JPH0775404B2 - Driving method for solid-state imaging device - Google Patents

Description

The present invention relates to a method for driving a CCD solid-state image pickup device, and more particularly to driving for discharging photocharges from an image pickup section of the solid-state image pickup device.

(B) Conventional technology Conventionally, in the image pickup device using the CCD solid-state image pickup device,
It is considered to electronically control exposure by utilizing the operating principle of CD. Such an exposure control method, for example, as disclosed in Japanese Patent Laid-Open No. 63-24764, transfers and discharges the photocharges accumulated in the image pickup unit in the middle of the photoelectric conversion period for each vertical scanning period, and leaves the residual charge. The photoelectric conversion period is expanded and contracted according to the change of the discharge timing of the photoelectric charges.

FIG. 6 is a block diagram when the above-described exposure control is executed, and FIG. 7 is a frame transfer type used for this.
It is a schematic diagram of CCD.

The frame transfer CCD solid-state image sensor (1) is
As shown in FIG. 7, it comprises an image pickup section (I), a storage section (S) and a horizontal transfer section (H). Is stored in the storage unit (S) and is then converted from the storage unit (S) through the horizontal transfer unit (H) into a voltage value in the output unit (F) and output as a video signal X _(t) . The video signal X _(t) is subjected to processing such as sample hold and gamma correction in the signal processing circuit (2), and is output to an external device as a video signal Y _(t) .

On the other hand, the CCD (1) is pulse-driven, the forward transfer clock φ _F or the reverse transfer clock φ _B is supplied to the image pickup unit (I), and the storage unit (S) and horizontal transfer unit (H) ) Is supplied with the storage transfer clock φ _S and the horizontal transfer clock φ _{H, respectively} . That is, the reverse transfer clock φ
Depending on _B , the photocharge of the image pickup section (I) is transferred in the direction opposite to the storage section (S) (indicated by a broken line in the figure), and the storage section (S) is transferred.
After being discharged to the discharge drain (D) provided on the side opposite to, the photocharge is accumulated in the imaging unit (I) for a predetermined period, and the photocharge is accumulated in the accumulation unit (S) according to the forward transfer clock φ _F. )
To (indicated by the solid line in the figure). Then, photocharges are transferred from the storage unit (S) to the horizontal transfer unit (H) for each horizontal line according to the storage transfer clock φ _S , and further from the horizontal transfer unit (H) according to the horizontal transfer unit clock φ _H. It is transferred to the output unit (F).

The forward transfer clock φ _F and the reverse transfer clock φ _B described above are generated by the read clock generation circuit (3) and the discharge clock generation circuit (4), respectively, and these clock generation circuits (3) and (4) are used. The read timing signal FT and the discharge timing signal BT are stored in the read timing control circuit (5).
And the discharge timing control circuit (6). Further, the exposure amount determination circuit (7) detects the exposure amount of the video signal X _(t) obtained from the CCD (1), and if this exposure amount is above the proper range, the exposure suppression signal CLOSE, below the proper range If there is, an exposure promotion signal OPEN is given to the discharge timing control circuit (6). Then, the discharge timing control circuit (6) sets the discharge timing of the photocharge according to the exposure suppression signal CLOSE and the exposure promotion signal OPEN.

FIG. 8 is a timing chart showing the operation of FIG.

The read timing signal FT has a timing pulse at a predetermined timing for each blanking period of the vertical scanning signal VD, and the read clock generating circuit (5) generates a clock pulse at the input of this timing pulse. Therefore,
The forward transfer clock φ _F generates a clock pulse during the blanking period of the vertical scanning signal VD, and CCD (1)
The photocharges of the image pickup unit (I) are transferred to the storage unit (S) during the blanking period.

On the other hand, the discharge timing signal BT has a timing pulse C at a timing corresponding to the exposure amount of the CCD (1), and a clock pulse D for discharge driving is generated according to this timing pulse. That is, the timing pulse of the ejection timing signal BT is configured such that the timing is delayed by the exposure suppression signal COLSE output from the exposure amount determination circuit (7) and is advanced by the exposure promotion signal OPEN. The photoelectric conversion period E, which is set during the period from the completion of driving to the start of reading driving, is expanded / contracted according to the exposure amount of the CCD (1).

