Backlight control device and display apparatus
AssigneePanasonic Corporation
InventorsTakahisa Hatano, Kosho Suzuki
Life of this patent
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Abstract
A PWM generation circuit generates a PWM pulse signal having a variable duty ratio in order to control the luminance of a backlight. An edge detection circuit outputs a leading edge signal in response to the rise of the PWM pulse signal generated by the PWM generation circuit. A set value pulse generation circuit generates a set width pulse signal in response to the rise of the leading edge signal. The pulse width of the set width pulse signal is set so as to be larger than the minimum PWM pulse width. An OR gate calculates the logical sum of the set width pulse signal and the PWM pulse signal. An inverter circuit feeds a driving signal to a backlight on the basis of an output signal of the OR gate.
Claims11
A backlight control device that controls the luminance of a backlight, comprising:
- an inverter that drives said backlight in response to a dimming pulse signal;
- a first pulse generator that generates a first pulse signal having a variable duty ratio to control the luminance of said backlight;
- and
- a dimming pulse generator that outputs said dimming pulse signal to said inverter on the basis of a first pulse signal generated by said first pulse generator,
- wherein said inverter is operable when said dimming pulse signal has a pulse width that is not less than a predetermined minimum pulse width, and
- said dimming pulse generator outputs the first pulse signal generated by said first pulse generator as said dimming pulse signal to said inverter when the pulse width of the first pulse signal generated by said first pulse generator is not less than said minimum pulse width, while outputting a second pulse signal having a pulse width that is not less than said minimum pulse width as said dimming pulse signal to said inverter when the pulse width of the first pulse signal generated by said first pulse generator is less than said minimum pulse width.
A display apparatus comprising:
- a signal processing circuit that converts an inputted video signal into a predetermined format;
- a display panel that displays as an image a video signal obtained by said signal processing circuit;
- a backlight provided on a back of said display panel;
- and
- a backlight control device that controls the luminance of said backlight,
- wherein said backlight control device includes
- an inverter that drives said backlight in response to a dimming pulse signal;
- a first pulse generator that generates a first pulse signal having a variable duty ratio to control the luminance of said backlight;
- and
- a dimming pulse generator that outputs said dimming pulse signal to said inverter on the basis of the first pulse signal generated by said first pulse generator,
- said inverter is operable when said dimming pulse signal has a pulse width that is not less than a predetermined minimum pulse width, and
- said dimming pulse generator outputs the first pulse signal generated by said first pulse generator as said dimming pulse signal to said inverter when the pulse width of the first pulse signal generated by said first pulse generator is not less than said minimum pulse width, while outputting a second pulse signal having a pulse width that is not less than said minimum pulse width as said dimming pulse signal to said inverter when the pulse width of the first pulse signal generated by said first pulse generator is less than said minimum pulse width.
Dependencies are inferred from the claim text.