JPH02274183A - Driving method for solid-state image pickup element - Google Patents

Abstract

PURPOSE:To reduce a smear by dissipating a potential barrier be tween a channel area and an overflow drain, and exhausting an unrequired photoelectric charge in the channel area to the overflow drain. CONSTITUTION:The potential of the overflow drain 12 is boosted, including even a channel stopping area by increasing the potential of the overflow drain area 12, and also, that of the channel area 13 is shallowed by decreasing the potential of a transfer electrode. Therefore, the potential barrier between the overflow drain 12 and the channel area 13 can be dissipated, and the photoelectric charge in the channel area 13 flows in the overflow drain 12. By employing such exhausting method of the photoelectric charge, the photoelectric charge in the channel area 13 of a CCD solid-state image pickup element can be exhausted simultaneously and in a short time, thereby reducing the smear.

Description

DETAILED DESCRIPTION OF THE INVENTION (A) Field of Industrial Application The present invention relates to a method for driving a CCD solid-state image sensor, and particularly relates to a drive for discharging photoelectric charges from an imaging section of a solid-state image sensor.

(B) Prior Art Conventionally, in an imaging device using a CCD solid-state imaging device, it has been considered to electronically control exposure by utilizing the operating principle of the CCD. Such an exposure control method, as disclosed in, for example, Japanese Patent Application Laid-open No. 63-24764, transfers and discharges the photocharges accumulated in the imaging section in the middle of the photoelectric conversion period of each vertical scanning period, and removes the remaining photoelectric charges. The photoelectric conversion period is configured to accumulate photoelectric charges obtained by photoelectric conversion during the photoelectric conversion period, and the photoelectric conversion period is expanded or contracted by changing the timing of discharging the photoelectric charges.

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

The frame transfer type CCD solid-state image sensor (1) consists of an imaging section (1), a storage section (S), and a horizontal transfer section (H), as shown in FIG. The photocharges are once transferred and accumulated as image information to the storage section (S), and are then transferred from the storage section (S) to the horizontal transfer section ()l).
The output section (F) converts it into a voltage value and outputs it as a video signal X [, ). This video signal X(1) is subjected to processing such as sample hold and gamma correction in a signal processing circuit (2), and the video signal Y6. ) is output to the external device.

On the other hand, C0D (1) is driven by pulses, and forward direction transfer lock≠ or reverse direction transfer lock φ8 is supplied to the imaging section (I), and the storage section (S) and horizontal transfer section ( 1() is supplied with an accumulation transfer lock φ and a horizontal transfer lock φ8, respectively. That is, depending on the reverse direction transfer lock φ3, the photocharge of the imaging unit <1) is transferred to the storage unit (S).
It is transferred in the opposite direction (indicated by the broken line in the figure) and transferred to the storage section (
After discharging to the discharge drain (D) provided on the side opposite to S), photocharge is accumulated in the imaging section (I) for a predetermined period,
This photocharge is forward-transferred to the storage section (
S) (indicated by a solid line in the figure). Then, photocharges are transferred from the storage section (S) to the horizontal transfer section (H) for each horizontal line by the storage transfer lock φ, and further, by the horizontal transfer lock φ8, the photocharge is transferred to the horizontal transfer section (1). from there to the output section (F).

The above-mentioned forward transfer lock φ and reverse transfer lock φ 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) ), the read timing signal FT and the discharge timing signal BT are connected to 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 If so, an exposure promotion signal 0PEN is given to the discharge timing control circuit (6). Then, the discharge timing control circuit (6) sets the discharge timing of photocharges according to the exposure suppression signal CLO3E and the i-light promotion signal 0PEN.

FIG. 8 is a timing diagram showing the operation of FIG. 6.

The read timing signal FT generates a timing pulse ■ at a predetermined timing in each blanking period of the vertical scanning signal VD.
The read clock generating circuit (5) generates a clock pulse O upon input of this timing pulse. Therefore,
The forward direction transfer lock φ2 generates a clock pulse @ during the blanking period of the vertical scanning signal VD, and C0D(1
) is transferred to the storage section (S) during the blanking period.

