Automatic frequency calibration

• US 7,719,367 B2
• Filed: 01/03/2007
• Issued: 05/18/2010
• Est. Priority Date: 01/03/2007
• Status: Active Grant

• Current Assignee: Apple Inc.
• Original Assignee: Apple Inc.
• Inventors: Krah, Christoph Horst
• Primary Examiner(s): Chang; Joseph
• Assistant Examiner(s): SHIN, JEFFREY M
• Application Number:
  US11/649,966
• Publication Number:
  US 20080157882A1
• Time in Patent Office: 1,231 Days
• Field of Search: 331/16, 331/17, 331/18, 331/34, 331/46, 331/177.R, 331/179, 345173-178, 178/18.01, 178 1803- 1807
• 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 independent of any fixed reference source;

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;

Controlling the frequency of the oscillating signal by modifying an attribute of the reference signal in accordance with the output signal of the frequency sensitive element; and

Sweeping the reference signal over a predefined range of tuning values and selecting a particular output signal of the frequency sensitive element to produce a desired oscillating signal frequency;

Wherein the predefined range of tuning values correspond to at least a pass frequency range of a band pass filter.

2. The method of claim 1, wherein the frequency sensitive element is a band pass filter.

3. The method of claim 1, wherein the pass frequency range of the band pass filter includes a desired frequency for the operation of an electronic device.

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

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

6. The method of claim 5, 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.

7. The method of claim 1, further including 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.

8. 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.

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

generating a reference signal independent of any fixed reference source;

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;

controlling the frequency of the oscillating signal by modifying an attribute of the reference signal in accordance with the output signal of the frequency sensitive element; and

sweeping the reference signal over a predefined range of tuning values and selecting a particular output signal of the frequency sensitive element to produce a desired oscillating signal frequency;

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.

10. The method of claim 9, further comprising:

determining two border tuning values which result in cut off frequencies which are at the edges of the pass band of the band pass filter; and

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

11. An electronic device comprising:

a feedback oscillator circuit configured to generate an oscillating signal whose frequency is based on an incoming reference signal independent of any fixed reference source;

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

a capacitive touch sensitive panel configured to receive the oscillating signal and generate an output signal based on the frequency of the oscillating signal; and

a controller configured to receive the output signal and modify the value of the control signal based on the value of the output signal.

12. The electronic device of claim 11, the capacitive touch sensitive panel comprising at least one sensing electrode configured to receive the oscillating signal and generate the output signal, the at least one sensing electrode having bandpass filter characteristics.