Adaptive frequency touchscreen controller using intermediate-frequency signal processing

• US 6,396,484 B1
• Filed: 09/29/1999
• Issued: 05/28/2002
• Est. Priority Date: 09/29/1999
• Status: Expired due to Fees

• Current Assignee: Tyco Electronics Corporation (TE Connectivity Limited)
• Original Assignee: Elo Touchsystems Incorporated (Elo Touch Solutions, Inc.)
• Inventors: Wilson, Geoffrey D., Adler, Robert, Ravid, Arie
• Primary Examiner(s): Saras, Steven
• Assistant Examiner(s): Anyaso, Uchendu O.
• Application Number:
  US09/408,818
• Time in Patent Office: 972 Days
• Field of Search: 345/173,175,177,176
• US Class Current: 345/177
• 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 pattern 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 outputting a frequency;

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;

an IF bandpass filter coupled to said first mixer;

a feedback loop circuit coupled to said IF filter and to said reference oscillator, said feedback loop circuit modifying said reference oscillator frequency;

a second mixer coupled to said reference oscillator;

an IF oscillator coupled to said second mixer;

a microprocessor; and

a burst circuit coupled to said second mixer, said microprocessor, and said at least one transmitting transducer, said burst circuit outputting said input signal to said at least one transmitting transducer.

2. The touchscreen system of claim 1, said feedback loop circuit further comprising a discriminator circuit coupled to said IF bandpass filter, said discriminator circuit outputting a control signal to said reference oscillator for controlling said reference oscillator frequency.

3. The touchscreen system of claim 2, said feedback loop circuit further comprising a sample and hold circuit.

4. The touchscreen system of claim 1, further comprising a detector coupled to said IF bandpass filter and to said microprocessor.

5. The touchscreen system of claim 1, wherein an IF oscillator frequency is substantially equivalent to a passband center frequency of said IF bandpass filter.

6. The touchscreen system of claim 1, wherein said reference oscillator frequency is greater than a characteristic frequency of said touchscreen.

7. The touchscreen system of claim 1, wherein at least a portion of said adaptive controller is bonded to said touchscreen substrate.

8. The touchscreen system of claim 1, wherein said reference oscillator is comprised of an oscillator circuit.

9. The touchscreen system of claim 8, wherein said reference oscillator further comprises a silicon chip, said silicon chip containing said oscillator circuit.

10. A method of controlling a touchscreen system including a touchscreen having a characteristic frequency, the method comprising the steps of:

generating a first frequency, wherein said first frequency is adjustable;

mixing an output from a receiving transducer with said first frequency to produce a second frequency;

passing said second frequency through a band pass filter;

comparing said filtered second frequency to said touchscreen characteristic frequency; and

adjusting said first frequency until said filtered second frequency is substantially equivalent to said desired frequency.

11. The method of claim 10, wherein said second frequency is approximately 500 kHz.

12. The method of claim 10, further comprising the steps of:

setting said first frequency to an initial frequency upon system initialization;

ramping said first frequency from said initial frequency through a range of frequencies; and

discontinuing said ramping step when said filtered second frequency is within a predetermined distance from said desired frequency.

13. The method of claim 10, further comprising the steps of:

mixing said first frequency with an IF oscillator output to produce a third frequency;

transmitting said third frequency to a burst circuit;

generating a burst signal; and

transmitting said burst signal to a transmitting transducer coupled to said touchscreen system.