Frequency modification circuitry for use in radio-frequency communication apparatus and associated methods

• US 20040077327A1
• Filed: 07/31/2003
• Published: 04/22/2004
• Est. Priority Date: 05/29/1998
• Status: Active Grant

• Current Assignee: Silicon Laboratories Incorporated
• Original Assignee: Silicon Laboratories Incorporated
• Inventors: Lim, Lysander, Maligeorgos, James
• Granted Patent: US 7,035,607 B2
• Time in Patent Office: Days
• US Class Current: 455/318
• CPC Class Codes: H03B 5/366 and comprising means for varying the frequency by a variable voltage or current
• CPC Class Codes: H03L 7/085 concerning mainly the frequency- or phase-detection arrangement including the filtering or amplification of its output signal H03L7/10 takes precedence; circuits for comparing the phase or frequency of two mutually-independent oscillations H03D13/00
• CPC Class Codes: H03L 7/087 using at least two phase detectors or a frequency and phase detector in the loop
• CPC Class Codes: H03L 7/091 the phase or frequency detector using a sampling device H03L7/087 takes precedence
• CPC Class Codes: H03L 7/099 concerning mainly the controlled oscillator of the loop
• CPC Class Codes: H03L 7/187 using means for coarse tuning the voltage controlled oscillator of the loop H03L7/191 - H03L7/195 take precedence
• CPC Class Codes: H03L 7/199 with reset of the frequency divider or the counter, e.g. for assuring initial synchronisation
• CPC Class Codes: H03L 7/23 with pulse counters or frequency dividers
• CPC Class Codes: H04B 1/0003 Software-defined radio [SDR] systems, i.e. systems wherein components typically implemented in hardware, e.g. filters or modulators/demodulators, are implented using software, e.g. by involving an AD or DA conversion stage such that at least part of the signal processing is performed in the digital domain digital baseband systems H04L25/00; digital modulation/demodulation H04L27/00; CDMA H04B1/707; TDMA H04B7/2643; image transmission H04N5/00
• CPC Class Codes: H04B 1/28 the receiver comprising at least one semiconductor device having three or more electrodes
• CPC Class Codes: H04B 1/406 with more than one transmission mode, e.g. analog and digital modes
• CPC Class Codes: H04B 15/02 Reducing interference from electric apparatus by means located at or near the interfering apparatus
• CPC Class Codes: H04B 15/04 the interference being caused by substantially sinusoidal oscillations, e.g. in a receiver or in a tape-recorder
• CPC Class Codes: H04B 2215/064 Reduction of clock or synthesizer reference frequency harmonics

Abstract

Frequency modification circuitry may be employed as part of a crystal oscillator circuit to generate a reference signal with adjustable frequency. The frequency modification circuitry may be implemented as part of a crystal oscillator circuit that includes digitally controlled crystal oscillator (“DCXO”) circuitry and a crystal. The frequency modification circuitry may adjust the frequency of the reference signal in response to one or more frequency control signals. In one example, the frequency modification circuitry may include variable capacitors such as one or more continuously variable and/or discretely variable capacitors for providing coarse and/or fine adjustment of the reference signal frequency.

Claims

1. A circuit for providing an adjustable reference signal to radio frequency (RF) circuitry, said circuit comprising:

frequency modification circuitry comprising at least one variable capacitance device, said frequency modification circuit being configured for coupling to a crystal to form a crystal oscillator circuit that is capable of providing said adjustable reference signal to one or more components of said RF circuitry; and

wherein said at least one variable capacitance device is configured to adjust the frequency of said adjustable reference signal.

2. The circuit of claim 1, wherein said at least one variable capacitance device is configured to adjust the frequency of said adjustable reference signal based at least in part on one or more frequency control signals received by said frequency modification circuitry.

3. The circuit of claim 2, wherein said at least one variable capacitance device comprises at least one continuously variable capacitor, and wherein said one or more frequency control signals comprises one or more analog signals.