On the other hand, the discharge timing signal BT has a timing pulse ◯ at a timing corresponding to the exposure amount of C0D(1), and a clock pulse O for discharge driving is generated in accordance with this timing pulse. That is, the timing pulse of the discharge timing signal BT is configured such that the timing is delayed by the exposure suppression signal CLO8E outputted from the exposure amount determination circuit (7) and is shortened by the exposure promotion signal 0PEN. The photoelectric conversion period E, which is set from the completion of the discharge drive to the start of the read drive, is C0D(
1) Expansion and contraction can be controlled according to the exposure amount.

(c) Problems to be Solved by the Invention In the CCD (1) mentioned above, even during the period when the photocharges of the imaging section (I) are being discharged, the photocharges of the storage section (S) are sequentially transferred and output. Therefore, there is a problem in that noise due to the clock pulse of the reverse transfer lock φ8 is superimposed on the photocharges 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, noise can be prevented from being superimposed; At least several H periods (IH is one horizontal scanning period) are required for ejection, and it is impossible to fit the clock pulse for ejection drive within the blanking period of the horizontal scanning signal HD.

Furthermore, when discharging the photocharges from the imaging section (I), smear occurs because the photocharges from all pixels cannot be discharged at the same time, as in the case of reading. The smear generated during the ejection drive is superimposed on the smear during the readout drive, so the smear component of the video signal X (l) obtained from C0D(1) increases.

(d) Means for Solving the Problems The present invention is intended to solve the above-mentioned problems, in which a plurality of channel regions that accumulate photocharges generated by photoelectric conversion are separated from each other by a channel stop region and arranged. In a driving method of a CCD solid-state image sensor, a transfer electrode is provided on the channel region, and excess photocharge in the channel region is received by an overflow drain provided in the channel stop region. With respect to the first potential applied to the transfer electrode when a potential barrier is formed between the overflow drain and the second potential applied to the overflow drain,
The potential barrier between the channel region and the overflow drain is eliminated by making the potential of the transfer electrode lower than the first potential and the potential of the overflow drain higher than the second potential. The method is characterized in that unnecessary photocharges in the channel region are discharged to the overflow drain.

(Book) Effect If the present invention is applied, the potential of the overflow drain is raised to deepen the potential of the overflow including the channel stop region, and the potential of the transfer electrode is lowered to increase the potential of the channel region. By making it shallow, there is no potential barrier between the overflow drain and the channel region, and photocharges in the channel region flow into the overflow drain.

According to such a method of discharging photocharges, the photocharges in each channel region of the CCD solid-state image sensing device are discharged simultaneously and in a short period of time.

(f) Example Embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a plan view of a main part of a CCD solid-state imaging device employing the driving method of the present invention, and FIG. 2 is a sectional view taken along line xx' in FIG. 1. Here, an imaging section of a frame transfer type CCD with a cross-gate structure is shown.

A plurality of channel stop regions (11) are formed in parallel on the negative side of the P-type substrate 10) by LOCO3, and an overflow drain <12) is formed below the channel stop regions (11). In addition, an N-type channel region (13) is formed between each channel stop region (11) by diffusion. A plurality of lower layer electrodes (14) are arranged in parallel at equal intervals in a direction perpendicular to the channel stop region (11), and a plurality of upper layer electrodes (14) are arranged in parallel at equal intervals in a direction perpendicular to the channel stop region (11).
5〉 is completely formed. This upper layer electrode (15) is formed with protrusions that cover the gap between the lower m electrodes (14) so as to alternate with the adjacent upper layer electrodes (15).

