JP2008306568A - Solid imaging apparatus - Google Patents

Abstract

A solid-state imaging device capable of performing pixel mixing without causing quality deterioration such as image unevenness.
A photodiode 200, a plurality of vertical CCDs 210, a horizontal CCD 220, and a VDr 110 that controls charge transfer by the vertical CCD 210, the vertical CCD 210 operates as a barrier region and a well region according to an applied voltage. The VDr 110 includes a plurality of charge transfer stages, and the vertical CCD 210 continuously transfers a plurality of packets, which are charges transferred in a continuous well region separated by a barrier region, and separates a plurality of packets. The standby period in which the charge transfer is stopped by this becomes longer than the transfer period in which the charge transfer by the packet is performed, and in the standby period, the charge transfer stage operating as the barrier region is among four or more charge transfer stages. The charge transfer by the vertical CCD 210 is controlled to be one stage.
[Selection] Figure 2A

Description

  The present invention relates to a solid-state imaging device, and more particularly to a CCD (Charge Coupled Device) type solid-state imaging device.

  In general, a CCD solid-state imaging device is used as a solid-state imaging device constituting an imaging device such as a video camera and a digital still camera. In a CCD type solid-state imaging device, signal charges generated by a photodiode upon incidence of light are read to a vertical CCD and transferred to a charge detection unit (FD unit) by the vertical CCD and horizontal CCD.

With regard to such a CCD solid-state imaging device, for example, Patent Document 1 discloses a technique for improving the output speed of a video signal by performing pixel mixing. In this CCD type solid-state imaging device, a transfer unit capable of controlling driving independently of the vertical CCDs in the other columns is provided at the final stage of the vertical CCD. The readout of signal charges from the vertical CCD to the horizontal CCD is controlled independently for each column, and the signal charges of a plurality of pixels are mixed in the horizontal CCD in the horizontal direction.
JP 2004-180284 A

  By the way, if the area of the CCD is reduced in order to reduce the size of the solid-state imaging device, the CCD barrier region is caused by the finish of the CCD gate dimensions, subtle variations in the impurity profile, or subtle variations in the gate insulating film. In this case, a transfer deterioration point occurs. For example, in a vertical CCD of 6-phase drive, a low level drive pulse is applied to two adjacent drive electrodes V5 and V6 as shown in the potential distribution in the vertical CCD of FIG. And a transfer deterioration point (A in FIG. 6A) occurs in the barrier region under V6. A part of the vertically transferred packet 400 (signal charge transferred in a continuous well region delimited by a barrier region) 400 is trapped in this transfer deterioration portion. When the vertical transfer is stopped, the trapped signal charge is released and added to the packet accumulated in the well region. The solid-state imaging device described in Patent Document 1 is affected by this phenomenon, and the charge amount of the transferred packet varies. This will be described in detail with reference to a change diagram of potential distribution in the vertical CCD of FIG.

  In the solid-state imaging device described in Patent Literature 1, for example, when performing pixel mixing (when performing pixel mixing of 9 pixels), instead of 1 packet (signal charge for 1 pixel), 3 packets (signal charge for 3 pixels) ) Is transferred to the horizontal CCD, and a standby period is reached in which the vertical transfer is stopped (FIG. 7A). At this time, a signal charge is trapped at a transfer deterioration portion (A in FIG. 7) in the barrier region. The trapped signal charge is added to the packet accumulated in the well region while the vertical transfer is stopped (FIG. 7B). When the vertical transfer is resumed, a part of the next packet that passes through the transfer deterioration point is trapped in the transfer deterioration point (FIG. 7C). The trapped signal charge is released when the transfer is stopped for a time longer than the time required to transfer the packet in one stage (the time required for the state to change from FIG. 7D to FIG. 7E). Therefore, the next two packets are continuously vertically transferred without being affected by the transfer deterioration portion (FIGS. 7D and 7E). Accordingly, the signal charge amount increases for some packets, and the signal charge amount decreases for some packets, resulting in variations in the signal charge amount transferred. This variation in the signal charge amount causes quality degradation such as image unevenness.

  In view of the above problems, an object of the present invention is to provide a solid-state imaging device capable of performing pixel mixing without causing quality deterioration such as image unevenness.

