JP2000050168A - Full-frame transfer type solid-state image pickup device and its driving method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize AF(automatic focusing), AE(automatic iris) due to an outputted signal of an imaging device itself without degrading release time lag characteristics and to further prevent the degradation of the AE and AF characteristics when an object with low luminance is photographed in a digital camera with a full-frame transfer type CCD imaging device. SOLUTION: This device is constituted by providing a storage area 2 to store an optional column in (n) columns of an image area 1 so that rows about a several percent of (n) are stored. Furthermore, the device is provided with a horizontal CCD(HCCD) 3 to receive signal electric charges which are photoelectrically converted by the image area 1 column by column and to output them to an output amplifier 4, an output amplifier to convert the signal electric charges of each pixel, to be transferred from the HCCD 3 into voltage signals and a horizontal drain 5 to sweep off unnecessary electric charges to be formed by holding it between the HCCD 3 and a channel stop.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a full frame transfer type solid-state image pickup device mainly used for a digital camera for photographing a still image requiring high sensitivity with a large number of pixels and a driving method thereof.

[0002]

2. Description of the Related Art In recent years, applications for handling images on a computer have been dramatically increased. Here, the commercialization of digital cameras for capturing images into computers has become active. As a solid-state imaging device used in such a digital camera, an interline transfer CCD, a frame transfer CCD imaging device, and a full frame transfer CCD imaging device are mainly used. Of these, full-frame CCDs are often used in digital cameras for photographing still images that require high sensitivity with multiple pixels, and are used for applications as large area reference pixel sensors.

As a development trend of such digital cameras, cameras handling still images have sharpened the direction to increase the number of pixels, and the number of pixels of an image sensor of a moving image camera is usually 250,000 to 40,000. Many pixels, whereas many cameras equipped with an imaging element exceeding 700,000 pixels have been put into practical use, further mega pixels, for example, 1 million pixels, 1.5 million pixels, 2 million pixels, 4 million pixels, 60
Cameras using a high-pixel image sensor such as 100,000 pixels have also been commercialized. As the number of pixels of the sensor increases, the trend of CCD products is being divided into two directions.

One is to increase the number of pixels without increasing the area of the image pickup area. In this direction, it is a problem to reduce the decrease in sensitivity due to the reduction in pixel size. Many interline CCD imaging devices are moving in this direction. On the other hand, there is a direction in which high sensitivity is required at the same time as a large number of pixels, and a digital still camera is required as a replacement for the conventional silver halide still camera. In this area, full-frame transfer type CCs are simpler in process than inter-line type CCD image sensors.
D imaging devices are often used.

[0005]

However, the above high pixel sensor has the following problems. Conventional 27
In the case of a CCD having about 10,000 to 600,000 pixels, usually, as a method of autofocus (AF), a movie is driven in the same manner as a video while normally scanning a focus of a lens, and a high frequency of a frame image signal to be read out is read. TV auto focus (TV-A) that detects the focus position where the output level of the component peaks
F) Control is performed, and as the exposure control, auto iris (AE) control for controlling the aperture or the shutter time so that the integral value of the image signal of the specific area of the frame image signal becomes an appropriate value is often performed. It has been done. However, in the case of a megapixel sensor, the readout time of all pixels is long, and AF and AE performed by performing such readout require an extremely long time. Therefore, the release time lag of the camera is practically acceptable. It will be too long. Therefore, a digital still camera having such a megapixel sensor needs to be able to repeatedly read out signal charges only in a required area in an image area of the sensor.

As described above, a full-frame transfer type C is usually used as a megapixel high-sensitivity image sensor.
A CD imaging device is used. However, in this image sensor, it is essential to close a shutter for blocking incident light at the time of reading charges, and it is extremely difficult to repeatedly (movingly read) the entire area or a specific partial area. For this reason, a digital still camera having this image sensor usually has a line sensor for AF and a photometric sensor for AE separately from the image sensor for photographing.

The present invention has been made in view of the above problems, and provides a structure and a driving method which enable repeated reading of a specific portion of a high pixel CCD, particularly a full frame transfer type CCD image pickup device. Accordingly, an object of the present invention is to realize AF and AE by an output signal of the image sensor itself without deteriorating the release time lag characteristic, which was extremely difficult with a digital camera having a conventional full frame transfer type CCD image sensor. Another object is to prevent AE and AF characteristics from deteriorating when a low-luminance subject is photographed.

[0008]

SUMMARY OF THE INVENTION A full-frame transfer type solid-state imaging device (hereinafter simply referred to as an imaging device) of the present invention converts optical information of an imaged subject into signal charges, accumulates the signals, and stores each signal. An image area having a plurality of vertical photoelectric conversion elements for transferring pixel signal charges in the vertical direction, and among signal charges transferred from the image area, only signal charges corresponding to pixels in an arbitrary partial area can be stored And a horizontal photoelectric conversion element for transferring the signal charges transferred from the storage region in the horizontal direction and reading out one line at a time.

In one aspect of the imaging device of the present invention, the charge storage capacity of each pixel in the storage area is larger than the charge storage capacity of a pixel in the image area.

In one aspect of the imaging apparatus of the present invention, a drive electrode is provided in each of the image area and the storage area.