4. The circuit of claim 2, wherein said at least one variable capacitance device comprises at least one discretely variable capacitor, and wherein said one or more frequency control signals comprises one or more digital signals.

5. The circuit of claim 2, wherein said frequency modification circuitry comprises at least one continuously variable capacitor and at least one discretely variable capacitor, each of said at least one continuously variable capacitor and said at least one discretely variable capacitor being configured to adjust the frequency of said adjustable reference signal in response to said one or more frequency control signals received by said frequency modification circuitry.

6. The circuit of claim 2, wherein said variable capacitance device comprises:

variable capacitor circuitry configured to adjust the frequency of said adjustable reference signal in response to a plurality of control voltage signals; and

control circuitry, the control circuitry configured to generate the plurality of control voltage signals in response to at least one of said one or more frequency control signals received by said frequency modification circuitry;

wherein the voltage level of each of the plurality of the control voltage signals differs by an offset voltage from the voltage level of the remaining signals in the plurality of control voltage signals.

7. The circuit of claim 6, wherein said control circuitry comprises a signal generator circuit adapted to generate the plurality of control signals having respective levels that are progressively offset from said at least one of said one or more frequency control signals.

8. The circuit of claim 6, wherein said variable capacitance device comprises a plurality of capacitor stages coupled in parallel.

9. The circuit of claim 8, wherein each of the plurality of capacitor stages comprises a first fixed capacitor coupled to a second fixed capacitor;

wherein said variable capacitance device further comprises a plurality of variable impedance devices, each of the plurality of variable impedance devices being coupled in parallel with the second capacitor in a respective one of the plurality of capacitor stages; and

wherein each of the plurality of control signals controls a respective variable impedance device in the plurality of variable impedance devices.

10. The circuit of claim 9, wherein one or more of said frequency control signals comprises a voltage signal.

11. The circuit of claim 9, wherein one or more of said frequency control signals comprises a current signal.

12. The circuit of claim 2, wherein said variable capacitance device comprises a digitally programmable capacitor array configured to adjust the frequency of said adjustable reference signal in response to a plurality of frequency control signals generated by a digitally programmable capacitor array register.

13. The circuit of claim 12, wherein said digitally programmable capacitor array comprises a plurality of capacitor stages coupled in parallel.

14. The circuit of claim 13, wherein each of the plurality of capacitor stages comprises a fixed capacitor;

wherein said digitally programmable capacitor array further comprises a plurality of transistors, each of the plurality of transistors being coupled in series with the fixed capacitor in a respective one of the plurality of capacitor stages; and

wherein each of the plurality of control signals controls a respective transistor in the plurality of transistors.

15. The circuit of claim 14, wherein said one or more of said frequency control signals comprises multiple bits of a digital signal.

16. The circuit of claim 3, wherein said one or more frequency control signals received by said frequency modification circuitry comprise one or more adjusted frequency control signals;

and wherein said circuit further comprises interface circuitry configured to receive one or more raw frequency control signals and to adjust the voltage of said one or more raw frequency control signals to produce said one or more adjusted frequency control signals.

17. The circuit of claim 16, wherein at least part of the voltage range of said one or more raw frequency control signals has a voltage magnitude that is not within the operating range of said variable capacitance device;

and wherein said interface circuitry is configured to adjust the voltage magnitude of said one or more raw frequency control signals to produce an adjusted frequency control signal having a voltage range that is within the operating range of said variable capacitance device.

18. A communication device, comprising:

RF circuitry, said RF circuitry comprising at least one of transmitter circuitry, receiver circuitry, or a combination thereof; and

frequency modification circuitry comprising at least one variable capacitance device, said frequency modification circuit being configured for coupling to a crystal to form a crystal oscillator circuit that is capable of providing an adjustable reference signal to at least one of said transmitter circuitry, receiver circuitry, or a combination thereof;

wherein said at least one variable capacitance device is configured to adjust the frequency of said adjustable reference signal.

19. The communication device of claim 18, wherein said at least one variable capacitance device of said frequency modification circuitry is configured to adjust the frequency of said adjustable reference signal based at least in part on one or more frequency control signals received by said frequency modification circuitry.

