Active pen, sensor controller, and position detection device configured for bidirection communication using time slots
An active pen communicates with a sensor controller using a series of time slots, to receive uplink signals from and transmit downlink signals to the sensor controller. The series of time slots are determined based on the reception timing, by the active pen, of an uplink signal used as a reference time. The active pen determines whether or not the uplink signal is received and, if yes, the active pen transmits a first downlink signal using a time within the series of time slots. If no, the active pen transmits a second downlink signal using both a time within the series of time slots and a time outside the series of time slots. The second downlink signal is formed by repeating a unit signal that is shorter in duration than each of the series of time slots, to ensure reception by the sensor controller of at least one unit signal.
1. An active pen that communicates with a sensor controller, the active pen comprising:
an electrode and a pen coil;
a transmission circuit that transmits a downlink signal to the sensor controller by changing a potential of the electrode; and
a reception circuit that receives an uplink signal transmitted in the form of a magnetic field generated by a loop coil of the sensor controller, by detecting an induced current generated in the pen coil,
wherein,
the transmission circuit and the reception circuit use a series of time slots to transmit downlink signals to the sensor controller and to receive uplink signals from the sensor controller, wherein the series of time slots are determined based on a reception timing by the active pen of one of the uplink signals transmitted from the sensor controller;
the transmission circuit, in operation, transmits a first downlink signal using a time within the series of time slots, and transmits a second downlink signal using both a time within the series of time slots and a time outside the series of time slots; and
the second downlink signal includes a first unit signal and a second unit signal, the first unit signal and the second unit signal each includes a gap, the gap included in the first unit signal is different in length from the gap included in the second unit signal, and the gap included in the first unit signal and the gap included in the second unit signal are each arranged between two temporally adjacent unit signals.
2. The active pen according to claim 1 ,
wherein the second downlink signal is formed by repeating a unit signal that is shorter in duration than each of the series of time slots.
3. The active pen according to claim 1 , comprising:
a pressure sensor that acquires a pen pressure value having a first number of bits based on a detection of a pressure applied to a pen tip,
wherein,
the first downlink signal includes a signal modulated by the pen pressure value,
the first unit signal includes a signal modulated by some of a predetermined number of high-order bits of the pen pressure value, and
the second unit signal includes a signal modulated by the rest of the predetermined number of high-order bits of the pen pressure value.
4. The active pen according to claim 3 ,
wherein the pen pressure value arranged partially in each of the first and second unit signals is updated at least two times during one transmission interval of the uplink signal.
5. The active pen according to claim 1 ,
wherein the active pen performs an operation of detecting the uplink signal in parallel with the transmission of the second downlink signal.