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Apparatus and method for dimming a backlight with pseudo-random phase delay

A phase delay, equipment technology, used in optics, light sources, electric light sources, etc.

Active Publication Date: 2014-07-23
TEXAS INSTR INC
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Problems solved by technology

Conventional PWM with figure 1 Operates in a similar fashion to that shown in , however, it has a bright and dark column "shimming" effect on a liquid crystal display (LCD), which is at least partially caused by backlight LED dimming and LCD-related parasitics of

Method used

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  • Apparatus and method for dimming a backlight with pseudo-random phase delay
  • Apparatus and method for dimming a backlight with pseudo-random phase delay
  • Apparatus and method for dimming a backlight with pseudo-random phase delay

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Embodiment Construction

[0033] Referring now to the drawings, elements depicted therein are not necessarily shown to scale for the sake of clarity, and identical or similar elements are designated by the same reference numerals throughout the several views.

[0034] refer to figure 2 , reference numeral 200 generally indicates a driving circuit according to an embodiment of the present invention. Circuit 200 generally includes state machine 202 , synchronization or synchronization register 204 , generator 206 and phase locked loop (PLL) 208 .

[0035] In operation, synchronization register 204 , generator 206 and PLL 208 each provide certain signals to state machine 202 . Preferably, the synchronous register 204 receives n bits / bits (e.g., 8 bits), driving period T ON , and output a driving period T synchronously with an input signal having a period T or a clock signal from the oscillator 210 ON . A generator 206, which is preferably a pseudo-random number generator, receives an input signal fro...

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Abstract

The present invention provides a method of generating a driving signal for a light source. Generates a random phase delay for each cycle of an input signal, where each cycle has a predetermined duration. The individual phase delays are superimposed over a predetermined drive period to generate a duration sum. Compare the total duration with the scheduled duration. Based on the comparison of the sum of the durations with the predetermined duration, at least one on-time and at least one off-time are calculated for each cycle of the input signal, and a drive signal with each on-time and each off-time is generated.

Description

technical field [0001] The present invention relates generally to circuits for powering light emitting diodes (LEDs), and more particularly to circuits employing phase delays to dim backlights. Background technique [0002] Refer to attached picture figure 1 , which shows a timing diagram describing the operation of a conventional pulse width modulator (PWM). In this timing diagram the LED current is shown as a function of time. Specifically, the duty cycle is 50% in the T period. Conventional PWM with figure 1 Operates in a similar fashion to that shown in , however, it has a bright and dark column "shimming" effect on a liquid crystal display (LCD), which is at least partially caused by backlight LED dimming and LCD-related parasitics of. The following patents are examples of some conventional PWMs: European Patent No. 1568044 and US Patent No. 7,279,995. Contents of the invention [0003] Accordingly, embodiments of the present invention provide a method for gener...

Claims

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Application Information

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Patent Type & Authority Patents(China)
IPC IPC(8): H05B41/234H03K3/017H03K7/08G02F1/13357
CPCH05B33/0818H05B45/10H05B45/325
Inventor J·徐X·曾X·孟
Owner TEXAS INSTR INC