(C) Problems to be Solved by the Invention In the CCD (1) described above, the photocharges of the storage unit (S) are sequentially transferred and output even while the photocharges of the imaging unit (I) are being discharged. Therefore, there is a problem that noise due to the clock pulse of the reverse transfer clock φ _B is superimposed on the photocharge transferred and output from the storage section (S). Therefore, if the clock pulse is kept within the blanking period of the horizontal scanning signal HD, superposition of noise can be prevented, but in a CCD with a large number of pixels in the vertical direction, all the photocharges of the image pickup unit (I) are It takes at least several hours (1H is one horizontal scanning period) for discharging, and it is impossible to put the clock pulse for discharging driving within the blanking period of the horizontal scanning signal HD.

Further, when the photocharge of the image pickup unit (I) is discharged, smear occurs because the photocharge of all pixels cannot be discharged at the same time as in the case of reading. The smear generated during the discharge driving is superimposed on the smear during the reading driving, so that the smear component of the video signal X _(t) obtained from the CCD (1) increases.

(D) Means for Solving the Problems The present invention is for solving the above problems, and a plurality of channel regions for accumulating photocharges generated by photoelectric conversion are arranged in a channel stop region so as to be separated from each other. A transfer electrode is provided on the channel region together with, and in the driving method of the CCD solid-state imaging device, which receives the excessive photocharge in the channel region to the overflow drain provided in the channel stop region, the channel region and The potential of the transfer electrode is set to the first potential applied to the transfer electrode and the second potential applied to the overflow drain when a potential barrier is formed between the drain and the overflow drain. The potential of the overflow drain and the potential of the overflow drain are higher than the second potential. It abolished the potential barrier between the band and the overflow drain, an unnecessary light charge in the channel region, characterized in that to discharge to the overflow drain.

(E) Action According to the present invention, the potential of the overflow drain is increased to deepen the potential of the overflow drain including the channel stop region, and the potential of the transfer electrode is lowered to shallow the potential of the channel region. At this point, the potential barrier (potential barrier) between the overflow drain and the channel region disappears, and the photocharges in the channel region flow into the overflow drain.

According to such a method of discharging photocharges, the photocharges in the respective channel regions of the CCD solid-state imaging device are discharged simultaneously and in a short time.

(F) Example An example of the present invention will be described with reference to the drawings.

FIG. 1 is a plan view of an essential part of a CCD solid-state image pickup device adopting the driving method of the present invention, and FIG. 2 is a sectional view taken along line XX ′ in FIG. Here, an image pickup unit of a frame transfer type CCD having a cross gate structure is shown.

A plurality of channel stop regions (11) are formed in parallel on one surface of the P type substrate (10) by LOCOS, and an overflow drain (12) is formed under the channel stop regions (11). In addition, an N-type channel region (13) is formed between the channel stop regions (11) by diffusion. A plurality of lower layer electrodes (14) are arranged in parallel at equal intervals in a direction orthogonal to the channel stop region (11), and the channel stop region (1
A plurality of upper layer electrodes (15) are formed along 1).
On the upper layer electrode (15), protruding portions that cover the gaps of the lower layer electrode (14) are formed so as to alternate with the adjacent upper layer electrode (15). Also, upper and lower layer electrodes (14)
A P ⁻ type light receiving region (17) is formed in the opening (16) surrounded by (15). The CCD itself having such a cross-gate structure is the same as that described in Japanese Patent Publication No. 63-8625 filed by the present applicant. Both electrodes (14) and (15) are pulse-driven by four-phase transfer clocks φ _{F1 to} φ _F4 ,
Transfer clocks φ _F1 and φ _F3 are alternately applied to the upper layer electrode (15), and transfer clocks φ _F2 and φ _F4 are applied to the lower layer electrode (14). Further, a control clock φ _OFD for controlling the potential of the overflow drain (12) is applied to the overflow drain (12).

