JPH0289474A - Drive method for solid-state image pickup device - Google Patents

Abstract

PURPOSE:To reduce field flicker by irradiating picture elements of odd and even number fields with lights of the same condition so as to adjust the shutter period or amplification factor in a way that output signals of both the fields are equal to each other. CONSTITUTION:For example, a period from a photodetection after a picture element of an odd number field in odd and even number fields is reset and a picture element charge of a photodetection section in charge transfer line l1, l2... is transferred to a storage section till the start of picture element charge transfer start of a CCD of the charge transfer lines is used as a shutter period of the odd number field. Then lights of the same condition are given to the picture elements so as to adjust the shutter period of the even number field in a way that the output signal of the odd and even number fields are equal to each other, then the ratio of video signal versus smear in each field scanning is made equal thereby reducing the field flicker. Moreover, the similar result is obtained by applying gain adjustment in a way that the output signals of each field are made equal.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a driving method for reading out signal charges of a charge accumulation type face-shaped imaging device applied to an electronic still camera, and particularly to a driving method for reading out signal charges while also using an electronic shutter operation. The present invention relates to a driving method for reading signal charges.

[Conventional technology]

The present invention is an invention previously filed by the present inventor (Japanese Patent Application No. 1983-
171879).

For many years, the present inventor has applied charge storage type solid-state imaging devices (so-called CCDs, BBDs, etc.) to electronic still cameras, and has conducted research and development to equip the charge storage type solid-state imaging devices themselves with an electronic shutter function. Ta.

As pointed out in a previous patent application, an electronic shutter using a conventional interline transfer type charge accumulation type solid-state imaging device performs vertical charge transfer of signal charges generated in pixel groups arranged in odd and even fields. During this field scanning readout, when transferred to the vertical charge transfer path facing the pixel, the signal charges of two adjacent pixels in the odd field and even field are mixed. As a result, only the signal charge of the field image can be obtained, and the vertical resolution is reduced to half of the actual pixel density.

In addition, the charge transfer path of the so-called storage section that temporarily holds signal charges requires at least the same number of charge transfer elements as the vertical charge transfer path of the light receiving section, so the area occupied by the storage section is large (as a semiconductor There was a problem with the chip size being thick.

Therefore, Japanese Patent Application No. 63-171879 discloses a method for driving an electronic shutter that can obtain a frame image with a resolution equal to the pixel density.

That is, in a method for driving a solid-state imaging device that detects a still image signal using a charge storage type solid-state imaging device using a frame interline transfer method, a signal charge generated in a pixel of either an odd field or an even field is received. The first step is to transfer the signal charges to the charge transfer path of the field and then to the storage section, and to transfer the signal charges generated in the pixels of the remaining field to the charge transfer path of the light receiving section while retaining the signal charges in the storage section. In the second step, the signal charges in the storage section are transferred to a horizontal C while the signal charges are held in the charge transfer path.
The third step is to output the signal charges in time series via the CD, and after transferring the signal charges corresponding to the pixels of the remaining fields held in the charge transfer path to the storage section, the signal charges in the storage section are outputted to the horizontal CCD. By reading out signal charges corresponding to a frame image through a fourth step of outputting them in time series through The present invention provides a driving method that can eliminate the decrease in resolution.

[Problem to be solved by the invention]

However, although the invention disclosed in Japanese Patent Application No. 171879/1983 achieved a significant improvement in resolution, there was a problem in that field flicker became more pronounced as the shutter speed became extremely fast.

That is, in the invention of this application, in order to read out signal charges corresponding to odd field pictures and signal charges corresponding to even field pictures with a time shift, (1) first, signal charges corresponding to odd field pictures are accumulated; During the holding period, the signal charge corresponding to the even field picture is transferred to the adjacent vertical charge transfer path, and (2) the signal charge corresponding to the odd field picture in the storage part is read out. ,
(3) Finally, read out the signal charges corresponding to the even field image.

