Estimating and compensating for crystal oscillator differences in a multi-crystal-oscillator radar

Patent metadata

Field	Value
Publication number	US-12455349-B2
Application number	US-202318476965-A
Country	US
Kind code	B2
Filing date	Sep 28, 2023
Priority date	Jul 27, 2023
Publication date	Oct 28, 2025
Grant date	Oct 28, 2025

Abstract

In some examples, a method includes receiving, at a first device, a radar signal transmitted by a second device at a transmission frequency offset from a local oscillator (LO) frequency of the first device by a target offset and reflected off a target. The method also includes determining an intermediate frequency (IF) of the radar signal based on the transmission frequency and the LO frequency. The method also includes determining a parts per million (ppm) offset between the first device and the second device based on the intermediate frequency and the target offset.

First claim

What is claimed is:

1. An apparatus, comprising:
a first oscillator;
a receiver circuit configured to receive a first signal having a first frequency, wherein the receiver circuit includes:
a clock circuit coupled to the first oscillator and configured to provide a local oscillator signal that has a second frequency based on the first frequency and a target offset;
a mixer coupled to receive the local oscillator signal and the first signal;
a filter coupled to the mixer and configured to provide an intermediate frequency signal based on the local oscillator signal and the first signal;
an analog-to-digital converter coupled to the filter and configured to provide a digitized intermediate frequency signal based on the intermediate frequency signal; and
a digital front end coupled to the analog-to-digital converter configured to:
determine an intermediate frequency associated with the digitized intermediate frequency signal; and
determine a variance between the first oscillator and a second oscillator based on a comparison of the intermediate frequency to the target offset.

2. The apparatus of claim 1 , wherein the digital front end is configured to determine the variance as a parts per million (ppm) offset according to: 1e6*(F IF −F offset )/F RF , where F IF is a peak frequency of intermediate frequency, F offset is the target offset, and F RF is the first frequency.

3. The apparatus of claim 1 , wherein:
the receiver is configured to receive a second signal at a third frequency;
the clock circuit is configured to provide a second local oscillator signal that has a fourth frequency based on the second frequency and the target offset;
the filter is configured to provide a second intermediate frequency signal based on the second local oscillator signal and the second signal;
the analog-to-digital converter is configured to provide a second digitized intermediate frequency signal based on the second intermediate frequency signal; and
the digital front end is configured to:
determine a second intermediate frequency associated with the second digitized intermediate frequency signal;
average the intermediate frequency and the second intermediate frequency to determine an average intermediate frequency; and
determine the variance between the first oscillator and the second oscillator based on a comparison of the average intermediate frequency to the target offset.

4. The apparatus of claim 3 , wherein the digital front end is configured to determine the variance as a parts per million (ppm) offset according to: 1e6*(F IF −F offset )/F RF , where F IF is a peak frequency of the average intermediate frequency, F offset is the target offset, and F RF is an average of the first frequency and the third frequency.

5. The apparatus of claim 1 , wherein:
the receiver is configured to receive a set of radar signals;
the analog-to-digital converter is configured to perform sampling, in a set of sampling windows, each sampling window corresponding to a respective one of the set of radar signals; and
offset a time shift to each successive sampling window of the set of sampling windows beginning with a second sampling window of the set of sampling windows.

6. The apparatus of claim 5 , wherein the digital front end is configured to determine the time shift (ΔD) according to: ΔD=ppm*1e−6*P signal , where P signal is a signal repetition period of the set of radar signals.

7. The apparatus of claim 6 , wherein each radar signal of the set of radar signals increases in frequency over time, and wherein a starting frequency of each successive radar signal of the set of radar signals beginning with a second radar signal of the set of radar signals is offset by a frequency shift (ΔF).

8. The apparatus of claim 7 , wherein the frequency shift (ΔF) is determined according to: F=ΔD*S, where S is a system parameter representing a slope of a respective radar signal of the set of radar signals.

9. A method, comprising:
receiving, at a first device, a radar signal transmitted by a second device at a transmission frequency offset from a local oscillator (LO) frequency of the first device by a target offset and reflected off a target;
determining an intermediate frequency (IF) of the radar signal based on the transmission frequency and the LO frequency; and
determining a parts per million (ppm) offset between the first device and the second device based on the intermediate frequency and the target offset.

10. The method of claim 9 , further comprising determining the ppm offset according to: 1e6*(F IF −F offset )/F RF , where F IF is a peak frequency of the intermediate frequency, F offset is the target offset, and F RF is the transmission frequency.

11. The method of claim 9 , further comprising:
receiving, at the first device, a second radar signal transmitted by the second device at a second transmission frequency offset from a second LO frequency of the first device by the target offset and reflected off the target;
determining a second intermediate frequency of the radar signal based on the second transmission frequency and the second LO frequency;
averaging the intermediate frequency and second intermediate frequency to determine an average intermediate frequency; and
determining the ppm offset between the first device and the second device based on the average intermediate frequency and the target offset.

12. The method of claim 11 , further comprising determining the ppm offset according to: 1e6*(F IF −F offset )/F RF , where F IF is a peak frequency of the average intermediate frequency, F offset is the target offset, and F RF is an average of the transmission frequency and the second transmission frequency.

13. The method of claim 9 , further comprising:
receiving, at the first device, a frame of radar signals transmitted by the second device and reflected off a second target; and
sampling, in a set of sampling windows the frame of radar signals, each sampling window corresponding to a respective signal of the frame of radar signals,
wherein each successive sampling window of the set of sampling windows beginning with a second sampling window of the set of sampling windows is shifted in time by a time shift (ΔD).

14. The method of claim 13 , wherein the time shift (ΔD) is: ΔD=ppm*1e−6*P signal , where P signal is a signal repetition period of the frame of radar signals.

15. The method of claim 14 , wherein each signal of the frame of radar signals is a frequency-modulated continuous-wave (FMCW) signal that increases in frequency over time, and wherein a starting frequency of each respective signal of the frame of radar signals beginning with a second signal of the frame of radar signals has a starting frequency offset by a frequency shift (ΔF) determined according to: F=ΔD*S, where S is a system parameter representing a slope of the respective radar signal of the frame of radar signals.

16. A system, comprising:
a first radar device configured to transmit a frame of radar signals, each signal of the frame of radar signals increasing in frequency over time, wherein a starting frequency of each respective signal of the frame of radar signals beginning with a second signal of the frame of radar signals has a starting frequency offset by a frequency shift (ΔF); and
a second radar device configured to:
receive a frame of reflected signals, the frame of reflected signals corresponding to the frame of radar signals reflected off a target; and
sample the reflected signals in a set of sampling windows, each sampling window of the set of sampling windows corresponding to one r

Assignees

• Texas Instruments Inc

Inventors

• Subburaj Karthik
• Rao Sandeep
• Ramasubramanian Karthik

Classifications

• G01S7/356

  involving particularities of FFT processing · CPC title

• G01S13/931

  of land vehicles · CPC title

• H03D3/00

  Demodulation of angle-, {frequency- or phase-} modulated oscillations (H03D5/00, H03D9/00, H03D11/00 take precedence) · CPC title

• G01S13/93

  for anti-collision purposes · CPC title

• G01S13/583

  using transmission of continuous unmodulated waves, amplitude-, frequency-, or phase-modulated waves and based upon the Doppler effect resulting from movement of targets · CPC title