U.S. patent application number 17/221324 was filed with the patent office on 2021-07-22 for radar device, signal processor, signal processing method, and mobile object.
The applicant listed for this patent is SONY SEMICONDUCTOR SOLUTIONS CORPORATION. Invention is credited to Sachio IIDA, Kenichi KAWASAKI.
Application Number | 20210223360 17/221324 |
Document ID | / |
Family ID | 1000005493147 |
Filed Date | 2021-07-22 |
United States Patent
Application |
20210223360 |
Kind Code |
A1 |
IIDA; Sachio ; et
al. |
July 22, 2021 |
RADAR DEVICE, SIGNAL PROCESSOR, SIGNAL PROCESSING METHOD, AND
MOBILE OBJECT
Abstract
To provide a radar device, capable of eliminating the influence
based on the local feedthrough in the FMCW radar device. There is
provided a radar device including: an oscillator configured to
oscillate a local signal; a transmitting antenna configured to emit
a transmission signal based on the local signal; a receiving
antenna configured to receive a reflected wave in which the
transmission signal is reflected from a target; a mixer configured
to multiply the reflected wave and the local signal by each other
to produce a multiplied signal; and a first shifter provided
between the oscillator and the mixer and configured to shift a
phase of the local signal.
Inventors: |
IIDA; Sachio; (Kanagawa,
JP) ; KAWASAKI; Kenichi; (Tokyo, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
SONY SEMICONDUCTOR SOLUTIONS CORPORATION |
Kanagawa |
|
JP |
|
|
Family ID: |
1000005493147 |
Appl. No.: |
17/221324 |
Filed: |
April 2, 2021 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
16306050 |
Nov 30, 2018 |
11002830 |
|
|
PCT/JP2017/019628 |
May 25, 2017 |
|
|
|
17221324 |
|
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G01S 7/354 20130101;
G01S 13/343 20130101; G01S 13/34 20130101; G01S 2013/93271
20200101; G01S 13/87 20130101; G01S 7/038 20130101; G01S 7/35
20130101; G01S 2013/93272 20200101; G01S 13/931 20130101 |
International
Class: |
G01S 7/35 20060101
G01S007/35; G01S 13/34 20060101 G01S013/34; G01S 7/03 20060101
G01S007/03; G01S 13/931 20060101 G01S013/931 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 19, 2016 |
JP |
2016-141648 |
Claims
1. A radar signal processor, comprising: a memory; chirp control
signal circuitry configured to generate a chirp control signal,
wherein the chirp control signal is used to form a transmission
signal which is transmitted to a target which provides a reflected
wave from the target; and phase control signal circuitry configured
to generate phase control signals for the chirp control signal,
wherein the memory receives a beat signal generated from the
product of the reflected wave and the chirp control signal and
wherein the chirp control signal receives a first phase shift from
a first phase control signal of the phase control signal circuitry
and the transmission signal receives the first phase shift and a
second phase shift from a second phase control signal of the phase
control signal circuitry.
2. The radar signal processor according to claim 1, wherein the
first phase control signal sets a shift amount to a first value at
a first-time transmission of the transmission signal and sets the
shift amount to a second value at a second-time transmission of the
transmission signal.
3. The radar signal processor according to claim 2, wherein the
memory stores a value of a difference between the beat signal at
the first-time transmission of the transmission signal and the beat
signal at the second-time transmission of the transmission
signal.
4. The radar signal processor according to claim 2, wherein a
difference between the first value and the second value is
approximately 180 degrees.
5. The radar signal processor according to claim 2, wherein a
difference between the first value and the second value is within a
range of 180 degrees.+-.22.5 degrees.
6. The radar signal processor according to claim 1, wherein the
chirp signal is a signal whose frequency increases or decreases
with time.
7. The radar signal processor according to claim 1, wherein the
chirp signal is a signal whose frequency linearly increases or
decreases with time.
8. A radar signal processor, comprising: a memory; chirp control
signal circuitry configured to generate a chirp control signal,
wherein the chirp control signal is used to form a transmission
signal which is transmitted to a target which provides a reflected
wave from the target; and phase control signal circuitry configured
to generate phase control signals for the chirp control signal,
wherein the memory receives a beat signal generated from the
product of the reflected wave and the chirp control signal, wherein
the chirp control signal receives a phase shift from a phase
control signal of the phase control signal circuitry, and wherein a
frequency of the chirp control signal is multiplied by N times.
9. The radar signal processor according to claim 8, wherein the
memory stores a value of a difference between the beat signal at a
first-time transmission of the transmission signal and the beat
signal at a second-time transmission of the transmission
signal.
10. The radar signal processor according to claim 8, wherein the
phase control signal sets a shift amount to a first value at a
first-time transmission of the transmission signal and sets the
shift amount to a second value at a second-time transmission of the
transmission signal.
11. The radar signal processor according to claim 10, wherein a
difference between the first value and the second value is
approximately 180 degrees.
12. The radar signal processor according to claim 10, wherein a
difference between the first value and the second value is within a
range of 180 degrees.+-.22.5 degrees.
13. The radar signal processor according to claim 8, wherein the
chirp signal is a signal whose frequency increases or decreases
with time.
14. The radar signal processor according to claim 8, wherein the
chirp signal is a signal whose frequency linearly increases or
decreases with time.
