JP2001016502A - Solid-state image pickup device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To internally execute noise suppression for to both of the interlaced output of a TV signal and progressive scanned output suited to a still picture system. SOLUTION: Two horizontal signal lines are provided, two noise-suppressing parts are provided in one vertical signal line, and these are respectively connected with the horizontal signal lines. This image pickup device has a function for suppressing the noise of optional desirably-adjacent two horizontal lines selected in a horizontal blanking period as a second horizontal period and simultaneously outputting the signals of the two horizontal lines in a signal read period as the next first horizontal period. The adjacent two horizontal lines are made different in the first field and the second field in pair.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid-state imaging device, and more particularly to an amplification type MOS (Metal Oxide Semiconductor) device.
r) A solid-state imaging device.

[0002]

2. Description of the Related Art Recently, as one of solid-state imaging devices, an imaging device using an amplification type MOS sensor has been proposed.
This solid-state imaging device amplifies a signal detected by a photodiode for each pixel with a transistor, and has a feature of high sensitivity. The fixed pattern noise, which has been an obstacle in practical use until now, can be reduced or suppressed to a level having no practical problem by using a new noise suppression method in recent years (Japanese Patent Laid-Open No. 9-247537). Gazette).

FIG. 13 shows an example of a typical configuration of a conventional solid-state imaging device. The vertical selector selects one horizontal line,
Noise and signals are read out separately from the pixels connected to the selected horizontal line in a time-division manner, sent to the noise suppression unit connected to one vertical signal line, and noise is suppressed by subtracting the noise from the signal. I do. The reading from the pixels and the suppression of noise are performed during the horizontal blanking period as shown in FIG. The noise-suppressed signals are selected one by one by a horizontal selection unit in a subsequent horizontal readout period, and are output to the outside of the imaging device by a horizontal signal line. MO with this configuration
The S-type sensor sequentially selects horizontal lines in the vertical direction. For example, a line is selected one by one from the top and returns to the bottom when it reaches the bottom. By repeating this cycle, a continuous image signal can be obtained. Although not shown, a timing line necessary for noise suppression is connected to the noise suppression unit.

In the case of a normal moving image CCD imaging device, the number of vertical transfer CCD stages is half of the number of horizontal lines, and when reading from pixels to the vertical transfer CCD, two pixels adjacent in the vertical direction are simultaneously read and mixed. By changing this adjacent pair for each field, interlacing is supported.

[0005] The CCD image pickup device for progressive scan has a vertical transfer CCD stage having the same number of horizontal lines.
Each pixel is output to the vertical transfer stage independently, and then sequentially transferred to the horizontal transfer CCD.
Is sent to and output. This progressive scan C
An imaging device having two horizontal transfer CCDs has been commercialized in order to make the CD imaging device compatible with interlaced moving images. By outputting two consecutive horizontal lines at the same time, color filter pixels required for color signal processing can be obtained in each field in accordance with one horizontal readout period of a TV signal. In the case of progressive scan, horizontal lines are sequentially output using only one horizontal transfer CCD.

In the CCD image pickup device, the effective accumulation time of all pixels is the same, and reading to the vertical transfer CCD stage is performed simultaneously. The so-called vertical CCD plays a role of a field memory or a frame memory. On the other hand, in the MOS type imaging device having the structure shown in FIG. 13, the imaging device does not have a portion serving as a field or a frame memory, and a noise reduction unit which is read out line by line and receives noise reduction is a horizontal transfer CCD. It also plays the role of line memory. In other words, the start and end of the MOS type effective accumulation period are different for each line. In order to obtain a high quality image, it is necessary to make the effective accumulation times of pixels in at least one field or one frame the same.

Here, the structure of a pixel and how signals and noise are extracted from the pixel will be described in detail with reference to FIG. Pixels include a photodiode that performs photoelectric conversion, an amplification transistor that amplifies an elementary signal, a selection transistor that selects a pixel from which a signal is read out,
It is composed of a reset transistor that discharges the charge of the gate of the amplification transistor. During the horizontal blanking period, one horizontal address line is activated by the vertical selection unit, and each selection transistor of the pixel connected to this is turned on.

