Dual-control ring voltage controlled oscillator

• US 6,396,358 B1
• Filed: 01/31/2001
• Issued: 05/28/2002
• Est. Priority Date: 01/31/2001
• Status: Expired due to Fees

• Current Assignee: International Business Machines Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: Poss, Joey Martin, Reynolds, Scott Kevin
• Primary Examiner(s): MIS, DAVID C
• Application Number:
  US09/773,338
• Time in Patent Office: 482 Days
• Field of Search: 331/34,36,57,177 R,177 V,179
• US Class Current: 331/57
• CPC Class Codes: H03K 2005/00071 by adding capacitance as a load
• CPC Class Codes: H03K 3/0315 Ring oscillators
• CPC Class Codes: H03K 5/133 using a chain of active delay devices
• CPC Class Codes: H03L 7/0998 using phase interpolation

Abstract

A circuit of a dual control voltage-controlled ring oscillator is disclosed having significantly less power and area while still maintaining a large frequency range and tune accuracy. The dual control ring oscillator has at least two delay paths which can be added or interpolated according to an interpolation variable set by a coarse tune and a fine tune code. In addition, moreover, each of the delay paths have a number of variable delay elements which are varied in response to another input code. When the variable delay elements are capacitors, the capacitance will be varied in accordance with another coarse tune code. In the preferred embodiment, the input codes are digital and the frequency range obtained can be greater than two to one. First, the variable delay elements are adjusted to obtain coarse tuning of the dual control ring oscillator then the interpolation variable is more finely adjusted to obtain fine tuning of the ring oscillator. Phase control can be similarly accomplished using coarse tuning by adjusting the delay of the paths, and then using fine tuning to interpolate the delay paths.

Claims

1. A dual-control ring voltage controlled oscillator, comprising:

(a) a delay interpolator connected to at least a short path and a long path;

(b) a plurality of delay stages at the output of the delay interpolator along each of the at least short path and long path, the short path having fewer delay stages than the long path;

(c) a plurality of variable capacitors interspersed among the plurality of delay stages;

(d) an input coarse tune code to vary the capacitance of the plurality of variable capacitors; and

(e) an input fine tune code to vary an interpolation variable thereby interpolating the delay through at least the short path and/or long path.

2. The dual-control ring voltage controlled oscillator of claim 1, further comprising:

(a) a coarse tune digital-to-analog converter to generate a coarse tune current input into the delay interpolator in response to the coarse tune code;

(b) a fine tune digital-to-analog converter to generate a fine tune current input into the delay interpolator in response to the fine tune code;

wherein the sum of the coarse tune current and the fine tune current is the control current input to the delay interpolator.

3. The dual-control ring voltage controlled oscillator of claim 2, wherein the coarse tune code comprises an A code input to each of the plurality of variable capacitors and a B code input to the coarse tune digital-to-analog converter.

4. The dual control ring voltage controlled oscillator of claim 3 having an output frequency range of at least two to one.

5. The dual control ring voltage controlled oscillator of claim 3, further comprising:

(a) a second plurality of phase tune variable capacitors connected between each of the plurality of delay stages in the at least short and/or long path;

(b) a coarse tune phase code to vary the capacitance of the second plurality of phase tune variable capacitors;

(c) a fine tune phase digital-to-analog converter to provide a phase tune current into the delay interpolator;

the control current input to the delay interpolator being the sum of the coarse tune current, the fine tune current, and the phase tune current.

6. The dual-control ring voltage controlled oscillator of claim 3, further comprising a logic synthesizer which receives the output of the last delay stage and the last variable capacitor of the at least short and/or long path and in response thereto generates the tune codes.

7. A dual-control ring voltage controlled oscillator, comprising:

(a) a delay interpolator connected to at least a short path and a long path;

(b) a plurality of delay stages at the output of the delay interpolator along each of the at least short path and long path, the short path having fewer delay stages than the long path;

(c) a plurality of variable capacitors interspersed among the plurality of delay stages;

(d) an input coarse tune code comprising an A code to vary the capacitance of the plurality of variable capacitors, and a B code input to a coarse tune digital-to-analog converter to generate a coarse tune current input into the delay interpolator to vary an interpolation variable thereby interpolating the delay through at least the short path and/or long path;

(e) an input fine tune code to a fine tune digital-to-analog converter to generate a fine tune current input into the delay interpolator to vary an interpolation variable thereby interpolating the delay through at least the short path and/or long path;

(f) a second plurality of phase tune variable capacitors connected between each of the plurality of delay stages in the at least short and/or long path;

(g) a coarse tune phase code to vary the capacitance of the second plurality of phase tune variable capacitors;

(h) a fine tune phase digital-to-analog converter to provide a phase tune current into the delay interpolator, the control current input to the delay interpolator being the sum of the coarse tune current, the fine tune current, and the phase tune current; and

(i) a logic synthesizer which receives the output of the last delay stage and the last variable capacitor of the at least short and/or long path and in response thereto generates the tune codes;

wherein the oscillator has an output frequency range of at least two to one.

8. A method to tune a ring voltage-controlled oscillator, comprising the steps of:

(a) inputting a capacitor tune code to vary the capacitance of a plurality of delay elements of a plurality of delay paths within a ring voltage-controlled oscillator;

(b) inputting a digital coarse tune code to select a first interpolation variable interpolating the delay between from the plurality of delay paths that a signal will traverse; and

(c) inputting a digital fine tune code to generate a second interpolation variable further interpolating delay from each of the plurality of delay paths to fine tune a frequency output by the voltage-controlled oscillator.

9. The method of claim 8, wherein further comprising:

(a) inputting a coarse phase tune code to vary the capacitance of a delay ring; and

(b) inputting a digital fine phase tune code to fine tune the frequency output by the voltage-controlled oscillator.

10. A dual-control ring voltage-controlled oscillator, comprising:

(a) means to input an oscillating signal into a ring oscillator;

(b) means to provide at least two delay paths for the oscillating signal;

(c) means to vary the delay in at least two delay paths; and

(d) means to interpolate the at least two delay paths.

11. The dual-control ring voltage-controlled oscillator of claim 10 wherein the means to vary the delay in the at least two delay paths further comprises means to vary the capacitance of a plurality of capacitive elements on the at least two delay paths.

12. The dual-control ring voltage-controlled oscillator of claim 11 wherein the means to interpolate the at least two delay paths further comprises:

(a) means to provide a coarse tune interpolation code for coarse tuning of the oscillator; and

(b) means to provide a fine tune interpolation code for fine tuning of the oscillator.

13. The dual-control ring voltage-controlled oscillator of claim 12, further comprising means to tune the phase of the oscillating signal using the means to vary the delay in the at least two delay paths and the means to interpolate the at least two delay paths.

14. The dual-control ring voltage-controlled oscillator of claim 12, further comprising means to provide feedback to the means to input the oscillating signal, and in response to the feedback, the means to vary the delay, the means to interpolate, and the means to tune the phase achieve an accurate frequency range greater than 2:

1.