Coordinate input device

• US 5,606,346 A
• Filed: 06/06/1995
• Issued: 02/25/1997
• Est. Priority Date: 12/22/1992
• Status: Expired due to Fees

• Current Assignee: Matsushita Electric Industrial Company Limited (Panasonic Holdings Corporation)
• Original Assignee: Matsushita Electric Industrial Company Limited (Panasonic Holdings Corporation)
• Inventors: Kai, Tsutomu, Matsunami, Masahito
• Primary Examiner(s): Weldon, Ulysses
• Application Number:
  US08/467,707
• Time in Patent Office: 630 Days
• Field of Search: 371/48, 371/57.2, 371/64, 345/173, 345/178, 345/104, 178/18, 178/19
• US Class Current: 345/173
• CPC Class Codes: G06F 1/1626 with a single-body enclosure integrating a flat display, e.g. Personal Digital Assistants [PDAs]
• CPC Class Codes: G06F 1/1643 the display being associated to a digitizer, e.g. laptops that can be used as penpads details related to the relative motion of the display enclosure with respect to the body enclosure, e.g. to move between laptop and tablet PC configuration G06F1/1615
• CPC Class Codes: G06F 1/169 the I/O peripheral being an integrated pointing device, e.g. trackball in the palm rest area, mini-joystick integrated between keyboard keys, touch pads or touch stripes G06F1/1643 takes precedence; constructional details of pointing devices G06F3/033
• CPC Class Codes: G06F 3/0412 Digitisers structurally integrated in a display
• CPC Class Codes: G06F 3/04184 Synchronisation with the driving of the display or the backlighting unit to avoid interferences generated internally
• CPC Class Codes: G06F 3/044 by capacitive means
• CPC Class Codes: G06F 3/0446 using a grid-like structure of electrodes in at least two directions, e.g. using row and column electrodes

Abstract

A coordinate input device including a matrix-type display panel having a plurality of row electrodes arranged in parallel, a plurality of column electrodes arranged in parallel, the row electrodes and the column electrodes being disposed to face each other, and liquid crystal disposed between the row electrodes and the column electrodes. The device also includes a row electrode driving circuit, a column electrode driving circuit, a controller for controlling these driving circuits, an input pad disposed to allow direct contact with the operator, and a coordinate detection circuit for calculating a coordinate value based on a signal input thereto through the input pad. When a position on the display panel is pressed with a finger, a driving signal supplied to the row electrode or the column electrode corresponding to the position is transmitted through the operator to the input pad. The coordinate of the position is detected based on the transmitted signal.

Claims

1. A coordinate input device comprising:

a display panel including;

a plurality of row electrodes and a plurality of column electrodes arranged in a matrix; and

a plurality of display elements, each connected to one of the crossings of the plurality of row electrodes and the plurality of column electrodes;

row electrode driving means for, during a display period and a row coordinate detection period, sequentially supplying row electrode driving signals to the plurality of row electrodes to effect scanning of the plurality of row electrodes, and for fixing the potential of the plurality of row electrodes constant during a column coordinate detection period;

column electrode driving means for sequentially supplying display signals to the plurality of column electrodes during the display period, for sequentially supplying column electrode driving signals to the plurality of column electrodes to effect scanning of the plurality of column electrodes during the column coordinate detection period, and for fixing the potential of the plurality of column electrodes constant during the row coordinate detection period;

coordinate detection means for detecting a coordinate value of an indicated position on the display panel;

a back light disposed on the back side of the display panel for illuminating the display panel;

an inverter circuit for generating a back light driving signal for driving the back light;

control means for effecting switching among the display period, the row coordinate detection period, and the column coordinate detection period, the control means controlling the row electrode driving means to supply the row electrode driving signals in Synchronization with the back light driving signals during the row coordinate detection period, and controlling the column electrode driving means to supply the column electrode driving signals in synchronization with the back light driving signals during the column coordinate detection period; and

further comprising status detection means for detecting the oscillating frequency and the amplitude of the back light driving signals correction value calculating means for calculating a correction value of the indicated position based on the detected oscillating frequency and the amplitude, correction means for receiving the coordinate value of the indicated position from the coordinate detection means and the correction value from the correction value calculating means and for subtracting the correction value from the coordinate value.

2. A coordinate input device according to claim 1, wherein the coordinate detection means detects coordinate values of at least two predetermined positions, and the status detection means compares the detected coordinate values with actual coordinate values of the at least two predetermined positions and detects the oscillating frequency and the amplitude of the back light driving signals based on any difference between the detected coordinate values and the actual coordinate values.