  In order to achieve the above object, a solid-state imaging device of the present invention includes a plurality of photoelectric conversion elements arranged in a two-dimensional manner, and a plurality of vertical transfer units that transfer charges generated in the photoelectric conversion elements in a column direction. A horizontal transfer unit that transfers the charges transferred by the plurality of vertical transfer units in a row direction, and a transfer control unit that controls charge transfer by the vertical transfer unit, the vertical transfer unit according to the applied voltage The transfer control unit is a packet in which the vertical transfer unit is a charge transferred in the continuous well region delimited by the barrier region. And a standby period in which charge transfer is stopped due to the separation of the plurality of packets is longer than a transfer period in which charge transfer is performed by the packets, and Wherein the waiting period, the charge transfer stage which operates as the barrier region, and controlling the charge transfer by the vertical transfer portions so that the first stage of the four or more stages of charge transfer stage.

  As a result, during the standby period, control is performed so that the charge transfer stage operating as the barrier region is one stage, that is, one gate barrier. Therefore, the fringe electric field becomes strong, and the signal charge trapped at the transfer degradation point is released in a time shorter than the time required to transfer one packet by the fringe electric field. Thus, the amount of signal charge to be transferred does not vary. As a result, pixel mixing can be performed without causing quality degradation such as image unevenness.

  Here, the vertical transfer unit includes an electrode for applying a voltage to the charge transfer stage provided in each of the four or more charge transfer stages, and relatively to the four or more electrodes, The transfer control unit includes a long electrode and a short electrode in a charge transfer direction, and the transfer control unit is configured such that, during the standby period, the charge transfer stage operating as the barrier region is a charge transfer stage provided with a long electrode. The charge transfer by the vertical transfer unit may be controlled.

  As a result, an increase in the area of the well region in charge transfer can be minimized, so that an increase in dark current can be minimized.

  The charge transfer stage provided with the long electrode may operate as a barrier region and a well region whose potential is inclined in the charge transfer direction.

  As a result, the signal charge is less likely to be trapped or not trapped at the transfer deterioration portion, and hence the variation in the signal charge amount can be further reduced.

  In addition, the transfer control unit is configured such that, during the standby period, the charge transfer stage located between the charge transfer stage closest to the horizontal transfer part among the charge transfer stages operating as the barrier region and the horizontal transfer part However, the charge transfer by the vertical transfer unit may be controlled to operate as a well region after operating as the barrier region.

  As a result, the potential difference between the horizontal transfer unit and the final stage of the vertical transfer unit can be increased, so that the packet can be transferred to the horizontal transfer unit without causing a transfer residue, It is possible to prevent deterioration in transfer efficiency with the transfer unit.

  According to the present invention, it is possible to realize a solid-state imaging device capable of performing pixel mixing without causing quality deterioration such as image unevenness.

  Hereinafter, solid-state imaging devices according to embodiments of the present invention will be described with reference to the drawings.

(First embodiment)
FIG. 1 is a diagram illustrating a schematic configuration of an imaging apparatus (camera) according to the present embodiment.

  This camera photoelectrically converts incident light and transfers a signal charge generated by the photoelectric conversion, a CCD solid-state imaging device 100, a clock driver (VDr) 110, a CDS (correlated double sampling) and an ADC (ADC). A pre-processing unit (CDS / AGC) 120 that performs analog / digital conversion processing, a digital signal processing unit (DSP) 130 that performs pixel interpolation, luminance / chrominance processing, and the like, and a timing generator (TG) 140). Note that the solid-state imaging device 100, the VDr 110, and the TG 140 constitute a solid-state imaging device of the present invention.

The VDr 110 is an example of a transfer control unit according to the present invention, controls charge transfer by the vertical CCD, the vertical CCD transfers a plurality of packets continuously, and the charge transfer is stopped by dividing a plurality of packets. The standby period is longer than the transfer period in which charge transfer is performed by packets, and in the standby period, the charge transfer stage operating as a barrier region is one of the four or more charge transfer stages. The charge transfer by the vertical CCD is controlled. Specifically, drive pulses φV1 to φV6, φV3R, φV3L, φV5R, and φV5L are generated from the logic signals V1 to V6, CH1, 2, 3, and 4 output from the TG 140, and the drive pulses φV1 to φV6, φV3R, and φV3L are generated. , ΦV5R and φV5L are supplied to the vertical CCD of the solid-state imaging device 100, and charge transfer by the vertical CCD is controlled. Drive pulse φV1~φV6, φV3R, φV3L, φV5R and φV5L the high-level potential V _H, the potential V voltage V _M of the lower middle level than _H, and 3 low low-level potential V _L than the potential V _M It is a pulse with two potentials. For example, the driving pulse φV1~φV6 is, 12V as voltage V _H, is a pulse having three potentials of -6V as 0V, and the potential V _L of the voltage V _M.