Further, a P-type light receiving region (17) is formed in the opening (16) surrounded by the upper and lower layer electrodes (14) and (15). The CCD itself having such a loss gate structure is the same as that described in Japanese Patent Publication No. 63-8625 by the applicant of the present application. Both electrodes (14) and (15) are pulse-driven by four-phase transfer locks φ, I to φ, 4, and the upper electrodes (15) Ni! -1: Transfer lock φFl
+ CAFj is applied alternately, and a transfer lock φ12. φ1. is applied. The overflow drain (12) is connected to a control clock φ that controls the potential of the overflow drain (12). FD is applied.

When accumulating photocharges in the channel region (13), for example, the transfer lock φ21 is fixed at a high level of positive potential, and the control clock φ.FD is fixed at a low level.
By increasing the potential of the channel region (15) and lowering the potential of the overflow drain (12), the potential of the channel region (13) is increased.
), as shown by the solid line in Figure 3, the potential of the channel region (13) becomes deeper and the potential of the light receiving region (13) becomes deeper.
7) and the channel stop region (11) become shallow, forming a potential barrier. Therefore,
Photocharges generated by the light incident on the aperture (16) flow from the light-receiving region (17) into the channel region (13) under the electrode (15) along the potential gradient. ) is accumulated in Then, both electrodes (1
4) By pulse-driving (15), photocharges are distributed along both electrodes (14) and (15) to the channel stop region (1
The data is transferred meandering between 1).

On the other hand, when discharging unnecessary photocharges in the channel region (13), for example, the transfer lock φF1 is set to a negative potential, and the control clock φ is set to a negative potential. 1 to high level (positive potential). By setting the upper layer electrode (15) to a negative potential, the channel region (
The potential of 13) is in the channel stop region (11)
The potential barrier between the channel region (13) and the channel stop region (11) disappears. Therefore, the photocharge of the light receiving area (17) is
Channel region < 13) and channel stop region (11
) to the overflow drain (12). At this time, if the potential of the overflow drain ink 12> is not deep enough, it will not be able to receive sufficient photocharge from the light receiving area (17), so the potential of the overflow drain ink 12) is increased to deepen the potential. are doing. Also, overflow drain (12)
By increasing the potential of the channel stop ff1 (11), the potential of the adjacent channel stop ff1 (11) is prevented from becoming shallow together with the potential of the channel region (13).

According to the method of discharging photocharges as described above, the discharging path of photocharges is extremely short compared to the method of discharging photocharges using reverse transfer as shown in Fig. Upon completion of the operation, photocharges can be discharged from any channel region (13) at the same timing.

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

The imaging unit of C0D(1) has a forward transfer lock φ.

is supplied from the read clock generation circuit (21), and the control clock φ is supplied to the overflow drain (12). , 0 are supplied from the control clock generation circuit (22). These clock generation circuits (21) and (22) are supplied with a read timing signal FT and a discharge period setting signal DT for setting the operation timing and operation period, respectively.
23) and the discharge period setting circuit (24).

The ejection period setting circuit (24) operates in the same manner as the readout timing generation circuit (6) in FIG. Set.

FIG. 5 is a timing diagram showing the operation of FIG. 4. The read timing signal FT has a timing pulse ○ at a predetermined timing during the blanking period of the vertical scanning signal VD, as in FIG. to occur.

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 sets the discharge period during the low level period. That is, the discharge period setting signal DT
When is at a low level, the lock φ, which is transferred during the blanking period of the horizontal scanning signal HD, has a negative potential and the control clock φ. ,0
is at a high level, and during the period when the discharge period setting signal DT is at a low level, the photocharges in the imaging section of the CCD (1) are discharged to the overflow drain.

