Analog active matrix emissive display

• US 6,417,825 B1
• Filed: 11/25/1998
• Issued: 07/09/2002
• Est. Priority Date: 09/29/1998
• Status: Expired due to Term

• Current Assignee: MEC Management, LLC (Three Affiliated Tribes of the Fort Berthold Reservation, North Dakota)
• Original Assignee: Sarnoff Corporation (SRI International, Inc.)
• Inventors: Stewart, Roger G., Ipri, Alfred C.
• Primary Examiner(s): Hjerpe, Richard
• Assistant Examiner(s): Nguyen, Kevin M.
• Application Number:
  US09/200,513
• Time in Patent Office: 1,322 Days
• Field of Search: 345/76, 345/78, 345/80, 345/205, 345/206, 345/90, 345/92, 345/147, 345/77, 345/148, 345/149
• US Class Current: 345/77
• CPC Class Codes: G09G 2300/0809 Several active elements per pixel in active matrix panels
• CPC Class Codes: G09G 2300/0842 forming a memory circuit, e.g. a dynamic memory with one capacitor
• CPC Class Codes: G09G 3/2011 by amplitude modulation
• CPC Class Codes: G09G 3/2018 by time modulation using two or more time intervals
• CPC Class Codes: G09G 3/2051 with use of a spatial dither pattern
• CPC Class Codes: G09G 3/30 using electroluminescent panels

Abstract

An emissive display device such as an active matrix electroluminescent display (AMEL display) has an improved method of operation. The AMEL display produces gray scale operation comprising an array of pixels, each pixel including a first transistor having its gate connected to a select line, its source connected to a data line, and its drain connected to the gate of a second transistor. The second transistor has its source adapted to receive a ramped voltage level, and its drain connected to a first electrode of an electroluminescent cell. The electroluminescent cell has a second electrode connected to an alternating current high voltage power source, wherein the electroluminescent cell is illuminated, when the ramp voltage level is less than a voltage level on the gate of the second transistor. The ramp voltage level is increased linearly during a frame duration, and the alternating current high voltage power source is on continuously during the same frame duration. The alternating current high voltage power source may also be varied in amplitude from a minimum peak-to-peak value to a maximum peak-to-peak value during the frame duration.

Claims

1. An emissive display having an array of pixels, each pixel comprising

a first transistor having its gate connected to a select line, its source connected to a data line, and its drain connected to the gate of a second transistor, for applying an illumination voltage level to the gate of the second transistor,

the second transistor having its source coupled to receive a ramped voltage level, and its drain connected to a first electrode of an emissive cell, and

said emissive cell having a second electrode connected to an alternating current high voltage power source,

wherein the emissive cell emits light when the ramp voltage level is lower than the illumination voltage level on the gate of the second transistor.

2. The emissive display of claim 1 further comprising a capacitor connected between the gate of the second transistor and a ground reference potential.

3. The emissive display of claim 1 wherein the ramp voltage level is increased linearly during a frame duration, and the alternating current high voltage power source is continuously active during the same frame duration.

4. The emissive display of claim 3 wherein the ramp voltage level is increased linearly from 0 volts to 7 volts during the frame duration.

5. The emissive display of claim 1 wherein the high voltage power source has a predetermined frequency, said predetermined frequency being selected from a range of frequencies wherein a higher frequency corresponds to an increased brightness while the pixel is emitting light.

6. An emissive display having an array of pixels, each pixel comprising

a first transistor having its gate connected to a select line, its source connected to a data line, and its drain connected to a gate of a second transistor,

the second transistor having its source connected to the data line, and its drain connected to a first electrode of an emissive cell,

said emissive cell having a second electrode connected to an alternating current high voltage power source, and

a capacitor having one terminal connected to the gate of the second transistor and another terminal which is coupled to receive a ramped voltage level,

wherein the emissive cell emits light when the ramped voltage level added to a voltage level of the data line is greater than a threshold voltage level of the second transistor.

