JP2004007468A - Digital camera - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a digital camera with which number of sheets for taking pictures does not decrease extremely even in a low-temperature environment. <P>SOLUTION: A system control circuit 40 of a digital still camera 10 switches operating modes by comparing the temperature detected by a temperature sensor 29 with a predetermined threshold. When the detected temperature is higher than the threshold, the control circuit 40 switches to a normal operating mode, and otherwise, to a power-saving operating mode. In the power-saving operating mode, a consumption current of the whole of the apparatus is reduced by lowering an operating frequency of the control circuit 40 and taking picture control circuit 42, for example, to a half of the frequency in the normal operating mode. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a digital camera, and more particularly to a digital camera that can operate in a power saving mode.
[0002]
[Prior art]
Conventionally, for example, digital still cameras often use batteries as a power source for convenience of carrying. However, since a digital still camera is required to be downsized, only a small amount of battery can be provided. Further, since the digital still camera is multifunctional and includes various electric circuits, power consumption is large in each operation. From the above, the digital still camera is required to have a function of suppressing power consumption.
[0003]
For the purpose of reducing power consumption, the digital still camera described in Patent Document 1 has a memory write stop command set when the ambient temperature falls below a predetermined threshold, and image data obtained by imaging the subject is stored in the memory. It is given directly to the display device without writing. The setting of this command stops writing of image data into the memory and reading of image data from the memory to the display device, thereby suppressing power consumption.
[0004]
[Patent Document 1]
Japanese Patent Application No. 2001-111946.
[0005]
[Problems to be solved by the invention]
Many digital still cameras can be operated with detachable batteries because of their portability, and many of them are easily available and inexpensive primary batteries can be used. In addition, since a digital still camera requires a large amount of current when the lens is operated or when a flash is charged, an alkaline battery is recommended as the primary battery. However, as shown in FIG. 2 and FIG. 3, the alkaline battery is known to have a temperature characteristic in which the internal impedance increases at a lower temperature than at a normal temperature. For this reason, when an alkaline battery is used at a low temperature, the voltage drop increases, resulting in a voltage range that cannot be used earlier than normal temperature.
[0006]
The digital still camera detects the voltage when the battery is used and determines that the battery capacity has decreased when the voltage is lower than a preset voltage value so that the photographing operation cannot be performed. When the temperature is low, the voltage drop is large due to the temperature characteristics of the battery, so that there is a problem that the number of images that can be photographed is reduced as compared to normal temperature. The battery can still be used at room temperature, so it may be used again after warming up.
[0007]
It is an object of the present invention to provide a digital camera control method that eliminates the drawbacks of the prior art and does not drastically reduce the number of images that can be captured even in a low temperature environment.
[0008]
[Means for Solving the Problems]
According to the present invention, an image pickup means for picking up an image of the scene and forming an image signal representing the scene, and controlling the overall operation of the camera in response to an operation of the operator. A digital camera including a control unit that drives and images the subject and a power source unit that supplies power to each unit includes a temperature detection unit that detects the temperature. The control unit normally captures the image of the object scene. The control means has a first operation mode performed in the operation described above and a second operation mode different from the first operation mode. When the detected temperature is higher than a predetermined threshold, the control means The operation mode is set, and when the detected temperature is not higher than a predetermined threshold value, the second operation mode is set. In the second operation mode, the camera is operated at a frequency lower than that of the first operation mode. And
[0009]
DETAILED DESCRIPTION OF THE INVENTION
Next, embodiments of a digital still camera according to the present invention will be described in detail with reference to the accompanying drawings.
[0010]
As shown in FIG. 1, the digital still camera 10 of the embodiment includes an optical lens system 11, a solid-state imaging device 12, a signal processing unit 13, a recording device 14, a photometry / ranging control circuit 15, a charging / light emission control circuit 16, The flash light emitting unit 17, the system control circuit 40, the imaging control circuit 42, the image display unit 24, the backlight control circuit 25, the backlight 26, the operation unit 27, the temperature detection circuit 28, the temperature sensor 29, and the power source 30 are provided. .
