JP2006270593A - Driving method of solid-state image sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of driving a solid-state image sensor capable of achieving a wide dynamic range without a reduction in sensitivity and an increase in horizontal drive frequency. <P>SOLUTION: The solid-state image sensor is equipped with a photosensor unit PS arranged in a matrix, a vertical transfer unit SR<SB>V</SB>and a horizontal transfer unit SR<SB>H</SB>which read out signal charge to transfer, and characterized by the fact that a one field period is divided into two so as to contain a first exposure time and a second exposure time shorter than the first exposure time. A first signal charge C1 is stored in the photosensor unit PS in the first exposure time and transferred to the vertical transfer unit SR<SB>V</SB>, a second signal charge C2 is stored in the photosensor PS in a second exposure time and transferred to the vertical transfer unit SR<SB>V</SB>, the first signal charge C1 and the second signal charge C2 produced in the same photosensor unit PS are mixed together into the mixed signal charge, and the mixed signal charge is transferred in the vertical direction through the vertical transfer unit SR<SB>V</SB>and furthermore transferred in the horizontal direction through the horizontal transfer unit SV<SB>H</SB>. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for driving a solid-state image sensor, and more particularly to a method for driving a CCD image sensor capable of widening the dynamic range.

In recent years, in a CCD image sensor used for a video camera, a digital camera, or the like, an expansion of a dynamic range has been demanded in order to improve image quality.
In order to improve the dynamic range of the CCD image sensor, for example, there is a method in which a long exposure signal generated by long exposure and a short exposure signal generated by short exposure are obtained and synthesized from these signals. Are known.

As the simplest method for obtaining a long exposure signal and a short exposure signal, there is a normal double speed driving method. The long exposure signal can be realized in a normal half period, and the short exposure signal can be realized by controlling the exposure period of the other half period by an electronic shutter function or the like.
However, since this method performs normal double speed driving, the exposure time is halved and the sensitivity is remarkably lowered, and the signal transfer failure occurs in the register section due to the increase in the horizontal driving frequency.

As another driving method, the long exposure signal charges of two adjacent pixels are read and added in the vertical register, and the short exposure signal charges of the adjacent pixels are read after the short exposure time has elapsed. There is a known driving method for obtaining a long-time exposure signal charge and a short-time exposure signal charge by adding them separately from the long-time exposure signal charge.
However, this method has a problem that it cannot be applied to the all-pixel readout method. In addition, since the long exposure signal and the short exposure signal are alternately transferred to double the signal amount of the vertical pixel, there is also a problem that the horizontal drive frequency is higher than that in the normal drive.

Patent Documents 1 and 2 describe a driving method in which one vertical video period as described above is divided into a plurality of parts, and signal charges accumulated during each divided video period are independently moved to the vertical transfer unit. is there.
Japanese Patent Laid-Open No. 9-284654 JP 2003-348458 A

  The problem to be solved by the present invention is that it is difficult to realize a wide dynamic range without lowering the sensitivity or increasing the horizontal driving frequency in the driving method of the solid-state imaging device.

  The solid-state imaging device driving method of the present invention is arranged in a matrix, and is provided adjacent to the photosensor unit that receives light to generate a signal charge, and reads the signal charge in the vertical direction. A solid-state image sensor driving method comprising: a vertical transfer unit that transfers the signal charge from the vertical transfer unit; and a horizontal transfer unit that transfers the signal charge from the vertical transfer unit in a horizontal direction. And one field period is divided so as to include a first exposure time and a second exposure time shorter than the first exposure time, and the first signal charge is generated in the photosensor unit during the first exposure time. A step of transferring the first signal charge to the vertical transfer unit, a step of storing a second signal charge in the photosensor unit during the second exposure time, and a step of storing the second signal charge. Drooping Transferring to the transfer unit and mixing the first signal charge and the second signal charge generated by the same photosensor unit to form a mixed signal charge; and the mixed signal charge in the vertical direction by the vertical transfer unit And a step of transferring the mixed signal charge in the horizontal direction by the horizontal transfer unit.

