Patent ID: 7924029

Claim:
An input device for receiving user input, the input device comprising: a first comparator including a first comparator input, a first comparator output, and a first reference voltage; a first capacitive element including a first capacitance, a first electrode coupled to the first comparator input, and a second electrode; a first biasing element coupled to the first electrode of the first capacitive element; a digitally-controlled voltage waveform generator for generating a varying waveform, the voltage waveform generator including a voltage waveform generator output coupled to the second electrode of the first capacitive element; a second capacitive element including a second capacitance and a third electrode coupled to the first comparator input such that a first output signal of the first comparator is dependent on a ratio of capacitances comprising the first capacitance and the second capacitance; and a controller coupled to the first comparator output, the controller programmed to control the digitally-controlled voltage waveform generator such that the varying waveform is controllably varied with a searching algorithm to cause a voltage at the first comparator input to be near the first reference voltage, and such that the varying waveform more quickly causes the voltage at the first comparator input to repeatedly cross the first reference voltage and trip the first comparator output, and wherein the controller is further configured to determine a measure of the ratio of capacitances from when the first comparator output tripped, and generate position information for objects in a sensing region from the measure of the ratio of capacitances, wherein: at least one of the first capacitive element and the second capacitive element is a variable capacitive element.