Field sequential color mode liquid crystal display

• US 8,643,587 B2
• Filed: 12/04/2006
• Issued: 02/04/2014
• Est. Priority Date: 02/09/2006
• Status: Active Grant

• Current Assignee: Samsung Electronics Co. Ltd.
• Original Assignee: Samsung Electronics Co. Ltd.
• Inventors: Ha, Chang Woo, Min, Byoung Own, Cheon, Jeong In, Jang, Yu Jin
• Primary Examiner(s): Eisen, Alexander
• Assistant Examiner(s): LAM, NELSON C
• Application Number:
  US11/566,505
• Publication Number:
  US 20070182699A1
• Time in Patent Office: 2,619 Days
• Field of Search: 345 87-104, 345 39- 46, 345 82- 83
• US Class Current: 345/102
• CPC Class Codes: G09G 2310/0235 Field-sequential colour display
• CPC Class Codes: G09G 2320/064 by time modulation of the brightness of the illumination source
• CPC Class Codes: G09G 3/3413 Details of control of colour illumination sources
• CPC Class Codes: H05B 45/38 using boost topology
• CPC Class Codes: Y02B 20/30 Semiconductor lamps, e.g. solid state lamps [SSL] light emitting diodes [LED] or organic LED [OLED]

Abstract

In an FSC mode LCD, a controller operates in response to an external adjustment, and a DC/DC converter converts a battery voltage into a driving voltage under control of the controller. A color LED backlight includes first, second and third color LED arrays connected in parallel, which are operated by the driving voltage. An FSC generator generates first, second and third color PWM signals according to an internal sawtooth voltage and a dimming voltage. A 3-channel current source generates first, second and third driving currents under control of the controller, and on/off switches paths of the first, second and third driving currents flowing through the first, second and third color LED arrays according to the first, second and third color PWM signals generated from the FSC generator, thereby adjusting luminance of the first, second and third color LED arrays of the color LED backlight.

Claims

1. A field sequential color (FSC) mode liquid crystal display (LCD), comprising:

a controller configured to operate in response to an external adjustment;

a direct-current-to-direct-current (DC/DC) converter configured to convert a battery voltage into a driving voltage under control of the controller;

a color light emitting diode (LED) backlight including first, second, and third color LED arrays connected in parallel and configured to be operated by the driving voltage outputted from the DC/DC converter;

an FSC generator configured to generate first, second, and third color PWM signals as field sequential signals according to an internal sawtooth voltage and a dimming voltage; and

a 3-channel current source configured to generate first, second, and third driving currents flowing through the first, second, and third color LED arrays of the color LED backlight, respectively, the 3-channel current source comprising respective on/off switching paths for the first, second, and third driving currents respectively controlled according to the first, second, and third color PWM signals generated from the FSC generator to adjust luminances of the first, second, and third color LED arrays of the color LED backlight, wherein

the FSC generator comprises;

a sawtooth voltage generating unit configured to generate the internal sawtooth voltage;

a comparing unit configured to compare the sawtooth voltage with the dimming voltage to output a PWM signal; and

an FSC logic unit configured to divide the PWM signal by two and four and operate a logic operation on the divided signals to generate the first, second, and third color PWM signals, and

the FSC logic unit comprises;

a first binary counter configured to divide an output signal of the comparing unit by two to generate a first divided signal;

a second binary counter configured to divide an output signal of the first binary counter by two to generate a second divided signal;

an inverter unit configured to invert the first divided signal and the second divided signal to output a first inverted signal and a second inverted signal;

a first AND gate unit configured to perform a logical sum (AND) operation of the first and second inverted signals to output a first logic signal, an AND operation of the first divided signal and the second inverted signal to output a second logic signal, an AND operation of the first inverted signal and the second divided signal to output a third logic signal, and an AND operation of the first and second divided signals to output a fourth logic signal; and

a second AND gate unit configured to perform a logical product (AND) operation of the first logic signal and the PWM signal to output a first color PWM signal, an AND operation of the second logic signal and the PWM signal to output a second color PWM signal, an AND operation of the third logic signal and the PWM signal to output a third color PWM signal, and an AND operation of the fourth logic signal and the PWM signal to output the second color PWM signal.

