ASIC controller for light-based touch screen
A controller including a chip package coupled with a light-based touch screen, emitter driver circuitry inside the chip package for selectively activating photoemitters that are outside of the chip package, detector driver circuitry inside the chip package for selectively activating photo detectors that are outside of the chip package, detector signal processing circuitry for generating detection signals representing amounts of light detected on the photo detectors, signal conducting pins for connecting the photoemitters to the emitter driver circuitry, signal conducting pins for connecting the photo detectors to the detector driver circuitry and to the detector signal processing circuitry, controller circuitry inside the chip package for controlling the emitter driver circuitry and the detector driver circuitry, and at least one input/output pin for outputting the detection signals to a host processor, for the host processor to identify one or more locations on the touch screen that are being touched.
1. A controller for a light-based touch screen comprising:
a chip package coupled with a screen, with a plurality of photoemitters, with a plurality of photo detectors and with a host processor, and comprising:
at least one register for storing pulse durations configured for the photoemitters;
an emitter driver for selectively activating the plurality of photoemitters that are outside of said chip package in accordance with the configured pulse durations;
a detector driver for selectively activating the plurality of photo detectors that are outside of said chip package;
a signal processor for generating detection signals representing measured amounts of light detected on the plurality of photo detectors; and
a scan controller for controlling said emitter driver and said detector driver to pair fewer emitter activations with detector activations in a low power mode, to pair more emitter activations with detector activations in a full power mode, and to activate at least 50 distinct emitter-detector pairs in 1 millisecond or less;
a first plurality of signal conducting pins for connecting the plurality of photoemitters outside the chip package to said emitter driver;
a second plurality of signal conducting pins for connecting the plurality of photo detectors outside the chip package to said detector driver and to said processor; and
at least one input/output pin for outputting the detection signals generated by said signal processor to the host processor, for the host processor to identify therefrom one or more locations on the screen that are being touched.
2. The controller of claim 1 , wherein said scan controller controls said emitter driver and said detector driver to activate the same photoemitter twice, once followed by activation of a first photo detector, and once followed by activation of a second photo detector.
3. The controller of claim 1 , wherein the host processor detects an initial touch location of a first of two fingers when a user places two fingers on the screen, and subsequently detects the second touch location of the two fingers based on the detected initial touch location.
4. The controller of claim 1 wherein said signal processor comprises:
an amplifier for amplifying the detection signals; and
an analog-to-digital controller (ADC) for digitizing the amplified detection signals,
wherein said scan controller conserves power by deactivating said amplifier and said ADC between detector activations.
5. The controller of claim 1 , wherein the host processor identifies touch locations at a rate of at least 100 Hz, and wherein the host processor enhances a signal-to-noise ratio for the identified touch locations based on statistics of multiple iterations of activating at least 50 emitter-detector pairs for each identified touch location.
6. The controller of claim 5 , wherein the controller consumes less than 22 milliwatts of power.
7. The controller of claim 1 , wherein the photoemitters and photo detectors are arranged such that beams emitted from adjacent photoemitters located along one edge of the screen are detected by the same detector located along the opposite edge of the screen, and wherein said scan controller controls said emitter driver and said detector driver to generate alternating scan sequences, which alternately activate one or the other of the neighboring photoemitters followed by activation of the opposite detector.
8. The controller of claim 1 , wherein said emitter driver comprises a programmable current source, for driving the photoemitters.
9. The controller of claim 1 , wherein said signal processor comprises circuitry for filtering current received from the photo detectors.
10. The controller of claim 9 , wherein said circuitry for filtering current comprises circuitry to perform a continuous feedback bandpass filter.
11. The controller of claim 10 , wherein said signal processor comprises circuitry for digitizing the bandpass filtered current.
12. The controller of claim 11 , wherein said signal processor subtracts a first current value representing an ambient light value from a second current value representing light detected during activation of a photoemitter.
13. The controller of claim 1 , wherein said scan controller controls said emitter driver and said detector driver to activate the photoemitters and the photo detectors in order according to a user-defined sequence.
14. The controller of claim 1 , wherein said scan controller controls said emitter driver and said detector driver to activate a user-defined subset of the photoemitters and a user-defined subset of the photo detectors in order according to a user-defined sequence.
15. A touch screen system in accordance with claim 1 , comprising:
a housing;
a surface mounted on said housing;
a host processor mounted in said housing, for determining touch locations on said surface;
a plurality of light emitters for emitting light that is transmitted over said surface;
a plurality of light detectors for producing output values based on detected light emitted by said emitters; and
first and second controllers, each being a controller according to claim 1 , each executing program code and each connected to said host processor, to respective first and second subsets of said light emitters and said light detectors, for receiving scan configuration settings from said host processor, for activating the respective first and second subsets of said light emitters and said light detectors in a sequence in accordance with the scan configuration settings, and for storing detector output values.
