MEMS-based, computer systems, clock generation and oscillator circuits and LC-tank apparatus for use therein

• US 7,157,984 B2
• Filed: 10/28/2005
• Issued: 01/02/2007
• Est. Priority Date: 02/26/2002
• Status: Expired due to Fees

• Current Assignee: Board of Regents of the University of Michigan (University of Michigan)
• Original Assignee: Board of Regents of the University of Michigan (University of Michigan)
• Inventors: Brown, Richard B., McCorquodale, Michael S.
• Primary Examiner(s): KINKEAD, ARNOLD M
• Application Number:
  US11/261,093
• Publication Number:
  US 20060049885A1
• Time in Patent Office: 431 Days
• Field of Search: 331/167, 331/117.FE, 331/117.R, 331/74, 331/177.R, 331/177.V
• US Class Current: 331/167
• CPC Class Codes: H01F 17/0006 Printed inductances printed coils for dynamo-electric machines H02K3/26; printed circuits H05K
• CPC Class Codes: H01G 5/40 Structural combinations of variable capacitors with other electric elements not covered by this subclass, the structure mainly consisting of a capacitor, e.g. RC combinations
• CPC Class Codes: H01L 23/5227 Inductive arrangements or effects of, or between, wiring layers other inductive arrangements H01L23/645
• CPC Class Codes: H01L 2924/00 Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
• CPC Class Codes: H01L 2924/0002 Not covered by any one of groups H01L24/00, H01L24/00 and H01L2224/00
• CPC Class Codes: H01L 2924/3011 Impedance
• CPC Class Codes: H03B 5/1212 the amplifier comprising a pair of transistors, wherein an output terminal of each being connected to an input terminal of the other, e.g. a cross coupled pair
• CPC Class Codes: H03B 5/1228 the amplifier comprising one or more field effect transistors
• CPC Class Codes: H03B 5/124 the means comprising a voltage dependent capacitance
• CPC Class Codes: H03B 5/18 with frequency-determining element comprising distributed inductance and capacitance
• CPC Class Codes: H03B 5/32 being a piezoelectric resonator selection of piezoelectric material H10N30/00
• CPC Class Codes: H03H 2007/006 MEMS
• CPC Class Codes: H03H 7/0115 comprising only inductors and capacitors H03H7/075, H03H7/09, H03H7/12, H03H7/13 take precedence

Abstract

MEMS-based, computer system, clock generation and oscillator circuits and LC-tank apparatus for use therein are provided and which are fabricated using a CMOS-compatible process. A micromachined inductor (L) and a pair of varactors (C) are developed in metal layers on a silicon substrate to realize the high quality factor LC-tank apparatus. This micromachined LC-tank apparatus is incorporated with CMOS transistor circuitry in order to realize a digital, tunable, low phase jitter, and low power clock, or time base, for synchronous integrated circuits. The synthesized clock signal can be divided down with digital circuitry from several GHz to tens of MHZ—a systemic approach that substantially improves stability as compared to the state of the art. Advanced circuit design techniques have been utilized to minimize power consumption and mitigate transistor flicker noise upconversion, thus enhancing clock stability.

Claims

1. A clock generation circuit, the circuit comprising:

a substrate;

a double-balanced, cross-coupled voltage-controlled, reference oscillator fabricated on the substrate and including a micro-electromechanical LC-tank apparatus for generating a differential sinusoidal periodic signal, the LC-tank apparatus comprising a parallel plate capacitor and an inductor fabricated in a plurality of CMOS metal interconnect layers, the parallel plate capacitor comprising a top plate suspended in air over the substrate and moveable in response to a control voltage, and the inductor supported in air over the substrate;

first circuitry also fabricated on the substrate for converting the differential sinusoidal periodic signal into a single-ended, high frequency, square-wave digital output signal; and

a cascoded current source coupled through at least one transistor to the reference oscillator.

2. The clock generation circuit as claimed in claim 1 wherein the differential sinusoidal periodic signal has an original frequency, wherein the square-wave digital output signal has a frequency of half of the original frequency, and wherein the circuit further comprises second circuitry also fabricated on the substrate for dividing the frequency of the square-wave digital output signal to at least one lower desired application frequency.

3. The clock generation circuit as claimed in claim 2 wherein the first and second circuitry and the voltage-controlled reference oscillator are fabricated on the substrate with a CMOS-compatible process.

4. The clock generation circuit as claimed in claim 1 wherein both the voltage-controlled reference oscillator and the first circuitry are fabricated on the substrate with a CMOS-compatible process.

