Multiplexed display element sequential color LCD panel

• US 6,535,196 B2
• Filed: 05/03/2001
• Issued: 03/18/2003
• Est. Priority Date: 12/20/1996
• Status: Expired due to Fees

• Current Assignee: Hanger Solutions, LLC (IP Investments Group LLC)
• Original Assignee: Duke University
• Inventors: Walker, Dale S., Knox, Richard M.
• Primary Examiner(s): WU, XIAO MIN
• Application Number:
  US09/846,851
• Publication Number:
  US 20010026261A1
• Time in Patent Office: 684 Days
• Field of Search: 345/87, 345/88, 345/89, 345/98, 345/99, 345/100, 345/102, 345/94, 345/95, 345/96, 345/211, 345/212, 345/213, 348/790, 348/791, 348/792, 353/77
• US Class Current: 345/102
• 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 method for displaying an image, comprising:

providing a plurality of liquid crystal display pixels; and

controlling at least one of the liquid crystal display pixels, wherein the controlling comprises,

storing a video signal corresponding to a first color of light to be emitted from a selected pixel during a video frame;

storing a video signal corresponding to a second color of light to be emitted from the selected pixel during the video frame;

storing a video signal corresponding to a third color of light to be emitted from the pixel during the video frame; and

comparing the video signals to a reference signal, wherein the selected pixel is enabled according to a result of the comparing.

2. The method of claim 1, wherein the comparing repeatedly cycles through the comparison of the stored video signals to the reference signal generating multiple output signals to the selected pixel for each of the colors of light until receipt of a next video frame and corresponding next video signals for the first, second and third colors of light.

3. The method of claim 1, wherein a comparator compares the stored video signals to the reference signal and the result is an output signal of the comparator, and wherein the reference signal defines a conversion between the video signals and the comparator output signal.

4. The method of claim 3, wherein the reference signal is one of a linear signal and a nonlinear signal that compensates for color effects of the video frame.

5. The method of claim 4, wherein the reference signal compensates for at least one of gamma, brightness, contrast, display characteristics and psycho-physics of the human eye.

6. The method of claim 5, wherein the reference signal is a falling sawtooth, and wherein the storage devices are comparators.

7. The method of claim 3, wherein the comparator output signal is a time-based signal.

8. The method of claim 3, further comprising selecting the video signals of the first, second, and third storage devices and passing the selected video signal to said comparator, wherein the selecting switches between the video signals of the first, second and third storage devices faster than three times a rate of approximately 60 to 72 Hz.

9. The method of claim 1, wherein the reference signal has a different waveform corresponding to each of the colors of light.

10. The method of claim 9, further comprising selecting each of the video signals from the first, second and third storage devices for comparing to the reference signal.

11. The method of claim 1, wherein the video signals are one of an analog voltage signal, an analog signal, an analog current signal and a digital signal.

12. The method of claim 1, further comprising color period counting for controlling selection of the first, second, and third storage devices to pass the corresponding video signal to the selected liquid crystal display pixel.

13. The method of claim 1, comprising selecting the video signals of the first, second and third storage devices for the comparing, wherein the selecting switches a plurality of times for each frame.

14. The method of claim 13, wherein the selecting switches one of at least about 600 Hz and faster than three times a rate of approximately 60-72 Hz.

15. The method of claim 1, comprising providing a waveform generator and a color interval counter, wherein the plurality of liquid crystal display pixels share the waveform generator and the color interval counter.

16. The method of claim 1, wherein the comparing repeatedly cycles through the comparison of the stored video signals to the reference signal generating multiple output signals to the selected pixel.

17. A method for displaying, comprising:

providing a plurality of liquid crystal display pixels; and

controlling each of the liquid crystal display pixels, wherein the controlling comprises,

storing an analog signal corresponding to a first color of light to be emitted from a selected pixel during a video frame,

storing an analog signal corresponding to a second color of light to be emitted from the selected pixel during a video frame,

storing an analog signal corresponding to a third color of light to be emitted from the selected pixel during a video frame, and

repeatedly comparing the analog signals to a reference signal, wherein the selected pixel is enabled responsive to results of the comparing.