Tunable ring oscillator

• US 20060091967A1
• Filed: 11/04/2004
• Published: 05/04/2006
• Est. Priority Date: 11/04/2004
• Status: Active Grant

• Current Assignee: Semtech Canada Corp. (Semtech Corporation)
• Original Assignee: Gennum Corporation
• Inventors: Iozsef, Eric, Shakiba, Hossein
• Granted Patent: US 7,180,378 B2
• Time in Patent Office: Days
• US Class Current: 331/57
• CPC Class Codes: H03K 17/04106 in field-effect transistor switches H03K17/0412, H03K17/0416 take precedence
• CPC Class Codes: H03K 3/0315 Ring oscillators

Abstract

A tunable ring oscillator, in accordance with the teachings described herein, may include one or more delay circuits having a coarse tuning circuitry and a fine tuning circuitry. The coarse tuning circuitry may be used to set one of a minimum time delay or a maximum time delay as a function of a coarse tuning input. The fine tuning circuitry may be used to adjust between the minimum time delay and the maximum time delay as a function of a fine tuning input.

Claims

1. A tunable ring oscillator having a delay circuit, the delay circuit comprising:

coarse tuning circuitry for setting one of a minimum time delay or a maximum time delay as a function of a coarse tuning input; and

fine tuning circuitry for adjusting between the minimum time delay and the maximum time delay as a function of a fine tuning input.

2. The tunable ring oscillator of claim 1, wherein the delay circuit further comprises:

a delay element operable to receive an input signal and delay the input signal to generate a delayed output signal;

wherein the coarse tuning circuitry is operable to set one of the minimum time delay or the maximum time delay by mixing the input signal and the delay output signal as a function of the coarse tuning input.

3. The tunable ring oscillator of claim 2, wherein the delay element is a buffer.

4. The tunable ring oscillator of claim 1, wherein the coarse tuning circuitry is a digital mixer.

5. The tunable ring oscillator of claim 4, wherein the coarse tuning input is a digital control word.

6. The tunable ring oscillator of claim 1, wherein the fine tuning circuitry is an analog mixer.

7. The tunable ring oscillator of claim 6, wherein the fine tuning input is a control voltage input to the tunable ring oscillator.

8. The tunable ring oscillator of claim 1, wherein the delay circuit further comprises:

a fast path delay operable to apply a first fixed time delay to an input signal to generate a first delayed output signal; and

a slow path delay operable to apply a second fixed time delay to an input signal to generate a second delayed output signal;

wherein the coarse tuning circuitry is operable to set one of the minimum time delay or the maximum time delay by mixing the first delayed output signal and the second delayed output signal as a function of the coarse tuning input.

9. The tunable ring oscillator of claim 1, wherein another one of the minimum time delay or the maximum time delay has a fixed value.

10. The tunable ring oscillator of claim 1, wherein the coarse tuning circuitry sets the maximum time delay, the delay circuit further comprising:

second coarse tuning circuitry for setting the minimum time delay.

11. The tunable ring oscillator of claim 10, wherein the second coarse tuning circuitry is operable to set the minimum time delay as a function of the coarse tuning input.

12. The tunable ring oscillator of claim 10, wherein the second coarse tuning circuitry is operable to set the minimum time delay as a function of a second coarse tuning input.

13. The tunable ring oscillator of claim 11, wherein the delay circuit further comprises:

a first delay element operable to apply a first fixed time delay to a delay element input signal to generate a first delayed output signal; and

a second delay element operable to apply a second fixed time delay to a fine tuning circuitry output signal to generate a second delayed output signal;

wherein the coarse tuning circuitry is operable to set the maximum time delay by mixing the delay element input signal and the first delay output signal as a function of the coarse tuning input, and the second coarse tuning circuitry is operable to set the minimum time delay by mixing the fine tuning circuitry output signal and the second delayed output signal as a function of the coarse tuning input.

14. The tunable ring oscillator of claim 13, wherein the first and second delay elements are buffers.

15. The tunable ring oscillator of claim 13, wherein the coarse tuning circuitry and the second course tuning circuitry are digital mixers and the coarse tuning input is a digital control word.

16. The tunable ring oscillator of claim 11, wherein the coarse tuning input may include a predetermined number of settings, and wherein the coarse tuning circuitry and the second coarse tuning circuitry are configured to apply a predetermined current weighting at each of the settings.

17. The tunable ring oscillator of claim 16, wherein the predetermined current weighting defines a constant oscillator gain having an equal value at each of the settings.

18. The tunable ring oscillator of claim 16, wherein the predetermined current weighting creates different oscillator gain values at two or more of the settings.

19. The tunable ring oscillator of claim 1, wherein the delay circuit is one of a plurality of delay circuits that are coupled in series in a feedback loop.

20. The tunable ring oscillator of claim 1, wherein the delay circuit is one of two delay circuits that are coupled in series, wherein an output a first of the two delay circuits is coupled as an input of a second of the two delay circuits and an output of the second of the two delay circuits is inverted and coupled as an input of the first of the two delay circuits.

21. In a ring oscillator having a plurality of delay circuits, the plurality of delay circuits each comprising:

means for causing a first time delay;

means for causing a second time delay;

means for setting a maximum time delay of the delay circuit by controlling an amount of the first time delay in a total time delay of the delay circuit;

means for setting a minimum time delay of the delay circuit by controlling an amount of the second time delay in the total time delay of the delay circuit; and

means for adjusting the total time delay of the delay circuit between the minimum time delay and the maximum time delay.

22. A method for controlling an operating frequency of a ring oscillator, comprising:

receiving a coarse tuning input signal;

receiving a fine tuning input signal;

setting a maximum operating frequency and a minimum operating frequency of the ring oscillator as a function of the coarse tuning input signal; and

adjusting the operating frequency of the ring oscillator between the minimum operating frequency and the maximum operating frequency using the fine tuning input signal.