JP2005156440A - Doppler radar apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a Doppler radar system of simple circuit configuration capable of measuring a velocity of an object stably against a temperature, by solving a problem wherein a conventional Doppler radar apparatus has a large-scaled circuit and a problem wherein measurement precision is varied greatly by a temperature in the conventional Doppler radar apparatus. <P>SOLUTION: In this Doppler radar apparatus for transmitting a transmission wave to receive a reception wave reflected from the object, and for detecting a frequency difference between the transmission wave and the reception wave to measure the velocity of the object, the reception signal is detected to extract a Doppler signal, the Doppler signal is pulse-shaped into a fixed amplitude and a fixed pulse width of pulse waveform by a pulse shaping circuit, and the pulse waveform is smoothed to obtain velocity information. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a Doppler radar device using a millimeter wave or quasi-millimeter wave band. In particular, the present invention relates to an on-vehicle Doppler radar device that operates stably with respect to temperature.

  In recent years, Doppler radar devices are mounted on vehicles for the purpose of collision prevention and auto cruise. In such a vehicle-mounted Doppler radar device, since the received wave reflected from the object is affected by the Doppler effect, by detecting the difference frequency between the radiated transmitted wave and the received received wave, It measures speed.

  A received wave affected by the Doppler effect can be extracted as a Doppler signal by detection. As a detection method, for example, the difference frequency component between the transmission wave and the reception wave can be extracted by mixing the transmission wave and the reception wave. The difference frequency component is a Doppler signal.

  In order to convert the Doppler signal into speed information, there is a method of reading the frequency directly from the Doppler signal with a frequency counter (see, for example, Patent Document 1). However, the method of converting to speed information using a frequency counter increases the circuit scale, and the measurement accuracy is determined by an oscillator built in the frequency counter. The oscillator varies greatly with temperature, and a crystal oscillator placed in an oven or the like is used.

  As another method of converting the Doppler signal into speed information, there is a method of converting the Doppler signal into a voltage using a frequency-voltage conversion circuit. The frequency-voltage conversion circuit includes a resonance circuit or a circuit using a filter attenuation region. FIG. 1 shows an operation principle of converting a Doppler signal into a voltage using a frequency-voltage conversion circuit using a low-pass filter. 1 (1) shows the frequency component of the Doppler signal, FIG. 1 (2) shows the frequency characteristic of the low-pass filter, and FIG. 1 (3) shows the time-lapse characteristic of the signal voltage that has passed through the low-pass filter. When the Doppler signal is converted into a constant amplitude, only the frequency varies depending on the speed of the object, as shown in FIG. This Doppler signal is input to a low-pass filter having a frequency characteristic shown in FIG. In the frequency characteristic shown in FIG. 1 (2), since the frequency component of the Doppler signal is in the attenuation region of the low-pass filter, the Doppler signal is converted into an amplitude corresponding to the frequency. An example of the time course of this amplitude is shown in FIG. By converting the amplitude value shown in FIG. 1 (3) into a speed, the speed of the object can be known.

However, the characteristics of the attenuation region of the low-pass filter are affected by temperature, and in particular, a vehicle-mounted Doppler radar device having a large temperature fluctuation requires a temperature correction circuit. Since the correction circuit is adapted to the temperature characteristics of each low-pass filter, much adjustment is required.
JP-A-6-75045

  Thus, the conventional Doppler radar device has a large circuit scale, and the measurement accuracy varies greatly with temperature. An object of the present invention is to provide a Doppler radar device that can measure the speed of an object stably with respect to temperature and has a simple circuit configuration.

  In order to achieve the above object, the present invention radiates a transmission wave, receives a reception wave reflected from the object, and detects the frequency difference between the transmission wave and the reception wave, thereby reducing the speed of the object. A Doppler radar device for measuring, detecting a received wave, extracting a Doppler signal, shaping the Doppler signal into a pulse waveform with a constant amplitude and a constant pulse width by a pulse shaping circuit, and smoothing the pulse waveform This is a Doppler radar device that obtains speed information. With such a circuit configuration, the Doppler radar device can be stably operated with respect to temperature.

