U.S. patent application number 14/637218 was filed with the patent office on 2015-10-01 for synchronization in fmcw radar systems.
The applicant listed for this patent is Texas Instruments Incorporated. Invention is credited to Sachin Bhardwaj, Karthik Ramasubramanian, Karthik Subburaj.
Application Number | 20150276918 14/637218 |
Document ID | / |
Family ID | 54190012 |
Filed Date | 2015-10-01 |
United States Patent
Application |
20150276918 |
Kind Code |
A1 |
Ramasubramanian; Karthik ;
et al. |
October 1, 2015 |
SYNCHRONIZATION IN FMCW RADAR SYSTEMS
Abstract
The disclosure provides a radar apparatus for estimating a
position and a velocity of the plurality of obstacles. The radar
apparatus includes a local oscillator that generates a first
signal. A first transmit unit receives the first signal from the
local oscillator and generates a first transmit signal. A frequency
shifter receives the first signal from the local oscillator and
generates a second signal. A second transmit unit receives the
second signal and generates a second transmit signal. The frequency
shifter provides a frequency offset to the first signal based on a
routing delay mismatch to generate the second signal such that the
first transmit signal is phase coherent with the second transmit
signal.
Inventors: |
Ramasubramanian; Karthik;
(Bangalore, IN) ; Subburaj; Karthik; (Bangalore,
IN) ; Bhardwaj; Sachin; (Bangalore, IN) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Texas Instruments Incorporated |
Dallas |
TX |
US |
|
|
Family ID: |
54190012 |
Appl. No.: |
14/637218 |
Filed: |
March 3, 2015 |
Current U.S.
Class: |
342/107 ;
342/175 |
Current CPC
Class: |
G01S 7/35 20130101; G01S
2013/0245 20130101; G01S 13/931 20130101; G01S 13/343 20130101;
G01S 13/584 20130101; G01S 13/726 20130101 |
International
Class: |
G01S 7/02 20060101
G01S007/02; G01S 13/06 20060101 G01S013/06; G01S 13/58 20060101
G01S013/58; G01S 13/02 20060101 G01S013/02 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 28, 2014 |
IN |
1667/CHE/2014 |
Claims
1. A radar apparatus comprising a local oscillator configured to
generate a first signal; a first transmit unit configured to
receive the first signal from the local oscillator and configured
to generate a first transmit signal, a frequency shifter configured
to receive the first signal from the local oscillator and
configured to generate a second signal; and a second transmit unit
configured to receive the second signal and configured to generate
a second transmit signal, wherein the frequency shifter is
configured to provide a frequency offset to the first signal based
on a routing delay mismatch to generate the second signal such that
the first transmit signal is phase coherent with the second
transmit signal.
2. The radar apparatus of claim 1, wherein the frequency shifter
comprises: a function generator configured to receive a frequency
offset value and generates a digital signal; a digital to analog
converter (DAC) coupled to the function generator and configured to
generate an analog signal corresponding to the digital signal, and
a mixer configured to multiply the analog signal and the first
signal to generate the second signal.
3. The radar apparatus of claim 1, wherein the first transmit unit
comprises: a first power amplifier coupled to the local oscillator
and configured to amplify the first signal to generate the first
transmit signal; and a first transmit antenna unit coupled to the
first power amplifier and configured to transmit the first transmit
signal received from the first power amplifier.
4. The radar apparatus of claim 1, wherein the second transmit unit
comprises: a second power amplifier coupled to the frequency
shifter and configured to amplify the second signal to generate the
second transmit signal; and a second transmit antenna unit coupled
to the second power amplifier and configured to transmit the second
transmit signal received from the second power amplifier.
5. The radar apparatus of claim 1, wherein the routing delay
mismatch is estimated from a routing delay from the local
oscillator to the first transmit antenna unit, and from a routing
delay from the local oscillator to the second transmit antenna
unit.
6. The radar apparatus of claim 1, wherein the first transmit
signal and the second transmit signal are scattered by a plurality
of obstacles to generate a scattered signal.
7. The radar apparatus of claim 1 further comprising a receive
unit, the receive unit comprising: a receive antenna unit
configured to receive the scattered signal; a low-noise amplifier
(LNA) coupled to the receive antenna unit and configured to amplify
the scattered signal to generate an amplified scattered signal; a
mixer coupled to the LNA and the local oscillator, the mixer
configured to mix the amplified scattered signal and the first
signal to generate an IF (intermediate frequency) signal; an ADC
(analog to digital converter) coupled to the mixer and configured
to sample the IF signal to generate a sampled data; and a processor
coupled to the ADC and configured to estimate a position and a
velocity of the plurality of obstacles from the sampled data.
