Capacitive touchscreen system with touch position encoding during analog-to-digital conversion
First Claim
1. A capacitive touchscreen system, comprising:
- a touchscreen comprising a first plurality of electrically conductive drive traces and a second plurality of electrically conductive sense traces, mutual capacitances existing between the first and second pluralities of traces at locations where the first and second pluralities of traces intersect to form pixels, such mutual capacitances changing in the presence of one or more fingers or touch devices brought into proximity thereto;
drive circuitry operably connected to the first plurality of drive traces;
sense circuitry operably connected to the second plurality of sense traces and comprising charge acquisition circuitry, the sense circuitry being configured to sense the mutual capacitances along each of the second plurality of sense traces and to generate a plurality of sense voltages corresponding to the sense traces;
a plurality of comparators configured to receive as inputs thereto a threshold voltage and the sense voltages, the comparators providing comparator output signals;
an analog multiplexer having as a first input thereto the sense voltages;
a plurality of logical AND gates configured to receive as inputs thereto the comparator output signals and to provide as outputs therefrom logical AND output signals, the AND output signals being inputs to a digital multiplexer operably connected to the outputs of the plurality of logical AND gates, the analog multiplexer receiving as a digital input thereto a digital output of the digital multiplexer;
a first sum circuit configured to receive as an input thereto an output from the analog multiplexer and to provide as an output therefrom an analog-to-digital converter (ADC) reference voltage representing a sum of the sense voltages corresponding to at least one cluster of pixels associated with at least one sensed touch on the touchscreen;
a second weighted sum circuit configured to receive as an input thereto the output from the analog multiplexer and to provide as an output therefrom an input to the ADC representing a weighted sum of the sense voltages corresponding to pixels of the cluster;
wherein the outputs of the comparators and the AND gates represent at least one cluster of pixels corresponding to at least one sensed touch on the touchscreen, the output of the second weighted sum circuit represents a weighted sum of the sense voltages corresponding to pixels of the cluster, and the ADC generates as an output therefrom a position code corresponding to an interpolated location of the sensed finger or device touch.
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Accused Products
Abstract
Disclosed herein are various embodiments of circuits and methods in a capacitive touchscreen system that eliminate the need to digitize an entire array of pixel signals obtained from a touchscreen. Instead, regions of interest, or projections of object or touch signal clusters, from touchscreen 90 are employed to encode the coordinates or positions of objects or touches in an analog-to-digital converter (ADC). Encoding of object positions occurs during digitization of the analog signal clusters, which eliminates the need to separately digitize individual touchscreen signals. The disclosed circuits and methods reduce the number of signal processor channels that might otherwise be required, and lead to power consumption reduction in the capacitive touchscreen system, as well as in reducing the area required to implement the circuit architecture in an integrated circuit.
13 Citations
26 Claims
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1. A capacitive touchscreen system, comprising:
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a touchscreen comprising a first plurality of electrically conductive drive traces and a second plurality of electrically conductive sense traces, mutual capacitances existing between the first and second pluralities of traces at locations where the first and second pluralities of traces intersect to form pixels, such mutual capacitances changing in the presence of one or more fingers or touch devices brought into proximity thereto; drive circuitry operably connected to the first plurality of drive traces; sense circuitry operably connected to the second plurality of sense traces and comprising charge acquisition circuitry, the sense circuitry being configured to sense the mutual capacitances along each of the second plurality of sense traces and to generate a plurality of sense voltages corresponding to the sense traces; a plurality of comparators configured to receive as inputs thereto a threshold voltage and the sense voltages, the comparators providing comparator output signals; an analog multiplexer having as a first input thereto the sense voltages; a plurality of logical AND gates configured to receive as inputs thereto the comparator output signals and to provide as outputs therefrom logical AND output signals, the AND output signals being inputs to a digital multiplexer operably connected to the outputs of the plurality of logical AND gates, the analog multiplexer receiving as a digital input thereto a digital output of the digital multiplexer; a first sum circuit configured to receive as an input thereto an output from the analog multiplexer and to provide as an output therefrom an analog-to-digital converter (ADC) reference voltage representing a sum of the sense voltages corresponding to at least one cluster of pixels associated with at least one sensed touch on the touchscreen; a second weighted sum circuit configured to receive as an input thereto the output from the analog multiplexer and to provide as an output therefrom an input to the ADC representing a weighted sum of the sense voltages corresponding to pixels of the cluster; wherein the outputs of the comparators and the AND gates represent at least one cluster of pixels corresponding to at least one sensed touch on the touchscreen, the output of the second weighted sum circuit represents a weighted sum of the sense voltages corresponding to pixels of the cluster, and the ADC generates as an output therefrom a position code corresponding to an interpolated location of the sensed finger or device touch. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13)
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14. A method of encoding detected touch or object positions in an analog-to-digital converter (ADC) included in a capacitive touchscreen system, comprising:
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providing drive signals to a first plurality of electrically conductive drive traces, a second plurality of electrically conductive sense traces being located in proximity to the first plurality of drive traces such that mutual capacitances are developed between the first and second pluralities of traces at locations where the first and second pluralities of traces intersect to form pixels, such mutual capacitances changing in the presence of one or more fingers or touch devices brought into proximity thereto; sensing of the mutual capacitances along each of the second plurality of sense traces and generating a plurality of sense voltages corresponding to each of the sense traces; providing a threshold voltage and the sense voltages to a plurality of comparators as inputs thereto, the comparators providing comparator output signals, the comparators receiving the input sense voltages as multiplexed input signals under the control of a first multiplexer operably connected to the plurality of comparators; providing the comparator output signals to a plurality of AND gates configured as inputs thereto and generating as outputs from the AND gates AND output signals, the AND output signals being multiplexed under control of a second multiplexer operably connected to the outputs of the plurality of AND gates, the first multiplexer receiving as an input thereto an output of the second multiplexer; providing to a first sum circuit as an input thereto an output from the first multiplexer, the first sum circuit generating as an output therefrom an ADC reference voltage; providing to a second weighted sum circuit as an input thereto the output from the first multiplexer and generating as an output therefrom an input to the ADC; wherein the outputs of the comparators and the AND gates represent at least one cluster of pixels corresponding to at least one sensed finger or device touch on the touchscreen, the output of the second weighted sum circuit represents a weighted sum of the sense voltages corresponding to pixels of the cluster, the ADC generating as an output therefrom a position code corresponding to an interpolated location of the sensed object or touch. - View Dependent Claims (15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26)
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Specification