JP2000299818A - Method for driving ccd type image pickup device and ccd type image pickup device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the buildup characteristic of an amplifier from having effect on an effective video signal and also to correct the scatter of an output terminal characteristics provided in each image pickup element by accumulating reference signal charges in the preliminarily defined number of preliminary gates and reading the accumulated reference signal charge just before a horizon tal effective video period. SOLUTION: Charges are transferred in the direction opposite to the normal transfer direction by adjusting the pulse timing of R1 to R3 and RL gates and injection negative charges are accumulated at a preliminary gate part. When accumulation is completed, video signal charges are transferred under the R2 and R3 gates of a gate of a horizontal charge transfer CCD by a TCK pulse and subsequently, the negative charges of the R2 gate are transferred under the R3 gate, both of them are put together, the horizontal charge transfer CCD is transferred in a forward direction to read a signal. Thus, the injection negative charges accumulated under the preliminary gate are read as an output signal, and subsequently, signal charges are continuously outputted.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a CCD type image pickup device having two or more output terminals, or two or more CCDs.
The present invention relates to a driving method of a CCD imaging device when a CCD imaging device is configured using the imaging device, and a CCD imaging device.

[0002]

2. Description of the Related Art Conventionally, in an image pickup device having a plurality of output terminals or an image pickup device having a plurality of image pickup devices such as a three-plate type or a four-plate type image pickup device, variations in the output characteristics of each signal output terminal are known. For the correction, there is a method of adjusting an offset component due to an optical black level signal, or a method of adjusting a gain of an external circuit. When the output terminal characteristics are to be corrected with higher accuracy, the characteristics of each output terminal are measured in advance, the data is stored in a memory, and the correction process is performed by a digital signal processing circuit. There is a way.

As for an amplification type solid-state imaging device, there is also known a technology of providing a reference signal generating circuit in the device to adjust the gain of an output amplifier (see Japanese Patent Application Laid-Open No. 8-289204).

[0004]

Among the above-mentioned methods, the method using a memory cannot cope with the temperature fluctuation of each output terminal characteristic and can temporarily correct the characteristic variation of each terminal. As time elapses, vertical stripes, boundaries, shifts in each region, and the like due to characteristic variations appear on the screen.

The technique disclosed in Japanese Patent Application Laid-Open No. 8-289204, which is capable of correcting variations in output circuits, is applicable to a MOS-type or amplifying-type image sensor which handles signal charges of the image sensor as current or voltage. However, the same technique cannot be applied to a CCD type image pickup device that handles a photoelectrically converted charge signal as a charge up to a detection amplifier.

Recently, in order to improve the output data rate of the image pickup device, not only the image pickup device has a plurality of output terminals but also a multi-output device which divides a light receiving surface into regions and has an output terminal in each region. Structural imaging devices have been developed. In an image sensor having such a structure, since there is no area for forming a dummy pixel at a region boundary, an effective video signal is output immediately when the signal reading operation is started, and the first pixel of the first pixel is affected by the rising characteristic of an amplifier on the image sensor. The phenomenon that the output level is different from the output levels of the other pixels has become a problem.

Further, the ringing characteristics of a circuit or a filter used outside the image pickup device may cause noise such as overshoot and undershoot at a boundary portion of a video period. Actually, the HDTV studio standard defines a period that is a little shorter than the effective image period called a clean aperture because it is a period that does not include such noises separately from the effective image period. In an image sensor which reads out such noise by dividing the light receiving surface,
After synthesizing the video signal, a boundary line is generated at the boundary of the divided area, which greatly affects the image quality of the captured video.

An object of the present invention is to provide a CCD type solid-state image pickup device having two or more output terminals or a CCD type image pickup device using two or more image pickup devices when outputting a video signal. Prevents the rise characteristics of the amplifier from affecting the effective video signal, corrects the variations in the characteristics of the output terminals provided on each image sensor, and effectively controls the dynamic characteristics of the external signal processing circuit. An object of the present invention is to provide a driving method of a CCD type image pickup device and a CCD type image pickup device which do not appear in a video signal.

