US-12618961-B2 - Phase adjusting fmcw radar system

US12618961B2US 12618961 B2US12618961 B2US 12618961B2US-12618961-B2

Abstract

In described examples, a frequency modulated continuous wave (FMCW) radar system includes an FMCW signal generator, a number N transmitters, N phase shifters, multiple receivers, and a processor. The FMCW signal generator is configured to generate FMCW chirps. Different ones of the phase shifters have different respective base phase shifts selected in response to N. The transmitter is configured to transmit the phase shifted FMCW chirps. The receivers are configured to receive an FMCW chirp reflected by an object in range of the FMCW radar system. The processor is configured to determine a location of the object in range in response to the received FMCW chirp.

Inventors

Karthik Subburaj
Kameswaran Vengattaramane
Shankar Ram NARAYANA MOORTHY
Vashishth Dudhia

Assignees

TEXAS INSTRUMENTS INCORPORATED

Dates

Publication Date: 20260505
Application Date: 20220920
Priority Date: 20220328

Claims (20)

1 . A radar system, comprising: a signal generator including an output, the signal generator configured to generate chirps; N transmitters, each of the N transmitters including an input, wherein N is an integer of 2 or greater; N phase shifters, each of the N phase shifters including an input and an output, the inputs of the N phase shifters coupled to the output of the signal generator, the outputs of the N phase shifters respectively coupled to the inputs of the N transmitters, each of the N phase shifters having a different base phase shift than the base phase shift of each of the other of the N phase shifters, the base phase shifts selected based on N, wherein the N phase shifters are configured to additionally phase shift the chirps by a same phase shift offset that is based on a performance characteristic of one or more of the N phase shifters; multiple receivers, each of the multiple receivers including an output, one or more of the multiple receivers configured to receive a signal reflected by an object in range of the radar system; and a processor configured to determine a location of the object in range in response to the received signal.
2 . The radar system of claim 1 , wherein a base phase shift vector of the N phase shifters is 2 ⁢ π × [ 0 1 N + 1 … N - 1 N + 1 ] in radians.
3 . The radar system of claim 1 , wherein the performance characteristic includes integral nonlinearities (INLs) of the one or more of the N phase shifters.
4 . The radar system of claim 3 , wherein a particular one of the N phase shifters has a corresponding phase shift vector of the form [0 a/b 2a/b . . . (b−1)a/b], in which a and b are integers; and wherein the phase shift offset is selected to reduce a measure of the INLs of the particular phase shifter in response to the corresponding phase shift vector.
5 . The radar system of claim 3 , wherein the phase shift offset is selected to reduce one or more of: a mean squared error of the INLs of a particular phase shifter, of the N phase shifter, with respect to ideal outputs of the particular phase shifter in response to the corresponding phase shift vector, or a variance of the INLs of the particular phase shifter with respect to ideal outputs of the particular phase shifter in response to the corresponding phase shift vector.
6 . The radar system of claim 3 , wherein the phase shift offset is selected to reduce one or more of: an inter-transmitter coupling level, or an amplitude of spurious amplitude spikes corresponding to harmonics of correct amplitude spikes in fast Fourier transforms (FFTs) of a signal received by the receivers, the correct amplitude spikes indicating one or more objects in range of the radar system.
7 . The radar system of claim 3 , wherein the inputs of the N phase shifters are first inputs of the N phase shifters, each of the N phase shifters including a second input; and further including a processor having an output coupled to the second inputs of the N phase shifters, the processor configured to control the N phase shifters to additionally phase shift the chirps by the phase shift offset.
8 . The radar system of claim 7 , further including: a temperature sensor; and a memory configured to store multiple phase shift offsets with corresponding temperature values; wherein the processor is configured to control the N phase shifters to additionally phase shift the chirps by the phase shift offset in response to a temperature sensed by the temperature sensor, and a phase shift offset stored in the memory that corresponds to the sensed temperature.
9 . The FMCW radar system of claim 1 , further including multiple mixers, each of the multiple mixers including a first input, a second input, and an output, the first inputs of the multiple mixers respectively coupled to the outputs of of the N receivers, the second inputs of the multiple mixers coupled to the output of the signal generator; and wherein the processor is coupled to the outputs of the multiple mixers.