  The TG 140 receives the pulses of the horizontal synchronization signal HD, the vertical synchronization signal VD, and the clock signal MCK from the DSP 130 and receives drive pulses φH1, φH2, and φR used for driving the solid-state imaging device 100, and logic signals V1 to V6, CH1, 2, 3, and 4 are generated, and a signal processing pulse PROC is output to the preprocessing unit 120 and the DSP 130.

  FIG. 2A is a schematic configuration diagram of the solid-state imaging device 100, and FIG. 2B is a schematic configuration diagram of the distribution transfer unit 230.

  As shown in FIG. 2A, the solid-state imaging device 100 includes a plurality of photodiodes 200, a plurality of vertical CCDs 210, a horizontal CCD 220, and a charge detection unit 250.

  The plurality of photodiodes 200 is an example of the photoelectric conversion element of the present invention, and are arranged in a two-dimensional shape (matrix shape) corresponding to the pixels, and the red (R), green (G), and blue (B) 3 Each color filter is arranged.

  The vertical CCD 210 is an example of a vertical transfer unit according to the present invention, and is configured by a CCD including drive electrodes V1 to V6, V3R, V3L, V5R, and V5L. The vertical CCD 210 transfers signal charges generated in the photodiode 200 in the column direction in response to application of the drive pulses φV1 to φV6, φV3R, φV3L, φV5R, and φV5L.

  The horizontal CCD 220 is an example of a horizontal transfer unit, and is configured by a CCD having drive electrodes H1 and H2, and transfers signal charges transferred by the plurality of vertical CCDs 210 in the row direction in response to application of drive pulses φH1 and φH2. To do.

  The readout of signal charges from the vertical CCD 210 to the horizontal CCD 220 is arranged between the horizontal CCD 220 and the imaging unit 240 formed by forming the plurality of photodiodes 200 and the vertical CCD 210 closest to the horizontal CCD 220 of the vertical CCD 210. A distribution transfer unit 230 that is controlled independently for each time is formed.

  As shown in FIG. 2B, the distribution transfer unit 230 has the same electrode structure every three columns. Specifically, the distribution transfer unit 230 of the vertical CCD 210 in the first column includes drive electrodes V1, V2, V3L, V4, V5L, and V6, and the distribution transfer unit 230 of the vertical CCD 210 in the second column includes the drive electrodes V1, V2, V3, V4, V5, and V6 are provided, and the sorting transfer unit 230 of the vertical CCD 210 in the third column includes drive electrodes V1, V2, V3R, V4, V5R, and V6. Here, the drive electrodes V1, V2, V4, and V6 are common electrodes over all the columns, and the drive electrodes V3, V3R, V3L, V5, V5R, and V5L are independent electrodes separated in an island shape in each column.

FIG. 3 is a cross-sectional view showing the structure of the vertical CCD 210 in the second row.
Two adjacent drive electrodes of the vertical CCD 210 are formed in a two-layer structure in which a part thereof overlaps each other, and the length of one of the drive electrodes constituting the two-layer structure in the charge transfer direction is relative to the other length. Long. Specifically, the length of the drive electrodes V1, V3, and V5 in the charge transfer direction is longer than the length of the drive electrodes V2, V4, and V6 in the charge transfer direction. As a result, the area of the transfer electrode provided on the signal charge readout path of the photodiode 200 to which the signal charge readout voltage of the photodiode 200, that is, the potential V _H is applied, is increased. As a result, even when the pixels are miniaturized, it is possible to secure a read channel width necessary for reading signal charges.

