Liquid crystal driving circuit, liquid crystal display, and step-up frequency control method
A liquid crystal driving circuit includes a step-up circuit that generates a voltage for driving a liquid crystal to display an image. A detection circuit processes the image data to detect information, such as the number of picture elements having a brightness level exceeding a reference level, or the number of displayable colors, from which the necessary liquid crystal driving current can be estimated. A step-up frequency control circuit controls the operating frequency of the step-up circuit according to the detected information. The step-up circuit can thereby be controlled to supply sufficient current without consuming unnecessary current itself.
1 . A liquid crystal driving circuit including a step-up circuit that generates a voltage for driving a liquid crystal to display an image, comprising:
a detection circuit for detecting image content from which necessary liquid crystal driving current is estimable; and
a step-up frequency control circuit for controlling an operating frequency of the step-up circuit according to the detected image content.
2 . The liquid crystal driving circuit of claim 1 , wherein the image comprises a plurality of successively scanned lines, and the image content is detected once per line.
3 . The liquid crystal driving circuit of claim 1 , wherein the image comprises a plurality of temporally successive frames, and the image content is detected once per frame.
4 . The liquid crystal driving circuit of claim 1 , wherein the detected image content includes brightness of picture elements.
5 . The liquid crystal driving circuit of claim 1 , wherein the detected image content includes number of displayable colors.
6 . The liquid crystal driving circuit of claim 1 , wherein the detection circuit counts image data satisfying a predetermined condition.
7 . The liquid crystal driving circuit of claim 6 , wherein the detection circuit compares the image data with a predetermined reference value to decide whether the predetermined condition is satisfied.
8 . The liquid crystal driving circuit of claim 6 , wherein:
the detection circuit includes
a first register storing a quantity, derived from the image data, from which the necessary liquid crystal driving current is estimable;
a second register storing a reference value for said quantity;
a first comparator comparing the quantity stored in the first register with the reference value stored in the second register to decide whether the predetermined condition is satisfied; and
a counter for counting outputs of the first comparator satisfying the predetermined condition; and
the step-up frequency control circuit includes a third register storing a reference value for the count obtained by the counter;
a second comparator comparing the count obtained by the counter with the reference value stored in the third register; and
a selector selecting a frequency division ratio for a divided clock signal that drives the step-up circuit, the frequency division ratio being selected according to the output of the second comparator.
9 . The liquid crystal driving circuit of claim 6 , wherein the detection circuit also detects a display mode setting.
10 . The liquid crystal driving circuit of claim 9 , wherein:
the detection circuit includes
a first register storing a quantity from which the necessary liquid crystal driving current is estimable;
a second register storing a reference value of said quantity;
a first comparator comparing the quantity stored in the first register with the reference value stored in the second register to decide whether the predetermined condition is satisfied; and
a counter for counting outputs of the first comparator satisfying the predetermined condition; and
a third register storing the display mode setting; and
the step-up frequency control circuit includes a fourth register storing a reference value for the count obtained by the counter;
a second comparator comparing the count obtained by the counter with the reference value stored in the fourth register;
a fifth register storing a reference value of the display mode setting;
a third comparator comparing the display mode setting stored in the third register with the reference value stored in the fifth register;
an algebraic adder for algebraically adding outputs of the second comparator and the third comparator; and
a selector selecting a frequency division ratio for a divided clock signal that drives the step-up circuit, the frequency division ratio being selected according to an output of the algebraic adder.
11 . A liquid crystal display device including the liquid crystal driving circuit of claim 1 , comprising:
a liquid crystal panel driven by said liquid crystal display driving circuit; and
a processing unit for transferring the image data to the liquid crystal driving circuit.
12 . A method of controlling the operating frequency of a step-up circuit that boosts a power supply voltage and supplies current to a load circuit at the boosted voltage, comprising:
detecting operating data of the load circuit, the operating data being data from which current drawn by the load circuit is estimable; and
setting the operating frequency of the step-up circuit according to the detected operating data.
13 . The method of claim 12 , wherein the load circuit drives a liquid crystal panel to display an image.
14 . The method of claim 13 , wherein detecting the operating data includes counting image data satisfying a predetermined condition.
15 . The method of claim 13 , wherein detecting the operating data includes comparing image data with at least one predetermined reference value.
16 . The method of claim 13 , wherein detecting the operating data includes determining a number of displayable colors.
17 . The method of claim 13 , wherein detecting the operating data includes determining a polarity inversion period.
18 . The method of claim 13 , wherein detecting the operating data includes determining a polarity inversion mode.
19 . The method of claim 13 , wherein detecting the operating data includes determining a frame rate.