15. A radar signal processor, comprising: a memory; chirp control
signal circuitry configured to generate a chirp control signal,
wherein the chirp control signal is used to form a transmission
signal which is transmitted to a target which provides a reflected
wave from the target; and phase control signal circuitry configured
to generate phase control signals for the chirp control signal,
wherein the memory receives a beat signal generated from the
product of the reflected wave and the chirp control signal, wherein
the transmission signal receives a phase shift from a phase control
signal of the phase control signal circuitry, and wherein a
frequency of the transmission signal is multiplied by N times.
16. The radar signal processor according to claim 15, wherein the
memory stores a value of a difference between the beat signal at a
first-time transmission of the transmission signal and the beat
signal at a second-time transmission of the transmission
signal.
17. The radar signal processor according to claim 15, wherein the
first phase control signal sets a shift amount to a first value at
a first-time transmission of the transmission signal and sets the
shift amount to a second value at a second-time transmission of the
transmission signal.
18. The radar signal processor according to claim 17, wherein a
difference between the first value and the second value is
approximately 180 degrees.
19. The radar signal processor according to claim 17, wherein a
difference between the first value and the second value is within a
range of 180 degrees.+-.22.5 degrees.
20. The radar signal processor according to claim 15, wherein the
chirp signal is a signal whose frequency increases or decreases
with time.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. application Ser.
No. 16/306,050 filed on Nov. 30, 2018, which is a national stage
application under 35 U.S.C. 371 and claims the benefit of PCT
Application No. PCT/JP2017/019628 having an international filing
date of May 25, 2017, which designated the United States, which PCT
application claimed the benefit of Japanese Patent Application No.
2016-141648 filed Jul. 19, 2016, the entire disclosures of each of
which are incorporated herein by reference.
TECHNICAL FIELD
[0002] The present disclosure relates to a radar device, a signal
processor, a signal processing method, and a mobile object.
BACKGROUND ART
[0003] A frequency-modulated continuous-wave (FMCW) radar device is
employed as a vehicle-mounted radar device in some cases. The
ranging performed by the FMCW radar device is as follows. A chirp
signal in which frequency linearly increases or decreases with time
is emitted as a transmission signal from a transmitting antenna,
and an echo signal reflected back from a target is caught by a
receiving antenna. Then, a local signal chirped at the same
frequency as the transmission signal and the echo signal are
multiplied by each other in a mixer and are subjected to direct
conversion reception. Then, at the time of direct conversion
reception, the frequency of the local signal varies during the
round trip time until the transmitted signal is reflected back from
the target, so a beat signal of the frequency proportional to the
distance to the target occurs.
[0004] It is known that the direct conversion reception causes
occurrence of a DC component based on a local feedthrough where the
local signal leaks from the receiving antenna due to incomplete
isolation between LO (local) and RF of a mixer. Thus, in one
example, there is a technique for eliminating the DC component
based on the local feedthrough, as disclosed in Patent Literature
1.
CITATION LIST
Patent Literature
[0005] Patent Literature 1: JP H5-235643A
DISCLOSURE OF INVENTION
Technical Problem
[0006] However, in the case of the FMCW radar device, both the
transmission signal and the local feedthrough are chirp signals, so
it is difficult to apply the technique for eliminating the DC
component as disclosed in Patent Literature 1.
[0007] In view of this, the present disclosure provides a novel and
improved radar device, signal processor, signal processing method,
and mobile object, capable of eliminating the influence based on
the local feedthrough in the FMCW radar device.
Solution to Problem
[0008] According to the present disclosure, there is provided a
radar device including: an oscillator configured to oscillate a
local signal; a transmitting antenna configured to emit a
transmission signal based on the local signal; a receiving antenna
configured to receive a reflected wave in which the transmission
signal is reflected from a target; a mixer configured to multiply
the reflected wave and the local signal by each other to produce a
multiplied signal; and a first shifter provided between the
oscillator and the mixer and configured to shift a phase of the
local signal.
[0009] In addition, according to the present disclosure, there is
provided a signal processor including: an oscillator configured to
oscillate a local signal; a mixer configured to multiply a
reflected wave in which a transmission signal based on the local
signal is reflected from a target and the local signal by each
other to produce a multiplied signal; and a shifter provided
between the oscillator and the mixer and configured to shift a
phase of the local signal.
[0010] In addition, according to the present disclosure, there is
provided a signal processing method including: oscillating, by an
oscillator, a local signal; emitting a transmission signal based on
the local signal from a transmitting antenna; receiving, by a
receiving antenna, a reflected wave in which the transmission
signal is reflected from a target; multiplying, by a mixer, the
reflected wave and the local signal by each other to produce a
multiplied signal; and shifting, by a shifter provided between the
oscillator and the mixer, a phase of the local signal.
[0011] Further, according to the present disclosure, there is
provided a mobile object including the radar device described
above.
Advantageous Effects of Invention
[0012] According to the present disclosure as described above,
there is provided a novel and improved radar device, signal
processor, signal processing method, and mobile object, capable of
eliminating the influence based on the local feedthrough in the
FMCW radar device.
[0013] Note that the effects described above are not necessarily
limitative. With or in the place of the above effects, there may be
achieved any one of the effects described in this specification or
other effects that may be grasped from this specification.
