Semiconductor integrated circuit outputting detection signal based on detection result of a detecting device and electronic device including the same

1. Field of the Invention

The present invention relates to a semiconductor integrated circuit and an electronic device including the same. Specifically, the present invention relates to a semiconductor integrated circuit outputting a detection signal based on a result of detection by a detecting device and to an electronic device including such a circuit.

2. Description of the Background Art

In an electronic device such as a liquid crystal television or a portable telephone including a detecting device represented by an illuminance sensor, a semiconductor integrated circuit outputting a detection signal based on the result of detection by the detecting device is used. By way of example, Japanese Patent Laying-Open No. 61-163738 (Patent Document 1) discloses a circuit that obtains a photoelectric conversion signal from a photoelectric conversion module.

In the semiconductor integrated circuit outputting a detection signal based on the result of detection by the detecting device, conventionally, a structure in which, for example, a current flowing through the detecting device is converted to a voltage by means of a resistor, and the converted voltage is converted to a digital signal by an AD (Analog to Digital) converter, has been used.

In the conventional semiconductor integrated circuit as such, however, the range of detection is limited by the dynamic range of the AD converter.

An object of the present invention is to provide a semiconductor integrated circuit capable of obtaining result of detection over a wide range and an electronic device including such a circuit.

According to an aspect, the present invention provides a semiconductor integrated circuit including: a first external terminal for receiving a voltage converted by a resistance portion from a current varying in response to an extrinsic factor; a second external terminal for externally outputting the voltage received at the first external terminal as a detection signal; a control circuit outputting a control signal for changing resistance value of the resistance portion based on the voltage received at the first external terminal; and a third external terminal for outputting the control signal to the resistance portion.

Preferably, the semiconductor integrated circuit further includes an AD converter converting the voltage received at the first external terminal to a digital signal and externally outputting the converted digital signal as the detection signal from the second external terminal.

According to another aspect, the present invention provides a semiconductor integrated circuit including: a resistance portion converting a current varying in response to an extrinsic factor to a voltage; an external terminal for externally outputting the converted voltage as a detection signal; and a control circuit outputting a control signal based on the converted voltage; wherein the resistance portion changes a resistance value based on the control signal received from the control circuit.

Preferably, the resistance portion includes a first resistor having a first terminal supplied with the current and a second terminal connected to a prescribed potential, a second resistor having a first terminal supplied with the current, and a switch element having a first terminal connected to a second terminal of the second resistor and a second terminal connected to the prescribed potential; and the switch element switches between an on state and an off state based on the control signal received from the control circuit.

According to a further aspect, the present invention provides an electronic device, including: a detecting device outputting a current varying in response to an extrinsic factor, a resistance portion converting the current received from the detecting device to a voltage and outputting the converted voltage; and a semiconductor integrated circuit; wherein the semiconductor integrated circuit includes a first external terminal for receiving the converted voltage, a second external terminal for externally outputting the voltage received at the first external terminal as a detection signal, a control circuit outputting a control signal based on the voltage received at the first external terminal, and a third external terminal for externally outputting the control signal; and the resistance portion changes resistance value based on the control signal received from the control circuit through the third external terminal.

According to a still further aspect, the present invention provides an electronic device, including: a detecting device outputting a current varying in response to an extrinsic factor; and a semiconductor integrated circuit; wherein the semiconductor integrated circuit includes a resistance portion converting the current received from the detecting device to a voltage, an external terminal for externally outputting the converted voltage as a detection signal, and a control circuit outputting a control signal based on the converted voltage; wherein the resistance portion changes a resistance value based on the control signal received from the control circuit.

By the present invention, it is possible to obtain the result of detection over a wide range.

The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.

FIG. 1 shows a configuration of a semiconductor integrated circuit in accordance with a first embodiment of the present invention.

FIG. 2A shows a relation between illuminance of light received by the illuminance sensor and an output current IS of the illuminance sensor, and FIG. 2B shows a relation between illuminance of light received by the illuminance sensor and a voltage VS received by an AD converter, of a conventional semiconductor integrated circuit.

FIG. 3A shows a relation between illuminance of light received by the illuminance sensor and an output current IS of the illuminance sensor, and FIG. 3B show a relation between illuminance of light received by the illuminance sensor and a voltage VS received by an AD converter of a semiconductor integrated circuit in accordance with a first embodiment.

FIG. 4 shows a configuration of an electronic device in accordance with the first embodiment of the present invention.

