Transconductance and current modulation for resonant frequency control and selection

• US 7,545,231 B2
• Filed: 04/28/2007
• Issued: 06/09/2009
• Est. Priority Date: 03/22/2004
• Status: Expired due to Fees

• Current Assignee: Integrated Device Technology Incorporated (Renesas Electronics Corporation)
• Original Assignee: Mobius Microsystems, Inc. (Renesas Electronics Corporation)
• Inventors: McCorquodale, Michael Shannon, Pernia, Scott Michael
• Primary Examiner(s): MIS, DAVID C
• Application Number:
  US11/796,820
• Publication Number:
  US 20070205842A1
• Time in Patent Office: 773 Days
• Field of Search: 331/1.A, 331/2, 331/8, 331/10, 331/11, 331 16- 18, 331/25, 331/36.C, 331/36.L, 331/44, 331/57, 331/117.R, 331/117.FE, 331/117.D, 331/158, 331/173, 331/175, 331/177.R, 331/177.V, 331/179, 331/DIG.2
• US Class Current: 331/179
• CPC Class Codes: H03B 2200/0038 including a current mirror
• CPC Class Codes: H03B 2200/005 including measures to switch a capacitor
• CPC Class Codes: H03B 2200/0098 having a balanced output signal
• CPC Class Codes: H03B 5/04 Modifications of generator to compensate for variations in physical values, e.g. power supply, load, temperature
• CPC Class Codes: H03B 5/1215 the current source or degeneration circuit being in common to both transistors of the pair, e.g. a cross-coupled long-tailed pair
• CPC Class Codes: H03B 5/1228 the amplifier comprising one or more field effect transistors
• CPC Class Codes: H03B 5/1243 the means comprising voltage variable capacitance diodes
• CPC Class Codes: H03B 5/1253 the transistors being field-effect transistors
• CPC Class Codes: H03B 5/1265 switched capacitors
• CPC Class Codes: H03J 2200/10 Tuning of a resonator by means of digitally controlled capacitor bank
• CPC Class Codes: H03L 1/00 Stabilisation of generator output against variations of physical values, e.g. power supply
• CPC Class Codes: H03L 1/02 against variations of temperature only
• CPC Class Codes: H03L 1/026 by using a memory for digitally storing correction values H03L1/025 takes precedence
• CPC Class Codes: H03L 7/00 Automatic control of frequency or phase; Synchronisation
• CPC Class Codes: H03L 7/06 using a reference signal applied to a frequency- or phase-locked loop
• CPC Class Codes: H03L 7/0812 and where no voltage or current controlled oscillator is used
• CPC Class Codes: H03L 7/099 concerning mainly the controlled oscillator of the loop
• CPC Class Codes: H03L 7/24 using a reference signal directly applied to the generator

Abstract

In various embodiments, the invention provides a frequency controller and a temperature compensator for frequency control and selection in a clock generator and/or a timing and frequency reference. The various apparatus embodiments include a resonator adapted to provide a first signal having a resonant frequency; an amplifier; a temperature compensator adapted to modify the resonant frequency in response to temperature; and a process variation compensator adapted to modify the resonant frequency in response to fabrication process variation. In addition, the various embodiments may also include a frequency divider adapted to divide the first signal having the resonant frequency into a plurality of second signals having a corresponding plurality of frequencies substantially equal to or lower than the resonant frequency; and a frequency selector adapted to provide an output signal from the plurality of second signals. The output signal may be provided in any of various forms, such as differential or single-ended, and substantially square-wave or sinusoidal.

Claims

1. An apparatus for frequency control of a reference signal, the apparatus comprising:

a reference resonator to provide the reference signal having a selectable resonant frequency;

a negative transconductance amplifier coupled to the reference resonator;

a frequency controller to maintain a selected resonant frequency within a predetermined range in response to a variation of a parameter.

2. The apparatus of claim 1, wherein the parameter is one or more of the following parameters:

temperature, fabrication process, voltage, and frequency.