BRIEF DESCRIPTION OF DRAWINGS
[0014] FIG. 1 is a diagram illustrated to describe a configuration
example of an FMCW radar device.
[0015] FIG. 2 is a diagram illustrated to describe an example of a
frequency of a transmission signal, a frequency of an echo signal,
and a frequency of a beat signal, which vary with time.
[0016] FIG. 3 is a diagram illustrated to describe influence caused
by a local feedthrough in the FMCW radar device.
[0017] FIG. 4 is a diagram illustrated to describe a first
configuration example of the FMCW radar device according to an
embodiment of the present disclosure.
[0018] FIG. 5 is a diagram illustrated to describe a beat signal
derived from a transmission signal and a beat signal derived from a
local feedthrough, in a first-time chirp and a second-time
chirp.
[0019] FIG. 6 is a diagram illustrated to describe a second
configuration example of the FMCW radar device according to the
present embodiment.
[0020] FIG. 7 is a diagram illustrated to describe a third
configuration example of the FMCW radar device according to the
present embodiment.
[0021] FIG. 8 is a diagram illustrated to describe an example of a
vehicle on which the FMCW radar device is mounted.
MODE(S) FOR CARRYING OUT THE INVENTION
[0022] Hereinafter, (a) preferred embodiment(s) of the present
disclosure will be described in detail with reference to the
appended drawings. Note that, in this specification and the
appended drawings, structural elements that have substantially the
same function and structure are denoted with the same reference
numerals, and repeated explanation of these structural elements is
omitted.
[0023] Moreover, the description will be given in the following
order.
[0024] 1. Embodiment of present disclosure
[0025] 1.1. Overview
[0026] 1.2. Configuration example
[0027] 1.2.1. First configuration example
[0028] 1.2.2. Second configuration example
[0029] 1.2.3. Third configuration example
[0030] 1.3. Application example
[0031] 2. Concluding remarks
1. Embodiment of Present Disclosure
1.1. Overview
[0032] An overview of an embodiment of the present disclosure will
be described and then the embodiment of the present disclosure will
be described in detail.
[0033] As described above, an FMCW radar device is employed as a
vehicle-mounted radar device in some cases. The ranging performed
by the FMCW radar device is as follows. A chirp signal in which
frequency linearly increases or decreases with time is emitted as a
transmission signal from a transmitting antenna, and an echo signal
reflected back from a target is caught by a receiving antenna.
Then, a local signal chirped at the same frequency as the
transmission signal and the echo signal are multiplied by each
other in a mixer and are subjected to direct conversion reception.
Then, at the time of direct conversion reception, the frequency of
the local signal varies during the round trip time until the
transmitted signal is reflected back from the target, so a beat
signal of the frequency proportional to the distance to the target
occurs.
[0034] FIG. 1 is a diagram illustrated to describe a configuration
example of the FMCW radar device. In the FMCW radar device
illustrated in FIG. 1, a local oscillator outputs a local signal on
the basis of a chirp control signal sent from an FMCW radar signal
processor. The local signal output from the local oscillator is
amplified by a power amplifier and then is emitted as a
transmission signal from a transmitting antenna.
[0035] The transmission signal is reflected from a target. The
receiving antenna receives an echo signal reflected back from the
target. The echo signal received by the receiving antenna is
multiplied by the local signal in the mixer to produce a beat
signal. The beat signal is sent to the FMCW radar signal processor
and is used for ranging the distance to the target.
[0036] FIG. 2 is a diagram illustrated to describe an example of a
frequency of a transmission signal, a frequency of an echo signal,
and a frequency of a beat signal, which vary with time. The
frequency of the transmission signal increases linearly with time
from f.sub.0 to f.sub.0+BW. The echo signal linearly increases with
time from f.sub.0 to f.sub.0+BW with a delay of a round trip time
.tau. until the transmission signal is reflected back from the
target. The frequency f.sub.B of the beat signal is proportional to
the round trip time .tau. until the transmission signal is
reflected back from the target. Thus, the FMCW radar device is
capable of recognizing the distance to the target by getting to
know the frequency f.sub.B of the beat signal.
[0037] It is generally known that the direct conversion reception
causes a local feedthrough where the local signal leaks from the
receiving antenna due to incomplete isolation between LO (local)
and RF. In addition, it is known that, when the frequency of the
local signal does not vary with time, the local feedthrough returns
to the receiving antenna and the local feedthrough is multiplied by
the local signal in the mixer, resulting in a DC component. Thus,
in one example, as disclosed in Patent Literature 1, there is a
technique of eliminating the DC component based on the local
feedthrough using AC coupling (serial capacitors) or a high-pass
filter.
[0038] However, in the case of the FMCW radar device, the
transmission signal emitted from the transmitting antenna and the
local feedthrough leaked from the receiving antenna are both chirp
signals. Thus, the elimination using AC coupling or a high-pass
filter fails to be achieved.
[0039] FIG. 3 is a diagram illustrated to describe the influence
caused by local feedthrough in the FMCW radar device. The
transmission signal emitted from the transmitting antenna is
reflected from the target and becomes an echo signal 1. On the
other hand, the local feedthrough leaked from the receiving antenna
is reflected from the target and becomes an echo signal 2. The
respective echo signals received by the receiving antenna are
multiplied by the local signal in the mixer to produce beat signals
1 and 2. These two beat signals fail to be separated because they
have the same frequency, and the beat signal 2 caused by the local
feedthrough fail to be eliminated using AC coupling or a high-pass
filter.