A p-type substrate 300 is disposed below the drive electrodes V <b> 1 to V <b> 6, and an n-type impurity region 310 as a part of the vertical CCD 210 is formed in the substrate 300. In the impurity region 310, an n ⁺ -type impurity region 320 having a higher concentration than the impurity region 310 and an n ⁻ -type impurity region 330 having a lower concentration than the impurity region 310 are formed due to the step of impurity implantation into the impurity region 310. Is formed. These impurity regions constitute six periodic charge transfer stages that operate as potential barrier regions and well regions in response to voltage application by the drive electrodes V1 to V6. Specifically, the first charge transfer stage 340 provided with the drive electrode V1, the second charge transfer stage 350 provided with the drive electrode V2, the third charge transfer stage 360 provided with the drive electrode V3, and the drive electrode V4. A fourth charge transfer stage 370 provided with a fifth charge transfer stage 380 provided with a drive electrode V5, and a sixth charge transfer stage 390 provided with a drive electrode V6. Therefore, these impurity regions function as a vertical charge transfer path (VCCD) for transferring signal charges.

  Since the impurity regions 310 and 330 having different impurity concentrations are provided in the impurity regions 310 below the drive electrodes V1, V3, and V5, respectively, the first charge transfer stage 340, the third charge transfer stage 360, and the fifth charge transfer. The stage 380 operates as a barrier region and a well region whose potential is inclined in the charge transfer direction.

  The vertical CCDs 210 in the first and third columns are the same as those in FIG. 3, although any one of the drive electrodes V3 is changed to the drive electrode V3R or V3L, and any one of the drive electrodes V5 is changed to the drive electrode V5R or V5L. It has the following structure.

  FIG. 4 is a potential distribution change diagram (potential distribution change diagram in the vertical CCD 210 in the second column) showing a packet transfer method in the vertical CCD 210 having the above-described structure. The transfer method is an example of a method for driving the solid-state imaging device of the present invention.

  At time t1 to t6, one packet of the vertical CCD 210 in the second column is transferred to the horizontal CCD 220. Thereafter, although not shown, the transferred packet is transferred by two pixels in the row direction, and one packet of the vertical CCD 210 in the third column is transferred to the horizontal CCD 220. After the transferred packet is transferred by two pixels in the row direction, one packet of the vertical CCD 210 in the first column is transferred to the horizontal CCD 220.

  Similarly, at time t7 to t12 and t13 to t17, one packet of the vertical CCD 210 in the second row is transferred to the horizontal CCD 220, and then one packet of the vertical CCD 210 in the third row and the first row is transferred to the horizontal CCD 220. The As a result, three packets of the vertical CCD 210 in each column are successively transferred to the horizontal CCD 220.

At time t18, the potential V _M of the middle level is applied to the drive electrodes V6, charge transfer stage which operates as a barrier region 1 stage of the charge transfer stage of the six stages (stages corresponding to the driving electrode V5) and so as After the vertical CCD 210 is controlled, the vertical transfer is stopped. The standby period in which the transfer is stopped, that is, the standby period in which the charge transfer is stopped due to the transfer break of 3 packets is a transfer period (time t1 to t6, time t7 to t12 or t13 to t13). longer than the period of t17). Thereafter, a plurality of packets in the horizontal CCD 220 are transferred to the charge detection unit 250. In the vertical CCDs 210 in the third and first columns, the charge transfer stage that operates as the barrier region is set to one of the six charge transfer stages during the standby period.

  By applying each drive pulse to the vertical CCD 210 and the horizontal CCD 220 so as to perform the packet transfer as described above, and driving the vertical CCD 210 and the horizontal CCD 220, the signal charges of three pixels are mixed in the horizontal CCD 220 in the row direction. .

  As described above, according to the camera of the present embodiment, as shown in FIG. 6B, the charge transfer stage operating as the barrier region during the standby period is one of the six charge transfer stages. (The stage corresponding to the drive electrode V6). Accordingly, the fringe electric field becomes strong, and the signal charge trapped in the transfer deterioration portion is released by the fringe electric field in a short period, that is, in a time shorter than the time required to transfer one packet in one stage. Unlike the solid-state imaging device described, the amount of signal charge transferred does not vary. As a result, it is possible to perform pixel mixing in the horizontal CCD without causing quality degradation such as image unevenness.