At this time, the load transistor is also turned on by a pulse to the load transistor common gate electrode, and a source follower circuit is constituted by the amplifying transistor and the load transistor. A voltage substantially equal to the voltage of the photodiode is applied to the vertical signal line. appear. Next, the vertical selection unit activates the reset line, turns on the reset transistor of the selected pixel, and discharges the signal charge of the photodiode. That is, a noise voltage that is a variation in the threshold voltage of the amplification transistor appears.

By outputting a reset pulse to the reset line without turning on the load transistor and the horizontal address line, signal charges accumulated in the photodiode can be discharged, which is used for an electronic shutter operation.

FIG. 15 shows another conventional example of a pixel and an image pickup device. In this configuration, a charge transfer transistor is provided between the gate of the amplification transistor of the pixel shown in FIG. 13 and the photodiode. The transfer control line of the vertical selection unit is connected to the gate of the charge transfer transistor. In this conventional example, during the horizontal blanking period, first, the reset line becomes active, and discharges the charge of the gate of the amplification transistor of the pixel.

Next, the horizontal address line and the load transistor are turned on, and a noise voltage, which is a variation in the threshold voltage of the amplification transistor of this pixel, appears on the vertical signal line. Next, by turning on the charge transfer transistor, the signal charge of the phototransistor is transferred to the gate of the amplification transistor, and the signal component appears on the vertical signal line. That is, the order of the signal and the noise is opposite to that in the case of FIG.

By turning on the charge transfer transistor without turning on the load transistor and the horizontal address line, the signal charges accumulated in the photodiode can be discharged, and this can be used for the electronic shutter operation.

The present example can also operate to output a signal first. For example, as shown in FIG. 13, first, the charge of the gate of the amplification transistor is discharged by a reset pulse, the charge transfer transistor is turned on at the same time as the load transistor and the horizontal address line are turned on, and the signal charge of the photodiode is reduced by the amplification transistor. And a signal component appears on the vertical signal line. Next, by discharging the gate charge of the amplification transistor by a reset pulse, a noise component appears on the vertical signal line.

Next, an example of a noise suppression technique will be described.

FIG. 16 is a timing chart. This example is shown in FIG.
This is an example of a case where a signal is read first at the timing shown in FIG. In the configuration of FIG.
During the horizontal blanking period, a signal voltage appears first on the vertical signal line, and then a noise voltage appears. When the signal voltage appears,
The clamp transistor is turned on, and is fixed to the common source voltage of the voltage clamp transistor on the clamp transistor side of the clamp capacitance and turned off.

Next, when a noise voltage appears on the vertical signal line, the voltage on the clamp transistor side of the clamp capacitor is:
The voltage change of the vertical signal line, that is, the signal voltage without noise obtained by subtracting the noise voltage from the signal charge appears superimposed on the voltage of the common source of the clamp transistor. When the sample-and-hold transistor is turned on, the signal voltage that suppresses this noise is transmitted to the hold capacitor. The sample and hold transistor is turned off, and in the signal reading period immediately after the horizontal blanking period, the horizontal selection unit turns on the horizontal selection transistor for each column, reads out the signal line of the hold capacitance to the horizontal signal line, and performs imaging. Output from the device.

What is important in these noise suppressing operations is the position of the trailing edge of the clamp pulse and the sample hold pulse. Both are in the period when the vertical signal line is activated by the load transistor and the amplification transistor of the pixel on the selected horizontal line, and the trailing edge of the clamp pulse is
This is the period during which the signal voltage appears on the vertical signal line, and the trailing edge of the sample and hold pulse is the period during which the noise voltage appears on the vertical signal line. Other noise suppression means are described in detail in the above-mentioned Japanese Patent Application Laid-Open No. 9-247537.

[0018]

A two-horizontal signal line structure that can perform progressive readout suitable for a digital still camera and output suitable for TV signal generation is described by M.
By adopting the OS type imaging device, M
An OS-type imaging device can be realized. However, for this purpose, it is necessary to consider a two-horizontal signal line structure for a MOS type imaging device completely different from a CCD imaging device. Especially 2
It is necessary to consider the configuration and timing of the noise suppression means that works effectively on the horizontal signal line. Furthermore, the effective storage time must be at least the same in a field or a frame.