8. The radar apparatus of claim 1, wherein the first signal is a
ramp segment having a start frequency and a fixed slope.
9. The radar apparatus of claim 8, wherein the frequency offset is
estimated from at least one of the routing delay mismatch and the
fixed slope.
10. A method comprising: generating a first signal; generating a
first transmit signal from a first signal; provide a frequency
offset to the first signal based on a routing delay mismatch to
generate a second signal; and generating a second transmit signal
from the second signal, wherein the first transmit signal is phase
coherent with the second transmit signal.
11. The method of claim 10 further comprising estimating the
routing delay mismatch from a time difference between a time
instant when the first signal is generated and a time instant when
the first transmit signal is transmitted, and from a time
difference between the time instant when the first signal is
generated and a time instant when the second transmit signal is
transmitted.
12. The method of claim 10 further comprising amplifying the first
signal to generate the first transmit signal, and amplifying the
second signal to generate the second transmit signal.
13. The method of claim 10 further comprising scattering of the
first transmit signal and the second transmit signal by a plurality
of obstacles to generate a scattered signal.
14. The method of claim 10 further comprising: amplifying the
scattered signal to generate an amplified scattered signal; mixing
the amplified scattered signal and the first signal to generate an
IF (intermediate frequency) signal; sampling the IF signal to
generate a sampled data, and estimating a position and a velocity
of the plurality of obstacles from the sampled data.
15. The method of claim 10, wherein the first signal is a ramp
segment having a start frequency and a fixed slope.
16. The method of claim 15 further comprising estimating the
frequency offset from at least one of the routing delay mismatch
and the fixed slope.
Description
CROSS REFERENCES TO RELATED APPLICATIONS
[0001] This application claims priority from India provisional
patent application No. 1667/CHE/2014 filed on Mar. 28, 2014 which
is hereby incorporated by reference in its entirety.
TECHNICAL FIELD
[0002] The present disclosure relates to radars, and more
particularly to estimating position and the velocity of one or more
obstacles using radars.
BACKGROUND
[0003] The use of radars in industrial and automotive applications
is evolving rapidly. Radars are used in many applications to detect
target objects such as airplanes, military targets, vehicles, and
pedestrians. Radar finds use in number of applications associated
with a vehicle such as adaptive cruise control, collision warning,
blind spot warning, lane change assist, parking assist and rear
collision warning. Pulse radar and FMCW (Frequency Modulation
Continuous Wave) radar are predominately used in such
applications.
[0004] In a radar system, a local oscillator generates a transmit
signal. The transmit signal is amplified and transmitted by one or
more transmit units. In an FMCW radar, a frequency of the transmit
signal is varied linearly with time. For example, the frequency of
the transmit signal increases at a constant rate from 77 GHz to 81
GHz in 100 micro-seconds. This transmit signal is referred as a
ramp signal or a chirp signal. One or more obstacles scatters the
transmit signal. The scattered signal is received by one or more
receive units in the radar system.
[0005] A signal obtained by mixing the transmitted signal and the
received scattered signal is termed as a beat signal. The beat
signal is sampled by an analog to digital converter (ADC) and
processed by a processor to estimate a distance and a velocity of
the one or more obstacles. The frequency of the beat signal is
proportional to the range (distance) of the one or more
obstacles.
[0006] For a moving obstacle, a phase of the beat signal varies
across multiple ramp signals transmitted by the radar system. The
frequency and phase of the beat signal from one or more receive
units are analyzed by the processor to estimate the position and
the velocity of the one or more obstacles.
[0007] The transmit signal from the local oscillator is provided to
the one or more transmit units, and the one or more receiver units,
which may be on one or multiple chips and/or semiconductor devices.
The multiple transmit units and the multiple receive unit are
required for beamforming. Beamforming requires signals transmitted
by the multiple transmit units to be phase coherent.
[0008] A phase coherence between multiple transmit units is
affected by routing delay mismatch. The one or more transmit or
receive units may be located at different distances from the local
oscillator which induces different routing delays in the transmit
signal from the local oscillator to each transmit or receive unit.
This routing delay mismatch causes errors in position and velocity
estimation of the one or more obstacles.
SUMMARY
[0009] According to an aspect of the disclosure, a radar apparatus
is provided. The radar apparatus includes a local oscillator that
generates a first signal. A first transmit unit receives the first
signal from the local oscillator and generates a first transmit
signal. A frequency shifter receives the first signal from the
local oscillator and generates a second signal. A second transmit
unit receives the second signal and generates a second transmit
signal. The frequency shifter provides a frequency offset to the
first signal based on a routing delay mismatch to generate the
second signal such that the first transmit signal is phase coherent
with the second transmit signal.