2. The FSC mode LCD of claim 1, wherein the FSC logic unit further comprises an OR gate unit configured to perform a logical sum (OR) operation of an output from the AND operation of the second logic signal and the PWM signal and an output from the AND operation of the fourth logic signal and the PWM signal, to output the second color PWM signal.

3. The FSC mode LCD of claim 1, wherein the second color LED array comprises a plurality of green LEDs.

4. The FSC mode LCD of claim 3, wherein the FSC logic unit is configured to sequentially supply a pulse by the first color PWM signal, a pulse by the second color PWM signal, a pulse by the third color PWM signal, and a pulse by the second color PWM signal at each period corresponding to four pulses of the PWM signal.

5. The FSC mode LCD of claim 4, wherein

the first color LED array comprises a plurality of blue LEDs, and

the third color LED array comprises a plurality of red LEDs, or vice versa.

6. The FSC mode LCD of claim 3, wherein

the first color LED array comprises a plurality of red LEDs, and

the third color LED array comprises a plurality of blue LEDs.

7. The FSC mode LCD of claim 3, wherein

the first color LED array comprises a plurality of blue LEDs, and

the third color LED array comprises a plurality of red LEDs.

8. The FSC mode LCD of claim 1, wherein the first, second, and third color PWM signals are sequential signals with the same width, and each has a high level in sequence without overlapping one another.

9. The FSC mode LCD of claim 1, further comprising:

an LCD panel being free of color filters.

10. A color light emitting diode (LED) backlight module for a field sequential color (FSC) mode liquid crystal display (LCD), the color LED backlight module comprising:

a direct-current-to-direct-current (DC/DC) converter electrically coupled to a controller and configured to convert a first voltage from a voltage source to a drive voltage;

a color LED backlight array electrically coupled to the DC/DC converter, the color LED backlight array comprising;

a red LED array comprising a plurality of red LEDs;

a green LED array comprising a plurality of green LEDs; and

a blue LED array comprising a plurality of blue LEDs;

an FSC generator configured to generate a red PWM signal, a green PWM signal, and a blue PWM signal, the FSC generator comprising;

a sawtooth voltage generating unit configured to generate a sawtooth voltage;

a comparing unit configured to compare the sawtooth voltage with a dimming voltage to output a PWM signal; and

an FSC logic unit configured to generate first to fourth logic signals each having a frequency of one-fourth of the frequency of the PWM signal, and to generate the red, green, and blue PWM signals; and

a 3-channel current source electrically coupled to the color LED backlight array and the FSC generator, the 3-channel current source being configured to selectively provide current paths for the red LED array, the green LED array, and the blue LED array based on the red, green, and blue PWM signals, wherein

the FSC logic unit comprises;

a first binary counter configured to divide an output signal of the comparing unit by two to generate a first divided signal;

a second binary counter configured to divide an output signal of the first binary counter by two to generate a second divided signal;

an inverter unit configured to invert the first divided signal and the second divided signal to output a first inverted signal and a second inverted signal;

a first AND gate unit configured to perform a logical sum (AND) operation of the first and second inverted signals to output a first logic signal, an AND operation of the first divided signal and the second inverted signal to output a second logic signal, an AND operation of the first inverted signal and the second divided signal to output a third logic signal, and an AND operation of the first and second divided signals to output a fourth logic signal; and

a second AND gate unit configured to perform a logical product (AND) operation of the first logic signal and the PWM signal to output a first color PWM signal, an AND operation of the second logic signal and the PWM signal to output a second color PWM signal, an AND operation of the third logic signal and the PWM signal to output a third color PWM signal, and an AND operation of the fourth logic signal and the PWM signal to output the second color PWM signal.

11. The color LED backlight module of claim 10, wherein the FSC logic unit is configured to sequentially supply a pulse by the red PWM signal, a pulse by the green PWM signal, a pulse by the blue PWM signal, and a pulse by the green PWM signal at each period corresponding to four pulses of the PWM signal.