FIG. 5 shows a configuration of a semiconductor integrated circuit in accordance with a second embodiment of the present invention.

FIG. 6 shows a relation between illuminance of light received by the illuminance sensor and the voltage VS received by the AD converter in the semiconductor integrated circuits in accordance with the first and second embodiments.

In the following, embodiments of the present invention will be described with reference to the figures. In the figures, the same or corresponding portions are denoted by the same reference characters and description thereof will not be repeated.

First Embodiment

[Configuration and Basic Operation]

FIG. 1 shows a configuration of a semiconductor integrated circuit in accordance with a first embodiment of the present invention. Referring to FIG. 1 , a semiconductor integrated circuit 101 includes an AD converter 1 , a control circuit 2 , an operation circuit 3 , a bias circuit 4 , an external terminal T 1 , and external terminals (first to third external terminals) T 2 to T 4 . Control circuit 2 includes a comparator G 1 .

Outside the semiconductor integrated circuit 101 , an illuminance sensor (detecting device) X 1 and a resistance portion 5 are arranged. Resistance portion 5 includes resistors R 1 and R 2 , and an N-channel MOS (Metal Oxide Semiconductor) transistor M 1 .

When light enters illuminance sensor X 1 , a current is output from illuminance sensor X 1 in accordance with the intensity of incident light.

Resistance portion 5 converts the current output from illuminance sensor X 1 to a voltage, and outputs the converted voltage through external terminal T 2 to AD converter 1 and control circuit 2 .

AD converter 1 converts the voltage, that is, an analogue voltage received from resistance portion 5 to a digital signal, and outputs the converted digital signal to operation circuit 3 .

Operation circuit 3 generates a detection signal based on the digital signal received from AD converter 1 , and outputs the generated detection signal through external terminal T 3 to the outside of semiconductor integrated circuit 101 .

Control circuit 2 detects the voltage received from resistance portion 5 , generates a control signal based on the detected voltage, and outputs the generated control signal through external terminal 4 to resistance portion 5 .

Resistance portion 5 changes a resistance value based on the control signal received from control circuit 2 through external terminal 4 .

Bias circuit 4 supplies a bias voltage to illuminance sensor X 1 .

[Operation]

Next, an operation of outputting the detection signal of the semiconductor integrated circuit in accordance with the first embodiment of the present invention will be described.

Comparator G 1 compares the detected voltage, that is, the voltage received from resistance portion 5 , with a reference voltage VREF 1 . If the detected voltage is higher than the reference voltage VREF 1 , the comparator outputs a control signal of a H-level to resistance portion 5 through external terminal T 4 , and if the detected voltage is lower than the reference voltage VREF 1 , outputs a control signal of a L-level to resistance portion 5 through external terminal T 4 .

N-channel MOS transistor M 1 at resistance portion 5 is turned on if the control signal received from comparator G 1 is at the H-level, and it is turned off if the control signal is at the L-level.

Specifically, when it is dark around illuminance sensor X 1 , the current output from illuminance sensor X 1 becomes smaller and the voltage value of detection voltage received by AD converter 1 becomes lower, and therefore it is necessary to accurately detect a small voltage. Therefore, control circuit 2 turns off the N-channel MOS transistor M 1 so that resistance portion 5 is implemented by resistor R 1 only, whereby resistance portion 5 comes to have a larger resistance value than when it is implemented by a parallel circuit of resistors R 1 and R 2 . Thus, the voltage received by AD converter 1 from resistance portion 5 is increased.

When it is bright around illuminance sensor X 1 , the current output from illuminance sensor X 1 becomes larger and the voltage received by AD converter 1 from resistance portion 5 becomes higher. Therefore, there arises a possibility that the voltage exceeds the dynamic range of AD converter 1 . For this reason, control circuit 2 turns on the N-channel MOS transistor M 1 so that resistance portion 5 is implemented by a parallel circuit of resistors R 1 and R 2 , whereby resistance portion 5 comes to have a smaller resistance value. Thus, the voltage received by AD converter 1 from resistance portion 5 is made smaller.

In the conventional semiconductor integrated semiconductor circuit, there is a problem that the range of detection is limited by the dynamic range of AD converter.

FIG. 2A shows the relation between the illuminance of light received by the illumninance sensor and the current IS output from the illuminance sensor. FIG. 2B shows the relation between the illuminance of light received by the illuminance sensor and the voltage VS received by the AD converter, in a conventional semiconductor integrated circuit. Z 1 represents an example in which a resistor converting the output current of the detecting device to a voltage has a small resistance value RS, and Z 2 shows an example in which the resistor has large resistance value RS. D represents the dynamic range of AD converter.

