Method and system for implementing a low power, high performance fractional-N PLL

• US 7,825,738 B2
• Filed: 12/29/2006
• Issued: 11/02/2010
• Est. Priority Date: 12/06/2006
• Status: Expired due to Fees

• Current Assignee: Avago Technologies General IP PTE Limited (Broadcom, Inc.)
• Original Assignee: Broadcom Corporation (Broadcom, Inc.)
• Inventors: Li, Dandan
• Primary Examiner(s): Pascal; Robert
• Assistant Examiner(s): Johnson; Ryan
• Application Number:
  US11/618,651
• Publication Number:
  US 20080136534A1
• Time in Patent Office: 1,404 Days
• Field of Search: 331/16, 331/17, 331/25, 327/156, 327/157, 327/148
• US Class Current: 331/17
• CPC Class Codes: H03L 7/0898 the source or sink current values being variable H03L7/0896 takes precedence
• CPC Class Codes: H03L 7/1976 using a phase accumulator for controlling the counter or frequency divider

Abstract

Aspects of a method and system for implementing a low power, high performance fractional-N PLL synthesizer are provided. The synthesizer comprises a reference generator/buffer, a charge pump, a divider, a VCO, a loop filter, and a phase-frequency detector (PFD). The reference generator/buffer may increase the frequency of the input reference signal to the PFD. The PFD may generate a single signal for controlling the charge pump utilizing the increased frequency input reference signal and a divider signal generated by the divider whose input frequency may be substantially the same as that of a VCO output signal. The single signal charges a charge up portion of the charge pump and a charge down portion is charged by a leakage current. The VCO signal may be generated based on a filtered output of the charge pump generated by the loop filter. The divider may utilize true single phase clock (TSPC) logic.

Claims

1. A method for signal processing, the method comprising:

in a reference generator, increasing a frequency of an input reference signal utilized by a phase-frequency detector (PFD) in a fractional-N phase-locked-loop (PLL) synthesizer comprising said reference generator, said PFD, a charge pump, a divider, a voltage controlled oscillator (VCO), and a loop filter;

generating an enable signal for said PFD utilizing said increased frequency input reference signal;

generating a single signal for controlling said charge pump utilizing said increased frequency input reference signal and a divider signal generated by said divider whose input frequency is substantially the same as that of a VCO signal generated by said fractional-N PLL synthesizer, wherein said single signal enables a switched charge up portion of said charge pump to charge said loop filter and wherein said loop filter is discharged by an unswitched leakage current in said charge pump that is independent of said single signal; and

generating said VCO signal based on a filtered output of said controlled charge pump, wherein said filtered output is generated by said loop filter.

2. The method according to claim 1, wherein said divider is a multi-modulus divider (MMD).

3. The method according to claim 1, wherein said divider utilizes true single phase clock (TSPC) logic to generate said divider signal.

4. The method according to claim 1, wherein said fractional-N PLL synthesizer is integrated on a chip.

5. The method according to claim 4, comprising generating said input reference signal to said PFD in said reference generator based on buffering a reference signal communicatively coupled to said chip or based on operating said reference generator as a crystal oscillator when communicatively coupled to an off-chip crystal.

6. The method according to claim 1, comprising programming said charge pump.

7. The method according to claim 1, comprising programming said loop filter.

8. The method according to claim 1, comprising configuring said divider to modify said generated VCO signal frequency.

9. The method according to claim 1, comprising configuring a conversion factor in said VCO.

10. The method according to claim 1, comprising generating said enable signal utilizing a flip-flop that receives said increased frequency input reference signal.

11. A system for signal processing, the system comprising:

a fractional-N phase-locked-loop (PLL) synthesizer comprising a reference generator, a charge pump, a divider, a voltage controlled oscillator (VCO), a loop filter, and a phase-frequency detector (PFD);

said reference generator enables increasing a frequency of an input reference signal to said PFD;

said increased frequency input reference signal is utilized to generate an enable signal for said PFD;

said PFD enables generation of a single signal for controlling said charge pump utilizing said increased frequency input reference signal and a divider signal generated by said divider whose input frequency is substantially the same as that of a VCO signal generated by said fractional-N PLL synthesizer, wherein said single signal enables a switched charge up portion of said charge pump to charge said loop filter and wherein said loop filter is discharged by an unswitched leakage current in said charge pump that is independent of said single signal; and

said VCO generates said VCO signal based on a filtered output of said controlled charge pump, wherein said filtered output is generated by said loop filter.

12. The system according to claim 11, wherein said divider is a multi-modulus divider (MMD).

13. The system according to claim 11, wherein said divider utilizes true single phase clock (TSPC) logic to generate said divider signal.

14. The system according to claim 11, wherein said fractional-N PLL synthesizer is integrated on a chip.

15. The system according to claim 14, wherein said reference generator enables generating said input reference signal to said PFD based on buffering a reference signal communicatively coupled to said chip or based on operating said reference generator as a crystal oscillator when communicatively coupled to an off-chip crystal.

16. The system according to claim 11, wherein said fractional-N PLL synthesizer enables programming of said charge pump.

17. The system according to claim 11, wherein said fractional-N PLL synthesizer enables programming of said loop filter.

18. The system according to claim 11, wherein said fractional-N PLL synthesizer enables configuration of said divider to modify said generated VCO signal frequency.

19. The system according to claim 11, wherein said fractional-N PLL synthesizer enables configuration of a conversion factor in said VCO.

20. The system according to claim 11, wherein said fractional-N PLL synthesizer enables generating said enable signal utilizing a flip-flop that receives said increased frequency input reference signal.