Method and apparatus for digital compensation of VCO nonlinearity in a radar system

• US 5,719,580 A
• Filed: 06/06/1996
• Issued: 02/17/1998
• Est. Priority Date: 06/06/1996
• Status: Expired due to Fees

• Current Assignee: TRW Inc. (Northrop Grumman Corporation)
• Original Assignee: TRW Inc. (Northrop Grumman Corporation)
• Inventors: Core, Mark Taylor
• Primary Examiner(s): ELDRED, JOHN W
• Application Number:
  US08/659,400
• Time in Patent Office: 621 Days
• Field of Search: 342/100, 342/132, 367/38, 367/43, 367/49, 371/72
• US Class Current: 342/100
• CPC Class Codes: G01S 13/282 using a frequency modulated carrier wave G01S13/286 takes precedence
• CPC Class Codes: G01S 13/343 using sawtooth modulation
• CPC Class Codes: G01S 2013/93271 in the front of the vehicles
• CPC Class Codes: G01S 7/4008 of transmitters

Abstract

An apparatus for correcting for nonlinearities in modulation systems includes a transmitter (24, 28, 48, 50, 52) for transmitting a time varying modulated radar signal (56). A receiver (58, 62) receives an echo signal (60) resulting from reflection of the transmitted modulated signal (56). A mixer (48) compares the transmitted signal against the echo signal and providing a comparison signal indicative of the comparison. The comparison signal is sampled by an A/D converter (74). The A/D convertor (74) provides a sampled comparison signal to a controller/DSP (22). Controller/DSP (22) resamples the sampled comparison signal at selected resample times and effectively varies the selected resample times to correct for nonlinearities in the comparison signal resulting from nonlinearities of the transmitted time varying modulated signal.

Claims

1. An apparatus for processing time varying signals, said apparatus comprising:

means for sampling a time varying signal and providing a sampled signal;

means for resampling said sampled signal at selected resample times; and

means for varying said selected resample times and providing a resampled time varying signal according to said varying selected resample times.

2. The apparatus of claim 1 wherein said means for varying said selected resample times includes control means for determining an algorithm for determining said selected resample times.

3. The apparatus of claim 1 wherein said means for varying said selected resample times includes means for controlling said resample times so that said resample times are continuously variable in duration.

4. The apparatus of claim 3 wherein the duration of said continuously variable resample times are non-uniform.

5. The apparatus of claim 3 wherein said continuously variable duration of said resample times is non-periodic.

6. The apparatus of claim 3 wherein said continuously variable resample times are stored in a look-up table.

7. An apparatus for correcting for nonlinearities in modulation systems, said apparatus comprising:

means for transmitting a time varying modulated signal;

means for receiving an echo signal resulting from reflection of said transmitted modulated signal;

means for comparing said transmitted signal against said received echo signal and providing a comparison signal indicative of said comparison;

means for sampling of said comparison signal and providing a sampled comparison signal;

means for resampling said sampled comparison signal at selected resample times; and

means for effectively varying said selected resample times so as to correct said comparison signal for nonlinearities in said comparison signal resulting from nonlinearities of the transmitted time varying modulated signal.

8. The apparatus of claim 7 wherein said means for effectively varying said selected resample times includes means for controlling said resample times so that said resample times are non-uniform.

9. The apparatus of claim 7 wherein said means for effectively varying said selected resample times includes means for controlling said resample times so that said resample times are non-uniform and said control means includes means for filtering said comparison signal with a continuously variable multi-rate interpolating filter.

10. The apparatus of claim 7 wherein said means for transmitting includes a voltage controlled oscillator and means for driving said voltage controlled oscillator with a ramp signal.

11. The apparatus of claim 10 wherein said means for comparing includes a mixer for providing a signal having a frequency functionally related to the difference in frequency between said transmitted signal and said echo signal.

12. The apparatus of claim 10 wherein said signal indicative of said difference is an intermediate frequency waveform.

13. The apparatus of claim 10 wherein said means for transmitting transmits a radar signal.

14. The apparatus of claim 13 wherein said frequency difference is functionally related to the distance between said means for transmitting and a target.

15. The apparatus of claim 7 wherein said means for transmitting includes means for transmitting a frequency modulated signal.

16. The apparatus of claim 7 wherein said varying selected resample times are stored in a look-up table.

17. A method for processing time varying signals, said method comprising the steps of:

sampling a time varying signal;

providing a sampled time varying signal;

resampling at selected times said sampled time varying signal;

varying said selected resampling times; and

providing a resampled time varying signal according to said varied selected resample times.

18. The method of claim 17 wherein said step of varying said selected resample times includes the step of controlling said selected resample time so that said selected resample times are continuously variable in duration.

19. The method of claim 17 wherein said step of varying said selected resample times includes the step of controlling the duration of said selected resample times so that said selected resample times are non-uniform.

20. The method of claim 18 wherein said step of varying said continuously variable selected resample times includes the step of controlling the duration of said continuously variable selected resample times so that said continuously variable selected resample times are non-periodic.

21. The method of claim 17 wherein the step of varying said selected resampling times includes the step of determining an algorithm for determining said selected resample times.

22. A method for correcting for nonlinearities in modulation systems, said method comprising the steps of;

transmitting a time varying modulated signal;

receiving an echo signal resulting from reflection of said transmitted modulated signal;

comparing said transmitted signal against said echo signal and providing a signal indicative of said comparison;

sampling said comparison signal and providing a sampled comparison signal;

resampling said sampled comparison signal at selected resample times; and

effectively varying said selected resample times so as to correct said comparison signal for deviations from a nominal constant frequency resulting from nonlinear frequency modulation of the transmitted signal.

23. The method of claim 22 wherein said step of effectively varying said resample times includes the step of controlling the resampling times of said samplings of said comparison signal so that said resampling times are non-uniformly spaced.

24. The method of claim 22 wherein said step of effectively varying said resample times includes the step of controlling said resample times so that said resample times are non-uniformly spaced, said varying of said resample times including the step of filtering said comparison signal using a continuously varying multi-rate interpolation filter.

25. The method of claim 22 wherein said step of transmitting a frequency modulated signal includes the step of varying the frequency of said time varying signal in response to a ramp function.

26. The method of claim 22 wherein said step of transmitting includes transmitting a frequency modulated signal and wherein said step of comparing includes the step of determining the frequency difference between the transmitted signal and the received echo signal.

27. The method of claim 22 wherein said step of transmitting includes transmitting a radar signal.