The above-described driving method of the solid-state imaging device of the present invention includes a photo sensor unit arranged in a matrix, a vertical transfer unit and a horizontal transfer unit that read and transfer signal charges from the photo sensor unit, and has one field period. Is a method of driving a solid-state imaging device that is divided so as to include a first exposure time and a second exposure time shorter than the first exposure time.
The first signal charge is accumulated in the photosensor unit during the first exposure time, the first signal charge is transferred to the vertical transfer unit, and the second signal charge is accumulated in the photosensor unit during the second exposure time. Is transferred to the vertical transfer unit, the first signal charge and the second signal charge generated by the same photosensor unit are mixed and transferred as a mixed signal charge in the vertical direction by the vertical transfer unit, and further in the horizontal direction by the horizontal transfer unit Forward to.

  The solid-state imaging device driving method of the present invention is arranged in a matrix and is provided adjacent to the photosensor unit that receives light to generate a signal charge, and reads the signal charge. A solid-state imaging device driving method having a charge transfer unit for transferring, wherein one field period is divided so as to include a first exposure time and a second exposure time shorter than the first exposure time, A step of accumulating a first signal charge in the photosensor unit during the first exposure time; a step of transferring the first signal charge to the charge transfer unit; and a second of the photosensor unit during the second exposure time. A step of accumulating signal charges, transferring the second signal charge to the charge transfer unit, and mixing the first signal charge and the second signal charge generated by the same photosensor unit to form a mixed signal charge And degree, the mixed signal charge by said charge transfer unit and a step of transferring.

The solid-state imaging device driving method of the present invention includes a photo sensor unit arranged in a matrix and a charge transfer unit that reads and transfers signal charges from the photo sensor unit, and the first exposure is performed in one field period. This is a method of driving a solid-state imaging device that is divided so as to include a time and a second exposure time shorter than this.
The first signal charge is accumulated in the photosensor unit during the first exposure time, the first signal charge is transferred to the charge transfer unit, and the second signal charge is accumulated in the photosensor unit during the second exposure time. Is transferred to the charge transfer unit, and the first signal charge and the second signal charge generated by the same photosensor unit are mixed and transferred as a mixed signal charge by the charge transfer unit.

  According to the driving method of the solid-state imaging device of the present invention, since the first signal charge of long exposure and the second signal charge of short exposure are simply added and read out, the sensitivity is reduced and the horizontal drive frequency is reduced. A wide dynamic range can be realized without increasing the speed.

  Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a configuration diagram of a CCD image pickup device according to the present embodiment. This CCD image sensor is an interlaced all-pixel readout type.
For example, photosensor parts PS that receive light and generate signal charges are arranged in a matrix to form a pixel, and the signal charges generated by the photosensor part PS are read adjacent to the photosensor part PS. Te vertical transfer unit SR _V is provided to transfer in the vertical direction, adjacent an end of the vertical transfer unit SR _V, the horizontal transfer unit SR _H for transferring signal charges from the vertical transfer unit SR _V horizontally provided It has been. For example, the photo sensor unit and the vertical and horizontal transfer units described above are provided on an N-type semiconductor substrate, and a vertical overflow drain that also functions as an electronic shutter is provided for each photo sensor. It is provided in connection with.

Vertical transfer unit SR _V is, for example, a three-phase drive voltage of Vφ1~3 is applied, for example Vφ2 is a read voltage.
The signal charges generated by the photosensor unit PS is transferred to the vertical transfer unit SR _V by driving the vertical transfer unit SR _V, it is further transferred to the horizontal transfer unit SR _H, etc. through the amplifier to the outside as an output VOUT Is output.

  The substrate voltage VSUB is conventionally an unadjusted method and only the substrate clock φSUB is AC-input, but in this embodiment, a voltage adjusted to a predetermined value as described later is DC-input.