In this way, the signal charges corresponding to odd field pictures are transferred from each pixel to the light-shielded storage section at high speed, but the signal charges corresponding to even field pictures are transferred until the signal charges corresponding to the odd field pictures are read out. Since the vertical charge transfer path is stopped during this period, smear components are mixed in during this stop period. The amount of smear component mixed into the signal charge corresponding to an even field image is larger than that of an odd field image, resulting in field flicker, and the faster the shutter speed is, the more the smear component is mixed into the signal charge. As the ratio increases, this field flicker becomes noticeable.

Figure 1 is a cross-sectional view showing the principle of mixing of smear components. During the period when signal charges corresponding to odd field pictures are temporarily held in the storage section, signal charges corresponding to even field pictures are transferred vertically. When it stops in the path, unnecessary light incident from between the pixel PD whose top surface is open and the vertical charge transfer path VCCD is reflected and passes through the vertical charge transfer path VC.
This causes smear by entering the CD or inducing unnecessary charges in the semiconductor substrate. For example, the smear value of a solid-state imaging device is S1, the charge transfer frequency is fH%, the output signal of a pixel in odd field scanning is V6, the output signal of a pixel in even field scanning under the same conditions is V
. , the shutter open period is T, then the relationship is as follows. More specifically, f H-I MHz, S
= 0.005%, Ts = t/60 seconds, Ls (horizontal scanning line number) = 525, then Vo = VEX 1.03, which is a field flicker of 1% or more that can be felt by the human eye. − will appear.

[Means to solve the problem]

The present invention aims to reduce such field flicker, and in order to achieve this purpose, the shutter period during one field scan is different from the shutter period during the second field scan. The ratio of signal charges to smear components generated in one field scan is made equal to the ratio of signal charges to smear components generated in the other field scan.

Alternatively, the output signal is amplified with different amplification factors for the odd and even fields, and the amplification factor is adjusted so that the signals read under the same conditions in the odd and even fields are equal. The ratio of the signal to smear component generated in one field scan may be made equal to the ratio of the signal to smear component generated in the other field scan.

[Effect]

In this way, by setting a time difference between the shutter period for one field scan and the shutter period for the other field scan so as to equalize the ratio of the smear component to the amount of signal charge obtained in each field scan, the field Flicker can be reduced. Furthermore, the amplification factor of the output signal is adjusted for each field scan so that the ratio of the signal to smear component generated in one field scan is equal to the ratio of the signal to smear component generated in the other field scan. Field flicker can also be reduced.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 schematically shows the structure of a charge storage type solid-state imaging device applied to this embodiment. First, to explain the structure, in the same figure, a plurality of light receiving elements PA formed on a semiconductor substrate,
~PAI,,,PH11-PB2hSPA31~PA3
．． 5PB4. ~PB4. ．． . . . are arranged in a matrix, and the odd-numbered rows of light-receiving elements PAz to P^1. ．．
, PA31-PA, . . . are odd-numbered fields, and even-numbered row photodetectors PB21-PB2-. PB41 to PB4h, etc. are even fields. l, ~β7, etc. are charge transfer paths formed vertically between these light receiving elements, and these charge transfer paths! 1~I! The upper surface of the o, etc. is shielded from light by a shielding film.

Between each light receiving element and the charge transfer path adjacent to them, there is a transfer gate for transferring the signal charge generated in the light receiving element to the charge transfer path.
．． 031~G311% G41~Gin etc. are provided. Also, the charge transfer path I! Charge transfer elements HA corresponding to these transfer gates
lt-HA+-1HB2. -HB,l,,HA,,
~HA, h.

)184, ~HB,,, etc. Between the transfer gate and these charge transfer elements, there are further charge transfer elements LAII~LAIn, LB21~B211.
．． Other transfer gates for generating LAs+ to LAtl1, LB41 to LB, h, etc. are formed.

