JP2620643B2 - Driving method of solid-state imaging device - Google Patents

Description

The present invention relates to a method for driving a solid-state imaging device for discharging information charges accumulated in a channel region of a CCD solid-state imaging device out of the channel region.

(B) Conventional technology Conventionally, in an imaging apparatus such as a television camera using a CCD solid-state imaging device, it has been considered to perform electronic exposure control using the operation principle of the CCD. Such an exposure control method, for example, as disclosed in Japanese Patent Application Laid-Open No. 63-24764, transfers and discharges information charges accumulated in an imaging unit up to the middle of a charge accumulation period for each vertical scanning period, and discharges the remaining information charges. Is configured to accumulate information charges obtained during the charge accumulation period. That is, the accumulation period of the information charge is expanded or contracted by changing the timing of discharging the information charge, and the discharge timing of the photocharge is set according to the video signal level output by the CCD. In this driving method, unnecessary information charges of the imaging unit are transferred and discharged in the direction opposite to the read transfer, but the discharge of the information charges due to the transfer in the reverse direction is performed for a certain period until the discharge is completed. However, there is a problem that smear is generated due to the necessity, and noise is superimposed on the video signal when the discharge is not completed within the retrace period of the horizontal scanning.

Accordingly, the present applicant has proposed a method of discharging information charges capable of solving the above-described problem in Japanese Patent Application Nos. 1-157369 and 1-183976. These driving methods are configured such that by increasing the height of the overflow drain and driving the transfer electrode in a pulsed manner for a predetermined period, the information charges in the channel region are transferred to the overflow drain while being transferred for a certain period. .

FIG. 5 is a block diagram showing a configuration of a solid-state imaging device employing the above-described driving method, and FIG. 6 is an operation timing diagram thereof.

Frame transfer type CCD solid-state image sensor (1)
Is an imaging unit (1I) that obtains information charges according to an irradiated video pattern, a storage unit (1S) that temporarily stores information charges of the imaging unit (1I), and information charges of the storage unit (1S) for each horizontal line. The driving circuit (2) outputs a video signal X _(t) after being pulse-driven by the driving circuit (2). The video signal X _(t) is subjected to processing such as sample hold and gamma correction in the signal processing circuit (3), and is output to the next circuit as a video signal Y _(t) .

The drive circuit (2) supplies the OFD clock φ _OFD to the overflow drain (OFD) of the CCD (1), the OFD clock generation circuit (2N), and the discharge transfer clock φ _R and the read transfer clock φ _F to the imaging unit (1I). discharge clock generating circuit providing (2R) and the read clock generating circuit (2F), and storage transfer clock phi _S and the storage clock generation circuit for supplying a horizontal transfer clock phi _H respective storage unit (1S) and the horizontal transfer portion (IH) ( 2S) and horizontal clock generation circuit (2H)
The operation timing is determined according to the discharge timing signal RT from the discharge timing setting circuit (4) and the read timing signal FT from the read timing setting circuit (5), respectively.

In addition, the video signal X _(t) is converted into an integration circuit (6) for each screen.
, And the integrated value I _(t) is calculated by an exposure determination circuit (7).
Given to. Then, the exposure determination circuit (7) determines whether or not the integrated value I _(t) is within the proper exposure range of the CCD (1), and outputs an exposure promotion signal OPEN or an exposure suppression signal CLOSE. That is, in the exposure determination circuit (7), the integrated value I _(t) is compared with a first reference value corresponding to the maximum value of the appropriate exposure range and a second reference value corresponding to the minimum value, and 1
The exposure suppression signal CLOSE is output if the value is larger than the reference value, and the exposure promotion signal OPEN is output if the value is smaller than the second reference value, and no signal is output if the value is between the first reference value and the second reference value. .

