Proximity/touch detector and calibration circuit
AssigneeApple Computer, Inc.
InventorsChristoph H. Krah, Richard D. Cappels
Life of this patent
Estimating the term…
Abstract
A calibration circuit and method for a proximity/touch detector allow automatic calibration to the proximity/touch detector components, chassis affects, and ambient conditions such that initial factory calibration and periodic manual calibration are not needed. The calibration circuit switches a capacitance into the input capacitance of a Schmitt trigger free running oscillator to change the output frequency of the oscillator. A capacitive sensor forms part of the input capacitance. The change in frequency simulates the frequency shift associated with the difference in input capacitance generated when an object, such as a finger, is touching the capacitive sensor and when the capacitive sensor is free from contact with the object.
Claims9
A calibration circuit, comprising:
- a transistor and a first capacitor coupled to each other;
- a second capacitor coupled in series with the first capacitor and the transistor;
- a capacitive sensor coupled in series with the second capacitor, the first capacitor and the transistor;
- an oscillator coupled to the capacitive sensor and the second capacitor;
- and
- a microprocessor coupled to turn the transistor “on” to decrease an actual input capacitance to the oscillator to simulate an input capacitance associated with an object not being in contact with the capacitive sensor or to turn the transistor “off” to increase an actual input capacitance to the oscillator to simulate an input capacitance associated with an object being in contact with the capacitive sensor.
Dependencies are inferred from the claim text.