System and method for coherent frequency switching in DDS architectures

• US 7,952,516 B2
• Filed: 09/26/2006
• Issued: 05/31/2011
• Est. Priority Date: 09/26/2006
• Status: Active Grant

• Current Assignee: Lockheed Martin Corporation (Martin Marietta Corporation)
• Original Assignee: Lockheed Martin Corporation (Martin Marietta Corporation)
• Inventors: Atherton, Adam T.
• Primary Examiner(s): Tarcza; Thomas H
• Assistant Examiner(s): Barker; Matthew M
• Application Number:
  US11/535,124
• Publication Number:
  US 20080074311A1
• Time in Patent Office: 1,708 Days
• Field of Search: 342/200, 342/202
• US Class Current: 342/200
• CPC Class Codes: G01S 13/28 with time compression of received pulses
• CPC Class Codes: G01S 7/282 Transmitters
• CPC Class Codes: G06F 1/0335 the phase increment itself being a composed function of two or more variables, e.g. frequency and phase
• CPC Class Codes: G06F 1/0342 for generating simultaneously two or more related waveforms, e.g. with different phase angles only

Abstract

The present invention is directed to an integrated circuit device that includes a primary signal synthesizer configured to generate a free-running first digital frequency signal and at least one secondary signal synthesizer disposed in parallel with the primary signal synthesizer and configured to generate a free-running at least one second digital frequency signal. A switch element includes a first switch input coupled to the primary signal synthesizer and at least one second switch input coupled to the at least one secondary signal synthesizer. The switch element is configured to select a switch output that provides either the free-running first digital frequency signal or the free-running at least one second digital frequency signal based on a switch control input.

Claims

1. An integrated circuit device comprising:

a primary signal synthesizer including a primary frequency accumulator in series with a primary phase accumulator, the primary frequency accumulator being configured to generate a primary digital modulation signal based on a predetermined modulation format and a primary frequency, the primary phase accumulator being configured to increment in response to a digital clock signal to thereby generate a free-running primary digital signal in accordance with the primary modulation signal;

at least one secondary signal synthesizer disposed in parallel with the primary signal synthesizer, the at least one secondary signal synthesizer including at least one secondary frequency accumulator in series with a corresponding one of at least one secondary phase accumulator, the at least one secondary frequency accumulator being configured to generate at least one secondary digital modulation signal based on at least one secondary frequency, the at least one secondary phase accumulator being configured to increment in response to the digital clock signal to thereby generate a free-running at least one secondary digital signal in accordance with the at least one secondary digital modulation signal; and

a switch element including a first switch input coupled to the primary signal synthesizer and at least one second switch input coupled to the at least one secondary signal synthesizer, the switch element being configured to select a switch output that provides either the primary digital signal or the at least one secondary digital signal based on a switch control input, a latter switch element output of the primary digital signal provided after the switch element output the at least one secondary digital signal being phase coherent with a former switch output of the primary digital signal provided before the switch element output the at least one secondary digital signal.

2. The integrated device of claim 1, wherein a latter switch element output of the at least one secondary digital signal provided after a switch element output of the primary digital signal being phase coherent with a former switch element output of the at least one secondary digital signal provided before the switch element output of the primary digital signal.

3. The integrated device of claim 1, further comprising a pulse control module coupled to an input of the primary frequency accumulator and an input of the at least one secondary frequency accumulator.

4. The integrated device of claim 3, wherein the pulse control module includes a modulation control circuit.

5. The integrated device of claim 4, wherein the modulation control circuit is configured to implement a modulation format including amplitude modulation, frequency modulation, and/or phase modulation.

6. The integrated device of claim 4, wherein the modulation control circuit is configured to implement a chirp modulation format.

7. The integrated device of claim 4, wherein the modulation control circuit is configured to implement a non-linear frequency modulation format.

8. The integrated device of claim 4, wherein the modulation control circuit is configured to implement a linear frequency modulation format.

9. The integrated device of claim 1, wherein the at least one secondary signal synthesizer further comprises N-secondary signal synthesizers, each of the N-secondary signal synthesizers being disposed in parallel with each other such that the switch element may be switched between N+1 inputs, N being an integer number.

10. The integrated device of claim 1, further comprising at least one look-up table (LUT) having address inputs coupled to the switch output, the at least one LUT having signal amplitude data stored therein, the signal amplitude data corresponding to a predetermined digital waveform.

11. The integrated device of claim 10, wherein the switch output is selected to apply the primary digital frequency signal to the address inputs when the primary signal synthesizer output is selected, the at least one LUT being configured to generate the predetermined digital waveform at the primary digital frequency.

12. The integrated device of claim 10, wherein the switch output is selected to apply the at least one secondary digital frequency signal to the address inputs when the at least one secondary signal synthesizer output is selected, the at least one LUT being configured to generate the predetermined digital waveform at the at least one secondary digital frequency.

13. The integrated device of claim 12, wherein the at least one secondary signal synthesizer further comprises N-secondary signal synthesizers, each of the N-secondary signal synthesizers being disposed in parallel with each other such that the switch output is configured to selectively apply one of N+1 digital frequency signals to the address inputs, N being an integer number.

14. The integrated device of claim 10, further comprising at least one digital-to-analog converter (DAC) coupled to the at least one LUT, the at least one DAC being configured to convert the predetermined digital waveform into a predetermined analog waveform.

15. The integrated device of claim 14, wherein the integrated device is implemented as an ASIC, and wherein the at least one DAC is an integrated part of the ASIC.

16. The integrated device of claim 14, wherein the integrated device is implemented as FPGA, and wherein the at least one DAC is not an integrated component disposed in the FPGA.

17. The integrated device of claim 10, wherein the at least one LUT includes an in-phase LUT configured to output a cosine digital waveform and a quadrature LUT configured to output a sine digital waveform, the cosine digital waveform and the sine digital waveform having a predetermined frequency determined in accordance with the switch control input.

18. The integrated device of claim 17, further comprising a first DAC coupled to an output of the in-phase LUT and a second DAC coupled to an input of the quadrature DAC.

19. The integrated device of claim 1, wherein the at least one secondary signal synthesizer further comprises N-secondary signal synthesizers, each of the N-secondary signal synthesizer being disposed in parallel with the primary signal synthesizer, the N-secondary signal synthesizers being and configured to generate a N-free running digital frequency signals, each of the N-free running digital frequency signals and the free-running first digital frequency signals having a different frequency and are phase coherent.

20. A coherent radar system comprising:

an antenna system configured to radiate RF radar signals and receive ambient RF signals;

a timing circuit configured to provide a digital clock signal;

a transmitter coupled to the antenna system and configured to direct the RF radar signals into the antenna system;

a receiver system coupled to the antenna system and configured to detect RF radar return signals in the ambient RF signals, the detected RF radar return signals corresponding to the radiated RF radar signals; and

a digital local oscillator coupled to the transmitter system and the receiver system, the digital local oscillator being implemented as an integrated circuit device, the digital local oscillator including,

a primary frequency accumulator configured to generate a primary digital modulation signal corresponding to a predetermined primary modulation format and a predetermined primary frequency,

a primary phase accumulator coupled in series with an output of the primary frequency accumulator, the primary phase accumulator being configured to increment in response to the digital clock signal to thereby generate a free-running primary digital frequency signal in accordance with the primary digital modulation signal,

at least one secondary frequency accumulator configured to generate at least one second digital modulation signal corresponding to at least one secondary frequency,

at least one secondary phase accumulator coupled in series with the at least one secondary frequency accumulator, the at least one secondary phase accumulator being configured to increment in response to the digital clock signal to thereby generate a free-running at least one second digital frequency signal in accordance with at least one second digital modulation signal, and

a switch element including a first switch input coupled to the primary phase accumulator and at least one second switch input coupled to the at least one secondary phase accumulator, the switch element being configured to provide a switch output that transmits either the free-running primary digital frequency signal or the free-running at least one second digital frequency signal based on a switch control input, a latter occurrence of the primary digital frequency signal provided after an occurrence of the at least one secondary digital frequency signal being phase coherent with a former occurrence of the primary digital frequency signal provided before the occurrence of the at least one secondary digital frequency signal, and a latter occurrence of the at least one secondary digital frequency signal provided after an occurrence of the primary digital frequency signal being phase coherent with a former occurrence of the at least one secondary digital frequency signal provided before the occurrence of the primary digital frequency signal.

21. The radar system of claim 20, further comprising a pulse control module coupled to an input of the primary frequency accumulator and an input of the secondary frequency accumulator, the pulse control module being configured to provide modulation format data.

22. The radar system of claim 21, wherein the pulse control module includes a non-linear frequency modulation chirp control circuit.

23. The radar system of claim 21, wherein the pulse control module includes a linear frequency modulation chirp control circuit.

24. The radar system of claim 20, wherein the at least one a secondary frequency accumulator further comprises N-secondary frequency accumulators and the at least one a secondary phase accumulator further comprises N-secondary phase accumulators each coupled to a corresponding one of the N-secondary frequency accumulators, each series combination of a secondary frequency accumulator and secondary phase accumulator being disposed in parallel with the N−

1 remaining series combinations of secondary frequency accumulators and secondary phase accumulators such that the switch element may be switched between N+1 inputs, N being an integer number.

25. The radar system of claim 24, further comprising at least one look-up table (LUT) having address inputs coupled to the switch output, the at least one LUT having signal amplitude data stored therein, the signal amplitude data corresponding to a predetermined digital waveform.

26. The radar system of claim 25, wherein the switch output is selected to apply the primary digital frequency signal to the address inputs when the primary phase accumulator output is selected, the at least one LUT being configured to generate the predetermined digital waveform at the primary digital frequency.

27. The radar system of claim 25, wherein the switch output is selected to apply one of N-secondary digital frequency signals to the address inputs when one of the N-secondary phase accumulator outputs is selected, the at least one LUT being configured to generate the predetermined digital waveform at a secondary digital frequency corresponding to the selected one of N-secondary digital frequency signals.

28. The radar system of claim 25, further comprising at least one digital-to-analog converter (DAC) coupled to the at least one LUT, the at least one DAC being configured to convert the predetermined digital waveform into a predetermined analog waveform.

29. The radar system of claim 28, wherein the at least one LUT includes an in-phase LUT configured to output a cosine digital waveform and a quadrature LUT configured to output a sine digital waveform, the cosine digital waveform and the sine digital waveform having a predetermined frequency determined in accordance with the switch control input.

30. The radar system of claim 28, further comprising a first DAC coupled to an output of the in-phase LUT and a second DAC coupled to an output of the quadrature LUT.

31. The radar system of claim 20, wherein the radar system is a pulsed radar system.

32. The radar system of claim 20, wherein the receiver is configured to perform Doppler processing functions.

33. The radar system of claim 20, wherein the integrated device is a FPGA.

34. The radar system of claim 33, wherein the FPGA is coupled to a DAC.

35. The radar system of claim 20, wherein the integrated device is an ASIC.

36. The system of claim 20, wherein the at least one secondary signal synthesizer further comprises N-secondary signal synthesizers, each of the N-secondary signal synthesizer being disposed in parallel with the primary signal synthesizer, the N-secondary signal synthesizers being and configured to generate a N-free running digital frequency signals, each of the N-free running digital frequency signals and the free-running first digital frequency signals having a different frequency and are phase coherent.