Image input apparatus operable under low power consumption without employing buffer memory

A compact image input apparatus is operable under low power consumption, while omitting a buffer memory for storing image data, which is originally required to transfer image data between this image input apparatus and a personal computer. The image input apparatus is arranged by an image sensor for optically sensing an image of an object to produce an analog image signal; an A/D (analog-to-digital) converter for A/D-converting the analog image signal derived from the image sensor into a digital image signal; an interface control unit for converting the digital image signal derived from the A/D converter into image data; an image sensor driving unit for driving the image sensor; an A/D converter driving unit for driving the A/D converter; a clock oscillator for oscillating a clock signal; a clock switching control unit for controlling a supply of the clock signal to the image sensor driving unit and the A/D converter driving unit in response to the clock signal produced from the clock oscillator, and both a transfer starting signal and a transfer clock signal supplied from the interface control unit; and a personal computer for receiving the image data converted by the interface control unit and for supplying the transfer starting signal to the interface control unit. The clock switching control unit includes drive means for supplying the clock signal produced form the clock oscillator to the image sensor, and also for not supplying the clock signal to the A/D converter driving unit within a preset time period after the transfer starting signal is received.

BACKGROUND OF THE INVENTION

1. Field of the invention

The present invention generally relates to an image input apparatus for inputting image information of an imaging object. More specifically, the present invention is directed to such a compact/low-cost image input apparatus operable under low power consumption without employing a buffer memory, while driving a CCD only during an imaging operation.

2. Description of the Related Art

While high grade type personal computers are commercially available and are popularized, various image applications such as television telephone, video mails, and electric albums are normally used. As a result, image input apparatuses used for personal computers, known as digital cameras, are gradually popularized. On the other hand, portable terminals such as notebook type personal computers and PDAs are developed, and are commercially available. Recently, cameras are connected to these portable terminals, or are assembled into these portable terminals. These cameras operable with the portable terminals must be made compact for the sake of portability thereof. In addition, since these portable terminals are mainly operated by batteries, the power consumption thereof must be reduced. Furthermore, since cameras are assembled into PHS and portable telephone, cost of these portable terminals must be lowered.

In one typical conventional image input apparatus used with a personal computer, there are provided; a lens for forming image light of an imaging object; a CCD for receiving the image light transferred from this lens; an A/D converter for converting an analog image signal derived from this CCD into digital image data; a buffer memory device for temporarily storing the digital image data derived from this A/D converter; an interface control unit for reading the digital image data from this buffer memory device to convert this read image data, and for transferring this converted image data to a personal computer; and further a drive control unit for controlling drive operations of these units.

However, the above-described conventional image input apparatus owns the following problems. That is, in the conventional image input apparatus for the personal computer, both the CCD and the A/D converter are driven in the constant time period to read the image data, whereas the transfer clock used between this image input apparatus and the personal computer is not produced in a constant time period, due to the load variation of the CPU. As a result, the buffer memory device capable of storing thereinto the image data is necessarily provided between the A/D converter and the interface control unit. Accordingly, this conventional image input apparatus for the personal computer is not suitable for compact/low power consumption/low cost aspects.

SUMMARY OF THE INVENTION

The present invention has been made to solve the above-explained problems, and therefore, has an object to provide a compact image input apparatus operable under low power consumption, and made in low cost. To achieve the above-described object, an image input apparatus, according to a first aspect of the present invention, is featured by comprising:

an image sensor for optically sensing an image of an object to produce an analog image signal;

an A/D (analog-to-digital) converter for A/D-converting the analog image signal derived from the image sensor into a digital image signal;

an interface control unit for converting the digital image signal derived from the A/D converter into image data;

an image sensor driving unit for driving the image sensor;

an A/D converter driving unit for driving the A/D converter;

a clock oscillator for oscillating a clock signal;

a clock switching control unit for controlling a supply of the clock signal to the image sensor driving unit and the A/D converter driving unit in response to the clock signal produced from the clock oscillator, and both a transfer starting signal and a transfer clock signal supplied from the interface control unit; and

a personal computer for receiving the image data converted by the interface control unit and for supplying the transfer starting signal to the interface control unit; wherein:

the clock switching control unit includes: drive means for supplying the clock signal produced from the clock oscillator to the image sensor, and also for not supplying the clock signal to the A/D converter driving unit within a preset time period after the transfer starting signal is received.

