SELF-TUNING DRIVE SOURCE EMPLOYING INPUT IMPEDANCE PHASE DETECTION

• US 20080150550A1
• Filed: 12/20/2006
• Published: 06/26/2008
• Est. Priority Date: 12/20/2006
• Status: Active Grant

• Current Assignee: 3M Innovative Properties Company (3M Company)
• Original Assignee: 3M Innovative Properties Company (3M Company)
• Inventors: Vos, Martin J.
• Granted Patent: US 7,956,851 B2
• Time in Patent Office: Days
• US Class Current: 324/655
• CPC Class Codes: G06F 3/03545 Pens or stylus
• CPC Class Codes: G06F 3/046 by electromagnetic means

Abstract

An untethered device is configured to inductively couple to a source device. The source device includes a driver circuit configured to generate a varying magnetic field and comprising a drive coil circuit. A phase detector is coupled to the driver circuit and configured to detect a phase of an input impedance of the driver circuit in response to the source device inductively coupling with the resonant circuit of the untethered device. A controller is coupled to the phase detector and the driver circuit, and is configured to adjust a frequency of a source voltage applied to the driver circuit in response to an output signal of the phase detector. The controller adjusts the source voltage frequency so that the phase of the input impedance as indicated by the output signal of the phase detector is substantially zero.

Claims

1. A source device configured to cooperate with an untethered device comprising a resonant circuit, the source device comprising:

a driver circuit configured to generate a varying magnetic field and comprising a drive coil circuit;

a phase detector coupled to the driver circuit and configured to detect a phase of an input impedance of the driver circuit in response to the source device inductively coupling with the resonant circuit of the untethered device; and

a controller coupled to the phase detector and the driver circuit, the controller configured to adjust a frequency of a source voltage applied to the driver circuit in response to an output signal of the phase detector, the controller adjusting the source voltage frequency so that the phase of the input impedance as indicated by the output signal of the phase detector is substantially zero.

2. The device of claim 1, wherein controller adjustment of the source voltage frequency compensates for a change in a resonance frequency of the resonant circuit of the untethered device.

3. The device of claim 1, wherein controller adjustment of the source voltage frequency compensates for a change in a parameter of the resonant circuit of the untethered device.

4. The device of claim 1, wherein the controller comprises a voltage controlled oscillator.

5. The device of claim 1, wherein the source device comprises a digitizer and the untethered device comprises a stylus.

6. The device of claim 1, wherein the source device comprises an RFID reader and the untethered device comprises an RFID tag.

7. A system, comprising:

an untethered device comprising a resonant circuit; and

a source device configured to inductively couple to the untethered device, the source device comprising;

a driver circuit configured to generate a varying magnetic field and comprising a drive coil circuit;

a phase detector coupled to the driver circuit and configured to detect a phase of an input impedance of the driver circuit in response to inductively coupling the source device and the untethered device; and

a controller coupled to the phase detector and the driver circuit, the controller configured to adjust a frequency of a source voltage applied to the driver circuit in response to an output signal of the phase detector, the controller adjusting the source voltage frequency so that the phase of the input impedance as indicated by the output signal of the phase detector is substantially zero.

8. The system of claim 7, wherein controller adjustment of the source voltage frequency compensates for a change in a resonance frequency of the resonant circuit of the untethered device.

9. The system of claim 7, wherein controller adjustment of the source voltage frequency compensates for a change in a parameter of the resonant circuit of the untethered device.

10. The system of claim 9, wherein the parameter of the resonant circuit subject to change comprises a parameter of one or more of a resistive element, inductive element, and a capacitive element of the resonant circuit.

11. The system of claim 7, wherein controller adjustment of the source voltage frequency maximizes a voltage developed over a capacitive element of the resonant circuit of the untethered device.

12. The system of claim 7, wherein the source device comprises an RFID reader and the untethered device comprises an RFID tag.

13. The system of claim 7, wherein the source device comprises a digitizer and the untethered device comprises a stylus.

14. A method implemented in a source device configured to inductively couple to an untethered device having a resonant circuit, the method comprising:

driving a drive coil circuit of the source device with a source voltage having an adjustable frequency, the drive coil circuit generating a varying magnetic field;

detecting a phase of an input impedance of the drive coil circuit in response to inductively coupling the source device and the untethered device; and

adjusting the source voltage frequency so that the phase of the input impedance of the drive coil circuit is substantially zero.

15. The method of claim 14, wherein adjusting of the source voltage frequency compensates for a change in a resonance frequency of the resonant circuit of the untethered device.

16. The method of claim 14, wherein adjusting of the source voltage frequency compensates for a change in a parameter of the resonant circuit of the untethered device.

17. The method of claim 16, wherein the parameter of the resonant circuit subject to change comprises a parameter of one or more of a resistive element, inductive element, and a capacitive element of the resonant circuit.

18. The method of claim 14, wherein adjusting of the source voltage frequency maximizes a voltage developed over a capacitive element of the resonant circuit of the untethered device.

19. The method of claim 14, wherein the source device comprises an RFID reader and the untethered device comprises an RFID tag.

20. The method of claim 14, wherein the source device comprises a digitizer and the untethered device comprises a stylus.