JPH0775025A - Solid-state image pickup element - Google Patents

Abstract

PURPOSE:To reproduce an image pickup pattern fined to a degree approximately same as the pitch of photodetectors on a monitor screen without lowering S/N. CONSTITUTION:Signal charge generated in the photodetector 11 is transferred through a first horizontal transfer part 14a or a second horizontal transfer part 14b to a first output part 15a or a second output part 15b, converted into a voltage signal in either output part and outputted. Voltage gains are mutually different in the first and second output parts and the output voltages of the first and second output parts are added in an addition part 16. Electric charge generated in the odd-numbered photodetectors of the photodetectors arrayed in a vertical direction is outputted from the first output part 15a in an odd- numbered field and outputted from the second output part 15b in an even- numbered field. For the electric charge of the even-numbered photodetectors, the output parts to be used are inverted in the respective fields.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid-state image sensor,
In particular, it relates to an interline solid-state image sensor.

[0002]

2. Description of the Related Art FIG. 4 is a block diagram of a conventional interline solid-state image pickup device. In the figure, reference numeral 41 is a light receiving portion for photoelectrically converting incident light to generate signal charges and accumulating the signal charges, and 42 is a vertical portion for vertically transferring the signal charges transferred from the light receiving portion 41. A transfer unit, 43 is a charge reading unit for reading the signal charges accumulated in the light receiving unit 41 to the vertical transfer unit 42, and 44 is a vertical transfer unit 4.
The horizontal transfer unit 45 horizontally transfers the signal charges transferred from the horizontal transfer unit 2, and the output unit 45 converts the signal charges transferred from the horizontal transfer unit 44 into a voltage signal.

When performing 2-to-1 interlace driving with this solid-state image pickup device, in an odd field, signal charges simultaneously generated by two vertically adjacent light receiving portions 41 are read out to the vertical transfer portion 42 and mixed. , To the horizontal transfer unit 44, and then the horizontal transfer unit 44 outputs to the output unit 45.
Then, the output section 45 converts the voltage signal into a voltage signal and outputs the voltage signal. In the even-numbered field, after the signal charges generated in the light-receiving sections that are shifted by one pixel from those in the adjacent two light-receiving sections are mixed in the vertical transfer section 42 and transferred to the horizontal transfer section 44. , And output as a voltage signal from the output unit 45. The odd field and even field signals are alternately output in the vertical direction on the monitor screen.

When an image pickup device using such an interline solid-state image pickup device picks up an image of a subject having a contrast as shown in FIG. 5A, it forms an image on the light receiving surface of the image pickup device having the pattern of the subject. The interval is shown in Fig. 5 (b).
As shown in FIG. 5C, when the pixel pitch in the vertical direction of the solid-state image pickup device becomes the same as the pixel pitch, when the accumulated charges shown in FIG. 5C are mixed, as shown in FIG. There is no difference between the output levels of the odd field signal and the even field signal, and it becomes impossible to reproduce the actual contrast of the subject pattern on the monitor screen.

As a means for solving such a phenomenon, there is a method of using a frame interline (FIT) type solid-state image pickup device. FIG. 6 is a schematic plan view of a frame interline solid-state image sensor. In the figure, the parts corresponding to the parts of the interline solid-state imaging device shown in FIG. 4 are denoted by the numbers having the same last digit, so that the duplicate description will be omitted, but the frame interline shown in FIG. The solid-state image pickup device includes a charge storage section 67 for temporarily storing the signal charge transferred from the vertical transfer section 62.
And a charge sweeping unit 68 for absorbing unnecessary charges swept from the horizontal transfer unit 64.

In the interline type solid-state image pickup device, the charge cannot be read from the light receiving part to the vertical transfer part while the charge is being transferred in the vertical transfer part due to its structure, but in the frame interline type solid-state image pickup device. , Fig. 6
As shown in (1), since the charge storage section 67 for temporarily storing the signal charge is provided in the subsequent stage of the vertical transfer section 62,
If the charges read out to the vertical transfer unit 62 are transferred to the charge storage unit 67 at high speed, the light receiving unit 6 is transferred within the original vertical transfer period.
It is possible to read the charges from 1 to the vertical transfer unit 62. FIG. 7 utilizes this function to reproduce the contrast of the image pickup pattern on the monitor when the vertical pitch of the pixels of the light receiving portion of the solid-state image pickup element and the pitch of the image pickup pattern are approximately the same as described above. FIG. 7 is a timing diagram of drive pulses when driving as described above.