[0011]
In the digital still camera 10 of the present embodiment, for example, an alkaline battery used for the power source 30 responds to a large voltage drop at a low temperature. Therefore, when the predetermined temperature is detected using the temperature detection circuit 28, the frequency divider 19 And 22 has a function of reducing current consumption by lowering the circuit operating frequency. Further, the camera has a normal operation mode that consumes a normal amount of power and a power saving operation mode that consumes less power than usual.
[0012]
The optical lens system 11 includes a zoom mechanism / focal length adjustment (AF) mechanism and a light amount adjustment (AE) diaphragm mechanism (both not shown). These mechanisms are driven by a control signal 100 supplied from the photometry / ranging control circuit 15. The photometry / ranging control circuit 15 has a function of supplying a control signal 113 corresponding to the operation mode supplied from the system control circuit 40 to the timing generation circuit 23. In the following description, a signal is designated by the reference number of the connecting line that appears.
[0013]
As the solid-state imaging device 12, a CCD imaging device or the like is used in this embodiment. A subject image is exposed to the solid-state imaging device 12 by the optical lens system 11, and photoelectrically converted in accordance with a timing pulse 101 input from the imaging control circuit 42, and an electric signal 102 as an image signal is output to the signal processing unit 13. .
[0014]
The signal processing unit 13 has a function of image data signal processing, and holds a buffer memory (not shown) for temporary storage. The signal processing unit 13 is controlled by the control signal 103 supplied from the system control circuit 40 and the control signal 112 supplied from the timing generation circuit 23, and with respect to the electric signal 102 of the image data output from the solid-state imaging device 12. White balance adjustment, gamma processing, analog / digital (A / D) conversion, and luminance / dye signal conversion (YC) processing are performed and stored in the buffer memory. Further, the digital / analog (D / A) conversion is performed by thinning out the YC signal subjected to the image processing for the compression / decompression processing for writing and reading of the recording device 14 and the image display of the image display unit 24.
[0015]
The recording device 14 has an information recording medium (not shown) and is controlled by a control signal 104 supplied from the system control circuit 40. The recording device 14 controls writing and reading of image data between the signal processing unit 13 and the information recording medium. The information recording medium may be detachably mounted using a package containing a rotating recording body such as a memory card on which a semiconductor memory is mounted or a magneto-optical disk.
[0016]
The flash light emitting unit 17 is a light emitting device that emits flash light that illuminates the object scene, controlled by a control signal 105 supplied from the charging / light emission control circuit 16. The charging / light emission control circuit 16 adjusts the amount of charging current to the flash light emitting unit 17 by the drive signal 106 supplied from the photometry / ranging control circuit 15 and controls the light emission timing. The charging / light emission control circuit 16 is supplied with an operation mode signal 115 from the system control circuit 40. The flash light emitting unit 17 uses a strobe or the like. In the power saving operation mode, the amount of charging current can be reduced and the current consumption of the entire apparatus can be reduced.
[0017]
The system control circuit 40 is configured by connecting a reference oscillator 18, a frequency dividing circuit 19, and a main control circuit 20 as shown in the figure. The main control circuit 20 is a control function unit that controls and controls the overall operation of the present apparatus in response to the operation signal 107 supplied from the operation unit 27. Particularly in relation to the present invention, the main control circuit 20 can switch the operation mode based on the result of comparing the temperature signal 109 supplied from the temperature detection circuit 28 with a predetermined threshold value. The main control circuit 20 supplies an operation mode to the photometry / ranging control circuit 15, the charge / light emission control circuit 16, and the timing generation circuit 23. The main control circuit 20 is connected to the reference oscillator 18 and the frequency dividing circuit 19 as illustrated. The reference oscillator 18 oscillates at a basic operating frequency of the main control circuit 20, for example, 50 MHz, and each circuit operates in synchronization with the basic operating frequency. The reference oscillator 18 has a basic operating frequency output 44 that is connected via a switch 46 to an input 48 of the main control circuit 20 and an input 50 of the divider circuit 19. The switch 46 is a selection circuit that alternatively connects the basic operating frequency output 44 to these inputs 48 or 50 under the control of the main control circuit 20. In the present embodiment, the frequency dividing circuit 19 is a frequency step-down circuit that divides the basic operating frequency 44 by half and supplies it to the main control circuit 20 from the output 52 thereof. The main control circuit 20 controls the switch 46 to connect the switch 46 to the connection line 48 side in the normal operation mode and supply the basic operating frequency 44 output from the reference oscillator 18 directly to the main control circuit 20. . In the power saving operation mode, the switch 46 is connected to the frequency dividing circuit 19 side, and the basic operating frequency is lowered to 25 MHz in this example by passing through the frequency dividing circuit 19, thereby reducing the current consumption of the entire apparatus. be able to.