  Furthermore, according to the camera of the present embodiment, as shown in FIG. 6B, the charge transfer stage that operates as the barrier region during the standby period is one of the six charge transfer stages (driving). A stage corresponding to the electrode V6). Accordingly, the fringe electric field becomes strong, and the signal charge trapped at the transfer deterioration portion is released by the fringe electric field in a short period, that is, in a time shorter than the time required to transfer one packet in one stage. Since the transfer operation is stopped and the transfer operation is stopped, the amount of signal charge to be transferred does not vary. As a result, camera shake prevention and electronic zoom can be performed without causing quality degradation such as image unevenness.

  In addition, in the solid-state imaging device and the driving method thereof according to the embodiment of the present invention, for example, in an EIS (Electric Image Stabilizer) solid-state imaging device, a plurality of packets are transferred and the transfer operation is stopped. By using the packet transfer according to the above in the EIS solid-state imaging device, it is possible to prevent quality degradation such as image unevenness in the EIS solid-state imaging device.

  Further, according to the camera of the present embodiment, as can be seen from the potential step below the drive electrode V5 in FIG. 6B, in the standby period, not the short drive electrode in the charge transfer direction but the long drive electrode (drive) The charge transfer stage provided with the electrode V5) is operated as a barrier region. Therefore, an increase in the area of the well region can be minimized, and an increase in dark current can be minimized.

  Further, according to the camera of the present embodiment, an impurity concentration distribution in which the potential decreases toward the adjacent charge transfer stage is formed in the charge transfer stage operated as the barrier region in the standby period. Therefore, this charge transfer stage operates as a barrier region and a well region whose potential is inclined in the charge transfer direction. As a result, the signal charge becomes difficult to be trapped or no longer trapped at the transfer deteriorated portion, so that the variation in the signal charge amount can be further reduced.

  In addition, according to the camera of the present embodiment, since signal charges are not discarded in pixel mixing, a video signal with high sensitivity can be obtained. In addition, since the center of gravity of each mixed pixel group has an equal interval in the horizontal CCD, an image signal with little moire and false signals can be obtained. As a result, it is possible to output a high-quality video signal at high speed without generating moire or false signals.

  As described above, the solid-state imaging device of the present invention has been described based on the embodiment, but the present invention is not limited to this embodiment. The present invention includes various modifications made by those skilled in the art without departing from the scope of the present invention.

For example, in the camera of the above embodiment, the charge transfer stage located between the horizontal CCD and the charge transfer stage closest to the horizontal CCD among the charge transfer stages that operate as the barrier area in the standby period operates as the barrier area. Then, charge transfer may be performed so as to operate as a well region in the standby period. As a result, the potential difference between the horizontal CCD and the final stage of the vertical CCD can be increased, so that one packet can be transferred to the horizontal CCD without generating a transfer residue. It is possible to prevent the transfer efficiency from being deteriorated. In this case, for example, packet transfer is performed according to a potential distribution change diagram of FIG. 5 (potential distribution change diagram of the vertical CCD 210 in the second column). In this transfer, a low potential _VL is applied to the drive electrode V6 at a time t18a between the time t17 and the time t18, and the charge transfer stage provided with the drive electrode V6 is operated as a barrier region. This is different from the packet transfer shown in

  In the above embodiment, the vertical CCD is a six-phase driving CCD having the transfer electrodes V1 to V6. However, the present invention is not limited to this, as long as it is a CCD to which the packet transfer of the above embodiment can be applied, that is, a CCD having four or more charge transfer stages and to which four or more phases of driving pulses are applied. It may be a four-phase drive CCD.

  Further, in the above embodiment, the potential gradient is formed by the step of impurity implantation into the impurity region. However, the potential gradient may be formed by utilizing the narrow channel effect that expands the channel width of charge transfer in the transfer direction.

  The present invention can be used for a solid-state imaging device, and in particular, for a CCD solid-state imaging device that performs pixel mixing.

It is a figure which shows schematic structure of the camera of the 1st Embodiment of this invention. It is a figure which shows the detailed structure of the solid-state image sensor of the embodiment. It is a schematic block diagram of a distribution transfer part. It is sectional drawing which shows the structure of the vertical CCD of the 2nd row of the embodiment. It is a potential distribution change diagram showing a packet transfer method in the vertical CCD of the second column of the embodiment. It is a potential distribution change diagram showing a packet transfer method in the vertical CCD of the second column of the embodiment. It is a figure which shows a mode that a packet is transferred in vertical CCD with a transfer degradation location. It is a figure which shows a mode that a packet is transferred in vertical CCD with a transfer degradation location.