In one aspect of the imaging apparatus of the present invention, the arbitrary partial area is a plurality of areas in the image area.

In one aspect of the imaging apparatus of the present invention, the storage area operates repeatedly so that the arbitrary partial area differs.

In one aspect of the imaging apparatus of the present invention, the storage area stores signal charges corresponding to pixels of at least two adjacent lines among signal charges transferred from the image area.

In one aspect of the imaging apparatus of the present invention, the addition of signal charges corresponding to pixels of at least two adjacent lines is performed in a first stage of the storage area adjacent to the image area.

In one aspect of the image pickup apparatus of the present invention, the addition of signal charges corresponding to pixels on at least two adjacent lines is performed by the horizontal photoelectric conversion element.

In one aspect of the image pickup apparatus of the present invention, the image area is provided between a drain adjacent to each of the vertical photoelectric conversion elements and for draining off signal charges, and between the vertical photoelectric conversion element and the drain. And a barrier whose height is made variable by voltage control.

In one aspect of the image pickup apparatus of the present invention, the height of the barrier is determined when the signal charges of all the pixels in the image area are read and the height of the signal corresponding to the pixels in an arbitrary partial area of the image area. Control is performed differently when reading out only the electric charge.

One embodiment of the image pickup apparatus according to the present invention has a shutter in front of the vertical photoelectric conversion element for blocking incident light, and the shutter is used to shield light when reading signal charges of all pixels in the image area. It is configured to be closed when reading out only signal charges corresponding to pixels in an arbitrary part of the image area,
The height of the barrier is such that the saturation charge amount of the vertical photoelectric conversion element is larger when reading out the signal charges of all the pixels than when reading out only the signal charges corresponding to the pixels in the arbitrary partial region. Is controlled.

In one aspect of the image pickup apparatus of the present invention, the storage area may be a signal charge corresponding to a pixel in an arbitrary partial area transferred from the image area, or may be the signal charge. Adding and accumulating signal charges corresponding to at least one pixel before and after a pixel in the region;
The height of the barrier is changed according to the number of pixels to be added.

In one aspect of the imaging device of the present invention, the height of the barrier is adjusted such that the amount of saturated charge of the vertical photoelectric conversion element is inversely proportional to the number of additions.

According to the method of driving an image pickup apparatus of the present invention, an image having a plurality of vertical photoelectric conversion elements for converting optical information of an imaged subject into signal charges and storing the signal charges and transferring the signal charges of each pixel in a vertical direction is provided. Of the signal charges transferred from the region, only the signal charges corresponding to the pixels in an arbitrary partial region can be stored in the storage region, and the signal charges transferred from the storage region are horizontally transferred by the horizontal photoelectric conversion element. And read out one line at a time.

In one aspect of the driving method of the image pickup apparatus according to the present invention, the charge storage capacity of each pixel in the storage area is made larger than the charge storage capacity of the pixel in the image area.

In one aspect of the driving method of the imaging apparatus according to the present invention, the arbitrary partial area is a plurality of areas in the image area.

In one aspect of the driving method of the image pickup apparatus of the present invention, the storage area is repeatedly operated so that the arbitrary partial area is different.

In one aspect of the driving method of the image pickup apparatus according to the present invention, of the signal charges transferred from the image area, signal charges corresponding to pixels of at least two adjacent lines are stored in the storage area. .

In one aspect of the driving method of the image pickup apparatus according to the present invention, the addition of signal charges corresponding to pixels of at least two adjacent arbitrary lines is performed in a first stage of the storage area adjacent to the image area.

In one embodiment of the driving method of the image pickup apparatus according to the present invention, the horizontal photoelectric conversion elements add signal charges corresponding to pixels of at least two adjacent lines.

In one aspect of the driving method of the image pickup apparatus according to the present invention, the driving circuit is provided between the vertical photoelectric conversion element and a drain adjacent to each of the vertical photoelectric conversion elements for sweeping out signal charges. Using a variable-height barrier, the height of the barrier is determined by reading the signal charges of all the pixels in the image area, and only the signal charges corresponding to pixels in an arbitrary part of the image area. Is controlled so as to be different from the time of reading.

In one embodiment of the driving method of the image pickup apparatus according to the present invention, when reading out the signal charges of all the pixels of the image area, the signal charges are closed for light shielding and correspond to pixels of an arbitrary partial area of the image area. When reading only the signal charge, use a shutter that is configured to be opened,
The height of the barrier is such that the amount of saturation charge of the vertical photoelectric conversion element is larger when reading out signal charges of all the pixels than when reading out only signal charges corresponding to pixels in the arbitrary partial region. To control.

In one embodiment of the driving method of the image pickup apparatus according to the present invention, the driving circuit is provided between the vertical photoelectric conversion element and a drain adjacent to each of the vertical photoelectric conversion elements for sweeping out signal charges, and is controlled by voltage control. Using a barrier with a variable height, the storage area may be used as it is for the signal charges corresponding to the pixels of any partial area transferred from the image area, The signal charges corresponding to at least one pixel before and after the pixel are added and accumulated, and the height of the barrier is changed according to the number of added pixels.

