Patent Application
20060066473
1. Field of the Invention
The present invention relates to a pulse wave radar device that uses a millimetric wave or a submillimetric wave. More specifically, it relates to a pulse wave radar device that has an improved ability of detecting a reflected wave from a target in a close range.
2. Description of the Related Art
A pulse wave radar device is used which sends a pulse-modulated transmitting pulse wave and receives a receiving pulse wave reflected from the target, to calculate a distance to this target. Since a round-trip distance to a target can be obtained by integrating the light velocity with a lapse of time from a moment of sending transmitting pulse waves to a moment of receiving reflected waves from the target, the pulse wave radar device measures a lapse of time from a moment of sending a transmitting pulse to a moment of receiving a reflected wave from a target, to calculate a distance to the target.
Recently, a radar device has been installed in a vehicle for the purpose of collision prevention or automatic cruising. Such a pulse wave radar device sends a transmitting pulse wave and then gets ready for receiving a receiving pulse wave reflected from a target in a close range. A vehicle-installed pulse wave radar device detects a target in a wide range from several tens of centimeters to several tens of meters and so needs to have a distance resolution of several tens of centimeters. Therefore, a narrow pulse having a pulse width of about 1 ns is used in it.
However, the pulse wave radar device is disturbed in detection of a target if transmitting pulses leak from a pulse generation circuit to a receiving circuit or transmitting pulse waves leak from a modulation circuit or a transmitting antenna to a demodulation circuit or a receiving antenna.
If the pulse wave radar device encounters leakage as shown in
To reduce such leakage, a technology is disclosed to provide a wave absorber in a radome so that wraparound from a transmitting antenna 23 to a receiving antenna 31 may be prevented (see Japanese Patent Application Laid-Open No. 287568, for example). Another technology is disclosed to provide a switch to a preceding stage of a pre-amplification circuit 32 so that a transmitting pulse may be prevented from turning around to the receiving circuit (see Japanese Utility Model Application No. 5-11080, for example).
A conventional pulse wave radar device and a main leakage path in it are shown in
As for the main leakage paths, leakage C occurs as turning around from the transmitting antenna 23 to the receiving antenna 31, leakage B occurs due to a transmitting pulse wave modulated in the pulse wave radar device, and leakage A occurs due to a transmitting pulse in the pulse wave radar device. If a leakage pulse wave due to the leakage is large, a receiving pulse wave cannot be received until it is saturated in a receiving circuit and comes back to a normal state. To avoid such saturation, it is desirable to take countermeasures against leakage at the preceding stage of a reception system as much as possible.
Conventionally, leakage C of
As described above, the recent pulse wave radar device detects a target in a wide range from several tens of centimeters to several tens of meters, so that a thin pulse having a pulse width of about 1 ns is being used. Therefore, leakage (leakage A of
In view of this problem, it is an object of the present invention to provide a pulse wave radar device that can reduce effects not only of transmitting pulse wave leakage but also of leakage of a transmitting pulse that occurs in a pulse wave radar device, to prevent error detection due to the leakage, thereby accurately detecting a distance to a target in a close range.
To this end, a pulse wave radar device according to the present invention cuts off an output of a demodulation circuit so that no leakage pulse may be detected, during a time when a transmitting pulse wave to be transmitted from a transmitting antenna or a transmitting pulse generated by a pulse generation circuit is leaking to a receiving antenna or a receiving circuit.
Specifically, the present invention provides a pulse wave radar device that includes a transmitting circuit for periodically sending a transmitting pulse wave obtained by modulating a transmitting pulse, a transmitting antenna for transmitting a transmitting pulse wave from the transmitting circuit, a receiving antenna for receiving a receiving pulse wave reflected from a target, a demodulation circuit for demodulating a receiving pulse wave from the receiving antenna, and a cutoff circuit for temporarily shifting an output of the demodulation circuit from a conductive state to a cutoff state, in which the cutoff circuit cuts off the output of the demodulation circuit during a time when the transmitting pulse or the transmitting pulse wave is leaking in the pulse wave radar device.
By the present invention, it is possible to prevent error detection due to leakage by reducing effects not only of transmitting pulse wave leakage but also of transmitting pulse leakage that occurs in the pulse wave radar device, thereby accurately detecting a distance to a target in a close range.