[0040] Thus, in view of the above-mentioned points, those who
conceived the present disclosure have conducted intensive studies
on the technology capable of eliminating the influence based on the
local feedthrough in the FMCW radar device. Accordingly, those who
conceived the present disclosure have devised the technology
capable of eliminating the influence based on the local feedthrough
in the FMCW radar device by using a phase shifter as described
below.
[0041] The overview of the embodiment of the present disclosure is
described above. The embodiment of the present disclosure is now
described in detail.
1.2. Configuration Example
1.2.1. First Configuration Example
[0042] FIG. 4 is a diagram illustrated to describe a first
configuration example of the FMCW radar device according to the
embodiment of the present disclosure. The first configuration
example of the FMCW radar device is now described with reference to
FIG. 4.
[0043] As illustrated in FIG. 4, the FMCW radar device 100 includes
an FMCW radar signal processor 110, a signal processing unit 120, a
transmitting antenna 130, and a receiving antenna 140.
[0044] The FMCW radar signal processor 110 controls the operation
of the signal processing unit 120 and also calculates the distance
between the FMCW radar device 100 and a target 10. The FMCW radar
signal processor 110 includes a beat signal memory 111. The beat
signal memory 111 temporarily stores a beat signal used to
calculate the distance between the FMCW radar device 100 and the
target 10.
[0045] The signal processing unit 120 includes a local oscillator
121, a power amplifier 122, a phase shifter 123, and a mixer
124.
[0046] The local oscillator 121 generates a local signal whose
frequency varies with time (chirped) on the basis of a chirp
control signal from the FMCW radar signal processor 110. The local
oscillator 121 outputs the generated local signal to the power
amplifier 122 and the phase shifter 123.
[0047] The power amplifier 122 amplifies the local signal generated
by the local oscillator 121. The local signal amplified by the
power amplifier 122 is sent to the transmitting antenna 130 and is
transmitted as a transmission signal from the transmitting antenna
130.
[0048] The phase shifter 123 shifts the phase of the local signal
generated by the local oscillator 121 by a predetermined amount.
The phase shifter 123 shifts the local signal by a shift amount
based on a phase control signal that is output from the FMCW radar
signal processor 110.
[0049] The present embodiment acquires twice the beat signal to
eliminate the influence based on the local feedthrough. In the
first-time acquisition, the phase shifter 123 shifts the phase of
the local signal by 0 degrees (i.e., no change in phase) on the
basis of the phase control signal. In the second-time acquisition,
the phase shifter 123 shifts the phase of the local signal by 180
degrees (i.e., a change in phase opposite to the phase in the
first-time acquisition) on the basis of the phase control
signal.
[0050] The mixer 124 multiplies the output of the phase shifter 123
by an echo signal received by the receiving antenna 140. The mixer
124, when multiplying the two signals by each other, outputs the
resultant multiplied signal (beat signal) to the FMCW radar signal
processor 110.
[0051] FIG. 5 is a diagram illustrated to describe the beat signal
derived from the transmission signal and the beat signal derived
from the local feedthrough, in the first-time chirp and the
second-time chirp. The beat signals generated twice are stored in
the beat signal memory 111. Then, the second-time beat signal is
subtracted from the first-time beat signal.
[0052] As illustrated in FIG. 5, the phases of the beat signals
derived from the transmission signal differ by 180 degrees between
the first-time chirp and the second-time chirp by the phase shifter
123, so the beat signals are added by subtracting the second-time
beat signal from the first-time beat signal. On the other hand, as
illustrated in FIG. 5, the phases of the beat signals derived from
the local feedthrough are the same between the first-time chirp and
the second-time chirp, so the beat signals are cancelled by
subtracting the second-time beat signal from the first-time beat
signal.
[0053] In other words, the phase shifter 123 that shifts the local
signal makes it possible for the FMCW radar device 100 according to
the present embodiment to eliminate the influence based on the
local feedthrough. Details thereof will be described later.
[0054] The transmitting antenna 130 transmits the local signal
amplified by the power amplifier 122 in a predetermined direction
as a transmission signal. The receiving antenna 140 receives an
echo signal in which the transmission signal transmitted from the
transmitting antenna 130 is reflected back from the target 10. The
echo signal received by the receiving antenna 140 is sent to the
mixer 124 described above.
[0055] The first configuration example of the FMCW radar device is
described above with reference to FIG. 4. The operation of the FMCW
radar device illustrated in FIG. 4 is now described.
[0056] The description is first given of the addition between the
beat signals derived from the transmission signal in subtracting
the second-time beat signal from the first-time beat signal when
the phase is shifted by 180 degrees by the phase shifter.
[0057] The frequency of the transmission signal increases linearly
with time from f.sub.0 to f.sub.0+BW by the chirp as expressed in
Formula (1) below. Moreover, although this example illustrates that
the frequency of the transmission signal increases linearly with
time, the frequency can decrease linearly with time. In addition,
the frequency of the transmission signal can increase or decrease
with time in a form other than linear.
[ Math . 1 ] f T X ( t ) = B W T chirp t + f 0 ( 0 .ltoreq. t
.ltoreq. T chirp ) ( 1 ) ##EQU00001##
[0058] In this event, the phase of the transmission signal is
obtained by time integrating the frequency, so it becomes a
quadratic function of the time t as expressed in Formula (2)
below.