10 . The FMCW radar system of claim 9 , further including: multiple filters respectively coupled to the multiple mixers; and multiple analog to digital converters (ADCs) respectively coupled to the multiple filters, the ADCs having outputs coupled to the processor.
11 . The FMCW radar system of claim 1 , wherein each of the N phase shifters are configured to phase shift the FMCW chirps by the base phase shift of the phase shifter with respect to a sequentially-previous FMCW chirp phase shifted by the phase shifter.
12 . The radar system of claim 1 , wherein the radar system is a frequency modulated continuous wave radar system.
13 . A radar system comprising: a signal generator including an output, the signal generator configured to generate FMCW chirps; N transmitters, ones of the transmitters including a respective input; N phase shifters, each of the N phase shifters including an input and an output, the inputs of the N phase shifters coupled to the output of the signal generator, the outputs of the N phase shifters respectively coupled to the inputs of the N transmitters, each of the N phase shifters having a different base phase shift than the base phase shift of each of the other N phase shifters, the base phase shifts based on N, and wherein the base phase shifts are multiples of 2 ⁢ π N + 1 in radians; multiple receivers, each of the multiple receivers including an output, one or more of the receivers configured to receive a signal reflected by an object in range of the FMCW radar system; and a processor configured to determine a location of the object in range in response to the received FMCW signal.
14 . A method of operating a radar system that includes N transmitters, the method comprising: generating N sets of chirps, wherein N is an integer of 2 or greater; phase shifting the N sets of chirps using N phase shifters to produce N sets of phase shifted chirps, respectively, each of the N phase shifters having a different base phase shift than the base phase shift of each of the other of the N phase shifters, wherein one of: the base phase shifts are multiples of 2 ⁢ π N + 1 in radians, and a base phase shift vector of the N phase shifters is 2 ⁢ π × [ 0 1 N + 1 … N - 1 N + 1 ] in radians; transmitting the N sets of phase shifted chirps using the N transmitters, respectively; receiving a signal at multiple receivers; and processing the received signal to determine information about at least one object in range of the FMCW radar system.
15 . The method of claim 13 , wherein the information about the at least one object includes presence and location of the at least one object in range of the radar system.
16 . A method of operating a radar system that includes N transmitters, the method comprising: generating sets of chirps; phase shifting the N sets of chirps using N phase shifters to produce N sets of phase shifted chirps, respectively, each of the N phase shifters having a different base phase shift than the base phase shift of each of the other of the N phase shifters, the base phase shifts selected based on N; wherein the N phase shifters are configured to additionally phase shift respective sets of the N sets of chirps by a same phase shift offset that is selected in response to integral nonlinearities (INLs) of one or more of the N phase shifters; transmitting the N sets of phase shifted chirps using the N transmitters, respectively; receiving a signal at multiple receivers; and processing the received signal to determine information about at least one object in range of the FMCW radar system.
17 . The method of claim 16 , wherein a particular one of the N phase shifters has a corresponding phase shift vector of the form [0 a/b 2a/b . . . (b−1)a/b], in which a and b are integers; and wherein the phase shift offset is selected to reduce a measure of the INLs of the particular phase shifter in response to the corresponding phase shift vector.
18 . The method of claim 16 , wherein the phase shift offset is selected to reduce one or more of: a mean squared error of the INLs of a particular phase shifter, of the N phase shifters, with respect to ideal outputs of the particular phase shifter in response to the corresponding phase shift vector, or a variance of the INLs of the particular phase shifter with respect to ideal outputs of the particular phase shifter in response to the corresponding phase shift vector.
19 . The method of claim 16 , wherein the phase shift offset is selected to reduce one or more of: an inter-transmitter coupling level, or an amplitude of spurious amplitude spikes corresponding to harmonics of correct amplitude spikes in fast Fourier transforms (FFTs) of a signal received by the receivers, the correct amplitude spikes indicating one or more objects in range of the radar system.
20 . The method of claim 16 , further including sensing a temperature; wherein the phase shift offset is determined in response to the temperature.