In one aspect of the driving method of the image pickup apparatus according to the present invention, the height of the barrier is adjusted so that the saturation charge of the vertical photoelectric conversion element is inversely proportional to the number of additions.

[0032]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a structural diagram of a full frame transfer type CCD image pickup device (hereinafter, referred to as an image pickup device of the present example) which is a main component of the present embodiment.

1 is m rows × n columns (hereinafter, a vertical arrangement is a column,
An image area of pixels in the horizontal arrangement is also constituted by n vertical CCDs (VCCDs) that are exposed in a frame transfer type CCD image sensor. here,
The VCCD is generally configured as a two- or four-phase drive or a quasi-one-phase drive CCD such as a virtual phase. In the former, a polysilicon gate covers the entire pixel portion, and the sensitivity to light having a wavelength in the blue region is reduced. become worse. In the case of the virtual phase, the clock gate for the transfer is 1
Since the virtual gate portion does not have a gate electrode, the virtual gate portion can sufficiently absorb light having a wavelength in the blue region and convert it into electric charge. In addition, the virtual phase has a small number of driving pulses and is easy to operate. Hereinafter, the sensor of the present invention will be described using a virtual phase CCD for convenience. A pulse for the CCD transfer in this area is φVI.

Reference numeral 2 denotes a storage area for storing an arbitrary column in the n columns of the image area 1. o is configured such that rows of about several percent of n can be stored. Therefore, the increase in the chip area of the image sensor due to the memory unit is extremely small. The pulse for the CCD transfer in this area is ΦVS. In this region, an aluminum layer for shielding light is formed on the upper portion.

Reference numeral 3 denotes a horizontal CCD (HCCD) for receiving each row of signal charges photoelectrically converted in the image area 1 and outputting the received signal charges to an output amplifier 4.
D3 is a transfer pulse.

Reference numeral 4 denotes an output amplifier for converting the signal charge of each pixel transferred from the HCCD 3 into a voltage signal, and is usually constituted by a floating diffusion amplifier.

Reference numeral 5 denotes a horizontal drain formed between the HCCD 3 and a channel stop (drain barrier) (not shown) for sweeping out unnecessary charges. Signal charges of unnecessary area pixels at the time of partial readout are transferred from the HCCD 3 to the channel. The liquid is discharged to the horizontal drain 5 beyond the stop.

An electrode is provided on the drain barrier between the HCCD 3 and the horizontal drain 5, and the voltage applied to the electrode is changed to make it possible to efficiently sweep out unnecessary charges.

Basically, in this configuration, a small storage area is provided in a normal full frame transfer type CCD image pickup device, so that partial reading can be performed at an arbitrary place.

FIG. 12 shows the pixel structure of the image area.
FIG. 12A is a plan view seen from above, and FIG.
(B) is the structure and potential profile of the II ′ cross section.

Reference numeral 201 denotes a clock gate electrode made of light transmissive polysilicon, and a semiconductor surface below the clock gate electrode 201 is a clock phase region. The clock phase region is divided into two regions by ion implantation, one of which is a clock barrier region 202.
The other is a clock well region 203 formed by implanting ions so as to have a higher potential than the clock barrier. 204 is P on the semiconductor surface.
This is a virtual gate for fixing a channel potential by forming a ⁺ layer, and this region is a virtual phase region. This region is also divided into two regions by implanting N-type ions into a layer deeper than the P ⁺ layer. One is a virtual barrier region 205 and the other is a virtual well region 206. Reference numeral 207 denotes an insulating layer such as an oxide film provided between the electrode and the semiconductor. 208 is
This is a channel stop for separating the channels of each VCCD.

Although not shown here, a function of preventing a blooming phenomenon in which electric charges overflow into adjacent pixels and generate a pseudo signal when strong light enters is added. A typical method is to provide a horizontal overflow drain. That is, a drain made of an N ⁺ layer is provided in contact with each VCCD, and an overflow drain barrier is provided between the overflow drain and the charge transfer channel. Charges that exceed the height of the overflow drain barrier will be swept to the drain. The height of the drain barrier is fixed by ion implantation, or by forming an electrode (over drain barrier electrode) on the overflow drain barrier, the height of the drain barrier is controlled by controlling the value of the voltage (VOD) applied to the drain electrode. (Hereinafter, the description will proceed with an imaging device having an overflow drain electrode.)

In the transfer of the VCCD, an electric charge is transferred in the direction of the HCCD 3 by applying an arbitrary pulse to the clock electrode 202 to move the potential of the clock phase up and down with respect to the potential of the virtual layer (FIG. 1).
In FIG. 2 (b), the concept of charge transfer is indicated by a circle. ).