BRIEF DESCRIPTION OF THE VIEWS OF DRAWINGS
[0010] FIG. 1 illustrates a radar apparatus, according to an
embodiment;
[0011] FIG. 2 illustrates a frequency shifter, according to an
embodiment;
[0012] FIG. 3 illustrates a transmit unit, according to an
embodiment;
[0013] FIG. 4 illustrates a transmit unit, according to an
embodiment; and
[0014] FIG. 5 illustrates a receive unit, according to an
embodiment.
DETAILED DESCRIPTION OF THE EMBODIMENTS
[0015] FIG. 1 illustrates a radar apparatus 100, according to an
embodiment. The radar apparatus 100 includes a local oscillator
102, a first transmit unit 104, a frequency shifter 106, a second
transmit unit 108 and a receive unit 110. In one version, the first
transmit unit 104 and the second transmit unit 108 are similar in
operation. The first transmit unit 104 and the frequency shifter
106 are coupled to the local oscillator 102. The second transmit
unit 108 is coupled to the frequency shifter 106.
[0016] The receive unit 110 is coupled to the local oscillator 102.
In one example, the radar apparatus 100 includes one or more
transmit units. In another example, the radar apparatus 100
includes one or more receive units. In one version, the first
transmit unit 104 and the second transmit unit 108 are integrated
on a same chip. In another version, the first transmit unit 104 and
the second transmit unit 108 are on different chip. In yet another
version, the receive unit 110 is on a chip different from the first
transmit unit 104 and the second transmit unit 108.
[0017] In an example, the radar apparatus 100 includes multiple
local oscillators. The radar apparatus 100 may include one or more
additional components known to those skilled in the relevant art
and are not discussed here for simplicity of the description.
[0018] The operation of the radar apparatus 100 illustrated in FIG.
1 is explained now. The local oscillator generates a first signal
114. In one version, a frequency of the first signal 114 is varied
linearly with time. For example, the frequency of the first signal
114 increases at a constant rate from 77 GHz to 81 GHz in 100
micro-seconds. This first signal 114 is also referred as a ramp
signal or a chirp signal. In another version, the first signal 114
is a ramp segment having a start frequency and a fixed slope.
[0019] The frequency of the local oscillator 102 is one of the
following ranges, but not limited to 76 GHz to 81 GHz or 18 GHz to
24 GHz. The frequency of the local oscillator 102, in one example,
is dependent on an operating frequency band of the radar apparatus
100. The first transmit unit 104 receives the first signal 114 from
the local oscillator 102, and generates a first transmit signal
116. The frequency shifter 106 receives the first signal 114 from
the local oscillator 102 and generates a second signal 118. The
second transmit unit 108 receives the second signal 118 from the
frequency shifter 106 and generates a second transmit signal
120.
[0020] The frequency shifter 106 provides a frequency offset to the
first signal 114 based on a routing delay mismatch to generate the
second signal 118. The frequency offset ensures that the first
transmit signal 116 is phase coherent with the second transmit
signal 120. The frequency offset is estimated from at least one of
the routing delay mismatch and the fixed slope.
[0021] In one example, when the routing delay mismatch is `d`, and
the fixed slope is `S`, the frequency offset provided by the
frequency shifter 106 is given as d*S/c. Further, c which
represents a speed of electromagnetic wave varies from 1 m/s to
3.times.10.sup.8m/s depending on a PCB or chip material used for
the radar apparatus 100. In one version, the fixed slope S is
selected based on a farthest obstacle required to be detected by
the radar apparatus 100. In another version, the slope S is in the
range of 1 MHz/micro-second to 200 MHz/micro-second.
[0022] The routing delay mismatch is estimated from a time
difference between a time instant when the first signal 114 is
generated by the local oscillator 102 and a time instant when the
first transmit signal 116 is transmitted by the first transmit unit
104. The routing delay mismatch is also estimated from a time
difference between the time instant when the first signal 114 is
generated by the local oscillator 102 and a time instant when the
second transmit signal 120 is transmitted by the second transmit
unit 108.
[0023] The first transmit unit 104 amplifies the first signal 114
to generate the first transmit signal 116. The second transmit unit
108 amplifies the second signal 118 to generate the second transmit
signal 120. The first transmit signal 116 and the second transmit
signal 120 are coherent in phase. The first transmit signal 116 and
the second transmit signal 120 are scattered by a plurality of
obstacles to generate a scattered signal 124.
