System and method for automatically tuning an antenna

• US 20030119469A1
• Filed: 10/21/2002
• Published: 06/26/2003
• Est. Priority Date: 10/26/2001
• Status: Active Grant

• Current Assignee: Microsoft Technology Licensing LLC (Microsoft Corporation)
• Original Assignee: Microsoft Corporation
• Inventors: Karr, Lawrence J., Gord, John Charles
• Granted Patent: US 6,907,234 B2
• Time in Patent Office: Days
• US Class Current: 455/307
• CPC Class Codes: G04R 20/16 Tuning or receiving; Circuits therefor
• CPC Class Codes: H01Q 1/273 Adaptation for carrying or wearing by persons or animals
• CPC Class Codes: H01Q 7/005 with variable reactance for tuning the antenna
• CPC Class Codes: H03J 2200/06 Tuning of antenna
• CPC Class Codes: H04B 1/0458 Arrangements for matching and coupling between power amplifier and antenna or between amplifying stages matching circuits in general H03H
• CPC Class Codes: H04B 1/18 Input circuits, e.g. for coupling to an antenna or a transmission line coupling networks between antennas or lines and receivers independent of the nature of the receiver H03H
• CPC Class Codes: H04B 1/3833 Hand-held transceivers
• CPC Class Codes: H04B 1/385 Transceivers carried on the body, e.g. in helmets

Abstract

An apparatus and method is related to a wireless system with an antenna that is automatically tuned to a desired frequency. The antenna is coupled to an adjustable tuning circuit to form a tuned antenna circuit that has a resonant frequency. The adjustable tuning circuit may be adjusted by activating a sweep generator that varies a tuning element over a broad frequency range. The sweep of the sweep generator is terminated after the proper frequency is found. Alternatively, the adjustable tuning circuit may be adjusted using an array of switched capacitors using a successive approximation method. The tuned antenna circuit may be employed to receive and/or transmit information. The resonant frequency is dynamically shifted in response to a data signal such that the antenna transmits FSK encoded signals.

Claims

1. An apparatus that includes an antenna that is automatically tuned, the apparatus comprising:

a tuned circuit that includes the antenna and an adjustable tuning circuit, wherein the tuned circuit has a resonant frequency that is adjustable with a control signal;

an amplifier circuit that is arranged to provide an output signal in response to an input signal that is received from the tuned circuit;

a feedback circuit that is arranged to selectively couple at least a portion of the output signal to the tuned circuit such that the tuned circuit, amplifier circuit, and feedback circuit operate as an oscillator that oscillates at the resonant frequency when the feedback circuit is active;

a receiver circuit that is tuned to a selected frequency is arranged to receive the output signal and to provide an indicator signal, wherein the indicator signal indicates a signal level of signals received at the selected frequency; and

a tuning adjustment circuit that is arranged to selectively provide the control signal such that the control signal is adjusted until the signal level of the indicator signal exceeds a predetermined threshold, wherein the signal level of the indicator signal exceeds the predetermined threshold when the resonant frequency of the tuned circuit is matched to the selected frequency of the receiver.

2. An apparatus as in claim 1, the tuning adjustment circuit further comprising a ramp generator that is arranged to provide the control signal, wherein the ramp generator adjusts the control signal from a start value to an end value when active, and the control signal is effective to adjust the resonant frequency of the tuned circuit over the operating range of the receiver.

3. An apparatus as in claim 2, wherein the ramp generator adjusts the control signal in at least one of identical discrete steps, non-identical discrete steps, a linear contiguous ramp, a non-linear contiguous ramp, and discrete predetermined levels.

4. An apparatus as in claim 1, the tuning adjustment circuit further comprising a discriminator circuit that is arranged to provide an enable signal when the signal level of the indicator signal is below the predetermined threshold, wherein the tuning adjustment circuit varies the control signal when the enable signal is a first logic level, and the tuning adjustment circuit maintains the control signal when the enable signal is a second logic level that is different from the first logic level.

