FREQUENCY SYNTHESIZER WITH MULTIPLE TUNING LOOPS

• US 20100207693A1
• Filed: 02/13/2009
• Published: 08/19/2010
• Est. Priority Date: 02/13/2009
• Status: Active Grant

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: Fagg, Russell John
• Granted Patent: US 8,378,751 B2
• Time in Patent Office: Days
• US Class Current: 331/10
• CPC Class Codes: H03L 2207/12 Indirect frequency synthesis using a mixer in the phase-locked loop
• CPC Class Codes: H03L 7/185 using a mixer in the loop H03L7/187 - H03L7/195 take precedence
• CPC Class Codes: H03L 7/1976 using a phase accumulator for controlling the counter or frequency divider
• CPC Class Codes: H03L 7/23 with pulse counters or frequency dividers

Abstract

A frequency synthesizer with multiple tuning loops, e.g., a fine tuning loop and a coarse tuning loop, is described. The fine tuning loop may operate over a limited tuning range and may have fine frequency resolution. The coarse tuning loop may operate over a wide tuning range and may have coarse frequency resolution. The fine tuning loop may receive a reference signal at a reference frequency and generate a fine tuning signal at a first frequency adjustable in fine steps. The coarse tuning loop may receive the reference signal, generate an output signal at an output frequency, and generate a coarse tuning signal at a second frequency based on the output signal and the fine tuning signal. The second frequency may be adjustable in coarse steps, e.g., in integer multiples of the reference frequency. The output frequency may be determined based on the first frequency and the second frequency.

Claims

1. An apparatus comprising:

a frequency synthesizer comprising

a fine tuning loop operative to receive a reference signal at a reference frequency and generate a fine tuning signal at a first frequency adjustable in fine steps, and

a coarse tuning loop coupled to the fine tuning loop and operative to receive the reference signal and generate an output signal at an output frequency, the output frequency being determined based on the first frequency and a second frequency, and the second frequency being adjustable in coarse steps.

2. The apparatus of claim 1, wherein the coarse tuning loop comprises

a mixer operative to receive the output signal and the fine tuning signal and provide a coarse tuning signal at the second frequency.

3. The apparatus of claim 2, wherein the mixer comprises a single sideband (SSB) mixer.

4. The apparatus of claim 2, wherein the coarse tuning loop further comprises

a divider operative to divide the coarse tuning signal in frequency and provide a feedback signal at the reference frequency,

a phase-frequency detector operative to receive the reference signal and the feedback signal and provide an error signal,

a charge pump operative to receive the error signal and provide a current signal,

a loop filter operative to filter the current signal and provide a control signal, and

a voltage-controlled oscillator (VCO) operative to receive the control signal and provide the output signal.

5. The apparatus of claim 4, wherein the divider is operative to divide the coarse tuning signal in frequency by an integer ratio, and wherein the second frequency is an integer multiple of the reference frequency.

6. The apparatus of claim 4, wherein the divider is operative to divide the coarse tuning signal in frequency by an integer ratio or a mid non-integer ratio.

7. The apparatus of claim 2, wherein the coarse tuning loop further comprises a divider operative to divide the output signal in frequency by an integer ratio and provide a divider output signal, and wherein the mixer is operative to receive the divider output signal and the fine tuning signal and provide the coarse tuning signal.

8. The apparatus of claim 1, wherein the fine tuning loop comprises

a ring oscillator operative to generate the fine tuning signal.

9. The apparatus of claim 1, wherein the fine tuning loop comprises

a multi-modulus divider operative to divide the fine tuning signal in frequency by a non-integer ratio and provide a feedback signal,

a delta-sigma modulator operative to receive a fractional portion of the non-integer ratio and provide a modulator output, and

a summer operative to sum the modulator output and an integer portion of the non-integer ratio and provide an instantaneous divider ratio to the multi-modulus divider.

10. The apparatus of claim 9, wherein the delta-sigma modulator is operative to receive a phase modulation signal or a frequency modulation signal.

11. The apparatus of claim 1, wherein a closed-loop bandwidth of the fine tuning loop is wider than a closed-loop bandwidth of the coarse tuning loop by a factor of at least two.

12. The apparatus of claim 1, wherein the coarse steps comprise integer multiples of the reference frequency.

13. The apparatus of claim 1, wherein the fine steps comprise integer multiples of a minimum step size corresponding to a fraction of the reference frequency.

14. An apparatus comprising:

a frequency synthesizer operative to receive a reference signal at a reference frequency, to generate an output signal at an output frequency, to obtain a fine tuning signal at a first frequency, and to generate a coarse tuning signal at a second frequency based on the output signal and the fine tuning signal, the second frequency being an integer multiple of the reference frequency, and the output frequency being a non-integer multiple of the reference frequency and determined by the first frequency and the second frequency.

15. The apparatus of claim 14, wherein the first frequency is adjustable in integer multiple of a minimum step size corresponding to a fraction of the reference frequency, and wherein the second frequency is adjustable in integer multiple of the reference frequency.

