JP4846549B2 - Semiconductor integrated circuit and electronic equipment - Google Patents

Description

  The present invention relates to a semiconductor integrated circuit and an electronic device, and more particularly to a semiconductor integrated circuit and an electronic device that supply current to a load based on an analog signal.

The brightness of an image displayed on a display such as a television apparatus differs depending on the type of image, for example, an indoor image and an outdoor image. Here, in order to prevent the viewer's eyes from fatigue and reduce power consumption, an illuminating device that changes the illuminance of the backlight of the display according to the brightness of the image itself has been developed. Such an illuminating device includes a driving IC (Integrated Circuit) that supplies current to an LED (Light Emitting Diode) that irradiates light to the display (see, for example, Patent Documents 1 and 2).
JP 2002-319707 A Japanese Patent Laid-Open No. 9-232635

  By the way, in such an illuminating device, the analysis of the brightness of an image is generally performed by a CPU (Central Processing Unit), for example, and the analysis result is generally obtained as a digital signal.

  Here, since the brightness of a moving image generally has a large amount of change per unit time, in the method of changing the illuminance of the backlight based on the digital signal, the driving IC decodes the digital signal and outputs it to the LED. A time lag occurs before the current value of the supply current is changed, and it is difficult to follow the change in the brightness of the image. In addition, since the change in the supply current of the driving IC is digital, that is, in a staircase pattern, the flickering of the screen increases and the screen becomes difficult to see.

  SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a semiconductor integrated circuit and an electronic apparatus capable of adjusting a current supplied to a load quickly and linearly according to a change in an analog signal.

  In order to solve the above problems, a semiconductor integrated circuit according to an aspect of the present invention includes a reference current source circuit that generates a reference current based on an analog signal received from the outside, and an amplification factor based on data received from the outside. And a variable amplifier circuit that amplifies the reference current received from the reference current source circuit with the determined amplification factor and outputs the amplified current to the load.

  Preferably, a display unit for displaying an image is arranged outside the semiconductor integrated circuit, the load is a light emitting element that irradiates light to the display unit, and the analog signal is an analog whose amplitude changes according to the brightness of the image. It is a signal, and data is data whose value changes according to the amount of ambient light.

  Preferably, the variable amplifier circuit is a current mirror circuit, and changes the mirror ratio based on data received from the outside.

Preferably, the load is an LED.
In order to solve the above problems, an electronic device according to an aspect of the present invention includes a display portion that displays an image, a light-emitting element that irradiates light to the display portion, an analog signal, and the brightness of the image. An image analysis circuit that changes the amplitude of the analog signal, a light detection circuit that receives light from the outside and generates data representing the amount of received light, a reference current source circuit that generates a reference current based on the analog signal, and data And a variable amplification circuit that amplifies the reference current received from the reference current source circuit with the determined amplification factor and outputs the amplified current to the light emitting element.

  According to the present invention, the current supplied to the load can be quickly and linearly adjusted according to the change of the analog signal.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals and description thereof will not be repeated.

<First Embodiment>
FIG. 1 is a diagram showing a configuration of a semiconductor integrated circuit according to the first embodiment of the present invention.

  Referring to FIG. 1, a semiconductor integrated circuit 101 includes a reference current source circuit 1, a variable amplifier circuit 2, and terminals T1 to T3. Reference current source circuit 1 includes operational amplifiers 11 and 12, resistors R1 to R5, and an N-channel MOS (Metal Oxide Semiconductor) transistor TR1.

  The reference current source circuit 1 generates a reference current IREF based on an external analog signal SX received via the capacitor C1 and the terminal T1. A DC component is removed from the external analog signal SX by the capacitor C1.

  When the output voltage of the operational amplifier 11 is VIN, the resistance values of the resistors R3 to R5 are R3 to R5, respectively, and the voltage value of the bias voltage VB supplied to the non-inverting input terminals of the operational amplifiers 11 and 12 is VB, the reference current IREF Is represented by the following equation.

