JPS6033343B2 - solid-state imaging device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a charge transfer imaging device (hereinafter abbreviated as a CCD imaging device).

) is related to a solid-state imaging device using. The basic operation of a CCD image sensor consists of accumulating information charges, transferring the charges, and reading out the charges. A CCD configured by two-dimensionally arranging a light-receiving element that photoelectrically converts optical information and stores the resulting charge, and a transfer section that transfers that charge.
A schematic diagram of the principle of an example of an image sensor is shown in FIG. In the figure, there are a large number of light receiving elements 1 arranged in a matrix, each of which operates as one pixel, and a vertical transfer section 2 that transfers charges in the vertical direction based on optical information accumulated in the light receiving elements 1.
Further, a CCD image sensor is constituted by a horizontal transfer section 4 that transfers charges to an output section 6 and a transfer gate electrode 3 that controls transfer of charges from the light receiving element 1 to the vertical transfer section 2. Further, the light shielding body 6 is provided so that light does not enter the light receiving element group 7 at at least one end in the horizontal scanning direction. An optical black signal is obtained from this light-receiving element group 7, and by using this as a black signal for video, CC
The influence of the step current of the D ray image element can be removed. An example of an Okamoto imaging device using this CCD imaging device is shown in FIG.

The object 8 is imaged onto a CCD image sensor 10 by a lens 9 . The CCD image sensor 1 is driven by a drive signal 12 from a drive circuit 11 and outputs an output signal 13 . The output signal 13 is amplified by a preamplifier 14 and then passed through a low pass filter 15 to obtain a video signal. This video signal is passed through a clamp circuit 16, and an optical black signal obtained from the light-receiving element group provided with the above-mentioned light shield is used as a clamp pulse 1.
Set to 7 to fix the black level. The video signal with a fixed black level undergoes processing such as y correction, white clipping, and black clipping in the process amplifier 18, and then outputs a blanking signal and synchronization signal 1.
9 is added and outputted from the output terminal 2. Next, the CCD
FIG. 3 shows the waveforms of the drive signal for the image sensor and the resulting video signal. 21 indicates a vertical planking signal.

A transfer gate pulse 22 is applied to the transfer gate electrode during the vertical blanking period, and charges based on optical information accumulated in each light receiving element are transferred to the vertical transfer section for each vertical line. Next, the vertical transfer signal 23 is added to the vertical transfer section, and 1
Charge is transferred from the vertical transfer section to the horizontal transfer section by a vertical transfer pulse 24 in each horizontal scanning period (hereinafter abbreviated as IH). The horizontal transfer section transfers charges to the output section using horizontal transfer pulses 25. In this way, the desired video output is obtained from the output section. In this figure, both the vertical transfer section and the horizontal transfer section are explained as two-phase driven CCDs. Generally CCD
In order to improve the yield of good products in the manufacturing process, efforts are being made to reduce the chip size of image sensors as much as possible, and the number of light-receiving elements in both the vertical and horizontal scanning directions is kept to the minimum necessary. Of these, the number of light receiving elements in the vertical direction is determined by the vertical planking period shown in FIG. 3 above (normally, the vertical planking period is about 20 days).
For example, compared to the standard number of scanning lines of 525 in the standard television system, the number of light receiving elements is equivalent to about 490 scanning lines. Conventionally, such C
As shown in Fig. 3, the CD image sensor is driven immediately after the charge from the last light-receiving element of one field is transferred to the horizontal transfer section using the vertical transfer pulse 26, or once or twice to eliminate any charge left behind. After empty transfer, the vertical transfer pulse is stopped, and during the period when the vertical transfer pulse is stopped, a transfer gate pulse 22 is applied to the transfer gate electrode to perform transfer from the light receiving element to the vertical transfer section.

A video signal obtained by amplifying the video output obtained from the CCD image pickup device by such a driving method and passing it through a low-pass filter is shown at 27 in FIG. 3, and a partially enlarged view is shown at 31. 28 is 1 transferred by vertical transfer pulse 26
It shows the video signal from the last light receiving element in the field.

29 is a signal obtained during a period when vertical transfer is not performed, and this is due to a slight floor current in the horizontal transfer section.

The signal 32 that provides optical black corresponds to the light-receiving element group that provides optical black shown in FIG. This is the output corresponding to the total floor current generated. Among these, the current in the vertical transfer section is larger than the step current of the light receiving element, and 32 is mostly due to the step current of the vertical transfer section. Also, 30' is to prevent noise caused by the transfer gate pulse 22 interfering with the output. Note that 33 corresponds to the horizontal planking period. The video signal thus obtained is fixed at a black level by the clamp circuit 16 shown in FIG. 2, which provides an optical black signal 32, thereby obtaining a video signal free from the influence of the dark current of the CCD image sensor. However, in a conventional solid-state imaging device using such a driving method, if there is a large level difference between the output 32 due to the floor current and the output 29 during the period in which vertical transfer is not performed, the black level of the clamped image changes significantly.

