JP2002112116A - Image pickup device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image pickup device that suppresses occurrence of a charge inverse injection due to the application of a high-voltage TG(transfer gate) pulse, so as to reduce the occurrence of pseudo-signals resulting from the TG pulse. SOLUTION: A TG block 106 controls the generation timings of the TG pulses TG1-TG5 respectively, corresponding to TG electrode divisions resulting from dividing a TG electrode. Since fluctuations in potential by the TG pulses are dispersed temporally by deviating the generating timing of the TG pulses TG1-TG5, the pseudo-signals due to electric charge inverse injection can be reduced. By overlapping the leading and trailing between one TG pulse with the other TG pulse, one can especially cancel the potential fluctuations, so as to efficiently reduce the production of the pseudo-signals due to the electric charge inverse injection.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image pickup apparatus, and more particularly to an image pickup apparatus for picking up a subject image using a solid-state image sensor such as a CCD.

[0002]

2. Description of the Related Art In recent years, digital still cameras (electronic cameras) for capturing a subject image with a solid-state imaging device such as a CCD and obtaining a video signal have been actively developed. In particular, recently, an image sensor tends to have a large number of pixels and a large area.

Accordingly, the readout time of one image increases in proportion to the number of pixels, so that the frame rate is required to be used for moving image recording, monitor output (electronic viewfinder function), and automatic control functions such as AF and AE. However, there is a difficulty that data is insufficient, and a high-speed (high frame rate) readout technique for solving this problem has been proposed.

One of such devices is disclosed in Japanese Patent Application Laid-Open No. 10-32.
There is a technique described in Japanese Patent Publication No. 2601. This is a vertical transfer clock of a plurality of transfer units corresponding to a plurality of pixels (rows) in a horizontal blanking period, which is a horizontal transfer stop period for each horizontal transfer period, in an all pixel readout type (sequential scanning type) solid-state imaging device. In the case of using the so-called vertical addition drive for outputting the signal charges, when the signal charges are read out from the photoelectric conversion storage unit to the vertical transfer path, the “rearrangement” for changing the arrangement order of the charges is performed, so that each row such as an RGB Bayer arrangement is performed. Even if a color-coded image sensor in which different colors are arranged is used, the same color charge addition can be performed. Use of this rearrangement addition readout technique is extremely advantageous in that a color image with a high frame rate can be obtained by trade-off with the number of vertical pixels (vertical resolution).

In order to rearrange the signal charges,
Recently, a transfer electrode (Transfer) for reading out (transferring) signal charges from a photoelectric conversion storage unit to a vertical transfer path.
Gate (TG electrode) is not considered to be all commonly connected as in the prior art, but various configurations have been started to be considered as periodic common connections.

Of course, when it is not necessary to perform the special signal reading as described above, that is, when charges are simultaneously transferred from the photoelectric conversion storage unit to the vertical transfer path, this transfer can be performed simultaneously for all pixels. In the related art, it is natural that the exposure timing of all pixels is completely the same.

[0007]

However, on the other hand, with the increase in the number of pixels and the area of the image pickup device, problems that have not been a problem in the past may become apparent. Specifically, when a charge transfer gate drive pulse (TG pulse) for transferring charges from the pixel portion (photoelectric conversion region) to the vertical transfer path is applied, the substrate potential in the vicinity of the pixel portion greatly changes. For this reason, a charge reverse injection phenomenon from the semiconductor substrate may occur, which may cause a pseudo signal.

More specifically, in a general CCD image pickup device of, for example, a four-phase drive system, the transfer electrodes of the vertical transfer path have four phases (that is, four corresponding drive input terminals). A high voltage (TG pulse (exemplary value +15 V)) having a polarity opposite to that during normal charge transfer (exemplary value -7 V) is applied to the electrode, which is assigned to charge transfer from the photoelectric conversion region to the vertical transfer path. This causes charge transfer. In other words, one phase also serves as a transfer electrode and a charge transfer gate electrode (transfer gate electrode) for charge transfer, and therefore, a high voltage TG pulse is required.