The discharge timing control circuit (4) is configured to set the discharge timing of the information charges in accordance with the output of the exposure determination circuit (7), and delays the discharge timing by inputting the exposure suppression signal CLOSE to store the information charges. And the discharge timing is accelerated by the input of the exposure promotion signal OPEN to extend the information charge accumulation period. That is, the read timing of the photo charge is fixed to a predetermined timing in the vertical scanning signal VD blanking period, and the period L from the end of the discharge of the information charge to the next read timing is the photo charge accumulation period. Therefore, the storage period of the information charges is set by changing the discharge timing of the photocharges.

The discharge of the information charge is performed only during the blanking period of the horizontal scanning signal HD in order to prevent the superposition of noise on the video signal X _(t) , and the discharge timing is set for each horizontal scanning period. That is, the OFD clock φ _OFD is equal to the integrated value I _(t)
High levels within the blanking period of the horizontal scanning signal HD for the corresponding timing (normal accumulation is fixed to low level.) And with made, discharge transfer clock phi _R imaging unit only to the blanking period (I). Therefore, the information charges accumulated in the channel region of the imaging unit (I) are rotated at a predetermined timing in the reverse direction by the discharge transfer clock φ _R and discharged to the substrate side by the OFD clock φ _OFD. The information charges accumulated from the end of the operation to the start of the next read operation constitute a video signal for one screen.

Figure 7 is a waveform diagram of the discharge transfer clock phi _R at the time of discharge driving information charges, shows the case of a four-phase drive, FIG. 8 is a diagram showing a state of a potential at each timing.

The transfer electrodes (11) (12) (13) (14) of the CCD (1)
It has a two-layer structure, and has a four-phase discharge transfer clock φ ₁ to
φ ₄ is applied. Until the information charges are driven to drain, only the clock φ ₂ is fixed at “H” (high level) and the other clocks φ ₁ , φ ₃ , φ ₄ are fixed at “L” (low level) as at the timing T ₀ . A potential well (15) as shown in FIG. 8 is formed below the transfer electrode (12), and information charges (e) are accumulated in the potential well (15). When discharging the information charge (e), first, the clock φ ₁ becomes “H”, and at the timing T ₁ , the information charge (e) below the transfer electrode (12) is transferred below the transfer electrode (11) as indicated by an arrow. You. This transfer direction is opposite to the read transfer direction, that is, the direction opposite to the storage unit (1S). And the timing T ₂
Then, each of the clocks φ _{1 to} φ ₄ is inverted and the transfer electrodes (1
1) The lower information charge (e) is further transferred. And
At time T _3, the clock phi ₁ to [phi] ₄ is a timing T ₁
Becomes the same as the state of potential in the CCD (1) is the same as the timing T _1. Thereafter, by repeating the state of the timing T ₁ and T _2, the information charges in the channel region (e) is the read transfer direction is transferred in the opposite direction.
As described above, during the period when the information charges (e) are transferred in the reverse direction, a high voltage is applied to the OFD provided adjacent to the channel region, and in the process of transferring the information charges (e). Since the information charges (e) are discharged to the OFD, the information charges (e) gradually decrease.

(C) Problems to be Solved by the Invention However, in the information charge discharging method as described above, since it is necessary to apply an extremely high potential to the OFD of the CCD (1), the driving capability of the driving circuit (2) is increased. It is necessary to perform a complicated circuit configuration and consume large power.
It is not suitable for general video cameras that operate on a power source such as a battery.

Also, when the number of pixels of the CCD (1) increases along with the increase in resolution, the period required to completely discharge the information charge (e) becomes longer, and the time required for the horizontal scanning line to be completely removed is reduced. Will not fit.

Therefore, the present invention provides an OFD necessary for discharging information charges.
And to complete the discharging operation in a short period of time.

