Imaging device to output an electric signal and vary gain based on temperature of an imaging element

According to an embodiment, an imaging device includes a first CCD which converts a first color component into a first electric signal, a second CCD which converts a second color component different from the first color component into a second electric signal, a third CCD which converts a third color component different from the first and second color components into a third electric signal, and a heat sink having first to third radiators which radiate heat from the first to third CODs. The first to third radiators are maintained at the same temperature by the function of the heat sink.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2008-273351, filed Oct. 23, 2008, the entire contents of which are incorporated herein by reference.

BACKGROUND

The present invention relates to an improvement (temperature compensation) in white balance in an imaging device such as an imaging device using a 3-CCD.

2. Description of the Related Art

It is known that an imaging device using a 3-CCD tends to lose white balance because of temperature rises in CCDs for R, G, and B.

Under such circumstances, there has already been proposed a method of inhibiting a change in the white balance in the imaging device using the CCD.

Japanese Patent Application Publication (KOKAI) No. Hei-1-259692 (first document) discloses a single-element solid-state imaging element, wherein the imaging elements are attached to a substrate, and heat of the substrate is radiated so that the imaging elements for R, G, and B may be uniform in temperature to restore the white balance.

Japanese Patent Application Publication (KOKAI) No. Hei-5-207486 (second document) discloses a solid-state imaging element of a 3-CCD using a color separation prism, wherein the imaging elements (R, G, and B) are cooled by an electronic cooler.

Japanese Patent Application Publication (KOKAI) No. 2008-72439 (third document) discloses an image processing apparatus which corrects the loss of the white balance in a CMOS sensor due to a temperature change, in accordance with the difference between a temperature during factory coordination and a current temperature.

The solid-state imaging element shown in the first document is an only one-element type, and there is no statement about the elimination of the loss of white balance due to a temperature rise in each element or due to a change in the sensitivity of each element caused by a temperature rise in the case where imaging elements for R, G, and B are independently provided.

The electronic cooler shown in the second document is known to be highly expensive and to increase an overall size (volume).

The image processing apparatus shown in the third document corrects the white balance in accordance with the difference between a temperature during factory coordination and a current temperature (in an installation environment), when driving the CMOS sensor. However, there is no statement about the elimination of the loss of the white balance due to the difference in temperature rise among the elements in the case where the imaging elements for R, G, and B are independently provided.

DETAILED DESCRIPTION

Various embodiments according to the invention will be described hereinafter with reference to the accompanying drawings. In general, according to one embodiment of the invention, an imaging device comprising: a first element configured to convert a first color component based on additive process into a first electric signal; a second element configured to convert a second color component different from the first color component into a second electric signal in accordance with the additive process; a third element configured to convert a third color component different from the first and second color components into a third electric signal in accordance with the additive process; a first radiator configured to radiate heat from the first element; a second radiator configured to radiate heat from the second element; and a third radiator configured to radiate heat from the third element, wherein the first radiator, the second radiator and the third radiator are maintained at the same temperature.

Embodiments of this invention will be described in detail with reference to the drawings. The various modules of the systems described herein can be implemented as software applications, hardware and/or software modules, or components on one or more computers, such as servers. While the various modules are illustrated separately, they may share some or all of the same underlying logic or code.

FIG. 1shows an example of a 3-CCD imaging device according to the embodiment of the invention.

An imaging device1shown inFIG. 1includes a lens3for receiving image light from a subject, a prism5for separating the image light input from the lens3into red (R), green (G) and blue (B) which are additive three primary colors, and a 3-COD sensor7(R, G, and B) for converting the image lights for R, G and B separated by the prism5into input image signals. In addition, the lens3is formed detachably from the prism5and the 3-COD sensor7owing to a cabinet3a, which is advantageous when the lens3needs to be replaced. Moreover, the prism5and the 3-GOD sensor7are integrally formed, and heat from the 3-COD sensor7is radiated by a heat conducting sheet9and by a heat sink11integrated with the prism5and the 3-GOD sensor7via the heat conducting sheet9. Further, one end of the heat sink11is connected to the cabinet3aoften made of a metal, which enhances heat radiation efficiency (ensures a great heat radiation amount).