Since the TG pulse is at a high voltage as described above, the potential of the semiconductor substrate (substrate) is disturbed at the start (rise) and end (fall) of the voltage application, and as a result, the pixel portion is disturbed. However, there is a high possibility that the charge reverse injection from the semiconductor substrate (substrate) occurs.

[0010] The present invention has been made in view of the above circumstances, and an object of the present invention is to effectively reduce the generation of a pseudo signal due to a TG pulse.

[0011]

In order to solve the above problems, the present invention provides a solid-state imaging device capable of driving a charge transfer gate from an image section constituting a pixel array to a vertical transfer path by dividing the gate into a plurality of phases. An image pickup apparatus comprising: an element; and a driving unit that supplies a plurality of charge transfer gate driving pulses (TG pulses) corresponding to the plurality of phases to the solid-state imaging device. When performing simultaneous charge transfer from all the pixel units, at least the plurality of charge transfer gate drive pulses (TG pulses) are transferred at timings such that simultaneous rise and fall do not occur. It is characterized in that it is configured to output a gate drive pulse (TG pulse).

This image pickup apparatus employs a structure in which a drive line of a charge transfer gate is divided into a plurality of lines and driven, and by adjusting the generation timing of a plurality of TG pulses, all the pixel portions in the pixel array are simultaneously controlled. Even when charge transfer is performed, simultaneous rise and fall do not occur between all of the plurality of TG pulses.
Thereby, for example, even when performing sequential scanning readout (progressive scanning) of individual information of all pixels,
Since the potential fluctuation due to the TG pulse is temporally dispersed, it is possible to reduce the pseudo signal due to the reverse charge injection.

In controlling the drive timing of the plurality of TG pulses, it is preferable to use timing such that at least one TG pulse rises simultaneously with another TG pulse fall. This makes it possible to cancel the potential fluctuation caused by the rise of a certain TG pulse and the potential fluctuation caused by the fall of another TG pulse, so that it is possible to greatly reduce the pseudo signal due to the reverse charge injection.

In the above-described driving control of a plurality of TG pulses, N (N ≧ N) of the plurality of TG pulses are simultaneously selected.
At the timing when the rising or falling of the TG pulse occurs in 2), control is performed so that at least the falling or rising of the N-1 TG pulses occur at the same time, and the simultaneous rising or falling of two or more TG pulses occurs simultaneously. It is desirable not to cause isolation by itself. This makes it possible to minimize potential fluctuations caused by overlapping of falling edges or rising edges.

[0015]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a configuration of an imaging device according to an embodiment of the present invention. Here, a case where the present invention is implemented as a digital camera will be described as an example.

In FIG. 1, reference numeral 101 denotes a lens system including various lenses; 102, a lens driving mechanism for driving the lens system 101; 103, an exposure control mechanism for controlling the diaphragm of the lens system 101; 104, a mechanical shutter; CCD color imaging device with a built-in Bayer color filter,
Reference numeral 106 denotes a TG block (timing generator TG, TG) which is a CCD drive circuit for driving the image sensor 105.
And SG), 107 is a pre-processing circuit (including a CDS which is a sample and hold circuit, a clamp circuit, an A / D converter, etc.) which is a pre-processing circuit for the CCD output signal, and 108 is a color signal generation process, a matrix conversion process , A digital process circuit for performing various digital processing, 109 is a card interface, 110
Denotes a memory card, and 111 denotes an LCD image display system.

As the CCD image pickup device 105, a progressive scan type (sequential scanning) type having an interline structure is used. In addition, a charge transfer gate electrode (TG electrode; transfer gate electrode) of the CCD image pickup device 105
Are divided into a plurality of phases (n phases), and the TG electrodes can be individually driven for each phase. That is, in order to perform the special driving by the conventionally known rearrangement addition readout, it is necessary to selectively transfer the electric charges from each pixel portion (photoelectric conversion region) to the vertical transfer path, not all the pixels at once. To realize such a function, TG
The electrodes are divided into groups of electrodes having an n-row cycle in order to perform the above-described selective charge transfer, and a charge transfer gate drive pulse (TG pulse) can be independently applied to each of the electrode groups.