5. The clock generation circuit as claimed in claim 4 wherein the CMOS-compatible process is a bulk or SOI CMOS process.

6. The clock generation circuit as claimed in claim 1 wherein the first circuitry also converts the differential sinusoidal periodic signal into the single-ended square-wave digital output signal at half of the original frequency.

7. The clock generation circuit as claimed in claim 2 wherein the second circuitry includes at least one flip-flop coupled to the first circuitry for dividing the frequency of the square-wave digital output signal to the at least one lower desired application frequency.

8. The clock generation circuit as claimed in claim 1 wherein the substrate is a bulk or SOI substrate.

9. An oscillator circuit comprising:

a substrate;

a double-balanced, cross-coupled micro-electromechanical LC-tank apparatus fabricated on the substrate with a CMOS-compatible process;

first circuitry fabricated on the substrate with the CMOS-compatible process and coupled to the LC-tank apparatus to generate a sinusoidal periodic signal having an original frequency;

second circuitry fabricated on the substrate with the CMOS-compatible process and coupled to the first circuitry to convert the sinusoidal periodic signal to a plurality of square-wave periodic signals having a corresponding plurality of application frequencies, each application frequency of the plurality of application frequencies equal to the original frequency divided by an integer; and

a cascoded current source coupled through at least one transistor to the LC-tank apparatus.

10. The oscillator circuit as claimed in claim 9 wherein the LC-tank apparatus is tunable in response to a control input to provide a variable original frequency.

11. The oscillator circuit as claimed in claim 9 wherein the CMOS-compatible process is a bulk or SOI CMOS process.

12. The oscillator circuit as claimed in claim 10 wherein the LC-tank includes at least one micromachined varactor having a capacitance which varies in response to the control input.

13. The oscillator circuit as claimed in claim 12 wherein the at least one varactor includes a top plate and wherein the circuitry includes bypass capacitors to block the control input to the top plate from the remainder of the circuitry.

14. A micromachined LC-tank apparatus, the apparatus comprising:

a substrate;

at least one micromachined, parallel plate varactor fabricated on the substrate with a CMOS-compatible process in conductive layers;

a micromachined inductor coupled to the at least one varactor and also fabricated on the substrate with the CMOS-compatible process in a conductive layer of the conductive layers;

a cascoded current source coupled through at least one transistor to the inductor or to the varactor;

wherein the varactor has a first predetermined size and the inductor has a second predetermined size to generate a sinusoidal signal having an original frequency during oscillation; and

circuitry coupled to the varactor and the inductor to divide the original frequency to a lower application frequency.

15. The apparatus as claimed in claim 14 wherein the at least one varactor has a variable capacitance to provide a tuning range for the apparatus.

16. The apparatus as claimed in claim 14 wherein the inductor is suspended above the substrate and released during or upon completion of the CMOS-compatible process.

17. The apparatus as claimed in claim 14 wherein the inductor is hollow.

18. The apparatus as claimed in claim 14 wherein the inductor is suspended above the substrate by anchors that are defined by the CMOS-compatible process.

19. The apparatus as claimed in claim 15 wherein the at least one varactor has a fixed bottom plate and a movable top plate suspended above the bottom plate and released during or upon completion of the CMOS-compatible process.

20. The apparatus as claimed in claim 19 wherein the top plate deflects based on a control input to tune the capacitance of the at least one varactor.

21. The apparatus as claimed in claim 19 wherein the top plate is suspended above the bottom plate by a mechanical suspension network defined by the CMOS-compatible process.

22. The apparatus as claimed in claim 14 wherein the plurality of conductive layers are metal layers.

23. The apparatus as claimed in claim 14 wherein the CMOS-compatible process is a bulk or SOI CMOS process.

24. The apparatus as claimed in claim 19 wherein the top plate has a plurality of etch holes to facilitate release of the top plate during or upon completion of the CMOS-compatible process.

25. The apparatus as claimed in claim 14 wherein the substrate is a bulk or SOI substrate.

26. The apparatus as claimed in claim 14 wherein the original frequency during oscillation is a resonant frequency.

27. The apparatus as claimed in claim 14 wherein the at least one varactor and the inductor are defined by one or more of the following:

metal-insulator-metal (MiM) layers or metal routing layers.

28. A computer system comprising:

a databus;

a central processing unit coupled to the databus;

a memory coupled to the databus; and

a clock generation circuit for generating a square-wave digital output signal, the clock generation circuit comprising;

a double-balanced, cross-coupled reference harmonic oscillator comprising an inductor and a capacitor for generating a reference sinusoidal periodic signal having a first frequency;

a cascoded current source coupled through at least one transistor to the reference harmonic oscillator; and

first circuitry fabricated on the substrate for converting the sinusoidal periodic signal into a square-wave digital output signal having a second frequency, the second frequency equal to or lower than the first frequency.