[0018]
The imaging control circuit 42 is configured by connecting a reference oscillator 21, a frequency dividing circuit 22, and a timing generation circuit 23 as illustrated. The timing generation circuit 23 generates a timing pulse for driving the solid-state imaging device 12 and a sampling pulse and a clamp pulse for urging the operation of the signal processing unit 13 based on the control signal 113 supplied from the photometry / ranging control circuit 15. Output to. The timing generation circuit 23 is connected to the reference oscillator 21 and the frequency dividing circuit 22 as shown in the figure. The reference oscillator 21 oscillates at an operating frequency of the timing generation circuit 23, for example, 60 MHz, and each circuit operates in synchronization with this operating frequency. The reference oscillator 21 has an operating frequency output 54 which is connected via a switch 56 to an input 58 of the timing generator circuit 23 and an input 60 of the divider circuit 22. The switch 56 is a selection circuit that is controlled by the control signal 120 supplied from the main control circuit 20 and selectively connects the operating frequency output 54 to these inputs 58 or 60. Alternatively, the connection state may be switched by a control signal 113 supplied via the photometry / ranging control circuit 15. In the present embodiment, the frequency dividing circuit 22 is a frequency step-down circuit that divides the operating frequency 54 by half and supplies it to the timing generation circuit 23 from the output 62 thereof. The timing generation circuit 23 controls the switch 56 to connect the switch 56 to the connection line 58 side in the normal operation mode and supply the operation frequency 54 output from the reference oscillator 21 directly to the timing generation circuit 23. In the power saving operation mode, the switch 56 is connected to the frequency dividing circuit 22 side, and the operating frequency is lowered to 30 MHz in this example by passing through the frequency dividing circuit 22 to reduce the current consumption of the entire apparatus. Can do.
[0019]
In this embodiment, the image display unit 24 includes a liquid crystal display device and is controlled by a control signal 110 supplied from the main control circuit 20. The image display unit 24 displays the image data supplied from the signal processing unit 13 as a visible image on the liquid crystal display device.
[0020]
The backlight control circuit 25 has a function of controlling the backlight 26 under the control of the control signal 111 supplied from the main control circuit 20. The backlight 26 is connected to the backlight control circuit 25 and has a function of illuminating the display screen of the image display unit 24. The backlight control circuit 25 is supplied with an operation mode signal 111 from the main control circuit 20. In the power saving operation mode, the power consumption of the backlight 26 can be reduced and the current consumption of the entire apparatus can be reduced.
[0021]
The operation unit 27 has a function of outputting an operation signal 107 corresponding to the manual operation state of the operator to the main control circuit 20. The operation unit 27 includes input and selection switches such as a shutter release, a power switch, and operation buttons.
[0022]
The temperature detection circuit 28 has a function of supplying the temperature signal 119 detected by the temperature sensor 29 to the main control circuit 20. In this embodiment, the temperature signal 109 supplied from the temperature detection circuit 28 to the main control circuit 20 is a flag obtained as a result of comparison between the temperature signal 119 and a predetermined threshold value in the temperature detection circuit 28. The temperature sensor 29 uses a thermistor or the like. In this embodiment, the temperature sensor 29 is installed in the vicinity of the power supply 30 or on the outer wall of the housing (not shown) of the digital still camera 10 in consideration of the influence of heat generation inside the apparatus. It is also conceivable to detect the temperature with higher accuracy by connecting the power source 30 which is a heating element and the temperature sensor 29 using a heat pipe or the like.