20. The communication device of claim 19, further comprising baseband processor circuitry coupled to said frequency modification circuitry, said baseband processor circuitry being configured to provide said one or more frequency control signals to said frequency modification circuitry.

21. The communication device of claim 20, wherein said frequency modification circuit is configured for coupling to a crystal to form a crystal oscillator circuit that is capable of providing an adjustable reference signal to said baseband processor circuitry.

22. The communication device of claim 20, wherein said at least one variable capacitance device comprises at least one continuously variable capacitor.

23. The communication device of claim 20, wherein said at least one variable capacitance device comprises at least one discretely variable capacitor.

24. The communication device of claim 20, wherein said frequency modification circuitry comprises at least one continuously variable capacitor and at least one discretely variable capacitor, each of said at least one continuously variable capacitor and said at least one discretely variable capacitor being configured to adjust the frequency of said adjustable reference signal in response to said one or more frequency control signals received by said frequency modification circuitry.

25. The communication device of claim 20, wherein said variable capacitance device comprises:

variable capacitor circuitry configured to adjust the frequency of said adjustable reference signal in response to a plurality of control voltage signals; and

control circuitry, the control circuitry configured to generate the plurality of control voltage signals in response to at least one of said one or more frequency control signals;

wherein the voltage level of each of the plurality of the control voltage signals differs by an offset voltage from the voltage level of the remaining signals in the plurality of control voltage signals.

26. The communication device of claim 25, wherein said variable capacitance device comprises a plurality of capacitor stages coupled in parallel, each of the plurality of capacitor stages comprises a first fixed capacitor coupled to a second fixed capacitor;

wherein said variable capacitance device further comprises a plurality of variable impedance devices, each of the plurality of variable impedance devices being coupled in parallel with the second capacitor in a respective one of the plurality of capacitor stages; and

wherein each of the plurality of control signals controls a respective variable impedance device in the plurality of variable impedance devices.

27. The communication device of claim 20, wherein said variable capacitance device comprises a digitally programmable capacitor array configured to adjust the frequency of said adjustable reference signal in response to a plurality of frequency control signals generated by a digitally programmable capacitor array register.

28. The communication device of claim 27, wherein said digitally programmable capacitor array comprises a plurality of capacitor stages coupled in parallel, each of the plurality of capacitor stages comprising a fixed capacitor;

wherein said digitally programmable capacitor array further comprises a plurality of transistors, each of the plurality of transistors being coupled in series with the fixed capacitor in a respective one of the plurality of capacitor stages; and

wherein each of the plurality of control signals controls a respective transistor in the plurality of transistors.

29. The communication device of claim 19, wherein said one or more frequency control signals received by said frequency modification circuitry comprise one or more adjusted frequency control signals;

and wherein said communication device further comprises;

baseband processor circuitry configured to provide one or more raw frequency control signals, and

interface circuitry coupled to said baseband processor circuitry and to said frequency modification circuitry, said interface circuitry being configured to receive said one or more raw frequency control signals from said baseband processor circuitry and to adjust the voltage of said one or more raw frequency control signals to produce said one or more adjusted frequency control signals and to provide said one or more adjusted frequency control signals to said frequency modification circuitry.

30. The Communication device of claim 29, wherein at least part of the voltage range of said one or more raw frequency control signals provided by said baseband processor circuitry has a voltage magnitude that is not within the operating range of said variable capacitance device;

and wherein said interface circuitry is configured to adjust the voltage magnitude of said one or more raw frequency control signals to produce an adjusted frequency control signal having a voltage range that is within the operating range of said variable capacitance device.

31. A method of operating a crystal oscillator circuit to provide an adjustable reference signal to radio frequency (RF) circuitry, comprising:

generating said adjustable reference signal using said crystal oscillator circuit, said crystal oscillator circuit comprising frequency modification circuitry that comprises at least one variable capacitance device and a crystal coupled to said frequency modification circuitry;

adjusting the frequency of said adjustable reference signal using said variable capacitance device; and

providing said adjustable reference signal to one or more components of said RF circuitry.