In the odd field vertical transfer period,
The period A is set in the odd-numbered light-receiving parts of the light-receiving parts arranged in the vertical direction.
The electric charge stored in the electric charge is read out to the vertical transfer unit 62 by the sweep-out electric charge read pulse a, and is discarded in the electric charge sweep-out unit 68 by the high-speed sweep-out pulse g (in the vertical blanking period) after the end of the normal vertical transfer pulse. To be done. In the odd-numbered light receiving portions, the charge accumulated in the period C is read out to the vertical transfer portion by the signal charge read pulse b, and in the even-numbered light receiving portions, the charge accumulated in the period B ′ is read out. The charges are read out to the vertical transfer unit by d, and both charges are mixed in the vertical transfer unit. The mixed charges are transferred to the charge storage unit 67 by the high-speed forward transfer pulse h in the vertical blanking period, transferred to the horizontal transfer unit 64 by the vertical transfer pulse i in the even field vertical transfer period, and transferred to the even field. Is output as a signal.

In the even field vertical transfer period, the charges accumulated in the period A'in the even-numbered light receiving unit are read out to the vertical transfer unit by the high-speed sweep-out charge read pulse e, and in the vertical blanking period. The high-speed sweep pulse j is discarded by the charge sweep section 68. In the subsequent period C ′, the charges accumulated in the even-numbered light receiving units are read out to the vertical transfer unit by the signal charge read pulse f, and in the odd-numbered light-receiving units, the charges accumulated in the period B are read out. The charges are read out to the vertical transfer unit by the pulse c, and both charges are mixed in the vertical transfer unit. The mixed charges are transferred to the charge storage unit 67 by the high-speed forward transfer pulse k in the vertical blanking period, transferred to the horizontal transfer unit 64 by the vertical transfer pulse in the odd field vertical transfer period, and transferred in the odd field. It is output as a signal charge.

Here, as shown in FIGS. 8A and 8B, the pitch of the image pickup pattern is equal to the pitch of the light receiving portions of the solid-state image pickup element, and the white pattern corresponds to the odd-numbered light receiving portions. If so, the amount of charge accumulated in each light receiving portion in the even field (charge output in the odd field) is as shown in FIG.
In addition, the amount of charge accumulated in each light receiving unit in the odd field (charge output in the even field)
Is as shown in FIG. Therefore, the video signal obtained by combining the odd field signal and the even field signal is as shown in FIG. 8E, and the imaging pattern of the subject is reproduced.

[0010]

In the conventional image pickup method using the above-mentioned frame interline type solid-state image pickup device, in order to make the sensitivity of the light receiving portion alternately different in the vertical direction, the charge accumulated in the light receiving portion is changed. Since some of the charges are discarded as unnecessary charges, the absolute amount of charges used as a video signal decreases, and as a result, the ratio of the video signal to the noise component decreases. For example, if the ratio of the sensitivities of the light receiving portions adjacent to each other in the vertical direction is set to 3: 1, the sensitivity for one field is reduced to two thirds as compared with the case of normal field accumulation, and S / N deteriorates.

[0011]

In order to solve the above-mentioned problems, according to the present invention, a plurality of light receiving portions arranged in a matrix and the light receiving portions arranged in each vertical row of the light receiving portions. A vertical transfer unit for vertically transferring the charges photoelectrically converted by the device, a first horizontal transfer unit for horizontally transferring the charges transferred from the vertical transfer unit, and the first horizontal transfer unit of the first horizontal transfer unit. A second horizontal transfer unit which is provided on the opposite side of the light receiving unit and horizontally transfers the charges transferred from the first horizontal transfer unit, and the charges transferred from the first horizontal transfer unit. A first output for converting the voltage signal to a voltage signal,
A second output unit that converts the charge transferred from the second horizontal transfer unit into a voltage signal and has a voltage gain different from that of the first output unit, the first output unit, and the second output unit. An adder that adds voltage signals from the output unit, and the charge transferred from the vertical transfer unit can be transferred to either the first horizontal transfer unit or the second horizontal transfer unit. A solid-state image sensor is provided.

[0012]

Embodiments of the present invention will now be described with reference to the drawings. FIG. 1 is a block diagram of a solid-state image sensor according to an embodiment of the present invention. As shown in the figure, this solid-state image sensor has a light receiving unit 11 arranged in a matrix.
And a vertical transfer unit 12 for vertically transferring the charges generated in the light receiving unit 11, and a charge reading unit 13 for reading the charges accumulated in the light receiving unit 11 into the vertical transfer unit 12.
And a first horizontal transfer unit 14a that transfers the charges transferred from the vertical transfer unit 12 in the horizontal direction, and a second horizontal transfer unit 14a that reads the charges of the first horizontal transfer unit 14a and transfers the charges in the horizontal direction. The transfer unit 14b, the first output unit 15a and the second output unit 15b that convert the charge transferred from the first horizontal transfer unit 14a and the second horizontal transfer unit 14b into a voltage signal, and the first output unit 15a and the second output unit 15b. Output unit 15a and second output unit 15
and an adder 16 for adding the voltage signals from b. Here, the voltage gain of the second output section 15b is set to 1/2 of that of the first output section 15a. This gain ratio can be determined, for example, by the area ratio of the floating diffusion layers forming the FDA (floating diffusion layer amplifier).