[0023]
The power supply 30 is a circuit that supplies power to the timing generation circuit 23 and other circuits as comprehensively shown by the main control circuit 20 and the connection line 117, and uses an AC adapter or a detachable battery. When using an AC adapter, the voltage is stepped down to a predetermined voltage value via a DC / DC converter. In the case of using a battery, a primary battery or a secondary battery is used. In this embodiment, an alkaline battery which is easily available and inexpensive is used. The alkaline battery has a temperature characteristic in which the internal impedance varies greatly depending on the temperature. In this embodiment, for example, as shown in FIG. 3, the curve has a steep slope at low temperatures and a gentle slope as the temperature approaches. An alkaline battery having typical temperature characteristics is used. Further, for example, an alkaline battery having a linear temperature characteristic as shown in FIG. 2 may be used, and the present invention uses a power supply having a temperature characteristic in which the internal resistance increases as the temperature decreases. A particularly advantageous effect is obtained. When these power supplies are used at a low temperature, the internal impedance becomes large and the voltage drop becomes large. In the normal operation mode, the necessary power may not be supplied to each circuit in the apparatus.
[0024]
Next, the operation of the digital still camera 10 will be briefly described. When the operator operates the operation unit 27 of the camera 10, for example, presses the shutter release, the main control circuit 20 generates a fundamental frequency in response to the operation signal 107 from the operation unit 27, and the photometry / ranging control circuit 15. This is supplied to the signal processing unit 13, the recording device 14, the image display unit 24, and the backlight control circuit 25. The timing generation circuit 23 is supplied with the fundamental frequency from the photometry / ranging control circuit 15, generates signals 101 and 112 having a frequency asynchronous with the main control circuit 20, and supplies them to the solid-state imaging device 12 and the signal processing unit 13, respectively. To do. The main control circuit 20 obtains an operation mode from the temperature signal 109 supplied from the temperature detection circuit 28, and controls the photometry / ranging control circuit 15, the charge / light emission control circuit 16, and the backlight control circuit 25 according to the mode. .
[0025]
The photometry / ranging control circuit 15 supplies a signal for instructing flash emission to the charge / light emission control circuit 16 according to the photometry state, and the flash light emitting unit 17 emits light as necessary. The photometry / ranging control circuit 15 also controls the optical lens system 11 to expose the subject image on the solid-state imaging device 12, and the solid-state imaging device 12 controlled by the timing generation circuit 23 performs photoelectric conversion to generate an electric signal 102. To do.
[0026]
The signal processing unit 13 is controlled by the control signal 103 supplied from the main control circuit 20 and the control signal 112 supplied from the timing generation circuit 23, and performs signal processing on the electric signal 102 output from the solid-state imaging device 12. And image data 122 is generated. The image data 122 generated by the signal processing unit 13 is recorded on the information recording medium by the control signal 104 supplied from the main control device 20 in the recording device 14, and is supplied from the main control device 20 in the image display unit 24. A visible image is displayed by the control signal 110. When image display is performed, the backlight control device 25 is controlled by a control signal 111 supplied from the main control device 20.
[0027]
In the present embodiment, the operating frequency of the circuit in the normal operation mode, 50 MHz in the present embodiment, is set so that the signal processing speed is the fastest but the current consumption is large (for example, 2 W). In the power saving operation mode, the frequency divider circuit Through 19 and 22, the operating frequency of the circuit is lower than the frequency of the normal operation mode, and in this embodiment, 25 MHz is set to reduce current consumption (for example, 1 W).
[0028]
In the normal operation mode, the current consumption is set to increase in order to increase the amount of charging current so as to shorten the charging time in the flash light emitting unit 17, and in the power saving operation mode, the charging current is increased even if the charging time is increased. This is a setting that reduces the current consumption by reducing the amount.
[0029]
In the normal operation mode, importance is placed on the visibility of the display screen of the image display unit 24. Therefore, the current consumption is increased in order to increase the number of LEDs that constitute the backlight 26. In the power saving operation mode, the backlight is set. This is a setting to reduce the current consumption by changing the brightness of the LED 26 to reduce the number of lighted LEDs.