Furthermore, to achieve the object, an image input apparatus, according to a second aspect of the present invention, is featured by comprising:

an image sensor driving unit for driving the image sensor;

an A/D converter driving unit for driving the A/D converter;

a clock oscillator for oscillating a clock signal;

a clock switching control unit for controlling a supply of the clock signal to the image sensor driving unit and the A/D converter driving unit in response to the clock signal produced from the clock oscillator, and both a transfer starting signal and a transfer clock signal supplied from the interface control unit; and

a personal computer for receiving the image data converted by the interface control unit and for supplying the transfer starting signal to the interface control unit; wherein:

the clock switching control unit includes:

first drive means for supplying the clock signal produced form the clock oscillator to the image sensor, and also for not supplying the clock signal to the A/D converter driving unit within a first preset time period after the transfer starting signal is received; and

second drive means for supplying the transfer clock signal derived from the interface control unit to both the image sensor driving unit and the A/D converter driving unit within a second preset time period after the first preset time period has passed.

Also, in the image input apparatus according to the first, or second aspect of the present invention, the image sensor includes: a lens for focusing the image of the object; and a CCD (charge-coupled device) for receiving the object image focused by the lens to produce the analog image signal.

Also, in the image input apparatus according to the first, or second aspect of the present invention, the clock oscillator oscillates a clock signal having a substantially constant frequency higher the the normal clock frequency.

Moreover, in the image input apparatus according to the first, or second aspect of the present invention, the interface control unit is constituted based upon the USB (universal serial bus interface standard.

Alternatively, the interface control unit is constituted based on the IEEE 1394 specification.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to drawings, various preferred embodiments of the present invention will be described in detail.

Arrangement of Image Input Apparatus

As indicated inFIG. 1, an image input apparatus, according to an embodiment of the present invention, is mainly constituted by a lens1, a CCD (charge-coupled device)2, an A/D (analog-to-digital) converter3, an USB (universal serial bus) interface control unit4, a personal computer6, a clock oscillator7, a clock switching unit8, a CCD drive unit9, and an A/D converter drive unit10.

Concretely specking, the lens1focuses image light101of an imaging object (not shown) onto the CCD2. Upon receipt of the image light101derived from the lens1, the CCD2produces an analog image signal102to be outputted. The A/D converter3converts the analog image signal102entered from the CCD2into a digital image signal103corresponding thereto. The USB interface control unit4converts the digital image signal103entered from the A/D converter3into USB image data105, and then supplies this USB image data105to the personal computer6.

On the other hand, the USB interface control unit4supplies both a transfer starting signal104entered from the personal computer6and a transfer clock signal106appearing on the USB interface control unit4to the clock switching unit8. The clock oscillator7oscillates a highspeed clock signal107having a constant frequency and then outputs this highspeed clock signal107to the clock switching unit8. This clock switching unit8does not output both the clock signal108and the clock signal109until the transfer starting signal104is received from the USB interface control unit4. Upon receipt of this transfer starting signal104supplied from the personal computer6, the clock switching unit8firstly outputs the highspeed clock signal107entered from the clock oscillator7as a clock108until the count value reaches one constant count value (a) after the transfer starting signal has been received. Next, in such a case that the count value reaches a predetermined count value (a) and until this count value reaches a next constant count value (b), the clock switching unit8outputs the transfer clock signal106entered from the USB interface control unit4as the clock108and another clock109. Next, the clock switching unit8again does not output both the clock108and the clock109when the count value reaches the above-described next constant count value (b).

The CCD drive unit9produces a CCD drive signal110by using the clock signal108as an original oscillation signal. As a consequence, when no clock signal108is entered, this CCD drive unit9never outputs such a CCD drive signal110. On the other hand, when the highspeed clock signal107is entered as the clock signal108to the CCD drive unit9, this CCD drive unit9outputs a highspeed CCD drive signal110in synchronism with this highspeed clock signal107, whereas when the transfer clock signal106is entered thereto, this CCD drive unit9outputs a CCD drive signal110in synchronism with this transfer clock signal106.

The A/D converter drive unit10produces an A/D converter drive signal111by using the clock signal109as an original oscillation signal. As a consequence, when no clock signal109is entered, this A/D converter drive unit10never outputs such an A/D converter drive signal111. On the other hand, when the transfer clock signal106is entered as the clock signal109, this A/D converter drive unit10outputs an A/D converter drive signal111in synchronism with this transfer clock signal106.

Operation of Image Input Apparatus

FIG. 2is a timing chart for explaining operation of the above-described image input apparatus, according to the embodiment, shown in FIG.1. Within a time period of201, since the clock switching unit8does not detect the transfer starting signal104, neither the CCD drive signal110, nor the A/D converter drive signal111is outputted therefrom. Within the next time period of202, since the clock switching unit8detects the transfer starting signal104, a drive signal in synchronism with the highspeed clock signal107is outputted as the CCD drive signal110therefrom until the count value reaches the constant count value (a). As a result, while the analog image signal102is outputted from the CCD2in a high speed, the A/D converter drive signal111is not outputted from the A/D converter drive unit10, so that this analog image signal102is discarded at this stage. In the subsequent time period of203, the transfer clock signal106is outputted as the CCD drive signal110and the A/D converter drive signal111until the count value reaches the constant count value (b) . As a result, the analog image signal102is outputted from the CCD2, and thereafter is A/D-converted into the digital image signal103by the A/D converter3. Then, this digital image signal103is transferred to the personal computer6.

