JP3238968B2 - Solid-state imaging device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid-state imaging device used for a video camera or the like.

[0002]

2. Description of the Related Art In a solid-state imaging device used in a video camera or the like, it is known that noise is generated due to various factors in a signal processing process. inside that,
Conventionally, two types of fixed pattern noise in a solid-state image sensor have been known: random uneven noise that produces an image like frosted glass, and streak noise arranged vertically or horizontally.

[0003] As a method of correcting these noises,
Conventionally, a method using a circuit as shown in FIG. 9 has been used. That is, the noise component data of the image sensor for one screen is stored in the frame memory 52 in advance.
Then, when outputting the imaging signal generated by the imaging element 51 to the process circuit 7, the subtractor 6 subtracts the noise component stored in the frame memory 52 from the imaging signal and outputs the result.

[0004]

However, in the above-mentioned conventional example, a frame memory for one screen having a large memory amount is required to store the noise component data of the image pickup device. And the problem of cost increase. By the way, in order to reduce the size of the device, noise correction may be performed using a line buffer that can save a memory amount. But,
In this case, there are the following problems. That is, since streak-like noise is generally most noticeable among fixed pattern noises, it is necessary to remove this noise effectively. However, when a line buffer is used, there is a problem that the streak-like noise cannot be accurately corrected because it is affected by uneven noise, which is another fixed pattern noise of the image sensor. .

Also, since the noise component data of the image pickup device stored in the frame memory is fixed, it is not possible to effectively remove, for example, dark current uneven noise that changes according to a change in temperature. There was a problem. Further, in the above-described conventional example, even when it is not necessary to correct the imaging signal, the correction is uniformly performed. In this case, instead of improving the image quality,
On the contrary, there is a problem that it deteriorates.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and has as its object to surely remove a noise component from an image pickup device without increasing the size of the entire apparatus.

[0007]

According to the present invention, there is provided a solid-state imaging device, wherein a plurality of photosensitive pixels, a plurality of vertical signal lines from which image signals of the plurality of photosensitive pixels are read out, and the plurality of vertical signal lines intersect. And a horizontal signal line that is sequentially scanned to select a plurality of photosensitive pixels from which the imaging signals are read, the dummy signal line being connected to the dummy signal line. Is selected, a noise signal is read out to the plurality of vertical signal lines.

According to another feature of the present invention, there is provided a subtraction means for subtracting the image signal and the noise signal read from the vertical signal line.

[0009]

As described above, according to the present invention, a dummy signal line which is provided so as to intersect with a plurality of vertical signal lines from which image signals of a plurality of photosensitive pixels are read and to which no photosensitive pixel is connected is selected. Thus, a noise signal is read out to a plurality of vertical signal lines, so that it is possible to perform noise correction that is not affected by photosensitive pixels without increasing the size of the device.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the solid-state imaging device according to the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram of a solid-state imaging device according to a first embodiment of the present invention. In FIG. 1, the portions denoted by the same reference numerals as those in the conventional solid-state imaging device shown in FIG. 9 indicate the same functional portions as those in the conventional solid-state imaging device.

The image pickup device 1 is driven by a driver 8. The driver 8 is driven by a drive pulse PDR generated from a synchronization signal generation circuit 9. The output signal from the image sensor 1 is switched by the switch 2, and when the movable terminal 2 a is switched to the fixed terminal A side, the terminal A
Is applied to one end of the subtractor 6 as an imaging output Y _S.
When the movable terminal 2a is switched to the fixed terminal B side, the output signal from the image sensor 1 is transmitted from the terminal B to the A / D
The data is input to the converter 3 and stored in the line buffer 4 as digital noise component data.

This noise component data is D / A converted by the D / A converter 5 and converted into analog noise component data Y.
_N is input to the other end of the subtractor 6. Then, the noise component data Y _N is subtracted from the above-described imaging output Y _S to obtain a correction signal Y. The correction signal Y generated in this way is input to the process circuit 7 and subjected to processing such as white clipping and aperture correction to obtain the video signal S.
output as v.