In the present embodiment, n = 5 and the same periodic electrode group (line group) configuration is used. In response to these, C.sub.G is set using independent TG pulses TG1 to TG5.
It is assumed that the CD imaging device 105 is driven. These TG1 to TG5 (+ 15V) are output from the TG block 106, and the generation timing of TG1 to TG5 is controlled by the TG block 106.

That is, the charge transfer is performed all at once (for example, when reading all the pixels individually (sequential scanning) or when performing a well-known n-line addition drive of adding and reading all the vertical n lines by a horizontal transfer path). When it is necessary to perform the operations simultaneously (simultaneously), it is usually necessary to simultaneously generate TG1 to TG5 to transfer the signal charges of all the pixels from the pixel portion to the vertical transfer path. ~ TG5
In order to prevent the charge reverse injection phenomenon due to the simultaneous occurrence (simultaneous rise and fall) of the TG block 106,
TG1 to TG5 are adjusted so that the rising edges and the falling edges of TG1 to TG5 do not all overlap at the same time.

In the figure, reference numeral 112 denotes a system controller (CPU) for overall control of each unit, 113 denotes an operation switch system including various operation buttons, and 114 denotes an operation for displaying an operation state, a mode state, and the like. Display system, 1
Reference numeral 15 denotes a lens driver for controlling the lens driving mechanism 102, 116 denotes a flash as a light emitting unit, 117 denotes an exposure control driver for controlling the flash 116 and the exposure control mechanism 103, and 118 denotes various setting information and the like. 1 shows a nonvolatile memory (EEPROM).

In the digital camera of the present embodiment,
The system controller 112 performs overall control, and in particular, controls the driving of the CCD image pickup device 105 by using the TG block 106 to perform exposure (charge accumulation) and signal reading, and the pre-processing circuit The data is taken into the buffer memory of the digital process circuit 108 via 107, subjected to various signal processings, and recorded on the memory card 110 via the card interface 109.

In the digital camera of the present embodiment,
Except for the above-described portions relating to the timing adjustment of TG1 to TG5, operations and controls similar to those of a normal digital camera are performed, and description of such known portions will be omitted.

Next, referring to FIG.
The basic electrode structure 05 will be described. In the CCD image pickup device 105, photoelectric conversion regions (pixel portions) including photodiodes are arranged in a matrix of rows and columns, and a vertical transfer path is provided for each pixel portion of one column in the vertical direction. A common horizontal transfer path is provided for each of the vertical transfer paths. FIG. 2 shows only the structure corresponding to the pixel portion for one column in the vertical direction and the corresponding vertical transfer path.

In FIG. 2, p1, p2, p3, p4
p5,... indicate pixel portions, and a, b, c, d are 4
The drive electrode (VCCD) of the vertical transfer path of the phase drive system is shown. Electrode a of these drive electrodes (VCCD)
Also serve as a transfer electrode (Transfer Gate: TG electrode) for transferring charges from the pixel portion to the vertical transfer path. The electrode a has a higher voltage TG than when the vertical transfer path is driven.
By applying the pulse, the charge is transferred from the pixel portion to the vertical transfer path. The electrodes b, c, and d are common to all pixel units. The electrode a (TG electrode) is common in the pixel units in the horizontal direction (row direction) in order to realize various same-color addition driving and pixel order rearrangement, but has an n-row cycle in the vertical direction, Each row is divided into electrode groups corresponding to each row. Of course, in the present embodiment, the purpose is to temporally disperse the degree of potential fluctuation due to the application of the TG pulse, so that any CCD image pickup device having an electrode structure capable of applying a plurality of TG pulses may be used. Is not limited.

