Monolithic Clock Generator and Timing/Frequency Reference

• US 20100019856A1
• Filed: 05/04/2009
• Published: 01/28/2010
• Est. Priority Date: 03/22/2004
• Status: Active Grant

• Current Assignee: Integrated Device Technology Incorporated (Renesas Electronics Corporation)
• Original Assignee: Mobius Microsystems, Inc. (Renesas Electronics Corporation)
• Inventors: McCorquodale, Michael Shannon, Pernia, Scott Michael, Basu, Amar Sarbbasesh
• Granted Patent: US 7,924,110 B2
• Time in Patent Office: Days
• 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 clock generator and/or a timing and frequency reference, with multiple operating modes, such power conservation, clock, reference, and pulsed modes. 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, comprising:

a reference resonator adapted to provide a first reference signal having a resonant frequency; and

a frequency controller coupled to the reference resonator, the frequency controller adapted to be calibrated to determine the resonant frequency having a first frequency of a plurality of frequencies.

2. The apparatus of claim 1, further comprising:

a frequency divider coupled to the reference resonator, the frequency divider adapted to divide the first frequency by a rational number into a plurality of second signals having a corresponding plurality of frequencies, the plurality of frequencies substantially equal to or lower than the first frequency.

3. The apparatus of claim 2, wherein the frequency divider further comprises a square-wave generator, the square-wave generator adapted to convert the first reference signal into a substantially square-wave signal having a substantially equal high and low duty cycle.

4. The apparatus of claim 2, further comprising:

a frequency selector coupled to the frequency divider, the frequency selector adapted to provide an output signal from the plurality of second signals.

5. The apparatus of claim 4, further comprising:

a mode selector coupled to the frequency selector, the mode selector adapted to provide a plurality of operating modes, the plurality of operating modes selected from a group comprising a clock mode, a timing and frequency reference mode, a power conservation mode, and a pulse mode.

6. The apparatus of claim 5, further comprising:

a synchronization circuit coupled to the mode selector; and

a controlled oscillator coupled to the synchronization circuit and adapted to provide a third signal;

wherein in the timing and reference mode, the mode selector is further adapted to couple the output signal to the synchronization circuit to control timing and frequency of the third signal.

7. The apparatus of claim 6, wherein the synchronization circuit is a delay-locked loop, a phase-locked loop, or an injection locking circuit.

8. The apparatus of claim 1, further comprising:

an amplifier coupled to the reference resonator.

9. The apparatus of claim 8, wherein the frequency controller further comprises:

a temperature compensator coupled to the amplifier;

a voltage isolator coupled to the reference resonator; and

a process variation compensator coupled to the reference resonator.

10. The apparatus of claim 8, wherein the amplifier further comprises a negative transconductance amplifier and wherein the frequency controller is further adapted to modify a current through the negative transconductance amplifier in response to temperature.

11. The apparatus of claim 10, wherein the frequency controller further comprises a current source responsive to temperature.

12. The apparatus of claim 11, wherein the current source further comprises one or more CTAT, PTAT, or PTAT² configurations.

13. The apparatus of claim 10, wherein the frequency controller is further adapted to modify a current through the negative transconductance amplifier to modify the resonant frequency of the reference resonator.

14. The apparatus of claim 10, wherein the frequency controller is further adapted to modify a transconductance of the negative transconductance amplifier to modify the resonant frequency of the reference resonator.

15. The apparatus of claim 10, wherein the frequency controller is further adapted to modify a current through the negative transconductance amplifier in response to a voltage.

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

17. The apparatus of claim 16, wherein the voltage isolator comprises a current mirror having a cascode configuration.

18. The apparatus of claim 1, wherein the frequency controller is further adapted to modify a capacitance or modify an inductance of the reference resonator in response to a temperature variation, a voltage variation, or both a temperature and voltage variation.

19. The apparatus of claim 1, wherein the frequency controller is further adapted to modify a capacitance or modify an inductance of the reference resonator when calibrated for fabrication process variation.

20. The apparatus of claim 1, wherein the frequency controller further comprises:

a coefficient register adapted to store a first plurality of calibration coefficients.

