Liquid crystal display with pen-input capability

• US 5,243,452 A
• Filed: 12/06/1991
• Issued: 09/07/1993
• Est. Priority Date: 12/06/1991
• Status: Expired due to Fees

• Current Assignee: NCR Corporation
• Original Assignee: NCR Corporation
• Inventors: Baur, Peter F.
• Primary Examiner(s): Sikes, William L.
• Assistant Examiner(s): MAI, HUY KIM
• Application Number:
  US07/805,450
• Time in Patent Office: 641 Days
• Field of Search: 359/43, 359/45, 359/55, 359/60, 359/85, 359/84, 340/706, 340/707, 340/708
• US Class Current: 345/104
• CPC Class Codes: G06F 3/0412 Digitisers structurally integrated in a display
• CPC Class Codes: G06F 3/042 by opto-electronic means

Abstract

In a liquid-crystal display, each pixel is associated with a sensor which detects incoming light projected by a light pen. In response to the detected light, the sensor produces a signal which causes its associated pixel to darken. Thus, as a user moves the light pen along the display, the pen leaves a trail of darkened pixels, analogous to a pen leaving a trail of ink on paper.

Claims

1. A video display in which individual pixels can be turned on and off by a video control, comprising:

a) a plurality of photodetectors, each in registration with a respective pixel, for detecting incoming light projected by a user and producing a current in response; and

b) sensing means for

i) receiving the currents;

ii) producing voltages in response; and

iii) transmitting the voltages to the video control as data which identifies the locations of the photodetectors receiving the light.

2. Apparatus according to claim 1 in which

c) the display comprises a liquid crystal sandwiched between first and second sheets;

and

d) the sensing means are carried on a third sheet.

3. A video display, comprising:

a) a liquid crystal contained between two sheets;

b) a plurality of parallel, conductive, row traces located on one sheet;

c) a plurality of parallel, conductive, column traces located on the other sheet, and generally perpendicular to the row traces;

d) a matrix of capacitors, each having

i) a first plate connected to a column trace and

ii) a second plate located near a row trace;

e) a plurality of photodiodes, each

i) connecting between a second plate and its nearby column trace and

ii) able to deliver charge to the capacitor in response to incoming light;

f) a plurality of sensing resistors, each in series with a respective column trace;

g) a plurality of differential amplifiers, each

i) receiving, as a differential input, a voltage developed across a respective sensing resistor and

ii) for producing a signal in response to the voltage developed; and

h) column register means for storing the signals produced by the differential amplifiers.