Constant calibration

• US 7,907,020 B2
• Filed: 11/29/2007
• Issued: 03/15/2011
• Est. Priority Date: 08/31/2007
• Status: Active Grant

• Current Assignee: Apple Inc.
• Original Assignee: Apple Inc.
• Inventors: Wilson, Thomas James
• Primary Examiner(s): Pascal; Robert
• Assistant Examiner(s): Goodley; James E
• Application Number:
  US11/947,730
• Publication Number:
  US 20090058535A1
• Time in Patent Office: 1,202 Days
• Field of Search: 331/16, 331/17, 331/44
• US Class Current: 331/44
• CPC Class Codes: G06F 3/041 Digitisers, e.g. for touch screens or touch pads, characterised by the transducing means
• CPC Class Codes: G06F 3/04166 Details of scanning methods, e.g. sampling time, grouping of sub areas or time sharing with display driving Synchronisation with the driving of the display or the backlighting unit to avoid interferences generated internally G06F3/04184
• CPC Class Codes: G06F 3/0446 using a grid-like structure of electrodes in at least two directions, e.g. using row and column electrodes
• 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 7/146 by using digital means for generating the oscillator control signal H03L7/141, H03L7/143 take precedence

Abstract

An oscillating signal of relatively precise frequency can be generated by tuning an oscillator using an external stable oscillating source as a reference. Calibration logic can be included to compare a signal from the local oscillator to the reference signal and vary the local signal to a desired frequency. In one embodiment, the frequency of the local signal can be constantly or periodically compared with a threshold value and if the frequency exceeds the threshold value, the local oscillator can be modified to produce a signal having a frequency that is closer to a desired frequency.

Claims

1. A method for tuning an oscillator of an event-sensitive device, comprising:

programmably configuring calibration logic to perform a first calibration process to initially tune the oscillator to a desired frequency, the first calibration process including

approximating a number of cycles of the desired frequency in one cycle of a reference signal by multiplying a programmable value and a granularity factor, the granularity factor for reducing a number of bits in the programmable value while maintaining a reduced but sufficient precision in the approximated number of cycles, and

iteratively adjusting an oscillator tuning value in accordance with a difference between a number of cycles of a measured oscillator frequency in one cycle of the reference signal and the approximated number of cycles; and

programmably reconfiguring the calibration logic to perform a second calibration process to maintain the oscillator at the desired frequency, the second calibration process including

initiating the second calibration process on a periodic basis by activating the reference signal, the initiation being independent of any detected frequency drift,

setting a threshold value corresponding to an acceptable frequency variation range,

determining an error count corresponding to a difference between the measured oscillator frequency and an approximated frequency associated with the approximated number of cycles,

determining if the error count exceeds the threshold value,

tuning the oscillator to a frequency that is closer to the approximated frequency if the error count exceeds the threshold value, and

discontinuing the second calibration process by deactivating the reference signal to conserve power during normal operation.

2. The method of claim 1, the first calibration process comprising:

initiating the first calibration process by activating the reference signal;

performing a binary search algorithm on the oscillator tuning value to iteratively tune the oscillator to the approximated frequency; and

deactivating the first calibration process by discontinuing the reference signal.

3. The method of claim 1, further comprising counting a number of cycles of the measured oscillator frequency in one cycle of the reference signal to determine the number of cycles of the measured oscillator frequency, the counting comprising starting a counter upon occurrence of a first event of the reference signal and stopping the counter upon occurrence of a second event of the reference signal.

4. The method of claim 3, wherein the first event is a first rising edge of the reference signal and the second event is a second rising edge of the reference signal.

5. The method of claim 3, further comprising storing the number of cycles counted in a memory unit.

6. The method of claim 1, wherein determining the error count comprises:

counting a number of clock cycles of the measured oscillator frequency during one cycle of the reference signal; and

determining a difference between the counted number of clock cycles and the approximated number of clock cycles.

7. The method of claim 6, further comprising tuning the oscillator to a lower frequency when the number of cycles counted is more than the approximated number of cycles.

24. The method of claim 1, further comprising:

tuning the oscillator to a plurality of test frequency values;

stimulating the event-sensitive device with the plurality of test frequency values; and

analyzing output from the event-sensitive device stimulated with the plurality of test frequency values to determine the desired frequency value.