[ Math . 2 ] .PHI. T X ( t ) = 2 .pi. ( B W 2 T chirp t 2 + f 0 t )
( 2 ) ##EQU00002##
[0059] Further, the phase of the echo signal is delayed by the time
.tau. when it takes the transmission signal to reciprocate the
distance to the target, so resulting in Formula (3) below.
[ Math . 3 ] .PHI. E c h o ( t ) = .PHI. T X ( t - .tau. ) = 2 .pi.
{ B W 2 T chirp ( t - .tau. ) 2 + f 0 ( t - .tau. ) } ( 3 )
##EQU00003##
[0060] The beat signal in the first-time chirp is first obtained.
In the phase of the local signal input to the mixer 124, the shift
amount by the phase shifter 123 is set to 0 degrees in the
first-time chirp, so the phase has the same phase as the
transmission signal, as expressed in Formula (4) below.
[ Math . 4 ] .PHI. L O 1 ( t ) = 2 .pi. ( B W 2 T chirp t 2 + f 0 t
) ( 4 ) ##EQU00004##
[0061] When the mixer 124 multiplies the local signal by the echo
signal, a phase difference between the local signal and the echo
signal becomes the phase of the beat signal as expressed in Formula
(5).
[ Math . 5 ] .PHI. B e a t 1 ( t ) = .PHI. LO 1 ( t ) - .PHI. E c h
o ( t ) = 2 .pi. { B W 2 T chirp ( 2 .tau. t - .tau. 2 ) + f 0
.tau. } ( 5 ) ##EQU00005##
[0062] In Formula (5), .tau..sup.2 is sufficiently smaller than the
other terms and so can be omitted. Assuming that the amplitude of
the beat signal is set to A, the beat signal in the first-time
chirp is as expressed in Formula (6) below.
[ Math . 6 ] S Beat 1 ( t ) = A cos { 2 .pi. ( B W T chirp .tau. t
+ f 0 .tau. ) } ( 6 ) ##EQU00006##
[0063] The beat signal in the second-time chirp is then obtained.
In the phase of the local signal input to the mixer 124, the shift
amount by the phase shifter 123 is set to 180 degrees in the
second-time chirp, so the phase becomes a phase obtained by adding
.pi. to Formula (4), as expressed in Formula (7) below.
[ Math . 7 ] .PHI. L O 2 ( t ) = 2 .pi. ( B W 2 T chirp t 2 + f 0 t
) + .pi. ( 7 ) ##EQU00007##
[0064] When the mixer 124 multiplies the local signal by the echo
signal, the phase difference between the local signal and the echo
signal becomes the phase of the beat signal as expressed in Formula
(8).
[ Math . 8 ] .PHI. B e a t 2 ( t ) = .PHI. L O 2 ( t ) - .PHI. E c
h o ( t ) = 2 .pi. { B W 2 T chirp ( 2 .tau.t - .tau. 2 ) + f 0
.tau. } + .pi. ( 8 ) ##EQU00008##
[0065] In Formula (8), .tau..sup.2 is sufficiently smaller than the
other terms and so can be omitted, which is similar to Formula (5).
Assuming that the amplitude of the beat signal is set to A, the
beat signal in the second-time chirp is as expressed in Formula (9)
below.
[ Math . 9 ] S Beat 2 ( t ) = A cos { 2 .pi. ( B W T chirp .tau. t
+ f 0 .tau. ) + .pi. } = - Acos { 2 .pi. ( B W T chirp .tau. t + f
0 .tau. ) } ( 9 ) ##EQU00009##
[0066] The second-time beat signal is subtracted from the
first-time beat signal obtained in this way, resulting in Formula
(10).
[ Math . 10 ] S B e a t ( t ) = S B e a t 1 ( t ) - S B e a t 2 ( t
) = 2 A cos { 2 .pi. ( B W T chirp .tau. t + f 0 .tau. ) } ( 9 )
##EQU00010##
[0067] Thus, as expressed in Formula (10), when the phase is
shifted by 180 degrees by the phase shifter, it is found that the
beat signals derived from the transmission signal are added in
subtracting the second-time beat signal from the first-time beat
signal.
[0068] Then, the description is given of the cancellation of the
beat signal derived from the local feedthrough in subtracting the
second-time beat signal from the first-time beat signal when the
phase is shifted by 180 degrees by the phase shifter.
[0069] The beat signal in the first-time chirp is first obtained.
In the phase of the local signal input to the mixer 124, the shift
amount by the phase shifter 123 is set to 0 degrees in the
first-time chirp, so the phase has the same phase as the
transmission signal, as expressed in Formula (11) below. The local
feedthrough is the leakage of the local signal input to the mixer
124, so the phase of the local feedthrough is the same as the phase
of the local signal.
[ Math . 11 ] .PHI. L O F T 1 ( t ) = .PHI. L O 1 ( t ) = 2 .pi. (
B W 2 T chirp t 2 + f 0 t ) ( 11 ) ##EQU00011##
[0070] The phase of the echo signal derived from the local
feedthrough is delayed by the time .tau. of reciprocating the
distance to the target, so resulting in Formula (12) below.