Next, with reference to FIG. 3 to FIG. 7, the generation timing of TG1 to TG5 when it is necessary to transfer the signal charges of all the pixels from the pixel portion to the vertical transfer path will be described.

FIG. 3 shows a normal timing at which all of TG1 to TG5 are simultaneously generated. In this case, TG1
TG5 rise and fall at the same time, the potential of the semiconductor substrate (substrate) is greatly disturbed at the start (rise) and end (fall) of the voltage application, and a pseudo signal is generated. Is caused.

FIG. 4 is a first timing example used in the present embodiment. As shown in FIG. 4, TG1 to TG5
Are sequentially generated at intervals of Δt. Thereby, the potential fluctuations at the time of generation and termination of the TG pulse are dispersed in time, as compared with the case where the generation timings of all the TG pulses overlap as shown in FIG.
The peak value of the potential fluctuation can be greatly reduced.

The value of Δt is a period from the fall of the preceding TG pulse to the rise of the subsequent TG pulse, and the value of Δt can be set arbitrarily. For example, the pulse width of each TG pulse is 2 μs and Δt is 1 μm.
In the case of s, the time T (the entire TG pulse width) required from the generation of the first TG pulse to the end of the generation of the last TG pulse is 14 μs, but by setting Δt to 0 μs, T
Can be set to 10 μs. The value of the total TG pulse width T corresponds to the shift amount of the exposure time (more precisely, T
The value obtained by subtracting the TG pulse width of 2 μs from the above is the shift amount. Therefore, it is preferable that the shift amount be as short as possible. However, when the ratio of the shift amount T to the original exposure time is within a certain value or less (eg, about 1% or less). If so, the effect on the imaging signal can be ignored.

When Δt is set to 0 μs, the fall of the preceding TG pulse and the rise of the subsequent TG pulse overlap, so that the potential change due to the fall of the TG pulse and the potential change due to the rise of the TG pulse are different. The offset makes it possible to more efficiently reduce the potential fluctuation.

FIG. 5 is a second timing example used in the present embodiment. As shown in FIG. 5, TG1 to TG5
Are generated sequentially at intervals of, for example, half the pulse width (1 μs) such that the pulse generation periods partially overlap. As a result, the time T required from the generation of the first TG pulse to the end of generation of the last TG pulse can be reduced to 6 μs. Further, the falling edge of TG1 and the rising edge of TG3 occur at the same time. Similarly, the falling edge of TG2 and the rising edge of TG4, and the falling edge of TG3 and the rising edge of TG5 occur at the same time. Fluctuations can be suppressed.

FIG. 6 is a third timing example used in the present embodiment. Here, it is assumed that up to two TG pulses, even if the simultaneous rise and fall thereof occur, the potential fluctuation caused by the simultaneous rise and fall is within an allowable range and the charge reverse injection phenomenon does not occur. That is, in FIG. 6, first, TG1 and TG2 are generated at the same time, and then TG1 and TG2 are simultaneously generated at the same time as the fall of TG1 and TG2.
3 and TG4 are generated simultaneously. And TG3 and TG
TG5 is generated at the same time as the falling edge of TG4. In this example, the simultaneous rise of the two TG pulses occurs solely at the timing when TG1 and TG2 are first generated. When the simultaneous rise of TG3 and TG4 occurs, the simultaneous fall of TG1 and TG2 occurs simultaneously. As such, potential fluctuations are offset. Furthermore, T
At the timing of simultaneous falling of G3 and TG4, TG5
Rises, the potential change is only the rise of one TG pulse.

FIG. 7 is a fourth timing example used in the present embodiment. In this example, the pulse generation timing is adjusted so that the simultaneous rise or fall of two or more TG pulses does not occur independently by itself. That is, first, TG1 is generated alone, and TG2 is generated simultaneously with the fall of TG1. Next, simultaneously with the falling of TG2, TG3 and TG
4 are generated simultaneously. In this case, the potential change is only the rising edge of one TG pulse.
Then, TG5 is generated at the same time when TG3 and TG4 fall. Also in this case, the potential variation is only the falling edge of one TG pulse.

