Method, apparatus and computer program product for controlling LED backlights and for improved pulse width modulation resolution

• US 7,728,809 B2
• Filed: 12/04/2006
• Issued: 06/01/2010
• Est. Priority Date: 04/12/2000
• Status: Expired due to Fees

• Current Assignee: Honeywell International Inc.
• Original Assignee: Honeywell International Inc.
• Inventors: Lewis, Roger
• Primary Examiner(s): Hjerpe; Richard
• Assistant Examiner(s): Said; Mansour M
• Application Number:
  US11/633,257
• Publication Number:
  US 20070115304A1
• Time in Patent Office: 1,275 Days
• Field of Search: 345/39, 345/44, 345 46- 48, 345 52- 54, 345 77- 78, 345 82- 84, 345 87- 88, 345 94- 96, 345/102, 345691-692, 318/811, 327/175, 327/172, 315/169.3, 315/312, 315/291, 315/362
• US Class Current: 345/102
• CPC Class Codes: G09G 2320/0606 Manual adjustment
• CPC Class Codes: G09G 2320/0626 for control of overall brightness
• CPC Class Codes: G09G 2320/064 by time modulation of the brightness of the illumination source
• CPC Class Codes: G09G 2330/021 Power management, e.g. power saving
• CPC Class Codes: G09G 3/3406 Control of illumination source illumination devices structurally associated with liquid crystal cells G02F1/1336

Abstract

A method for driving an LED backlight device using pulse width modulation with an additional timer to manage the power consumption, thermal output, and lighting level of the device with improved resolution. The method includes receiving a commanded brightness level, and using an n bit pulse width modulator that has a nominal time period (P_n) to assert a plurality of pulses in accordance with an output of the n bit pulse modulator. A modulator output value is assigned to each one of K states of a K state timer that has a timer period (P_T). The plurality of pulses is output according to the modulator output value during each nominal time period occurring within the timer period. Power to the display is supplied in accordance with the plurality of pulses.

Claims

1. A method for controlling the brightness of a display using pulse width modulation comprising the steps of:

receiving a commanded brightness level;

using an n bit pulse width modulator to assert a plurality of pulses in accordance with an output of said n bit pulse modulator wherein said modulator has a nominal time period P_n;

assigning a modulator output value to each one of K states of a K state timer, wherein K is greater than 2 and said timer has a timer period P_T;

outputting said plurality of pulses according to said modulator output value during each nominal time period P_n occurring within timer period P_T; and

supplying power to the display in accordance with said plurality of pulses.

2. The method of claim 1 wherein P_T is an integer multiple of P_n.

3. The method of claim 1 wherein said pulse width modulator includes an overflow bit.

4. The method of claim 1 wherein P_T=P_n.

5. An LED backlit display comprising:

an array of LEDs;

an n bit pulse width modulator having a nominal period of P_n;

a timer having K states and a timer period of P_T;

a computing device coupled to said pulse width modulator and said timer for assigning a modulator output value to each of said K states of said timer;

whereby said pulse width modulator outputs a plurality of pulses according to said modulator output value during each nominal period occurring within said timer period P_T and whereby said pulse width modulator has a resolution of n+log₂ (K); and

a driver coupled to said pulse width modulator for supplying power to said array in accordance with said pulse width modulator output.

6. The display of claims 5 wherein P_T is an integer multiple of P_n.

7. The display of claim 5 wherein P_T is other than an integer multiple of P_n and P_T>

>

P_n.

8. The display of claim 5 wherein said modulator further comprises an overflow bit.

9. A method for controlling the brightness of a display using pulse width modulation comprising the steps of:

receiving a commanded brightness level;

using an n bit pulse width modulator to assert a plurality of pulses in accordance with an output of said n bit pulse modulator wherein said modulator has a nominal time period P_n;

assigning a modulator output value to each one of K states of a K state timer, wherein K is greater than 2, said timer has a timer period P_T, and P_T is an integer multiple of P_n;

outputting said plurality of pulses according to said modulator output value during each nominal time period P_n occurring within timer period P_T; and

supplying power to the display in accordance with said plurality of pulses.