21. The apparatus of claim 20, wherein the coefficient register is embodied as a single memory circuit or a plurality of memory circuits.

22. The apparatus of claim 20, wherein the frequency controller further comprises:

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.

23. The apparatus of claim 22, wherein the frequency controller further comprises:

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

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

24. The apparatus of claim 20, wherein the frequency controller further comprises:

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.

25. The apparatus of claim 20, wherein the frequency controller further comprises:

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.

26. The apparatus of claim 25, wherein at least one of the first voltage and second voltage is a fixed voltage.

27. The apparatus of claim 25, wherein at least one of the first voltage and second voltage is a variable voltage.

28. The apparatus of claim 20, wherein the frequency controller further comprises:

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

29. The apparatus of claim 20, wherein the frequency controller further comprises:

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 fixed capacitance and a fuse, each switchable capacitive module responsive to a corresponding coefficient of the first plurality of calibration coefficients to open circuit the fuse.

30. The apparatus of claim 1, further comprising:

a frequency calibration module coupled to the frequency controller, the frequency calibration module adapted to determine the calibration of the frequency controller in response to a second reference signal.

31. The apparatus of claim 30, wherein the frequency calibration module comprises:

a frequency divider coupled to the frequency controller, the frequency divider adapted to convert an output signal derived from the first reference signal having the first frequency to a lower frequency to provide a divided signal;

a frequency detector coupled to the frequency divider, the frequency detector adapted to compare the second reference signal to the divided signal and provide one or more up signals or down signals; and

a pulse counter coupled to the frequency detector, the pulse counter adapted to determine a difference between the one or more up signals or down signals as an indicator of a difference between the output signal and the second reference signal.

32. The apparatus of claim 1, wherein the reference resonator comprises an inductor (L) and a capacitor (C) coupled to form an LC-tank.

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

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

34. The apparatus of claim 1, wherein the apparatus is integrated monolithically with a second circuit to form a single integrated circuit.

35. The apparatus of claim 34, wherein the second circuit is a microprocessor, a digital signal processor, a radio frequency circuit, or a communications circuit.

36. The apparatus of claim 1, further comprising:

a second oscillator providing a second oscillator output signal; and

a mode selector coupled to the frequency controller and to the second oscillator, the mode selector adapted to switch to the second oscillator output signal to provide a power conservation mode.

37. The apparatus of claim 36, wherein the second oscillator is a ring oscillator, a relaxation oscillator, or a phase shift oscillator.

38. An apparatus, comprising:

a reference resonator adapted to provide a first reference signal having a resonant frequency; and

a frequency controller coupled to the reference resonator, the frequency controller adapted, when calibrated, to select the resonant frequency having a first frequency of a plurality of frequencies.

39. The apparatus of claim 38 wherein the frequency controller is further adapted to modify a capacitance or modify an inductance of the reference resonator when calibrated for fabrication process variation.

40. The apparatus of claim 38, wherein the frequency controller further comprises:

a coefficient register adapted to store a first plurality of calibration coefficients.

41. The apparatus of claim 40, wherein the coefficient register is embodied as a single memory circuit or a plurality of memory circuits.

42. The apparatus of claim 40, wherein the frequency controller further comprises:

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.

43. The apparatus of claim 42, wherein the frequency controller further comprises:

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

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

44. The apparatus of claim 40, wherein the frequency controller further comprises:

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.

45. The apparatus of claim 40, wherein the frequency controller further comprises:

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.

46. The apparatus of claim 45, wherein at least one of the first voltage and second voltage is a fixed voltage.

47. The apparatus of claim 45, wherein at least one of the first voltage and second voltage is a variable voltage.

48. The apparatus of claim 38, wherein the frequency controller further comprises:

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

49. The apparatus of claim 38, wherein further comprising:

a negative transconductance amplifier coupled to the reference resonator; and

wherein the frequency controller is further adapted to modify a current through the negative transconductance amplifier in response to temperature.

50. The apparatus of claim 49, wherein the frequency controller further comprises a current source responsive to temperature.

51. The apparatus of claim 50, wherein the current source further comprises one or more CTAT, PTAT, or PTAT² configurations.