32. The method of claim 31, further comprising adjusting the frequency of said adjustable reference signal using said variable capacitance device based at least in part on one or more frequency control signals received by said frequency modification circuitry.

33. The method of claim 32, wherein said at least one variable capacitance device comprises at least one continuously variable capacitor, and wherein said one or more frequency control signals comprises one or more analog signals.

34. The method of claim 32, wherein said at least one variable capacitance device comprises at least one discretely variable capacitor, and wherein said one or more frequency control signals comprises one or more digital signals.

35. The method of claim 32, wherein said frequency modification circuitry comprises at least one continuously variable capacitor and at least one discretely variable capacitor, and wherein said method further comprises adjusting the frequency of said adjustable reference signal using said at least one continuously variable capacitor and using said at least one discretely variable capacitor in response to said one or more frequency control signals received by said frequency modification circuitry.

36. The method of claim 35, wherein said frequency modification circuitry comprises at least one continuously variable capacitor and at least one discretely variable capacitor, and wherein said method further comprises first adjusting the frequency of said adjustable reference signal using said at least one discretely variable capacitor in response to at least one of said one or more frequency control signals received by said frequency modification circuitry;

and then further adjusting the frequency of said adjustable reference signal using said at least one continuously variable capacitor in response to at least one of said one or more frequency control signals received by said frequency modification circuitry.

37. The method of claim 32, further comprising:

generating a plurality of control voltage signals in response to at least one of said one or more frequency control signals received by said frequency modification circuitry, wherein the voltage level of each of the plurality of the control voltage signals differs by an offset voltage from the voltage level of the remaining signals in the plurality of control voltage signals; and

adjusting the frequency of said adjustable reference signal in response to said plurality of control voltage signals.

38. The method of claim 37, further comprising generating said plurality of control signals to have respective levels that are progressively offset from said at least one of said one or more frequency control signals.

39. The method of claim 37, wherein said variable capacitance device comprises a plurality of capacitor stages coupled in parallel, each of the plurality of capacitor stages comprising a first fixed capacitor coupled to a second fixed capacitor;

wherein said variable capacitance device further comprises a plurality of variable impedance devices, each of the plurality of variable impedance devices being coupled in parallel with the second capacitor in a respective one of the plurality of capacitor stages; and

wherein said method further comprises using each of the plurality of control signals to control a respective variable impedance device in the plurality of variable impedance devices.

40. The method of claim 32, further comprising adjusting the frequency of said adjustable reference signal in response to said plurality of frequency control signals using a digitally programmable capacitor array.

41. The method of claim 40, wherein said digitally programmable capacitor array comprises a plurality of capacitor stages coupled in parallel, wherein each of the plurality of capacitor stages comprises a fixed capacitor;

wherein said digitally programmable capacitor array further comprises a plurality of transistors, each of the plurality of transistors being coupled in series with the fixed capacitor in a respective one of the plurality of capacitor stages; and

wherein said method further comprises using each of the plurality of control signals to control a respective transistor in the plurality of transistors.

42. The method of claim 41, wherein said one or more of said frequency control signals comprises multiple bits of a digital signal.

43. The method of claim 33, wherein said one or more frequency control signals received by said frequency modification circuitry comprise one or more adjusted frequency control signals;

and wherein said method further comprises adjusting the voltage of one or more raw frequency control signals to produce said one or more adjusted frequency control signals, and adjusting the frequency of said adjustable reference signal using said variable capacitance device based at least in part on said one or more adjusted frequency control signals.

44. The method of claim 43, wherein at least part of the voltage range of said one or more raw frequency control signals has a voltage magnitude that is not within the operating range of said variable capacitance device;

and wherein said method further comprises adjusting the voltage magnitude of said one or more raw frequency control signals to produce an adjusted frequency control signal having a voltage range that is within the operating range of said variable capacitance device.

