Adaptive spread spectrum

• US 6,980,581 B1
• Filed: 07/18/2000
• Issued: 12/27/2005
• Est. Priority Date: 07/18/2000
• Status: Active Grant

• Current Assignee: Intel Corporation
• Original Assignee: Cypress Semiconductor Corporation (Infineon Technologies AG)
• Inventors: Sha, I-Teh, Chen, Kuang-Yu, Chen, Albert
• Primary Examiner(s): Corrielus, Jean B.
• Application Number:
  US09/618,622
• Time in Patent Office: 1,988 Days
• Field of Search: 331/57, 331/10, 331/1.A, 331/2, 331/8, 331/17, 331/25, 331/23, 375/130, 375/147, 375/367, 375/362, 375/371
• US Class Current: 375/130
• CPC Class Codes: G06F 1/08 Clock generators with changeable or programmable clock frequency
• CPC Class Codes: H03L 7/0898 the source or sink current values being variable H03L7/0896 takes precedence
• CPC Class Codes: H03L 7/093 using special filtering or amplification characteristics in the loop H03L7/087 - H03L7/091 take precedence
• CPC Class Codes: H03L 7/099 concerning mainly the controlled oscillator of the loop
• CPC Class Codes: H03L 7/197 a time difference being used for locking the loop, the counter counting between numbers which are variable in time or the frequency divider dividing by a factor variable in time, e.g. for obtaining fractional frequency division H03L7/1806 takes precedence
• CPC Class Codes: H04L 27/0014 Carrier regulation of chaotic carriers H04L27/001; for multicarrier receivers H04L27/2657

Abstract

An apparatus comprising a circuit configured to generate a spread spectrum clock signal. The circuit may comprise a voltage controlled oscillator with a gain that may be automatically controlled.

Claims

1. An apparatus comprising:

a circuit configured to generate a spread spectrum clock signal in response to an input signal, wherein (i) said circuit comprises a voltage controlled oscillator having an automatically controlled nonlinear gain, (ii) said nonlinear gain varies according to a function curve in response to changes in frequency of said input signal and (iii) said function curve for said nonlinear gain is determined according to predetermined criteria.

2. The apparatus according to claim 1, wherein said function curve is a parabolic curve.

3. The apparatus according to claim 1, wherein said function curve is a second degree or higher polynomial.

4. The apparatus according to claim 1, wherein a computer program is used to generate said function curve for said gain.

5. The apparatus according to claim 1, wherein said spread spectrum clock signal is generated in response to a reference signal having any frequency from 50 to 170 MHZ.

6. The apparatus according to claim 1, wherein said circuit further comprises a single set of ROM codes configured to generate said spread spectrum clock signal having any frequency from 50 to 170 MHZ.

7. The apparatus according to claim 6, wherein said ROM codes determine a frequency modulation profile for said spread spectrum clock signal.

8. The apparatus according to claim 7, wherein said circuit further comprises a divider circuit.

9. The apparatus according to claim 8, wherein said ROM codes control said divider circuit.

10. An apparatus comprising:

a voltage controlled oscillator (VCO) configured to generate a spread spectrum clock signal in response to a control signal, wherein (i) said VCO has a nonlinear gain that is automatically controlled (ii) said nonlinear rain varies according to a rain function in response to changes in frequency of a reference signal and (iii) said gain function is determined according to predetermined criteria; and

a control circuit configured to generate said control signal in response to (i) said reference signal, (ii) said spread spectrum clock signal, and (iii) a set of ROM codes.

11. A method for adapting a single spread spectrum ROM code to generate a spread spectrum clock signal over a wide continuous range of frequencies comprising the steps of:

(A) determining a nonlinear gain function for a voltage controlled oscillator (VCO) according to predetermined criteria;

(B) adjusting a gain of said VCO according to said gain function in response to changes in frequency of an input signal; and

(C) configuring said VCO to generate said spread spectrum clock signal.

12. A method for adapting a single spread spectrum ROM code to generate a spread spectrum clock signal over a wide continuous range of frequencies comprising the steps of:

(A) determining a nonlinear gain function for a voltage controlled oscillator (VCO) according to predetermined criteria;

(B) adjusting a gain of said VCO according to said gain function in response to changes in frequency of an input signal; and

(C) configuring said VCO to generate said spread spectrum clock signal, wherein step A comprises the sub-steps of;

(A-1) selecting a target frequency for said VCO;

(A-2) setting a gain value for said VCO;

(A-3) simulating a spread spectrum phase lock loop comprising said VCO for a number of modulation cycles using said target frequency and said gain value; and

(A-4) calculating an accumulated error deviation between a modulation profile resulting from simulating said spread spectrum phase lock loop and an ideal modulation profile.

13. The method according to claim 12, further comprising the sub-step of:

(A-5) repeating steps A-2 through A-4 for a range of gains.

14. The method according to claim 13, further comprising the sub-step of:

(A-6) repeating steps A-1 through A-5 for a range of frequencies.

15. A computer readable media comprising instructions for performing the sub-steps according to claim 12.

16. A computer readable media comprising instructions for performing the sub-steps according to claim 13.

17. A computer readable media comprising instructions for performing the sub-steps according to claim 14.

18. The method according to claim 12, further comprising the step of:

determining a gain value for said VCO that produces a least amount of said error deviation.

19. The method according to claim 14, further comprising the step of:

determining a gain function curve for said VCO that produces a least amount of said error deviation for said range of frequencies.

20. An apparatus comprising:

a circuit configured to generate a spread spectrum clock signal, wherein (i) said circuit comprises a voltage controlled oscillator having an automatically controlled nonlinear gain, (ii) said nonlinear gain varies in response to a frequency of said spread spectrum clock signal and (iii) a function curve for said nonlinear gain is configured to minimize an error deviation of said spread spectrum clock signal from an ideal modulation profile over a predetermined frequency range.

21. An apparatus comprising:

a voltage controlled oscillator (VCO) configured to generate a spread spectrum clock signal in response to a control signal, wherein (i) said VCO has a nonlinear gain that is automatically controlled and varied in response to a frequency of said spread spectrum clock signal and (ii) a function curve for said nonlinear gain is configured to minimize an error deviation of said spread spectrum clock signal from an ideal modulation profile over a predetermined frequency range; and

a control circuit configured to generate said control signal in response to (i) a reference signal, (ii) said spread spectrum clock signal, and (iii) a set of ROM codes.