Field of the Disclosure
The present invention relates to a touch detecting circuit and a semiconductor integrated circuit including the same, and particularly to, a touch panel control circuit which can be suitably used as a touch panel control circuit that is connected to a touch panel that is mounted on a display panel so as to overlap therewith.
Description of the Related Art
A touch panel is mounted on a display panel that is used in a smart phone or a tablet terminal so as to overlap the display panel, and a user can operate an apparatus by touching (touching or tracing) a display screen with a finger and the like. To detect a touched position, various types are suggested. For example, in an electrostatic capacitance type, touched coordinates are detected by detecting a variation in an electrostatic capacitance which occurs when a finger or the like approaches sensor capacitors arranged in a matrix shape on a touch panel. The electrostatic capacitance type is classified into a mutual-capacitance type and a self-capacitance type. In the mutual-capacitance type, one side of the electrodes which constitute a sensor capacitor is set as a transmission side, and the other side is set as a reception side, and the mutual-capacitance type uses a phenomenon in which coupling capacitance generated between the transmission side and the reception side decreases due to approaching of a finger and the like. AY electrode as a drive electrode and an X electrode as a detection electrode are arranged to be perpendicular to each other with a dielectric disposed therebetween, whereby a capacitor (sensor capacitor) is constituted at each intersection. If capacitance due to a finger or a hand is present in the vicinity of the sensor capacitor, mutual capacitance at the intersection is reduced from a capacitance value of the sensor capacitor by a division amount of electric charges that are charged by the capacitance by the finger or the hand. A touch panel control circuit detects the intersection at which a variation of the mutual capacitance occurs and the magnitude thereof. In the self-capacitance type, one electrode of the sensor capacitor is set to a ground potential, and the self-capacitance type uses a phenomenon in which when a finer and the like of the human body that is grounded approaches the sensor capacitor, a capacitive component is added to the sensor capacitor.
In a touch panel control circuit disclosed in JP-A-2012-234474, a pulse-shaped AC drive voltage is repetitively applied to a sensor capacitor from the Y electrode, and electric charges corresponding to a capacitance value of the sensor capacitor at that time are transmitted and are accumulatively added by an integration circuit connected to the X electrode, thereby detecting a capacitance value of the sensor capacitor. At this time, the amplitude of the AC drive voltage that is applied is increased in order to increase the signal level (amount of electric charges that are transmitted), and the timing between signals that drive the display panel is retarded in order to decrease a noise level that is affected by a display drive signal, thereby improving a signal/noise ratio (S/N ratio).
In a display device disclosed in JP-A-2012-59265, a display panel operating period and a touch sensing period are divided in a time division manner, thereby preventing a display drive signal from having an effect on touch detection as a noise.
JP-A-2011-14527 discloses a self-capacitance type touch detecting circuit. Electrodes in an X-direction and electrodes in a Y-direction are arranged in a lattice shape, and a sensor capacitor is formed at each intersection. With respect to a capacitor selected by a combination of the electrodes in the X-direction and the Y-direction, a charging operation and the subsequent discharging operation are performed to detect a variation in an electrostatic capacitance.
JP-A-2013-242699 discloses a touch detecting circuit in combination of the self-capacitance type and the mutual-capacitance type. In a case where multi-touch is detected by the self-capacitance type, detection of touch coordinates is performed by the mutual-capacitance type with a focus on a touched electrode.