Automatic frequency calibration

• US 20080157882A1
• Filed: 01/03/2007
• Published: 07/03/2008
• Est. Priority Date: 01/03/2007
• Status: Active Grant

• Current Assignee: Apple Inc.
• Original Assignee: Apple Inc.
• Inventors: Krah, Christoph Horst
• Granted Patent: US 7,719,367 B2
• Time in Patent Office: Days
• US Class Current: 331/18
• 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 7/02 using a frequency discriminator comprising a passive frequency-determining element
• CPC Class Codes: H03L 7/12 using a scanning signal

Abstract

Disclosed is a system and method for providing an oscillating signal of relatively precise frequency without using a signal provided by a crystal as a reference. Disclosed is a feedback oscillator circuit configured to output an oscillating signal having a frequency defined by a reference signal. The oscillating signal can be sent to one or more circuits including at least one frequency sensitive element. The frequency sensitive element produces an output signal which depends on the frequency of the oscillating signal. A controller controls the reference signal in order to cause an attribute of the output signal to have a value within a desired range.

Claims

1. A method for providing an oscillating signal, comprising:

generating a reference signal;

generating an oscillating signal whose frequency is based on the reference signal;

sending the oscillating signal to a frequency sensitive element;

producing an output signal from the frequency sensitive element, said output signal depending on the frequency of the oscillating signal, wherein the output signal does not depend on a crystal oscillator; and

controlling the frequency of the oscillating signal by modifying an attribute of the reference signal until an attribute of the output signal of the frequency sensing element falls within a desired range of values.

5. The method of claim 1, wherein the attribute of the reference signal is controlled by modifying a digital tuning value.

6. The method of claim 5, wherein controlling the frequency of the oscillating signal by modifying the an attribute of the reference signal further comprises:

scanning a predefined range by periodically changing the tuning value so that it encompasses a plurality of values within the range;

detecting a plurality of values for the attribute of the output signal, each value of the plurality of values being associated with a respective tuning value;

choosing a desirable tuning value based on the values of the attribute of the output signal; and

setting the tuning value to the desirable tuning value.

7. The method of claim 6, wherein:

the frequency sensitive element is a multi touch panel comprising a band pass filter;

sending the oscillating signal to a frequency sensitive element further comprises generating a stimulation signal, the frequency of the stimulation signal being based on the frequency of the oscillating signal and sending the stimulation signal through the band pass filter; and

the output signal is at least partially based on an output of the band pass filter resulting from the sending of the stimulation signal through the band pass filter.

8. The method of claim 7, wherein the attribute of the output signal is a voltage of the output signal, and the method further comprises:

processing the detected plurality of values for the voltage of the output signal and their associated tuning values to determine two border tuning values which result in cut off frequencies which are at the edges of the pass band of the band pass filter;

retrieving two previously stored expected cut off frequencies; and

correlating the expected cutoff frequencies with the border tuning values to derive a relationship between tuning values and their resulting stimulation frequencies.

9. The method of claim 1, wherein the attribute of the reference signal is the current of the reference signal.

10. The method of claim 9, wherein modifying an attribute of the reference signal further comprises selectively connecting and disconnecting one or more current sources in order to modify the current of the reference signal.

11. The method of claim 1, further including the step of generating a digital signal, associated with a particular value of the attribute of the reference signal, wherein the reference signal is generated based on the digital signal.

12. The method of claim 1, wherein the frequency sensitive element performs other useful functions, in addition to assisting with the generation of an oscillating signal, at least one of the other useful functions being based on the frequency of the oscillating signal.

2. The method of claim 2, wherein the frequency sensitive element is a band pass filter and the attribute of the output signal of the frequency sensitive element is the voltage of said output signal.

3. The method of claim 2, wherein the desired range of values comprises high voltage values resulting from a pass frequency range of the band pass filter.

4. The method of claim 3, wherein the pass frequency range of the band pass filter includes a desired frequency for the operation of an electronic device.

13. A method for tuning the frequency of an oscillating signal comprising:

scanning a reference signal by periodically changing the reference signal so that a plurality of different versions of the reference signal within a scanning range are generated;

generating an oscillating signal, the frequency of the oscillating signal being based on the reference signal;

sending the oscillating signal to a frequency sensitive element;

monitoring an output of the frequency sensitive element for each different version of the reference signal. wherein the output of the frequency sensitive element does not depend on a crystal oscillator;

selecting a desirable version of the reference signal based on the monitored output of the frequency sensitive element;

setting the reference signal at the desirable version of the reference signal.

14. The method of claim 13, wherein the different versions of the reference signal are reference signals with different currents, and monitoring the output of the frequency sensitive element comprises monitoring the voltage of the frequency sensitive element.

15. The method of claim 13, further comprising generating a digital signal, wherein one or more values of the digital signal are associated with respective versions of the reference signal, and the steps of periodically changing the reference signal and setting the reference signal are performed by changing the value of the digital signal.

