Control Voltage Generator for a Clock, Frequency Reference, and Other Reference Signal Generator

• US 20090146719A1
• Filed: 01/12/2008
• Published: 06/11/2009
• Est. Priority Date: 12/05/2007
• 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, Kubba, Sundus, Beaudouin, Ralph, O'Day, Justin, Nguyen, Nam Duc
• Granted Patent: US 7,978,017 B2
• Time in Patent Office: Days
• US Class Current: 327/291
• 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: H03K 3/011 Modifications of generator to compensate for variations in physical values, e.g. voltage, temperature to maintain energy constant H03K3/015
• CPC Class Codes: H03L 1/00 Stabilisation of generator output against variations of physical values, e.g. power supply
• CPC Class Codes: H03L 1/026 by using a memory for digitally storing correction values H03L1/025 takes precedence
• CPC Class Codes: H03L 5/00 Automatic control of voltage, current, or power
• CPC Class Codes: H03L 7/00 Automatic control of frequency or phase; Synchronisation

Abstract

Exemplary embodiments of the invention provide a reference signal generator, system and method. An exemplary apparatus to generate a harmonic reference signal includes a reference resonator, such as an LC-tank, a control voltage generator adapted to provide a temperature-dependent control voltage; and a plurality of variable reactance modules. The reference resonator generates a first reference signal having a resonant frequency, and each reactance module is adapted to modify a corresponding reactance in response to the control voltage to maintain the resonant frequency substantially constant or within a predetermined variance over a predetermined temperature range. A frequency controller may also be included to maintain substantially constant a magnitude of a peak amplitude of the first reference signal and maintains substantially constant a common mode voltage level of the reference resonator.

Claims

1. An apparatus to generate a harmonic reference signal, the apparatus comprising:

a reference resonator to generate a first reference signal having a resonant frequency;

a control voltage generator adapted to provide a temperature-dependent control voltage; and

a plurality of variable reactance modules couplable to the reference resonator and couplable to the control voltage generator, each reactance module of the plurality of variable reactance modules adapted to modify a corresponding reactance in response to the control voltage to maintain the resonant frequency within a predetermined variance over a predetermined temperature range.

2. The apparatus of claim 1, wherein the control voltage generator comprises:

a first current source adapted to generate a temperature-dependent current; and

a variable resistance coupled to the first current source, an amount of resistance of the variable resistance selectable to determine a variation in the temperature-dependent current for a corresponding variation in temperature.

3. The apparatus of claim 2, wherein the variable resistance further comprises:

a plurality of resistors, each resistor of the plurality of resistors having a fixed resistance; and

a plurality of switches correspondingly coupled to the plurality of resistors, each switch of the plurality of switches responsive to a control coefficient to couple or uncouple a corresponding resistor of the plurality of resistors to provide the variable resistance.

4. The apparatus of claim 3, wherein the plurality of resistors have a R-2R circuit configuration.

5. The apparatus of claim 4, wherein the variable resistance further comprises:

a plurality of current mirrors or current sources correspondingly couplable through the plurality of switches to the plurality of resistors.

6. The apparatus of claim 3, wherein the plurality of resistors are all a same type of resistor.

7. The apparatus of claim 3, wherein a plurality of control coefficients are temperature coded.

8. The apparatus of claim 2, wherein the variable resistance further comprises:

at least one second current source; and

at least two resistors coupled to the second current source.

9. The apparatus of claim 8, wherein the second current source further comprises:

a plurality of current unit cells, each current unit cell comprising at least one p-type transistor and at least one n-type transistor; and

a decode logic block for selection of each current unit cell.

10. The apparatus of claim 2, wherein the first current source has at least one CTAT, PTAT, or PTAT² configuration.

11. The apparatus of claim 2, wherein the first current source further comprises:

a CTAT current source; and

a PTAT current source coupled to the CTAT current source.

12. The apparatus of claim 2, wherein the control voltage generator further comprises:

a reference voltage generator to generate a reference voltage; and

a first operational amplifier coupled to the reference voltage generator, the first current source, and the variable resistance.