3. The apparatus of claim 1, wherein the frequency controller further is to modify a current through the negative transconductance amplifier in response to a temperature variation.

4. The apparatus of claim 3, wherein the frequency controller further comprises a current source responsive to temperature.

5. The apparatus of claim 4, wherein the current source has at least one CTAT, PTAT, or PTAT² configuration.

6. The apparatus of claim 1, wherein the frequency controller further is to modify a current through the negative transconductance amplifier to select the resonant frequency.

7. The apparatus of claim 1, wherein the frequency controller further is to modify a transconductance of the negative transconductance amplifier to select the resonant frequency.

8. The apparatus of claim 1, wherein the frequency controller further is to modify a current through the negative transconductance amplifier in response to a voltage variation.

9. The apparatus of claim 1, wherein the frequency controller further is to modify a transconductance of the negative transconductance amplifier when calibrated for a fabrication process variation.

10. The apparatus of claim 1, wherein the frequency controller further is to modify a current through the negative transconductance amplifier when calibrated for a fabrication process variation.

11. The apparatus of claim 1, wherein the frequency controller further comprises a voltage isolator coupled to the reference resonator to substantially isolate the reference resonator from a voltage variation.

12. The apparatus of claim 11, wherein the voltage isolator comprises a current mirror.

13. The apparatus of claim 12, wherein the current mirror has a cascode configuration.

14. The apparatus of claim 1, wherein the reference resonator is at least one of the following resonators:

an inductor (L) and a capacitor (C) configured to form an LC-tank resonator;

a ceramic resonator, a mechanical resonator, a microelectromechanical resonator, or a film bulk acoustic resonator.

17. The apparatus of claim 1, wherein the reference resonator further comprises at least one variable capacitor responsive to a control voltage provided by the frequency controller.

18. The apparatus of claim 1, wherein the resonant frequency is selectable through calibration to a second reference signal.

19. The apparatus of claim 1, wherein the predetermined range is plus or minus twenty-five hundredths of a percent (±

0.25%).

15. The apparatus of clime 1, further comprising:

at least one variable capacitor coupled to the reference resonator and responsive to a control voltage to modify the effective reactance of the reference resonator.

16. The apparatus of claim 15, wherein the frequency controller provides the control voltage and wherein the control voltage is variable in response to temperature variation.

20. An apparatus, comprising:

a reference resonator, the reference resonator to provide a reference signal having a selectable resonant frequency;

a negative transconductance amplifier coupled to the reference resonator; and

a temperature compensator coupled to the negative transconductance amplifier or to the reference resonator, the temperature compensator to maintain a selected resonant frequency substantially within a predetermined range in response to a temperature variation.

21. The apparatus of claim 20, wherein the temperature compensator further is to modify a current through the negative transconductance amplifier in response to the temperature variation.

22. The apparatus of claim 21, wherein the temperature compensator further comprises a current source responsive to temperature.

23. The apparatus of claim 22, wherein the current source has a CTAT, PTAT, or PTAT² configuration.

24. The apparatus of claim 22, further comprising a plurality of current sources having at least two different CTAT, PTAT, or PTAT² configurations.

25. The apparatus of claim 22, wherein the current source is coupled though one or more current mirrors to the negative transconductance amplifier.

26. The apparatus of claim 20, further comprising:

a coefficient register embodied as one or more memory circuits to store a first plurality of calibration coefficients.

27. The apparatus of claim 26, further comprising:

a first array having a plurality of switchable capacitive modules coupled to the coefficient register and to the reference resonator, each switchable capacitive module having a fixed capacitance and a variable capacitance, each switchable capacitive module responsive to a corresponding coefficient of the first plurality of calibration coefficients to switch between the fixed capacitance and the variable capacitance and to switch each variable capacitance to a control voltage.