The region where these light receiving element groups and charge transfer path groups are arranged is a light receiving section for imaging, and an accumulation section consisting only of charge transfer paths is provided below the light receiving section, and each charge in the accumulation section is Transfer gates are formed in the transfer path so that the same number of charge transfer elements as in the charge transfer path of the light receiving section are generated, and the upper surface of the storage section is shielded so that no light enters. Note that each transfer gate of the light receiving section receives drive signals V1p, V2p, V3p, and V4 at predetermined timings, which will be described later.
P, V S, V25. V3S.

V4S is applied.

Further, a horizontal CCD connected to the charge transfer element at the final end of the storage section is provided, and the signal charge transferred from the storage section is converted into a so-called two-phase drive signal φ8. It is serially transferred to the output amplifier according to φ2.

Next, the shutter operation and readout operation of the charge storage type solid-state imaging device will be explained based on FIG. 2.

First, a reset operation is performed to sweep out unnecessary signal charges to the outside. That is, at a certain time t, the drive signal V1
p, V3p, and V4p are set to "M" level (level between "H" level and "L" level), drive signal V2F is set to "L" level, and furthermore, at time t2, drive signal V
By setting IP to the "H" level for a certain period of time, transfer gates G11. G
12~Glp, G31+G32~Island 7,
Gs It 65□ to GS+, etc. are turned on to turn on the odd field light receiving elements PAI1. PA, 2~PA,,
,,PA31゜PA32~PA3h, PASl, P
Transfer unnecessary signal charges such as AS□ to PAs to the charge transfer element, and then, at time t3, drive signal V3P
By setting ``H'' level for a certain period of time, transfer game 1' G2 l, which is located in an even field,
62□~G2a, 64++642~G411, al
11, 662 to G8+s, etc. are turned on, and the even field light receiving elements PB2□PR2, to PB2. ,,pe,
.

, PB42 to PB4-. Pes+, PB62~PB
Transfer unnecessary signal charges such as 6- to the charge transfer element. Then, a predetermined period T from the next time t to time t5.

Drive signals V1p, V2p, V3p, V4
By performing four-phase drive blade type charge transfer using p, unnecessary signal charges in the light receiving section are transferred to the horizontal CCD, and a reset operation is achieved.

Further, during this reset operation period, that is, the charge transfer period To for sweeping out the unnecessary signal charges, all the transfer gates are in the off state, so all the light receiving elements perform a photoelectric conversion operation. Then, at a certain time t6, the drive signals V1p, V3p, and V4p are set to "M", and the level drive signal V2p is set to "L" level, and furthermore, at time t7, the drive signal V+p is set to "H" level, so that light reception in odd fields is performed. Element PAI1. PA12~PA+
n, PA3+, PA32-PA311, PA3. .

Signal charges generated in PAS□ to PAs-, etc. are transferred to charge transfer elements. Therefore, from time t2 to time t.

The period up to TS+ becomes the shutter period for the light receiving elements arranged in odd fields.

Next, during the period T□1 from time t8 to time t, the drive signal V+pt V2PI V3PI V by the four-phase drive blade type is applied.
At 4PIVIS, V2S+v3s, and v4s, all signal charges in the charge transfer path of the light receiving section are transferred to the storage section. During this period THI, all the transfer gates are in the off state, so only signal charges of odd fields are transferred to the storage section.

Next, at time tlO when a predetermined shutter period TS2 has elapsed from time t3, the drive signal Vlp is activated.

By setting V2F to "L" level, drive signal V3p to "H" and level drive signal V4P to "M" level, transfer gate G211G located in an even field
22 ~G2n% G411G42 ~Gah
, G61.662 ~G611~, etc. are turned on to turn on the even-field light receiving elements PB21. PB22~PBa
-1B4LIB42~PB4r,,PBg+.

Transfer signal charges such as PBs2 to PBg to charge transfer elements. In this way, at time t1° after a predetermined shutter period TS2 has elapsed from time t, the drive signal VI
P, V2P to “L” level, Kuri i64M No. V 3
P is set to "H" level and drive signal V4P is set to "M" level.