29. A clock generation circuit, the circuit comprising:

a balanced, cross-coupled reference harmonic oscillator for generating a reference sinusoidal signal having an original frequency, the reference harmonic oscillator comprising an inductor coupled to a capacitor;

a cascoded current source coupled to the reference harmonic oscillator;

first circuitry coupled to the reference harmonic oscillator to convert the reference sinusoidal signal into a square-wave digital output signal having a first frequency, the first frequency lower than the original frequency; and

second circuitry fabricated on the substrate for dividing the first frequency of the square-wave digital output signal to at least one application frequency, the at least one application frequency lower than the first frequency.

30. The clock generation circuit as claimed in claim 29 wherein the reference signal is a differential signal and wherein the first circuitry converts the reference sinusoidal differential signal into a sinusoidal single-ended signal.

31. The clock generation circuit as claimed in claim 30 wherein the first circuitry also converts the sinusoidal single-ended signal into the square-wave digital output signal having a first frequency of half of the original frequency.

32. The clock generation circuit as claimed in claim 29 wherein the second circuitry includes at least one flip-flop coupled to the first circuitry for dividing the frequency of the square-wave digital output signal to the at least one application frequency.

33. An oscillator oscillator circuit for generating a periodic signal, the oscillator circuit comprising:

a substrate;

a double-balanced, cross-coupled LC-tank apparatus fabricated on the substrate with a CMOS-compatible process, the LC-tank comprising at least one micromachined varactor having a capacitance which varies in response to the control input and having a top plate;

a cascoded current source coupled to the LC-tank apparatus;

circuitry fabricated on the substrate with the CMOS-compatible process and coupled to the LC-tank apparatus to generate the periodic signal and including a bypass capacitor to block the control input to the top plate from the remainder of the circuitry.

34. An LC-tank apparatus, the apparatus comprising:

a substrate;

at least one voltage-controlled micromachined varactor fabricated on the substrate with a CMOS-compatible process, the at least one micromachined varactor having a variable capacitance to provide a tuning range for the apparatus, the at least one micromachined varactor comprising a fixed bottom plate and a movable top plate suspended above the bottom plate;

a micromachined inductor coupled to the at least one varactor and fabricated on the substrate with the CMOS-compatible process; and

a cascoded current source coupled to the micromachined varactor or the micromachined inductor.

35. An integrated clock generation circuit, comprising:

a reference harmonic oscillator circuit to generate a first, reference differential periodic signal having a first frequency, the reference harmonic oscillator circuit comprising an inductor coupled to a capacitor;

a cascoded current source coupled through at least one transistor to the reference harmonic oscillator circuit;

a frequency divider circuit coupled to the oscillator circuit to convert the first, reference differential periodic signal to a plurality of single-ended square-wave periodic application signals, each periodic application signal having a different frequency equal to a fraction of the first frequency.

36. The integrated clock generation circuit of claim 35, wherein a clock signal is a selected periodic application signal of the plurality of square-wave periodic application signals.

37. The integrated clock generation circuit of claim 35, wherein the reference harmonic oscillator circuit further comprises a plurality of active devices adapted to operate at or near weak inversion.

38. The integrated clock generation circuit of claim 35, wherein the frequency divider circuit comprises:

a plurality of flip-flops coupled in succession, a clock input of a first flip-flop of the plurality coupled to the reference harmonic oscillator circuit to receive the first, reference differential periodic signal, and the output of each flip-flop providing a corresponding periodic application signal.

39. The integrated clock generation circuit of claim 35, wherein the inductor and capacitor are micromachined.

40. The integrated clock generation circuit of claim 35, wherein the inductor and capacitor are fabricated from one or more CMOS-compatible layers.

41. The integrated clock generation circuit of claim 40, wherein the one or more CMOS-compatible layers are one or more metal layers.

42. The integrated clock generation circuit of claim 41, wherein the inductor is supported in air over the substrate and the capacitor is suspended in air over the substrate.

43. The integrated clock generation circuit of claim 42, wherein the inductor and capacitor, following CMOS fabrication defining bond pad openings, are released in a maskless etch process.

44. The integrated clock generation circuit of claim 35, wherein the capacitor is metal-insulator-metal (MiM).

45. The integrated clock generation circuit of claim 35, wherein the capacitor is formed of CMOS-compatible metal routing layers.

46. The integrated clock generation circuit of claim 35, further comprising:

a microprocessor.

47. The integrated clock generation circuit of claim 35, further comprising:

a microcontroller.

48. The integrated clock generation circuit of claim 35, wherein phase noise decreases with each successive frequency division performed by the frequency divider.

