JPS5983473A - Solid-state image pickup device - Google Patents

Abstract

PURPOSE:To reduce the vertical smear and to obtain a video signal with high quality, by transmitting a pseudo signal from a charge coupling element used for vertical scanning in a direction opposite to the transfer direction of a video signal at a vertical blanking period. CONSTITUTION:A photo diode 1 being photo sensing picture elements arranged in array horizontally and vertically is connected to a vertical transfer CCD3 via a transfer gate 2, and the vertical transfer CCD3 is connected to a horizontal transfer CCD4. The picture information stored on the photo diode 1 is transferred to the CCD3 with the impression of the pulse to gate lines 7, 8, 9, 10 and then to the CCD4. The vertical smear signal mixed in the CCD3 is eliminated by transferring the signal to a vertical smear signal sweep-out section 14 during the vertical blanking period by means of a sweep-out gate 15 independently of the turning on/off of the transfer gate 2.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to vertical smear suppression in a solid-state image sensor.

[Prior art]

In imaging devices that convert a subject image into an electrical signal, a solid-state imaging device as shown in FIG. 1, which is obtained by semiconductor integrated circuit technology, has recently been used as a photoelectric conversion device. By using a solid-state imaging device, the imaging device can be made smaller, more reliable, and have a longer lifespan than a one-tube type vehicle.

However, in a solid-state imaging device as shown in Figure 1, it is desirable that the photosensitive portion is only the photodiode 1, but for example, charges generated deep in the substrate move by diffusion and are connected to charge coupling for direct vertical transfer. (hereinafter abbreviated as COD) K. In addition, the photocharge generated in the photodiode 1 is transferred to the O of the transfer gate 2.
N.

It may get mixed into the vertical transfer CCD 3 regardless of whether it is OFF or not. Therefore, the optical information projected onto the surface of the solid-state image sensor is transferred from the vertical transfer CCD 3 to the horizontal transfer CCD 4.
The above-mentioned pseudo signals are mixed before being transferred to. In other words, the signal of the projected subject image is transferred to the CCD for vertical transfer.
3, pseudo-signal components from hundreds of photodiodes lined up one after the other are accumulated while being transferred to the horizontal transfer CCD 4. When a subject image with a bright part as shown in Figure 2(a) is captured, this pseudo signal appears as a trailing image in the vertical direction on the playback screen, as shown in Figure 2(b). Decrease image quality.

This kind of noise component unique to solid-state image sensors is called vertical smear.

[Purpose of the invention]

An object of the present invention is to provide a solid-state image sensor that can reduce vertical smear.

[Detailed description of the invention]

The present invention will be described in detail below, but first a general description will be given of the driving method of the CCDC solid-state image sensor used in the example of the description.

In the CCDC solid-state imaging probe shown in FIG. 1, φ
By applying the V1 pulse, the signals accumulated in the odd-numbered photodiodes are transferred to the vertical transfer CCD 3 via the transfer gate 2.

Then, φVl,
φV2. φv3. φV4 is applied, and the horizontal transfer CCD 4t transfers two rows at a time during one horizontal scanning period. However, the high level of the φV1 and φV2 pulses performs transfer at a potential that does not turn on the transfer gate. The signal sent to the horizontal transfer CCD 4 is taken out from the output end 6 via the amplifier 5 every horizontal scanning period. In the next field, the signals of the photodiodes in the even rows are defeated by the φV3 pulse, and the same operation as described above is performed to complete the operation of one frame. Thereafter, similar operations are repeated to perform interlace operations.

Here, as described above, the vertical smear signal mixes into the vertical transfer CCD 3 regardless of whether the transfer gate 2 is ON or OFF. Therefore, in order to reduce this, it is effective to increase the transfer speed of the vertical transfer CCD 3 and shorten the vertical smear accumulation time.
Since a memory is required to store each signal until it is taken out to the outside, the circuit becomes complicated and the chip area of the device increases, which is a major drawback. On the other hand, before transferring the photodiode 1 to the vertical transfer CCD 3 during the vertical retrace period, the vertical smear signal accumulated up to that point is transferred to the horizontal transfer CCD 3.
If it is swept out to the outside via 0D4, vertical smear can be reduced without using the memory as described above. However, in order to sweep the vertical smear signal to the outside, the horizontal transfer CCD 4 is connected to the horizontal drive pulses φH1, φH2, φH.
3 causes the inconvenience of having to drive only during a certain period of the vertical retrace period. In view of these points, in this patent, the CCD 4 for horizontal transfer and the CC for vertical transfer on the opposite side
A vertical smear sweeping section is provided at the end of D3, and the signal of photodiode 1 is transferred to CCD 3 for vertical transfer within the vertical retrace period.
A method was devised to reduce vertical smear by reversing the transfer direction of the vertical transfer CCD 3 and transferring the vertical smear signal to the sweep section.