[ Math . 12 ] .PHI. E c h o 1 ( t ) = .PHI. L O F T I ( t - .tau. )
= 2 .pi. { B W 2 T chirp ( t - .tau. ) 2 + f 0 ( t - .tau. ) } ( 12
) ##EQU00012##
[0071] The phase of the beat signal is expressed by Formula (13) by
allowing the mixer 124 to output the phase difference between the
local signal and the echo signal.
[ Math . 13 ] .PHI. Beat 1 ( t ) = .PHI. L O 1 ( t ) - .PHI. E c h
o 1 ( t ) = 2 .pi. { B W 2 T chirp ( 2 .tau. t - .tau. 2 ) + f 0
.tau. } ( 13 ) ##EQU00013##
[0072] In Formula (13), .tau..sup.2 is sufficiently smaller than
the other terms and so can be omitted. Assuming that the amplitude
of the beat signal is set to B, the beat signal caused by the local
feedthrough in the first-time chirp is expressed in Formula (14)
below.
[ Math . 14 ] S B e a t 1 ( t ) = B cos { 2 .pi. ( B W T chirp
.tau. t + f 0 .tau. ) } ( 14 ) ##EQU00014##
[0073] The beat signal in the second-time chirp is then obtained.
In the phase of the local signal input to the mixer 124, the shift
amount by the phase shifter 123 is set to 180 degrees in the
second-time chirp, so the phase becomes a phase obtained by adding
.pi. to Formula (11), as expressed in Formula (15) below.
[ Math . 15 ] .PHI. L O F T 2 ( t ) = .PHI. L O 2 ( t ) = 2 .pi. (
B W 2 T chirp t 2 + f 0 t ) + .pi. ( 15 ) ##EQU00015##
[0074] The phase of the echo signal derived from the local
feedthrough is delayed by the time .tau. of reciprocating the
distance to the target, so resulting in Formula (16) below.
[ Math . 16 ] .PHI. E c h o 2 ( t ) = .PHI. L O F T 2 ( t - .tau. )
= 2 .pi. { B W 2 T chirp ( t - .tau. ) 2 + f 0 ( t - .tau. ) } +
.pi. ( 16 ) ##EQU00016##
[0075] The phase of the beat signal is expressed by Formula (17) by
allowing the mixer 124 to output the phase difference between the
local signal and the echo signal.
[ Math . 17 ] .PHI. B e a t 2 ( t ) = .PHI. L O 2 ( t ) - .PHI. E c
h o 2 ( t ) = 2 .pi. { B W 2 T chirp ( 2 .tau. t - .tau. 2 ) + f 0
.tau. } ( 17 ) ##EQU00017##
[0076] In Formula (17), .tau..sup.2 is sufficiently smaller than
the other terms and so can be omitted, which is similar to Formula
(13). Assuming that the amplitude of the beat signal is set to B,
the beat signal caused by the local feedthrough in the second-time
chirp is as expressed in Formula (18) below.
[ Math . 18 ] S Beat 2 ( t ) = B cos { 2 .pi. ( B W T chirp .tau. t
+ f 0 .tau. ) } ( 18 ) ##EQU00018##
[0077] The subtraction of the second-time beat signal from the
first-time beat signal obtained in this way produces Formula
(19).
[Math. 19]
S.sub.Beat(t)=S.sub.Beat1(t)-S.sub.Beat2(t)=0 (19)
[0078] In other words, it can be found that, as expressed in
Formula 19, the beat signals caused by the local feedthrough are
canceled in subtracting the beat signal caused by the second-time
local feedthrough from the beat signal caused by the first-time
local feedthrough when the phase is shifted by 180 degrees by the
phase shifter.
[0079] Thus, the FMCW radar device 100 according to the embodiment
of the present disclosure, when acquiring twice the beat signal
obtained by allowing the phase shifter to shift the local signal by
180 degrees, makes it possible to cancel the beat signal caused by
the local feedthrough, thereby obtaining only the beat signal
derived from the local signal. The FMCW radar device 100 according
to the embodiment of the present disclosure is capable of
cancelling the beat signal caused by the local feedthrough and
obtaining only the beat signal derived from the local signal,
thereby achieving accurate measurement of the distance to the
target.
1.2.2. Second Configuration Example
[0080] A second configuration example of the FMCW radar device is
now described. FIG. 6 is a diagram illustrated to describe the
second configuration example of the FMCW radar device according to
the embodiment of the present disclosure. The second configuration
example of the FMCW radar device illustrated in FIG. 6 differs from
the first configuration example illustrated in FIG. 4 in that two
phase shifters are provided.
[0081] A phase shifter 123a shifts the phase of the local signal
generated by the local oscillator 121 by a predetermined amount,
which is similar to the first configuration example illustrated in
FIG. 4. The phase shifter 123a shifts the local signal by the shift
amount based on the phase control signal that is output from the
FMCW radar signal processor 110. In one example, the phase shifter
123a shifts the phase by 0 degrees or 180 degrees on the basis of
the phase control signal. The output from the phase shifter 123a is
sent to the mixer 124 and a phase shifter 123b.
[0082] The phase shifter 123b further shifts the phase of the
signal output from the phase shifter 123a by a predetermined
amount. The phase shifter 123b shifts the signal output from the
phase shifter 123a by the shift amount based on the phase control
signal that is output from the FMCW radar signal processor 110. In
one example, the phase shifter 123b shifts the phase by 0 degrees
or 180 degrees on the basis of the phase control signal.