[0009]

In order to achieve the above object, according to the present invention, a reference signal or a dummy signal having a continuity as a pixel level (hereinafter referred to as a reference signal) is provided immediately before a horizontal effective video period in an image sensor. Output)
In addition, the present invention provides a CCD type imaging device that outputs a dummy signal immediately after the horizontal effective video period, which reduces the adverse effect on the video output during the horizontal effective video period due to variations in characteristics of the output terminals of each image sensor. The purpose is to do. Further, the present invention provides a novel CCD type image pickup device driving method which generates the above-mentioned reference signal and dummy signal without changing the element configuration of the existing CCD type image pickup device at all. Further, by correcting the characteristics of the output circuit of the CCD type imaging device with reference to the reference signal, real-time correction is possible, and it is possible to cope with a temporal change in the output circuit characteristics.

That is, in the driving method of the CCD type image pickup device according to the present invention, the read signal reset transistor is turned on for a predetermined period, and the potential of the reset power supply connected to the read signal reset transistor is changed to the horizontal charge during the period. By lowering the potential barrier level at the SG gate of the transfer CCD, a reference signal charge of a predetermined level is injected below the preliminary gate at the final stage of the horizontal charge transfer CCD, and the charge transfer direction of the horizontal charge transfer CCD is changed to an effective image. By applying a transfer pulse having a timing opposite to the transfer direction of the period to the horizontal charge transfer CCD, the reference signal charge is accumulated in a predetermined number of spare gates inside the horizontal charge transfer CCD, The stored reference signal charge is read immediately before a horizontal effective video period. It is characterized in that it has as to be in.

Further, in the driving method of the CCD type image pickup device according to the present invention, the height of the potential barrier level is adjusted by controlling the voltage applied to the SG gate electrode immediately before the injection of the reference signal charge, thereby making the preliminary It is characterized in that the amount of signal charge injected under the gate is adjusted so that the injected charge can be controlled to an arbitrary level.

Further, in the driving method of the CCD type image pickup device according to the present invention, the read signal reset transistor is turned off for a predetermined period immediately after the horizontal effective image period of the CCD type image pickup device. It is characterized in that an output at a pixel level can be held.

Further, the CCD type image pickup device of the present invention comprises a CCD type image pickup device or a plurality of CCD type image pickup devices having a light receiving area divided into a plurality of areas and having an image signal output terminal for each of the divided areas. In the CCD imaging device configured using the CCD imaging device, the CCD imaging device is a CCD imaging device to which a reference signal having a predetermined level is added and output in a period immediately before a horizontal effective image period. Things.

The CCD type imaging apparatus of the present invention further comprises a reference power supply for adjusting a potential barrier level, and the SG of the horizontal charge transfer CCD immediately before injecting a signal charge corresponding to the reference signal level for adding the reference signal. By adjusting the height of the potential barrier level by controlling the voltage applied to the gate electrode, the amount of injected charge is adjusted, and the reference signal level can be arbitrarily varied. .

Further, the CCD type image pickup apparatus of the present invention is turned off for a predetermined period immediately after the horizontal effective image period so that the output of the last pixel level of the horizontal effective image period of the CCD type image pickup device can be held. A read signal reset transistor is provided.

Further, the CCD type imaging apparatus according to the present invention further comprises a gain control amplifier whose amplifier gain is controlled by a signal related to the reference signal.

Further, the CCD type imaging apparatus according to the present invention is characterized in that
The reference signal having a predetermined level added in a period immediately before the horizontal effective video period of the CD-type image sensor is a reference signal including a plurality of levels each having a predetermined level. .

Further, the CCD type imaging apparatus according to the present invention divides a light receiving area into a plurality of areas, and uses a CCD type imaging device having an imaging signal output terminal for each of the divided areas. In the device, the SG gate electrode of the horizontal charge transfer CCD for each region is connected to the region where the leftmost pixel of each region is adjacent to another region during a period immediately before the horizontal effective video period for each region. It is an SG gate electrode whose applied voltage is controlled such that the level of the reference signal to be added is the same as the level of the pixel in the rightmost column one line before the adjacent region.