(D) Means for Solving the Problems The present invention has been made to solve the above problems, and is characterized by a plurality of channel regions for storing and transferring information charges generated by photoelectric conversion. A plurality of transfer electrodes arranged and formed separately from each other in the region and controlling the potential state of the channel region are formed and arranged on the channel region, and receive excess information charges in the channel region to the overflow drain region. In the solid-state imaging device, the potential of the overflow drain region is set higher than a potential at which a potential barrier can be formed between the channel region and the overflow drain region, and the potential in the channel region is pinned or in a state close to pinning. The period during which the potential for forming the gate electrode is simultaneously applied to the transfer electrodes is set. And the multi-phase transfer clock pulse driven by applying to the transfer electrode is to discharge to the overflow drain region the information charges from the channel region.

(E) Function According to the present invention, the potential barrier between the channel region and the overflow drain region becomes smaller by setting the period during which the potential is in the pinning state when the transfer electrode is pulse-driven. In addition, it is not necessary to make the charge of the overflow drain region extremely high. In addition, since the information charge moves within a certain range in the channel region, a portion where the information charge is hardly partially discharged due to manufacturing variations, that is, a potential barrier between the channel region and the overflow drain region is formed. Even if there is a portion that is difficult to disappear, the information charges in that portion are discharged to the overflow drain region while moving in the channel region.

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

FIG. 1 is a potential diagram showing the driving method of the present invention,
FIG. 2 shows the same parts as in FIG. 8, and FIG. 2 is a waveform diagram of the discharge transfer clock.

First, the timing T ₀ is a state before the discharge of the information charges (e), and only the clock φ ₂ is fixed to “H” as in the timing T _{0 in} FIGS. 7 and 8, and the transfer electrode ( 1
2) Information charges (e) are accumulated in the potential well (16) formed below.

Therefore, when discharging the information charge (e), the clock φ ₁ is once set to “H” as at the timing T _{1 to set} the information charge (e).
After the transfer under the transfer electrode (11), all as shown in the timing T ₂ clocks phi ₁ to [phi] ₄ is "L". When the clocks φ _{1 to} φ ₄ are set to “L”, the potential of the channel region becomes a pinning state (a state where the potential does not become shallower even if the potential is lowered by the transfer electrode) or a state close to the pinning. The potential becomes shallow overall, and information charges easily flow from the channel region to the OFD.

The clock phi ₃ as shown in the timing T _3, phi ₄ a timing T ₂ at remaining information charges (e) collected under the transfer data (13) as "H", each as shown again in the timing T ₄ The clocks φ _{1 to} φ ₄ are set to “L” to lower the potential of the channel region.

That is, the feature of the present invention is that, as shown in FIGS. 7 and 8, when the information charges are transferred in the direction opposite to the read transfer direction, each clock φ _{1 to} φ ₄ changes at each clock φ _1.
Lies in the fact that ~φ ₄ has set the period at the same time becomes the "L". Therefore, the information charges (e) in the channel region are efficiently discharged to the OFD while moving in a certain range.

FIG. 3 is a potential diagram showing another embodiment of the driving method of the present invention, and FIG. 4 is a waveform diagram of a discharge transfer clock.

Timing T before discharge of information charge (e) starts
₀ is the same as the timing T _{0 in} FIGS. 1 and 2,
Information charges are accumulated in the potential well (16) below the transfer electrode (12). When the clock φ _{2 is set} to “L” as shown at the timing T ₁ , the potential well below the transfer electrode (12) disappears, and the information charge (e) is reduced below the transfer electrodes (11) and (13) on both sides. It is distributed to. All clocks φ ₁
Even when to [phi] ₄ is "L", the difference in depth of the potential as shown in FIG. 3 depending on the impurity concentration difference or the like of the channel region occurs, the transfer electrodes (11) (13) a shallow potential well below Is formed. Subsequently, the clock φ _{4 is set} to “H” to collect the information charges (e) under the transfer electrodes (11) and (13) on both sides in a potential well (17) formed under the transfer charges (14), and then the clock is re-started. transfer electrodes phi ₄ as "L" (1
4) The information charge (e) in the lower potential well (17) is distributed to both sides under the transfer electrodes (11) and (13). Thereafter, the information charges (e) are discharged by repeating the inversion of the clocks φ ₂ and φ ₄ alternately in the same manner. That is, when the information charges (e) in the potential wells (16) and (17) below the transfer electrodes (12) and (14) are distributed to the OFD, the information charges (e) are repeated each time the above operation is repeated. ) OFD
Is discharged.