IREF = VB / R4− (R5 × R3 × VB + R4 × R5 × VIN) / (R4 × (R4 × R5 + R4 × R3 + R5 × R3))
The variable amplifier circuit 2 determines an amplification factor based on data DX received from the outside via the terminal T2, amplifies the reference current IREF received from the reference current source circuit 1 with the determined amplification factor, and an amplified current Is supplied to the LED 3 as a load as a supply current ID. The load is not limited to the LED, but may be another light emitting element.

  FIG. 2 is a diagram showing a configuration of the variable amplifier circuit 2 in the semiconductor integrated circuit according to the first embodiment of the present invention.

  Referring to FIG. 2, variable amplifier circuit 2 includes an N channel MOS transistor TR11, n (n is a natural number of 2 or more) N channel MOS transistors, and (n-1) switches. FIG. 2 representatively shows N channel MOS transistors TR21 to TR23 among n N channel MOS transistors. FIG. 2 representatively shows the switches SW1 and SW2 among the (n−1) switches.

  The variable amplifier circuit 2 is a current mirror circuit, and changes the mirror ratio based on data DX received from the outside.

  N channel MOS transistor TR11 has a drain connected to the output of reference current source circuit 1. That is, the reference current IREF received from the reference current source circuit 1 becomes the drain current of the N-channel MOS transistor TR11.

  N N-channel MOS transistors including N-channel MOS transistors TR21 to TR23 constitute a current mirror circuit with N-channel MOS transistor TR11. That is, each of the n N-channel MOS transistors outputs a current having substantially the same current value as the reference current IREF received from the reference current source circuit 1.

  Based on the data DX, the (n−1) switches including the switches SW1 and SW2 are the bases of the N channel MOS transistors other than the N channel MOS transistor TR21 and the reference current source circuit among the n N channel MOS transistors. The connection and disconnection with the output of 1 are switched respectively. The data DX has, for example, a data width of (n-1) bits, and (n-1) bits of data and (n-1) switches have a one-to-one correspondence.

  That is, the variable amplifier circuit 2 outputs a supply current ID that is 1 to n times the reference current IREF to the LED 3 based on the data DX received from the outside.

  By the way, in the method of changing the illuminance of the backlight based on the digital signal, there is a time lag until the drive IC changes the current value of the current supplied to the LED by decoding the digital signal, resulting in a change in the brightness of the image. It is difficult to follow. In addition, since the change in the supply current of the driving IC is digital, that is, in a staircase pattern, the flickering of the screen increases and the screen becomes difficult to see. However, in the semiconductor integrated circuit according to the first embodiment of the present invention, the reference current source circuit 1 changes the current value of the reference current IREF based on the analog signal SX received from the outside. Then, the variable amplifier circuit 2 amplifies the reference current received from the reference current source circuit and outputs it to the load. Therefore, in the semiconductor integrated circuit according to the first embodiment of the present invention, the current supplied to the load can be quickly and linearly adjusted, for example, according to an analog signal that changes according to the brightness of the image.

  Next, another embodiment of the present invention will be described with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals and description thereof will not be repeated.

<Second Embodiment>
The present embodiment relates to an electronic apparatus including the semiconductor integrated circuit according to the first embodiment. The contents other than those described below are the same as those of the semiconductor integrated circuit according to the first embodiment.

FIG. 3 is a diagram showing a configuration of an electronic apparatus according to the second embodiment of the present invention.
Referring to FIG. 3, an electronic device 201 is, for example, a mobile phone, and includes a semiconductor integrated circuit 101, an image analysis circuit 51, a filter 52, a DA (Digital to Analog) converter 53, a photodetection circuit 54, A display (display unit) 55, a capacitor C1, and an LED 3 are provided.

  The display 55 is an LCD (Liquid Crystal Display), for example, and displays a still image and a moving image.

