logical inverter 30
The output of is taken out.

A logical inverter (NOT) 30 used as a basic component of such a digital circuit inverts an input logical value and outputs the inverted logical value. As shown in FIG. 2, when a digital delay circuit 32 is inserted between the input and the output to form a closed circuit,
Oscillates with a rectangular wave whose cycle is twice as long as the delay time of the digital delay circuit 32. This is because a rectangular wave having a certain cycle has an input and an output of the logical inverter 30 in phase with each other due to a transmission delay in the digital delay circuit 32. The source of oscillation is noise generated in the circuit. The logic inverter 30 can be regarded as a high gain inversion amplifier in an analog manner, and the noise generated near the threshold value of the logic level is amplified and finally oscillates.

In the circuit of this embodiment, basically the same phenomenon occurs, and the circuit oscillates at the above-described resonance frequency.

[0027]

As described above, according to the present invention,
Since the distance is measured using oscillation of a closed circuit including an amplifier, a subcarrier oscillation circuit, a PLL circuit, and the like are not required, and the circuit can be simplified.

Further, by controlling the amplitude of the amplified signal to a predetermined value, it is possible to maintain oscillation at an amplification factor of 1 or more and to prevent the oscillation from becoming too large.

Further, by controlling the amplitude of the amplified signal to a predetermined value, the oscillation can be maintained by maintaining the amplification factor at 1 or more, and the oscillation can be prevented from becoming too large. Further, the frequency modulation can be easily performed by the voltage controlled oscillator, and the attenuation of the reflected wave and the influence of noise can be reduced by the frequency modulation.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating an overall configuration of an apparatus according to an embodiment.

FIG. 2 is a diagram illustrating oscillation.

[Explanation of symbols]

Reference Signs List 10 voltage controlled oscillator, 12 transmitting antenna, 14 receiving antenna, 16 FM receiver, 18 voltage comparator, 2
0 Logical inverter, 22 digital delay circuit, 24 amplitude adjuster, 26 voltage adder, 28 power supply for setting transmission frequency, 30 frequency counter.

Claims (3)

[Claims] 1. A transmitter for outputting a transmission wave modulated in accordance with an input signal, a transmission antenna for transmitting a transmission wave from the transmitter, and an object for the transmission wave transmitted from the transmission antenna. A receiving antenna for receiving a reflected wave, a receiver for demodulating a received wave received by the receiving antenna, and an amplifier for amplifying an output of the receiver and supplying an amplified signal to the oscillator as an input signal. A distance measuring device that forms a closed circuit including a reciprocating path to the object by using these, operates the closed circuit as a resonance circuit, and measures a distance to the object by detecting a resonance frequency of the resonance circuit. . 2. The distance measuring device according to claim 1, further comprising an amplitude control unit that controls an amplitude of the amplified signal to a predetermined value. 3. The distance measuring device according to claim 1, wherein the transmitter is a voltage-controlled oscillator, and outputs a transmission wave frequency-modulated according to an input signal.