28. The apparatus of claim 27, further comprising:

a second array having a plurality of switchable resistive modules coupled to the coefficient register and further having a capacitive module, the capacitive module and the plurality of switchable resistive modules further coupled to a node to provide the control voltage, each switchable resistive module responsive to a corresponding coefficient of a second plurality of coefficients stored in the coefficient register to switch the switchable resistive module to the control voltage node; and

wherein the temperature compensator comprises a temperature-dependent current source coupled through a current mirror to the second array.

29. The apparatus of claim 26, further comprising:

an array having a plurality of switchable capacitive modules coupled to the coefficient register and to the reference resonator, each switchable capacitive module having a first fixed capacitance and a second fixed capacitance, each switchable capacitive module responsive to a corresponding coefficient of the first plurality of calibration coefficients to switch between the first fixed capacitance and the second fixed capacitance.

30. The apparatus of claim 26, further comprising:

an array having a plurality of switchable variable capacitive modules coupled to the coefficient register and to the reference resonator, each switchable variable capacitive module responsive to a corresponding coefficient of the first plurality of calibration coefficients to switch between a first voltage and a second voltage.

31. The apparatus of claim 30, wherein at least one of the first voltage and second voltage is a fixed voltage.

32. The apparatus of claim 30, wherein at least one of the first voltage and second voltage is a variable voltage.

33. The apparatus of claim 20, further comprising:

an array having a plurality of variable capacitive modules coupled to the reference resonator and to a control voltage.

34. The apparatus of claim 20, further comprising:

at least one variable capacitor coupled to the reference resonator and responsive to a control voltage to modify the effective reactance of the reference resonator.

35. The apparatus of claim 34, wherein the temperature compensator provides the control voltage and wherein the control voltage is variable to temperature variation.

36. An apparatus, comprising:

a reference resonator, the reference resonator to provide a reference signal having a selectable resonant frequency;

a negative transconductance amplifier coupled to the reference resonator;

a current mirror coupled to the negative transconductance amplifier; and

a current source coupled to the current mirror, the current source to maintain the resonant frequency substantially within a predetermined range by varying a current through the current mirror and the negative transconductance amplifier in response to a temperature variation.

37. The apparatus of claim 36, wherein the current source has at least one CTAT, PTAT, or PTAT² configuration.

38. The apparatus of claim 36, further comprising a plurality of current sources coupled to the current mirror, the plurality of current sources having at least two different CTAT, PTAT, or PTAT² configurations.

39. An apparatus, comprising:

a reference oscillator, the reference oscillator to provide a reference signal having a selectable oscillation frequency;

a negative transconductance amplifier coupled to the reference oscillator; and

a temperature compensator coupled to the reference oscillator, the temperature compensator to maintain a selected oscillation frequency substantially within a predetermined range in response to a temperature variation.

40. The apparatus of claim 39, wherein the temperature compensator further comprises a current source responsive to temperature.

41. The apparatus of claim 40, wherein the current source has at least one CTAT, PTAT, or PTAT² configurations.

42. The apparatus of claim 39, wherein the reference oscillator is at least one of the following oscillators:

an inductor (L) and a capacitor (C) configured to form an LC-tank oscillator;

a resonator (R) and a capacitor (C) configured to form an RC oscillator;

a ceramic oscillator;

a mechanical oscillator;

a microelectromechanical oscillator;

a ring oscillator;

a surface acoustic wave (SAW) oscillator;

or a film bulk acoustic oscillator.

43. The apparatus of claim 39, further comprising:

at least one variable capacitor coupled to the reference oscillator and responsive to a control voltage to modify the effective reactance to the reference oscillator.

44. The apparatus of claim 43, wherein the temperature compensator provides the control voltage and wherein the control voltage is variable in response to temperature variation.

45. The apparatus of claim 43, further comprising:

a coefficient register coupled to the temperature compensator, the coefficient register to store a plurality of coefficients, the plurality of coefficients calibrated over temperature variation and provided to the temperature compensator to generate a corresponding control voltage.

46. The apparatus of claim 39, wherein the reference oscillator further comprises at least one variable capacitor responsive to a control voltage provided by the temperature compensator.