The present invention has been made to solve the above-mentioned problem, and suppresses noise while enabling simultaneous reading of two horizontal lines even if the photosensitive cell portion is constituted by a MOS type sensor. It is an object of the present invention to provide a solid-state imaging device capable of performing such operations.

[0020]

In order to achieve the above object, a solid-state imaging device according to a first basic structure of the present invention comprises a photoelectric conversion means, a signal charge storage means, a signal charge discharge means, An imaging region in which photosensitive cells each including a selection unit and an amplification unit are two-dimensionally arranged; a plurality of vertical selection lines arranged in a row direction of the imaging region; and a vertical selection unit that drives these vertical selection lines; A plurality of vertical signal lines arranged in the column direction for reading the output of the amplifying means, a plurality of vertical signal line driving auxiliary means provided on these vertical signal lines, and a vertical signal line provided at an end of the vertical signal line; A plurality of noise suppression means for taking in and subtracting noise and a signal appearing with a time difference on the signal line, a plurality of horizontal signal lines arranged in the row direction adjacent to each other corresponding to each noise suppression means, Horizontal signal lines and corresponding A horizontal reading unit for connecting an output of the noise suppressing unit; and a horizontal selecting unit for driving the horizontal reading unit. There is a second horizontal period, and in the second horizontal period, the vertical selection means selects a plurality of rows of photosensitive cells via a vertical selection line, and suppresses noise and signals of the selected plurality of rows by noise suppression. In the following first horizontal period, signals in a plurality of rows are simultaneously read out on a plurality of horizontal signal lines, and selection of two adjacent rows is performed in the first vertical reading period and the first vertical reading period. 2
In the vertical readout period.

In the solid-state imaging device according to the second basic configuration of the present invention, the photoelectric conversion means, the signal charge storage means, the signal voltage conversion means, and the signal charge storage means are provided on the semiconductor substrate. An image pickup area in which photosensitive cells each including a charge transfer means for transferring a charge, a signal charge discharge means for discharging charge from a charge-voltage conversion means, a row selection means, and an amplification means are two-dimensionally arranged; A plurality of vertical selection lines, vertical selection means for driving these vertical selection lines, a plurality of vertical signal lines arranged in the column direction for reading out the output of the amplification means, and a plurality of vertical signal lines. A plurality of vertical signal line driving auxiliary means, a plurality of noise suppressing means for taking in and subtracting noise and a signal appearing with a time difference in a vertical signal line provided at the end of the vertical signal line, and corresponding to each noise suppressing means. A plurality of horizontal signal lines arranged one by one adjacently in the row direction, a horizontal readout unit for connecting each horizontal select line and an output of the corresponding noise suppression unit, and a horizontal select unit for driving the horizontal readout unit Means, wherein a first horizontal period during which a signal is read out to the horizontal signal line and a second horizontal period other than the first horizontal period exist. Selects a plurality of rows of photosensitive cells via a vertical selection line, takes in the noises and signals of the selected plurality of rows into respective noise suppression means to suppress noise, and in a subsequent first horizontal period, a plurality of rows of photosensitive cells are selected. Are read out simultaneously by a plurality of horizontal signal lines, and the selection of two adjacent rows is different between a first vertical reading period and a second vertical reading period.

Further, in the solid-state image pickup device according to the first and second basic configurations, one vertical signal line has two noise suppressing means, two horizontal signal lines, and a photosensitive cell which is selected at the same time. The rows are two adjacent rows, and during the second horizontal period, the noise and the signal of the selected two rows are taken into the noise suppression means assigned to each row, and noise suppression is performed.
In the subsequent first horizontal period, the signals of these two rows may be specifically read out from the respectively assigned horizontal signal lines at the same time.

In the above specific configuration, the solid-state imaging device has means for changing the effective charge accumulation time by means of signal charge discharging means in the photosensitive cell, and the charge accumulation period of the selected two adjacent rows. May be configured to be set to have the same charge accumulation period.