Referring to FIG. 2 , with the small resistance value RS, the voltage VS received by the AD converter when the illuminance of light received by the illuminance sensor is low becomes smaller than the dynamic range of the AD converter. Therefore, the semiconductor integrated circuit cannot output the detection signal representing the illuminance in the range of X.

On the other hand, with large resistance value RS, the voltage VS received by the AD converter when the illuminance of light received by the illuminance sensor is high becomes larger than the dynamic range of the AD converter. Therefore, the semiconductor integrated circuit cannot output the detection signal representing the illuminance in the range of Y.

In the semiconductor integrated circuit in accordance with the first embodiment of the present invention, however, control circuit 2 detects the voltage received from resistance portion 5 , generates the control signal from the detected voltage, and outputs the generated control signal through external terminal 4 to resistance portion 5 . Resistance portion 5 changes the resistance value based on the control signal received from control circuit 2 through external terminal 4 .

FIG. 3A shows the relation between the illuminance of light received by the illuminance sensor and the current IS output from the illuminance sensor. FIG. 3B shows the relation between the illuminance of light received by the illuminance sensor and the voltage VS received by the AD converter in the semiconductor integrated circuit in accordance with the first embodiment of the present invention. Z 1 shows an example, in which the resistor converting the output current of the detecting device to a voltage has small resistance value RS, and Z 2 shows an example in which the resistance value RS is large. D represents the dynamic range of AD converter.

Referring to FIG. 3 , comparator G 1 compares the voltage VS, that is, the detected voltage, with the reference voltage VREF 1 , and if the detected voltage is higher than the reference voltage VREF 1 , outputs a control signal of H-level to resistance portion 5 through external terminal 4 . Then, N-channel MOS transistor M 1 at resistance portion 5 is turned on and resistance portion 5 comes to have smaller resistance value, whereby the voltage received by AD converter 1 from resistance portion 5 becomes smaller ( FIG. 3C ).

In the conventional semiconductor integrated circuit, it has been impossible to output a detection signal representing illuminance larger than A, because of the limitation by the dynamic range of AD converter. In the semiconductor integrated circuit in accordance with the first embodiment of the present invention, because of the arrangement described above, it becomes possible to obtain the result of detection to the illuminance B larger than A.

Therefore, in the semiconductor integrated circuit in accordance with the first embodiment of the present invention, the resistance value of resistance portion 5 can be changed appropriately in accordance with the increase in output current of illuminance sensor X 1 , and the result of detection over a wide range can be obtained.

In the semiconductor integrated circuit in accordance with the first embodiment of the present invention, semiconductor integrated circuit 101 has been described as including AD converter 1 and operation circuit 3 . The description is not limiting, and AD converter 1 and operation circuit 3 may be arranged outside of semiconductor integrated circuit 101 , and the voltage received from resistance portion 5 through external terminal T 2 may be output as the detection signal from external terminal T 3 to the outside of semiconductor integrated circuit 101 .

In the semiconductor integrated circuit in accordance with the first embodiment of the present invention, a configuration has been described in which illuminance sensor (detecting device) X 1 and resistance portion 5 are arranged outside of semiconductor integrated circuit 101 . The arrangement is not limiting, and semiconductor integrated circuit 101 may additionally include at least one of the illuminance sensor (detecting device) X 1 and resistance portion 5 .

A sensor which detects an extrinsic factor such as temperature, frequency of signal, vibration, acceleration or rotating velocity and outputs a current indicating the result of detection, that is, a current varying in response to the result of detection may be arranged instead of the illuminance sensor.

[Electronic Device]

FIG. 4 shows a configuration of an electronic device in accordance with the first embodiment of the present invention. Referring to FIG. 4 , an electronic device 201 includes semiconductor integrated circuit 101 , a backlight device 151 , illuminance sensor X 1 and resistance portion 5 .

Semiconductor integrated circuit 101 outputs a detection signal to backlight device 151 based on the result of detection of illuminance sensor X 1 .

Based on the detection signal received from semiconductor integrated circuit 101 , backlight device 151 determines the amount of light to be incident on a liquid crystal panel or the like.

In this manner, the semiconductor integrated circuit in accordance with the first embodiment of the present invention can be applied to the electronic device such as the portable telephone or a liquid crystal television.