The above is the pixel structure of the image area.
The pixel structure of the storage area also follows this. However, in this region, since the upper part of the pixel is shielded from aluminum, it is not necessary to prevent blooming, so that the overflow drain is omitted. The HCCD also has a virtual phase structure, but arranges a layout of a clock phase region and a virtual phase phase region so that electric charges from the VCCD can be received and transferred horizontally. The charge saturation amount of each pixel in the image area, the storage area, and the HCCD area is as follows: image area <storage area <HCCD area (condition 1). This prevents the charge exceeding the charge saturation capacity of the pixels in the traveling direction from remaining in the remaining transfer state and becoming a pseudo signal if the charge saturation capacity of the pixels in the respective traveling directions is smaller. To do that. Usually HCC
The charge saturation capacity of D is designed to be at least twice the charge saturation capacity of the image area. The area of the storage area can be reduced by reducing the difference between the charge saturation capacities of the pixels in the image area and the storage area. Then, by controlling the voltage value (VOD) of the overflow drain electrode in the image area so that the charge saturation capacity of the image area becomes smaller than the charge saturation capacity of the storage area when the sensor is used, the height of the barrier of the overflow barrier is controlled. Is controlled and adjusted. As a result, the above condition can be reliably realized, and it is not necessary to increase the difference in pixel area between the image area and the storage area.

First, normal reading in a digital camera using the CCD image pickup device of FIG. 1 will be described with reference to the timing chart of FIG. In the normal photographing using the CCD image pickup device of FIG. 1, the mechanical shutter provided on the front surface of the image pickup device is closed at first, and ΦVI, ΦVS, Φ
A high-speed pulse is applied to S, and at this time, VOD becomes HC
By opening the CD so that the electric charge of the CD is swept away by the clear drain 6 (VOD is at a high level), a clear operation of sweeping out the electric charge of the image area and the storage area is performed (Tclear). ΦVI, ΦVS, ΦS at this time
The number of pulses is equal to or greater than the number n + o of transfer stages of the VCCD, and charges in the image area and the storage area are changed to H
The CCD is discharged to the horizontal drain and the horizontal drain beyond the floating diffusion amplifier. If the image pickup device has a gate between the HCCD and the horizontal drain, the gate can be opened only during the clear period, whereby more efficient unnecessary charge discharge can be performed.

Immediately after the clear operation is completed, the mechanical shutter is opened, and when the time for obtaining an appropriate exposure amount has been reached, the mechanical shutter is closed. This period is defined as an exposure time (or accumulation time) (Tstorage).
During the accumulation time, the VCCD is stopped (ΦVI, ΦV
S is low level).

Signal charges generated in response to light incident on the sensor surface of the CCD image sensor (image light passing through the imaging lens in front of the sensor and being imaged on the sensor surface) are integrated in virtual wells in each pixel. Is done. Then, when the amount of charge exceeds the height of the overflow drain barrier, the charge generated further is discarded by the overflow drain. Since the storage area is shielded from light, each pixel is empty with no signal charge.

When the mechanical shutter is closed, first, vertical transfer for o lines is performed (Tcm). By this operation, the first line of the image area (the line adjacent to the storage area) is moved to the head of the storage area (HCC
D). This first line transfer is performed continuously. Next, before the first line of the image area is transferred to the HCCD, the HCCD is transferred once for all the stages of the HCCD in order to clear the charges (Tch). As a result, unnecessary charges remaining in the HCCD at the time of clearing the image area and the storage area (Tstorage) and charges of the dark current of the storage area collected in the HCCD by clearing the storage area (Tcm) are discharged.

Now, clear the storage area (this is because the signal of the first line in the image area is
This is also a read set operation that proceeds to the final stage of the CCD. ), And as soon as the HCCD clear is completed, the signal charges in the image area are sequentially changed to H from the first line.
The signal is transferred to the CCD, and the signal for each line is sequentially read (Tread). The signal charge read out in this way is C
The signal is converted into a digital signal by a pre-processing circuit including a DS circuit, an amplifier circuit, and an A / D conversion circuit, and the image signal is processed.

Next, repetitive partial reading for AF and AE of a digital camera using the image pickup device of this embodiment will be described with reference to FIG. Normally, a full frame transfer type CCD image sensor requires a shutter to be closed at the time of transfer. Therefore, an image sensor for AF and AE is separately provided. On the other hand, in this CCD image pickup device, a part of the image area can be repeatedly read out with the shutter kept open.

First, the signal charge of the o line (no line) at an arbitrary position in the image area is accumulated in the storage area, and the signal charge of the image area (nf) preceding the arbitrary o line to be accumulated is discharged. A pre-clear transfer for sweeping out the charge of the o + nf lines is performed (Tcf). As a result, the signal charges accumulated in the no line in the accumulation period (Ts) before the previous-stage clear Tcf are accumulated in the storage area. Immediately thereafter, the HCCD is cleared (Tch), which sweeps away the remaining charge of the previous clear Tcf remaining in the HCCD. After this, the storage area no
The signal charges of the lines are transferred to the HCCD line by line, and are sequentially read from the output amplifier (Tr). Then, no
When the reading of the line signal is completed, the clear operation of all stages of the image sensor is performed (Tcr). Then, after the accumulation period Ts again, the previous stage clear operation, the no line signal read Tr, and again the all stage clear Tcr are repeated in the same manner.

