Stylus pen, touch sensing system and driving method thereof

1. A touch sensing system comprising:

a touchscreen including a plurality of touch electrodes and a plurality of sensor lines connected to the plurality of touch electrodes;

a touch driver for applying a touchscreen driving signal to the touchscreen and sensing a capacitance variation in the touchscreen, the touch driver including:

a touch sensor channel part connected to the plurality of touch electrodes through the plurality of sensor lines;

a common voltage buffer that outputs a common voltage;

a multiplexor;

a switch array connected to the touch sensor channel part, the common voltage buffer, and the multiplexor, the switch array switching between connecting the touch sensor channel part to the common voltage buffer during a display driving period for display an image and connecting the touch sensor channel part to the multiplexor during a touch sensing period for sensing a touch of the touch screen;

a sensing unit that amplifies charges received from the plurality of touch electrodes, integrates the amplified charges into a voltage, and converts the voltage to digital data responsive to the multiplexor and the switch array connecting the touch sensor channel part to the sensing unit during the touch sensing period;

a first timing control signal generator that generates a touch enable signal having a first level and a second level that is distinct from the first level, the first level indicative of the display driving period, and the second level indicative of the touch sensing period;

a second timing control signal generator configured to generate one or more timing signals and a clock signal to control timing operation of the multiplexor and the sensing unit;

a DTX compensator configured to remove noise from the digital data;

a first memory connected to the DTX compensator, the first memory storing the digital data with the noise removed from the digital data based on at least one of the timing signals generated by the second timing control signal generator; and

a microcontroller unit configured to receive the digital data stored by the first memory and compare the digital data with a threshold value, the comparison indicative of whether the touchscreen was touched; and

an active stylus pen for generating a pen driving signal and transmitting the pen driving signal to the touchscreen,

wherein the active stylus pen comprises:

a pressure sensing unit for sensing pressure when the touchscreen is touched to generate writing pressure information, the pressure sensing unit including:

a variable resistance unit having a resistance that varies based on changes in the sensed pressure;

a voltage converter coupled to the variable resistance unit, the voltage converter generating an output voltage that varies based on the varying resistance of the variable resistance unit, and

an analog-to-digital converter (ADC) that converts the output voltage into a digital signal that is representative of the writing pressure information;

a signal processor for generating the pen driving signal synchronized with the touchscreen driving signal received from the touchscreen and varying the pen driving signal in response to a signal level of the digital signal that is representative of the writing pressure information.

2. The touch sensing system of claim 1 , wherein the signal processor modulates a pulse amplitude of the pen driving signal in response to the signal level of the digital signal that is representative of the writing pressure information.

3. The touch sensing system of claim 1 , wherein the signal processor modulates a number of pulses of the pen driving signal generated for one touch sensor driving period in response to the signal level of the digital signal that is representative of the writing pressure information.

4. The touch sensing system of claim 1 , wherein the signal processor modulates a pulse duty of the pen driving signal in response to the signal level of the digital signal that is representative of the writing pressure information.

5. The touch sensing system of claim 1 , wherein the signal processor modulates the pen driving signal in each frame in response to the signal level of the digital signal that is representative of the writing pressure information, and

wherein a digital pen driving signal in which the writing pressure information has been reflected is allocated to each frame by one bit.

6. The touch sensing system of claim 5 , wherein the signal processor modulates a pulse amplitude, a number of pulses and a pulse duty of the pen driving signal within a range.

7. The touch sensing system of claim 1 , wherein the touch sensor channel part, the common voltage buffer, the multiplexor, the switch array, the sensing unit, the first timing control signal generator, the second timing control signal generator, the DTX compensator, and the first memory are integrated into a driver integrated circuit of the touch driver, and

wherein the microcontroller unit is a separate integrated circuit from the driver integrated circuit.

8. The touch sensing system of claim 1 , wherein the touch sensor channel part, the common voltage buffer, the multiplexor, the switch array, the sensing unit, the first timing control signal generator, the second timing control signal generator, the DTX compensator, the first memory, and the microcontroller unit are integrated into a driver integrated circuit of the touch driver.

9. The touch sensing system of claim 8 , wherein the touch driver further comprises:

a second memory that is external to the driver integrated circuit, the second memory storing register values associated with timing information,

wherein the register values are loaded into the first timing signal control generator and the second timing control signal generator to generate the touch enable signal, the one or more timing signals, and the clock signal.