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Active stylus and control circuit thereof

  • US 9,965,056 B2
  • Filed: 03/02/2016
  • Issued: 05/08/2018
  • Est. Priority Date: 03/02/2016
  • Status: Active Grant
First Claim
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1. 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, andwherein 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.

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