Further, the CCD type imaging apparatus of the present invention has
The G gate electrode further includes a horizontal charge transfer CC for each of the regions.
D is an SG gate electrode whose applied voltage is controlled so that signals of different levels are respectively injected into a plurality of charge storage cells in the spare gate.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below based on embodiments of the present invention with reference to the accompanying drawings. Prior to describing the present invention, for comparison with the present invention, first,
A driving method of a conventional CCD image sensor will be described.
FIG. 1 shows a configuration around an output amplifier of a conventional CCD image sensor using a three-phase transfer method as a horizontal charge transfer CCD.

In FIG. 1, the general flow of signal charges in a CCD type image pickup device is as follows. That is, the signal charge (minus charge) photoelectrically converted by the light receiving unit
Is transferred to a horizontal charge transfer CCD for each line via a vertical charge transfer CCD (not shown). R1, R in FIG.
2 and R3 are three-phase transfer gates that handle signal charge transfer of one pixel. The signal charges transferred to the horizontal charge transfer CCD are sequentially transferred to the left by driving the horizontal charge transfer CCD with three-phase driving pulses.
From the last gate RL through the gate SG set to a constant bias, and transferred to the node A. Node A
The charge is charged in the charge detection capacitor C, converted into a voltage signal, amplified by an output amplifier, and then output from the output terminal of the image sensor.

Charge detection capacitance C charged by signal charge
Next, the reset gate RG is turned on to reset to a constant reset potential Vd. After the reset, the reset gate RG is turned off to prepare for charging the signal charge of the next pixel. By repeating this operation, the signal charges of the pixels can be read one after another. During the horizontal blanking period, the operation of the horizontal charge transfer CCD is stopped, so that no charge is transferred to the node A and the reset gate R
Only G is ON / OFF. The above is the description of the operation of the related art.

Next, a driving method of the CCD type image pickup device according to the present invention will be described. FIG. 2 shows the timing of the driving pulse in the driving method of the CCD type imaging device of the present invention. According to the driving method of the present invention, the reset potential V
By basically lowering d, the reference signal charge (minus charge) is injected into the horizontal charge transfer CCD, and is read out as a reference signal at the time of reading out the next signal charge.

This is because, in principle, the reset gate RG is turned on during a part of the horizontal blanking period, and during that time, the reset electric potential Vd is lowered below the potential barrier level immediately below the SG gate to transfer the negative electric charge to the horizontal electric charge transfer. C
This is achieved by injection under the RL gate of the CD.

Actually, as shown in FIG. 2, the reset gate RG is driven at the clock frequency of the horizontal charge transfer CCD during the horizontal blanking period in the same manner as when reading out the signal charge.
Even if an operation of repeating N / OFF is performed, the potential of the reset potential Vd reaches the node A during the ON period, so that charges can be injected under the RL gate of the horizontal charge transfer CCD without any problem.

Next, by adjusting the pulse timing of the R1, R2, R3, and RL gates, the charges are transferred in the direction opposite to the normal transfer direction (forward direction), and the injected minus charges are transferred to the spare gate portion ( (See FIG. 1). At the time when the accumulation is completed, the video signal charge from the light receiving section is transferred under the gates R2 and R3 of the horizontal charge transfer CCD by the TCK pulse, and then the negative charge of the gate R2 is transferred under the gate R3 to combine them. Then, a signal is read by transferring the horizontal charge transfer CCD in the forward direction.

As a result, first, the injected negative charges accumulated under the spare gate are read out as an output signal, and thereafter, the signal charges are continuously output. Further, at the time when the last video signal charge is transferred to the charge detection capacitor C, if the reset operation is stopped for a certain period, the level of the last pixel of one line is held and output from the output amplifier of the image sensor.

