Multiple capacitance measuring circuits and methods

This patent document claims the benefit under 35 U.S.C. § 119(e) of U.S. Provisional Patent Application Ser. No. 61/017,451, entitled “Multiple Capacitance Measuring Circuits and Methods” as was filed on Dec. 28, 2007, the disclosure of which is incorporated by reference herein in its entirety.

The present invention relates generally to circuits and methods for measuring multiple capacitances, and to systems such as capacitive touch sensing systems that utilize multiple capacitance measuring circuits and methods, and in particular to mitigating current flow between capacitance measurement locations in such circuits and methods.

Touch sensitive devices allow a user to conveniently interface with electronic systems and displays by reducing or eliminating the need for mechanical buttons, keypads, keyboards, and pointing devices. For example, a user can carry out a complicated sequence of instructions by simply touching an on-display touch screen at a location identified by an icon. In many touch sensitive devices, the input is sensed when a conductive object in the sensor is capacitively coupled to a conductive touch implement such as a user\'s finger. Such devices measure capacitance at multiple locations due to the touch disturbance, and use the measured capacitances to determine touch position.

In certain embodiments, the present invention provides methods (and corresponding circuitry) for use in a touch sensor device that measures capacitances at a plurality of locations on a touch surface in response to a touch object coupling to the touch surface at a touch position, the capacitances being measured by applying electrical charge to the plurality of locations to ramp respective voltage signals between a first reference level and a second reference level. Such methods include controlling the phase of the voltage signal ramps to mitigate currents flowing between the locations. In certain embodiments, controlling the phase of the voltage signal ramps includes concurrently starting the voltage signal ramps, for example by effecting a delay on at least one signal channel that has reached a voltage threshold, or by regulating all the voltage ramps according to a fixed frequency. In certain embodiments, time differentials between when respective voltage signal ramps reach a threshold level can be determined, and subsequent ramp starting times can be adjusted in response.

In certain embodiments, the present invention provides methods for use with a device that measures capacitances at a plurality of locations, each location associated with a capacitance measurement channel to ramp respective voltage signals on the respective capacitances. Such methods include (a) concurrently initiating forward-direction voltage signal ramps on multiple channels, and (b) effecting a delay on the forward-direction voltage signal ramp of at least one channel in response to reaching a voltage signal threshold. In certain embodiments, such methods can further include (c) concurrently initiating reverse-direction voltage signal ramps on the multiple channels, and (d) effecting a delay on the reverse-direction voltage signal ramp of at least one channel in response to reaching a low voltage signal threshold. Such alternate forward and reverse ramping can be repeated a desired number of times.

In certain embodiments, the present invention provides capacitive touch sensor devices for determining touch position by measuring capacitances at a plurality of locations on a touch surface in response to a touch object coupling to the touch surface at the touch position. Such devices include circuitry associated with each location to ramp respective voltage signals between a first reference level and a second reference level by applying an electrical charge, and circuitry to control the phase of the voltage signal ramps to mitigate currents flowing between the locations.

The above summary of the present invention is not intended to describe each embodiment or every implementation of the present invention. Advantages and attainments, together with a more complete understanding of the invention, will become apparent and appreciated by referring to the following detailed description and claims taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure may be more completely understood and appreciated in consideration of the following detailed description of various embodiments in connection with the accompanying drawings, in which:

FIGS. 1A and 1B schematically show exemplary touch sensor systems useful in certain embodiments of the present invention;

FIG. 2 schematically shows an exemplary control circuit useful in certain embodiments of the present invention;

FIG. 3 schematically shows a timing diagram indicating operation of a multiple capacitance measurement circuit in accordance with certain embodiments of the present invention;

FIG. 4 schematically shows a timing diagram indicating operation of a multiple capacitance measurement circuit in accordance with certain embodiments of the present invention;

FIG. 5 schematically shows a timing diagram indicating operation of a multiple capacitance measurement circuit in accordance with certain embodiments of the present invention;

FIG. 6 schematically shows a timing diagram indicating operation of a multiple capacitance measurement circuit in accordance with certain embodiments of the present invention;

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