45. A method of operating a radio-frequency (RF) device, comprising:

generating an adjustable reference signal using a crystal oscillator circuit, said crystal oscillator circuit comprising frequency modification circuitry that comprises at least one variable capacitance device and a crystal coupled to said frequency modification circuitry;

adjusting the frequency of said adjustable reference signal using said variable capacitance device; and

providing said adjustable reference signal or a signal based on said adjustable reference signal to at least one RF circuitry component of said RF device, said at least one RF circuitry component comprising transmitter circuitry, receiver circuitry, or a combination thereof.

46. The method of claim 45, further comprising adjusting the frequency of said adjustable reference signal using said variable capacitance device based at least in part on one or more frequency control signals received by said frequency modification circuitry.

47. The method of claim 46, further comprising receiving said one or more frequency control signals in said frequency modification circuitry, said frequency control signals comprising one or more signals provided from baseband processor circuitry coupled to said crystal oscillator circuit or comprising one or more signals based on one or more signals provided from baseband processor circuitry coupled to said crystal oscillator circuit.

48. The method of claim 47, further comprising providing said adjustable reference signal or a signal based on said adjustable reference signal to said baseband processor circuitry.

49. The method of claim 47, wherein said at least one variable capacitance device comprises at least one continuously variable capacitor.

50. The method of claim 47, wherein said at least one variable capacitance device comprises at least one discretely variable capacitor.

51. The method of claim 47, wherein said frequency modification circuitry comprises at least one continuously variable capacitor and at least one discretely variable capacitor, and wherein said method further comprises adjusting the frequency of said adjustable reference signal using said at least one continuously variable capacitor and using said at least one discretely variable capacitor in response to said one or more frequency control signals received by said frequency modification circuitry.

52. The method of claim 47, further comprising:

generating a plurality of control voltage signals in response to at least one of said one or more frequency control signals received by said frequency modification circuitry, wherein the voltage level of each of the plurality of the control voltage signals differs by an offset voltage from the voltage level of the remaining signals in the plurality of control voltage signals; and

adjusting the frequency of said adjustable reference signal in response to said plurality of control voltage signals.

53. The method of claim 52, wherein said variable capacitance device comprises a plurality of capacitor stages coupled in parallel, each of the plurality of capacitor stages comprising a first fixed capacitor coupled to a second fixed capacitor;

wherein said variable capacitance device further comprises a plurality of variable impedance devices, each of the plurality of variable impedance devices being coupled in parallel with the second capacitor in a respective one of the plurality of capacitor stages; and

wherein said method further comprises using each of the plurality of control signals to control a respective variable impedance device in the plurality of variable impedance devices.

54. The method of claim 47, further comprising adjusting the frequency of said adjustable reference signal in response to said plurality of frequency control signals using a digitally programmable capacitor array.

55. The method of claim 54, wherein said digitally programmable capacitor array comprises a plurality of capacitor stages coupled in parallel, wherein each of the plurality of capacitor stages comprises a fixed capacitor;

wherein said digitally programmable capacitor array further comprises a plurality of transistors, each of the plurality of transistors being coupled in series with the fixed capacitor in a respective one of the plurality of capacitor stages; and

wherein said method further comprises using each of the plurality of control signals to control a respective transistor in the plurality of variable transistors.

56. The method of claim 46, wherein said one or more frequency control signals received by said frequency modification circuitry comprise one or more adjusted frequency control signals;

and wherein said method further comprises receiving one or more raw frequency control signals from baseband processor circuitry, adjusting the voltage of said one or more raw frequency control signals to produce said one or more adjusted frequency control signals, and adjusting the frequency of said adjustable reference signal using said variable capacitance device based at least in part on said one or more adjusted frequency control signals.

57. The method of claim 56, wherein at least part of the voltage range of said one or more raw frequency control signals received from said baseband processor circuitry has a voltage magnitude that is not within the operating range of said variable capacitance device;

and wherein said method further comprises adjusting the voltage magnitude of said one or more raw frequency control signals to produce an adjusted frequency control signal having a voltage range that is within the operating range of said variable capacitance device.