Digital gray scale methods and devices

1. A method of operating a display device, the method comprising:

receiving input image data including a plurality of binary weighted bit values; and

controlling a display pixel to generate gray scale for a component color of the input image data using digital pulse width modulation between a first light modulating state and a second light modulating state, wherein at least one of the binary weighted bit values is represented in a first modulated waveform during a first display cycle and in a second modulated waveform during a second display cycle, and wherein at least one of the binary weighted bit values is represented in one of the first or the second modulated waveforms but not in the other of the first or the second modulated waveforms.

2. The method of claim 1 , wherein the first modulated waveform corresponds to a first subset of the plurality of binary weighted bit values and the second modulated waveform corresponds to a second subset of the plurality of binary weighted bit values.

3. The method of claim 2 , wherein the plurality of binary weighted bit values comprise eight-bit values, the eight-bit values including bits zero through seven, and wherein bits four through seven of the eight-bit values are included in both the first subset and the second subset of the plurality of binary weighted bit values.

4. The method of claim 3 , wherein each bit value of bit values zero through three of the eight-bit values are included in one of the first subset or the second subset of the plurality of binary weighted bit values but not the other of the first subset or the second subset of the plurality of binary weighted bit values.

5. The method of claim 2 , wherein the plurality of binary weighted bit values comprise eight-bit values, the eight-bit values including bits zero through seven, and wherein each of the first subset and the second subset of the plurality of binary weighted bit values comprise six bit values of the eight-bit values.

6. The method of claim 2 , wherein the first subset and the second subset comprise the plurality of binary weighted bit values not including the least-significant-bit, and wherein the least-significant-bit is added to one of the first subset or the second subset of the plurality of binary weighted bit values.

7. The method of claim 6 , wherein the plurality of binary weighted bit values comprise eight-bit values, the eight-bit values including bits zero through seven, and wherein the first subset and the second subset comprise seven-bit values not including bit zero of the plurality of binary weighted bit values, and wherein bit zero of the plurality of binary weighted bit values is added to one of the first subset or the second subset of the plurality of binary weighted bit values.

8. A display device comprising:

an array of active pixels, each active pixel electronically controllable to operate in a first light-modulating state that substantially prevents light output from the display device associated with the active pixel and a second light-modulating state that substantially allows light output from the display device associated with the active pixel; and

control circuitry to control operation of the array of active pixels to generate grayscale using digital pulse width modulation of binary weighted bit values of input image data, the digital pulse width modulation including a first digital pulse width modulation waveform during a first display cycle and a second digital pulse width modulation waveform during a second display cycle, and wherein at least one bit value of the binary weighted bit values is represented in both the first digital pulse width modulation waveform and the second digital pulse width modulation waveform, and wherein at least one bit value of the binary weighted bit values is represented in one of the first or the second digital pulse width modulation waveforms but not in the other of the first or the second digital pulse width modulation waveforms.

9. The display device of claim 8 , further comprising a digital interface for receiving the input image data, an array of memory cells coupled to the digital interface for storing image data, a ramp counter coupled to the digital interface for generating a ramp signal, and logic circuits for reading the image data from the memory cells and comparing the image data with the ramp signal, wherein each display cycle is divided into a plurality of time slots, and wherein during each time slot the image data is read from the array of memory cells and compared with the ramp signal.

10. The display device of claim 9 , wherein the display device produces full-color images of eight-bit grayscale resolution with less than 512 data comparisons per color per field.

11. The display device of claim 9 , wherein the display device has 32 data comparisons during the first display cycle and 64 data comparisons during the second display cycle.

12. The display device of claim 9 , wherein the ramp signal comprises a seven-bit ramp signal in both the first and second display cycles.

13. The display device of claim 12 , wherein pixels of the array of active pixels have pixel data values based on the input image data, and wherein a first pixel with the least significant bit asserted in an associated first pixel data value switches one time slot later in one of the first or the second display cycles than a pixel with the least significant bit not asserted in an associated second pixel data value.

14. The display device of claim 9 , wherein full-color images are displayed using field sequential color at a color-field rate of six times the input field frequency.

15. The display device of claim 9 , wherein the duration of each time slot is less than 10.9 microseconds.

16. A display device, comprising:

an array of active pixels arranged in rows and columns;

an array of memory cells arranged in rows and columns that stores encoded image data;

a row of sense amplifiers operable to read the encoded image data from the array of memory cells;

a column data processor that receives the encoded image data from the sense amplifiers, the column data processor operable to decode the encoded image data and

compare decoded image data to a reference signal to control light-modulating states of the active pixels;

a counter circuit that generates the reference signal for the column data processor; and

a control unit coupled to the array of memory cells, the column data processor, and the counter circuit, the control unit operable to receive the image data;

wherein the reference signal is ramped more than once during a display field for a component color of the image, the column data processor comparing a first subset of binary weighted bit-planes of the decoded image data to the reference signal during a first ramp of the reference signal and comparing a second subset of binary weighted bit-planes of the decoded image data to the reference signal during a second ramp of the reference signal.

17. The display device of claim 16 , further comprising a line buffer that temporarily stores the encoded data for the memory cells, wherein reading encoded data from the array of memory cells to the sense amplifiers is interleaved with writing encoded data to the array of memory cells from the line buffer.

18. The display device of claim 16 , wherein the display device is fabricated on a common semiconductor substrate, and wherein each pixel of the array of active pixels comprises a pixel electrode and a portion of the array of memory cells is located in the common semiconductor substrate vertically below the pixel electrodes of the array of active pixels.

19. The display device of claim 16 , wherein the array of active pixels is split into an upper half of the array of active pixels and a lower half of the array of active pixels and the column data processor comprises an upper column data processor and a lower column data processor, the upper column data processor performing the data processing for the upper half of the array of active pixels and the lower column data processor performing the data processing for the lower half of the array of active pixels.