Next, a predetermined period TRI from time t to time t12
In the drive signals VIP, V2P, V3P,
While V4P is held at a constant level, the drive signal VIS,
V25°V3. , performs a four-phase drive blade type charge transfer operation using only V4S, transfers the signal charges for one row of the storage section to the horizontal CCD, and further transfers the horizontal CCD drive signal φ1. By serially transferring this to the output amplifier by φ2, it is outputted from the output amplifier in time series, and by repeating this output operation for all the signal charges in the storage section, the signal charges of odd fields are outputted in time series.

Drive signal VIPI V2F, V3PI during this period
By keeping V4p at a constant level, signal charges in the charge transfer path of the light receiving section accumulate in the row of photodiodes from which they are read out, making it possible to suppress the reduction in smear that causes vertical streaks compared to the conventional method. can.

Next, during the period TH2 from time t13 to time t14, the drive signal VI P + v2 P + by the four-phase drive method is generated.
V 3 P + V 4 P rVIS, V2SI
At V3SI V4S, all signal charges in the charge transfer path of the light receiving section are transferred to the storage section. During this period TH2, all the transfer gates are off, so only the signal charges of even fields are transferred to the storage section.

Next, during the period TR2 from time tls to time t16, the drive signals VIS, V2SI V3SI V4
A charge transfer operation using a four-phase drive method using S only is performed, and the signal charge for one row of the storage section is transferred to the horizontal CCD, and then the signal charge is transferred to the horizontal CCD.
CD drive signal φ0. By serially transferring this to the output amplifier using φ2, it is outputted from the output amplifier in time series,
By repeating this output operation for all signal charges in the storage section, even field signal charges are output in time series.

Here, based on the principle described below, a time difference is provided between the shutter period (exposure time) T,1 of the odd field and the shutter period TS2 of the even field.

The respective shutter periods T are set so that the output signal V01 of the odd field and the output signal VO2 of the even field obtained by scanning the pixels of the odd field and the pixel of the even field are equal, respectively, by applying light under the same conditions.
SI and T'sa are detected in advance in correspondence with a desired shutter period. That is, as shown in the above equation (1), field flicker is recognized when a difference of about 1% or more occurs in the output signals read in each field scan, so the following is a modification of the above equation (1). The shutter periods TSI and TS2 are set so that the left and right sides of equation (2) are equal.

Further, by transforming the above equation (2), in the above equation (3), the output signal V. Since l+ VO2 and Tsmr are constants, it is possible to calculate the shutter period TS2 of the even field with respect to the shutter period TS+ of the odd field. This calculation is performed in advance for all shutter speeds, and when a shutter speed is specified during actual shooting, the shutter periods T s 1 and T s 2 corresponding to the shutter speed are automatically calculated.
Configure to set.

Note that this shutter period is set at time t and/or tl in FIG. This is achieved by adjusting the timing of signal readout.

In this way, by adjusting the shutter period so as to equalize the ratio of the smear component to the signal charge in each field scan, it is possible to suppress the occurrence of field flicker.

Furthermore, the period To from the above-mentioned time t1 to time tlli
Since the signal charges for one frame, that is, the signal charges generated in all pixels can be read out, the resolution can be doubled compared to the conventional method.

In this embodiment, the case where the signal charges of the odd field are read out first and then the signal charges of the even field are read out, but depending on the mode of use, the signal charges of the even field are read out first and then the signal charges of the odd field are read out. It is clear that signal charges of can be read out.

FIG. 3 shows another embodiment. This is the video signal S read out from the output amplifier of the solid-state imaging device shown in FIG. U
7, and the variable gain amplifier synchronizes the amplification factors of the video signal read out during the odd field scanning period and the video signal read out during the even field scanning period with the charge transfer lock signal. It is designed so that it can be switched by

That is, if the amplification factor of the variable gain amplifier in odd field scanning is AI, and the case of even field scanning is A2, the above equation (3) becomes the following equation (4), and the amplification factors A1 and A2 of the variable gain amplifier can be appropriately set. By adjusting, field flicker can be reduced. Here, the shutter period TSI and TS2 in each field scan
The flicker may be reduced by keeping them equal and adjusting the amplification factors A and A2 appropriately, or by appropriately combining the shutter period T's+ and TS2 and the amplification factors At and A2. You can adjust it.