As schematically illustrated inFIG. 2, the input image signals output from the respective components of the 3-COD sensor7(R, G, and B) are amplified to a predetermined gain by a process circuit block13. Then, the input image signals are subjected to analog-to-digital conversion and to predetermined signal processing by a signal processing circuit block15, and output as an R signal output, a G signal output and a B signal output. In addition, the process circuit block13includes a correlated double sampling (CDS) circuit for removing a noise component from the input image signals output from the R, G, and B CCD sensors, a gain control amplifier (GCA) for providing the output of the CDS circuit with a predetermined gain, an analog-to-digital converter for converting (the analog input image signals) into digital signals and outputting the digital signals, etc.

The signal processing circuit block15includes a shading correction unit, a gamma (γ) correction unit, etc. The shading correction unit corrects the difference in amount between the image light passed through the center of the lens3and the image light passed around the lens3, out of the signals output from the respective CCD sensors7. The gamma correction unit corrects the contrast of the input image signals.

The R, G, and B image signals output from the signal processing circuit block15are output to, for example, an unshown display unit (monitor unit) or image data storage unit (mass storage unit) which is connected at a subsequent stage via an image output circuit (camera link driver).

FIG. 3shows an example of the positional relation between a reflection plane of the prism5and prisms for the respective colors. The reflection plane of the prism5causes the input image light to enter the respective channels of the CCD sensor7, that is, CCD sensors7R,7G,7B for the respective colors.

Out of the input image light which has entered the prism5, a blue image component to be received by, for example, a B channel, that is, the COD7B is reflected by a first wavelength selection film5B, reflected by a light incidence plane5I, and guided to a light receiving plane of the COD7B which is not described in detail. Further, out of the input image light which has entered the prism5, a red image component to be received by, for example, an R channel, that is, the CCD7R penetrates through the first wavelength selection film5B. Thus, the red image component is reflected by a second wavelength selection film5R, again reflected by the back surface of the first wavelength selection film5B, and guided to a light receiving plane of the COD7R which is not described in detail. In addition, out of the input image light which has entered the prism5, a green image component to be received by, for example, a G channel, that is, the CCD7G penetrates through the first wavelength selection film5B and the second wavelength selection film5R, and is guided to a light receiving plane of the COD7G which is not described in detail. Moreover, the CCD sensors7R,7G,7B integrally have independent heat sinks7a,7b,7cfor radiating the heat of the CCD sensors.

FIG. 4shows the characteristics of the shape of the heat sink in the imaging device shown inFIG. 1according to the embodiment.

As shown inFIG. 4, the heat sink11is connected to the prism5and the 3-CCD sensor7laterally via the heat conducting sheet9which is provided integrally with the prism5and the 3-OCD sensor7. In addition, in contrast with the independent heat sinks7a,7b,7cthat are separately provided for the respective CCD sensors, the heat sink11is in an integrated form to equalize the heat from the independent heat sinks7a,7b,7cprovided for the CCD sensors7R,7G,7B of the 3-CCD sensor7(the heat sink11is formed into a single plate having great areas of contact with the CCD sensors7R,7G,7B via the heat conducting sheet9).

According to this configuration, the blue (B) CCD7B, green (G) CCD7G and red (R) CCD7R have the same temperature rise, so that the difference of sensitivity among the independent CCDs due to the temperature is reduced, and the white balance in the imaging device1is stabilized.

FIG. 5shows another example of the heat sink shown inFIG. 4in the embodiment.

As shown inFIG. 5, the heat sinks11are connected to the prism5and the 3-CCD sensor7laterally via the heat conducting sheet9which is provided integrally with the prism5and the 3-CCD sensor7. In addition, the heat sinks11are independently provided for each of the mono-CCD sensors7R,7G,7B of the 3-CCD sensor7in accordance with the independent heat sinks7a,7b,7cthat are provided for the mono-COD sensors7R,7G,7B. In this case, on the assumption that the heat from the each of the mono-CCD sensors7R,7G,7B is relatively small in amount, the heat sinks11do not necessarily have to be connected to the cabinet3aas shown inFIG. 1.

