Local oscillator with non-harmonic ratio between oscillator and RF frequencies using XOR operation
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.
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;
first circuitry for generating a first quadrature pair including in-phase and quadrature signals at a second frequency in response to said first signal;
second circuitry for receiving said in-phase signal and operative to generate a second quadrature pair including in-phase and quadrature signals at a third frequency;
third circuitry for logically mixing 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; and
a logical XOR function 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.
2. The apparatus according to claim 1 , wherein said third circuitry comprises a logical XOR function.
3. The apparatus according to claim 1 , further comprising circuitry for filtering said in-phase output signal to attenuate unwanted harmonics therefrom.
4. The apparatus according to claim 1 , further comprising circuitry for filtering said quadrature output signal to attenuate unwanted harmonics therefrom.
5. The apparatus according to claim 1 , wherein said first frequency is substantially equal to four-thirds of said output frequency.
6. The apparatus according to claim 1 , wherein said first frequency is substantially equal to two-thirds of said output frequency.
7. The apparatus according to claim 1 , wherein said first frequency and said second frequency are substantially equal.
8. The apparatus according to claim 1 , wherein said second frequency is substantially equal to two-thirds of said output frequency.
9. The apparatus according to claim 1 , wherein said third frequency is substantially equal to one-third of said output frequency.
10. The apparatus according to claim 1 , wherein said first circuitry comprises a divider.
11. 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;
first circuitry 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;
second circuitry for receiving 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
third circuitry 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.
12. The apparatus according to claim 11 , further comprising circuitry for filtering said in-phase output signal to attenuate unwanted harmonics therefrom.
13. The apparatus according to claim 11 , further comprising second circuitry 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.
14. The apparatus according to claim 13 , further comprising circuitry for filtering said quadrature output signal to attenuate unwanted harmonics therefrom.
15. The apparatus according to claim 11 , wherein said first frequency is substantially equal to two-thirds of said output frequency.
16. The apparatus according to claim 11 , wherein said first frequency and said second frequency are substantially equal.
17. The apparatus according to claim 11 , wherein said first circuitry comprises a divider.
18. The apparatus according to claim 11 , wherein said first frequency is substantially equal to four-thirds of said output frequency.
19. A method of generating in an apparatus a local oscillator signal having an output frequency, said method comprising the steps of:
generating a first signal at a first frequency;
generating a first quadrature pair including in-phase and quadrature signals at a second frequency in response to said first signal;
dividing said in-phase signal to generate a second quadrature pair including in-phase and quadrature signals at a third frequency;
logically mixing 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; and
applying a logical XOR function to said first quadrature pair and said second quadrature pair to generate a quadrature output signal having a frequency substantially equal to said output frequency.
20. The method according to claim 19 , wherein said step of logically mixing comprises applying a logical XOR function.
21. The method according to claim 19 , further comprising the step of filtering said in-phase output signal to attenuate unwanted harmonics therefrom.
22. The method according to claim 19 , further comprising the step of filtering said quadrature output signal to attenuate unwanted harmonics therefrom.
23. The method according to claim 19 , wherein said first frequency is substantially equal to four-thirds of said output frequency.
24. The method according to claim 19 , wherein said second frequency is substantially equal to two-thirds of said output frequency.
25. The method according to claim 19 , wherein said third frequency is substantially equal to one-third of said output frequency.
26. The method according to claim 19 , wherein said first frequency is substantially equal to two-thirds of said output frequency.
27. The method according to claim 19 , wherein said first frequency and said second frequency are substantially equal.
28. A transceiver, 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;
circuitry 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.
29. The radio according to claim 28 , further comprising circuitry for filtering said in-phase output signal to remove attenuate harmonics therefrom.
30. The radio according to claim 28 , further comprising second circuitry 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.
31. The radio according to claim 30 , further comprising circuitry for filtering said quadrature output signal to attenuate unwanted harmonics therefrom.
32. The apparatus according to claim 1 , wherein said output frequency is a non-integer division of said first frequency.
33. The apparatus according to claim 1 , wherein there is a non-harmonic ratio between said output frequency and said first frequency.
34. The apparatus according to claim 11 , wherein said output frequency is a non-integer division of said first frequency.
35. The apparatus according to claim 11 , wherein there is a non-harmonic ratio between said output frequency and said first frequency.
36. The method according to claim 19 , wherein said output frequency is a non-integer division of said first frequency.
37. The method according to claim 19 , wherein there is a non-harmonic ratio between said output frequency and said first frequency.
38. The apparatus according to claim 28 , wherein said output frequency is a non-integer division of said frequency of said first signal.
39. The apparatus according to claim 28 , wherein there is a non-harmonic ratio between said output frequency and said frequency of said first signal.