Touch-and-display device operated with active stylus

1. A touch-and-display device operated with an active stylus, the touch-and-display device comprising:

a touch-and-display panel comprising a plurality of sensing electrodes; and

a circuit electrically connected to the sensing electrodes through a plurality of sensing lines,

wherein in a touch detection period, the circuit is configured to detect a touch position according to a plurality of first signals on the sensing lines,

wherein in a stylus detection period, the circuit is configured to transmit an uplink signal to the sensing electrodes and detect a downlink signal and a stylus position according to a plurality of second signals on the sensing lines,

wherein when the downlink signal is detected, the circuit is configured to determine if a distance between the stylus position and the touch position is less than or equal to a first predetermined distance,

wherein if the distance between the stylus position and the touch position is greater than the first predetermined distance, the circuit is configured to enter a stylus mode, wherein the touch position is not detected in the stylus mode,

wherein if the distance between the stylus position and the touch position is less than or equal to the first predetermined distance, the circuit is configured not to enter the stylus mode.

2. The touch-and-display device of claim 1 , wherein the circuit comprises:

a demodulator electrically connected to the sensing lines and configured to output a plurality of demodulated signals according to the second signals;

an analogy-to-digital converter electrically connected the demodulator and configured to output a stylus value corresponding to each of the sensing electrodes according to the demodulated signals; and

a computing circuit electrically connected to the analogy-to-digital converter and configured to calculate the stylus position according to the stylus values and determine if the stylus values are greater than a first threshold,

wherein if one of the stylus values is greater than the first threshold, the computing circuit is configured to determine that the downlink signal is detected.

3. The touch-and-display device of claim 2 , wherein the computing circuit is configured to calculate a weighting sum of positions of the sensing electrodes as the stylus position, and a weight of each of the sensing electrodes is proportional to the corresponding stylus.

4. The touch-and-display device of claim 2 , wherein if the distance between the stylus position and the touch position is less than or equal to the first predetermined distance, the circuit is configured to determine if the stylus values are greater than a second threshold which is greater than the first threshold,

wherein if the stylus values are less than or equal to the second threshold, the circuit is configured to ignore the downlink signal and not enter the stylus mode.

5. The touch-and-display device of claim 4 , wherein if one of the stylus values is greater than the second threshold, the circuit is configured to enter the stylus mode.

6. The touch-and-display device of claim 4 , wherein if the stylus position is same as the touch position, the circuit is configured not to enter the stylus mode.

7. The touch-and-display device of claim 1 , wherein if the downlink signal is not detected for a predetermined time, the circuit is configured to end the stylus mode and re-detect the touch position.

8. The touch-and-display device of claim 1 , wherein the touch-and-display device is connected to a charger.

9. A sensing method of an active stylus for a touch-and-display device which comprises a plurality of sensing electrodes, wherein a plurality of sensing lines are connected to the sensing electrodes respectively, and the sensing method comprises:

in a touch detection period, detecting a touch position according to a plurality of first signals on the sensing lines;

in a stylus detection period, transmitting an uplink signal to the sensing electrodes and detecting a downlink signal and a stylus position according to a plurality of second signals on the sensing lines;

when the downlink signal is detected, determining if a distance between the stylus position and the touch position is less than or equal to a first predetermined distance;

if the distance between the stylus position and the touch position is greater than the first predetermined distance, entering a stylus mode, wherein the touch position is not detected in the stylus mode; and

if the distance between the stylus position and the touch position is less than or equal to the first predetermined distance, not entering the stylus mode.

10. The sensing method of claim 9 , further comprising:

outputting, by a demodulator, a plurality of demodulated signals according to the second signals;

outputting, by an analogy-to-digital converter, a stylus value corresponding to each of the sensing electrode according to the demodulated signals;

calculating the stylus position according to the stylus values and determining if the stylus values are greater than a first threshold; and

if one of the stylus values is greater than the first threshold, determining that the downlink signal is detected.

11. The sensing method of claim 10 , further comprising:

calculate a weighting sum of positions of the sensing electrodes as the stylus position, wherein a weight of each of the sensing electrodes is proportional to the corresponding stylus value.

12. The sensing method of claim 10 , further comprising:

if the distance between the stylus position and the touch position is less than or equal to the first predetermined distance, determining if the stylus values are greater than a second threshold which is greater than the first threshold; and

if the stylus values are less than or equal to the second threshold, ignoring the downlink signal and not entering the stylus mode.

13. The sensing method of claim 12 , further comprising:

if one of the stylus values is greater than the second threshold, entering the stylus mode.

14. The sensing method of claim 12 , further comprising:

if the stylus position is same as the touch position, not entering the stylus mode.

15. The sensing method of claim 9 , further comprising:

if the downlink signal is not detected for a predetermined time, ending the stylus mode and re-detecting the touch position.