FIGS. 3A, 3B and 3C show the signal charge readout during the horizontal effective image period, the negative charge injection performed during the horizontal blanking period according to the present invention, and after the negative charge injection. FIG. 4 shows potential diagrams of electrons around an output amplifier of an image sensor when a reset potential is returned to an original potential. First, at the time of reading out signal charges in the horizontal effective image period, as shown in FIG. 3A, the signal charges sent from the horizontal charge transfer CCD are detected at the node A, and after reading out the signal charges, the signal charges are fixed through the reset gate RG. It is absorbed by the potential Vd0.

According to the present invention, at the time of charge injection during the horizontal blanking period, as shown in FIG. 3B, first, at the time of reading, the voltage of the last-stage gate RL of the pulse-driven horizontal charge transfer CCD is increased. (Lower the potential of the electrons) so as to be able to accumulate the charges, and then raise the reset potential Vd above the potential level under the SG gate (lower the potential) to reduce the nodes A and S
The charge is injected under the G and RL gates. After the charge injection, the set potential Vd is restored to the original Vd as shown in FIG.
By returning to 0, unnecessary injected charges are absorbed and SG
A charge corresponding to the potential difference between the gate and the RL gate remains immediately below the RL gate.

As shown in FIG. 4B, the charge remaining immediately below the RL gate is transferred by one stage in the direction opposite to the normal signal charge readout (see FIG. 4A), thereby obtaining a reference signal. The charge can be sent inside the horizontal charge transfer CCD. By repeating the above operation, the reference signal charges can be accumulated in the spare gate portion in the horizontal charge transfer CCD over a plurality of pixels. By starting driving the horizontal charge transfer CCD immediately before the end of the horizontal blanking period and reading out the signal, a reference signal can be obtained for a certain period immediately before the effective video period, as shown in FIG. Can be prevented from affecting the effective video signal. FIG. 5A shows a case of driving a conventional CCD image sensor to which the present invention is not applied.

Further, as described above, the final pixel level can be output during the reset pulse (pulse applied to the reset gate RG) stop period immediately after the end of the horizontal effective period (see FIG. 5B). The effect of the dynamic characteristics of the external signal processing circuit can be prevented from appearing in the effective video signal.

On the other hand, the reference signal level of the output signal,
In addition, the video signal level is affected by the gain of the output amplifier, and causes a variation in the gain of the video signals read from the plurality of output terminals.

FIG. 6 shows an example of a gain correction circuit for correcting a variation in gain of video signals read from a plurality of output terminals. In this example, a reference signal output for each horizontal line is stored in a capacitor C by a switch SW, a voltage converted by the storage is compared with a reference voltage Vs by a comparator, and the output is used as a gain control signal to output a video signal. It is configured to control the input gain control amplifier. In this way, it is possible to correct variations between the regions of the multi-output structure type imaging device and variations between the plurality of CCD type imaging devices.

FIG. 7 shows that, just before the injection of the signal charge corresponding to the reference signal level, the level of the potential barrier level is adjusted by controlling the voltage applied to the SG gate electrode of the horizontal charge transfer CCD. A driving method of a CCD type image pickup device in which a charge amount is adjusted and a level of a reference signal can be arbitrarily changed is shown. In FIG. 7, by controlling the voltage applied to the SG gate, the barrier level below the SG gate (see FIG. 3) changes, and the amount of charge that can be injected can be controlled.

FIG. 8 shows an example of the configuration of a CCD type image pickup apparatus constructed by this driving method (shown in FIG. 7). In FIG. 8, the pixels in the light receiving area are divided into three areas, a horizontal charge transfer CCD 1 and a horizontal charge transfer CCD.
2 and the horizontal charge transfer CCD 3 respectively. Now, when reading out the pixels on the (n-1) th line, the output levels of the last pixel on the (n-1) th line in the region 1 and the region 2 are turned on by the switches SW1 and SW2.
By doing so, they are stored in the capacitors C1 and C2, respectively.
By applying a DC bias (the output of the differential amplifier in this example) corresponding to the accumulation level to SG2 and SG3, the amount of injected charges accumulated in the spare gates 2 and 3 is made equal to the pixel signal level of can do.