Within the next time period of204, both the CCD drive signal110and the A/D converter drive signal111are not again outputted. This operation condition is equal to that of the above-explained time period of201. The image input apparatus repeatedly performs the above-explained operation. Now, the reason why both the CCD drive signal110and the A/D converter drive signal111are not outputted within the first time period of201will be explained as follows: In general, a semiconductor device, or element consumes electric power in direct proportional to an operation clock thereof. Within the first time period of201, since the personal computer6does not request the image input apparatus to transfer the image signal, this image input apparatus is not required to image the imaging object, but also both the CCD2and the A/D converter3need not be driven. At this time, if producing of both the CCD drive signal110and the A/D converter drive signal111is interrupted, then the overall power consumption of this image input apparatus can be reduced. Subsequently, the reason why the analog image signal102is discarded within the time period of202will be explained as follows: In general, a photodiode of a CCD photo-converts incident light into electric charges. These electric charges are sequentially transferred by this CCD to be outputted as a serial signal. On the other and, since the electric charges are continuously accumulated in the CCD2due to the dark current of the semiconductor element, these accumulated electric charges cause noise, so that the S/N ratio of the image signal is deteriorated. In the first time period of201, since the CCD drive signal110is not outputted, the noise components are accumulated in the CCD2during this time period. As a result, in the next time period of202, the highspeed CCD drive signal110is outputted and the noise components accumulated in this CCD2must be swept out.

Finally, the reason why the digital image signal is produced in synchronism with the transfer clock signal106within the time period of203will be explained as follows: In general, the personal computer6executes various process operations other than the process operation of the image signal entered from the image input apparatus. As a consequence, for example, even when the constant time transfer operation is carried out, for instance, the isochronous transfer mode executed in the USB interface control unit4, such a fact is well known. That is, the transfer clock signal106never owns the completely constant time period, because of very small variations in a load of a CPU employed in this personal computer6. Since both the transfer clock signal110and the A/D converter drive signal111are synchronized with the transfer clock signal106, the digital image signal103can be transferred to the personal computer6without employing any buffer memory device. Also, another fact is known in this field. That is, when the CCD drive signal110does not own such a constant time period, the electric charge accumulation time in the CCD2is varied, resulting in image fluctuations. To the contrary, in accordance with this embodiment, although very small time variations are produced in the isochronous transfer mode of th USB interface control unit4, these very small time variations never cause image fluctuations which may be visually confirmed by human eyes. Moreover, when a further highspeed interface defined by IEEE 1394 (trade name) specification is employed, the above-explained adverse influence may be furthermore mitigated.

As previously described, in the conventional image input apparatus for the personal computer, the CCD is driven in the constant time period in order to avoid the noise adverse influence caused by the dark current. To the contrary, in accordance with the present invention, since the CCD is driven in the high speed immediately before the image data is read out from the CCD so as to sweep out the accumulated electric charges, the driving operation of this CCD can be stopped while no imaging operation is carried out.

Also, in the conventional image input apparatus for the personal computer, both the CCD and the A/D converter are driven in the constant time period to read the image data, whereas the transfer clock used between this image input apparatus and the personal computer is not produced in a constant time period, due to the load variation of the CPU. As a result, the buffer memory device capable of storing thereinto the image data is necessarily provided between the A/D converter and the interface control unit. To the contrary, in accordance with the image input apparatus of the present invention, since the CCD2is driven in such a high speed immediately before the image data is read out from the CCD2so as to sweep out the electric charges accumulated in this CCD2, the CCD2is no longer driven in such a constant time period. As a result, the buffer memory device is no longer required by synchronizing the drive signal for this CCD2with the transfer clock signal used between this image input apparatus and the personal computer.

As apparent from the foregoing description, in the image input apparatus of the present invention, the CCD is not required to be driven except that the imaging operation is carried out by driving this CCD. Furthermore, since the buffer memory device is no longer required, this image input apparatus can be made compact and in low cost, and further can be driven under low power consumption.

It is thus apparent that the present invention is not limited to the above embodiments but may be changed and modified without departing from the scope and spirit of the invention.

Finally, the present application claims the priority of Japanese Patent Application No. Hei10-071898 filed on Mar. 20, 1998, which is herein incorporated by reference.