2A to 2C are schematic views for explaining a method of driving the CCD image pickup device of the present embodiment.
In the CCD image pickup device of this embodiment, it is assumed that one field period is divided so as to include a first exposure time T1 and a second exposure time T2 shorter than the first exposure time T1.

First, as shown in FIG. 2A, the first signal charge C1 is accumulated in the photosensor part PS at the first exposure time T1. This is also referred to as long exposure. Transferring the stored first signal charges C1 to the vertical transfer unit SR _V.

  Next, as shown in FIG. 2B, the second signal charge C2 is accumulated in the photosensor part PS at the second exposure time T2. This is also referred to as short time exposure.

Next, as shown in FIG. 2 (c), and transfers the second signal charge C2 to the vertical transfer unit SR _V, the first signal charge C1 generated by the same photosensor portion PS of the second signal charges C2 mixing Thus, a mixed signal charge is obtained.

  As described above, the corresponding mixed signal charges are obtained from all the photosensor units, transferred in the vertical direction by the vertical transfer unit, and further transferred in the horizontal direction by the horizontal transfer unit. The mixed signal charge is output to the outside.

Here, in the process of accumulating the first signal charge C1, the saturation amount of the signal charge of the photosensor part PS is adjusted to a predetermined amount smaller than the saturation amount at the time of no adjustment.
In order to realize this, the substrate voltage VSUB is adjusted to a predetermined value, for example, so that the saturation amount of the signal charge becomes 2/3 or 1/2 of the normal driving.
For example, the substrate voltages at which the saturation amount of the signal charge is 2/3 or 1/2 during normal driving are A1 and A2, respectively.
The modulation of the substrate voltage VSUB can be switched by, for example, an external switch before and after signal reading.

Further, for example, in the step of transferring the first signal charges C1 to the vertical transfer unit SR _V, so that incomplete transfer, leaving a portion of the signal charge, transferred at a lower read voltage than the read voltage to complete transfer.
This is based on the premise that the amount of charge handled by each photosensor is the same for all pixels in the CCD image sensor of the present embodiment, and the saturation amount of the signal charge due to the modulation of the substrate voltage is different for each photosensor. This is to suppress the fluctuation.

As described above, when the incomplete transfer, leaving a portion of the signal charges when transferring first signal charges C1 to the vertical transfer unit SR _V, a step of transferring the first signal charges to the vertical transfer section All signal charges remaining in the photosensor portion are discarded during the process of accumulating the second signal charges. This can be done, for example, by allowing the vertical overflow drain to function as an electronic shutter, thereby allowing the second signal charge to begin to accumulate from zero.
The first signal charge is incomplete transfer, while the second signal charge is complete transfer.

FIG. 3 is a timing chart for one field illustrating a driving method of the CCD image pickup device of the present embodiment. Figure 3 (a) ~ (c) is a drive voltage Vφ1~3 vertical transfer units SR _V respectively, FIG. 3 (d) is a substrate clock .phi.SUB, FIG 3 (e) is a substrate voltage VSUB.
Charges held in the vertical transfer unit SR _V by driving the driving voltage Vφ1~3 vertical transfer units SR _V is gradually being transferred to the vertical direction.

  Here, the exposure time for accumulating signal charges in the photosensor unit is defined at the application timing of φSUB and Vφ2, and in the driving method of the CCD image pickup device according to the present embodiment, one field period is defined as the first exposure time T1. The second exposure time T2 is shorter than the first exposure time T1.

  Here, the second exposure time T2 is selected so that the length of the second exposure time T2 is a predetermined ratio with respect to the length of the first exposure time T1, for example, T2 having a length of 1/5 with respect to T1. Alternatively, the length is 1/10, such as T2 ′. The length of the second exposure time T2 is such that, for example, a pulse for reading out the second signal charge as described above is prepared in advance, and the Vφ2 application timing at the end of the second exposure time T2 by external control. It can be made selectable by adjusting.

  The applied voltage of Vφ2 at the end of the first exposure time T1 is applied to Vφ2 at the end of the second exposure time T2 (or T2 ′) so that incomplete transfer is performed with some signal charges remaining. Set lower than the voltage.