Description

CROSS-REFERENCE TO RELATED APPLICATION This application claims the benefit of and priority to India Provisional Application No. 202241018046, filed Mar. 28, 2022, which is incorporated herein by reference. TECHNICAL FIELD This application relates generally to short-range frequency modulated continuous wave (FMCW) radar for automotive and industrial applications, and more particularly to selecting phase shifts of signals corresponding to different transmitters in an FMCW system. BACKGROUND An FMCW radar transmits an electromagnetic radiation (EMR) signal with a known frequency that is modulated to vary up and down over time. The radar receives a reflected signal corresponding to the transmitted signal, and uses the received signal to determine presence, distance, angle of arrival, speed, and direction of movement of objects within a detection distance limit of the FMCW radar. Speed and direction of movement together correspond to a velocity of a detected object. SUMMARY In described examples, a frequency modulated continuous wave (FMCW) radar system includes an FMCW signal generator, a number N transmitters, N phase shifters, multiple receivers, and a processor. The FMCW signal generator is configured to generate FMCW chirps. Different ones of the phase shifters have different respective base phase shifts selected in response to N. The transmitter is configured to transmit the phase shifted FMCW chirps. The receivers are configured to receive an FMCW chirp reflected by an object in range of the FMCW radar system. The processor is configured to determine a location of the object in range in response to the received FMCW chirp. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows a graph of an example FMCW signal to be transmitted by an automotive or industrial FMCW radar system. FIG. 2A shows a diagram of an example Doppler division multiple access (DDMA) FMCW transmission. FIG. 2B shows a graph of an example received reflected FMCW signal corresponding to the DDMA FMCW transmission of FIG. 2A. FIG. 3 shows a functional block diagram of an example FMCW radar system for transmitting a DDMA FMCW transmission as shown in FIG. 2A, and receiving reflected FMCW chirps as shown in FIG. 2B. FIG. 4 illustrates a process for determining range and velocity using FMCW chirps transmitted and received by the FMCW radar system of FIG. 3. FIG. 5 illustrates a set of two dimensional fast Fourier transforms (FFTs) generated by applying the process of FIG. 4 to DDMA FMCW signals received by the first, second, third, and fourth receivers of FIG. 3. FIGS. 6A, 6B, 6C, and 6D show graphs of Doppler shift versus amplitude of FFTs of example received FMCW signals, received using the FMCW radar system of FIG. 3. FIG. 7 shows graphs of Doppler shift versus amplitude of example received FMCW signals 100 transmitted by two different transmitters of the FMCW radar system of FIG. 3. FIG. 8 shows an example graph relating phase shift input to phase shifter output error. The same reference numbers or other reference designators are used in the drawings to designate the same or similar (structurally and/or functionally) features. DETAILED DESCRIPTION FIG. 1 shows a graph of an example FMCW signal 100 to be transmitted by an automotive or industrial FMCW radar system. The vertical axis corresponds to frequency, and the horizontal axis corresponds to time. The FMCW signal 100 is modulated to define FMCW chirps 102. The duration of an FMCW chirp 102 is referred to herein as the ramp time 104. During an FMCW chirp 102, the transmitter frequency may ramp upwards like a sawtooth wave, from a base frequency F0 106 to a maximum frequency F1 108. An FMCW chirp 102 has a slope S=(F1−F0)/ramp time. The slope of the FMCW signal 100 corresponds to a change in frequency per unit of time, for example, ΔHz/s. Between FMCW chirps 102 are idle times 110. An idle time 110 is a period during which a transmitter transmitting the FMCW signal 100 is turned off. The time from the beginning of one FMCW chirp 102 to the beginning of the next FMCW chirp 102 is referred to as the pulse repetition interval (PRI) 112 of the FMCW signal 100, and equals the ramp time 104 plus the idle time 110. The inverse of the PRI 112 is the pulse repetition frequency (PRF) of the FMCW signal 100. Fast time refers to the different time slots composing a PRI 112 during a single FMCW chirp 102, and is dependent on the rate at which a received signal is sampled. Slow time updates after each PRI 112, and refers to time over the course of multiple FMCW chirps 102. FIG. 2A shows a diagram of an example Doppler division multiple access (DDMA) FMCW transmission 200. An FMCW synthesizer 202 (see FIG. 3, also referred to as an FMCW signal generator) generates an FMCW signal 100. The FMCW synthesizer 202 outputs the FMCW signal 100 to a first phase shifter (phase shifter 1) 204a, a second phase shifter (phase shifter 2) 204b, and a third phase shifter (phase shifter 3) 204c. The first phase shifter 204a