Differential-difference-amplifier-based touch sensor interface
AssigneeShenzhen Goodix Technology Co., Ltd.
InventorsMohamed ELSAYED, Cheng ZHU
Life of this patent
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Abstract
Techniques are described for touch event sensing in a capacitive touch panel that is integrated with a display. In some such environments, a large amount of display noise is capacitively coupled with the touch sensing signals. This can degrade performance of conventional sensing approaches, which tend to use a buffering stage followed by a difference amplifier stage. Embodiments provide a single-stage, differential-difference-amplifier-based touch event sensing approach that pre-cancels coupled display noise from adjacent channels by common-mode rejection prior to amplifying, thereby generating amplified differential output signals that include substantially only the desired touch sensing information.
Claims19
A system for sensing a touch event in a touch panel integrated with a display, the system comprising:
- a differential difference amplifier (DDA) comprising:
- a differential pair of amplifier outputs having a positive output and a negative output, each to output a respective one of a differential pair of output signals;
- a first differential pair of amplifier inputs having a first positive input and a first negative input, the first positive input coupled with a first channel response signal corresponding to a first capacitive response of a first channel capacitor combined with coupled display noise, and the first negative input coupled with a second channel response signal corresponding to a second capacitive response of a second channel capacitor combined with the coupled display noise;
- and
- a second differential pair of amplifier inputs having a second positive input and a second negative input, the second positive input coupled in feedback with the positive output, and the second negative input coupled in feedback with the negative output,
- such that the differential pair of outputs corresponds to an amplified version of a difference between the first capacitive response and the second capacitive response.
A display system comprising:
- a touch panel for integration with a display, the touch panel comprising N touch sense channels formed by a grid of row lines and column lines, each nth touch sense channel manifesting an nth capacitive response to presence of a touch event local to the nth touch sense channel, N being an integer greater than 1;
- and
- N−1 differential difference amplifiers (DDAs), each nth DDA comprising:
- an nth differential pair of amplifier outputs having an nth positive output and an nth negative output, each to output a respective one of an nth differential pair of output signals;
- an nth first differential pair of amplifier inputs having an nth first positive input and an nth first negative input, the nth first positive input to receive, via the nth touch sense channel, an nth channel response signal indicating the nth capacitive response combined with coupled display noise, and the nth first negative input to receive, via the (n+1)th touch sense channel, an (n+1)th channel response signal indicating the (n+1)th capacitive response combined with coupled display noise;
- and
- an nth second differential pair of amplifier inputs having an nth second positive input and an nth second negative input, the nth second positive input coupled in feedback with the nth positive output, and the nth second negative input coupled in feedback with the nth negative output,
- such that each nth differential pair of outputs corresponds to an amplified version of a difference between the nth capacitive response and the (n+1)th capacitive response.
A method for touch event sensing, the method comprising:
- generating first and second differential output signals at a differential pair of amplifier outputs by:
- receiving, at a first of a first differential pair of amplifier inputs via a first touch sense channel of a touch panel, a first channel response signal manifesting a first touch response and a display noise, the first touch response indicating whether there is presence of a touch event local to the first touch sense channel;
- receiving, at a second of the first differential pair of amplifier inputs via a second touch sense channel of a touch panel, a second channel response signal manifesting a second touch response and the display noise, the second touch response indicating whether there is presence of a touch event local to the second touch sense channel;
- receiving, at a first of a second differential pair of amplifier inputs via a first voltage divider branch, feedback of the first differential output signal;
- and
- receiving, at a second of the second differential pair of amplifier inputs via a second voltage divider branch, feedback of the second differential output signal,
- such that the first and second differential output signals include an amplified version of a difference between the first touch response and the second touch response with the display noise at least partially canceled.
Dependencies are inferred from the claim text.