Multiplexed display element sequential color LCD panel

• US 5,977,942 A
• Filed: 12/20/1996
• Issued: 11/02/1999
• Est. Priority Date: 12/20/1996
• Status: Expired due to Fees

• Current Assignee: Hanger Solutions, LLC (IP Investments Group LLC)
• Original Assignee: Compaq Computer Corporation (HP Inc.)
• Inventors: Walker, Dale S., Knox, Richard M.
• Primary Examiner(s): WU, XIAO MIN
• Application Number:
  US08/771,191
• Time in Patent Office: 1,047 Days
• Field of Search: 345/102, 345/87, 345/89, 345/88, 345/98, 345/100, 345/99, 345/97, 345/94, 345/95, 345/96, 345/211, 345/212, 345/213, 345/208, 345/210, 348/790, 348/791, 348/792, 353/77
• US Class Current: 345/97
• CPC Class Codes: G09G 2300/0809 Several active elements per pixel in active matrix panels
• CPC Class Codes: G09G 2300/0814 used for selection purposes, e.g. logical AND for partial update
• CPC Class Codes: G09G 2300/0852 being a dynamic memory with more than one capacitor
• CPC Class Codes: G09G 2310/0235 Field-sequential colour display
• CPC Class Codes: G09G 2310/0259 with use of an analog or digital ramp generator in the column driver or in the pixel circuit
• CPC Class Codes: G09G 2310/066 Waveforms comprising a gently increasing or decreasing portion, e.g. ramp
• CPC Class Codes: G09G 2320/0276 for the purpose of adaptation to the characteristics of a display device, i.e. gamma correction
• 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 3/3648 using an active matrix G09G3/367 - G09G3/3696 take precedence
• CPC Class Codes: G09G 3/3651 using multistable liquid crystals, e.g. ferroelectric liquid crystals
• CPC Class Codes: H04N 2005/745 Control circuits therefor
• CPC Class Codes: H04N 5/66 Transforming electric information into light information scanning details H04N3/00
• CPC Class Codes: H04N 9/30 using solid-state colour display devices

Abstract

In a color sequential system using LCDs, the LCD must operate faster than the frame rate because red, green, and blue are done sequentially. Ferroelectric LCDs can do this, but they are not analog devices and so cannot provide analog display levels. Instead, a pulse width modulation (PWM) technique is used. In the system of the present invention, each pixel has three storage devices to hold RGB analog levels. A latch is used to load these values in parallel. Then an analog 3:1 multiplexer is used to select the proper storage device for the current sequential color. The multiplexer output goes to a comparator, which has a sawtooth waveform input at much faster than the frame rate. The comparator output changes with the sawtooth level, so that PWM control is provided for each pixel. As an alternative, standard analog LCD pixels can be sequentially switched between three color input storage devices.

Claims

1. A display apparatus comprising:

a plurality of ferroelectric liquid crystal display pixels;

a controller for each ferroelectric liquid crystal display (FLCD) pixel, each controller including;

a first storage device for storing an analog voltage signal corresponding to a first color of light to be emitted from the pixel during a video frame;

a second storage device for storing an analog voltage signal corresponding to a second color of light to be emitted from the pixel during a video frame;

a third storage device for storing an analog voltage signal corresponding to a third color of light to be emitted from the pixel during a video frame;

a comparator device for sequentially comparing the analog voltage signals to a voltage input signal, the comparator device having an output signal which is fed to the ferroelectric liquid crystal display pixel;

a voltage input signal generator providing the voltage input signal;

means for sequentially selecting the first, second, and third storage devices of each controller for the FLCD pixels;

a light source; and

a filter for sequentially selecting different colors of light.

2. The display apparatus of claim 1, further comprising:

a video controller for providing the input video signal.

3. The display apparatus of claim 1, wherein said storage devices are capacitors.

4. The display apparatus of claim 1, wherein the means for sequentially selecting the first, second, and third storage devices of each controller for the FLCD pixels comprises a multiplexer.

5. The display apparatus of claim 1, wherein said filter is a rotating disk with red, green, and blue filters.

6. The display apparatus of claim 1, wherein said filter is a digitally switched filter.

7. The display apparatus of claim 1, said filter is a reflective filter.

8. The display apparatus of claim 1, wherein the plurality of pixels is located between the light source and the display.

9. The display apparatus of claim 1, wherein the voltage input signal comprises a falling sawtooth signal.

10. The display apparatus of claim 1, wherein the voltage input signal comprises a gamma-corrected sawtooth signal.

11. The display apparatus of claim 1, wherein the voltage input signal comprises a sawtooth signal having a different gamma-corrected waveform corresponding to each light color.

12. The display apparatus of claim 1 further comprising:

three analog switches coupled to said storage devices and receiving red, green, and blue analog signals, wherein said switches pass said red, green, and blue analog signals responsive to a decoded row column address corresponding to the pixel.

13. The display apparatus of claim 1, wherein the ferroelectric liquid crystal display pixels are provided by a ferroelectric liquid crystal display with a reflective surface, wherein the controller for each pixel is located beneath the reflective surface as part of an integrated surface.

14. The display apparatus of claim 1, wherein the frequency of the voltage signal is at least about 600 Hz.