Phase calibration for capacitance touch sensing device
In an embodiment of the techniques presented herein, a touch detection system includes a touch sensor array having transmit lines, receive lines, and unit cells defined at intersections of the transmit lines and the receive lines, a transmit sequencer configured to generate a transmit signal on the transmit lines, an analog-to-digital-converter module configured to measure responses of the unit cells to the transmit signal, and a calibration unit configured to determine a first phase offset for a first unit cell of the unit cells based on a first response, of the responses, of the first unit cell, determine a second phase offset for a second unit cell of the unit cells based on a second response, of the responses, of the second unit cell, and set a phase offset parameter of the touch sensor array based on the first phase offset and the second phase offset.
1 . A method for touch detection, comprising:
determining a first phase offset for a first unit cell of a touch sensor array based on a measured response of the first unit cell;
determining a second phase offset for a second unit cell of the touch sensor array based on a measured response of the second unit cell;
determining a third phase offset for the first unit cell using a model of the touch sensor array;
determining a fourth phase offset for the second unit cell using the model of the touch sensor array; and
setting a phase offset parameter of the touch sensor array based on one of a measured response comprising the first phase offset and the second phase offset or a modeled response comprising the third phase offset and the fourth phase offset.
2 . The method of claim 1 , wherein:
the touch sensor array comprises transmit lines and receive lines;
unit cells are defined at intersections of the transmit lines and the receive lines; and
the phase offset parameter comprises a phase offset parameter of a transmit signal applied to the transmit lines.
3 . The method of claim 1 , wherein:
the touch sensor array comprises transmit lines and receive lines;
unit cells are defined at intersections of the transmit lines and the receive lines; and
the phase offset parameter comprises a phase offset of a demodulator connected to the receive lines.
4 . The method of claim 3 , wherein:
the demodulator is configured to multiply an output of an analog-to-digital converter connected to the receive lines by a demodulator reference signal; and
the phase offset parameter comprises a phase offset of the demodulator reference signal.
5 . The method of claim 1 , wherein:
the touch sensor array comprises transmit lines and receive lines;
unit cells are defined at intersections of the transmit lines and the receive lines;
the first unit cell is located at a first end of a selected transmit line of the transmit lines;
the second unit cell is located at a second end of the selected transmit line of the transmit lines; and
the phase offset parameter comprises a phase offset of a transmit signal applied to the selected transmit line of the transmit lines.
6 . The method of claim 1 , wherein:
the touch sensor array comprises transmit lines and receive lines;
unit cells are defined at intersections of the transmit lines and the receive lines;
the first unit cell is located at a first end of a selected receive line of the receive lines;
the second unit cell is located at a second end of the selected receive line of the receive lines;
the selected receive line of the receive lines is connected to a sensing channel comprising:
an analog-to-digital-converter; and
a demodulator configured to multiply an output of the analog-to-digital converter by a demodulator reference signal; and
the phase offset parameter comprises a phase offset of the demodulator reference signal.
7 . The method of claim 1 , wherein:
the model of the touch sensor array defines lumped resistance and capacitance parameters for the first unit cell and the second unit cell.
8 . A touch detection system, comprising:
a touch sensor array comprising:
transmit lines;
receive lines; and
unit cells defined at intersections of the transmit lines and the receive lines;
a transmit sequencer configured to generate a transmit signal on the transmit lines;
an analog-to-digital-converter module connected to the receive lines and configured to measure responses of the unit cells to the transmit signal;
a demodulator connected to the analog-to-digital-converter module; and
a calibration unit configured to:
determine a first phase offset for a first unit cell of the unit cells based on a first response, of the responses, of the first unit cell;
determine a second phase offset for a second unit cell of the unit cells based on a second response, of the responses, of the second unit cell; and
set a phase offset parameter of the demodulator based on the first phase offset and the second phase offset.
9 . The touch detection system of claim 8 , comprising:
a demodulator connected to the analog-to-digital-converter module, wherein:
the phase offset parameter comprises a phase offset parameter of the demodulator.
10 . The touch detection system of claim 9 , wherein:
the demodulator is configured to multiply an output of the analog-to-digital-converter module by a demodulator reference signal; and
the phase offset parameter comprises a phase offset of the demodulator reference signal.
11 . The touch detection system of claim 8 , wherein:
the first unit cell is located at a first end of a selected transmit line of the transmit lines; and
the second unit cell is located at a second end of the selected transmit line of the transmit lines.
12 . The touch detection system of claim 8 , wherein:
the first unit cell is located at a first end of a selected receive line of the receive lines;
the second unit cell is located at a second end of the selected receive line of the receive lines;
the selected receive line of the receive lines is connected to a sensing channel comprising:
an analog-to-digital-converter; and
a demodulator configured to multiply an output of the analog-to-digital converter by a demodulator reference signal; and
the phase offset parameter comprises a phase offset of the demodulator reference signal.
13 . The touch detection system of claim 12 , wherein:
the sensing channel comprises:
a filter connected to the demodulator configured to generate a response of the selected receive line of the receive lines based on an output of the demodulator.
14 . The touch detection system of claim 8 , wherein:
the calibration unit is configured to:
determine a third phase offset for the first unit cell using a model of the touch sensor array
determine a fourth phase offset for the second unit cell using the model of the touch sensor array; and
select one of a measured response comprising the first phase offset and the second phase offset or a modeled response comprising the third phase offset and the fourth phase offset to set the phase offset parameter of the demodulator.
15 . The touch detection system of claim 14 , wherein:
the model of the touch sensor array defines lumped resistance and capacitance parameters for the first unit cell and the second unit cell.
16 . A device, comprising:
a display comprising a touch sensor array having transmit lines, receive lines, and unit cells defined at intersections of the transmit lines and the receive lines;
a transmit sequencer configured to generate transmit signals on the transmit lines of the touch sensor array;
an analog-to-digital-converter module comprising a demodulator configured to measure responses of the receive lines to the transmit signals; and
a calibration unit configured to:
determine a first phase offset for a first unit cell of the unit cells based on a first response, of the responses, of the first unit cell;
determine a second phase offset for a second unit cell of the unit cells based on a second response, of the responses, of the second unit cell; and
set a phase offset parameter for the demodulator based on the first phase offset and the second phase offset.
17 . The device of claim 16 , wherein:
the demodulator is configured to multiply an output of the analog-to-digital-converter module by a demodulator reference signal; and
the phase offset parameter comprises a phase offset of the demodulator reference signal.
18 . The device of claim 16 , comprising:
a sensing channel connected to a selected receive line of the receive lines, comprising:
an analog-to-digital-converter in the analog-to-digital-converter module and connected to the demodulator;
and
a filter connected to the demodulator and configured to generate a response of the selected receive line of the receive lines based on an output of the demodulator, wherein:
the first unit cell is located at a first end of the selected receive line of the receive lines;
the second unit cell is located at a second end of the selected receive line of the receive lines;
the demodulator is configured to multiply an output of the analog-to-digital converter by a demodulator reference signal; and
the phase offset parameter comprises a phase offset of the demodulator reference signal.
19 . The device of claim 16 , wherein:
the calibration unit is configured to:
determine a third phase offset for the first unit cell using a model of the touch sensor array
determine a fourth phase offset for the second unit cell using the model of the touch sensor array; and
select one of a measured response comprising the first phase offset and the second phase offset or a modeled response comprising the third phase offset and the fourth phase offset to set the phase offset parameter of the demodulator.
20 . The device of claim 19 , wherein:
the model of the touch sensor array defines lumped resistance and capacitance parameters for the first unit cell and the second unit cell.