Reduction of Electromagnetic Interference in a Capacitive Touchscreen System
First Claim
13. A processor for a capacitive touchscreen system comprising a touchscreen comprising a first plurality of electrically conductive drive electrodes arranged in rows or columns, and a second plurality of electrically conductive, sense electrodes arranged in rows or columns arranged at an angle with respect to the rows or columns of the first plurality of electrodes, mutual capacitances existing between the first and second pluralities of electrodes at locations where the first and second pluralities of electrodes intersect, such mutual capacitances changing in the presence of one or more fingers or touch devices brought into proximity thereto, a system ground being associated with the capacitive touchscreen system, an electric field ground being associated with the one or more fingers or touch devices and the touchscreen, the processor comprising:
- at least one drive circuit operably connected to the first plurality of electrodes and configured to provide drive signals of high and low states thereto;
a plurality of sense circuits, one each of the sense circuits being operably connected to corresponding ones of the second plurality of electrodes;
wherein each of the sense circuits comprises a charge integrator circuit and a switched capacitance filtering circuit, the charge integrator circuit being configured to receive input signals provided by a corresponding one of the second plurality of electrodes and to provide integrated signals to the switched capacitance filtering circuit, the switched capacitance filtering circuit being configured to sample and store in first and second capacitors, respectively, first and second integrated signals delivered thereto by the charge integrator circuit where the first integrated signal corresponds to the high state drive signal, and the second integrated signal corresponds to the low state drive signal, the switched to capacitance filtering circuit being configured to provide an output signal representative of the mutual capacitance of the one of the second plurality of electrodes corresponding to the sense circuit and further having an electromagnetic interference voltage between the system ground and the electric field ground substantially filtered therefrom by the twitched capacitance filtering is circuit.
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Accused Products
Abstract
Disclosed herein are various embodiments of circuits and methods for reducing electromagnetic interference in mutual capacitance measurement or sensing systems, devices, components and methods such as capacitive touchscreens. Charge integrator circuits and switched capacitance filtering circuits are disclosed that improve the signal-to-noise ratio (or the ratio of a desired sensed mutual capacitance signal to an undesired EMI signal) in a capacitive sensor readout circuit without the need to increase the amplitude of the drive signal. The various embodiments of the charge integrator and switched capacitance filtering circuits described herein permit an improvement in noise immunity without requiring the excessive power levels typically associated with high amplitude drive circuitry, and moreover result in boosting signal-to-noise ratios during early stages of signal processing.
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Citations
39 Claims
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13. A processor for a capacitive touchscreen system comprising a touchscreen comprising a first plurality of electrically conductive drive electrodes arranged in rows or columns, and a second plurality of electrically conductive, sense electrodes arranged in rows or columns arranged at an angle with respect to the rows or columns of the first plurality of electrodes, mutual capacitances existing between the first and second pluralities of electrodes at locations where the first and second pluralities of electrodes intersect, such mutual capacitances changing in the presence of one or more fingers or touch devices brought into proximity thereto, a system ground being associated with the capacitive touchscreen system, an electric field ground being associated with the one or more fingers or touch devices and the touchscreen, the processor comprising:
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at least one drive circuit operably connected to the first plurality of electrodes and configured to provide drive signals of high and low states thereto; a plurality of sense circuits, one each of the sense circuits being operably connected to corresponding ones of the second plurality of electrodes; wherein each of the sense circuits comprises a charge integrator circuit and a switched capacitance filtering circuit, the charge integrator circuit being configured to receive input signals provided by a corresponding one of the second plurality of electrodes and to provide integrated signals to the switched capacitance filtering circuit, the switched capacitance filtering circuit being configured to sample and store in first and second capacitors, respectively, first and second integrated signals delivered thereto by the charge integrator circuit where the first integrated signal corresponds to the high state drive signal, and the second integrated signal corresponds to the low state drive signal, the switched to capacitance filtering circuit being configured to provide an output signal representative of the mutual capacitance of the one of the second plurality of electrodes corresponding to the sense circuit and further having an electromagnetic interference voltage between the system ground and the electric field ground substantially filtered therefrom by the twitched capacitance filtering is circuit. - View Dependent Claims (1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27)
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24-1. The processor of claim 13, further comprising a reset circuit configured to drain charge remaining on each of the second plurality of electrodes after a sense cycle has been completed.
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28. A method of reducing electromagnetic interference in a capacitive touchscreen system comprising a touchscreen comprising a first plurality of electrically conductive drive electrodes arranged in rows or columns, and a second plurality of electrically conductive sense electrodes arranged in rows or columns arranged at an angle with respect to the rows or columns of the first plurality of electrodes, mutual capacitances existing between the first and second pluralities of electrodes at locations where the first and second pluralities of electrodes intersect, such mutual capacitances changing in the presence of one or more fingers or touch devices brought into proximity thereto, a system ground being associated with the capacitive touchscreen system, an electric field ground being associated with the one or more fingers or touch devices and the touchscreen, the method comprising:
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sequentially driving the first plurality of electrodes with alternating high and low state drive signals; sensing the mutual capacitances associated with each of the second plurality of electrodes during the high and low state drive signals with a charge integrator circuit for each sense circuit; for each charge integrator circuit, providing first and second integrated signals corresponding to the high and low state drive signals, respectively, to a switched capacitance filtering circuit; sampling and storing in first and second capacitors, respectively, of the switched capacitance filtering circuit the first and second integrated signals; providing, with the switched capacitance filtering circuit, an output signal representative of the mutual capacitance of the one of the second plurality of electrodes corresponding to the sense circuit and further having an electromagnetic interference voltage between the system ground and the electric field ground substantially filtered therefrom by the switched capacitance filtering circuit. - View Dependent Claims (29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39)
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Specification