During the movie drive of the signal in the specific area, the focus lens for AF is moved little by little, and the signal level in the specific frequency band of the signal in the specific area reaches the peak. A so-called television AF operation for stopping the focus lens is performed. Of course, such a partial readout of the CCD image pickup device is not only used in the TV AF system, but also a phase difference lens is provided in front of the CCD image pickup device, and the phase difference for performing AF by measuring the phase difference of the image formation. Also used for AF. And
In order to read these AFs, about three places in the image area are read, for example, in the first sequence (Tcr-
Ts-Tcf-Tr), the signal on the HCCD side is read in one sequence of the second time, the signal on the opposite side of the HCCD is read in one sequence of the HCCD, and one sequence of the third time, and the reading of these three stages is repeated. Measure the difference between the three focus positions,
Weighting is also performed. For AE, the exposure condition is controlled from the integrated value of the signal of an arbitrary no line.

In this way, in the image pickup device of this embodiment, movie driving of a specific no line can be performed, and other than the specific line can be discarded at a high speed, so that the operation needs to be completed in a short time. Driving at a speed sufficient for performing AF and AE becomes possible. In addition, by performing the pre-stage clearing and the all-stage clearing after reading the necessary signal charges by the high-speed transfer, the smear component of the signal of the required no line is extremely small, and is suppressed to a level that does not cause a problem due to AF and AE.

As described above, the method of changing the read location in each cycle of the partial read operation has been described. The signals at a plurality of locations are read in one cycle (accumulation in the storage area).
It is also possible. For example, o
Immediately after inserting the / 2 line, the voltage of the electrode in the storage area is set to high (that is, a wall for stopping the transfer of the signal charge from the image area is formed), and the charge up to the next required line is transferred to the VCCD of the image area. In order to transfer to the virtual well of the last stage, pulses for the number of stages up to the next required signal are applied to the electrodes in the image area. As a result, the charges until the next necessary signal are transferred to the virtual well in the final stage, and the charges exceeding the overflow barrier are removed to the overflow drain.

Next, o / 2 is applied as a transfer pulse to drive electrodes provided in the image area and the storage area, respectively.
When the pulse is applied, the signal of the signal line of (o / 2) 11 lines in the second area is accumulated in the storage area after the first o / 2 line and after the remaining invalid line in the middle part after clearing. Will be. Further, if these signals are to be captured in three regions, the second intermediate signal may be cleared after capturing the second signal to capture the signals in the third region. Needless to say, if the capture area increases, the number of capture lines at each location decreases. If data at a plurality of locations are read in one cycle in this way, AF and AE can be performed at a faster speed than when another location is read out in each previous cycle.

Now, as described above, the image area and the HCCD
By providing a storage area far less than the number of lines in the image area, the movie read operation of a specific line for AF and AE can be performed. In this case, since the storage area is extremely small, the chip size of the CCD image pickup device does not change so much.
This is no different from the D imaging device. Further, it is not necessary to provide a CCD image pickup device in both AF and AE, which is necessary for a digital camera using a conventional full frame CCD image pickup device. This reduces the circuit scale, the size of the camera body, and the cost. Can be brought. Furthermore, CC
By using the imaging signal itself of the D image sensor for AF and AE, it is possible to perform extremely accurate focus adjustment and iris adjustment.

By the way, AF requires the same accuracy in photographing in a dark place as in a bright place. However, if the same driving method as described above is used, the amount of signal charge decreases, the ratio of signal to noise deteriorates, and sufficient AF accuracy cannot be obtained. To avoid this, when the brightness of the subject decreases, the accumulation period Ts is extended. However, if Ts becomes too long, the cycle of signal readout becomes shorter, and A
The operation of F becomes slow, and the mobility of the digital camera is impaired.

Although the amplifier gain is increased, the noise also increases by the gain increase, so that S / S
N is not improved, and the amount of improvement in AF accuracy is small. For this reason, when it is determined that the output from the image sensor is low although the luminance is lowered and Ts is the maximum within the specified value, the addition of a plurality of lines of the image sensor is performed.

Hereinafter, a description will be given of a state of the addition driving of a plurality of lines in the repeated partial reading with reference to FIGS. O + nf of ΦV1, ΦVS, and ΦS during the Tcf period in FIG.
The required signal charges to be stored in the storage area in the last pulse of the pulses are stored in the storage area. FIG. 4 shows the period during which the last necessary signal charge is transferred from the image area to the storage area as Tt.
FIG. 5 shows the pulses in the Tc and Tt periods in the non-addition repetitive partial read driving method described in FIG. 3 in detail. The same pulse is applied to both Tcf and Tt.

FIG. 6 shows the drive timing in the case of two-line addition. The pulses of ΦVS and ΦS during the Tt period are as follows:
Missing every other pulse. FIG. 7 is a potential diagram illustrating the pixel addition operation at this drive timing. Here, reference numeral 801 denotes a signal charge lump. T1, T in FIG.
The potential profiles at the time points 2, 3, T4, and T5 are indicated by thick black lines in FIG. ΦV-high level means a channel potential when a high potential is applied to the vertical transfer electrode ΦVI or ΦVS,
Low level means vertical transfer electrode ΦVI or ΦV
It shows a channel potential when a low potential is applied to S. As shown in FIG. 7, pixel addition is performed in a virtual well adjacent to the storage area in the image area using the clock phase of the storage area as a barrier.