16. The touch screen system of claim 15 wherein the first and second subsets are such that a light detector belongs to both subsets and receives light from a first light emitter belonging to the first subset and receives light from a second light emitter belonging to the second subset, and wherein the detector output values for detected light emitted by the first light emitter are stored by said first controller and the detector output values for detected light emitted by the second light emitter are stored by said second controller.
17. The controller of claim 1 , wherein said chip package comprises at least one additional register connected to said signal processor for storing detection signal values generated by a sequence of photoemitter activations and photo detector activations, and wherein said chip package outputs the stored detection signal values to the host processor after completion of the sequence of activations, for the host processor to identify one or more locations on the screen that are being touched.
18. A controller for a light-based touch screen comprising:
a chip package coupled with a screen, with a plurality of photoemitters, with a plurality of photo detectors and with a host processor, the photoemitters being coupled with refracting lenses that generate three directional beams for each photoemitter, the three beams diverging at approximately 45° from one another, and comprising:
at least one register for storing pulse durations configured for the photoemitters;
an emitter driver for selectively activating the plurality of photoemitters that are outside of said chip package in accordance with the configured pulse durations;
a detector driver for selectively activating the plurality of photo detectors that are outside of said chip package;
a signal processor for generating detection signals representing measured amounts of light detected on the plurality of photo detectors; and
a scan controller for controlling said emitter driver and said detector driver to pair fewer emitter activations with detector activations in a low power mode, to pair more emitter activations with detector activations in a full power mode, and to activate the photoemitters and the photo detectors so that each of the three directional beams for each photoemitter is detected by a photo detector;
a first plurality of signal conducting pins for connecting the plurality of photoemitters outside the chip package to said emitter driver;
a second plurality of signal conducting pins for connecting the plurality of photo detectors outside the chip package to said detector driver and to said processor; and
at least one input/output pin for outputting the detection signals generated by said signal processor to the host processor, for the host processor to identify therefrom one or more locations on the screen that are being touched.
19. The controller of claim 18 , wherein said scan controller controls said emitter driver and said detector driver to activate the same photoemitter twice, once followed by activation of a first photo detector, and once followed by activation of a second photo detector.
20. The controller of claim 18 wherein said signal processor comprises:
an amplifier for amplifying the detection signals; and
an analog-to-digital controller (ADC) for digitizing the amplified detection signals,
wherein said scan controller conserves power by deactivating said amplifier and said ADC between detector activations.
21. The controller of claim 18 , wherein the photoemitters and photo detectors are arranged such that beams emitted from adjacent photoemitters located along one edge of the screen are detected by the same detector located along the opposite edge of the screen, and wherein said scan controller controls said emitter driver and said detector driver to generate alternating scan sequences, which alternately activate one or the other of the neighboring photoemitters followed by activation of the opposite detector.
22. The controller of claim 18 , wherein said emitter driver comprises a programmable current source, for driving the photoemitters.
23. The controller of claim 18 , wherein said signal processor comprises circuitry for filtering current received from the photo detectors.
24. The controller of claim 23 , wherein said circuitry for filtering current comprises circuitry to perform a continuous feedback bandpass filter.
25. The controller of claim 24 , wherein said signal processor comprises circuitry for digitizing the bandpass filtered current.
26. The controller of claim 25 , wherein said signal processor subtracts a first current value representing an ambient light value from a second current value representing light detected during activation of a photoemitter.
27. The controller of claim 18 , wherein said scan controller controls said emitter driver and said detector driver to activate the photoemitters and the photo detectors in order according to a user-defined sequence.
28. The controller of claim 18 , wherein said scan controller controls said emitter driver and said detector driver to activate a user-defined subset of the photoemitters and a user-defined subset of the photo detectors in order according to a user-defined sequence.
29. A touch screen system in accordance with claim 18 , comprising:
a housing;
a surface mounted on said housing;
a host processor mounted in said housing, for determining touch locations on said surface;
a plurality of light emitters for emitting light that is transmitted over said surface;
a plurality of light detectors for producing output values based on detected light emitted by said emitters; and
first and second controllers, each being a controller according to claim 18 , each executing program code and each connected to said host processor, to respective first and second subsets of said light emitters and said light detectors, for receiving scan configuration settings from said host processor, for activating the respective first and second subsets of said light emitters and said light detectors in a sequence in accordance with the scan configuration settings, and for storing detector output values.
30. The touch screen system of claim 29 wherein the first and second subsets are such that a light detector belongs to both subsets and receives light from a first light emitter belonging to the first subset and receives light from a second light emitter belonging to the second subset, and wherein the detector output values for detected light emitted by the first light emitter are stored by said first controller and the detector output values for detected light emitted by the second light emitter are stored by said second controller.
31. The controller of claim 18 , wherein said chip package comprises at least one additional register connected to said signal processor for storing detection signal values generated by a sequence of photoemitter activations and photo detector activations, and wherein said chip package outputs the stored detection signal values to the host processor after completion of the sequence of activations, for the host processor to identify one or more locations on the screen that are being touched.