5. An apparatus as in claim 1, wherein the adjustable tuning circuit is a variable capacitance circuit that includes at least one of a capacitor, a varactor diode, and an electronic circuit that is arranged to operate as a variable capacitance.

6. An apparatus as in claim 1, the feedback circuit further comprising a capacitance circuit and a switching circuit, wherein the capacitance circuit is arranged to couple the at least a portion of the output signal to the tuned circuit when the switching circuit is in a closed position, and the resonant frequency of the tuned circuit does not change when the switching circuit is in an open position.

7. An apparatus as in claim 1, wherein the feedback circuit is active and the tuning adjustment circuit is arranged to adjust the control signal in response to an information signal when the apparatus is in a transmit mode such that the resonant frequency of the tuned circuit is adjusted in response to the information signal and the antenna transmits a transmission signal corresponding to the information signal.

8. An apparatus as in claim 1, wherein the feedback circuit is active when the apparatus is in a tune mode, and the feedback circuit is inactive when the apparatus is in a receive mode.

9. An apparatus as in claim 8, wherein the receiver is arranged to provide a demodulated signal when the receiver is in the receive mode, the demodulated signal corresponding to an information signal that is received by the antenna as a modulated signal that is modulated at the selected frequency.

10. A method for automatically tuning an antenna, comprising:

selecting a desired frequency;

initializing a control signal to a start value at the beginning of the tune mode, the start value corresponding to a frequency at one end of the operating spectrum of the wireless system;

arranging the antenna to oscillate at a resonant frequency with a tuning circuit, the tuning circuit having an adjustable tuning element that is arranged to adjust the resonant frequency in response to the control signal;

determining a signal strength of the output signal at a selected frequency;

changing the control signal to another value when the signal strength is below a predetermined threshold level; and

maintaining the control signal when the signal strength is above the predetermined threshold level, whereby the resonant frequency is substantially the same as the selected frequency when the signal strength is above the predetermined threshold level such that the antenna is tuned.

11. A method as in claim 10, changing the control signal to another value further comprising at least one of sweeping the control signal in a linear manner, sweeping the control signal in a non-linear manner, changing the control signal by discrete steps of equal size, and changing the control signal to predetermined discrete values.

12. A method as in claim 10, arranging the antenna to oscillate further comprising:

coupling the antenna to the tuning circuit, the antenna and the tuning circuit forming a tuned antenna circuit that has a resonant frequency;

coupling an output of the tuned antenna circuit to an input of an amplifier circuit; and

coupling an output of the amplifier circuit to the tuned antenna circuit such that the tuned antenna circuit oscillates at the resonant frequency.

13. A method for using a tuned antenna, comprising:

arranging an antenna with a tuning circuit, the antenna and the tuning circuit forming a tuned antenna circuit that has a resonant frequency;

selecting an operating mode and a desired frequency;

coupling the tuned antenna circuit to an amplifier circuit when the operating mode is a tune mode such that the tuned antenna circuit oscillates at the resonant frequency;

sweeping the resonant frequency over a range of values when the operating mode is the tune mode and the resonant frequency is substantially different from the desired frequency; and

stopping the sweep when the resonant frequency is substantially the same as the desired frequency and the operating mode is the tune mode.

14. A method as in claim 13, further comprising:

coupling the tuned antenna circuit to an amplifier circuit when the operating mode is a transmit mode such that the tuned antenna circuit oscillates at the resonant frequency; and

shifting the resonant frequency in response to an information signal such that the antenna transmits frequency shift keyed signals corresponding to the information signal when the operating mode is the transmit mode.

15. A method as in claim 13, further comprising:

disconnecting feedback between the tuned antenna circuit and the amplifier circuit when the operating mode is a receive mode; and

receiving a transmission signal with the tuned antenna circuit, wherein the transmission signal is an information signal that is transmitted on a carrier signal at the selected frequency.