FIG. 2 is a diagram showing a detailed configuration of the image pickup device 1, and here, a MOS type image pickup device is taken as an example. That is, one pixel includes a MOS-FET (MOS type field effect transistor) 11 and a photodiode 12. A predetermined number of pixels are regularly arranged in the horizontal direction and the vertical direction, respectively, to form a photosensitive portion. The charge generated in the photosensitive section is read out via a horizontal signal line 13 and a vertical signal line 14 connected to each pixel.

The charge read operation will be described in more detail. First, in the vertical direction, an address signal ADR for specifying a read line is input to the decoder 15, and the specified read line is transmitted to the vertical register 16. Then, the designated horizontal lines 13 are sequentially scanned in accordance with the address signal ADR. Next, in the horizontal direction, the signal of each pixel connected to one horizontal line specified by the address signal ADR is applied to the horizontal register 1 via the vertical signal line 14.
7 are sequentially output.

The present embodiment is characterized in that a dummy line 18 to which no photosensitive pixel is connected is provided at the top of this horizontal line. The dummy line 18 is designated when a fixed pattern noise in the vertical direction described later is captured.

Next, the overall operation of the solid-state imaging device of this embodiment shown in FIG. 1 will be described in detail with reference to the timing chart of FIG.

FIG. 3A shows a vertical synchronization signal VD.
And (b) shows the vertical blanking signal VB. First, when the timing enters a vertical blanking period as shown in FIG. 3B, the address signal ADR becomes
As shown in (c), the dummy line 18 shown in FIG. 2 is specified. As described above, since no photosensitive pixel is connected to the dummy line 18, the signal output from the dummy line 18 is only a noise component, and is used as fixed pattern noise of the image sensor 1.

In the vertical blanking period,
As shown in FIG. 3D, the switch signal PSW is supplied to the switch 2 so that the movable terminal 2a selects the fixed terminal B side. Thereby, the noise component data output from the image sensor 1 is input to the A / D converter 3. Furthermore,
The A / D converter pulse PCNT1 is turned on as shown in FIG. 3E, and the A / D converter 3 starts operating. Thus, the noise component data for one horizontal line is A / D converted, and this is stored in the line buffer 4 as a digital signal.

Next, when the vertical blanking period ends and the valid period starts, as shown in FIG. 3D, the switch signal PSW is applied to the switch 2 so that the movable terminal 2a selects the fixed terminal A side. Given. As a result, the imaging output Y _S in the effective line designated by the address signal ADR during the effective period is input to one end of the subtractor 6.

During this valid period, the D / A converter pulse PCNT2 for driving the D / A converter 5 is:
Figure 3 turned on (f), the input to the other end of the subtracter 6 noise component data stored in the line buffer 4 during the vertical blanking period of the above is converted into an analog noise component data Y _N Is done. In the subtractor 6, Y =
Y _S -Y _N becomes operation is performed, thereby the fixed pattern noise correction signal Y component is removed is obtained. Then, the correction signal Y is input to the process circuit 7, where a synchronizing signal and the like are added thereto and output as a video signal Sv.

In the first embodiment described above, the case where the subtraction processing in the subtracter 6 is performed using an analog signal has been described. However, the subtraction processing may be performed using a digital signal. FIG. 4 is a diagram illustrating a solid-state imaging device according to a second embodiment in which the subtraction process is performed digitally in this manner. In FIG. 4, the same functional portions as those of the solid-state imaging device shown in FIG. 1 are denoted by the same reference numerals.

In FIG. 4, an output signal from the image sensor 1 is A / D converted by an A / D converter 3 to be a digital signal. The output signal from the image pickup device 1 is an image pickup output or noise component data of the image pickup device 1 which is switched and output at the operation timings as shown in FIGS. .

When the digital signal output from the A / D converter 3 is obtained by A / D conversion of the image output of the image sensor 1, this digital signal is imaged at one end of a subtractor 20 by switching a switch 19. Directly input as output Y _SD . The digital signal output from the A / D converter 3 converts the noise component data of the image sensor 1 into an A / D signal.
When the digital signal is converted, the digital signal is input to the line buffer 4 by switching of the switch 19, temporarily stored, and then converted as noise component data Y _{ND into the} subtracter 20.
Is input to the other end.