49. The integrated clock generation circuit of claim 35, wherein periodic application signal stability improves with each successive frequency division performed by the frequency divider.

50. An integrated clock generation circuit, comprising:

a reference oscillator circuit to generate a first, reference differential periodic signal having a first frequency, the oscillator circuit comprising an inductor coupled to a capacitor;

an amplifier coupled to the reference oscillator circuit to convert the first, reference differential periodic signal to a single-ended signal having a second frequency; and

a frequency divider circuit coupled to the amplifier to convert the single-ended signal to a plurality of square-wave periodic application signals, each periodic application signal having a different frequency equal to or less than the second frequency.

51. The integrated clock generation circuit of claim 50, wherein a clock signal is a selected periodic application signal of the plurality of square-wave periodic application signals.

52. The integrated clock generation circuit of claim 50, wherein the second frequency is equal to the first frequency.

53. The integrated clock generation circuit of claim 50, wherein the frequency divider circuit comprises:

a plurality of flip-flops coupled in succession, a clock input of a first flip-flop of the plurality coupled to the amplifier to receive the single-ended signal, and the output of each flip-flop providing a corresponding periodic application signal.

54. The integrated clock generation circuit of claim 52, wherein the inductor and capacitor are micro-electromechanical.

55. The integrated clock generation circuit of claim 50, wherein the inductor and capacitor are fabricated from one or more CMOS-compatible metal layers.

56. The integrated clock generation circuit of claim 55, wherein the inductor is supported in air over the substrate and the capacitor is suspended in air over the substrate.

57. The integrated clock generation circuit of claim 56, wherein the inductor and capacitor, following CMOS fabrication defining bond pad openings, are released in a maskless etch process.

58. The integrated clock generation circuit of claim 50, wherein the capacitor is metal-insulator-metal.

59. An integrated clock generation circuit, comprising:

a double-balanced harmonic oscillator circuit, the harmonic oscillator circuit for generating a reference differential periodic signal having a first frequency, the harmonic oscillator circuit comprising an inductor and a capacitor;

an amplifier coupled to the reference oscillator circuit to convert the reference differential periodic signal to a single-ended signal having a second frequency; and

a frequency divider circuit coupled to the amplifier to convert the single-ended signal to a plurality of square-wave periodic application signals, each periodic application signal having a different frequency equal to a division of the second frequency, wherein a periodic application signal of the plurality of square-wave periodic application signals is a clock signal.

60. A clock generation circuit, comprising:

a voltage controlled, reference harmonic oscillator circuit for generating a differential, reference sinusoidal signal having a first frequency, the reference harmonic oscillator comprising an inductor and a first capacitor;

a second, common-mode capacitor coupled to the reference harmonic oscillator circuit;

a cascoded current source coupled to the reference harmonic oscillator circuit; and

first circuitry coupled to the reference harmonic oscillator circuit to convert the differential, reference sinusoidal signal to a single-ended square-wave periodic signal having a second frequency, the second frequency equal to a fraction of the first frequency.

61. The clock generation circuit of claim 60, further comprising:

a bypass capacitor coupled to the cascoded current source.

62. The clock generation circuit of claim 60, wherein the cascoded current source is adapted to operate at or near weak inversion.

63. The clock generation circuit of claim 60, wherein the first circuitry further comprises a frequency divider circuit.

64. The clock generation circuit of claim 63, wherein the frequency divider circuit provides a plurality of square-wave periodic signals having a plurality of different application frequencies.

65. The clock generation circuit of claim 63, wherein the reference sinusoidal signal is a differential signal.

66. The clock generation circuit of claim 65, wherein the first circuitry further comprises an amplifier coupled to the reference harmonic oscillator circuit and to the frequency divider circuit, the amplifier adapted to convert the differential signal to a single-ended signal.

67. An integrated clock generation circuit, comprising:

a voltage-controlled, double-balanced reference harmonic oscillator circuit to generate a differential reference periodic signal having a first frequency, the reference harmonic oscillator circuit comprising an inductor coupled to a varactor;

a cascoded current source coupled to the reference harmonic oscillator circuit;

first circuitry coupled to the reference harmonic oscillator circuit to convert the differential reference periodic signal to a single-ended signal having a second frequency; and

a frequency divider circuit coupled to the first circuitry to convert the single-ended signal to a plurality of square-wave periodic application signals, each periodic application signal having a different frequency equal to or less than the second frequency, wherein a clock signal is an application signal of the plurality of square-wave periodic application signals.

68. The integrated clock generation circuit of claim 67, wherein the frequency divider circuit is adapted to divide the second frequency arbitrarily to any output frequency.