The present invention provides another pulse wave radar device that includes a transmitting circuit for periodically sending a transmitting pulse wave obtained by modulating a transmitting pulse, a transmitting antenna for transmitting a transmitting pulse wave from the transmitting circuit, a receiving antenna for receiving a receiving pulse wave reflected from a target, a demodulation circuit for demodulating a receiving pulse wave from the receiving antenna, and a cutoff circuit for temporarily shifting an output of the demodulation circuit from a conductive state to a cutoff state, in which the cutoff circuit cuts off the output of the demodulation circuit until a moment timing that corresponds to a minimum detectable distance.
According to the present invention, by cutting off an output of the demodulation circuit until a moment timing which corresponds to a minimum detectable distance, it is possible to prevent error detection due to leakage by reducing effects not only of transmitting pulse wave leakage but also of transmitting pulse leakage which occurs in the pulse wave radar device.
In the pulse wave radar device of the present invention, preferably the cutoff circuit cuts off the output of the demodulation circuit starting from a moment timing that corresponds to a maximum detectable distance.
According to the present invention, by cutting off the output of the demodulation circuit starting from the moment timing that corresponds to the maximum detectable distance, it is possible to prevent error detection due to leakage by reducing effects not only of transmitting pulse wave leakage but also of transmitting pulse leakage which occurs in the pulse wave radar device.
Further, in the pulse wave radar device of the present invention, preferably the cutoff circuit shifts from a conductive state to a cutoff state and/or vice versa through a time-wise gradient.
By the present invention, occurrence of a noise owing to a cutoff operation can be reduced while cutting off leakage pulses, so that it is possible to prevent error detection due to leakage, thereby accurately detecting a distance to a target in a close range also.
Further, in the pulse wave radar device of the present invention, preferably the cutoff circuit is controlled to shift from a conductive state to a cutoff state and/or vice versa by a pulse wave-shape that changes through a time-wise gradient of a leading edge and/or a trailing edge.
By the present invention, occurrence of a noise owing to a cutoff operation can be reduced while cutting off leakage pulses, so that it is possible to prevent error detection due to leakage, thereby accurately detecting a distance to a target in a close range also.
Further, the pulse wave radar device of the present invention may further include a round-trip propagation time calculation circuit for calculating a round-trip propagation time to a target based on a difference in time between a timing when a transmitting pulse wave is transmitted from the transmitting antenna and a timing when a receiving pulse wave is received by the receiving antenna.
By the present invention, the round-trip propagation time to the target can be calculated easily.
The time-wise gradient in the present invention means a time-wise slope over which a rectangular wave passed through a primary or secondary low-pass filter rises or falls gradually.
By the present invention, it is possible to provide a pulse wave radar device that can prevent error detection due to leakage by reducing effects not only of transmitting pulse wave leakage but also of transmitting pulse leakage that occurs in the pulse wave radar device, thereby accurately detecting a distance to a target in a close range.
The following will describe embodiments of the present invention with reference to drawings. However, the present invention is not limited to the following embodiments.
A transmitting circuit includes the pulse generation circuit 11, the oscillator 12, the modulation circuit 21, and the power amplification circuit 22. A receiving circuit includes the oscillator 12, the pre-amplification circuit 32, the demodulation circuit 33, the baseband amplification circuit 34, the signal processing circuit 35, and the cutoff circuit 36.
First, a configuration of a transmission system of the pulse wave radar device is described with reference to
Next, a configuration of a reception system of the pulse wave radar device is described with reference to
Further, the signal processing circuit 35 may calculate a round-trip propagation time to the target based on a difference in time between a timing when a transmitting pulse from the transmitting circuit and a timing when a receiving pulse from the receiving circuit is detected. In
Furthermore, the signal processing circuit 35 may calculate a round-trip distance to the target by integrating the light velocity with the round-trip propagation time.
In the pulse wave radar device shown in
The cutoff circuit 36 is controlled at a timing when a transmitting pulse is output from the pulse generation circuit 11. That is, by measuring beforehand a timing at which a transmitting pulse or a transmitting pulse wave leaks, it is possible to set a period during which the output of the demodulation circuit 33 is to be cut off by the cutoff circuit 36 under the control from the pulse generation circuit 11.