  The image analysis circuit 51 generates a digital signal having a value corresponding to the brightness of the image displayed on the display 55, and outputs the generated digital signal to the filter 52. For example, the image analysis circuit 51 calculates the maximum value of the brightness of a plurality of pixels in the image, the average value of the brightness of the plurality of pixels in the image, and the average of the brightness of the plurality of pixels each weighted in the image. The brightness of the pixel having the highest frequency in the frequency distribution of the brightness of the plurality of pixels in the image and the like are calculated as the brightness of the image.

  The filter 52 performs a predetermined filter process on the digital signal received from the image analysis circuit 51 and outputs the digital signal after the filter process to the DA converter 53.

  The DA converter 53 converts the digital signal received from the filter 52 into an analog signal SX and outputs the analog signal SX to the semiconductor integrated circuit 101 via the capacitor C1.

  Therefore, the analog signal SX received by the semiconductor integrated circuit 101 is an analog signal whose amplitude changes according to the brightness of the image.

  The photodetection circuit 54 receives light from the outside, generates data DX representing the amount of received light, and outputs the data DX to the variable amplifier circuit 2 in the semiconductor integrated circuit 101.

  Here, the brightness of a moving image has a larger amount of change per unit time than ambient light. Therefore, in the electronic device according to the second embodiment of the present invention, the variable amplifier circuit 2 changes the mirror ratio based on the data DX corresponding to the ambient light of the electronic device, and the reference current source circuit 1 Based on the analog signal SX corresponding to the brightness of the image displayed on the display 55, the current value of the reference current IREF is changed quickly and linearly. With such a configuration, the amount of light applied to the display 55 can be appropriately adjusted according to the amount of ambient light and the brightness of the image. Can be prevented and power consumption can be reduced.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

1 is a diagram showing a configuration of a semiconductor integrated circuit according to a first embodiment of the present invention. 1 is a diagram showing a configuration of a variable amplifier circuit 2 in a semiconductor integrated circuit according to a first embodiment of the present invention. It is a figure which shows the structure of the electronic device which concerns on the 2nd Embodiment of this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 Reference current source circuit, 2 Variable amplifier circuit, 3 LED, 11, 12 operational amplifier, 51 Image analysis circuit, 52 Filter, 53 DA converter, 54 Photodetection circuit, 55 Display (display part), 101 Semiconductor integrated circuit, 201 Electronics Equipment, C1 capacitor, R1-R5 resistors, TR1, TR11 N-channel MOS transistors, T1-T3 terminals.

Claims (5)

A reference current source circuit that generates a reference current based on an analog signal received from the outside;
A variable amplification circuit that determines an amplification factor based on data received from outside, amplifies the reference current received from the reference current source circuit at the determined amplification factor, and outputs the amplified current to a load; Semiconductor integrated circuit. A display unit for displaying an image is disposed outside the semiconductor integrated circuit,
The load is a light emitting element that emits light to the display unit,
The analog signal is an analog signal whose amplitude changes according to the brightness of the image,
The semiconductor integrated circuit according to claim 1, wherein the data is data whose value changes according to the amount of ambient light.   The semiconductor integrated circuit according to claim 1, wherein the variable amplifier circuit is a current mirror circuit, and changes a mirror ratio based on data received from the outside.   The semiconductor integrated circuit according to claim 1, wherein the load is an LED. A display for displaying an image;
A light emitting element for irradiating the display with light;
An image analysis circuit that generates an analog signal and changes the amplitude of the analog signal according to the brightness of the image;
A light detection circuit that receives light from outside and generates data representing the amount of received light;
A reference current source circuit for generating a reference current based on the analog signal;
An electronic device comprising: a variable amplification circuit that determines an amplification factor based on the data, amplifies a reference current received from the reference current source circuit with the determined amplification factor, and outputs the amplified current to the light emitting element; machine.

Images