13. The apparatus of claim 12, wherein the reference voltage is selectable or adjustable.

14. The apparatus of claim 12, wherein the control voltage generator further comprises:

at least one second current source coupled to the first operational amplifier to provide a DC offset for the control voltage.

15. The apparatus of claim 12, wherein the reference voltage generator further comprises a band-gap voltage generator.

16. The apparatus of claim 12, wherein the reference voltage generator further comprises:

a variable current source; and

a resistor coupled to the variable current source and to the first operational amplifier.

17. The apparatus of claim 12, wherein the control voltage generator further comprises:

a second current source coupled to an input of the first operational amplifier; and

a second operational amplifier coupled through a resistance to the second current source and the input of the first operational amplifier.

18. The apparatus of claim 1, wherein the control voltage varies substantially linearly with temperature.

19. The apparatus of claim 1, wherein the control voltage generator comprises:

a first current source providing an increased current level in response to an increase in temperature; and

a second current source providing a decreased current level in response to an increase in temperature.

20. The apparatus of claim 1, wherein the control voltage generator comprises:

at least two current sources having opposing current responses to temperature variation.

21. The apparatus of claim 1, wherein the control voltage generator provides an open-loop control of the resonant frequency with temperature variation.

22. The apparatus of claim 1, wherein the plurality of variable reactance modules further comprise:

a plurality of variable capacitors; and

a plurality of switches correspondingly coupled to the plurality of variable capacitors, the plurality of switches adapted to couple each variable capacitor of the plurality of variable capacitors to either the control voltage or a fixed voltage.

23. The apparatus of claim 22, further comprising:

a coefficient register adapted to store a plurality of control coefficients; and

wherein each switch of the plurality of switches is responsive to a corresponding control coefficient or inverted control coefficient to couple or uncouple a corresponding variable capacitor to or from either the control voltage or the fixed voltage.

24. The apparatus of claim 1, wherein the plurality of variable reactance modules further comprise:

a plurality of variable impedance circuit elements; and

a plurality of switches correspondingly coupled to the plurality of variable impedance circuit elements, the plurality of switches adapted to couple each variable impedance circuit element of the plurality of variable impedance circuit elements to either the control voltage or a fixed voltage.

25. The apparatus of claim 24, wherein the plurality of switches are transistors and/or transmission gates.

26. The apparatus of claim 1, further comprising:

a plurality of fixed reactance modules couplable to the reference resonator.

27. The apparatus of claim 26, wherein the plurality of fixed reactance modules further comprise:

a plurality of capacitors having fixed capacitances; and

a plurality of switches correspondingly coupled to the plurality of capacitors, the plurality of switches adapted to couple or uncouple each capacitor of the plurality of capacitors to or from the reference resonator to select or modify the resonant frequency.

28. The apparatus of claim 27, further comprising:

a coefficient register adapted to store a plurality of control coefficients; and

wherein each switch of the plurality of switches is responsive to a corresponding control coefficient or inverted control coefficient to couple or uncouple a corresponding capacitor to or from the reference resonator.

29. The apparatus of claim 27, wherein the plurality of capacitors are binary-weighted or unit-weighted.

30. The apparatus of claim 26, wherein the plurality of fixed reactance modules further comprise:

a plurality of fixed-impedance circuit elements; and

a plurality of switches correspondingly coupled to the plurality of fixed-impedance circuit elements, the plurality of switches adapted to couple or uncouple each fixed-impedance circuit element of the plurality of fixed-impedance circuit elements to or from the reference resonator to select or modify the resonant frequency.

31. The apparatus of claim 1, further comprising:

a frequency controller coupled to the reference resonator, the frequency controller adapted to maintain substantially constant a peak amplitude of the first reference signal and a common mode voltage level of the reference resonator.

32. The apparatus of claim 31, further comprising:

a first variable current source to provide a current to the reference resonator; and

wherein the frequency controller is further adapted to generate a first control signal to the first variable current source to modify the current to the reference resonator to maintain the peak amplitude of the first reference signal substantially constant at a predetermined magnitude.