As described above, by arranging the cutoff circuit 36 to a stage following the demodulation circuit 33, it is possible to prevent error detection due to leakage by reducing effects not only of leakage pieces B and C but also of leakage A of
The following will describe another embodiment of the pulse wave radar device with reference to
By such arrangement, a noise generated by the cutoff circuit 36 is not amplified by the baseband amplification circuit 34 so that a receiving pulse may be detected, thus having less influence on the detection of the receiving pulse. Further, even in a case where a pulse due to leakage is so large that a saturation level of the baseband amplification circuit 34 may be reached, this pulse due to leakage has a constant size, so that if a normal operation is recovered from the saturation state quickly, it is possible to reduce effects to the leakage by the cutoff circuit 36 easily.
In the pulse wave radar device shown in
The cutoff circuit 36 is controlled at a timing when a transmitting pulse is output from the pulse generation circuit 11. That is, by measuring beforehand a timing at which a transmitting pulse or a transmitting pulse wave leaks, it is possible to set a period during which the output of the baseband amplification circuit 34 is to be cut off by the cutoff circuit 36 under the control from the pulse generation circuit 11.
As described above, by arranging the cutoff circuit 36 to a stage following the baseband amplification circuit 34, it is possible to prevent error detection due to leakage by reducing effects not only of leakage pieces B and C but also of leakage A of
The pulse wave radar device shown in
A timing at which the cutoff circuit in the pulse wave radar device shown in
If the receiving pulse 42 is reflected from the target in a close range, to detect the receiving pulse 42, the cutoff circuit 36 needs to be back in a conductive state. A timing at which the leakage pulse 41 occurs can be acquired from the pulse generation circuit 11. Based on timing information from the pulse generation circuit 11, the circuit shifts from a conductive state to a cutoff state to provide the cutoff period 43. In the cutoff period 43, the circuit cuts off the pulse 41 that occurs owing to leakage and then passes through the transition period 44 from the cutoff state to the conductive state, to come back to the conductive state.
By such an operation, it is possible to properly detect the receiving pulse 42 from the target in a condition where the leakage pulse 41 is cut off, thereby preventing error detection due to leakage so that a distance to a target in a close range may be detected accurately.
A configuration example of the cutoff circuit 36 shown in
If a receiving pulse from a target at a minimum detectable distance reaches the input terminal (In), the FET comes back to the conductive state, so that the receiving pulse is transferred from the source terminal (S) to the drain terminal (D) of the FET and output from an output terminal (Out) to the baseband amplification circuit 34 or the signal processing circuit 35.
Although the present embodiment has used a GaAs-HEMT to constitute a main component of the cutoff circuit 36, the cutoff circuit can be constituted similarly using an MOS-FET or a silicon-made bipolar transistor.
Waveforms at the terminals of the cutoff circuit 36 shown in
The leakage pulse 41 and the receiving pulse 42 shown in
If such noises 45 and 46 are input to the signal processing circuit 35, they are mistakenly detected as a receiving pulse. Further, a steep transition from a conductive state to a cutoff state or vice versa is liable to cause a malfunction if a timing error has occurred. That is, if the control signal occurs too early, a leakage pulse remains as it is, and if the control signal occurs too late, a normal of receiving pulse is cut off.
To solve this problem, preferably the cutoff circuit has a configuration shown in
Waveforms at the terminals of the cutoff circuit 36 shown in
The leakage pulse 41 and the receiving pulse 42 shown in
By such an operation, it is possible to suppress occurrence of noises owing to cutoff operations in a condition where the leakage pulse 41 is cut off, thereby preventing error detection due to leakage so that a distance to a target in a close range may be detected accurately.
Since the conductive state is shifted to the cutoff state or vice versa gradually through a time-wise gradient, a timing error, if any, does not easily cause malfunction. That is, even if the control signal occurs too early, a leakage pulse remains only a little, and even if the control signal occurs too late, a normal of receiving pulse is not completely cut off. In particular, a receiving pulse from a close range immediately after recovery is made from the cutoff state has a large level, so that even if the control signal occurs too late, this receiving pulse can maintain a magnitude large enough to be detected by the signal processing circuit.
Although the control terminal (Cont) in the cutoff circuit 36 shown in
Further, if the control signal having a small pulse width is input to the control terminal (Cont), a noise is liable to occur at the output terminal (Out) of the cutoff circuit owing to leakage from the control terminal (Cont) to the output terminal (Out). To solve this problem, preferably the control terminal (Cont) is supplied with such a control signal as to gradually change through a time-wise gradient as shown in
Since control is conducted in such a manner that the conductive state may be shifted to the cutoff state or vice versa gradually through a time-wise gradient, a timing error, if any, does not easily cause malfunction. That is, even if the control signal occurs too early, a leakage pulse remains only a little, and even if the control signal occurs too late, a normal of receiving pulse is not completely cut off. In particular, a pulse received from a close range immediately after recovery is made from the cutoff state has a large level, so that even if the control signal occurs too late, this receiving pulse can maintain a magnitude large enough to be detected by the signal processing circuit.
