Light control circuit and a liquid-crystal-display control drive device

Abstract

A light control circuit that makes it possible to, when the light intensity of the area surrounding a display screen varies in a relatively short time, prevent the brightness of a backlight from being erroneously adjusted as the result of the variation being detected is provided. The light control circuit controls the backlight of a display panel. This light control circuit is provided with functions of performing the following operation: detection signals from multiple optical sensors are taken into a common sampling means in a time division manner to acquire multiple sampling values temporally dispersed; a surrounding light intensity is determined by majority decision based on the multiple sampling values, and the result of determination is externally outputted.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating the overall configuration of a light control circuit provided with a function of detecting the light intensity of a liquid crystal display unit and a backlight control function, according to the invention;

FIG. 2 is a timing diagram that explains the integrating operation of an integrator circuit that constructs a backlight control circuit in an embodiment;

FIG. 3 is a timing diagram that explains the determination by majority decision of the outputs of optical sensors in a backlight control circuit in an embodiment;

FIG. 4 is a timing diagram indicating the timing with which the outputs of optical sensors are sampled in a backlight control circuit of an embodiment;

FIG. 5 is a characteristic diagram that indicates the characteristics of an optical sensor used in a backlight control circuit in an embodiment;

FIG. 6 is an input/output characteristic diagram that explains the hysteresis characteristics of a comparator that constructs a backlight control circuit in an embodiment;

FIG. 7 is a block diagram illustrating an embodiment of a liquid crystal control driver mounted with the light control circuit illustrated in FIG. 1 as a backlight control circuit;

FIG. 8 is a block diagram illustrating the overall configuration of a liquid crystal display unit to which the liquid crystal control driver in FIG. 7 is applied; and

FIG. 9 is a plan view illustrating an example of the composition of layout of a liquid crystal control driver 200 that incorporates the backlight control circuit illustrated in FIG. 7.

Claims

1. A light control circuit comprising: a plurality of input terminals to each of which an optical sensor is connected;a common sampling means that samples the outputs of the optical sensors inputted through the input terminals;a level determination circuit that determines the levels of voltages sampled by the sampling means;an output terminal through which the result of determination by the level determination circuit is outputted; andan input selecting means provided between the input terminals and the sampling means,wherein the sampling means samples the outputs of the optical sensors sequentially inputted through the input terminals in a temporally dispersed manner by the input selecting means.

2. A light control circuit comprising: a plurality of input terminals to each of which an optical sensor is connected;a common integrator circuit that integrates currents inputted through the input terminals to sample voltages corresponding to the outputs of the optical sensors;a level determination circuit that determines the levels of voltages sampled by the integrator circuit;an output terminal through which the result of determination by the level determination circuit is outputted; andan input selecting means provided between the input terminals and the integrator circuit and that inputs a current inputted through any input terminal to the integrator circuit,wherein the integrator circuit integrates currents sequentially inputted through the input terminals in a temporally dispersed manner by the input selecting means.

3. The light control circuit of claim 2, wherein the level determination circuit discriminates the levels of voltages sampled by the integrator circuit using a plurality of threshold voltages, holds a plurality of discrimination results corresponding to the outputs of the optical sensors in chronological order, determines the majority of the discrimination results and outputs the result of majority determination as the result of the determination.

4. The light control circuit of claim 3, wherein the level determination circuit includes: a comparator that is inputted with voltages sampled by the integrator circuit and a predetermined reference voltage;a resistance type voltage divider circuit that generates the reference voltage; andregisters that hold a plurality of set values corresponding to the threshold voltages, and supplies any of the set values held in the registers to the resistance type voltage divider circuit and thereby inputs the predetermined reference voltage to the comparator.

5. The light control circuit of claim 4, wherein the level determination circuit includes: a plurality of shift registers that take in and hold three or more outputs of the comparator in chronological order; anda plurality of majority decision determination circuits that determine the majority of the discrimination results based on the values held in the shift registers.

6. The light control circuit of claim 5, wherein the outputs of the majority decision determination circuits are encoded, and the result of encoding is outputted as the result of the determination.

7. The light control circuit of claims 2, further comprising: a current source circuit that passes a predetermined current; andan external terminal through which a current passed by the current source circuit is outputted,wherein the current source circuit is so constructed as to output or interrupt the predetermined current to the external terminal according to the result of determination by the level determination circuit.

8. The light control circuit of claim 7, further comprising: a second external terminal to which the other terminal of a light-emitting device connected to the external terminal is connected; a third external terminal to which a constant potential is externally applied; and a switch element provided between the second external terminal and the third external terminal,wherein the switch element is kept on while the constant-current source circuit passes the constant current according to the result of determination by the level determination circuit.

9. A liquid-crystal-display control drive device comprising: a light control circuit that includes: a plurality of input terminals to each of which an optical sensor is connected,a common integrator circuit that integrates currents inputted through the input terminals to sample voltages corresponding to the outputs of the optical sensors,a level determination circuit that determines the levels of voltages sampled by the integrator circuit, andan output terminal through which the result of determination by the level determination circuit is outputted, and that is provided, between the input terminals and the integrator circuit, with a selecting means that inputs a current inputted through any input terminal to the integrator circuit, the integrator circuit being so constructed as to integrate currents sequentially inputted through the input terminals in a time division manner;a first drive circuit that outputs a driving signal applied to a scanning line of a liquid crystal display panel;a display memory that stores displayed data displayed on the liquid crystal display panel; anda second drive circuit that outputs a driving signal applied to a signal line of the liquid crystal display panel according to displayed data read from the display memory,the liquid-crystal-display control drive device being formed over a single semiconductor substrate.

10. The liquid-crystal-display control drive device of claim 9, wherein the integrator circuit performs integrating operation during a display blank period within a frame period that is the scanning period for one screen page in the liquid crystal display panel.

11. The liquid-crystal-display control drive device of claim 10, wherein the integrator circuit performs a plurality of times of integrating operation during one display blank period, and the level determination circuit discriminates the levels of a plurality of voltages sampled by a plurality of times of integrating operation by the integrator circuit during one display blank period, using a plurality of threshold voltages, holds a plurality of discrimination results across a plurality of frames in a chronological order, determines the majority of the discrimination results, and outputs the result of majority determination as the result of the determination.