In addition to this, when noise due to interference of transfer gate pulses appears significantly, clamping of the noise due to interference of transfer gate pulses causes a phenomenon in which the black level of the clamped image changes greatly. This change occurred even within the effective screen, causing the upper part of the screen to sink to black or, conversely, to rise to white. Furthermore, when interlaced scanning is used, the start of the image is shifted by 1/2 in odd fields and corner fields, so the effect of the black level change described above differs from field to field, resulting in flickering at the top of the screen. . The present invention has been made to eliminate the above-mentioned drawbacks, and its purpose is to provide a solid-state imaging device that does not cause flickering, darkening, or whitening at the top of the screen.

According to the present invention, from a plurality of light receiving elements provided at predetermined pitches in the horizontal scanning direction and a vertical scanning direction in the same imaging plane, a plurality of vertical transfer parts extending in the vertical scanning direction, and the light receiving element. A solid-state using a charge transfer image sensor, which has a transfer gate electrode that controls charge transfer to a vertical transfer section, and is provided with a light shield to prevent light from entering a group of light receiving elements at at least one end in the horizontal scanning direction. A solid-state imaging device is obtained, characterized in that a correction signal is added to a video signal obtained from the light receiving element in the imaging device. The present invention will be explained in detail below with reference to the drawings.

FIG. 4 is a schematic diagram showing the first embodiment of the present invention, and FIG. 5 is a waveform diagram for explaining its operation. Figures 4 and 5
In the figures, the same components as in FIGS. 2 and 3 are designated by the same reference numerals. In the figure, a case is shown in which the CCD image pickup device is composed of two-phase CCDs in both the vertical transfer section and the horizontal transfer section. Of the two phase transfer electrodes in the vertical transfer section, the light receiving element has one corresponding to the transfer electrode of one phase and one corresponding to the transfer electrode of the other phase.
It is made up of groups. Based on the optical information accumulated in these two groups of light-receiving elements, the electric charge is calculated by vertically increasing the charge accumulated in the light-receiving element corresponding to one of the two-phase transfer electrodes in a certain field. Transfer it to the transfer unit and read it,
Next, in the other field, interlacing is performed by reading out the charge accumulated in the light receiving element corresponding to the transfer electrode of the other phase. Figure 5 shows even field'
It is a figure which shows the operation waveform in this.

In FIGS. 4 and 5, a correction signal 35 from a drive circuit 34 is added to a video signal 27 in a mix circuit 36.
As shown in FIG. 5, the correction signal 35 is a correction signal 37 for a portion where vertical transfer is not performed during the vertical blanking period.
and a noise correction signal 38 of the transfer gate pulse. The correction signal 35 corrects the level difference between the signal 32 giving optical black and the output 29 due to the floor current of the horizontal transfer section in FIG. The level difference with the signal 30 is corrected. After this correction signal 35 is added and the signal levels within the vertical blanking period are uniformly aligned, the video signal 39 will not have its black level fluctuated even if it is clamped by the clamp circuit 16. Although FIG. 5 shows the waveform and operation during the vertical blanking period of the corner field, the operation is exactly the same in the odd field, so the explanation will be omitted. FIG. 6 is a waveform diagram showing the operation in an even field of the second embodiment of the present invention.

In the figure, 21 indicates a vertical planking period.
After the charge from the last light-receiving element in the even field is transferred by the vertical transfer pulse 40, the vertical transfer pulse is applied without stopping until the charge starts to be transferred from the first light-receiving element in the next field at 41. Continuing, empty transfer is performed in the vertical transfer section. Then, within the period from the first vertical transfer pulse 41 of each field to the previous vertical transfer pulse 42, and in each field, the horizontal transfer section receives the light from the light receiving element group provided with the light shield. When the time equivalent to the time to transfer and send out the charge to the output section is reduced.
, a transfer gate pulse 43 is applied to transfer the charge accumulated in the light receiving element to the vertical transfer section. Next, this charge is transferred to the horizontal transfer unit for each IH using the two-phase vertical transfer pulse 23, and horizontally transferred using the horizontal transfer pulse 25. If the obtained green image output is passed through a low-pass filter with a boundary axis, the image shown in 44 is obtained. I get a signal. The noise component 45 caused by the transfer gate pulse 43 contained in the video signal 44 is equivalent to a normal video signal since the time corresponding to the time for outputting the charges of the optically provided light receiving element group is avoided as described above. Therefore, fluctuations in the black level in the clamp circuit described above do not occur. By the way, as mentioned above, the signal that gives optical black is mostly due to the floor current of the vertical transfer section, so the output 46 corresponding to the period in which the vertical transfer section is idle transfer is the signal that gives optical black. However, when the dark current of the light receiving element is so large that it cannot be ignored, or when the ambient temperature rises and the 8 tone current of the light receiving element increases, the level of this light receiving element increases. It is necessary to correct the current.