FIG. 2 (a) is a sectional view taken along the line AA 'in FIG. 1, and FIGS. 2 (b) and 2 (c) are respectively FIG. 2 (a).
FIG. 3 is a potential distribution diagram in the cross section of FIG. 4 and a timing diagram of each drive pulse. In FIG. 2A, 21 is a p-well formed on an n-type semiconductor substrate (not shown), and 22 is a p-well.
An n-type diffusion layer forming a charge transfer region formed in the surface region of the well 21, 23 is a vertical transfer electrode of a vertical transfer unit, 24a is a first horizontal transfer electrode of a first horizontal transfer unit, Reference numeral 24b denotes a second horizontal transfer electrode of the second horizontal transfer unit, and a vertical transfer pulse φV and horizontal transfer pulses φHa and φHb are applied to each transfer electrode.

As shown in FIG. 2C, at time t ₁ within the horizontal blanking period, both φHa and φHb are at the medium potential H _M. Here, the signal charge is transferred from the vertical transfer section to below the first horizontal transfer electrode. Time t ₂
In, when φHa becomes the low potential H _L and φHb becomes the high potential H _H , the signal charge is transferred to the lower side of the second horizontal transfer electrode 24b. At time t ₃ , both φHa and φHb are returned to the intermediate potential H _M , but the signal charge remains below the second horizontal transfer electrode. After the end of the horizontal blanking period, this signal charge is transferred to the second horizontal transfer unit and then transferred to the second horizontal transfer unit.
Is output from the output section of. After the signal charges have been transferred from the vertical transfer section to below the first horizontal transfer electrode 24a, φHa and φHb are changed over the entire horizontal blanking period thereafter.
When both keep the medium potential H _M , the signal charge is
Stays below the horizontal transfer electrode 24a, is transferred to the first horizontal transfer unit 14a after the horizontal blanking period, and is output from the first output unit 15a.

In the solid-state image sensor of this embodiment, FIG. 3 shows a pattern of a subject on a monitor screen when a stripe-shaped pattern having the same pitch as the vertical pitch of the light-receiving portions of the solid-state image sensor is formed on the light-receiving surface. FIG. 9 is a timing chart of drive pulses for driving so as to be reproduced. The charges generated in the odd-numbered light-receiving portions of the light-receiving portions arranged in the vertical direction are transferred to the first output portion 15a by the first horizontal transfer portion 14a and output in the odd-numbered field. In the even-numbered field, the data is first transferred to the first horizontal transfer unit 14a within the horizontal blanking period, then transferred to the second horizontal transfer unit 14b, and output from the second output unit 15b. On the other hand, regarding the charges generated in the even-numbered light-receiving portions, the horizontal transfer portion and the output portion used in the odd-numbered field and the even-numbered field are opposite to those in the case of the odd-numbered light-receiving portion. That is, in an odd field, the data is transferred to the second horizontal transfer unit 14b via the first horizontal transfer unit 14a and output from the second output unit 15b via the second horizontal transfer unit 14b.
In the even field, the first horizontal transfer unit 14a transfers and outputs the first horizontal output unit 15a.

When the solid-state image pickup device of FIG. 1 is driven in this way, the voltage gains of the first output section 15a and the second output section 15b are different, so that the sensitivities of the light receiving sections arranged in the horizontal direction alternate. It will be in a different state. First and second output section 15
The signal voltages obtained in a and 15b are added in the adder 16. This addition operation corresponds to the operation of mixing the charges of the odd-numbered and even-numbered light receiving portions in the frame interline solid-state image sensor, and with this configuration, the image formation pattern of the subject on the light-receiving surface of the solid-state image sensor is Even if the vertical interval is reduced to the vertical pitch of the light receiving portions of the image sensor, the pattern of the subject can be reproduced on the monitor screen as in the case shown in FIG. 8E. Moreover, in the present invention, since the electric charge sweeping operation is not performed, the same amount of electric charge as that in the normal field accumulation can be used as a video signal, so that the S / N ratio as in the conventional example in which the sweeping operation is performed is performed. Does not occur. Incidentally, in the solid-state image sensor according to the present invention,
Since the signal charges of two pixels vertically adjacent to each other are transferred to the horizontal transfer unit without being mixed in the vertical transfer unit,
It is necessary that the electrode structure of the vertical transfer unit is three phases or more per one light receiving unit.