  A Doppler signal is a signal obtained by demodulating a reflected wave of a radio wave radiated to a moving object. Generally, it includes at least an amplitude fluctuation due to a frequency shift due to the Doppler effect and a reflectance fluctuation of the object.

  Specifically, the present invention includes a transmission circuit for transmitting a transmission wave, a transmission antenna for radiating a transmission wave from the transmission circuit, a reception antenna for receiving a reception wave reflected from an object, and the reception antenna. A receiving circuit that detects a received wave of the received signal and outputs a Doppler signal, and a pulse train that has a pulse waveform with a constant amplitude and a constant pulse width from the receiving circuit, and that appears at a frequency corresponding to the frequency of the Doppler signal A Doppler radar device comprising: a pulse shaping circuit that performs pulse shaping; and a low-pass filter that smoothes a pulse waveform from the pulse shaping circuit.

  The present invention includes a Doppler radar device characterized in that a transmission wave transmitted from the transmission circuit has a constant frequency. By using a transmission wave having a constant frequency, the detection operation in the receiving circuit can be facilitated.

  In the present invention, the pulse shaping circuit differentiates the output from the amplitude limiting circuit into a pulse waveform having a constant amplitude from the Doppler signal from the receiving circuit, and outputs a rising or falling waveform. Also included is a Doppler radar device characterized by having a differentiating circuit and a monostable multivibrator circuit that uses the output from the differentiating circuit as a trigger to generate a pulse waveform with a constant amplitude and a constant pulse width. The pulse shaping circuit has a simple configuration, and the Doppler radar device can be stably operated with respect to temperature.

  The present invention also includes a Doppler radar device characterized in that the pulse width of the pulse waveform from the monostable multivibrator circuit is shorter than the minimum period of the Doppler signal. It can accurately measure the maximum measurement range of the speed of the Doppler radar device.

The present invention also includes a Doppler radar device characterized in that a low-pass cutoff frequency of the low-pass filter is lower than a maximum frequency of the Doppler signal. It is possible to measure accurately to the minimum measurement range of the speed of the Doppler radar device.
Note that the low-pass cutoff frequency of the low-pass filter is a frequency at which the frequency characteristic of the low-pass filter attenuates by 3 dB.

  The Doppler radar device of the present invention can be stably operated with respect to temperature with a simple circuit configuration.

  The best mode for carrying out the present invention will be described below with reference to the accompanying drawings. FIG. 2 is a diagram for explaining an embodiment of the Doppler radar device according to the present invention, and is a block diagram of the Doppler radar device. In FIG. 2, reference numeral 11 denotes an oscillator which oscillates at a constant frequency within a frequency band used by the Doppler wave radar device. Reference numeral 12 denotes a distributor. Reference numeral 14 denotes a power amplification circuit, which amplifies the power of the transmission wave radiated by the Doppler wave radar device. The oscillator 11, the distributor 12, and the power amplifier circuit 14 constitute a transmission circuit. A transmission antenna 15 radiates a transmission wave. The transmission antenna 15 may be composed of a plurality of antennas. Reference numeral 21 denotes a receiving antenna that receives a received wave reflected from an object. The receiving antenna 21 may also be composed of a plurality of antennas. A preamplifier circuit 22 amplifies a weak received wave. A mixing circuit 23 detects a received wave at a frequency in a frequency band used by the Doppler radar device and outputs a Doppler signal. A pulse shaping circuit 24 shapes the Doppler signal into a pulse waveform having a constant amplitude and a constant pulse width. A low-pass filter 25 smoothes the pulse waveform. The preamplifier circuit 22, the mixing circuit 23, the oscillator 11, and the distributor 12 constitute a receiving circuit.