Further, in the above more specific configuration,
The solid-state imaging device includes a noise suppression mode in which one row is selected in the second horizontal period to perform noise suppression, and a 1st row in the subsequent first horizontal period.
A signal readout mode for reading out signals by the horizontal signal lines, and it is possible to select either the noise suppression mode or the signal readout mode by an operation switching signal given to the solid-state imaging device. good.

With the above configuration, the CMO
The S-type imaging device has two horizontal signal lines, and has two noise suppression units for one vertical signal line. Also two consecutive
There is a mode in which pixel signals of a horizontal line are read out by two horizontal signal lines, and a mode in which pixel signals of one horizontal line are read out by one horizontal signal line.

One vertical signal line for reading out a signal and noise from a pixel is connected to two noise suppression means, and each noise suppression means is connected to two horizontal signal lines. In the pixels of the two horizontal lines selected for reading, the signal and the noise are read out at different times in the same horizontal blanking period, and the noise and the noise are suppressed by the noise suppression means assigned to each horizontal line. . In the subsequent horizontal reading period, the signals of the two horizontal lines are read simultaneously through the two horizontal signal lines.

In order to support interlacing, the two horizontal lines selected are two consecutive horizontal lines,
Further, in the first field and the second field, the combination is selected differently. That is, in the first field, the first and second lines, the third and fourth lines,..., And in the second field, the second and third lines, the fourth and fifth lines.
The line ...

Further, the vertical selection unit operates the signal charge discharging function of the pixel so that the two selected effective accumulation times become the same, so that the effective accumulation time between lines can be made equal.

[0029]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the solid-state imaging device according to the present invention will be described below in detail with reference to the accompanying drawings.

FIG. 1 is a schematic configuration diagram showing a solid-state imaging device according to a first embodiment of the present invention. The solid-state imaging device according to the first embodiment has two horizontal signal lines, two noise suppressing units provided on one vertical signal line, and one noise suppressing unit for each of the conventional examples of FIG. It is connected to a horizontal signal line, and can output two horizontal lines at the same time. In addition, the imaging apparatus has a progressive output progressive output mode in an interlace mode corresponding to the interlace output using the two-line output.

This so-called progressive scan output method is a reading method suitable for a digital still camera system using one frame of image data or a moving image system having no interlace structure. In a color digital still camera system using one solid-state imaging device, one color filter is formed in one pixel of the solid-state imaging device, and a plurality of types of the color filters are used as shown in FIGS. 2A and 2B, for example. Using the array, a luminance signal and a color signal are created from this. Since this color signal processing is created not only from one pixel but also including peripheral pixels, if the horizontal lines are continuously output from the imaging device, there is no need to have a temporary storage memory for line rearrangement in the system. .

However, when used in a current TV signal system having an interlace structure, it is necessary to adopt an output method that takes the interlace structure into consideration. That is, it is necessary to output 30 frames / sec at 60 fields / sec from the imaging device or to generate the signal from the output of the imaging device by signal processing. If selection output is simply performed every other line to support interlacing, as shown in FIG. 2, a signal of a color filter required to create a color signal cannot be obtained in one field, and , It is necessary to have a temporary storage memory. To read out all the pixels in one field in order to perform color signal processing, it is necessary to read out the imaging device at high speed. One horizontal read period is one of the TV signals.
Half of the horizontal readout period, the output of the imaging device is set to TV
In order to match the horizontal readout period of the signal, a process for extending the time axis is required.

In the case of a normal moving image CCD image pickup apparatus, the number of vertical transfer CCD stages is half the number of horizontal lines, and when pixels are read out from the vertical transfer CCD, two vertically adjacent pixels are simultaneously read and mixed. By changing this adjacent pair for each field, interlacing is supported. FIG. 3 is a configuration diagram of an example of noise suppression. A clamp capacitor is connected to the vertical signal line, and is composed of a clamp transistor, a sample hold transistor, and a hold capacitor.

The solid-state imaging device shown in FIG. 1 reads out signal charges at the timing shown in FIG. In the timing chart of FIG. 4, the vertical signal line reads out the signal and the noise in the i-th row and the signal and the noise in the (i + 1) th row adjacent thereto in the horizontal section ranking period as the second horizontal read-out period.