Further, directly near the output side to the cutoff circuit 36 in the pulse generation circuit 11 shown in
By such an operation, it is possible to suppress occurrence of noises owing to cutoff operations in a condition where the leakage pulse 41 is cut off, thereby preventing error detection due to leakage so that a distance to a target in a close range may be detected accurately.
In the signal processing circuit shown in
In a certain configuration of the round-trip propagation time calculation circuit, an S-R type flip-flop circuit which is set at a timing when the pulse generation circuit 11 outputs a transmitting pulse and reset at a timing when the baseband amplification circuit 34 outputs a receiving pulse is combined with a low-pass filter that extracts a low-frequency component of an output of this S-R type flip-flop circuit. An example of the configuration of the round-trip propagation time calculation circuit is shown in
As shown in
The low-pass filter 39 extracts a low-frequency component of an output of the S-R type flip-flop circuit 38. That is, if a lapse of time is long from a timing when the pulse generation circuit outputs a transmitting pulse to a timing when a detector circuit outputs a receiving pulse, an output of the low-pass filter 39 has a large low-frequency component, and if the lapse of time is short from the timing when the pulse generation circuit outputs the transmitting pulse to the timing when the detector circuit outputs the receiving pulse, the output of the low-pass filter 39 has a small low-frequency component. By detecting the output of this low-pass filter 39, a round-trip propagation time to a target can be calculated. To display a distance to the target, the output of the low-pass filter 39 can be converted into a digital value.
In calculation of the distance to the target, a delay time through the transmitting circuit or the receiving circuit in the pulse wave radar device may be compensated by shifting a bias of an output level of the round-trip propagation time calculation circuit by as much as corresponding to the delay time or when calculating a distance to the target from the output of the round-trip propagation time calculation circuit.
Another round-trip propagation time calculation circuit may be a pulse count circuit in which a timing when a transmitting pulse is output from the pulse generation circuit is as a set input and a timing when a receiving pulse is output from the baseband amplification circuit is as a reset input. By generating a pulse that has a constant duration in a lapse of time from a set input to a reset timing and counting the number of pulses during the lapse of time by the pulse count circuit, a round-trip propagation time to the target can be calculated.
In either of the round-trip propagation time calculation circuits, by dividing a round-trip propagation time output from it by twice the light velocity, a distance to the target can be calculated.
Although the above embodiments have been described with respect to a case where the cutoff circuit 36 is put in a cutoff state at a timing of occurring of the leakage pulse 41, the present invention is not limited to this; for example, the cutoff circuit 36 may be held in the cutoff state until a timing which corresponds to a minimum detectable distance of the pulse wave radar device so that this cutoff circuit 36 would be put in the conductive state to pass a receiving pulse after that timing. Specifically, supposing the receiving pulse 42 shown in
Although the above embodiments have been described with respect to a case where the cutoff circuit 36 is put in the cutoff state at a timing when the leakage pulse 41 is generated and then shifted to the conductive state to pass the receiving pulse 42, the present invention is not limited to it; for example, when a lapse of time that corresponds to the maximum detectable distance of the pulse wave radar device elapses after the cutoff circuit 36 comes back to the conductive state, the cutoff circuit 36 may be shifted further to the cutoff state. By thus controlling the cutoff circuit, it is possible to prevent error detection from occurring due to an interference wave or noise from any other device that is received at a timing outside a detectable range. It is to be noted that in this case also, a transition period may be arranged when shifting the cutoff circuit 36 from the cutoff state to the conductive state.
As described above, even if a transmitting pulse wave leaks from a transmitting antenna or modulated circuit, or a transmitting pulse leaks from a pulse generation circuit, a pulse wave radar device comprising a cutoff circuit of the present invention can reduce effects not only of leakage of the transmitting pulse wave but also of leakage of the transmitting pulse that occurs in the pulse wave radar device, thereby preventing error detection due to the leakage so that a distance to a target in a close range can also be detected accurately.
A pulse wave radar device of the present invention can be applied as a vehicle-installed device for the purpose of collision prevention or automatic cruising and also as a fixed pulse wave radar device.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2004-283182 | Sep 2004 | JP | national |
