Digitally controlled oscillators

• US 8,125,285 B2
• Filed: 09/10/2009
• Issued: 02/28/2012
• Est. Priority Date: 09/10/2009
• Status: Active Grant

• Current Assignee: Analog Devices, Inc.
• Original Assignee: Analog Devices, Inc.
• Inventors: Titus, Ward
• Primary Examiner(s): KINKEAD, ARNOLD M
• Application Number:
  US12/557,141
• Publication Number:
  US 20110057738A1
• Time in Patent Office: 901 Days
• Field of Search: 331/16, 331/34, 331/177.V, 331/117.R, 331/167, 331/117.FE, 331/1.A, 327/156, 327/159
• US Class Current: 331/177.V
• CPC Class Codes: H03L 2207/06 Phase locked loops with a controlled oscillator having at least two frequency control terminals
• 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

Abstract

The problems of large oscillator signal frequency change per bit, small runtime tuning bandwidth, and large wiring layout (and therefore large integrated circuit (IC) layout) in digitally-controlled oscillators are addressed by using an array of addressable tuning units, storing a data bit with respect to each tuning unit, and based on the data bit and an address bit, adjusting the output of each tuning unit.

Claims

1. A digitally-controlled oscillator comprising:

an array of addressable tuning units, each of the tuning units presenting an electrical characteristic at an output thereof, each tuning unit including a variable capacitor;

a driver unit coupled to the variable capacitor of each tuning unit via an RC circuit; and

a storage element associated with each tuning unit for storing a data bit in accordance with a received address bit corresponding thereto,

wherein the electrical characteristic of each tuning unit is controlled through the driver unit associated therewith in accordance with the associated stored data bit, the electrical characteristics of all of the tuning units of the array combining to control a frequency of an output signal of the oscillator.

2. The digitally-controlled oscillator of claim 1, wherein the variable capacitor of each tuning unit includes a voltage-controlled capacitor.

3. The digitally-controlled oscillator of claim 1, wherein the variable capacitor of each tuning unit includes a switchable capacitor.

4. The digitally-controlled oscillator of claim 1, wherein the storage element associated with each tuning unit includes a flip-flop.

5. The digitally-controlled oscillator of claim 1, wherein an addressing unit, coupled to the tuning unit array, decodes a tuning control word to generate addressing signals for uniquely addressing each tuning unit.

14. The digitally-controlled oscillator of claim 1, wherein only one tuning unit is operational at a time.

15. The digitally-controlled oscillator of claim 1 further comprising:

a frequency switch unit including a plurality of variable heavy capacitors, each heavy variable capacitor presenting a switching capacitance at an output thereof in response to a coarse control word,

wherein the tuning capacitance corresponds to a finer granularity in frequency change than the switching capacitance.

18. The digitally-controlled oscillator of claim 1, wherein the oscillator is part of a clock and data recovery circuit.

6. A digitally-controlled oscillator comprising:

an array of addressable tuning units, each of the tuning units presenting an electrical characteristic at an output thereof, the array being a two-dimensional array, the tuning units being arranged in rows and columns;

an addressing unit, coupled to the tuning unit array, decodes a tuning control word to generate addressing signals for uniquely addressing each tuning unit, the addressing unit comprising;

a row binary-to-decimal decoder for decoding a first set of tuning control word bits to generate row-addressing signals to uniquely address each tuning unit row; and

a column binary-to-decimal decoder for decoding a second set of the tuning control word bits to generate column-addressing signals to uniquely address each tuning unit column,

wherein each pair of the row and column-addressing signals received at a tuning unit are combined therein using an AND gate to generate the addressing bit thereof, and the first and second bit sets are non-overlapping; and

a storage element associated with each tuning unit for storing a data bit in accordance with the generated addressing bit corresponding thereto,

wherein the electrical characteristic of each tuning unit is controlled in accordance with the associated stored data bit, the electrical characteristics of all of the tuning units of the array combining to control a frequency of an output signal of the oscillator.

7. The digitally-controlled oscillator of claim 6, wherein each tuning unit includes a variable capacitor.

8. The digitally-controlled oscillator of claim 7, wherein the electrical characteristic of each tuning unit is a tuning capacitance of the respective tuning unit.

9. The digitally-controlled oscillator of claim 7, wherein the electrical characteristic of each tuning unit is controlled through a driver unit associated therewith.

10. The digitally-controlled oscillator of claim 7, wherein the driver unit is an inverter circuit for providing a voltage signal to control the variable capacitor of each tuning unit.

11. The digitally-controlled oscillator of claim 10, wherein the addressing unit further comprises at least one AND gate for combining a data line with one of the row-addressing signals to generate the data bit for the tuning unit row addressed by the one of the row-addressing signals.

12. The digitally-controlled oscillator of claim 11, wherein a calibration unit, coupled between the tuning unit array and the addressing unit, operates more than one tuning units simultaneously in response to a calibration signal.