As described above, in the present embodiment, T
By dividing the G electrode into a plurality of parts and adjusting the generation timing of a plurality of TG pulses corresponding to each of the plurality of divided TG electrodes, it is possible to prevent occurrence of a charge reverse injection phenomenon caused by application of a high-voltage TG pulse. can do.

Although the generation timing of the TG pulse is adjusted in the present embodiment, the pulse width of each TG pulse may be adjusted together. Further, the control of the TGs 1 to 5 according to the present embodiment is not limited to a digital still camera, but can be applied to any imaging device including a movie camera.

Further, the present invention is not limited to the above-described embodiment, and can be variously modified in an implementation stage without departing from the gist thereof. Further, the embodiments include inventions at various stages, and various inventions can be extracted by appropriately combining a plurality of disclosed constituent elements. For example, even if some components are deleted from all the components shown in the embodiment, the problem described in the column of the problem to be solved by the invention can be solved, and the effects described in the column of the effect of the invention can be solved. If you get
A configuration from which this configuration requirement is deleted can be extracted as an invention.

[0036]

As described above, according to the present invention,
The generation of a pseudo signal due to the TG pulse can be effectively prevented. In particular, by overlapping the rise and fall of a certain TG pulse with another TG pulse, potential fluctuations can be canceled out, and the generation of a pseudo signal due to charge reverse injection can be greatly reduced.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of an imaging apparatus according to an embodiment of the present invention.

FIG. 2 is an exemplary view for explaining a basic electrode structure of a solid-state imaging device used in the imaging device of the embodiment.

FIG. 3 is a diagram for explaining a normal timing at which all of TG1 to TG5 are simultaneously generated.

FIG. 4 is an exemplary view for explaining a first example of generation timing of TG1 to TG5 in the embodiment.

FIG. 5 is an exemplary view for explaining a second example of generation timing of TG1 to TG5 in the embodiment.

FIG. 6 is an exemplary view for explaining a third example of generation timing of TG1 to TG5 in the embodiment.

FIG. 7 is an exemplary view for explaining a fourth example of generation timing of TG1 to TG5 in the embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 101 ... Imaging lens 102 ... Lens drive mechanism 103 ... Exposure control mechanism 104 ... Mechanical shutter 105 ... CCD color imaging element 106 ... TG block 107 ... Pre-process circuit 108 ... Digital process circuit 112 ... System controller 1a-5a ... TG electrode

Claims (3)

[Claims] 1. A solid-state imaging device capable of driving a charge transfer gate from an image section constituting a pixel array to a vertical transfer path by dividing the charge transfer gate into a plurality of phases, and a plurality of charge transfer gates corresponding to the plurality of phases. A driving unit that supplies a driving pulse (TG pulse) to the solid-state imaging device, wherein the driving unit is configured to perform at least the plurality of driving when simultaneously transferring charges from all pixel units in the pixel array. The plurality of charge transfer gate drive pulses (TG pulses) are output at timings such that the rise and fall of all the charge transfer gate drive pulses (TG pulses) do not occur simultaneously. An imaging device characterized by the above-mentioned. 2. The method according to claim 1, wherein the driving means includes at least one of the plurality of charge transfer gate driving pulses (TG pulses).
2. The imaging apparatus according to claim 1, wherein the plurality of charge transfer gate drive pulses (TG pulses) are output at timings such that a rise of a G pulse and a fall of another TG pulse occur simultaneously. 3. The driving means according to claim 2, wherein said driving means comprises a plurality of charge transfer gate driving pulses (TG pulses) simultaneously (N ≧ N).
At the timing at which the rising or falling of the TG pulse occurs in 2), the plurality of charge transfer gate drive pulses (TG pulses) are output so that at least the falling or rising of the N-1 TG pulses occur simultaneously. The imaging device according to claim 1, wherein: