Local oscillator with non-harmonic ratio between oscillator and RF frequencies using XOR operation

• US 20080056337A1
• Filed: 08/23/2007
• Published: 03/06/2008
• Est. Priority Date: 08/29/2006
• Status: Active Grant

• Current Assignee: Texas Instruments, Inc.
• Original Assignee: Texas Instruments, Inc.
• Inventors: Lerner, Gregory, Staszewski, Robert B., Tsfaty, Yossi, Tal, Nir
• Granted Patent: US 8,121,214 B2
• Time in Patent Office: Days
• US Class Current: 375/219
• CPC Class Codes: H03B 21/02 by plural beating, i.e. for frequency synthesis ; Beating in combination with multiplication or division of frequency digital frequency synthesis using a ROM G06F1/02; digital frequency synthesis in general H03K; indirect frequency synthesis using a PLL H03L7/16

Abstract

A novel and useful apparatus for and method of local oscillator (LO) generation with non-integer multiplication ratio between the local oscillator and RF frequencies. The LO generation schemes presented are operative to generate I and Q square waves at a designated frequency while avoiding the well known issue of harmonic pulling. A synthesizer provides 4/3 the desired frequency f_RF. This frequency is divided by two to obtain in-phase and quadrature square waves at ⅔ f_RF. The in-phase signal is divided by two again to obtain in-phase and quadrature square waves at ⅓ f_RF. The signals are then logically combined using XOR operations to obtain I and Q branch signals containing spectral spurs. Since the spurs are located in non-disturbing bands, they can be filtered out resulting in the desired output signal.

Claims

1. An apparatus for generating a local oscillator signal having an output frequency, comprising:

an oscillator circuit operative to generate a first signal at a first frequency;

generating means for generating a first quadrature pair including in-phase and quadrature signals at a second frequency in response to said first signal;

a second frequency divider coupled to receive said in-phase signal and operative to generate a second quadrature pair at a third frequency; and

first means for logically mixing said first quadrature pair and said second quadrature pair to generate an in-phase output signal having a frequency substantially equal to said output frequency.

2. The apparatus according to claim 1, wherein said first means for logically mixing comprises a logical XOR function.

3. The apparatus according to claim 1, further comprising means for filtering said in-phase output signal to attenuate unwanted harmonics therefrom.

4. The apparatus according to claim 1, further comprising second means for logically mixing said first quadrature pair and said second quadrature pair to generate a quadrature output signal having a frequency substantially equal to said output frequency.

5. The apparatus according to claim 4, wherein said second means for logically mixing comprises a logical XOR function.

6. The apparatus according to claim 4, further comprising means for filtering said quadrature output signal to attenuate unwanted harmonics therefrom.

7. The apparatus according to claim 1, wherein said first frequency is substantially equal to four-thirds of said output frequency.

8. The apparatus according to claim 1, wherein said first frequency is substantially equal to two-thirds of said output frequency.

9. The apparatus according to claim 1, wherein said first frequency and said second frequency are substantially equal.

10. The apparatus according to claim 1, wherein said second frequency is substantially equal to two-thirds of said output frequency.

11. The apparatus according to claim 1, wherein said third frequency is substantially equal to one-third of said output frequency.

12. The apparatus according to claim 1, wherein said generating means comprises a divider.

13. An apparatus for generating a local oscillator signal having an output frequency, comprising:

an oscillator circuit operative to generate a first signal, said first signal having a first frequency substantially equal to an integer multiple of one-third said output frequency;

generating means for generating first in-phase and first quadrature signals at a second frequency substantially equal to two-thirds said output frequency in response to said first signal;

a second frequency divider coupled to receive said first in-phase signal and operative to generate second in-phase and second quadrature signals at a frequency substantially equal to one-third said output frequency; and

first means for logically XORing said first quadrature signal and said second quadrature signal to generate an in-phase output signal having a frequency substantially equal to said output frequency.

14. The apparatus according to claim 13, further comprising means for filtering said in-phase output signal to attenuate unwanted harmonics therefrom.

15. The apparatus according to claim 13, further comprising second means for logically XORing said first quadrature signal and said second in-phase signal to generate a quadrature output signal having a frequency substantially equal to said output frequency.

16. The apparatus according to claim 15, further comprising means for filtering said quadrature output signal to attenuate unwanted harmonics therefrom.

17. The apparatus according to claim 13, wherein said first frequency is substantially equal to two-thirds of said output frequency.

18. The apparatus according to claim 13, wherein said first frequency and said second frequency are substantially equal.

19. The apparatus according to claim 13, wherein said generating means comprises a divider.

20. The apparatus according to claim 13, wherein said first frequency is substantially equal to four-thirds of said output frequency.

21. A method of generating a local oscillator signal having an output frequency, said method comprising the steps of:

first generating a first signal at a first frequency;

second generating a first quadrature pair including in-phase and quadrature signals at a second frequency in response to said first signal;

second dividing said in-phase signal to generate a second quadrature pair at a third frequency; and

first logically mixing said first quadrature pair and said second quadrature pair to generate an in-phase output signal having a frequency substantially equal to said output frequency.

22. The method according to claim 21, wherein said step of first logically mixing comprises applying a logical XOR function.

23. The method according to claim 21, further comprising the step of filtering said in-phase output signal to attenuate unwanted harmonics therefrom.

24. The method according to claim 21, further comprising the step of second logically mixing said first quadrature pair and said second quadrature pair to generate a quadrature output signal having a frequency substantially equal to said output frequency.

25. The method according to claim 24, wherein said step of second logically mixing comprises applying a logical XOR function.

26. The method according to claim 24, further comprising the step of filtering said quadrature output signal to attenuate unwanted harmonics therefrom.

27. The method according to claim 21, wherein said first frequency is substantially equal to four-thirds of said output frequency.

28. The method according to claim 21, wherein said second frequency is substantially equal to two-thirds of said output frequency.

29. The method according to claim 21, wherein said third frequency is substantially equal to one-third of said output frequency.

30. The method according to claim 21, wherein said first frequency is substantially equal to two-thirds of said output frequency.

31. The method according to claim 21, wherein said first frequency and said second frequency are substantially equal.

32. A radio, comprising:

a transmitter coupled to an antenna, said transmitter comprising a local oscillator having an output frequency, said local oscillator comprising;

an oscillator circuit operative to generate a first signal, said first signal having a frequency substantially equal to a multiple of one-third said output frequency;

a circuit to receive said first signal and operative to generate first in-phase and first quadrature signals at a frequency substantially equal to two-thirds said output frequency;

a second frequency divider coupled to receive said first in-phase signal and operative to generate second in-phase and second quadrature signals at a frequency substantially equal to one-third said output frequency;

first means for logically XORing said first quadrature signal and said second quadrature signal to generate an in-phase output signal having a frequency substantially equal to said output frequency;

a receiver coupled to said antenna; and

a baseband processor coupled to said transmitter and said receiver.

33. The radio according to claim 32, further comprising means for filtering said in-phase output signal to remove attenuate harmonics therefrom.

34. The radio according to claim 32, further comprising second means for logically XORing said first quadrature signal and said second in-phase signal to generate a quadrature output signal having a frequency substantially equal to said output frequency.

35. The radio according to claim 34, further comprising means for filtering said quadrature output signal to attenuate unwanted harmonics therefrom.