This operation will be described with reference to the timing chart of FIG. In the interlace mode, the vertical signal line selects two continuous horizontal lines during the horizontal blanking period. First, the signal and noise of one row are read from each pixel, and the noise is suppressed by the noise suppression unit 1, and then the signal is held as it is. The signal and noise in the next row are read from each pixel, and after the noise is suppressed by the noise suppression unit 2, the signal is held in the same manner. The noise suppression technique is the technique shown in the conventional example. The two-line signals in which noise has been suppressed are successively selected by the horizontal selection unit in the subsequent signal readout period, and are simultaneously read out through the horizontal signal lines.
In the next horizontal blanking period, the following two rows are read out,
Noise suppression is performed, and this is repeated one after another.

In the progressive mode, one horizontal line is selected during one horizontal blanking period. At this time, one horizontal signal line is a valid output. In the interlace mode, one vertical cycle operates twice as long as in the progressive mode, and an output corresponding to the interlace structure of the TV signal can be obtained. Therefore, a pair of horizontal lines selected in one horizontal blanking differs between the first field and the twelfth field. As shown in FIG. 6, in the first field, the i-th row and the i + 1-th row are paired, and in the second field, the i-th row and the i + 3 row are paired.
Row and i + 2 row, and i + 3 row and i + 4 row are a pair. In the interlace mode, the vertical selection unit is set to select a horizontal line in this manner.

FIG. 7 shows the state in the progressive mode.
5 shows a timing chart when two consecutive rows are read out simultaneously in a frame. In this mode, the number of times of reading one frame is half the number of lines in the vertical direction, but this is an effective reading method when a reduced image is obtained.
For example, a luminance signal and a chrominance signal are generated from two lines to be read simultaneously and two pixels in the horizontal direction.

FIG. 8 is a block diagram showing the configuration of the solid-state imaging device according to the second embodiment of the present invention. The solid-state imaging device according to the second embodiment is different from the first embodiment shown in FIG. 1 in that a charge transfer transistor is interposed between a gate of an amplification transistor in a pixel and a photodiode, and is perpendicular to the gate of the transistor. The point is that the transfer control line is connected from the selection unit. With such a configuration, as described with reference to FIG. 15 of the conventional example, noise can be first output from the pixel, and then the signal component can be output. As described in the conventional example, the signal can be output first.

The operation of the solid-state imaging device according to the second embodiment shown in FIG. 8 is shown in FIG. 9 and FIG. In the timing chart of FIG. 9, as in FIG. 4, the vertical signal line has the signal and noise of the i-th row and the signal and noise of the i + 1-th row adjacent thereto in the horizontal section ranking period as the second horizontal readout period. Is being read.

FIG. 10 is a timing chart showing the timing when the charge of the signal line is read out by a method different from that of FIG. In FIG. 10, the timing of the rising edge of the reset signal is set between the signal and noise of the i-th row read in the horizontal section ranking period as the second horizontal period and the signal and noise of the (i + 1) -th row adjacent thereto. A gap is provided.

FIG. 11 explains the details of the timing in the interlace mode. As shown in the upper part of the figure, in the progressive mode, one line is read for one horizontal synchronization signal. By performing the reading operation, the signal charges accumulated in the photodiode of each pixel are discharged, and new signal charges are accumulated. In this timing example, the charge is not discharged halfway, that is, the electronic shutter operation is not performed.

At this time, the accumulation time is one frame period, that is, 525 horizontal periods. Similarly, in the case of the interlaced mode in which the electronic shutter operation is not performed, since the pairs to be read are different between the first field and the second field, the effective accumulation times of the two fields differ by one horizontal period. Therefore, in the interlace mode, even if the electronic shutter operation is not set, as shown in the lower part of FIG. Must be output to

FIG. 12 shows an example when the electronic shutter is set. In the progressive mode, the effective accumulation time is 521 horizontal periods.
An example of the effective accumulation time for the 58 horizontal periods is shown. When the interlaced mode is set, as shown in the figure, the set electronic shutter, that is, the effective accumulation time is set by performing pixel reset of two lines for reading out pixels in the same horizontal blanking period in the next field at the same timing as shown in the figure. It is the same in the field and between the fields, and the image quality is not deteriorated.