Therefore, in this second embodiment, a correction signal 49 for correcting the floor current of the light receiving element is added to the video signal 44.

The correction signal 49 corrects the rhombus V between the output 46 due to the current of the vertical transfer section, which corresponds to the step current of the light receiving element, and the signal 47 giving optical black.・Correction signal 49
The operation after the addition and correction is the same as the operation of the first embodiment.

Since the magnitude of the floor current changes depending on the temperature, more complete correction can be achieved by detecting its value in both the first and second embodiments and changing the magnitude of the correction signal according to the magnitude of the floor current. It can be performed.

As described in detail above, the present invention is designed to solve the problem of screen backlashes that occur in a solid-state imaging device that uses a CCD image sensor that is equipped with a group of light-receiving elements that provide optical black and has a smaller number of light-receiving elements than a prescribed scanning line. It stabilizes the black level of the image and eliminates it by correcting the image signal to prevent image deterioration. In the above explanation, the CCD image sensor is a two-phase drive device, and the solid-state image sensor is a single-chip standard monochrome image device. The present invention can be carried out in the same way even when the interbody imaging device is a monochrome or color imaging device using a single plate or a plurality of CCD imaging elements, and when the imaging method is a method other than the standard method. .

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing an example of a CCD image sensor, FIG. 2 is a schematic diagram showing a conventional solid-state imaging device, FIG. 3 is a waveform diagram for explaining the operation of the conventional solid-state imaging device, and FIG. The figure is a schematic diagram showing the first embodiment of the present invention, FIG. 5 is a waveform diagram for explaining the operation of the first embodiment, and FIG. 6 is a waveform diagram for explaining the operation of the second embodiment. FIG. In the figure, 1... light receiving element, 2...
...Vertical transfer section, 3...Transfer gate electrode, 4.
...Horizontal transfer section, 5...Output section, 6...
... Light shielding body, 7 ... Light receiving element group for obtaining an optical black signal, 8 ... Subject, 9 ...
・Lens, 10... CCD image sensor, 11 drive circuit, 12... Drive pulse, 13... Output signal, 14... Front direct amplifier, 15...・・・・・・
Low-pass filter, 16...clamp circuit,
17...Clamp pulse, 18...Process amplifier, 1
9... Planking signal and synchronization signal, 20...
Output terminal, 21... Vertical planking signal, 2
2, 43... Transfer gate pulse, 23, 24,
26, 40, 41, 42... Vertical transfer pulse, 25...
Horizontal transfer pulse, 27, 31, 39, 44...
Video signal, 28, 48...Video signal from the last light receiving element of one field, 29...Output due to floor current of horizontal transfer section, 30, 45...Transfer gate pulse Output due to noise, 32... Signal giving optical black, 33... Horizontal planking period, 34... Drive circuit, 35... Correction Signal, 36...Mix circuit, 37...Correction signal for period when vertical transfer is not performed, 38...
Signal for correcting transfer gate pulse noise, 46...
... Output due to the floor current of the vertical transfer section, 47...
・Output due to the floor current of the light receiving element and vertical transfer section, 49...
...This is a signal for correcting the floor current of the light receiving element. younger brother'
Diagram 2 Diagram 3 Dictionary 4 Diagram Polys S Diagram Inferior Diagram

Claims (1)

[Scope of Claims] 1. A plurality of light receiving elements provided in the same imaging plane with predetermined pitches in the horizontal scanning direction and the vertical scanning direction, a plurality of vertical transfer sections extending in the vertical scanning direction, and the light receiving element. A charge transfer image sensor is used, which has a transfer gate electrode that controls charge transfer from the charge transfer section to the vertical transfer section, and is provided with a light shield to prevent light from entering the light receiving element group at at least one end in the horizontal scanning direction. In a solid-state imaging device, the charge transfer is performed in accordance with the period from vertical transfer in which charges are transferred from the last light-receiving element in each field to vertical transfer in which charges are transferred from the first light-receiving element in the next field. A solid state characterized in that a correction signal is added to a video signal obtained from an image sensor to match the magnitude of an output signal corresponding to the light receiving element group provided with the light shielding body and an output signal corresponding to the period. Imaging device. 2. The solid-state imaging device according to claim 1, wherein the correction signal is a signal for correcting a dark current component of the vertical transfer section. 3. During the period from vertical transfer for transferring charges from the last light-receiving element in each field to vertical transfer for transferring charges from the first light-receiving element of the next field, the vertical transfer section is idle-transferred, 2. The solid-state imaging device according to claim 1, wherein the correction signal is a signal for correcting the dark current of the light receiving element during a period in which the vertical transfer section is performing idle transfer. 4. The solid-state imaging device according to claim 1, wherein the correction signal is a signal for correcting dark current of both the light receiving element and the vertical transfer section. 5. The solid-state imaging device according to claim 1, wherein the correction signal includes a correction signal for correcting noise of a transfer gate pulse applied to the transfer gate electrode.