7. An emissive display having an array of pixels, each pixel comprising

a first transistor having its gate connected to a select line, its source connected to a data line, and its drain connected to a gate of a second transistor, for applying an illumination voltage level to the gate of the second transistor,

the second transistor having its source connected to a ground reference potential, and its drain connected to a first electrode of an emissive cell,

said emissive cell having a second electrode connected to an alternating current high voltage power source, and

a capacitor having one terminal connected to the gate of the second transistor and another terminal which is coupled to receive a ramped voltage level,

wherein the emissive cell emits light when the ramped voltage level added to a voltage level of the data line is greater than a threshold voltage level of the second transistor.

8. In an emissive display having an array of pixels, each pixel including a circuit for controlling application of energy to an emissive cell associated with each pixel, a method for providing gray scale illumination during a frame duration comprising the steps of:

a) applying a data signal voltage level to the circuit along a data line and applying a select signal to the circuit along a select line;

b) storing the data signal within the circuit;

c) applying an alternating current high voltage to the emissive cell during the entire frame duration, a peak-to-peak value of the high voltage changing from a minimum peak-to-peak value to a maximum peak-to-peak value during the entire frame duration; and

d) applying a ramp signal to the circuit along a further line, the ramp signal changing gradually from a first predetermined voltage level to a second predetermined voltage level over substantially the entire frame duration;

wherein the emissive cell is illuminated during a portion of the frame duration in which the ramp signal voltage level is lower than the data signal voltage level.

9. The method of claim 8 wherein step (d) further includes the step of linearly ramping the ramp signal from a low reference level to a high reference level during the entire frame duration.

10. In an emissive display having an array of pixels, each pixel including a circuit for controlling application of energy to an emissive cell associated with each pixel, a method for providing gray scale illumination during a frame duration comprising the steps of:

a) applying a data signal voltage level to the circuit along a data line and applying a select signal to the circuit along a select line;

b) storing the data signal within the circuit;

c) applying an alternating current high voltage to the emissive cell during the entire frame duration;

d) applying a ramp signal to the circuit along a further line, the ramp signal linearly ramping from a low reference level to a high reference level during a first interval of the frame duration; and

e) inhibiting the emissive cell from illuminating during a second interval of the frame duration by setting the voltage level of the ramp signal to the high reference level during the second interval;

wherein the emissive cell is illuminated during a portion of the frame duration in which the ramp signal voltage level is lower than the data signal voltage level.

11. In an emissive display having an array of pixels, each pixel including a circuit for controlling application of energy to an emissive cell associated with each pixel, a method for providing gray scale illumination during a frame duration comprising the steps of:

a) applying a data signal voltage level to the circuit along a data line and applying a select signal to the circuit along a select line;

b) storing the data signal within the circuit;

c) applying an alternating current high voltage to the emissive cell during the entire frame duration;

d) applying a ramp signal to the circuit along a further line, the ramp signal linearly ramping from a low reference level to a high reference level during an entire first frame duration; and

e) modifying the ramping voltage during a second frame duration by (i) linearly ramping the voltage level from a low reference level to a high reference level during a first interval of the second frame duration, (ii) inhibiting the emissive cell from illuminating during a second interval of the frame duration by setting the voltage level of the ramp signal to the high reference level during the second interval, and (iii) alternating the first frame duration and the second frame duration;

wherein the emissive cell is illuminated during a portion of the frame duration in which the ramp signal voltage level is lower than the data signal voltage level.

12. A method for providing a gray scale illumination for a display having an array of pixels comprising the steps of:

a) illuminating a pixel during a succession of frame intervals,

b) ramping a voltage level applied to the pixel from a first predetermined voltage level to a second predetermined voltage level over substantially an entire frame time during each of the frame intervals, the ramp signal providing a voltage level that stops the illumination in each frame interval, wherein a first ramp signal is applied during a first frame interval and a second ramp signal is applied during a second frame interval,

c) superimposing a first inhibit pulse during a first sub-interval of the first frame interval on the first ramp signal to stop the illumination during the first sub-interval, the illumination being responsive to the first ramp signal during the remainder of the first frame interval,

d) superimposing a second inhibit pulse during a second sub-interval of the second frame interval on the second ramp signal to stop the illumination during the second sub-interval, the illumination being responsive to the second ramp signal during the remainder of the second frame interval, and

e) sequentially repeating steps (c) and (d) during the succession of frame intervals.