33. The apparatus of claim 32, wherein the frequency controller further comprises:

an amplitude detector to detect a magnitude of the peak amplitude of the first reference signal; and

an operational amplifier coupled to the amplitude detector and the first current source, the operational amplifier adapted to generate the first control signal to the first variable current source to modify the current level when the detected magnitude is not substantially equal to the predetermined magnitude.

34. The apparatus of claim 33, wherein the predetermined magnitude corresponds to a first reference voltage level;

and

wherein the apparatus further comprises;

a band-gap voltage generator to provide a band-gap reference voltage; and

a voltage conditioning circuit coupled to the band-gap voltage generator and the operational amplifier, the voltage conditioning circuit adapted to modify the band-gap reference voltage to provide the first reference voltage level to the operational amplifier.

35. The apparatus of claim 32, wherein the frequency controller further comprises:

an amplitude detector to detect a magnitude of the peak amplitude of the first reference signal; and

a comparator coupled to the amplitude detector and the first variable current source, the comparator adapted to generate the first control signal to the first variable current source to modify the current level when the detected magnitude is not substantially equal to the predetermined magnitude.

36. The apparatus of claim 32, further comprising:

a second variable current source to provide the current to the reference resonator; and

wherein the frequency controller is further adapted to generate a second control signal to the second variable current source to modify the current to the reference resonator to maintain the common mode voltage level of the reference resonator substantially constant at a predetermined voltage level.

37. The apparatus of claim 36, wherein the frequency controller further comprises:

a voltage detector to detect the common mode voltage level of the reference resonator; and

an operational amplifier coupled to the voltage detector and the second variable current source, the operational amplifier adapted to generate the second control signal to the second variable current source to modify the current level when the detected common mode voltage level is not substantially equal to the predetermined common mode voltage level.

38. The apparatus of claim 36, wherein the frequency controller further comprises:

a voltage detector to detect the common mode voltage level of the reference resonator; and

a comparator coupled to the voltage detector and the second variable current source, the comparator adapted to generate the second control signal to the second variable current source to modify the current level when the detected common mode voltage level is not substantially equal to the predetermined common mode voltage level.

39. The apparatus of claim 1, further comprising:

a current mirror to provide a fixed current to the reference resonator, the current mirror having a cascode configuration; and

a fixed current source coupled to the current mirror.

40. The apparatus of claim 1, wherein the reference resonator comprises an inductor (L) and a capacitor (C) in a circuit having at least one configuration of the following configurations:

a double-balanced, differential LC configuration;

a differential n-MOS cross-coupled topology;

a differential p-MOS cross-coupled topology;

a single-ended Colpitts LC configuration;

a single-ended Hartley LC configuration;

a differential, common base Colpitts LC configuration;

a differential, common collector Colpitts LC configuration;

a differential, common base Hartley LC configuration;

a differential, common collector Hartley LC configuration;

a single-ended Pierce LC oscillator, or a quadrature LC oscillator configuration.

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

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

42. A reference oscillator apparatus, the apparatus comprising:

a reference resonator to generate a reference signal having a resonant frequency;

a control voltage generator adapted to provide a temperature-dependent control voltage;

a plurality of variable reactance modules couplable to the reference resonator and couplable to the control voltage generator, each reactance module of the plurality of variable reactance modules adapted to modify a corresponding reactance in response to the control voltage to maintain the resonant frequency within a predetermined variance over a predetermined temperature range; and

at least one feedback circuit coupled to the reference resonator, the at least one feedback circuit adapted to maintain substantially constant a peak amplitude of the reference signal or a common mode voltage level of the reference resonator.

43. The apparatus of claim 42, wherein the control voltage generator comprises:

a first current source adapted to generate a temperature-dependent current; and

a variable resistance coupled to the first current source, an amount of resistance of the variable resistance selectable to determine a variation in the temperature-dependent current for a corresponding variation in temperature.

44. The apparatus of claim 43, wherein the variable resistance further comprises:

a plurality of resistors of a same type, each resistor of the plurality of resistors having a fixed resistance; and

a plurality of switches correspondingly coupled to the plurality of resistors, each switch of the plurality of switches responsive to a control coefficient to couple or uncouple a corresponding resistor of the plurality of resistors to provide the variable resistance.