  Further, in the first exposure time T1 in which the first signal charge is accumulated, the saturation amount of the signal charge of the photosensor unit is adjusted to a predetermined amount that is smaller than the saturation amount at the time of no adjustment, for example, the substrate voltage VSUB is described above. To a voltage such as A1 or A2.

(Example)
FIG. 4 shows the first exposure time with respect to the saturation amount S during normal driving by setting the substrate voltage at the first exposure time to A1 or A2 in the driving method of the CCD image pickup device according to the present embodiment. The signal charge saturation amount at 2 is set to a value such as 2 / 3S or 1 / 2S, and the second exposure time is set to 1/5 or 1/10 the length of the first exposure time. It is a graph which shows the amount of incident light required until it reaches saturation.

  A thin line a indicates an output signal with respect to the incident light amount in the comparative example in which the second exposure time is not set, and the following comparison is performed using the incident light amount I required until saturation in this case as a reference value of the incident light amount. The amount of incident light at the time of saturation corresponds to the dynamic range at that time.

A broken line b indicates an output signal with respect to an incident light amount when the substrate voltage is A1, the saturation amount is 2 / 3S, and the second exposure time is set to 1/5 of the first exposure time in the first exposure time.
The process is the same as in the comparative example until the incident light quantity is 2 / 3I and the output signal is 2 / 3S, but the slope after reaching 2 / 3S is the ratio of the second exposure time to the first exposure time 1 / 5 corresponds to 1/5 times the normal slope, and therefore the amount of incident light necessary to reach the saturation amount S is
2 / 3I + 1 / 3I × 5 = 7 / 3I≈2.3I
It becomes.

A broken line c indicates an output signal with respect to the amount of incident light when the substrate voltage is A1, the saturation amount is 2 / 3S, and the second exposure time is set to 1/10 of the first exposure time in the first exposure time.
It is the same as the comparative example until the incident light quantity is 2 / 3I and the output signal is 2 / 3S, but the inclination after reaching 2 / 3S is 1/10 times the normal inclination, and therefore the saturation amount. The amount of incident light required to reach S is
2 / 3I + 1 / 3I × 10 = 1/12 / 3I = 4I
It becomes.

A thick line d indicates an output signal with respect to the amount of incident light when the substrate voltage is set to A2, the saturation amount is set to 1 / 2S, and the second exposure time is set to 1/5 of the first exposure time in the first exposure time.
It is the same as the comparative example until the incident light quantity becomes 1 / 2I and the output signal becomes 1 / 2S, but the inclination after reaching 1 / 2S becomes 1/5 times the normal inclination, and therefore the saturation amount. The amount of incident light necessary to reach S is
1 / 2I + 1 / 2I × 5 = 6 / 2I = 3I
It becomes.

A thick line e indicates an output signal with respect to the amount of incident light when the substrate voltage is A2 in the first exposure time, the saturation amount is 1 / 2S, and the second light time is set to 1/10 of the first exposure time.
It is the same as the comparative example until the incident light quantity becomes 1 / 2I and the output signal becomes 1 / 2S, but the inclination after reaching 1 / 2S becomes 1/10 times the normal inclination, and therefore the saturation amount. The amount of incident light necessary to reach S is
1 / 2I + 1 / 2I × 10 = 11 / 2I = 5.5I
It becomes.

As described above, the dynamic range can be improved by 2.3 to 5.5 times the normal dynamic range by switching between the two types of substrate voltages prepared in advance and the pulse defining the second exposure time. Is made.
If the brightness difference of the imaging target is large, the setting of the thick line d or e is selected, and if the brightness difference of the imaging target is not large, the setting of the broken line b or c is selected. By doing so, it is possible to appropriately widen the dynamic range.