16. A wireless watch device including an antenna that is automatically tuned to a selected frequency, comprising:

a means for tuning that is coupled to the antenna such that the antenna and the means for tuning have a resonant frequency;

a means for amplifying that is arranged to provide an output signal in response to an input signal from the antenna;

a means for oscillating that is arranged to provide feedback of the output signal to the antenna such that the antenna and the means for tuning oscillate at the resonant frequency when selected;

a means for receiving that is arranged to receive the output signal and provide a signal strength that indicates a level of the output signal that is tuned to the selected frequency;

a means for discriminating that is arranged to activate an enable signal when the signal strength is substantially below a predetermined threshold, and the enable signal is deactivated when the signal strength reaches or exceeds the predetermined threshold; and

a means for adjusting that is arranged to adjust the resonant frequency of the means for tuning when the enable signal is active such that the resonant frequency is adjusted until tuned to the selected frequency.

17. An apparatus that includes an antenna that is automatically tuned, the apparatus comprising:

a tuned circuit that includes the antenna and a tuning array, wherein the tuned circuit has a resonant frequency that is associated with a tuning control signal that is provided to the tuning array;

an oscillator circuit that is coupled to the tuned circuit such that the tuned circuit and the oscillator circuit form a resonant circuit that provides an antenna oscillation signal that oscillates at the resonant frequency when the oscillator circuit is enabled;

a comparator circuit that is coupled to the tuned circuit such that the comparator circuit produces a comparator output signal in response to the antenna oscillation signal when the comparator circuit is enabled;

a counter circuit that is coupled to the comparator circuit such that the counter detects a number of oscillations associated with the comparator output signal during a time interval; and

a successive approximation register that is arranged to provide the tuning control signal, wherein the tuning control signal is adjusted in response to a carryout signal from the counter at the end of the time interval when the successive approximation register is enabled.

18. The apparatus of claim 17, the tuning array further comprising:

a decoder circuit that is arranged to provide an array of selection control signals, and an array of selectable capacitor circuits that are each selected in response to an associated one of the selection control signals, wherein each of the selectable capacitor circuits is coupled to the antenna such that the antenna and the selected capacitor circuits form the tuned circuit.

19. The apparatus of claim 17, wherein the counter circuit is arranged to preload a specified count before each time interval, wherein the specified count is associated with a selected station frequency.

20. The apparatus of claim 17, wherein the counter circuit is arranged to preload a specified count before each time interval, wherein the specified count is associated with a selected station frequency, and wherein the counter circuit is also arranged to provide the carryout signal to the successive approximation register when the number of oscillations exceeds the specified count at the end of the time interval.

21. The apparatus of claim 17, wherein the oscillator circuit, the comparator circuit, and the successive approximation register are enabled when a tuning mode is selected in the apparatus.

22. The apparatus of claim 17, wherein the oscillator circuit is enabled when a transmit mode is selected in the apparatus.

23. A method for automatically tuning an antenna, comprising:

selecting a desired frequency;

initializing a tuning control signal to an initial value at the beginning of the tuning mode, the initial value corresponding to a frequency at one end of the operating spectrum;

configuring the antenna to oscillate such that the antenna provides an oscillator signal with an associated resonant frequency, wherein the resonant frequency is related to the tuning control signal;

initiating tuning cycles when the tune mode is active, wherein each tuning cycle includes;

counting a number of oscillations in the oscillator signal over the predetermined time interval; and

adjusting the tuning control signal in response to the number of oscillations counted over the predetermined time interval.

24. The method of claim 23, wherein each tuning cycle further comprises:

adjusting the tuning control signal to increase the resonant frequency when the number of oscillations counted over the predetermined time interval exceeds a predetermined amount, and adjusting the tuning control signal to decreases the resonant frequency when the number of oscillations counted over the predetermined time interval is below the predetermined amount.

25. The method of claim 23, further comprising coupling additional capacitors to the antenna in response to the tuning control signals when the number of oscillations counted over the predetermined time interval exceed a predetermined amount, and decoupling capacitors from the antenna in response to the tuning control signals when the number of oscillations counted over the predetermined time interval is below the predetermined amount.