45. The apparatus of claim 43, wherein the variable resistance further comprises:

at least one second current source; and

at least two resistors coupled to the second current source.

46. The apparatus of claim 45, wherein the second current source further comprises:

a plurality of current unit cells, each current unit cell comprising at least one p-type transistor and at least one n-type transistor; and

a decode logic block for selection of each current unit cell.

47. The apparatus of claim 43, wherein the first current source has at least one CTAT, PTAT, or PTAT² configuration.

48. The apparatus of claim 43, wherein the first current source further comprises:

a CTAT current source; and

a PTAT current source coupled to the CTAT current source.

49. The apparatus of claim 43, wherein the control voltage generator further comprises:

a reference voltage generator to generate a reference voltage; and

a first operational amplifier coupled to the reference voltage generator, the first current source, and the variable resistance.

50. The apparatus of claim 49, wherein the reference voltage generator further comprises a band-gap voltage generator.

51. The apparatus of claim 49, wherein the reference voltage generator further comprises:

a variable current source; and

a resistor coupled to the variable current source and to the first operational amplifier.

52. The apparatus of claim 49, wherein the control voltage generator further comprises:

a second current source coupled to an input of the first operational amplifier; and

a second operational amplifier coupled through a resistance to the second current source and the input of the first operational amplifier.

53. The apparatus of claim 42, wherein the at least one feedback circuit comprises:

a first variable current source to provide a current to the reference resonator;

an amplitude detector to detect a magnitude of the peak amplitude of the reference signal; and

an operational amplifier coupled to the amplitude detector and the first variable current source, the operational amplifier adapted to generate the first control signal to the first current source to modify the current level when the detected magnitude is not substantially equal to a predetermined magnitude.

54. The apparatus of claim 53, wherein the at least one feedback circuit further comprises:

a second variable current source to provide the current to the reference resonator; and

a voltage detector to detect the common mode voltage level of the reference resonator; and

an operational amplifier coupled to the voltage detector and the second current source, the operational amplifier adapted to generate the second control signal to the second current source to modify the current level when the detected common mode voltage level is not substantially equal to a predetermined common mode voltage level.

55. The apparatus of claim 42, wherein the plurality of variable reactance modules further comprise:

a plurality of variable capacitors; and

a plurality of switches correspondingly coupled to the plurality of variable capacitors, the plurality of switches adapted to couple each variable capacitor of the plurality of variable capacitors to either the control voltage or a fixed voltage.

56. The apparatus of claim 55, further comprising:

a coefficient register adapted to store a plurality of control coefficients; and

wherein each switch of the plurality of switches is responsive to a corresponding control coefficient or inverted control coefficient to couple or uncouple a corresponding variable capacitor to or from either the control voltage or the fixed voltage.

57. The apparatus of claim 42, further comprising:

a plurality of fixed reactance modules couplable to the reference resonator.

58. The apparatus of claim 57, wherein the plurality of fixed reactance modules further comprise:

a plurality of capacitors having fixed capacitances; and

a plurality of switches correspondingly coupled to the plurality of capacitors, the plurality of switches adapted to couple or uncouple each capacitor of the plurality of capacitors to or from the reference resonator to select or modify the resonant frequency.

59. The apparatus of claim 58, further comprising:

a coefficient register adapted to store a plurality of control coefficients; and

wherein each switch of the plurality of switches is responsive to a corresponding control coefficient or inverted control coefficient to couple or uncouple a corresponding capacitor to or from the reference resonator.

60. The apparatus of claim 42, wherein the control voltage generator provides an open-loop control of the resonant frequency with temperature variation and wherein the at least one feedback circuit is a closed-loop feedback circuits.

61. An integrated circuit, comprising:

a reference oscillator to generate a reference signal having a reference frequency;

a controller coupled to the reference oscillator, the controller adapted to maintain substantially constant a peak amplitude of the reference signal and a common mode voltage level of the reference oscillator;

a control voltage generator adapted to provide a control voltage which varies substantially linearly in response to temperature, the control voltage generator comprising a configurable resistance, a first current source and a second current source, the first and second current sources having opposing current responses to temperature variation; and

a plurality of varactors adapted to receive the control voltage and provide a corresponding capacitance to maintain the reference frequency within a predetermined variance of a predetermined frequency in response to temperature variation.