[0030]
The main control circuit 20 operates the charging / light emission control circuit 16 and the backlight control circuit 25 so that the camera is operated in the normal operation mode when the temperature is higher than a predetermined threshold, and the camera is operated in the power saving operation mode when the temperature is low. And the imaging control circuit 42 is controlled. This predetermined threshold is set in accordance with the internal impedance of the alkaline battery in the power source 30, and when the voltage drop becomes large at low temperatures, the current consumption of the circuit is reduced so that the number of images that can be shot is not automatically reduced. To do.
[0031]
As another example, a temperature value, not a flag, may be used as the temperature signal 109 supplied from the temperature detection circuit 28 to the main control circuit 20. At this time, two types of temperatures set in advance as threshold values to be compared in the main control circuit 20 can be set, and three types of operation modes can be controlled. As described above, by using a numerical value for the temperature signal 109, it is possible to have a plurality of threshold values, and further, stepless control is possible. The threshold value to be set is desirably set by estimating the temperature characteristics of the battery. When a plurality of threshold values are set, it is advantageous to set the amount of power consumption together.
[0032]
【The invention's effect】
As described above, according to the present invention, the digital still camera can set the temperature numerical value as one or a plurality of thresholds for determining the environment or the power supply temperature, and the operating frequency or the amount of current used in each circuit differs for each threshold. Multiple operation modes can be maintained. This makes it possible to control the switching of the operation mode by automatically detecting the temperature, so that the current consumption can be reduced in accordance with the temperature characteristics of the battery at low temperatures, and the number of images that can be shot is drastically reduced. Is preventing.
[Brief description of the drawings]
FIG. 1 is a block diagram showing an embodiment of a digital still camera to which the present invention is applied.
FIG. 2 is a graph showing the temperature characteristics of an alkaline battery in which the internal resistance changes linearly with changes in ambient temperature.
FIG. 3 is a graph showing temperature characteristics of an alkaline battery in which the internal resistance changes in a curve according to a change in ambient temperature.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 Digital still camera 11 Optical lens system 12 Solid-state image sensor 13 Signal processing part 14 Recording apparatus 15 Photometry / ranging control circuit 16 Charging / light emission control circuit 17 Flash light emission part 18, 21 Reference oscillator 19, 22 Frequency divider circuit 20 Main control Circuit 23 Timing generation circuit 24 Image display unit 25 Backlight control device 26 Backlight 27 Operation unit 28 Temperature detection circuit 29 Temperature sensor 30 Power supply 40 System control circuit 42 Imaging control circuit 46, 56 Switch

Claims (6)

Imaging means for imaging the scene and forming an image signal representing the scene;
Control means for controlling the overall operation of the camera in response to an operator's operation, driving the imaging means to image the subject,
In a digital camera including power supply means for supplying power to each part, the camera includes:
Including temperature detecting means for detecting the temperature;
The control means has a first operation mode in which imaging of the object scene is performed in a normal operation, and a second operation mode different from the first operation mode,
The control means takes a first operation mode when the detected temperature is higher than a predetermined threshold, and takes a second operation mode when the detected temperature is not higher than the predetermined threshold. In the second operation mode, the digital camera operates the camera at a frequency lower than that in the first operation mode. 2. The digital camera according to claim 1, wherein the control means reduces a frequency for driving the imaging means in the second operation mode. 2. The digital camera according to claim 1, wherein the camera includes display means for visually displaying an image represented by the image signal, and the control means reduces display luminance on the display means in the second operation mode. A digital camera characterized by this. 2. The digital camera according to claim 1, wherein the camera includes light emitting means for illuminating the object scene, and the control means reduces the current for charging the light emitting means in the second operation mode. A featured digital camera. 2. The digital camera according to claim 1, wherein the temperature detecting means is disposed at or near the power supply means and detects the temperature of the power supply means. 2. The digital camera according to claim 1, wherein the temperature detecting means detects an environmental temperature of the camera.

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