When accumulating photocharges in the channel region (13), for example, the transfer clock φ _F1 is fixed at a high level of positive potential, and the control clock φ _OFD is fixed at a low level. By increasing the potential of the upper layer electrode (15) and decreasing the potential of the overflow drain (12), the potential of the channel region (13) is deeper as shown by the solid line in FIG. As a result, the potentials of the light receiving region (17) and the channel stop region (11) become shallow to form a potential barrier. Therefore, the photocharge generated by the light incident on the opening (16) flows from the light receiving region (17) into the channel region (13) below the electrode (15) along the potential gradient, Accumulated in (13). Then, by pulse-driving the both electrodes (14) and (15), photocharges are transferred while meandering between the channel stop regions (11) along the both electrodes (14) and (15).

On the other hand, when discharging unnecessary photocharges in the channel region (13), for example, the transfer clock φ _{F1 is set} to a negative potential and the control clock φ _{OFD is set} to a high level (positive potential).
By setting the upper electrode (15) to a negative potential, the potential of the channel region (13) below the upper electrode (15) becomes shallower than that of the channel stop region (11) as indicated by the broken line in FIG. The potential barrier between the region (13) and the channel stop region (11) disappears. Therefore, the photocharge in the light receiving region (17) is
And through the channel stop region (11) to the overflow drain (12). At this time, if the potential of the overflow drain (12) is not sufficiently deep, the photocharge from the light receiving region (17) cannot be sufficiently received. Therefore, the potential of the overflow drain (12) is increased to deepen the potential. ing. Further, by increasing the potential of the overflow drain (12), the potential of the channel stop region (11) adjacent to the overflow drain (12) is prevented from becoming shallow with the potential of the channel region (13).

According to the above-described method of discharging the photocharges, the discharge path of the photocharges is extremely short as compared with the method of discharging the photocharges using the reverse transfer as shown in FIG. When the operation is completed, photocharges can be discharged at the same timing in any of the channel regions (13).

FIG. 4 is a block diagram when exposure control of the CCD solid-state imaging device is performed by using the above-described driving method. In this figure, the CCD (1), the signal processing circuit (2) and the exposure control circuit (7) are the same as those in FIG. 6, and the same parts are designated by the same reference numerals.

The forward transfer clock φ _F is supplied from the read clock generation circuit (21) to the image pickup section of the CCD (1), and the control clock φ _OFD is supplied from the control clock generation circuit (22) to the overflow drain (12). . A read timing signal FT and a discharge period setting signal DT for setting the operation timing and the operation period are supplied to the clock generating circuits (21) and (22) from the read timing generating circuit (23) and the discharge period setting circuit (24), respectively. To be done. The discharge period setting circuit (24)
It operates similarly to the read timing generation circuit (6) in FIG. 6, and sets the discharge period according to the exposure suppression signal CLOSE and the exposure promotion signal OPEN from the exposure amount determination circuit (7).

FIG. 5 is a timing diagram showing the operation of FIG. The read timing signal FT is the vertical scanning signal VD as in FIG.
Has a timing pulse D at a predetermined timing in the blanking period, and the read clock generation circuit (21) generates a clock pulse H at the input of this timing pulse. The discharge period setting signal DT becomes low level at the rising timing of the vertical scanning signal VD and becomes high level at a specific timing of the vertical scanning period, and the discharge period is set in the low level period. That is, the discharge period setting signal
When DT is at a low level, the transfer clock φ _F is at a negative potential and the control clock φ _OFD is at a high level during the blanking period of the horizontal scanning signal HD, and the discharge period setting signal DT is at a low level. The photocharges of the image pickup unit of the CCD (1) are discharged to the overflow drain. The rising timing of the discharge period setting signal DT is delayed by the exposure suppression signal CLOSE from the exposure amount determination circuit (7) and advanced by the exposure promotion signal OPEN, similarly to the discharge timing signal BT shown in FIG. Such a configuration has, for example, a step counter that counts up with the horizontal scanning signal HD, a rising timing stored in the number of horizontal scanning lines, and an exposure suppression signal CLOSE.
Uses an up-down counter that counts up with, and counts down with the exposure promotion signal OPEN, and the comparator detects whether the outputs of both counters match. Then, the output of the comparator is used as the set input of the flip-flop, the rising edge of the vertical scanning signal VD is used as the reset input, and the output of the flip-flop is used as the discharge period setting signal DT. Therefore, the photocharge of the image pickup part of CCD (1) is
The vertical scanning signal VD is discharged to the overflow drain in the period from the rising timing to the timing determined according to the exposure amount. The period from the end of this discharging operation to the start of the read driving is the photoelectric conversion period. It is set as E. Since the read drive timing is fixed, the photoelectric conversion period E is determined by the expansion and contraction of the discharge period. Here, the transfer clock φ _F and the control clock φ _OFD are changing in synchronization with the blanking period of the horizontal scanning signal HD during the discharging period because the video information X ₍ which is sequentially output from the CCD (1) _This is to prevent the discharge driving noise from being superimposed on _t) , and it does not matter if either one is fixed.