Explanation of symbols

100 Solid-state image sensor 110 Clock driver (VDr)
120 Pre-processing unit (CDS / AGC)
130 Digital signal processor (DSP)
140 Timing generator (TG)
200 Photodiode 210 Vertical CCD
220 horizontal CCD
230 Transfer and transfer unit 240 Imaging unit 250 Charge detection unit 300 Substrate 310, 320, 330 Impurity region 400 packets

Claims (11)

A plurality of photoelectric conversion elements arranged two-dimensionally;
A plurality of vertical transfer units for transferring charges generated in the photoelectric conversion elements in a column direction;
A horizontal transfer unit that transfers charges transferred by the plurality of vertical transfer units in a row direction;
A transfer control unit for controlling charge transfer by the vertical transfer unit,
The vertical transfer unit includes four or more charge transfer stages that operate as a barrier region and a well region according to an applied voltage,
The transfer control unit
The vertical transfer unit continuously transfers a plurality of packets that are charges transferred in the continuous well region divided by the barrier region, and
A waiting period in which charge transfer stops due to the separation of the plurality of packets is longer than a transfer period in which charge transfer by the packets is performed; and
In the standby period, the charge transfer by the vertical transfer unit is controlled so that the charge transfer stage operating as the barrier region is one of the four or more charge transfer stages. Imaging device. 2. The vertical transfer unit continuously transfers a plurality of packets, which are charges transferred in the continuous well regions separated by the barrier region, at the time of pixel mixture. Solid-state imaging device. The vertical transfer unit continuously transfers a plurality of packets, which are charges transferred in the continuous well region divided by the barrier region, at the time of camera shake prevention or electronic zoom. The solid-state imaging device according to claim 1. The vertical transfer unit has electrodes for applying a voltage to the charge transfer stage provided in each of the four or more charge transfer stages,
The four or more electrodes include a relatively long electrode and a short electrode in the charge transfer direction,
The transfer control unit controls charge transfer by the vertical transfer unit so that the charge transfer stage operating as the barrier region is a charge transfer stage provided with a long electrode during the standby period. The solid-state imaging device according to claim 1. The solid-state imaging device according to claim 4, wherein the charge transfer stage provided with the long electrode operates as a barrier region and a well region whose potential is inclined in the charge transfer direction. The solid-state imaging device according to claim 5, wherein the potential gradient is formed by an impurity injection step in the charge transfer stage provided with the long electrode. 6. The potential gradient is formed in the charge transfer stage provided with the long electrode by utilizing a narrow channel effect that expands a channel width of charge transfer in a transfer direction. The solid-state imaging device described. In the standby period, the transfer control unit includes a charge transfer stage located between the charge transfer stage closest to the horizontal transfer part among the charge transfer stages operating as the barrier region and the horizontal transfer part. 2. The solid-state imaging device according to claim 1, wherein charge transfer by the vertical transfer unit is controlled to operate as a well region after being operated as the barrier region and to stand by. A plurality of photoelectric conversion elements arranged in a two-dimensional manner, a plurality of vertical transfer units that transfer charges generated in the photoelectric conversion elements in a column direction, and charges transferred by the plurality of vertical transfer units in a row direction A solid-state imaging device driving method comprising a horizontal transfer unit for transferring,
The vertical transfer unit includes four or more charge transfer stages that operate as a barrier region and a well region according to an applied voltage,
The driving method is:
The vertical transfer unit continuously transfers a plurality of packets that are charges transferred in the continuous well region divided by the barrier region, and
A waiting period in which charge transfer stops due to the separation of the plurality of packets is longer than a transfer period in which charge transfer by the plurality of packets is performed; and
In the standby period, the solid-state imaging device is driven so that a charge transfer stage operating as the barrier region is one of the four or more charge transfer stages. Driving method. 10. The vertical transfer unit continuously transfers a plurality of packets, which are charges transferred in the continuous well regions divided by the barrier region, at the time of pixel mixture. Driving method for a solid-state imaging device. The vertical transfer unit continuously transfers a plurality of packets, which are charges transferred in the continuous well region divided by the barrier region, at the time of camera shake prevention or electronic zoom. The method for driving a solid-state imaging device according to claim 9.

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