[0044]

According to the above configuration,
MOS type imaging that can support both the interlaced readout method and the progressive readout method, and can read out signals of two horizontal lines at a time with low noise during a blanking period as a second horizontal period. The device can be provided.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a solid-state imaging device according to a first embodiment of the present invention.

FIG. 2 is an example of a color filter array used in a solid-state imaging device.

FIG. 3 is a configuration example of a noise suppression unit of the solid-state imaging device.

FIG. 4 is a timing chart illustrating a read operation at a first timing in the solid-state imaging device in FIG. 1;

FIG. 5 is a timing chart illustrating the operation of FIG.

FIG. 6 is a timing chart illustrating the operation of FIG.

FIG. 7 is a timing chart showing a progressive two-line read operation in the first embodiment.

FIG. 8 is a block diagram illustrating a configuration of a solid-state imaging device according to a second embodiment of the present invention.

FIG. 9 is a timing chart showing a read operation of the second embodiment.

FIG. 10 is a timing chart showing a different read operation of the second embodiment.

FIG. 11 is a timing chart showing a read operation in the second embodiment.

FIG. 12 is a timing chart showing a read operation in the second embodiment.

FIG. 13 is a block diagram showing a configuration of a first conventional MOS imaging device.

FIG. 14 is a timing chart illustrating the operation of FIG.

FIG. 15 is a block diagram showing a configuration of a second conventional MOS imaging device.

FIG. 16 is a timing chart illustrating the operation of FIG.

[Explanation of symbols]

 i, i + 1 two adjacent horizontal lines

Claims (4)

[Claims] 1. An imaging area in which photosensitive cells each comprising a photoelectric conversion means, a signal charge accumulation means, a signal charge discharge means, a row selection means and an amplification means are two-dimensionally arranged on a semiconductor substrate, and a row direction of the imaging area. A plurality of vertical selection lines, vertical selection means for driving these vertical selection lines, a plurality of vertical signal lines arranged in a column direction for reading the output of the amplification means, and these vertical signal lines. A plurality of vertical signal line driving auxiliary means provided; a plurality of noise suppressing means for taking in and subtracting noise and a signal appearing with a time difference in a vertical signal line provided at an end of the vertical signal line; and each noise suppressing means A plurality of horizontal signal lines arranged one by one adjacent to each other in the row direction, horizontal reading means for connecting each horizontal signal line and the output of the corresponding noise suppressing means, and horizontal reading means. Driving horizontal A first horizontal period in which a signal is read out to the horizontal signal line, and a second horizontal period other than the first horizontal period. In the second horizontal period, the vertical selection unit A plurality of rows of photosensitive cells are selected via a selection line, and noise and signals of the selected plurality of rows are taken into each noise suppression unit to perform noise suppression. In a subsequent first horizontal period, a plurality of rows of photosensitive cells are selected. A solid-state imaging device wherein signals are simultaneously read out by a plurality of horizontal signal lines, and selection of two adjacent rows is different between a first vertical reading period and a second vertical reading period. 2. One vertical signal line has two noise suppression means, two horizontal signal lines corresponding to the noise suppression means, and a row of photosensitive cells selected at the same time is adjacent to two adjacent signal lines.
In the second horizontal period, the noise and the signal of the selected two rows are taken into the noise suppression means assigned to each row, and noise suppression is performed. The signal is assigned to each horizontal signal line,
The solid-state imaging device according to claim 1, wherein reading is performed simultaneously. 3. The solid-state imaging device has means for changing an effective charge accumulation time by means of signal charge discharging means in a photosensitive cell, and charge accumulation periods of two selected adjacent rows are the same charge accumulation period. The solid-state imaging device according to claim 2, wherein: 4. A solid-state imaging device includes: a noise suppression mode in which one row is selected in a second horizontal period to suppress noise; and a signal reading mode in which a signal is read out by one horizontal signal line in a subsequent first horizontal period. 4. The solid-state imaging device according to claim 3, wherein the device is configured to be able to select one of the noise suppression mode and the signal reading mode by an operation switching signal given to the solid-state imaging device.