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

Second Embodiment

The present embodiment relates to a semiconductor integrated circuit in which configurations of the control circuit and the resistance portion are made different from those of the semiconductor integrated circuit of the first embodiment. Except for the points described in the following, the semiconductor integrated circuit is the same as that of the first embodiment.

FIG. 5 shows a configuration of the semiconductor integrated circuit in accordance with the second embodiment of the present invention.

Referring to FIG. 5 , a semiconductor integrated circuit 102 includes AD converter 1 , a control circuit 7 , operation circuit 3 , bias circuit 4 and external terminals T 1 to T 5 . Control circuit 7 includes comparators G 1 and G 2 . Outside the semiconductor integrated circuit 102 , illuminance sensor (detecting device) X 1 and resistance portion 8 are arranged. Resistance portion 8 includes resistors R 1 to R 3 and N-channel MOS transistors M 1 and M 2 .

Next, an operation of outputting a detection signal of the semiconductor integrated circuit in accordance with the second embodiment of the present invention will be described.

Comparator G 1 compares the detected voltage, that is, the voltage received from resistance portion 8 , with the reference voltage VREF 1 , and if the detected voltage is higher than the reference voltage VREF 1 , it outputs a control signal of H-level through external terminal T 4 to N-channel MOS transistor M 1 , and if the detected voltage is lower than the reference voltage VREF 1 , it outputs a control signal of L-level through external terminal T 4 to N-channel MOS transistor M 1 .

Comparator G 2 compares the detected voltage, that is, the voltage received from resistance portion 8 , with a reference voltage VREF 2 , and if the detected voltage is higher than the reference voltage VREF 2 , it outputs a control signal of H-level through external terminal T 5 to N-channel MOS transistor M 2 , and if the detected voltage is lower than the reference voltage VREF 2 , it outputs a control signal of L-level through external terminal T 5 to N-channel MOS transistor M 2 .

N-channel MOS transistors M 1 and M 2 at resistance portion 8 are turned on if the control signals received from comparators G 1 and G 2 are at the H level, and turned off if the control signals are at the L level, respectively.

FIG. 6 represents the relation between the illuminance of light received by the illuminance sensor and the voltage VS received by the AD converter, in the semiconductor integrated circuit in accordance with the first and second embodiments of the present invention. Z 3 represents the example of the semiconductor integrated circuit in accordance with the first embodiment of the present invention, and Z 4 represents the example of the semiconductor integrated circuit in accordance with the second embodiment of the present invention. D represents the dynamic range of AD converter. Here, description will be given assuming that reference voltage VREF 1 is higher than reference voltage VREF 2 .

Referring to FIG. 6 , when the voltage VS, that is, the detected voltage, is not higher than the reference voltage VREF 2 , control circuit 7 turns off N-channel MOS transistors M 1 and M 2 , so that resistance portion 8 is implemented by resistor R 1 only, whereby resistance portion 8 comes to have a larger resistance value than when it is implemented by a parallel circuit of resistors. Thus, the voltage received by AD converter 1 from resistance portion 8 is increased.

When the voltage VS is higher than the reference voltage VREF 2 and not higher than the reference voltage VREF 1 , control circuit 7 turns off N-channel MOS transistor M 1 and turns on N-channel MOS transistor M 2 , whereby resistance portion comes to be implemented by a parallel circuit of resistors R 1 and R 3 , so that resistance portion 8 comes to have a smaller resistance value. Thus, the voltage received by AD converter 1 from resistance portion 8 is made smaller.

When the voltage VS becomes higher than the reference voltage VREF 1 , control circuit 7 turns on N-channel MOS transistors M 1 and M 2 , whereby resistance portion comes to be implemented by a parallel circuit of resistors R 1 to R 3 , so that resistance portion 8 comes to have even smaller resistance value. Thus, the voltage received by AD converter 1 from resistance portion 8 is made smaller.

In the semiconductor integrated circuit in accordance with the first embodiment, it has been impossible to output a detection signal representing an illuminance higher than E. Because of the configuration described above, it becomes possible by the semiconductor integrated circuit in accordance with the second embodiment to widen the range of detection to the illuminance indicated by F.

Therefore, in the semiconductor integrated circuit in accordance with the second embodiment of the present invention, the range of detection can further be widened than the semiconductor integrated circuit in accordance with the first embodiment.

Although the present invention has been described and illustrated in detail, it is clearly understood that the same is by way of illustration and example only and is not to be taken by way of limitation, the spirit and scope of the present invention being limited only by the terms of the appended claims.