Synaptics Corporation

Farzaneh Shahrokhi

Adam L Schwartz

Tracy Scott Dattalo

Joseph Kurth Reynolds

Shahrooz Shahparnia

Petr Shepelev

Eric Scott Bohannon

David A Sobel

Vivek Pant

John Weinerth

Murat Ozbas

Jeremy Roberson

Zheming Li

Rafael Betancourt

Tae-Song Chung

Saikrishna Ganta

An example a processing system for a capacitive sensing device includes a reference transmitter coupled to a reference capacitance. The processing system further includes a charge accumulation circuit having an input coupled to the reference transmitter through the reference capacitance and configured to generate an integrated signal, a demodulator circuit having an input coupled to an output of the charge accumulation circuit and configured to demodulate the integrated signal to generate at least one demodulated signal, a sampling circuit having an input coupled to an output of the demodulator circuit and configured to sample the demodulated signal(s), a first reference buffer coupled to an output of the sampling circuit, the first reference buffer outputting a first voltage reference for the capacitive sensing device, and a second reference buffer coupled to the output of the sampling circuit, the second reference buffer outputting a second voltage reference for the capacitive sensing device.

Capacitive sensing device with single reference channel

Embodiments described herein include an input device with a plurality of capacitive sensor electrodes configured to receive a signal. The input device also includes a processing system coupled to the plurality of capacitive sensor electrodes. The processing system includes an analog front end (AFE). The AFE includes an anti-aliasing filter comprising a continuous time analog infinite impulse response (IIR) filter configured to filter out interference from the received signal at frequencies higher than a signal frequency of the processing system to produce an anti-aliased signal. The AFE also includes a charge integrator configured to integrate the anti-aliased signal.

Continuous time anti-alias filter for capacitive touch sensing

A capacitance measurement circuit comprises a differential amplifier with first and second inputs and an output, first and second feedback capacitances, and a reset mechanism. The first input is coupled to a modulated reference voltage and the second input is coupled with a sensor electrode. A first feedback capacitance is coupled between the output and the second input. A second feedback capacitance is coupled between the output and the second input. The reset mechanism resets the first feedback capacitance to a first level of charge and the second feedback capacitance to a second level of charge. During an absolute capacitance measurement phase, the differential amplifier charges the sensor electrode while balancing voltages on the first and second inputs to a voltage level associated with the modulated reference voltage and integrates charge on the sensor electrode to measure capacitance corresponding to a coupling between the sensor electrode and an input object.

Capacitance measurement

An interference determining circuit for a capacitive sensor device comprises an amplifier, absolute differential circuitry, and comparator circuitry. The amplifier is configured for receiving a reference voltage at a first input and for receiving a resulting signal at a second input. The resulting signal is from a sensor electrode of the capacitive sensor device. The absolute differential circuitry is coupled with an output of the amplifier and configured for outputting a difference signal. The difference signal represents an absolute differential between currents utilized in the amplifier. The comparator circuitry is coupled with the absolute differential circuitry and configured for generating a non-linearity indication based on a comparison of the difference signal with at least one reference signal.

Input device interference determination

A capacitance measurement circuit cancels background capacitance while reducing charge leakage and supply ripples during reset phases and integrate phases. The capacitance measurement circuit operates a first switch into a linear mode causing a first resistance in the first switch, and after a delay, operates a second switch into a saturation mode causing a second resistance in parallel to the first resistance.

Multi-step incremental switching scheme

A method for detecting interference in an input device, the method involving: driving a transmitter signal onto a transmitter sensor electrode of the input device; receiving a resulting signal from a receiver sensor electrode of the input device; sampling a first value associated with the resulting signal during a first half of a sensing cycle; sampling a second value associated with the resulting signal during a second half of the sensing cycle; generating an interference value based on the first value and the second value; determining, based on the first value and the second value, an input in a sensing region of the input device; and comparing the interference value to a noise threshold.

Detecting interference in an input device having electrodes

A differential amplifier has an output and differential first and second inputs. A switch disposed between a sensor electrode and the second input is opened to initiate a reset phase where the sensor electrode and the differential amplifier are decoupled. A feedback capacitance disposed between the second input and the output is reset to a first level of charge. The switch is closed to initiate a measurement phase where the second input and sensor electrode are coupled. In the measurement phase: charge is balanced between the sensor electrode and the feedback capacitance such that a sensor electrode voltage equals a voltage of the first input equals a voltage of the second input, and the sensor electrode is charged; and the differential amplifier is utilized to integrate charge on the sensor electrode, such that an absolute capacitance corresponding to a coupling between the sensor electrode and an input object is measured.

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San Jose, CA, United States of America

Farzaneh Shahrokhi