Active stylus and control circuit thereof
AssigneeFiftyThree, Inc.
InventorGary Gordon
Life of this patent
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Abstract
The present disclosure provides systems and methods for receiving an input signal from a touch-sensitive interface via a first electrode associated with a tip of an active stylus. An input signal may be amplified via a control circuit that adjusts the gain of one or more amplifiers to compensate for changes in tip capacitance between the tip of the active stylus and the touch-sensitive interface. Changes in tip capacitance may be indirectly detected and compensated for by comparing the tip capacitance with that of a reference capacitor via a differential amplification circuit that includes one or more differential amplifiers.
Claims27
A control circuit for an active stylus comprising:
- a first electrode associated with the tip of an active stylus configured to receive an input signal from a touch-sensitive interface and support;
- a capacitive bridge comprising at least three capacitors, including a first capacitor connecting the first electrode to a second capacitor and a reference capacitor connecting the second capacitor to a second electrode;
- a transformer comprising a primary winding and a secondary winding, wherein the secondary winding connects a junction of the first capacitor and the second capacitor to the second electrode;
- a first differential amplifier with a first input connected to the first electrode and a second input connected to a junction of the second capacitor and the reference capacitor;
- a compensation amplifier configured to amplify a signal from the junction of the second capacitor and the reference capacitor;
- and
- a second differential amplifier with a first input connected to an output of the first differential amplifier and a second input connected to an output of the compensation amplifier,
- wherein the primary winding of the transformer connects the output of the second differential amplifier to the second electrode, and
- wherein the gain of the compensation amplifier is dynamically adjusted based at least partially on a difference between a capacitance of the reference capacitor and a capacitance between the first electrode and the touch-sensitive interface.
An active stylus comprising:
- an elongated body comprising an outer housing;
- a tip for contacting a surface of a touch-sensitive device, wherein the tip is associated with a first electrode;
- a second electrode;
- and
- a control circuit configured to adjust a gain of at least one amplification stage based on a difference in (1) a capacitance of a fixed reference capacitor and (2) tip capacitance, wherein the tip capacitance is based at least in part on a capacitance of the first electrode relative to the touch-sensitive device.
Dependencies are inferred from the claim text.