The broken line in FIG. 7 indicates the potential of the barrier of the horizontal overflow drain provided in the image area. If the signal charge exceeds this level, excess charge is discharged to the drain. The dashed line indicates the potential of the channel stop. The amount of charge saturation in the image area is determined by the potential of the clock well and the potential of the overflow barrier. However, the charge saturation capacity of the storage region is determined by the virtual well capacity determined by the potentials of the virtual well and the virtual barrier, or by the clock well capacity determined by the potentials of the rock well and the clock barrier. Here, when a charge exceeding the charge saturation determined by the virtual well capacitance or the clock well capacitance is injected into one pixel (one element) of the storage region from the image region, the charge exceeding the charge saturation is transferred during charge transfer. It is not transferred and remains in the original element. However, if the addition of the charges is performed in the virtual well adjacent to the storage area of the image area using the clock phase of the storage area as a barrier as described above, the charge exceeding the saturation charge of the image area when added is obtained. Is discharged to the drain across the overflow barrier.

As shown in the condition 1, the height of the overflow barrier is set so that the saturation charge in the image area is smaller than the saturation charge in the storage area. There is no charge remaining in the storage area. (It goes without saying that the storage area is shielded from light by the aluminum layer,
Since there is no charge generation due to light, if the saturation capacity is higher than the saturation capacity of the image area, the phenomenon of remaining charges cannot occur. ).

Now, with respect to the set value of the overflow barrier, a condition to be added to the condition 1 when such a partial read driving is performed occurs. That is, in the case of normal reading in which charge transfer is performed when the mechanical shutter is closed, only condition 1 needs to be satisfied.
Therefore, the potential of the overflow barrier in the image area may be at the same level as the clock barrier, or the height of the barrier may be low (high potential).

However, in the partial read repetitive drive for AF and AE, the mechanical shutter is opened.
Therefore, during the high-speed clear Tcr and the transfer of the charge of the necessary line to the storage area (and the clearing of the unnecessary signal charge in the preceding stage of the necessary line) Tcf, there is a charge generated due to the incident light. When the pixel charges in the image area cross the clock barrier due to the signal charges generated during such charge transfer, the excess charges are left untransferred and cause blooming. Therefore, the height of the overflow barrier is adjusted to be somewhat lower than that of the clock barrier so that the generated charges during such transfer do not cause blooming. The setting level of this adjustment level varies depending on the required level of the blooming ability. Usually, the light quantity several hundred times the light quantity reaching the saturated charge amount is adjusted as the limit value for the blooming.

The saturation charge (Vsatim) determined by the overflow barrier and the saturation charge (Vsatim) determined by the clock barrier
sat) and blooming surplus charge (Vab) have the following relationship. Vsatim = Vsat-Vab (Condition 2) Vab may be 0 in normal all-pixel readout in which charge transfer is performed when the mechanical shutter is closed, and is a charge amount for securing necessary blooming capability in partial readout. Therefore, in the digital camera using the CCD image pickup device of the present embodiment, the voltage of the overflow drain electrode is set at the time of the partial repetitive read driving for AF and AE in which the electric charge is transferred when the mechanical shutter is opened. The height of the overflow barrier is switched between the readout driving of all pixels in which charge transfer is performed when the mechanical shutter is closed (that is, the value of the voltage VOD of the electrode above the overflow barrier is changed). In this way, an image with a high dynamic range can be obtained by setting the saturation charge high when all pixels of a still image are captured, and the repetitive partial readout drive for AF and AE can be performed like blooming. It is possible to prevent an error from occurring in data due to a false signal.

FIG. 8 is a timing chart when four pixels are added in the same manner. As described above, the number of pixels to be added can be changed by changing the number of pulses thinned out from ΦVS and ΦS.

As described above, by adding information of a plurality of lines by adding pixels, that is, data having substantially increased sensitivity, the time for AF and AE can be increased without increasing the time for AF and AE. A with high accuracy
F and AE can be performed. (If the amplifier gain is increased without performing line addition, the noise component is increased by this method, and the accuracy of AF and AE is limited. ).

FIG. 9 is a drive timing diagram for performing pixel addition in the storage area, and FIG. 10 is a potential diagram for clarifying the pixel addition operation at this drive timing. As shown, the pixels are made in the first stage clock well of the storage area. It should be noted that in this pixel addition method, the voltage of VOD must be adjusted so that the pixel saturation capacity of the image area is equal to or less than half of the pixel saturation area of the storage area.

As described above, blooming occurs when the pixel-added charge exceeds the pixel saturation capacity of the storage area.

FIG. 11 is a timing chart of 4-pixel addition by the addition method in the storage area. VOD indicates that the charge saturation capacity of the image area is 1/1 that of the storage area.
It is adjusted to be 4 or less. Thus, condition 3 is added in this addition method. That is, when the number of pixel addition stages is n, the saturation charge capacity Vsati
m needs to be adjusted so that the charge saturation capacity Vsats of the storage region becomes as follows. Vsatim> (n · Vsats) (Condition 3) That is, in a camera using such an addition method, the VOD can be changed according to the number of addition stages in order to satisfy Condition 3.

As described above, by providing a small storage area in the full frame transfer type CCD image pickup device, AF, AE (that is, TTL) using the image pickup image pickup device itself, which has been difficult with the conventional device.
Becomes possible. Further, by performing the charge addition driving with such a sensor, AF and AE can be performed with high accuracy even in the case of low luminance. Note that the pixel addition method described here is not limited to a full frame transfer type CCD imaging device, but is also effective in a frame transfer type CCD imaging device or a frame interline type CCD imaging device.

