Active row backlight, column shutter LCD with one shutter transition per row

• US 5,311,206 A
• Filed: 04/16/1993
• Issued: 05/10/1994
• Est. Priority Date: 04/16/1993
• Status: Expired due to Fees

• Current Assignee: Telcordia Technologies Incorporated (Telefonaktiebolaget LM Ericsson)
• Original Assignee: Bell Communications Research, Inc. (Telefonaktiebolaget LM Ericsson)
• Inventors: Nelson, Terence J.
• Primary Examiner(s): Hjerpe, Richard
• Assistant Examiner(s): CHIN, VIVIAN C
• Application Number:
  US08/049,038
• Time in Patent Office: 389 Days
• Field of Search: 345/89, 345/102, 345/148, 345/98, 345/87
• US Class Current: 345/89
• CPC Class Codes: G09G 2310/024 Scrolling of light from the illumination source over the display in combination with the scanning of the display screen
• CPC Class Codes: G09G 3/2014 by modulation of the duration of a single pulse during which the logic level remains constant
• CPC Class Codes: G09G 3/342 using several illumination sources separately controlled corresponding to different display panel areas, e.g. along one dimension such as lines
• CPC Class Codes: G09G 3/36 using liquid crystals

Abstract

A flat-panel display device 500, 600 with an active array of parallel longitudinal row backlights 520, 620 disposed in a first plane is disclosed. The row backlights sequentially emit a row of light for a fixed-duration row-interval of time t in successive row periods of duration p. Each row is illuminated once in each frame. The flat panel display device also has an array of longitudinal parallel liquid-crystal column shutters 531, 631 disposed in a second plane parallel to the first plane. The column shutters are oriented orthogonally to the row backlights so as to define pixels at each intersection of a column shutter and a row backlight. A driver 590, 690 is provided for causing the column shutters to make, at most, one transition from the "off" state to the "on" state or vice-versa every row period.

Claims

1. A flat-panel display device for displaying images formed from a sequence of frames comprising:

a linear array of longitudinal active backlights disposed in a first plane, each backlight successively emitting light once per frame for a fixed duration time interval t in successive time periods of duration p, where t≦

p,

a linear array of longitudinal liquid-crystal shutters disposed in a second plane parallel to said first plane and oriented perpendicularly to said backlights, each of said shutters having first and second states, and

a shutter driver for causing each shutter to make at most one transition between its states during each time period, the time of the shutter transition within a time period being dependent on a desired intensity of a pixel defined by the intersection of the shutter and the particular backlight illuminated in the time interval.

2. The display of claim 1 wherein said shutters are formed with a liquid-crystal material having memory and wherein said shutter driver produces voltage pulses of a fixed width to cause said shutters to undergo said transitions at said transition times.

3. The display of claim 2 wherein said shutter driver produces one pulse per transition, said pulses alternating in polarity so that said voltage has no DC component.

4. The display of claim 2 wherein said liquid-crystal material is a ferroelectric liquid-crystal material.

5. The display of claim 1 further comprising:

a liquid-crystal modulator disposed in a third plane parallel to said first and second planes on the same side of said first plane as said second plane, said modulator having first and second states, and

a modulator driver for causing said modulator to make a transition between its states during each successive time period.

6. The display of claim 5 wherein a pixel appears bright for a fraction of the time interval during which the corresponding back light is emitting light, which fraction is delimited by a transition of a shutter and a transition of said modulator.

7. The display of claim 5 wherein said modulator driver applies a voltage for causing said modulator transitions to occur approximately at the end of each time interval.

8. The display of claim 5 wherein during a time interval, a pixel appears bright if said modulator and said shutter are in the same state and said pixel appears dark if said shutter and said modulator are in different states.

9. The display of claim 5 wherein if all pixels defined by the intersection of said backlights and a particular shutter have the same intensity, said shutter driver applies a voltage, which has no DC component, for causing said shutter to undergo transitions.

10. The display of claim 5 wherein the initial state in which said modulator is driven at the beginning of each frame alternates in successive frames.

11. The display of claim 1 wherein said shutter driver comprises a shift register having one cell for each shutter, each cell comprising:

a memory for periodically receiving and storing an m+1 bit number D_m D_m-1 . . . D₀, where the m^th bit D_m is the most significant bit and wherein the 0^th bit D₀ is the least significant bit,

means for receiving m+1 delay signals which each correspond to one of said m+1 bits, the delay signal associated with each bit having twice the period of the delay signal associated with a preceding bit, said means for receiving said delay signals also setting each bit to logic zero, one at a time from the m^th bit to the 0^th bit, after a delay equal to one half the period of the delay signal corresponding to the bit, and

an output for driving said associated shutter with a voltage depending, at any time, on whether said m bit number stored, in said memory is zero or non-zero.

12. A flat-panel display device for displaying images formed from a sequence of frames comprising:

a linear array of longitudinal active backlights, each backlight successively emitting light once per frame for a fixed duration time interval t in successive time periods of duration p, where t≦

p,

a linear array of longitudinal liquid-crystal shutters oriented perpendicularly to said backlights, each of said shutters receiving said emitted light of said backlights and having first and second states for blocking and transmitting said light, each shutter remaining in the state into which the shutter is driven, and

a shutter driver for causing each shutter to make at most one transition between its states during each time period, the time of the shutter transition within a time period being dependent on a desired intensity of a pixel defined by the intersection of the shutter and the particular backlight illuminated in the time interval.

13. A flat-panel display device for displaying images formed from a sequence of frames comprising:

a linear array of longitudinal active backlights disposed in a first plane, each backlight successively emitting light once per frame for a fixed duration time interval t in successive time periods of duration p, where t≦

p,

a linear array of longitudinal liquid-crystal shutters disposed in a second plane parallel to said first plane and oriented perpendicularly to said backlights, each of said shutters having first and second states,

a liquid-crystal modulator disposed in a third plane parallel to said first and second planes on the same side of said first plane as said second plane, said modulator having first and second states,

a modulator driver for causing said modulator to make a single transition between its states during each successive time period, and

a shutter driver for causing each shutter to make at most one transition between its states during each time period, so that light is transmitted during a fraction of the associated time interval delimited by a transition time of said modulator and a transition time of the column shutter.