Active stylus self-capacitance measurement

摘要

In one embodiment, a method includes modifying an amount of charge of a capacitance of a touch sensor. The modified amount of charge results in a voltage at the capacitance being a first pre-determined voltage level. The method also includes applying a first pre-determined amount of charge to the capacitance. The application of the first pre-determined amount of charge to the capacitance modifies the voltage at the capacitance from the first pre-determined voltage level to a first charging voltage level. The method also includes determining a first voltage at a sampling capacitor. The first voltage is proportional to a difference between the first charging voltage level and a reference voltage level. The method also includes determining whether a touch and stylus input to the touch sensor has occurred based on the first voltage and a second voltage.

主权项

1. A method comprising:
modifying an amount of charge of a capacitance of a touch sensor, the modified amount of charge resulting in a voltage at the capacitance being a first pre-determined voltage level; applying a first pre-determined amount of charge to the capacitance, the application of the first pre-determined amount of charge to the capacitance modifying the voltage at the capacitance from the first pre-determined voltage level to a first charging voltage level; determining a first voltage at a sampling capacitor, the first voltage being proportional to a difference between the first charging voltage level and a reference voltage level; applying, while holding the capacitance at the reference voltage level, a second pre-determined amount of charge to the capacitance by a first edge of a signal transmitted by a stylus, wherein applying the first predetermined amount of charge comprises applying a first amount of current to the capacitance prior to receiving the first edge of the signal transmitted by the stylus; determining a second voltage at the sampling capacitor, the second voltage being proportional to the second pre-determined amount of charge; and determining whether a touch and stylus input to the touch sensor has occurred based on the first voltage and the second voltage.