[0083] The shift amounts twice by the phase shifters 123a and 123b
are set so that the phases are the same as the local signal
generated by the local oscillator 121. In addition, the shift
amounts by the phase shifters 123a and 123b are set so that the
beat signal derived from the transmission signal is different in
phase by 180 degrees between the first-time chirp and the
second-time chirp, as in the first configuration example.
[0084] Specifically, in the FMCW radar device illustrated in FIG.
6, the beat signal derived from the transmission signal is made to
be different in phase by 180 degrees between the first-time chirp
and the second-time chirp by the phase shifter 123a, as in the
first configuration example of the FMCW radar device illustrated in
FIG. 4. Thus, the signals are added by subtracting the second-time
beat signal from the first-time beat signal. On the other hand, the
beat signal derived from the local feedthrough is identical in
phase between the first-time chirp and the second-time chirp, so it
is canceled by subtracting the second-time beat signal from the
first-time beat signal.
[0085] In other words, the phase shifter 123 that shifts the local
signal makes it possible for the FMCW radar device 100 according to
the present embodiment to eliminate the influence based on the
local feedthrough.
1.2.3. Third Configuration Example
[0086] A third configuration example of the FMCW radar device is
now described. FIG. 7 is a diagram illustrated to describe a third
configuration example of the FMCW radar device according to the
embodiment of the present disclosure. The third configuration
example of the FMCW radar device illustrated in FIG. 7 differs from
the first configuration example illustrated in FIG. 4 in that a
transmission signal multiplier 126a and a local signal multiplier
126b are provided. In addition, in the third configuration example
of the FMCW radar device illustrated in FIG. 7, the shift amount by
a phase shifter 125 is determined on the basis of the
multiplication amounts of the transmission signal multiplier 126a
and the local signal multiplier 126b.
[0087] The transmission signal multiplier 126a multiplies the
frequency of the local signal output from the local oscillator 121
by N times. In addition, the local signal multiplier 126b
multiplies the frequency of the local signal whose phase is shifted
by the phase shifter 125 by N times. The phase shifter 125 shifts
the phase of the local signal output from the local oscillator 121
by the shift amount based on the phase control signal output from
the FMCW radar signal processor 110. In the example illustrated in
FIG. 7, the phase shifter 125 shifts the phase of the local signal
output from the local oscillator 121 by 0 degrees or X degrees.
[0088] The shift amount X by the phase shifter 125 and the
multiplication amount N by the transmission signal multiplier 126a
and the local signal multiplier 126b are assumed to have the
following relationship.
[Math. 20]
mod(NX,360)=180 (20)
[0089] In other words, the shift amount X by the phase shifter 125
is set to a value that becomes 180 when it is multiplied by N times
and is wrapped at 360. In one example, X=180/N or X=180+180/N if N
is an even number, and X=180/N or X=180 if N is an odd number.
[0090] In the FMCW radar device 100 illustrated in FIG. 7, the
transmission signal multiplier 126a provided as described above
makes it possible for the transmission signal to increase in
frequency and to be transmitted even when the local oscillator 121
fails to oscillate at a high frequency. In addition, the FMCW radar
device 100 illustrated in FIG. 7 provided with the local signal
multiplier 126b makes it possible to make the phase of the local
signal different by 180 degrees between two chirps, which is
similar to the first configuration example and the second
configuration example described above. Then, the FMCW radar device
100 illustrated in FIG. 7 cancels the beat signal derived from the
local feedthrough by subtracting the second-time beat signal from
the first-time beat signal.
1.3. Application Example
[0091] The FMCW radar device 100 according to the embodiment of the
present disclosure is capable of eliminating the influence based on
the local feedthrough, so it is applicable to a radar device of a
system supporting safe driving of a car, which is necessary to
perform ranging with high accuracy.
[0092] FIG. 8 is a diagram illustrated to describe an example of a
vehicle 2 on which FMCW radar devices 100a to 100f are mounted. The
FMCW radar devices 100a to 100f illustrated in FIG. 8 are assumed
to be any of the FMCW radar devices 100 according to the embodiment
of the present disclosure described above. The FMCW radar devices
100a to 100f are any of radar devices for short-range,
medium-range, and long-range, and are used for detecting objects or
the like around the vehicle 2.
[0093] As described above, the FMCW radar device 100 according to
the embodiment of the present disclosure is applicable as a radar
device of a system supporting safe driving of a vehicle, so it is
possible to contribute to higher performance of the system
described above.
2. Concluding Remarks
[0094] According to the embodiment of the present disclosure as
described above, there is provided an FMCW radar device capable of
eliminating the influence of the beat signal caused by the local
feedthrough and performing ranging with high accuracy.
[0095] The preferred embodiment(s) of the present disclosure
has/have been described above with reference to the accompanying
drawings, whilst the present disclosure is not limited to the above
examples. A person skilled in the art may find various alterations
and modifications within the scope of the appended claims, and it
should be understood that they will naturally come under the
technical scope of the present disclosure.