〔Effect of the invention〕

As explained above, according to the present invention, in a method for driving a solid-state imaging device that detects a still image signal using a charge storage type solid-state imaging device using a frame transfer interline method, pixels in an odd field and pixels in an even field are The shutter period and/or the amplification factor of the signal after readout are adjusted so that the output signal of the odd field and the output signal of the even field obtained by each scan are equal to each other by applying light under the same conditions. ,
The ratio of video signal to smear in each field scan becomes equal, and field flicker can be reduced.

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram of a solid-state imaging device applied to an embodiment of the present invention; FIG. 2 is a timing chart for explaining the operation of the embodiment; FIG. 3 is a block diagram showing another embodiment; FIG. 4 is a sectional view of a main part for explaining the conventional problems. In the figure: PAII, PAI2-PA, h. PA31. To P32~PA3. . PASl, PAS2-PA3. ,; Light receiving element (odd field PB2 +, PB22 ~ PB2-. PB41, PB4□ ~ PB, h. PBg+, PBg2 ~ PBs-; Light receiving element (even field') Gll, GI2 ~ G,, SG31+
632 ~G3h %Gs+. Gsz~G5,,G21
, G22-G2. , G4 1+ 64□～G, G61
．． G6□~G6h; Transfer gate 1+, 12~1. , ;Charge transfer path HA+ +, HA+□~HA, . ,)IA31. HA3
□〜llA3. , HASI, HAS2 ~HAsII
SHB21, HB22~HB2,1, HB41, Ha
-2 ~HB4. SHBG+, HB62 ~ Hag,. Charge transfer element 1; Charge storage type solid-state imaging device 2; Variable gain amplifier 3; Charge transfer lock generation circuit agent (8107) Patent attorney Kiyotaka Sasaki 1゛＼ゞ、eha）(and 3 others) v 3rd Figure 4 Figure v Procedural amendment November 17, 1988

Claims (1)

[Scope of Claims] 1] A method for driving a solid-state imaging device that detects a still image signal using a charge storage solid-state imaging device using a frame interline transfer method, wherein pixels in either an odd field or an even field are After resetting, the signal charge generated by light reception is transferred to the charge transfer path of the light receiving section, and then transferred to the storage section.
A first processing step in which the period from the reception of light by the pixel to the start of transfer of the signal charge to the charge transfer path is a shutter period of either an odd field or an even field, and before the transfer of the signal charge to the storage section. The pixels of the remaining field are reset and the signal charge generated by light reception is transferred to the charge transfer path of the light receiving section after the transfer of the signal charge to the storage section is completed, and the signal charge is transferred from the light reception of the pixel of the remaining field. a second processing step in which the period until the start of transfer to the charge path is the shutter period for the remaining field; and a second processing step in which the signal charge in the storage section is transferred while the signal charge of the remaining field is held in the charge transfer path of the light receiving section. The third processing step is to output the signal charges in time series via the horizontal CCD, and after transferring the signal charges corresponding to the pixels of the remaining field held in the charge transfer path to the storage section, the signal charges in the storage section are and a fourth processing step of outputting in time series via a horizontal CCD, and setting the shutter period so that the outputs obtained from each pixel in the odd field and even field are equal under the same imaging conditions. A method for driving a solid-state imaging device, characterized in that: 2] In the method for driving a solid-state imaging device according to claim 1, the shutter periods of the odd and even fields are made equal, and the outputs obtained from each pixel of the odd and even fields under the same imaging conditions are It is characterized in that the amplification factors of the output signals are adjusted so that they are equal.