In the above description, the charge addition at the final stage of the VCCD in the image area and the pixel addition at the first stage of the VCCD in the storage area have been described. It should be noted that pixel addition at the HCCD is also possible. In this case, since a plurality of lines in the storage area are added, the number of signal lines output after the addition decreases as the number of addition stages increases. That is, if two pixels are added, the signal line is 1 /
In the case of adding two or three pixels, the signal line becomes 1/3 (the charge addition at the last stage of the VCCD in the image area and the pixel addition at the first stage of the VCCD in the storage area result in 0 lines after the addition. , So that the 0 line after the addition is output.)

In the camera using the CCD image pickup device according to the present embodiment, the operation is performed with the mechanical shutter opened during AF and AE, and after the completion of AF and AE, the mechanical shutter is closed and the inside of the CCD image pickup device is removed. After clearing the unnecessary charges, the mechanical shutter is opened again,
The shutter is closed in such a time that the appropriate amount of light enters,
The reading of all the pixels of the CCD image sensor is performed. As described above, the value of VOD can be changed between AF and AE and when all pixels are read.

[0074]

According to the present invention, by providing a storage area for accumulating a small number of lines in a full frame transfer type CCD image pickup device, a specific portion can be repeatedly read out with a mechanical shutter opened. . This makes it extremely difficult for a digital camera having a conventional full frame transfer type CCD image pickup device to achieve AF, A based on the output signal of the image pickup device itself.
E is realized without deteriorating the release time lag characteristic. In addition, by performing AE and AF weighting (comparison operation based on data from a plurality of areas of a subject) by a driving method of outputting signals of a plurality of parts of an image area, more accurate AE and AF control is performed. Can be.

[Brief description of the drawings]

FIG. 1 is a schematic diagram illustrating a structure of an embodiment of a full-frame transfer solid-state imaging device (hereinafter, simply referred to as an imaging device) according to the present invention.

FIG. 2 is a drive timing chart in an embodiment of the imaging device according to the present invention.

FIG. 3 is a drive timing chart in one embodiment of the image sensor according to the present invention.

FIG. 4 is a drive timing chart in an embodiment of the imaging device according to the present invention.

FIG. 5 is a drive timing chart in an embodiment of the image sensor according to the present invention.

FIG. 6 is a drive timing chart in an embodiment of the image sensor according to the present invention.

FIG. 7 is a driving potential diagram in an embodiment of the imaging device according to the present invention.

FIG. 8 is a drive timing chart in an embodiment of the imaging device according to the present invention.

FIG. 9 is a drive timing chart in an embodiment of the image sensor according to the present invention.

FIG. 10 is a driving potential diagram in an embodiment of the imaging device according to the present invention.

FIG. 11 is a drive timing chart in one embodiment of the image sensor according to the present invention.

FIG. 12 is a schematic diagram illustrating a pixel structure in an embodiment of an imaging device according to the present invention.

[Explanation of symbols]

 Reference Signs List 1 image area 2 storage area 3 horizontal CCD (HCCD) 4 output amplifier 5 horizontal drain 201 clock gate electrode 202 clock barrier area 203 clock well area 204 virtual gate 205 virtual barrier area 206 virtual well area 207 insulating layer 208 channel stop

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4M118 AA10 AB01 BA12 BA13 CB14 DA23 DB01 DB05 DB06 DB07 DB08 FA06 FA14 FA40 FA45 GB11 5C024 AA01 BA01 CA00 EA01 FA01 FA11 GA11 GA15 GA43 GA48 JA10 JA21

Claims (24)