Next, when the reading of the pixels on the n-th line is started, the pixels stored in the spare gate before the first effective pixel in the area 2 and the area 3 are read out,
The same amount of signals as the level of the adjacent pixel is read out, and the discontinuous component caused by the influence of the dynamic characteristic of the external signal processing circuit generated when the area is divided can be suppressed.
This example shows an example in which there are three horizontal charge transfer CCDs. This is a case where the pixels in the light receiving area are divided into two or more areas and two or more horizontal charge transfer CCDs are included. It is always possible as a configuration.

FIG. 9 shows an example of the configuration of a CCD type imaging apparatus in which the adjustment of the amplifier gain can be realized simultaneously in the configuration shown in FIG. In principle, various reference signal levels can be output at the time of output by increasing the number of stages of the spare gate and injecting signals of different levels into a plurality of charge storage cells in the spare gate from the outside.

FIG. 9 shows a specific example in which two charge storage cells R3 (R23 and R13) are provided in the spare gate. First, in the first charge injection, the switch SW
3. SW4 is connected so that a signal of the same level as the pixel output of the adjacent area is injected. The charge is injected, the horizontal charge transfer CCD is driven in the reverse direction, and the injected charge is stored immediately below the gate R23. Next, the switches SW3 and SW4 are connected such that the reference voltage A (which is different from the reference voltage applied to the comparator) is connected to SG1, SG2 and SG3, and a signal having the same level as the reference voltage A is injected. I do. By driving the horizontal charge transfer CCD in the reverse direction, signal charges at the same level as the reference voltage A are accumulated immediately below R23,
Further, the signal charge of the same level as the pixel output of the adjacent region, which has been injected in advance, is transferred to R13 and accumulated.

At the time of signal reading, these injected charges are sequentially read out. First, a signal charge having the same level as the reference voltage A common to each amplifier is read out, and this is used as a reference signal for adjusting the amplifier gain. it can. In addition, the signal charge of the same level as that of the pixel output of the adjacent region to be output next can be used as a signal for correcting the variation between the regions, as in the example shown in FIG.

[0040]

According to the present invention, when a CCD type imaging device having two or more output terminals, or a CCD type imaging device using two or more CCD type imaging devices,
It is possible to accurately correct variations in characteristics of the output terminals of the respective image pickup devices, which have conventionally been regarded as a problem, for each output terminal.

According to the present invention, there is provided a CCD type image pickup device having two or more output terminals, or two or more CCDs.
In the case where a CCD type image pickup device is constructed using a type image pickup device, it is possible to eliminate the level fluctuation of the initial output portion of each line due to the dynamic characteristics of the output circuit and the ringing of the filter or the like in the signal processing circuit.

[Brief description of the drawings]

FIG. 1 shows a configuration around an output amplifier of a conventional CCD image sensor using a three-phase transfer method as a horizontal charge transfer CCD.

FIG. 2 shows the timing of a driving pulse in a driving method of a CCD type imaging device according to the present invention.

FIG. 3 shows an output of an image sensor at the time of reading out signal charges during a horizontal effective video period, at the time of injecting negative charges performed during a horizontal blanking period according to the present invention, and when returning a reset potential to the original potential after injecting negative charges. Each potential diagram of electrons around the amplifier is shown.

FIG. 4 shows a drive pulse timing of a horizontal charge transfer CCD at the time of reading out signal charges during a horizontal effective video period and at the time of injecting negative charges during a horizontal blanking period according to the present invention.

FIG. 5 shows output video signals for one horizontal period obtained by a conventional driving method of a CCD type imaging device and a driving method of injecting a negative charge during a horizontal blanking period according to the present invention.

FIG. 6 illustrates an example of a gain correction circuit that corrects a variation in gain of video signals read from a plurality of output terminals.

FIG. 7: Immediately before the injection of signal charges corresponding to the reference signal level, the height of the potential barrier level is adjusted by suppressing the voltage applied to the SG gate electrode of the horizontal charge transfer CCD, thereby reducing the amount of injected charges. The figure shows a driving method of a CCD type image pickup device that can be adjusted and the reference signal level can be arbitrarily changed.