Then, the aforementioned image pickup output Y _{SD is} output by the subtractor 20.
The noise component data Y _ND is subtracted from the
_D is obtained. The correction signal Y _D is input to the D / A converter 5 after being added with a synchronization signal and the like by the process circuit 7, is converted into an analog signal, and is output as the video signal Sv.

In the first and second embodiments described above, the number of times of taking in the noise component data from the dummy line 18 is not described in detail, but the number is not limited to one. For example, if the number of captures is increased and the average value is taken, more accurate noise component data can be obtained.

As described above, according to the first and second embodiments, the signal obtained in units of one line from the dummy line 18 to which the photosensitive pixel is not connected is converted into the line buffer 4 having a smaller memory amount than the frame memory. Is stored as noise component data, and noise correction is performed based on the noise component data.Therefore, it is possible to perform noise correction without being affected by photosensitive pixels without unnecessarily increasing the size of the device, and Image quality can be obtained. Also,
The noise component data can be taken in line by line, and the amount of memory for storing the noise component data can be reduced.

Next, a third embodiment of the present invention will be described. In the third embodiment, appropriate noise correction can be performed according to the state of noise at the time of shooting. FIG. 5 is a block diagram illustrating the solid-state imaging device according to the present embodiment. First, the overall operation of this embodiment will be briefly described with reference to FIG.

In FIG. 5, when a shutter button (not shown) is turned on, the light shielding plate 31 is opened, and an object image is formed on an image pickup surface of the CCD 32 by an optical system (not shown) provided in front of the light shielding plate 31. The image is photoelectrically converted by the CCD 32. The image signal thus obtained is subjected to A / D conversion by the A / D converter 33 and then stored in the frame memory 34 as an image signal.

Next, photoelectric conversion is performed by the CCD 32 in the dark state with the light shielding plate 31 closed. Image signal obtained thereby, since is obtained by photoelectric conversion performed by blocking all light from the outside of the CCD 32, it is used as the noise component data S _N of the fixed pattern noise of the CCD 32.

The noise component data _SN obtained in this manner is directly input to one end of the subtractor 36 without being subjected to A / D conversion or the like by the A / D converter 33. The reading of the noise component data S _N is not performed when it is determined that the noise component data S _N is unnecessary by a determination operation described later.

Then, in synchronization with the input of the noise component data S _N to the subtractor 36, the frame memory 34
The image signal of the subject stored in the D / A converter 35
And is input to the other end of the subtractor 36 as an analog image signal _SD . Then, S =
A subtraction process of S _D -S _N is performed to obtain a correction signal S from which noise components of the CCD 32 have been removed.

The correction signal S is supplied to the terminal B of the switch 37.
Is input to The uncorrected image signal _SD is input to the terminal A of the switch 37, and the system controller 42
, The correction signal S or the uncorrected signal _SD is selected. The method for this determination will be described later. Then, the selected signal is given to the recording device 39 after predetermined processing is performed in the process circuit 38, and is recorded.

Next, a method of determining the terminal selection of the switch 37 by the system controller 42 will be described with reference to FIG.
This will be described with reference to the flowchart of FIG. First, step S1
When the shutter is turned on at step S2, the light shielding plate 3 is set at step S2.
1 is opened, the photoelectric conversion of the subject is performed in step S3, and the imaging signal (subject data) is stored in the frame memory 34.
It is taken in.

In step S4, a histogram process of the luminance distribution of the captured subject data is performed, and a highlight point HP and a dark point DP of the image are determined from the processing result. FIG. 7 is a diagram illustrating an example of a result of the histogram processing. In this processing result, pixels are classified into 256 steps based on the captured subject data and arranged in the order of brightness. The value of 99% of the whole is defined as the highlight point HP, and the value of 1% is defined as the dark point DP.

Further, from the combination of the highlight point HP and the dark point DP thus obtained, an index (INDEX) is determined based on, for example, a chart shown in FIG. Here, the index is O
If N, the noise component is read out, and if the index is OFF, the noise component is not read out.