52. The apparatus of claim 38, further comprising:

a frequency divider coupled to the reference resonator, the frequency divider adapted to divide the first frequency by a rational number into a plurality of second signals having a corresponding plurality of frequencies, the plurality of frequencies substantially equal to or lower than the first frequency.

53. The apparatus of claim 52, wherein the frequency divider further comprises a square-wave generator, the square-wave generator adapted to convert the first reference signal into a substantially square-wave signal having a substantially equal high and low duty cycle.

54. An apparatus, comprising:

a reference oscillator adapted to provide a first reference signal having an oscillation frequency;

an amplifier coupled to the reference oscillator;

a process variation compensator coupled to the reference oscillator, the process variation compensator adapted to determine the oscillation frequency when calibrated for fabrication process variation; and

a temperature compensator coupled to the amplifier or the reference oscillator, the temperature compensator adapted to maintain substantially the determined oscillation frequency of the reference oscillator in response to a temperature variation.

55. The apparatus of claim 54, wherein the reference oscillator is a reference resonator.

56. The apparatus of claim 55, wherein the reference resonator comprises an inductor and a capacitor.

57. The apparatus of claim 54, further comprising:

a frequency divider coupled to the reference oscillator, the frequency divider adapted to divide the determined oscillation frequency into a plurality of second signals having a corresponding plurality of frequencies, the plurality of frequencies substantially equal to or lower than the determined oscillation frequency; and

a frequency selector coupled to the frequency divider, the frequency selector adapted to provide an output signal from the plurality of second signals.

58. The apparatus of claim 54, wherein the amplifier further comprises a negative transconductance amplifier and wherein the temperature compensator is further adapted to modify a current through the negative transconductance amplifier in response to the temperature variation.

59. The apparatus of claim 54, wherein the temperature compensator is further adapted to modify a capacitance of the reference oscillator in response to the temperature variation.

60. The apparatus of claim 54, further comprising:

a voltage isolator adapted to substantially isolate the reference oscillator from a voltage variation.

61. The apparatus of claim 54, wherein the temperature compensator further comprises:

a coefficient register adapted to store a first plurality of coefficients and a second plurality of coefficients;

a first array having a plurality of binary-weighted switchable capacitance branches coupled to the coefficient register and to the reference oscillator, each switchable capacitance branch having a fixed capacitance and a variable capacitance and responsive to a corresponding coefficient of the first plurality of coefficients to switch between the fixed capacitance and the variable capacitance and to switch the variable capacitance to a control voltage node;

a second array coupled to the control voltage node, the second array having a plurality of switchable resistances coupled to the coefficient register and further having a fixed capacitance, each switchable resistive module responsive to a corresponding coefficient of the second plurality of coefficients to switch the switchable resistive module to the control voltage node; and

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

62. The apparatus of claim 54, wherein the process variation compensator further comprises:

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

63. The apparatus of claim 62, wherein the process variation compensator further comprises:

a first array having a plurality of switchable capacitive modules coupled to the coefficient register and to the reference oscillator, 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.

64. The apparatus of claim 62, wherein the process variation compensator further comprises:

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

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

65. The apparatus of claim 62, wherein the process variation compensator further comprises:

an array having a plurality of switchable capacitive modules coupled to the coefficient register and to the reference oscillator, 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.

66. The apparatus of claim 62, wherein the process variation compensator further comprises:

an array having a plurality of switchable variable capacitive modules coupled to the coefficient register and to the reference oscillator, 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.

67. The apparatus of claim 66, wherein at least one of the first voltage and second voltage is a fixed voltage.

68. The apparatus of claim 66, wherein at least one of the first voltage and second voltage is a variable voltage.

69. The apparatus of claim 54, wherein the process variation compensator further comprises:

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

70. An apparatus, comprising:

a resonator adapted to provide a first signal having a first frequency;

a frequency divider coupled to the resonator, the frequency divider adapted to divide the first frequency into a plurality of second signals having a plurality of frequencies, the plurality of frequencies substantially equal to or lower than the first frequency; and

a frequency selector coupled to the frequency divider, the frequency selector comprising a multiplexer and a glitch-suppressor, the frequency selector adapted to provide an output signal from the plurality of second signals.