Adaptive frequency touchscreen controller employing digital signal processing

• US 6,473,075 B1
• Filed: 09/29/1999
• Issued: 10/29/2002
• Est. Priority Date: 09/29/1999
• Status: Expired due to Term

• Current Assignee: Elo Touch Solutions, Inc.
• Original Assignee: Elo Touchsystems Incorporated (Elo Touch Solutions, Inc.)
• Inventors: Ravid, Arie, Gomes, Paulo Irulegui, Kent, Joel, Kaneda, Hiroshi, Kambara, Shigeki
• Primary Examiner(s): Chauhan, Ulka J.
• Assistant Examiner(s): Eisen, Alexander
• Application Number:
  US09/408,591
• Time in Patent Office: 1,126 Days
• Field of Search: 345/173-178, 178/18.01, 178/18.09, 178/19-1-, 178/20-1-
• US Class Current: 345/177
• CPC Class Codes: G06F 3/0418 for error correction or compensation, e.g. based on parallax, calibration or alignment
• CPC Class Codes: G06F 3/0436 in which generating transducers and detecting transducers are attached to a single acoustic waves transmission substrate

Abstract

A method and apparatus for adapting an acoustic touchscreen controller to the operating frequency requirements of a specific touchscreen are provided. The adaptive controller can either utilize look-up tables to achieve the desired output frequency or the it can use a multi-step process in which it first determines the frequency requirements of the touchscreen, and then adjusts the burst frequency characteristics, the receiver circuit center frequency, or both in accordance with the touchscreen requirements. In one embodiment, the adaptive controller compensates for global frequency mismatch errors. In this embodiment a digital multiplier is used to modify the output of a crystal reference oscillator. The reference oscillator output is used to control the frequency of the signal from the receiving transducers and/or to generate the desired frequency of the tone burst sent to the transmitting transducers. In another embodiment that is intended to compensate for both global and local frequency variations, the adaptive controller uses a digital signal processor. The digital signal processor, based on correction values contained in memory, defines a specific center frequency which preferably varies according to the signal delay, thus taking into account variations caused by localized variations in the acoustic wave reflective array. In yet another embodiment, a non-crystal local oscillator is used to provide the reference signal in the adaptive controller. The use of such an oscillator allows the controller to be miniaturized to a sufficient extent that it can be mounted directly to a touchscreen substrate. A feedback loop is used to compensate for oscillator drift. A discriminator circuit determines the degree of deviation from the desired frequency. The output from the discriminator is used to adjust the frequency of the local oscillator such that it tracks the frequency of the touchscreen.

Claims

1. A touchscreen system, comprising:

a touchscreen substrate, said substrate capable of propagating acoustic waves;

at least one transmitting transducer coupled to said substrate, said transmitting transducer initiating an acoustic wave of a first burst length in response to an input signal;

a reflective array comprised of a plurality of acoustic wave reflectors coupled to said substrate, said reflective array stretching said first burst length to form a second burst length acoustic wave;

at least one receiving transducer coupled to said substrate, said receiving transducer receiving said acoustic wave of said second burst length; and

an adaptive controller coupled to said at least one transmitting transducer and to said at least one receiving transducer, said adaptive controller comprising;

a reference oscillator generating a first frequency;

a microprocessor coupled to said reference oscillator;

a digital burst circuit coupled to said microprocessor, said reference oscillator, and to said at least one transmitting transducer, said digital burst circuit outputting said input signal to said at least one transmitting transducer in response to a burst control signal; and

a memory coupled to said microprocessor, said memory containing a set of frequency correction values, wherein said microprocessor receives the first frequency and correction instructions regarding a desired center frequency from the memory based upon the set of frequency correction values and generates and outputs said burst control signal to said digital burst circuit based upon the correction instructions.

2. The touchscreen system of claim 1, wherein said reference oscillator is a crystal oscillator.

3. The touchscreen system of claim 1, wherein said burst control signal is a bit pattern.

4. The touchscreen system of claim 1, wherein said set of frequency correction values is communicated to said memory by said microprocessor.

5. The touchscreen system of claim 1, further comprising a burst amplifier coupled to said digital burst circuit.

6. The touchscreen system of claim 1, further comprising a frequency divider coupled to said reference oscillator.

7. The touchscreen system of claim 1, wherein said at least one transmitting transducer is a grating transducer.

8. A touchscreen system, comprising:

a touchscreen substrate, said substrate capable of propagating acoustic waves;

at least one transmitting transducer coupled to said substrate, said transmitting transducer initiating an acoustic wave of a first burst length in response to an input signal;

a reflective array comprised of a plurality of acoustic wave reflectors coupled to said substrate, said reflective array stretching said first burst length to form a second burst length acoustic wave;

at least one receiving transducer coupled to said substrate, said receiving transducer receiving said acoustic wave of said second burst length; and

an adaptive controller coupled to said at least one transmitting transducer and to said at least one receiving transducer, said adaptive controller comprising;

a reference oscillator generating a first frequency;

a microprocessor coupled to said reference oscillator;

a first mixer coupled to said at least one receiving transducer and to said reference oscillator, said first mixer outputting a first mixer output signal;

a phase shifter coupled to said reference oscillator for shifting a phase corresponding to an output of said reference oscillator by 90 degrees;

a second mixer coupled to said at least one receiving transducer and to said phase shifted output of said phase shifter, said second mixer outputting a second mixer output signal;

a first A-D converter coupled to said first mixer;

a second A-D converter coupled to said second mixer;

a digital signal processor coupled to said first and second A-D converters and to said microprocessor;

a digital burst circuit coupled to said microprocessor, said reference oscillator, and to said at least one transmitting transducer, said digital burst circuit outputting said input signal to said at least one transmitting transducer in response to a burst control signal; and

a memory coupled to said digital signal processor and to said microprocessor, said memory containing a set of frequency correction values, wherein said microprocessor receives the first frequency and correction instructions regarding a desired center frequency from the memory based upon the set of frequency correction values and generates and outputs said burst control signal to said digital burst circuit based upon the correction instructions.

9. The touchscreen system of claims 8, wherein said reference oscillator is a crystal oscillator.

10. The touchscreen system of claim 8, wherein said burst control signal is a bit pattern.

11. The touchscreen system of claim 8, wherein said set of frequency correction values is communicated to said memory by said microprocessor.

12. The touchscreen system of claim 8, further comprising a burst amplifier coupled to said digital burst circuit.

13. The touchscreen system of claim 8, further comprising a frequency divider coupled to said reference oscillator.

14. The touchscreen system of claim 8, wherein said at least one transmitting transducer is a grating transducer.