The preferred embodiment has been described above.
The present invention is not limited to the above embodiment,
Various modifications can be made within the scope of the present invention described in the claims. For example, in the embodiment, the first,
Although the charge-voltage conversion efficiency of the second output section is fixed, it is possible to change the voltage gain of either or both of them to be variable. The voltage gain can be changed, for example, by connecting an additional capacitance to the floating diffusion layer.

[0018]

As described above, in the solid-state image pickup device of the present invention, the horizontal transfer section is divided into the first horizontal transfer section and the second horizontal transfer section, and the first and second horizontal transfer sections have different voltage gains. An output unit that connects the 1st output unit and the 2nd output unit and outputs the electric charge generated in the odd-numbered light-receiving unit and the electric charge generated in the even-numbered light-receiving unit among the light-receiving units arranged in the vertical direction. Since the unit is divided into the first output unit and the second output unit, and the output units are alternately switched for each field, according to the present invention, the S / N ratio of the output video signal is not reduced. It is possible to reproduce, on the monitor screen, an imaging pattern that has been miniaturized to the vertical pitch of the light receiving portions of the solid-state imaging device.

[Brief description of drawings]

FIG. 1 is a schematic plan view showing the configuration of an embodiment of the present invention.

FIG. 2 is a cross-sectional view taken along the line AA ′ in FIG. 1, a potential distribution diagram in the cross section, and a timing diagram of drive pulses applied to each transfer electrode.

FIG. 3 is a timing diagram of drive pulses for the first and second horizontal transfer electrodes of the solid-state image sensor of FIG.

FIG. 4 is a schematic plan view of a conventional interline solid-state imaging device.

FIG. 5 is an operation explanatory diagram of FIG. 4;

FIG. 6 is a schematic plan view of a conventional frame interline type solid-state imaging device.

FIG. 7 is a timing diagram of drive pulses for the solid-state imaging device shown in FIG.

FIG. 8 is an operation explanatory diagram of the solid-state imaging device shown in FIG. 6.

[Explanation of symbols]

 11, 41, 61 Light receiving part 12, 42, 62 Vertical transfer part 13, 43, 63 Charge reading part 14a First horizontal transfer part 14b Second horizontal transfer part 44, 64 Horizontal transfer part 15a First output part 15b Second output section 45, 65 Output section 16 Addition section 21 p-well 22 n-type diffusion layer 23 Vertical transfer electrode 24a First horizontal transfer electrode 24b Second horizontal transfer electrode 67 Charge storage section 68 Charge sweep section

Claims (4)

[Claims] 1. A plurality of light receiving portions arranged in a matrix, and a vertical transfer portion arranged in each vertical column of the light receiving portions, for vertically transferring the charges generated by photoelectric conversion in the light receiving portions. , A first horizontal transfer unit that transfers charges transferred from the vertical transfer unit in the horizontal direction, and the first horizontal transfer unit that is provided on the opposite side of the first horizontal transfer unit from the light receiving unit. A second horizontal transfer section for horizontally transferring the charges read from the unit, a first output section for converting the charges transferred from the first horizontal transfer section into a voltage signal, and the second horizontal transfer section. A second output unit that converts the charge transferred from the transfer unit into a voltage signal and has a voltage gain different from that of the first output unit; the first output unit and the second output unit;
An adding unit that adds the voltage signals from the output unit of
The solid-state imaging device, wherein the charges transferred from the vertical transfer unit can be transferred to either the first horizontal transfer unit or the second horizontal transfer unit. 2. The even-numbered photodetector outputs the electric charge generated by an odd-numbered photodetector of the photodetectors arranged in the vertical direction by using either the first output unit or the second output unit. 2. The solid-state imaging device according to claim 1, wherein the electric charge generated by the light-receiving unit is output from an output unit other than the output unit that outputs the electric charge generated by the odd-numbered light-receiving unit. 3. An output unit for outputting charges generated by odd-numbered light-receiving units of the light-receiving units arranged in the vertical direction and an output unit for outputting charges generated by even-numbered light-receiving units are arranged for each field. 3. The solid-state image sensor according to claim 1, wherein the solid-state image sensor is replaced with. 4. The solid-state image sensor according to claim 1, wherein one or both of the first output section and the second output section are capable of changing the voltage gain thereof.