13. A method for providing a gray scale illumination for a display having an array of pixels comprising the steps of:

a) illuminating a pixel during a succession of frame intervals,

b) ramping a voltage level applied to the pixel from a first predetermined voltage level to a second predetermined voltage level over substantially an entire frame interval during each of the frame intervals, the ramp signal providing a voltage level that stops the illumination in each frame interval, wherein a first ramp signal is applied during a first frame interval and a second ramp signal is applied during a second frame interval,

c) superimposing a first inhibit pulse during a first sub-interval of the first frame interval on the first ramp signal to stop the illumination during the first sub-interval, the illumination being responsive to the first ramp signal during the remainder of the first frame interval,

d) repeating step (c) during the succession of frame intervals.

14. A method for providing a gray scale illumination for a display having an array of pixels comprising the steps of:

a) illuminating a pixel during a succession of frame intervals,

b) ramping a voltage level applied to the pixel from a first predetermined voltage level to a second predetermined voltage level over substantially an entire frame interval during each of the frame intervals, the ramp signal providing a voltage level that stops the illumination in each frame interval, wherein a first ramp signal is applied during a first frame interval and a second ramp signal is applied during a second frame interval,

c) superimposing a first inhibit pulse during a first sub-interval of the first frame interval on the first ramp signal to stop the illumination during the first sub-interval,

d) superimposing a second inhibit pulse during a second sub-interval of the first frame interval on the first ramp signal to stop the illumination during the second sub-interval,

wherein the illumination is responsive to the first ramp signal during the remainder of the first frame interval, and

e) repeating steps (c) and (d) during the succession of frame intervals.

15. A method for providing a gray scale illumination for a display having an array of pixels comprising the steps of:

a) illuminating a first pixel and a second pixel during a succession of frame intervals,

b) ramping a first ramp signal and a second ramp signal applied to the first and second pixels respectively from a respective initial voltage level to a respective final voltage level, each of the ramp signals being ramped over substantially an entire frame time, the ramp signal providing a voltage level that stops the illumination of each pixel, wherein a first ramp signal is applied during a first frame interval and a second ramp signal is applied during a second frame interval,

c) superimposing a first inhibit pulse during a first sub-interval of the first frame interval on the first ramp signal to stop the illumination during the first sub-interval, the illumination being responsive to the first ramp signal during the remainder of the first frame interval,

d) superimposing a second inhibit pulse during a second sub-interval of the second frame interval on the second ramp signal to stop the illumination during the second sub-interval, the illumination being responsive to the second ramp signal during the remainder of the second frame interval, and

e) repeating steps (c) and (d) during the succession of frame intervals.

16. A method for providing a gray scale illumination for a display having an array of pixels comprising the steps of:

a) illuminating a first pixel and a second pixel during a succession of frame intervals,

b) ramping a first ramp signal and a second ramp signal applied to the first and second pixels respectively from a respective initial voltage level to a respective final voltage level, each of the ramp signals being ramped over substantially an entire frame time, the ramp signal providing a voltage level that stops the illumination of each pixel, wherein a first ramp signal is applied during a first frame interval and a second ramp signal is applied during a second frame interval,

c) superimposing a first inhibit pulse during a first sub-interval of the first frame interval on the first ramp signal to stop the illumination during the first sub-interval,

d) superimposing a second inhibit pulse during a second sub-interval of the first frame interval on the first ramp signal to stop the illumination during the second sub-interval,

wherein the illumination is responsive to the first ramp signal during the remainder of the first frame interval, and

e) repeating steps (c) and (d) during the succession of frame intervals.