26. A method for using an antenna, comprising:

coupling the antenna to a tuning array such that the antenna and the tuning array form a tuned circuit that has a resonant frequency;

selecting an operating mode and a desired frequency;

activating an oscillator circuit when the operating mode is a tune mode, wherein the oscillator circuit excites the tuned circuit such that the tuned circuit oscillates at the resonant frequency;

adjusting the resonant frequency when the operating mode is the tune mode and the resonant frequency is substantially different from the desired frequency, wherein adjusting the resonant frequency includes;

counting a number of oscillations in the tuned circuit over a time interval;

activating additional elements in the tuning array when the number of oscillations in the tuned circuit is above a predetermined amount at the end of the time interval; and

deactivating elements in the tuning array when the number of oscillations in the tuned circuit is below the predetermined amount at the end of the time interval.

27. The method of claim 26, further comprising receiving a transmission signal with the tuned circuit when the selected operating mode corresponds to a receive mode, wherein the transmission signal is an information signal that is transmitted on a carrier signal at the selected frequency.

28. A method as in claim 26, further comprising:

activating the oscillator circuit when the operating mode is a transmit mode, wherein the oscillator circuit excites the tuned circuit such that the tuned circuit oscillates at the resonant frequency, and shifting the resonant frequency in response to an information signal such that the antenna transmits frequency shift keyed signals corresponding to the information signal when the operating mode is the transmit mode.

29. A method as in claim 26, further comprising:

activating the oscillator circuit when the operating mode is a transmit mode, wherein the oscillator circuit excites the tuned circuit such that the tuned circuit oscillates at the resonant frequency, and shifting the resonant frequency in response to an information signal such that the antenna transmits frequency shift keyed signals corresponding to the information signal when the operating mode is the transmit mode.

30. An apparatus that includes an antenna for transmitting an information signal, the apparatus comprising:

a tuning array that is coupled to the antenna, wherein the tuning array is responsive to a tuning control signal;

a modulation tuner that is coupled to the antenna, wherein the modulation tuner includes a tuning element that is responsive to a modulation control signal, wherein the tuning array, the modulation tuner, and the antenna form a tuned circuit that has an associated resonant frequency;

an oscillator that is coupled to the tuned circuit such that the oscillator and the tuned circuit form a resonant circuit that provides an antenna oscillation signal that oscillates at the resonant frequency when the oscillator circuit is enabled; and

a phase detector that is arranged to provide the modulation control signal by comparing the phase of the antenna oscillation signal to an IF oscillation signal, wherein the IF oscillation signal corresponds to a local oscillator signal that is modulated in response to the information signal such that the resonant frequency of the tuned circuit changes in response to the information signal.

31. The apparatus of claim 30, further comprising:

an IF oscillator that is arranged to provide the IF oscillation signal in response to a local oscillator signal and the information signal, wherein the IF oscillation signal corresponds to a modulation of the local oscillator signal in response to the information signal.

32. The apparatus of claim 30, further comprising:

an IF oscillator that is arranged to provide the IF oscillation signal in response to a local oscillator signal and a DAC output signal, and a DAC that is arranged to provide the DAC output signal in response to the information signal, wherein the DAC output signal corresponds to an digital-to-analog conversion of the information signal, and wherein the IF oscillation signal corresponds to a modulation of the local oscillator signal in response to the DAC output signal.

33. A method for transmitting an information signal with an antenna, the method comprising:

configuring the antenna to oscillate such that the antenna provides an antenna oscillator signal with an associated resonant frequency;

generating an IF oscillator signal, wherein the IF oscillator signal corresponds to a frequency shift keyed signal that is shifted in response to the information signal;

comparing the phase of the antenna oscillator signal to the phase of an IF oscillation signal to provide a phase difference signal; and

adjusting the resonant frequency with a modulation tuner in response to the phase difference signal such that the antenna transmits the information signal as an FM modulated signal using FSK encoding.