The rise timing of the discharge period setting signal DT is delayed by the exposure suppression signal CLO8E from the exposure amount determination circuit (7) and advanced by the exposure promotion signal 0PEN, similarly to the discharge timing signal BT shown in FIG. Such a configuration is
For example, by using a step counter that counts up with the horizontal scanning signal HD, and an up/down counter that stores the rising timing in terms of the number of horizontal scanning lines, counts up with the exposure suppression signal CLO8E, and counts down with the exposure promotion signal 0PEN, both counters can be used. Detect matching of outputs using a comparator. This can be realized by using the output of the comparator as the set input of the flip-flop, using the rising edge of the vertical scanning signal VD as the reset input, and using the output of the flip-flop as the discharge period setting signal DT. Therefore, the photocharges in the imaging section of C0D(1) will be discharged to the overflow drain during the period from the rising edge of the vertical scanning signal VD to the timing determined according to the exposure amount, and this discharge operation will be terminated. The period from when the reading operation starts until the reading drive starts is set as the photoelectric conversion period E. Since the readout drive timing is fixed, this photoelectric conversion period E is determined depending on the expansion or contraction of the discharge period. Here, the transfer lock φ and the control clock φ. ,t
, and fluctuating in synchronization with the blanking period of the horizontal scanning signal HD during the discharge period is the video information X0 . ) to prevent the noise of the discharge drive from being superimposed on the drive, and there is no problem even if one of them is fixed.

In this embodiment, the ejection period is set to the period from the rise of the vertical scanning signal VD to the timing determined according to the exposure amount, but if the ejection drive ends at the same time, the ejection drive The start does not need to coincide with the rising timing of the vertical scanning signal VD.

(G) Effects of the Invention According to the present invention, it is possible to discharge unnecessary photocharges from the imaging section of a CCD solid-state image sensor in an extremely short time and from all pixels at the same time. The photoelectric charge can be discharged within the blanking period of 20 seconds, making it possible to realize an extremely effective electronic shutter with reduced smear.

[Brief explanation of drawings]

FIG. 1 is a plan view of the main parts of a CCD solid-state image sensor that employs the driving method of the present invention, FIG. 2 is a sectional view taken along the line X-X' of FIG. 1, FIG. 3 is a potential diagram, and FIG. A block diagram of an exposure control method employing the invention driving method, FIG. 5 is a timing diagram thereof, and FIG. 6 is a block diagram of a conventional exposure control circuit.
FIG. 7 is a schematic plan view of a frame transfer type CCD solid-state imaging device, and FIG. 8 is a timing diagram of FIG. 6. (1)...CCD solid-state image sensor, (3)(21)・
... Read clock generation circuit, (4) ... Ejection clock generation circuit, (5) (23) ... Read timing generation circuit, (7) ... Exposure amount judgment circuit, (11>
... Channel stop, (12) ... Overflow drain, (13) ... Channel region, (1
4)...Upper layer electrode, (15)...Upper layer electrode, <2
2)...Control clock generation circuit, (24)...Emission period setting circuit.

Claims (3)

[Claims] (1) A plurality of channel regions that accumulate photocharges generated by photoelectric conversion are arranged so as to be separated from each other by a channel stop region, and a transfer electrode is provided on the channel region, and an excess amount in the channel region is arranged. In a method for driving a CCD solid-state imaging device in which photocharges are received by an overflow drain provided in the channel stop region, an electric charge is applied to the transfer electrode when a potential barrier is formed between the channel region and the overflow drain. With respect to the first potential applied to the overflow drain and the second potential applied to the overflow drain, the potential of the transfer electrode is set lower than the first potential, and the potential of the overflow drain is set lower than the second potential. A method for driving a solid-state imaging device, characterized in that a high potential is applied to eliminate a potential barrier between the channel region and the overflow drain, and unnecessary photocharges in the channel region are discharged to the overflow drain. . (2) In the method for driving a solid-state imaging device according to claim 1, during a vertical scanning period of the solid-state imaging device that is scanned in the horizontal and vertical directions, the photocharges in the channel region are transferred to the After discharging to the overflow drain, a potential barrier is formed between the channel region and the overflow drain in the remaining second period to accumulate photocharges in the channel region, and the photocharges are accumulated in the second period. A method for driving a solid-state image sensor, characterized in that photoelectric charges are obtained as video information for one screen. (3) The method for driving a solid-state imaging device according to claim 2, characterized in that the photocharges in the channel region are discharged to the overflow drain only during the retrace period of the horizontal scanning line. A method for driving a solid-state image sensor.