FIG. 8 is a CCD configured by the driving method shown in FIG.
1 shows an example of a configuration of a portable imaging device.

FIG. 9 shows an example of a configuration of a CCD imaging apparatus in which adjustment of an amplifier gain can be simultaneously realized in the configuration shown in FIG.

Claims (10)

[Claims] 1. A read signal reset transistor is turned on for a predetermined period, and a potential of a reset power supply connected to the read signal reset transistor is lower than a potential barrier level of an SG gate of a horizontal charge transfer CCD during the period. This causes a reference signal charge of a predetermined level to be injected under the preliminary gate at the final stage of the horizontal charge transfer CCD, and further, the timing at which the charge transfer direction of the horizontal charge transfer CCD is opposite to the transfer direction of the effective video period. Transfer pulse of the horizontal charge transfer CCD
So that the reference signal charge is stored in a predetermined number of spare gates inside the horizontal charge transfer CCD so that the stored reference signal charge can be read out immediately before a horizontal effective image period. A driving method for a CCD type image pickup device, characterized in that: 2. The method according to claim 1, wherein a voltage applied to an SG gate electrode is controlled immediately before the injection of the reference signal charge to adjust the height of the potential barrier level. A method of driving a CCD type imaging device, wherein the amount of signal charges injected under the spare gate is adjusted so that the injected charges can be controlled to an arbitrary level. 3. The method for driving a CCD type imaging device according to claim 1, further comprising the step of turning off the read signal reset transistor for a predetermined period immediately after a horizontal effective video period of the CCD type imaging device. Wherein the output of the last pixel level in the horizontal effective video period can be held. 4. A CCD type image pickup device having a light receiving area divided into a plurality of areas and an image pickup signal output terminal for each of the divided areas or a CCD type image pickup apparatus constituted by using a plurality of CCD type image pickup elements. 5. The CCD imaging device according to claim 1, wherein the CCD imaging device is a CCD imaging device to which a reference signal having a predetermined level is added and output in a period immediately before a horizontal effective video period. 5. The CCD type imaging device according to claim 4, further comprising a reference power supply for adjusting a potential barrier level, and immediately before injecting a signal charge corresponding to a reference signal level for adding said reference signal. Horizontal charge transfer CCD
Wherein the voltage applied to the SG gate electrode is controlled to adjust the height of the potential barrier level, thereby adjusting the amount of injected charge and arbitrarily changing the reference signal level. Type imaging device. 6. The CCD type imaging device according to claim 4, wherein said imaging device further holds an output of a final effective pixel level of the horizontal effective video period of the CCD type imaging device. A CCD type imaging device comprising a read signal reset transistor which is turned off immediately after a predetermined period. 7. C according to claim 4, wherein
A CCD type imaging apparatus, wherein the imaging apparatus further includes a gain control amplifier whose amplifier gain is controlled by a signal related to the reference signal. 8. C according to any one of claims 4 to 7,
In the CD imaging device, the reference signal having a predetermined level added in a period immediately before the horizontal effective video period of the CCD imaging device is a reference signal including a plurality of levels each having a predetermined level. C characterized by
CD type imaging device. 9. A CCD type image pickup apparatus comprising a light receiving area divided into a plurality of areas and using a CCD type image pickup device having an image pickup signal output terminal for each of the divided areas. The SG gate electrode of the transfer CCD has a level of a reference signal added to a period immediately before a horizontal effective video period for each region in a region where the leftmost pixel of each region is adjacent to another region. A CCD type image pickup device characterized by being an SG gate electrode whose applied voltage is controlled so as to be at the same level as the level of a pixel in the rightmost column one line before the adjacent region. 10. The CCD type imaging device according to claim 9, wherein the SG gate electrode further injects signals of different levels into a plurality of charge storage cells in a spare gate of the horizontal charge transfer CCD for each area. Characterized in that it is an SG gate electrode whose applied voltage is controlled as described above.
CD type imaging device.