  The operation of the Doppler radar device according to the present embodiment will be described with reference to FIGS. 3 and 4 are waveforms in each circuit of the Doppler radar device of the present embodiment, and (A), (B), (C), (F), and (G) in FIG. Each waveform in A, B, C, F, and G shown is represented. 3 and 4, the horizontal axis represents time. The oscillator 11 in FIG. 2 oscillates a transmission wave having a constant frequency within a frequency band used by the Doppler wave radar device. An oscillation waveform at a constant frequency is shown in FIG. The distributor 12 of FIG. 2 distributes the transmission wave from the oscillator 11 into two, and outputs one to the power amplifier circuit 14 and the other to the mixing circuit 23. The power amplification circuit 14 amplifies the transmission wave from the distributor 12 and sends it to the transmission antenna 15. The transmission antenna 15 radiates the transmission wave from the power amplification circuit 14 toward the object.

  When reflected from the object, a frequency shift depending on the speed of the object occurs due to the Doppler effect. The reception wave reflected by the object is received by the reception antenna 21 and amplified by the preamplifier circuit 22 with a predetermined amplification degree. The preamplifier circuit 22 is preferably a low noise amplifier circuit while matching impedance with the receiving antenna 21. An output waveform from the preamplifier circuit 22 is shown in FIG. As can be seen from FIG. 3B, a frequency shift due to the Doppler effect occurs compared to FIG. In addition, the amplitude varies due to variations in reflectance of the object and propagation characteristics to the object. Next, in the mixing circuit 23 of FIG. 2, the output from the preamplifier circuit 22 is detected by the transmission wave from the distributor 12, and a Doppler signal is output. The Doppler signal is shown in FIG. As can be seen from FIG. 3C, the Doppler signal also shows a frequency shift due to the Doppler effect according to the velocity of the object, and an amplitude variation due to a variation in the reflectance of the object and propagation characteristics to the object. In addition, in the relationship between FIG. 3 (A), FIG. 3 (B), and FIG. 3 (C), the frequency is not necessarily displayed correctly.

  The obtained Doppler signal is pulse-shaped by a pulse shaping circuit 24 into a pulse waveform having a constant amplitude and a constant pulse width. FIG. 4C shows the Doppler signal, and FIG. 4F shows the pulse waveform after pulse shaping. In the pulse waveform (FIG. 4 (F)) from the pulse shaping circuit 24, amplitude fluctuation information due to fluctuations in the reflectance of the object and the propagation characteristics from the Doppler signal (FIG. 4 (C)) to the object is removed. Only the frequency shift information due to the Doppler effect is extracted as the pulse density. That is, when the approaching speed is fast, the pulse density is high, and when the approaching speed is slow, the pulse density is low.

  The pulse width of the pulse waveform (FIG. 4F) from the pulse shaping circuit 24 is preferably shorter than the period of the Doppler signal (FIG. 4C). In other words, the pulse width of the pulse waveform from the pulse shaping circuit 24 is made shorter than the period at the maximum frequency of the Doppler signal, so that the trailing edge of the pulse waveform pulse-shaped by the pulse shaping circuit 24 and the pulse of the pulse adjacent to it. Since the leading edge of the waveform does not overlap, the measurement accuracy of the Doppler radar device can be prevented from deteriorating.

  When the pulse waveform from the pulse shaping circuit 24 of FIG. 2 is smoothed by the low-pass filter 25, an output level corresponding to the speed of the object is obtained. A waveform of the output level is shown in FIG. That is, when the pulse density is high, the output level is high, and when the pulse density is low, the output level is low. Therefore, the output level of the low-pass filter 25 corresponds to the speed of the object. FIG. 7 shows the relationship between the Doppler signal and the frequency characteristics of the low-pass filter. FIG. 7A shows an example of the frequency characteristic of the Doppler signal, and FIG. 7B shows an example of the frequency characteristic of the low-pass filter. Fc in FIG. 7 (2) is a low-pass cutoff frequency at which the frequency characteristic of the low-pass filter attenuates by 3 dB. The low-pass cutoff frequency of the low-pass filter 25 is preferably set lower than the maximum frequency of the Doppler signal. The basic frequency of the pulse waveform output from the pulse shaping circuit is lower than the maximum frequency of the Doppler signal, and if the low-pass cutoff frequency of the low-pass filter is set lower than the maximum frequency of the Doppler signal, the low-pass filter pulses The fundamental frequency of the waveform can be removed, and the pulse waveform can be smoothed. If the high frequency component of the pulse waveform that has been pulse-shaped can be smoothed, deterioration of measurement accuracy can be prevented.