According to the above driving method, the discharge of the information charges (e) can be completed in a very short period. Specifically, the operation shown in FIG. 1 and FIG. 2 or FIG. 3 and FIG.
The present applicants have confirmed that the discharge of information charges in the channel region can be completed by repeating the process about twice. For example NT
In the case of the SC method, the invalid period of the horizontal scanning period is about 10 μsec, so that the cycle of each of the clocks φ _{1 to} φ ₄ may be set to ₁ μsec or less. Actually, each clock φ _{1 to} φ ₄
Is set to about 0.3 μsec.
The period of the cycle (3 μsec) falls sufficiently within the invalid period of the horizontal scanning. Therefore, if the driving method of the present invention is applied to the solid-state imaging device as shown in FIG. 5, the discharge of unnecessary information charges can be completed within the retrace period of horizontal scanning, so that the information is not superimposed on the video signal without noise. The expansion / contraction control of the charge accumulation period can be performed.

In addition, since the potential of the channel region becomes shallower, the potential of the OFD does not need to be too high, and a booster circuit for generating the OFD clock φ _OFD for controlling the potential of the OFD is not required, and the driving circuit is simplified. it can.

In the present embodiment, the OFD receiving the information charges in the channel region may be provided in the channel separation region, a so-called vertical OFD structure in which the substrate forming the CCD itself is the OFD, or the like.

(G) Effects of the Invention According to the present invention, information in the channel region can be stored in an extremely short period of time without extremely increasing the potential of the OFD.
To control the expansion and contraction of the information charge accumulation period without superimposing noise on the video signal, simplify the drive circuit, and reduce power consumption. An inexpensive, compact and lightweight video camera can be realized.

[Brief description of the drawings]

FIG. 1 is a potential diagram showing one embodiment of the present invention, FIG.
FIG. 3 is a waveform diagram of the discharge transfer clock, FIG. 3 is a potential diagram showing another embodiment, FIG. 4 is a waveform diagram of the discharge transfer clock, FIG. 5 is a block diagram of the solid-state imaging device, and FIG.
FIG. 7 is an operation timing diagram, FIG. 7 is a waveform diagram of a discharge transfer clock showing a conventional method of driving a solid-state imaging device, and FIG. 8 is a potential diagram thereof. (1) ... CCD solid-state image sensor, (2) ... drive circuit,
(4) ... discharge timing setting circuit, (5) ... readout timing setting circuit, (7) ... exposure determination circuit, (11)
(12) (13) (14) ... Transfer electrode, (15) (16) (17)
…… potential well.

Claims (2)

(57) [Claims] A plurality of channel regions for accumulating and transferring information charges generated by photoelectric conversion are separated and formed in a channel separation region, and a plurality of transfer electrodes for controlling a potential state of the channel region are provided. In a driving method for discharging unnecessary information charges in the channel region to an overflow drain region adjacent to the channel region in a frame transfer type solid-state imaging device arrayed and formed on the channel region, the potential of the overflow drain region may be reduced. Is higher than a potential at which a potential barrier is formed between the channel region and the overflow drain region, and a potential for forming a pinning or near pinning potential in the channel region is simultaneously applied to the plurality of transfer electrodes. Multi-phase transfer with set period The driving method of a solid-state imaging device to a lock applied to the transfer electrode pulse driving to the information charges from the channel region, characterized in that the discharge to the overflow drain region. 2. An information charge generated in a first period during a vertical scanning period of the solid-state imaging device scanned in horizontal and vertical directions is discharged to the overflow drain region, and is generated in a remaining second period. 2. The method according to claim 1, wherein information charges are accumulated in the channel region, and the information charges obtained during the second period are output as video information of one screen.