In the present embodiment, the discharge period is set to the period from the rising of the vertical scanning signal VD to the timing determined according to the exposure amount, but if the discharge driving end time is the same, The start does not have to coincide with the rising timing of the vertical scanning signal VD.

(G) Effect of the Invention According to the present invention, it becomes possible to discharge the unnecessary photocharges of the image pickup section of the CCD solid-state image pickup device at the same time in a very short time. The photocharges can be discharged within the blanking period, and an extremely effective electronic shutter with reduced smear can be realized.

[Brief description of drawings]

FIG. 1 is a plan view of a main part of a CCD solid-state image pickup device adopting the driving method of the present invention, FIG. 2 is a sectional view taken along line XX ′ in FIG. 1, FIG. 3 is a potential diagram, and FIG. FIG. 5 is a block diagram of an exposure control method adopting the inventive driving method, FIG. 5 is its timing diagram, FIG. 6 is a block diagram of a conventional exposure control circuit, and FIG.
FIG. 8 is a schematic plan view of a frame transfer type CCD solid-state image pickup device, and FIG. 8 is a timing diagram of FIG. (1) ... CCD solid-state image sensor, (3) (21) ... read clock generation circuit, (4) ... discharge clock generation circuit,
(5) (23) …… Read timing generation circuit, (7) ……
Exposure amount judgment circuit, (11) …… Channel stop, (12)
...... Overflow drain, (13) …… Channel region, (14) …… Lower layer electrode, (15) …… Upper layer electrode, (22)
...... Control clock generation circuit, (24) …… Discharge period setting circuit.

Claims (3)

[Claims] 1. A plurality of channel regions for accumulating photocharges generated by photoelectric conversion are arranged separately from each other in a channel stop region, and a plurality of transfer electrodes are arranged on the channel region. In a method of driving a CCD solid-state image sensor, which receives an excessive photocharge in an overflow drain provided in the channel stop region, a photoelectric charge is formed by forming a potential barrier between the channel region and the overflow drain. The potential applied to the transfer electrode is lower than the first potential with respect to the first potential applied to the transfer electrode and the second potential applied to the overflow drain when accumulating in the channel region. And the potential applied to the overflow drain is made higher than the second potential, the channel region It abolished the potential barrier between said overflow drain, the method for driving the solid-state imaging device characterized by unwanted light charge in the channel region to discharge to the overflow drain. 2. The method for driving a solid-state image pickup device according to claim 1, wherein during the vertical scanning period of the solid-state image pickup device which is scanned in the horizontal and vertical directions, the first to the middle of the vertical scanning period. After the photocharges in the channel region are discharged to the overflow drain during the period, the potential barrier is formed between the channel region and the overflow drain in the remaining second period, and the photocharge is applied to the channel region. A method for driving a solid-state image pickup device, characterized by accumulating and obtaining image information for one screen from the photocharges accumulated in the second period. 3. The method for driving a solid-state image pickup device according to claim 2, wherein the photocharge in the channel region is discharged to the overflow drain only within a blanking period of horizontal scanning. Method for driving solid-state image sensor.