PULSE WIDTH MODULATION SIGNAL GENERATING DEVICE, IMAGE DISPLAY APPARATUS INCLUDING PULSE WIDTH MODULATION SIGNAL GENERATING DEVICE, AND PULSE WIDTH MODULATION SIGNAL GENERATING METHOD

• US 20090310633A1
• Filed: 05/15/2009
• Published: 12/17/2009
• Est. Priority Date: 06/17/2008
• Status: Active Grant

• Current Assignee: Seiko Epson Corporation (Seiko Group)
• Original Assignee: Seiko Epson Corporation (Seiko Group)
• Inventors: IKEGAMI, Tomio
• Granted Patent: US 8,058,633 B2
• Time in Patent Office: Days
• US Class Current: 372/26
• CPC Class Codes: H01S 5/0427 for applying modulation to the laser
• CPC Class Codes: H04N 9/3123 using pulse width modulation
• CPC Class Codes: H04N 9/3129 scanning a light beam on the display screen scanning a light beam on a screen in displays other than projection devices G09G3/02; scanning systems in general G02B26/10; projectors using laser light sources in general H04N9/3161

Abstract

A pulse width modulation signal generating device which generates a pulse width modulation signal for modulating laser beam according to image data includes: a cycle signal output circuit which outputs a cycle signal having a cycle corresponding to a drawing rate for drawing the image data by the laser beam; and a pulse width modulation circuit which receives supply of the image data and the cycle signal and modulates a pulse wave having a cycle determined by the cycle signal by changing duty ratio of the pulse wave based on the image data to produce the pulse width modulation signal.

Claims

1. A pulse width modulation signal generating device which generates a pulse width modulation signal for modulating laser beam according to image data, comprising:

a cycle signal output circuit adopted to output a cycle signal having a cycle corresponding to a drawing rate for drawing the image data by the laser beam; and

a pulse width modulation circuit adopted to receive the image data and the cycle signal and modulate a pulse wave having a cycle determined by the cycle signal by changing duty ratio of the pulse wave based on the image data to produce the pulse width modulation signal.

2. The pulse width modulation signal generating device according to claim 1, wherein the cycle signal output circuit includes a phase synchronization circuit adopted to receive a drawing clock having a cycle corresponding to the drawing rate and output a signal having frequency equal to and phase synchronized with the drawing clock as the cycle signal.

3. The pulse width modulation signal generating device according to claim 2, wherein the cycle signal is a signal having ramp wave, triangle wave, or saw tooth wave.

4. The pulse width modulation signal generating device according to claim 1, wherein the drawing rate increases as the drawing position rises in the vertical direction of the drawing image.

5. The pulse width modulation signal generating device according to claim 4, wherein the drawing rate becomes the maximum at the center in the horizontal direction at the same position in the vertical direction, and decreases as the position shifts from the center toward the outside.

6. The pulse width modulation signal generating device according to claim 1, further comprising:

an image data memory unit adopted to temporarily store the image data, and adopted to cyclically output respective pixel data constituting the image data based on a data read clock received by the image data memory unit,

wherein the cycle signal output circuit includes

a parameter calculating unit adopted to calculate the position of pixel data to be read from the image data memory unit on the image data in the vertical direction and calculate a parameter corresponding to the drawing rate determined by the position in the vertical direction,

a phase synchronization circuit adopted to receive a system clock having a predetermined cycle and the parameter and output a signal having a cycle calculated by dividing the predetermined cycle by a number corresponding to the parameter as the cycle signal, and

a waveform shaper adopted to shape an oscillation signal from the phase synchronization circuit and output the shaped signal as the data read clock.

7. The pulse width modulation signal generating device according to claim 6, wherein the cycle signal is a signal having ramp wave, triangle wave, or saw tooth wave.

8. The pulse width modulation signal generating device according to claim 6, wherein the drawing rate increases as the drawing position rises in the vertical direction of the drawing image.

9. An image display apparatus comprising:

the pulse width modulation signal generating device according to claim 1; and

an upper device adopted to receive an image signal containing the image data from the outside, and adopted to transmit the drawing clock based on the image signal to the pulse width modulation signal generating device.

10. An image display apparatus comprising:

the pulse width modulation signal generating device according to claim 6; and

an upper device adopted to receive an image signal from the outside, and adopted to transmit image data contained in the image signal to the image data memory unit, and a vertical synchronous signal and a horizontal synchronous signal contained in the image signal to the parameter calculating unit.

11. A pulse width modulation signal generating method which generates a pulse width modulation signal for modulating laser beam according to image data, comprising:

outputting a cycle signal having a cycle corresponding to a drawing rate for drawing the image data by the laser beam; and

receiving the image data and the cycle signal and modulating a pulse wave having a cycle determined by the cycle signal by changing duty ratio of the pulse wave based on the image data to produce the pulse width modulation signal.