[0024] The scattered signal 124 is received by the receive unit
110. The receive unit 110 amplifies the scattered signal 124 to
generate an amplified scattered signal. The amplified scattered
signal is mixed with the first signal 114 to generate an IF
(intermediate frequency) signal. The IF signal is sampled in the
receive unit 110 to generate a sampled data. A position and a
velocity of the plurality of obstacles is estimated from the
sampled data.
[0025] In another embodiment, the frequency shifter 106 is between
the receive unit 110 and the local oscillator 102. The first signal
114 generated by the local oscillator 102 is provided a frequency
offset by the frequency shifter 106, and a signal generated by the
frequency shifter 106 is provided to the receive unit.
[0026] Thus, the radar apparatus 100 provides compensation of
routing delay mismatches by providing frequency offset. The
frequency shifter 106 provides that the transmit and receive units
can be on one or multiple chips and/or semiconductor devices
without any concern about routing delay mismatch. Intra-chip
routing delay mismatches can also be compensated using techniques
discussed in connection with radar apparatus 100.
[0027] As frequency range of newly developed FMCW radar increases
to a range of 160 GHz, the use of beamforming is required for
correct estimation of the position and the velocity of the
plurality of obstacles. The radar apparatus 100 provides that a
phase coherence between multiple transmit units (for example, first
transmit unit 104 and the second transmit unit 108) is not affected
by routing delay mismatch.
[0028] FIG. 2 illustrates a frequency shifter 200, according to an
embodiment. The frequency shifter 200 is similar in connections and
operation to the frequency shifter 106 illustrated in FIG. 1. The
frequency shifter 200 is explained in connection with the radar
apparatus 100. The frequency shifter 200 includes a function
generator 202, a digital to analog converter (DAC) 204 and a mixer
208.
[0029] The function generator 202 receives a frequency offset value
and generates a digital signal. In an example, the function
generator 202 receives the frequency offset value from a processor
in the radar apparatus 100. In another example, the function
generator 202 maintains a look-up table of sine and cosine function
values.
[0030] The DAC 204 is coupled to the function generator 202. The
DAC 204 generates an analog signal 206 corresponding to the digital
signal received from the function generator 202. A mixer 208 is
coupled the DAC 204. The mixer 208 receives the analog signal 206
and a first signal 214. The first signal 214 is similar to the
first signal 114 generated by the local oscillator 102 (illustrated
in FIG. 1).
[0031] The mixer 208 multiplies the analog signal 206 and the first
signal 214 to generate the second signal 218. The second signal 218
is similar to the second signal 118 generated by the frequency
shifter 106 in radar apparatus 100. The second signal 218 thus
generated by the mixer 208 is obtained by providing a frequency
offset to the first signal 214. The frequency offset is defined by
the frequency offset value received in the function generator
202.
[0032] In another embodiment, the frequency shifter 200 is
implemented using a variable delay line. In this method, the first
signal 214 is sent through the variable delay line, whose delay is
varied in proportion to the frequency offset, such that a desired
frequency shift is provided to the first signal 214.
[0033] FIG. 3 illustrates a transmit unit 300, according to an
embodiment. The transmit unit 300 is similar to the first transmit
unit 104 in connection and operation. The transmit unit 300
includes a conditioner 304 that receives a first signal 302. The
first signal 302 is similar to the first signal 114 generated by
the local oscillator 102 in the radar apparatus 100.
[0034] A first power amplifier 306 is coupled to the conditioner
304. In an embodiment, the transmit unit 300 does not include the
conditioner 304 and the first power amplifier 306 receives the
first signal 302. A first transmit antenna unit 308 is coupled to
the first power amplifier 306. The transmit unit 300 may include
one or more additional components known to those skilled in the
relevant art and are not discussed here for simplicity of the
description.
[0035] The operation of the transmit unit 300 illustrated in FIG. 3
is explained now. The conditioner 304 is configured to perform at
least one of a phase shift operation, a frequency multiplication
and a pre-amplification of the first signal 302. In an example, the
conditioner 304 is configured to generate an output signal which is
an integer multiple of a frequency of the first signal 302. In one
version, the integer is one of the following (but not limited to)
1, 2, 3 and 4.
[0036] The first power amplifier 306 receives the first signal 302
from the conditioner 304 and amplifies the first signal 302 to
generate the first transmit signal. The first transmit antenna unit
308 transmits the first transmit signal received from the first
power amplifier 306.