According to this configuration, the blue (B) CCD7B, the green (G) CCD7G and the red (R) CCD7R have the same temperature rise, so that the difference of sensitivity among the each of the mono-CCDs due to the temperature is reduced, and the white balance in the imaging device1is stabilized.

FIG. 6shows still another example of the heat sink shown inFIG. 4in the embodiment.

As shown inFIG. 6, the heat sinks11are independently provided, through the heat conducting sheet9(at two places), only in the heat sinks7a(sensor7R) and7c(sensor7B) which are provided for the red (R) CCD sensor7R and the blue (B) CCD sensor7B of the 3-CCD sensor7and contacts the prism5. In this case, on the assumption that the heat from the CCD sensor7G is relatively small in amount, the heat sinks11do not have to be connected to the cabinet3aas shown inFIG. 1.

According to this configuration, temperature rises in the blue (B) CCD sensor75and the red (R) CCD sensor7R are suitably controlled on the basis of the green (G) CCD sensor7G for which the number of reflections by the prism5is smaller than other CCD sensors. In other words, while the G component is fixed, the R component and the B component are corrected, so that color irregularities (loss of white balance) can be inhibited.

FIGS. 7 and 8show the relation between an amplifier gain and the outputs of the red (R) CCD sensor and the blue (B) CCD sensor that use a signal processing circuit shown inFIG. 2.

FIG. 7shows an example of the red (A) CCD sensor (CCD7R inFIG. 1). In this example, a video level, that is, a CCD output increases along with rises in the ambient temperature and the temperature of the CCD sensor (an example where a thermistor which increases in resistance along with a temperature rise is used).

In the example shown inFIG. 7, although not shown, the gain is controlled by, for example, a gain control amplifier in the process circuit block13so that there may be substantially no increase in the CCD output due to rises in the ambient temperature and the temperature of the CCD sensor.

FIG. 8shows an example of the blue (B) CCD sensor (CCD7B inFIG. 1). In this example, the video level, that is, the CCD output decreases along with rises in the ambient temperature and the temperature of the CCD sensor (an example where a thermistor which decreases in resistance along with a temperature rise is used).

In the example shown inFIG. 8, although not shown, the gain is controlled by, for example, the gain control amplifier in the process circuit block13so that there may be substantially no decrease in the CCD output due to rises in the ambient temperature and the temperature of the CCD sensor.

It should be understood thatFIGS. 7 and 8are illustrative only. When, for example, the output of the blue (B) CCD sensor increases because of rises in the ambient temperature and the temperature of the CCD sensor, the amplifier gain (correction signal level) decreases as in the example shown inFIG. 7. When, for example, the output of the red (R) CCD sensor decreases because of rises in the ambient temperature and the temperature of the CCD sensor, the amplifier gain (correction signal level) increases as in the example shown inFIG. 8. That is, the thermistor showing reverse temperature characteristics is used in accordance whether the output gain increases or decreases along with a temperature rise, such that a variation of the output level of each CCD with the temperature is counteracted, and the white balance is stabilized.

FIG. 9shows a circuit example for a detailed explanation of the signal processing circuit shown by way of example inFIG. 2.

As shown in (b) ofFIG. 9, a noise component is removed by a G-CDS circuit17G from the output of the green (G) CCD sensor7G of the 3-CCD sensor7that is schematically shown inFIGS. 1 and 3. Then, the output of the green (G) CCD sensor7G is amplified to a predetermined level by a gain control unit19G which includes a serial resistance RG1, a negative feedback amplifier G-GCA and a feedback resistance RG2.

On the contrary, as shown in (a) ofFIG. 9, a noise component is removed by an R-CDS circuit17R from the output of the red (R) COD sensor7R of the 3-CCD sensor7that is schematically shown inFIGS. 1 and 3. Then, the output of the red (R) COD sensor7R is amplified to a predetermined level by a gain control unit19R which includes serial resistances RR1and RR3, a negative feedback amplifier R-GCA, a feedback resistance RR2and a thermistor RTH. In addition, the thermistor RTH is grounded between the serial resistances RR1and RR3.