8. A method for tuning a frequency of an oscillating signal comprising:

programmably configuring calibration logic to perform a first calibration process to initially tune the oscillating signal to a desired frequency, the first calibration process including

approximating a number of cycles of the desired frequency in one cycle of a reference signal by multiplying a programmable value and a granularity factor, the granularity factor for reducing a number of bits in the programmable value while maintaining a reduced but sufficient precision in the approximated number of cycles, and

iteratively adjusting an oscillator tuning value in accordance with a difference between a number of cycles of a measured oscillator frequency in one cycle of the reference signal and the approximated number of cycles; and

programmably reconfiguring the calibration logic to perform a second calibration process to maintain the oscillating signal at the desired frequency, the second calibration process including

initiating the second calibration process on a periodic basis by activating the reference signal, the initiation independent of any detected frequency drift,

determining a desired clock count corresponding to an approximated frequency of associated with the approximated number of cycles,

outputting a local the measured oscillator frequency,

counting a measured clock count corresponding to the measured oscillator frequency,

determining an error count based on the measured clock count,

comparing the error count with a threshold value,

modifying the oscillator frequency of the local oscillator signal to a second frequency if the error count exceeds the threshold value, and

discontinuing the second calibration process by deactivating the reference signal to conserve power during normal operation.

9. The method of claim 8, wherein the measured clock count is a total number of cycles the measured oscillator frequency counted during one cycle of the reference signal.

10. The method of claim 8, wherein modifying the oscillator frequency further comprises decrementing an oscillator tuning value associated with a voltage applied to the local oscillator, when the error count is greater than the desired clock count.

11. The method of claim 8, wherein modifying the oscillator frequency further comprises incrementing an oscillator tuning value associated with a voltage applied to the local oscillator, when the error count is lower than the desired clock count.

12. A multi-event sensor device comprising:

a local oscillator circuit configured to generate an oscillating signal having a frequency at least partially based on an incoming control signal;

a reference signal generator configured to be activated and generate a reference signal to initiate first and second calibration processes, the second calibration process initiated on a periodic basis independent of any detected frequency drift, and further configured to be deactivated to discontinue the first and second calibration processes and conserve power; and

programmable calibration logic configurable to perform the first calibration process to initially tune the local oscillator circuit to a desired frequency, and reconfigurable to perform the second calibration process to maintain the local oscillator circuit at the desired frequency by comparing the frequency of the oscillating signal with a frequency of the reference signal and re-tuning the local oscillator circuit so that the frequency of the local oscillator circuit falls within a desired range;

wherein the programmable calibration logic is configured to perform the first calibration process by

approximating a number of cycles of the desired frequency in one cycle of the reference signal by multiplying a programmable value and a granularity factor, the granularity factor for reducing a number of bits in the programmable value while maintaining a reduced but sufficient precision in the approximated number of cycles, and

iteratively adjusting an oscillator tuning value in accordance with a difference between a number of cycles of a measured oscillator frequency in one cycle of the reference signal and the approximated number of cycles.

13. The multi-event sensor device of claim 12, wherein the local oscillator circuit is a voltage controlled oscillator.

14. The multi-event sensor device of claim 12, further comprising a touch sensitive panel comprising:

a plurality of event-sensing nodes configured to receive the oscillating signal and provide one or more panel output signals; and

event sensor circuitry configured to process the panel output signal to determine whether an event has occurred.

15. The multi-event sensor device of claim 14, wherein the event-sensing nodes include at least two electrodes and output results from capacitances formed as a result of the interaction among the at least two electrodes.

16. The multi-event sensor device of claim 12, wherein the calibration logic comprises a counter that starts counting a number of cycles of the measured oscillator frequency upon an occurrence of first event triggered by the reference signal and stops counting the number of cycles in the oscillating signal upon an occurrence of a second event triggered by the reference signal to determine the number of cycles of the measured oscillator frequency.

17. The multi-event sensor device of claim 12, wherein the multi-event sensor device is an integral portion of a mobile telephone unit.

18. The multi-event sensor device of claim 12, wherein the multi-event sensor device is an integral portion of a portable audio player unit.