[0096] In one example, although the shift amount by the phase
shifter is set to 180 degrees in the embodiment described above,
the present technology is not limited to such example. The shift
amount by the phase shifter is not necessarily set to exactly 180
degrees, but in one example, the shift amount by the phase shifter
can fall within the range of 180 degrees.+-.22.5 degrees, in which
22.5 degrees is an angle corresponding to .pi./8, and cos (.pi./8)
is approximately 0.93. The subtraction for the beat signals
obtained by a chirp two times makes it possible for the beat signal
caused by the local feedthrough to be suppressed to 10% or less.
Thus, it is possible to reduce significantly the influence of the
beat signal caused by the local feedthrough without exactly setting
the shift amount by the phase shifter to 180 degrees.
[0097] Further, the effects described in this specification are
merely illustrative or exemplified effects, and are not limitative.
That is, with or in the place of the above effects, the technology
according to the present disclosure may achieve other effects that
are clear to those skilled in the art from the description of this
specification.
[0098] Additionally, the present technology may also be configured
as below.
[0099] (1) A radar device including: [0100] an oscillator
configured to oscillate a local signal; [0101] a transmitting
antenna configured to emit a transmission signal based on the local
signal; [0102] a receiving antenna configured to receive a
reflected wave in which the transmission signal is reflected from a
target; [0103] a mixer configured to multiply the reflected wave
and the local signal by each other to produce a multiplied signal;
and [0104] a first shifter provided between the oscillator and the
mixer and configured to shift a phase of the local signal.
[0105] (2) The radar device according to (1), further including:
[0106] a second shifter configured to shift a phase of a signal
output by the first shifter between the first shifter and the
transmitting antenna.
[0107] (3) The radar device according to (1) or (2), [0108] in
which the first shifter sets a shift amount to a first value at
first-time transmission of the transmission signal and sets the
shift amount to a second value at second-time transmission of the
transmission signal.
[0109] (4) The radar device according to (3), including: [0110] a
calculation unit configured to perform subtraction between an
output of the mixer at the first-time transmission of the
transmission signal and an output of the mixer at the second-time
transmission of the transmission signal.
[0111] (5) The radar device according to (3) or (4), [0112] in
which a difference between the first value and the second value is
approximately 180 degrees.
[0113] (6) The radar device according to any of (3) to (5), [0114]
in which a difference between the first value and the second value
is within a range of 180 degrees.+-.22.5 degrees.
[0115] (7) The radar device according to any of (1) to (6), further
including: [0116] a multiplier configured to multiply a frequency
of a signal output by the first shifter by N times between the
first shifter and the mixer.
[0117] (8) The radar device according to (7), including: [0118] a
calculation unit configured to perform subtraction between an
output of the mixer at first-time transmission of the transmission
signal and an output of the mixer at second-time transmission of
the transmission signal.
[0119] (9) The radar device according to (7), [0120] in which the
first shifter sets a shift amount to a first value at first-time
transmission of the transmission signal and sets the shift amount
to a second value at second-time transmission of the transmission
signal, and a difference between the first value and the second
value is a value which becomes approximately 180 degrees when the
difference is multiplied by N times and wrapped at 360.
[0121] (10) The radar device according to (7), [0122] in which the
first shifter sets a shift amount to a first value at first-time
transmission of the transmission signal and sets the shift amount
to a second value at second-time transmission of the transmission
signal, and a difference between the first value and the second
value is within a range of 180 degrees.+-.22.5 degrees when the
difference is multiplied by N times and wrapped at 360.
[0123] (11) The radar device according to any of (1) to (10),
further including: [0124] a multiplier configured to multiply a
frequency of a signal output by the oscillator by N times between
the oscillator and the first shifter.
[0125] (12) The radar device according to any of (1) to (11),
[0126] in which the local signal is a signal whose frequency
increases or decreases with time.
[0127] (13) The radar device according to (12), [0128] in which the
local signal is a signal whose frequency linearly increases or
decreases with time.
[0129] (14) A signal processor including: [0130] an oscillator
configured to oscillate a local signal; [0131] a mixer configured
to multiply a reflected wave in which a transmission signal based
on the local signal is reflected from a target and the local signal
by each other to produce a multiplied signal; and [0132] a first
shifter provided between the oscillator and the mixer and
configured to shift a phase of the local signal.
[0133] (15) A signal processing method including: [0134]
oscillating, by an oscillator, a local signal; [0135] emitting a
transmission signal based on the local signal from a transmitting
antenna; [0136] receiving, by a receiving antenna, a reflected wave
in which the transmission signal is reflected from a target; [0137]
multiplying, by a mixer, the reflected wave and the local signal by
each other to produce a multiplied signal; and [0138] shifting, by
a shifter provided between the oscillator and the mixer, a phase of
the local signal.
[0139] (16) A mobile object including: [0140] the radar device
according to any of (1) to (13).
REFERENCE SIGNS LIST
[0140] [0141] 2 vehicle [0142] 10 target [0143] 100 FMCW radar
device [0144] 110 FMCW radar signal processor [0145] 111 beat
signal memory [0146] 120 signal processing unit [0147] 121 local
oscillator [0148] 122 power amplifier [0149] 123 phase shifter
[0150] 123a phase shifter [0151] 123b phase shifter [0152] 124
mixer [0153] 125 phase shifter [0154] 126a transmission signal
multiplier [0155] 126b local signal multiplier [0156] 130
transmitting antenna [0157] 140 receiving antenna
* * * * *