16. The apparatus of claim 14, wherein the frequency synthesizer comprises

a mixer operative to receive the output signal and the fine tuning signal and provide the coarse tuning signal.

17. The apparatus of claim 14, wherein the frequency synthesizer is further operative to generate the fine tuning signal based on the reference signal.

18. A wireless device comprising:

a frequency synthesizer operative to generate a fine tuning signal at a first frequency based on a reference signal at a reference frequency and to generate an output signal at an output frequency based on the fine tuning signal and the reference signal, the output frequency being determined based on the first frequency and a second frequency, the first frequency being adjustable in fine steps, and the second frequency being adjustable in coarse steps;

a local oscillator (LO) generator coupled to the frequency synthesizer and operative to receive the output signal and generate an LO signal;

a frequency converter coupled to the LO generator and operative to frequency convert an input signal with the LO signal and provide a frequency converted signal; and

an antenna operatively coupled to the frequency converter.

19. The wireless device of claim 18, wherein the frequency converter comprises a downconverter operative to frequency downconvert an input radio frequency (RF) signal with the LO signal and provide a downconverted signal.

20. The wireless device of claim 18, wherein the frequency converter comprises an upconverter operative to frequency upconvert an input baseband signal with the LO signal and provide an upconverted signal.

21. The wireless device of claim 18, further comprising:

a processor operative to provide a first integer ratio and a non-integer ratio for the first frequency and to provide a second integer ratio for the second frequency to the frequency synthesizer.

22. A method comprising:

generating a fine tuning signal at a first frequency based on a reference signal at a reference frequency, the first frequency being adjustable in fine steps; and

generating an output signal at an output frequency based on the fine tuning signal and the reference signal, the output frequency being determined based on the first frequency and a second frequency, and the second frequency being adjustable in coarse steps.

23. The method of claim 22, wherein the generating the output signal comprises generating a coarse tuning signal at the second frequency based on the output signal and the fine tuning signal.

24. The method of claim 23, wherein the generating the output signal further comprises

dividing the coarse tuning signal in frequency to obtain a feedback signal at the reference frequency,

generating an error signal based on the reference signal and the feedback signal, and

filtering the error signal to obtain a control signal for adjusting the output frequency of the output signal.

25. The method of claim 24, wherein the dividing the coarse tuning signal comprises dividing the coarse tuning signal in frequency by an integer ratio, and wherein the second frequency is an integer multiple of the reference frequency.

26. The method of claim 23, wherein the generating the output signal further comprises dividing the output signal in frequency by an integer ratio to obtain a divider output signal, and wherein the coarse tuning signal is generated based on the divider output signal and the fine tuning signal.

27. The method of claim 22, wherein the generating the fine tuning signal comprises

dividing the fine tuning signal in frequency by a non-integer ratio to obtain a feedback signal,

generating a bit sequence based on a fractional portion of the non-integer ratio, and

determining an instantaneous divider ratio for dividing the fine tuning signal based on the bit sequence and an integer portion of the non-integer ratio.

28. The method of claim 22, wherein the generating the output signal comprises generating the output signal with a coarse tuning loop having a first closed- loop bandwidth, and wherein the generating the fine tuning signal comprises generating the fine tuning signal with a fine tuning loop having a second closed-loop bandwidth wider than the first closed-loop bandwidth by a factor of at least two.

29. An apparatus comprising:

means for generating a fine tuning signal at a first frequency based on a reference signal at a reference frequency, the first frequency being adjustable in fine steps; and

means for generating an output signal at an output frequency based on the fine tuning signal and the reference signal, the output frequency being determined based on the first frequency and a second frequency, and the second frequency being adjustable in coarse steps.

30. The apparatus of claim 29, wherein the means for generating the output signal comprises means for generating a coarse tuning signal at the second frequency based on the output signal and the fine tuning signal.

31. The apparatus of claim 30, wherein the means for generating the output signal further comprises

means for dividing the coarse tuning signal in frequency to obtain a feedback signal at the reference frequency,

means for generating an error signal based on the reference signal and the feedback signal,

means for filtering the error signal to obtain a control signal for adjusting the output frequency of the output signal.

32. The apparatus of claim 29, wherein the means for generating the fine tuning signal comprises

means for dividing the fine tuning signal in frequency by a non-integer ratio to obtain a feedback signal,

means for generating a bit sequence based on a fractional portion of the non-integer ratio, and

means for determining an instantaneous divider ratio for dividing the fine tuning signal based on the bit sequence and an integer portion of the non-integer ratio.

33. A computer program product, comprising:

a computer-readable medium comprising;

code for causing at least one computer to provide first control to generate a fine tuning signal at a first frequency based on a reference signal at a reference frequency, the first frequency being adjustable in fine steps, and

code for causing the at least one computer to provide second control to generate an output signal at an output frequency determined based on the first frequency and a second frequency, the second frequency being adjustable in coarse steps.