[Claims] 1. An image area having a plurality of vertical photoelectric conversion elements for converting optical information of an imaged subject into signal charges, accumulating the signal charges, and transferring the signal charges of each pixel in a vertical direction, and transferring the image charges from the image area. A storage area capable of storing only signal charges corresponding to pixels in an arbitrary part of signal charges to be transferred, and a signal charge transferred from the storage area is transferred in a horizontal direction and read out line by line. A full-frame transfer type solid-state imaging device comprising: 2. The full-frame transfer solid-state imaging device according to claim 1, wherein a charge storage capacity of each pixel in the storage area is larger than a charge storage capacity of a pixel in the image area. 3. The full frame transfer type solid-state imaging device according to claim 1, wherein a drive electrode is provided in each of the image area and the storage area. 4. The apparatus according to claim 1, wherein the arbitrary partial area is a plurality of areas in the image area.
The full-frame transfer type solid-state imaging device according to any one of the above. 5. The full-frame transfer type solid-state imaging device according to claim 1, wherein the storage area operates repeatedly so that the arbitrary partial area is different. 6. The storage area according to claim 1, wherein the storage area stores signal charges corresponding to at least two adjacent pixels of the signal charges transferred from the image area. The full-frame transfer-type solid-state imaging device according to any one of the preceding claims. 7. The full according to claim 6, wherein the addition of the signal charges corresponding to the pixels of at least two adjacent lines is performed in the first stage of the storage area adjacent to the image area. Frame transfer type solid-state imaging device. 8. The full-frame transfer solid-state imaging device according to claim 6, wherein addition of signal charges corresponding to pixels of at least two adjacent lines is performed by the horizontal photoelectric conversion element. . 9. The image area is provided with a drain adjacent to each of the vertical photoelectric conversion elements for sweeping out signal charges, and between the vertical photoelectric conversion element and the drain, and has a height controlled by voltage control. The full-frame transfer type solid-state imaging device according to any one of claims 1 to 8, further comprising a variable barrier. 10. The height of the barrier differs between when reading out signal charges of all pixels in the image area and when reading out only signal charges corresponding to pixels in an arbitrary part of the image area. The full-frame transfer type solid-state imaging device according to claim 9, wherein: 11. A shutter for blocking incident light at a stage preceding the vertical photoelectric conversion element, wherein the shutter is closed to block light when reading out signal charges of all pixels in the image area, and the shutter is closed. It is configured to be opened when only the signal charges corresponding to the pixels in an arbitrary partial area are read out, and the height of the barrier is set so that the saturation charge amount of the vertical photoelectric conversion element is read out of the signal charges of all the pixels. 11. The full-frame transfer type solid-state imaging device according to claim 10, wherein the time is controlled so as to be larger than the time of reading out only the signal charges corresponding to the pixels in the arbitrary partial region. 12. The storage area may include a signal charge corresponding to a pixel in an arbitrary partial area transferred from the image area, or may include at least one pixel before and after a pixel in the partial area in the signal charge. 10. The full-frame transfer type solid-state imaging device according to claim 9, wherein the signal charges corresponding to the pixel values are added and accumulated, and the height of the barrier is changed according to the number of pixels to be added. 13. The full frame transfer type solid according to claim 12, wherein a height of the barrier is adjusted such that a saturation charge amount of the vertical photoelectric conversion element is inversely proportional to the addition number. Imaging device. 14. The signal charge transferred from an image area having a plurality of vertical photoelectric conversion elements for converting optical information of an imaged subject into signal charges, accumulating the signal charges, and transferring the signal charges of each pixel in a vertical direction. Of these, it is possible to store only signal charges corresponding to pixels in an arbitrary partial region in the storage region, and transfer the signal charges transferred from the storage region by the horizontal photoelectric conversion element in the horizontal direction and read out one line at a time. A method for driving a full-frame transfer type solid-state imaging device. 15. The full-frame transfer type solid-state imaging device according to claim 14, wherein a charge storage capacity of each pixel in the storage area is larger than a charge storage capacity of a pixel in the image area. Drive method. 16. The apparatus according to claim 14, wherein the arbitrary partial area is a plurality of areas within the image area.
Or the driving method of the full frame transfer type solid-state imaging device according to 15. 17. The method according to claim 17, wherein the arbitrary partial areas are different.
16. The driving method for a full-frame transfer type solid-state imaging device according to claim 14, wherein the storage area is repeatedly operated. 18. The storage device according to claim 14, wherein, of the signal charges transferred from the image area, signal charges corresponding to pixels of at least two adjacent lines are stored in the storage area. A method for driving a frame transfer type solid-state imaging device. 19. The full frame according to claim 18, wherein the addition of signal charges corresponding to at least two adjacent lines of pixels is performed in a first stage of the storage area adjacent to the image area. A method for driving a transfer-type solid-state imaging device. 20. The solid-state imaging device according to claim 18, wherein addition of signal charges corresponding to pixels of at least two adjacent lines is performed by the horizontal photoelectric conversion element. Drive method. 21. A barrier provided between the vertical photoelectric conversion element and a drain adjacent to each of the vertical photoelectric conversion elements for sweeping away signal charges, and having a height variable by voltage control, The height of the barrier is controlled so as to be different when reading signal charges of all pixels in the image area and when reading only signal charges corresponding to pixels in an arbitrary part of the image area. The driving method of a full-frame transfer type solid-state imaging device according to any one of claims 14 to 20, wherein: 22. It is configured to be closed for light shielding when reading signal charges of all pixels in the image area, and to be opened when reading only signal charges corresponding to pixels in an arbitrary part of the image area. Using a shutter, the height of the barrier, the amount of saturation charge of the vertical photoelectric conversion element when reading out the signal charge of all the pixels is better for only the signal charge corresponding to the pixel in the arbitrary partial area 22. The driving method of a full-frame transfer type solid-state imaging device according to claim 21, wherein control is performed so as to be larger than at the time of reading. 23. A barrier provided between the vertical photoelectric conversion element and a drain adjacent to each of the vertical photoelectric conversion elements for sweeping away signal charges, and having a height variable by voltage control, In the storage area, a signal charge corresponding to a pixel in an arbitrary partial area transferred from the image area may be used as it is, or a signal charge corresponding to at least one pixel before and after a pixel in the partial area may be added to the signal charge. 21. The full-frame transfer solid-state imaging device according to claim 14, wherein the height of the barrier is changed according to the number of pixels to be added. Method. 24. The full-frame transfer type solid-state imaging device according to claim 23, wherein the height of the barrier is adjusted so that a saturation charge amount of the vertical photoelectric conversion element is inversely proportional to the addition number. How to drive the device.