19. A multi-event sensor device, comprising:

oscillator generation means for generating an oscillating signal;

reference signal generation means configured to be activated and generate a reference signal to initiate first and second calibration processes, the second calibration process initiated on a periodic basis independent of any detected frequency drift, and further configured to be deactivated to discontinue the first and second calibration processes and conserve power;

programmable calibration means configurable for performing the first calibration process to initially tune the oscillator generation means to a desired frequency, and reconfigurable for performing the second calibration process to maintain the oscillator generation means within a predetermined range; and

event sensitive means for sensing a plurality of events occurring simultaneously or nearly simultaneously on an event-sensing panel;

wherein the programmable calibration means are configured to perform the first calibration process by

approximating a number of cycles of the desired frequency in one cycle of a reference signal by multiplying a programmable value and a granularity factor, the granularity factor for reducing a number of bits in the programmable value while maintaining a reduced but sufficient precision in the approximated number of cycles, and

iteratively adjusting an oscillator tuning value in accordance with a difference between a number of cycles of a measured oscillator frequency in one cycle of the reference signal and the approximated number of cycles.

20. The multi-event sensor device of claim 19, wherein the first calibration process uses a binary search algorithm to calibrate the oscillator generation means.

21. An electronic device comprising:

an event sensitive panel configured to receive an oscillating signal and generate an output signal based on the received oscillating signal;

an oscillating circuit configured to generate the oscillating signal having a frequency;

a reference signal generator configured to be activated and generate a reference signal to initiate first and second calibration processes, the second calibration process initiated on a periodic basis independent of any detected frequency drift, and further configured to be deactivated to discontinue the first and second calibration processes and conserve power; and

a programmable calibration controller configurable to perform the first calibration process by initially tuning the oscillating circuit to a desired frequency, and reconfigurable to perform the second calibration process to maintain the oscillating signal within the desired frequency range;

wherein the programmable calibration controller is configured to perform the first calibration process by

approximating a number of cycles of the desired frequency in one cycle of the reference signal by multiplying a programmable value and a granularity factor, the granularity factor for reducing a number of bits in the programmable value while maintaining a reduced but sufficient precision in the approximated number of cycles, and

iteratively adjusting an oscillator tuning value in accordance with a difference between a number of cycles of a measured oscillator frequency in one cycle of the reference signal and the approximated number of cycles.

22. The electronic device of claim 21, wherein the electronic device is a portable audio player.

23. The electronic device of claim 21, wherein the electronic device is a mobile telephone.

25. An apparatus for stimulating a touch sensor panel, comprising:

a reference oscillator configured for generating a reference signal only during a calibration phase;

a local oscillator circuit including a voltage controlled oscillator configured for receiving a control signal and generating a clock signal for use in stimulating the touch sensor panel; and

programmable calibration logic coupled between the reference oscillator and the local oscillator circuit for receiving the reference signal and the clock signal and generating the control signal;

wherein the programmable calibration logic is configurable for entering a first calibration phase to calibrate the clock signal against the reference signal and initially tune the clock signal to a desired frequency, and is reconfigurable for entering a second calibration phase only upon receiving the reference signal to maintain the clock signal at the desired frequency, the reference signal being generated on a periodic basis independent of any detected frequency drift;

wherein the programmable calibration logic is further configurable for entering a touch sensing phase and generating the control signal for the local oscillator circuit in an absence of the reference signal when the reference signal is not being generated; and

wherein the programmable calibration logic is configured to perform the first calibration phase by

approximating a number of cycles of the desired frequency in one cycle of a reference signal by multiplying a programmable value and a granularity factor, the granularity, factor for reducing a number of bits in the programmable value while maintaining a reduced but sufficient precision in the approximated number of cycles, and

iteratively adjusting an oscillator tuning value in accordance with a difference between a number of cycles of a measured oscillator frequency in one cycle of the reference signal and the approximated number of cycles.

26. The apparatus of claim 25, the calibration logic further configured for:

determining a programmable value representative of the desired frequency value of the clock signal; and

generating the control signal based on the programmable value, the control signal intended to generate the desired frequency.

27. The apparatus of claim 26, the calibration logic further configured for performing a binary search algorithm during the first calibration phase to adjust the control signal until the local oscillator circuit generates the desired frequency.

28. The apparatus of claim 26, the calibration logic further configured for:

tuning the local oscillator circuit to a plurality of test frequency values;

stimulating the touch sensor panel with the plurality of test frequency values; and

analyzing output from the touch sensor panel stimulated with the plurality of test frequency values to determine the desired frequency.

29. The apparatus of claim 26, the calibration logic further configured for receiving a series of different programmable values to calibrate and tune the clock signal to a series of different frequencies to mitigate effects of static interference.