16. The method of claim 13, where in the tuning of an oscillating signal is used to compensate for variances in a circuits for generating the reference signal as well as variances in the frequency response of the frequency sensitive element.

17. An electronic device comprising:

a feedback oscillator circuit configured to generate an oscillating signal whose frequency is based on an incoming reference signal;

a reference signal generator configured to generate the reference signal based on a control signal; and

a frequency sensitive element, configured to receive the oscillating signal and generate an output signal based on the frequency of the oscillating signal, and not based on a crystal oscillator;

a controller configured to receive the output signal, and modify the value of the control signal based on the value of the output signal in order to bring the output signal into a range of predetermined desired values.

18. The electronic device of claim 17, wherein the controller is a digital controller and the control signal is a digital signal.

19. The electronic device of claim 17, further comprising a touch sensitive panel comprising:

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

touch sensor circuitry configured to process the panel output signal to determine where and whether a touch has occurred,

wherein the frequency sensitive element is a band pass filter comprising one or more of the plurality electrodes and the output signal is one of the one or more panel output signals.

20. The electronic device of claim 19, wherein the frequency sensitive element includes at least two electrodes and results from capacitances formed as a result of the interaction among the at least two electrodes, as well as between one or more of the at least two electrodes and other elements.

21. The electronic device of claim 17, wherein the feedback oscillator circuit comprises:

a current comparator configured to compare the current of the incoming reference signal and a feedback current and produce an incoming voltage associated with the difference of said currents;

a voltage controlled oscillator, configured to generate an oscillating signal, whose frequency is based on the incoming voltage; and

a frequency to current converter, configured to generate the feedback signal, so that the feedback signal'"'"'s current is based on the frequency of the oscillating signal.

22. The electronic device of claim 17, wherein the frequency sensitive element has additional functionality other than assisting in the generation of the oscillating signal.

23. A circuit for generating an oscillating signal comprising:

a feedback oscillator circuit configured to generate an oscillating signal whose frequency is based on an incoming reference signal and send the oscillating signal to a frequency sensitive element, configured to receive the oscillating signal and generate an output signal based on the frequency of the oscillating signal and not based on a crystal oscillator;

a reference signal generator configured to generate the reference signal based on a control signal;

a controller configured to receive the output signal, and modify the value of the control signal based on the value of the output signal in order to bring the output signal into a range of predetermined desired values.

24. The circuit of claim 23, wherein the frequency sensitive element features other functionality in addition to assisting the circuit in generating the oscillating signal.

25. An electronic device comprising:

a touch sensitive panel configured to receive an oscillating signal and generate an output signal based on the received oscillating signal and is not based on a crystal oscillator;

an oscillating circuit configured to generate the oscillating signal; and

a controller configured to control the frequency of the oscillating signal by controlling the oscillating circuit,

wherein the controller is further configured to receive the output signal, and control the frequency of the oscillating signal so that a desired value of an attribute of the output signal is achieved.

26. The electronic device of claim 25, wherein the output signal is also based on whether a user is touching the touch sensitive panel.

27. The electronic device of claim 25, wherein the electronic device further comprises a reference signal generator configured to generate a reference signal and send it to the oscillating circuit, wherein the oscillating circuit is configured to generate the oscillating signal having a frequency associated with the reference signal, and the controller is configured to control the oscillating circuit by controlling the reference signal generator.

28. The electronic device of claim 27, wherein the reference signal generator receives a control signal from the controller, and the reference signal is based on the control signal.

29. The electronic device of claim 28, wherein the controller is digital, and the control signal is a digital signal.

30. The electronic device of claim 27, wherein the controller is configured to:

sweep the reference signal by sending a plurality of different control signals which cause the reference signal generator to produce a plurality of reference signals, having different values within a predefined sweep range;

detect the resulting output signals for each of the plurality of different control signals;

find a desirable control signal associated with a desirable detected output signal; and

set the control signal to the desirable control signal.

31. The electronic device of claim 27, wherein the electronic device is a computing system.

32. The electronic device of claim 27, wherein the electronic device is a mobile telephone.

33. The electronic device of claim 27, wherein the electronic device is a digital audio player.

34. A mobile telephone comprising:

a feedback oscillator circuit configured to generate an oscillating signal whose frequency is based on an incoming reference signal and is not based on a crystal oscillator;

a reference signal generator configured to generate the reference signal based on a control signal; and

a frequency sensitive element, configured to receive the oscillating signal and generate an output signal based on the frequency of the oscillating signal;

a controller configured to receive the output signal, and modify the value of the control signal based on the value of the output signal in order to bring the output signal into a range of predetermined desired values.

35. A portable audio player comprising:

a feedback oscillator circuit configured to generate an oscillating signal whose frequency is based on an incoming reference signal and is not based on a crystal oscillator;

a reference signal generator configured to generate the reference signal based on a control signal; and

a frequency sensitive element, configured to receive the oscillating signal and generate an output signal based on the frequency of the oscillating signal;

a controller configured to receive the output signal, and modify the value of the control signal based on the value of the output signal in order to bring the output signal into a range of predetermined desired values.