13. The digitally-controlled oscillator of claim 12, wherein the data bit for at least one operated tuning unit is set at a high voltage level.

16. A digitally-controlled oscillator comprising:

an array of addressable tuning units, each of the tuning units including a variable capacitor and presenting a tuning capacitance of the respective tuning unit at an output thereof;

a fine control unit for presenting a fine control capacitance at an output thereof in response to a fine control word; and

a storage element associated with each tuning unit of the array for storing a data bit in accordance with a received address bit corresponding thereto,

wherein the tuning capacitance of each tuning unit is controlled in accordance with the associated stored data bit, the tuning capacitance of all of the tuning units of the array combining to control a frequency of an output signal of the oscillator, and

wherein the tuning capacitance corresponds to a coarser granularity in frequency change than the fine control capacitance.

17. A digitally-controlled oscillator comprising:

an array of addressable tuning units, each of the tuning units presenting an electrical characteristic at an output thereof; and

a storage element associated with each tuning unit for storing a data bit in accordance with a received address bit corresponding thereto,

wherein the electrical characteristic of each tuning unit is controlled in accordance with the associated stored data bit, the electrical characteristics of all of the tuning units of the array combining to control a frequency of an output signal of the oscillator, the frequency of an oscillator output signal tracking frequency variations of a signal having frequency at least approximately equal to 6 GHz.

19. A method of controlling an oscillator signal frequency comprising:

providing an array of addressable tuning units, each of the tuning units presenting an electrical characteristic at an output thereof, and each of the tuning units including a variable capacitor;

coupling a driver unit to the variable capacitor of each tuning unit using an RC circuit, wherein the electrical characteristic of each tuning unit is controlled through a driver unit associated therewith;

storing a unique data bit with respect to each of the tuning units of the array in accordance with a received addressing bit corresponding thereto; and

controlling the electrical characteristic of each tuning unit in accordance with the associated stored data bit,

wherein the electrical characteristics of all of the tuning units combine to control a frequency of an output signal of the oscillator.

26. The method of claim 19 further comprising:

providing an addressing unit coupled to the tuning unit array; and

decoding a tuning control word at the addressing unit for generating addressing signals to uniquely address each tuning unit.

31. The method of claim 19, wherein only one tuning unit is operational at a time.

20. A method of controlling an oscillator signal frequency comprising:

providing an array of addressable tuning units, each of the tuning units presenting an electrical characteristic at an output thereof, wherein the array is a two-dimensional array, the tuning units of the array being arranged in rows and columns;

storing a data bit with respect to each of the tuning units of the array in accordance with a received addressing bit corresponding thereto;

controlling the electrical characteristic of each tuning unit in accordance with the associated stored data bit;

providing an addressing unit coupled to the tuning unit array; and

decoding a tuning control word at the addressing unit for generating addressing signals to uniquely address each tuning unit, comprising;

decoding a first set of tuning control word bits to generate row-addressing signals to uniquely address each tuning unit row; and

decoding a second set of the tuning control word bits to generate column-addressing signals to uniquely address each tuning unit column, wherein the first and second bit sets are non-overlapping,

wherein the electrical characteristics of all of the tuning units combine to control a frequency of an output signal of the oscillator.

21. The method of claim 20, wherein each tuning unit includes a variable capacitor.

22. The method of claim 21, wherein the electrical characteristic of each tuning unit includes a tuning capacitance of the respective tuning unit.

23. The method of claim 21, wherein the electrical characteristic of each tuning unit is controlled through a driver unit associated therewith.

24. The method of claim 23 further comprising providing a voltage signal from the driver unit to the variable capacitor of each tuning unit, wherein the driver unit is an inverter circuit.

25. The method of claim 23 further comprising coupling the driver unit to the variable capacitor of each tuning unit using an RC circuit.

27. The method of claim 20 further comprising:

receiving a pair of the row and column-addressing signals at one tuning unit of the array; and

combining the pair using an AND gate of the one tuning unit of the array to generate the addressing bit thereof.

28. The method of claim 20, wherein the decoding step further comprises combining a data line with one of the row-addressing signals using an AND gate to generate the data bit for the tuning unit row addressed by the one of the row-addressing signals.

29. The method of claim 28 further comprising providing a calibration unit, coupled between the tuning unit array and the addressing unit, for operating more than one tuning units simultaneously in response to a calibration signal.

30. The method of claim 29, wherein the data bit for at least one operated tuning unit is set at a high voltage level.

32. A method of controlling an oscillator signal frequency comprising:

providing an array of addressable tuning units, each of the tuning units presenting an electrical characteristic at an output thereof;

storing a unique data bit with respect to each of the tuning units of the array in accordance with a received addressing bit corresponding thereto; and

controlling the electrical characteristic of each tuning unit in accordance with the associated stored data bit,

wherein the electrical characteristics of all of the tuning units combine to control a frequency of an output signal of the oscillator, and wherein the frequency of the oscillator signal tracks frequency variations of a signal having a frequency at least approximately equal to 6 GHz.