On the other hand, as shown in (c) ofFIG. 9, a noise component is removed by a B-CDS circuit17B from the output of the blue (B) CCD sensor7B of the 3-CCD sensor7that is schematically shown inFIGS. 1 and 3. Then, the output of the blue (B) COD sensor7B is amplified to a predetermined level by a gain control unit19B which includes a serial resistance RB1, a negative feedback amplifier B-GCA, a feedback resistance RB2and a thermistor BTH provided in series to the feedback resistance RB2.

In addition, the gain control units shown in (a) ofFIG. 9, (b) ofFIG. 9and (c) ofFIG. 9can be combined together suitably to any color. For example, the gain control unit shown in (a) ofFIG. 9or the gain control unit shown in (c) ofFIG. 9may be used for both the R output and the B output except for the output of the green (G) CCD sensor7G. Alternatively, the gain control unit shown in (a) ofFIG. 9or the gain control unit shown in (c) ofFIG. 9may be used for all the R, G, and B CCD sensors7R,7G,7B.

When the prism5and the 3-CCD sensor7shown inFIG. 3are used, the input image light which is input via the lens3is converted to the input image signals for the respective colors R, G, and B. In the embodiment shown inFIG. 3, the number of times that the green image component guided to the G channel, that is, the CCD7G is reflected by the prism5is the smallest. Thus, there is no thermistor for the green (G) COD sensor7G as shown in (b) ofFIG. 9. That is, while the G component is fixed, the R component and the B component are corrected. Consequently, the color irregularities (loss of white balance) can be more stably inhibited.

FIG. 10shows another example of the signal processing circuit shown by way of example inFIG. 2.

The signal processing circuit shown inFIG. 10includes a process circuit25. For the respective color components (R, G, and B) in the input image signals output from the 3-COD sensor7(R, G, and B), the process circuit25has CDS circuits21R,21G and21B for removing a noise component from the input image signals output from the each of the mono-CCD sensors7R,7G and7B, and variable amplifier circuits23R,23G and23B for providing the outputs of the CDS circuits with predetermined gains. The outputs from the process circuit25, that is, from the variable amplifier circuits23R,23G and23B for the respective color components are input to the signal processing circuit block15described withFIG. 2.

In addition, the gains (adjustment amounts) of the variable amplifier circuits23R,23G and23B of the process circuit25are set by a microcomputer unit29. The microcomputer unit29acquires the output of a temperature sensor27provided in the vicinity of the prism5and the 3-COD sensor7to set an instruction value for correcting the outputs of the each of the mono-COD sensors7R,7G and7B for the respective color components, thereby deciding whether to make corrections by the variable amplifier circuits23R,23G and23B and also deciding a correction value. That is, the temperature around the 3-CCD sensor7is detected by the temperature sensor27. Then, in accordance with the temperature detected by the temperature sensor27, the gain of the process circuit25is controlled for each of R, G, and B by the microcomputer unit29in which the output level of each of the R, G, and B (mono-) CCDs dependent on temperature is prestored. Consequently, the outputs of the each of the mono-COD sensors7R,7G and7B can be more finely corrected, and the white balance can be maintained in a more satisfactory manner.

As described above, when the output characteristics of the CCD sensors for the respective colors vary because of the change of the ambient temperature or because of a rise in the temperature of the CCD sensor, the white balance is lost and correct color reproduction is impossible. This problem can be ameliorated by the use of one of the embodiments of the present invention.

Furthermore, for example, temperature rises in all the independent CCD sensors can be controlled by heat radiation through a single heat sink to reduce variations in the outputs of the independent CCD sensors with the temperature change.

Still further, variations in the outputs of the independent CCD sensors with temperature rises in the independent CCD sensors are corrected on the basis the temperature detected by the temperature sensor provided in the vicinity of the CCD sensor, so that an imaging device with a more stable white balance can be obtained.