Next, the index is turned on in step S5.
Or OFF. If it is determined that the index is ON, the process proceeds to close the light-shielding plate 31 in step S6, reads the noise component data S _N in step S7 CCD 32 is inputted to one end of the subtractor 36. Next, in step S8, the movable terminal 37a of the switch 37 is switched to the terminal B side, whereby the subtracter 3
The correction signal S generated in step 6 is selected, and the correction signal S is recorded in the recording device 39 in step S10.

In step S5, if the index is OF
If it is determined to be F, the process proceeds to step S9 without reading out the noise component data _SN in steps S6 and S7, and the uncorrected signal _SD is selected by switching the movable terminal 37a to the terminal A side. In S10, the uncorrected signal _SD is recorded in the recording device 39.

In the above description of the present embodiment, the image pickup signal itself in the dark state captured at one time is
Although the case of using as the noise component data S _N of No. 2 has been described, the present invention is not limited to this. For example, by averaging image signals in a dark state captured a plurality of times using a line buffer or the like and performing noise correction using the average, the effect of random noise can be reduced.

Further, the selection of whether to read the noise component data S _N has been described for the case of performing on the basis of the result of histogram processing, when increasing the gain of the image signal, the noise component data S _N It is also possible to always read and perform noise correction. Further, the fact that the subtraction operation in the subtractor 36 may be performed digitally is the same as in the case of the above-described second embodiment.

As described above, according to the third embodiment, the image signal in the dark state generated by closing the light shielding plate is used as noise component data of the image sensor, and correction of fixed pattern noise of the image sensor is performed based on the data. So that
It is possible to obtain noise component data according to the shooting situation for each shooting of one screen, and it is possible to perform optimal noise correction according to the noise state at the time of shooting. Furthermore, it is determined whether or not to perform the noise correction according to the state of the image signal stored in the frame memory, and when the correction is not necessary, the noise correction is not performed. Optimum noise correction can be performed, and the photographing time of one image can be reduced.

[0041]

As described above, according to the present invention, the dummy signal lines which are provided so as to intersect with the plurality of vertical signal lines from which the imaging signals of the plurality of photosensitive pixels are read out and which are not connected to the photosensitive pixels are provided. By selecting, the noise signal is read out to a plurality of vertical signal lines, so that it is possible to perform noise correction not affected by the photosensitive pixels, and to reduce the fixed pattern noise of the image sensor without increasing the size of the device. It is possible to obtain a good image quality that is reliably removed.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a solid-state imaging device according to a first embodiment.

FIG. 2 is a diagram illustrating a detailed configuration of an image sensor.

FIG. 3 is a timing chart showing the overall operation timing of the solid-state imaging device.

FIG. 4 is a block diagram illustrating a solid-state imaging device according to a second embodiment.

FIG. 5 is a block diagram illustrating a solid-state imaging device according to a third embodiment.

FIG. 6 is a flowchart for explaining the operation of the third embodiment.

FIG. 7 is a diagram illustrating an example of a result of the histogram processing.

FIG. 8 is a diagram showing an index determined from a result of the histogram processing.

FIG. 9 is a block diagram illustrating a configuration of a conventional solid-state imaging device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Image sensor 2 Switch 2a Movable terminal 3 A / D converter 4 Line buffer 5 D / A converter 6 Subtractor 7 Process circuit 9 Synchronous signal generation circuit 13 Horizontal signal line 14 Vertical signal line 18 Dummy line 19 Switch 20 Subtractor 31 Light shielding Board 32 CCD 33 A / D converter 34 Frame memory 35 D / A converter 36 Subtractor 37 Switch 37a Movable terminal 38 Process circuit 39 Recording device 42 System controller

Claims (2)

(57) [Claims] 1. A plurality of photosensitive pixels, a plurality of vertical signal lines from which image signals of the plurality of photosensitive pixels are read, and a plurality of vertical signal lines are provided so as to intersect with the plurality of vertical signal lines, and the photosensitive pixels are connected to each other. A plurality of vertical signal lines, a plurality of vertical signal lines, and a plurality of photosensitive pixels from which the image pickup signals are read out. And a noise signal read out to the plurality of vertical signal lines. 2. The solid-state imaging device according to claim 1, further comprising a subtraction unit that performs a subtraction process between the imaging signal read from the vertical signal line and the noise signal.