〔Example〕

゛゛　The present invention will be explained using examples.

FIG. 3 shows an example of a solid-state image sensor according to the present invention. 14
15 is a vertical smear signal sweeper, and 15 is a CCD for vertical transfer.
This is a sweep gate for transferring the vertical smear signal from 3 to the vertical smear signal sweep section 14. C for vertical transfer
FIG. 4 shows a vertical cross-sectional structure of the solid-state image sensor 7) extending from the CD 3 to the vertical smear signal sweep-out section 14. 17 and 18 are transfer electrodes of the vertical transfer CCD 3. Reference numeral 19 is a diffusion layer, and in the case of a buried channel COD, it is an n-swelled diffusion layer made of phosphorus (P 2 ) or the like. On the other hand, in the case of a single surface channel COD, the diffusion layer 19 is not required. 21 is a P layer, and 22 is an n-type 8i substrate. Here, 14 is a vertical smear signal sweep-out section, and the concentration of phosphorus (P) in the n-type wave diffusion layer 19 is
This is a diffusion layer with a high donor concentration, that is, a low resistance value. Since this vertical smear signal sweeping section 14 is fixed at a finite voltage of 0 or + by 20, the vertical smear signal transferred by applying a voltage to the sweeping gate electrode 5 is transferred to the vertical smear signal sweeping section 20. 14
More of this will be swept outside.

FIG. 5 shows a timing chart of pulses used for vertical smear signal sweeping drive. The vertical smear signal sweeping operation is
Since it must be completed within the vertical retrace period until the photodiode signal is transferred to the vertical transfer COD, high-speed driving (LM) of around 12) is required. Therefore, by taking advantage of the fact that the vertical smear signal amount is minute compared to the photodiode signal amount, the transfer speed was increased by two-phase driving using φVl and φV2. The high level of φV1 and φV2 pulses during two-phase drive by φVl and φv2 is V
M. Letting the low level be vL, φV3 and φV4
is fixed to a constant DC voltage VM' such that VL<VM'<VM. Further, a constant DC voltage VS with ■s≧VM as φS is applied to the sweep gate electrode for transferring the vertical smear signal from the vertical transfer CCD to the vertical smear signal sweep section only during the sweep drive. However, if φS does not interfere with the transfer to the vertical smear sweeping section, especially V
It is not limited to a DC voltage with the relationship S≧VM.

In addition, the power supply 20 is set to the same voltage as the potential VS of φS or higher than ■S at times tl + tt + t3 + t4 and t in the timing chart of FIG.
FIG. 6 shows how the vertical smear signal is transferred in the IC and swept out to the outside using a schematic diagram of a potential well.

〔Effect of the invention〕

As explained above, by performing the vertical smear sweeping drive according to the present invention, vertical smear can be reduced and a high-quality video signal can be obtained. ? ! In addition, the vertical smear reduction method of the present invention is extremely easy to implement, and furthermore, the vertical CCD
Since it is sufficient to provide a sweep gate 15 common to all columns and a sweep diffusion layer 14 at one end, an increase in chip area does not become a problem. Therefore, the manufacturing yield does not decrease.

In the above description, the npn three-layer structure was explained, but the gist of the present invention does not change even if the np two-layer structure is used. In addition, although the vertical transfer CCD is described as having four-phase drive, and the horizontal transfer CCD is described as being three-phase drive, the gist of the present invention also applies to CCDs that transfer using other single drive methods such as two-phase, three-phase, or four-phase. are the same.

[Brief explanation of the drawing]

FIG. 1 is a diagram for explaining the signal readout method of a conventional CCD solid-state image sensor, FIG. 2 is a diagram for explaining vertical smear, and FIG. 3 is an example of a CCD solid-state image sensor according to the present invention. , FIG. 4 is a diagram showing a vertical cross-sectional structure of the main part of the present invention, FIG. 5 is a timing diagram of four driving pulses for vertical smear sweeping out, and FIG. 6 is a diagram for explaining how the vertical smear signal is swept out. Agent Patent Attorney Toshiyuki Usuda 1st (2) fH391-12'pH1 Fig. 2 (0-) (b) Fig. 3 $ η Each moi

Claims (1)

[Claims] 1. In a solid-state image sensor that uses charge-coupled devices in photosensitive pixel columns arranged in an array in the horizontal and vertical directions and in the vertical and horizontal scanning sections for extracting signals accumulated in the photosensitive pixel columns, the vertical blanking line is During the period, the charge-coupled device used for vertical scanning transfers a pseudo signal in the opposite direction to the transfer direction of the video signal. A solid-state imaging device characterized in that the pseudo signal is swept out from a signal sweeping section.