62. The apparatus of claim 61, wherein the configurable resistance further comprises:

a plurality of resistors, each resistor of the plurality of resistors having a fixed resistance; and

a plurality of switches correspondingly coupled to the plurality of resistors, each switch of the plurality of switches responsive to a control coefficient to couple or uncouple a corresponding resistor of the plurality of resistors to provide the variable resistance.

63. The apparatus of claim 61, wherein the configurable resistance further comprises:

at least one third current source; and

at least two resistors coupled to the third current source.

64. The apparatus of claim 63, wherein the third current source further comprises:

a plurality of current unit cells, each current unit cell comprising at least one p-type transistor and at least one n-type transistor; and

a decode logic block for selection of each current unit cell.

65. The apparatus of claim 61, wherein the first and second current sources each have a CTAT, PTAT, or PTAT² configuration.

66. The apparatus of claim 61, wherein the control voltage generator further comprises:

a band-gap voltage generator to generate a reference voltage; and

a first operational amplifier coupled to the band-gap voltage generator, the first and second current sources, and the variable resistance.

67. The integrated circuit of claim 61, wherein the controller comprises:

a third, variable current source to provide a current to the reference oscillator;

an amplitude sensor to provide an amplitude voltage corresponding to the magnitude of the peak amplitude of the reference signal; and

an operational amplifier coupled to the amplitude detector and the third current source, the operational amplifier adapted to generate the first control signal to the third current source to modify the current level when the amplitude voltage is not substantially equal to a first reference voltage level.

68. The integrated circuit of claim 67, wherein the controller further comprises:

a fourth, variable current source to provide the current to the reference oscillator; and

a voltage detector to detect the common mode voltage level of the reference oscillator; and

an operational amplifier coupled to the voltage detector and the fourth current source, the operational amplifier adapted to generate the second control signal to the fourth current source to modify the current level when the detected common mode voltage level is not substantially equal to a second reference voltage level.

69. The integrated circuit of claim 61, further comprising:

a coefficient register adapted to store a plurality of control coefficients; and

a plurality of switches correspondingly coupled to the plurality of varactors, each switch of the plurality of switches responsive to a corresponding control coefficient or inverted control coefficient to couple or uncouple a corresponding varactor to or from either the control voltage or a fixed voltage

70. The integrated circuit of claim 61, further comprising:

a coefficient register adapted to store a plurality of control coefficients;

a plurality of capacitors having fixed capacitances; and

a plurality of switches correspondingly coupled to the plurality of capacitors, each switch of the plurality of switches is responsive to a corresponding control coefficient or inverted control coefficient to couple or uncouple a corresponding capacitor to or from the reference oscillator to select the predetermined frequency or to modify the reference frequency.

71. A reference signal generator, comprising:

a reference oscillator to generate a reference signal having a reference frequency, the reference oscillator having a differential circuit configuration;

a control voltage generator adapted to provide a control voltage which varies substantially linearly in response to temperature;

a plurality of varactors adapted to receive the control voltage and provide a corresponding capacitance to maintain the reference frequency within a predetermined variance of a predetermined frequency in response to temperature variation;

a first variable current source to provide a current to the reference oscillator;

an amplitude detector to detect a magnitude of the peak amplitude of the reference signal;

a first operational amplifier coupled to the amplitude detector and the first variable current source, the operational amplifier adapted to generate a first control signal to the first current source to maintain a peak amplitude of the reference signal substantially constant at a predetermined magnitude;

a second variable current source to provide the current to the reference oscillator;

a voltage detector to detect the common mode voltage level of the reference oscillator; and

a second operational amplifier coupled to the voltage detector and the second current source, the second operational amplifier adapted to generate the second control signal to the second current source to maintain a common mode voltage level of the reference oscillator substantially constant at a predetermined voltage level, and the second feedback circuit adapted to operate at a comparatively faster speed than the first feedback circuit.