According to the driving method of the solid-state imaging device of the present embodiment described above, it is possible to cope with all-pixel readout, and it is possible to realize a wide dynamic range of the output signal without lowering the sensitivity or increasing the horizontal driving frequency.
It does not require complicated signal processing such as applying a weight to the long-time exposure signal and the short-time exposure signal, which is performed by the conventional method, and obtaining a composite signal. It can be easily adjusted from the outside, and there is an advantage that a natural image can be obtained in any scene.

The present invention is not limited to the description of the above embodiment.
For example, the first signal charge and the second signal charge having different exposure times may be accumulated and combined in the state of the charge to obtain one signal. The length of the first exposure time and the second exposure time The ratio and the saturation amount of the first signal charge can be set and selected as appropriate.
The charge transfer unit may be driven by any number of phases in addition to three-phase driving.
In addition, various modifications can be made without departing from the scope of the present invention.

FIG. 1 is a configuration diagram of a CCD image sensor according to an embodiment of the present invention. 2A to 2C are schematic views for explaining a method of driving the CCD image pickup device according to the embodiment of the present invention. FIGS. 3A to 3E are timing charts for one field for explaining a method of driving the CCD image sensor according to the embodiment of the present invention. FIG. 4 is a graph showing the amount of incident light necessary until the output signal of the CCD image sensor in the embodiment of the present invention reaches saturation.

Explanation of symbols

PS: Photo sensor unit, SR _V : Vertical transfer unit, SR _H : Horizontal transfer unit, C1: First signal charge, C2: Second signal charge

Claims (7)

A photosensor unit that is arranged in a matrix and receives light to generate a signal charge, a vertical transfer unit that is provided adjacent to the photosensor unit and reads the signal charge and transfers it in the vertical direction, and the vertical transfer A solid-state imaging device having a horizontal transfer unit provided adjacent to an end of the unit and transferring the signal charge from the vertical transfer unit in a horizontal direction,
One field period is divided so as to include a first exposure time and a second exposure time shorter than the first exposure time;
Accumulating a first signal charge in the photosensor unit during the first exposure time;
Transferring the first signal charge to the vertical transfer unit;
Accumulating a second signal charge in the photosensor unit during the second exposure time;
Transferring the second signal charge to the vertical transfer unit and mixing the first signal charge and the second signal charge generated by the same photosensor unit into a mixed signal charge;
Transferring the mixed signal charge in the vertical direction by the vertical transfer unit;
And a step of transferring the mixed signal charge in a horizontal direction by the horizontal transfer unit. The method for driving a solid-state imaging device according to claim 1, wherein in the step of accumulating the first signal charge, the saturation amount of the signal charge of the photosensor unit is adjusted to a predetermined amount smaller than a saturation amount at the time of no adjustment. . The method for driving a solid-state imaging device according to claim 1, wherein in the step of transferring the first signal charge to the vertical transfer unit, transfer is performed at a read voltage that causes incomplete transfer while leaving a part of the signal charge. The method includes a step of discarding all signal charges remaining in the photosensor unit between the step of transferring the first signal charge to the vertical transfer unit and the step of accumulating the second signal charge. 4. A method for driving a solid-state imaging device according to 3. The method for driving a solid-state imaging device according to claim 1, wherein the step of accumulating the second signal charge is performed by selecting a ratio of a length of the second exposure time to the first exposure time. The method for driving a solid-state imaging device according to claim 1, wherein the mixed signal charge corresponding to each of the photosensor units is obtained. Driving a solid-state imaging device that is arranged in a matrix and has a photo sensor unit that receives light and generates signal charges, and a charge transfer unit that is provided adjacent to the photo sensor unit and reads and transfers the signal charges A method,
One field period is divided so as to include a first exposure time and a second exposure time shorter than the first exposure time;
Accumulating a first signal charge in the photosensor unit during the first exposure time;
Transferring the first signal charge to the charge transfer unit;
Accumulating a second signal charge in the photosensor unit during the second exposure time;
Transferring the second signal charge to the charge transfer unit, and mixing the first signal charge and the second signal charge generated by the same photosensor unit into a mixed signal charge;
And a step of transferring the mixed signal charge by the charge transfer unit.

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