  If the output level shown in FIG. 4G is converted into a speed, a speed display can be obtained. The output level shown in FIG. 4G may correspond to the speed as an analog signal, or the output level shown in FIG. 4G may correspond to the speed by digital processing after A / D conversion.

  Since the Doppler radar device having the configuration shown in FIG. 2 does not use the attenuation region of the low-pass filter, stable characteristics with respect to temperature can be obtained. Therefore, the Doppler radar device of this embodiment can stably measure the speed of the object with respect to the temperature.

  Instead of the oscillator 11 shown in FIG. 2, it may be a pulse oscillator that oscillates in a pulse with a constant period within a frequency band used by the Doppler wave radar device. In this case, after radiating the transmission wave from the transmission antenna at a constant cycle, the reception wave reflected from the object is received after a time corresponding to the round trip time to the object, and the mixing circuit 23 shown in FIG. A Doppler signal is output at a period.

  Instead of the oscillator 11 shown in FIG. 2, a frequency modulation oscillator that oscillates by frequency-modulating with a sawtooth wave within a frequency band used by the Doppler wave radar device may be used. In this case, when the received wave reflected from the object is received, the mixing circuit 23 shown in FIG. 2 outputs a signal having a frequency having a frequency shift corresponding to the round trip time to the object.

  A specific example of the above-described pulse shaping circuit will be described. A configuration example of the pulse shaping circuit of FIG. 2 is shown in FIG. In FIG. 5, reference numeral 24 denotes a pulse shaping circuit, which pulses a Doppler signal into a pulse waveform having a constant amplitude and a constant pulse width. Reference numeral 31 denotes an amplitude limiting circuit, which makes the Doppler signal a pulse waveform with a constant amplitude. A differentiation circuit 32 differentiates the signal and outputs a rising or falling waveform. Reference numeral 33 denotes a monostable multivibrator circuit which converts a signal into a pulse waveform having a constant amplitude and a constant pulse width.

  The operation of the pulse shaping circuit of the present invention will be described with reference to FIGS. FIG. 6 is a waveform in each part of the pulse shaping circuit of the present embodiment, and (C), (D), (E), and (F) in the figure are C, D, E, and F shown in FIG. Each waveform in is represented. In FIG. 6, the horizontal axis represents time. The amplitude limiting circuit 31 shown in FIG. 5 converts the Doppler signal from the mixing circuit 23 shown in FIG. As the amplitude limiting circuit, a comparison circuit that converts a constant value into a binary signal can be applied. The comparison circuit has a simple circuit configuration and stable characteristics with respect to temperature. As the amplitude limiting circuit, a Schmitt trigger circuit that converts to a binary signal with two threshold values can be applied. Since the Schmitt trigger circuit also has hysteresis with respect to the input signal, it can be a circuit that is resistant to noise.

  The waveform of the Doppler signal from the mixing circuit 23 is shown in FIG. 6C, and the pulse waveform of a constant amplitude from the amplitude limiting circuit 31 is shown in FIG. 6D. Since the mixing circuit 23 outputs beats of the transmission wave and the reception wave, the amplitude is uneven and the frequency is modulated as shown in FIG. In order to extract only frequency information from this waveform, the amplitude limiting circuit 31 generates a pulse waveform having a constant amplitude as shown in FIG.

  In the differentiating circuit 32 shown in FIG. 5, a pulse waveform having a constant amplitude is differentiated and a rising or falling waveform is output. An output waveform from the differentiation circuit 32 is shown in FIG. The differentiation circuit 32 obtains a differentiated waveform in order to drive a monostable multivibrator circuit described later. Here, as shown in FIG. 6E, only the rising waveform of the differential waveform is used.

  Next, the monostable multivibrator circuit 33 shown in FIG. 5 outputs a pulse waveform having a constant amplitude and a constant pulse width using the differential waveform from the differentiation circuit 32 as a trigger. The monostable multivibrator circuit is used for generating a pulse having a constant amplitude and a constant pulse width starting from a trigger signal. The pulse waveform output from the monostable multivibrator circuit 33 is shown in FIG. When the monostable multivibrator is driven using the differential waveform of FIG. 6E as a trigger, a pulse waveform having a constant amplitude and a constant pulse width corresponding to the period of the differential waveform is obtained as shown in FIG. 6F. When the pulse waveform shown in FIG. 6F is smoothed by the low-pass filter 25 shown in FIG. 2, an output level corresponding to the speed of the object is obtained as shown in FIG. 4G. That is, when the pulse density is high, the output level is high, and when the pulse density is low, the output level is also low. Therefore, the output level corresponds to the speed of the object.

  The pulse shaping circuit described in FIG. 5 does not use a circuit sensitive to temperature, and thus operates stably with respect to temperature. Therefore, by applying this pulse shaping circuit to the Doppler radar device of FIG. 2, the Doppler radar device can measure the velocity of the object stably with respect to temperature.

   As described above, the Doppler radar device according to the present embodiment can be realized with a simple circuit configuration, and does not use a temperature unstable component, so that the object is stable with respect to temperature. Can be measured. Since the Doppler radar device of the present embodiment operates stably even with respect to temperature, when mounted on a vehicle, the speed of the object is fixed if the target is a fixed object, and the mounted vehicle if the target is a moving object. It is possible to accurately measure the relative speed between the object and the object.

  The Doppler radar device of the present invention can be applied to a vehicle-mounted device for vehicle collision prevention and auto cruise purposes, and can also be used as a fixed Doppler radar device.

It is a figure which shows the operation | movement principle which converts a Doppler signal into a voltage using a frequency-voltage conversion circuit using a low-pass filter. It is a figure explaining embodiment of the Doppler radar apparatus which is this invention, Comprising: It is a block diagram explaining the structure of a Doppler radar apparatus. It is a figure explaining the waveform in each circuit of the Doppler radar apparatus of this Embodiment. It is a figure explaining the waveform in each circuit of the Doppler radar apparatus of this Embodiment. It is a figure explaining the structural example of the pulse shaping circuit applied to the pulse wave radar apparatus which is this invention. It is a figure explaining the waveform in each part of the pulse shaping circuit of this Embodiment. It is a figure explaining the relationship between the frequency characteristic of the low-pass filter used in this Embodiment, and the frequency characteristic of a Doppler signal.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Oscillator 12 Divider 14 Power amplifier circuit 15 Transmitting antenna 21 Reception antenna 22 Preamplifier circuit 23 Mixing circuit 24 Pulse shaping circuit 25 Low-pass filter 31 Amplitude limiting circuit 32 Differentiating circuit 33 Monostable multivibrator circuit

Claims (5)

A transmission circuit for transmitting a transmission wave;
A transmission antenna that radiates a transmission wave from the transmission circuit;
A receiving antenna for receiving a received wave reflected from an object;
A receiving circuit for detecting a received wave from the receiving antenna and outputting a Doppler signal;
A pulse shaping circuit for shaping the Doppler signal from the receiving circuit into a pulse train having a pulse waveform having a constant amplitude and a constant pulse width and appearing at a frequency according to the frequency of the Doppler signal;
A low-pass filter for smoothing a pulse waveform from the pulse shaping circuit;
Doppler radar device. The Doppler radar device according to claim 1, wherein a transmission wave transmitted from the transmission circuit has a constant frequency. The pulse shaping circuit comprises:
An amplitude limiting circuit for converting the Doppler signal from the receiving circuit into a pulse waveform having a constant amplitude;
A differentiating circuit for differentiating the output from the amplitude limiting circuit and outputting a rising or falling waveform;
The Doppler radar device according to claim 1, further comprising: a monostable multivibrator circuit that uses an output from the differentiating circuit as a trigger to generate a pulse waveform with a constant amplitude and a constant pulse width. 4. The Doppler radar device according to claim 1, wherein a pulse width of a pulse waveform from the pulse shaping circuit is shorter than a minimum period of the Doppler signal. 5. 5. The Doppler radar device according to claim 1, wherein a low-frequency cutoff frequency of the low-pass filter is lower than a maximum frequency of the Doppler signal.

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