[0037] FIG. 4 illustrates a transmit unit 400, according to an
embodiment. The transmit unit 400 is similar to the second transmit
unit 108 in connection and operation. The transmit unit 400
includes a conditioner 404 that receives a second signal 402. The
second signal 402 is similar to the second signal 118 generated by
the frequency shifter 106 in the radar apparatus 100.
[0038] A second power amplifier 406 is coupled to the conditioner
404. In an embodiment, the transmit unit 400 does not include the
conditioner 404 and the second power amplifier 406 receives the
second signal 402. A second transmit antenna unit 408 is coupled to
the second power amplifier 406. The transmit unit 400 may include
one or more additional components known to those skilled in the
relevant art and are not discussed here for simplicity of the
description.
[0039] The operation of the transmit unit 400 illustrated in FIG. 4
is explained now. The conditioner 404 is configured to perform at
least one of a phase shift operation, a frequency multiplication
and a pre-amplification of the second signal 402. In an example,
the conditioner 404 is configured to generate an output signal
which is an integer multiple of a frequency of the second signal
402. In one version, the integer is one of the following (but not
limited to) 1, 2, 3 and 4.
[0040] The second power amplifier 406 receives the second signal
402 from the conditioner 404 and amplifies the second signal 402 to
generate the second transmit signal. The second transmit antenna
unit 408 transmits the second transmit signal received from the
second power amplifier 406.
[0041] In one example, a routing delay between the second power
amplifier 406 and the second transmit antenna unit 408 is greater
than a routing delay between the first power amplifier 306 and the
first transmit antenna unit 308. This introduces routing delay
mismatch in the radar apparatus 100. The radar apparatus 100
provides compensation of routing delay mismatches by providing
frequency offset using the frequency shifter 106.
[0042] FIG. 5 illustrates a receive unit 500, according to an
embodiment. The receive unit 500 is similar to the receive unit 110
in the radar apparatus 100. The receive unit 500 includes a receive
antenna unit 502. A low-noise amplifier (LNA) 504 is coupled to the
receive antenna unit 502. A mixer 506 is coupled to the LNA 504 and
also receives a first signal 508. The first signal 508 is similar
to the first signal 114 generated by the local oscillator 102 in
the radar apparatus 100.
[0043] In one example, a multiplier receives the first signal 508
and provides the first signal 508 to the mixer 506. A baseband
filter 510 is coupled to the mixer 506. An ADC 512 is coupled to
the baseband filter 510. In an embodiment, the baseband filter 510
is not present in the receive unit 500 and the ADC 512 is coupled
to the mixer 506. A processor 514 is coupled to the ADC 512. The
receive unit 500 may include one or more additional components
known to those skilled in the relevant art and are not discussed
here for simplicity of the description.
[0044] The operation of the receive unit 500 illustrated in FIG. 5
is explained now. In radar apparatus 100, the first transmit signal
116 and the second transmit signal 120 are scattered by a plurality
of obstacles to generate a scattered signal. The receive antenna
unit 502 receives the scattered signal. The LNA 504 amplifies the
scattered signal to generate an amplified scattered signal.
[0045] The mixer 506 mixes the amplified scattered signal from the
LNA 504 and the first signal 508 to generate an intermediate
frequency (IF) signal. In one example, the first signal 508 is
received through a conditioner which is configured to amplify and
filter the first signal 508. The baseband filter 510 filters the IF
signal.
[0046] The ADC 512 receives the IF signal and samples the IF signal
to generate a sampled data. The processor 514 receives the sampled
data from the ADC 512 and estimates a position and a velocity of
the plurality of obstacles from the sampled data. In an example, in
the radar apparatus 100, the processor 514 is coupled to the
frequency shifter 106. The processor 514 provided a frequency
offset value to the frequency shifter 106.
[0047] In one example, the processor 514 estimates the frequency
offset from at least one of the routing delay mismatch and a fixed
slope of the first signal 508. In another example, the processor
514 is coupled to a local oscillator, for example the local
oscillator 102 in the radar apparatus 100. The processor 514
provides values of a start frequency and a fixed slope of the first
signal 508 (or the first signal 114).
[0048] The foregoing description sets forth numerous specific
details to convey a thorough understanding of the invention.
However, it will be apparent to one skilled in the art that the
invention may be practiced without these specific details.
Well-known features are sometimes not described in detail in order
to avoid obscuring the invention. Other variations and embodiments
are possible in light of above teachings, and it is thus intended
that the scope of invention not be limited by this Detailed
Description, but only by the following Claims.
* * * * *