JP2009182405A - Ccd solid-state imaging device and output signal correction method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To eliminate image non-uniformity due to characteristic variations among a plurality of floating diffusion amplifiers in a CCD solid-state imaging device having a charge transfer line for output divided into a plurality of parts. <P>SOLUTION: The CCD solid-state imaging device is provided in which a light receiving surface for receiving incident light from a subject is divided into a plurality of regions and the charge transfer lines for output each of which includes a floating diffusion amplifier for each of the divided region are provided, and the CCD solid-state imaging device includes: a storage element 43 stored with correction values for correcting characteristic variations among the plurality of floating diffusion amplifiers 22a to 22n; and a correction means 42 which corrects an imaged image signal read out from each divided region and output from the amplifier 22i corresponding to the divided region, by the correction value. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a CCD solid-state imaging device and an output signal correction method thereof, and more particularly to a CCD solid-state imaging device including a plurality of output charge transfer paths and an output signal correction method thereof.

  The CCD solid-state imaging device is disadvantageous in terms of high-speed reading of a picked-up image signal as compared with a CMOS solid-state imaging device because the transfer speed of the output charge transfer path becomes a bottleneck. For this reason, in the CCD type solid-state image pickup device in which the recent increase in the number of pixels has progressed, the output charge transfer path is divided into a plurality of parts to cope with the increase in speed.

  For example, in the CCD solid-state imaging device described in Patent Document 1 below, a plurality of pixels formed in a two-dimensional array are divided into a pixel in the left half region and a pixel in the right half region and horizontal charge transfer is performed. The road is also divided into left and right, the signal detected by the pixel in the left area is output on the left horizontal charge transfer path, the signal detected by the pixel in the right area is output on the right horizontal charge transfer path, and the signal output speed is doubled I have to.

JP 2002-300477 A

  By dividing the output charge transfer path into a plurality of parts and dividing the output into a plurality of parts, the signal reading speed from the solid-state imaging device is increased. For this reason, it is possible to increase the speed as the number of divisions is increased.

  However, a floating diffusion amplifier is provided at the output stage of the output charge transfer path, and this amplifier outputs a voltage value signal corresponding to the charge amount of the transferred signal charge as a captured image signal. If the characteristics of a plurality of amplifiers provided for the number of divided charge transfer paths are not matched, there is a problem in that the amplifier gain differs for each amplifier and unevenness occurs in the image.

  However, it is extremely difficult to manufacture a plurality of amplifiers on a semiconductor substrate so that their characteristics coincide with each other, and this is a cause of reducing the manufacturing yield of a CCD solid-state imaging device in which an output charge transfer path is divided into a plurality of parts. It has become.

  An object of the present invention is to provide a CCD type solid-state imaging device capable of suppressing unevenness in a captured image even when an output charge transfer path is divided into a plurality, and an output signal correction method thereof.

  The CCD solid-state image pickup device of the present invention is a CCD solid-state image pickup device that includes an output charge transfer path having a floating diffusion amplifier for each divided region, in which a light receiving surface that receives incident light from a subject is divided into a plurality of regions. A storage element storing a correction value for correcting a characteristic difference between the plurality of floating diffusion amplifiers, and a captured image signal read from each divided area and output from the floating diffusion amplifier corresponding to the divided area. And a correction means for correcting at.

  The CCD type solid-state imaging device of the present invention is characterized in that the storage device has a capacity for storing variable-length measurement data.

  The correction unit of the CCD solid-state imaging device according to the present invention is characterized in that the correction is performed with a correction value obtained by performing an interpolation operation on the correction value stored in the storage element.

  An output signal correction method for a CCD type solid-state imaging device according to the present invention includes a CCD having an output charge transfer path that divides a light-receiving surface that receives incident light from a subject into a plurality of regions and has a floating diffusion amplifier in each divided region. In a method for correcting an output signal of a solid-state solid-state imaging device, a correction value for correcting a characteristic difference between the plurality of floating diffusion amplifiers is read from a storage element, read from each divided region, and output from the floating diffusion amplifier corresponding to the divided region The captured image signal thus corrected is corrected with the correction value.

  According to the present invention, since the difference in characteristics of each amplifier is corrected, it is possible to improve the manufacturing yield of a CCD type solid-state imaging device in which an output charge transfer path is divided into a plurality.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

  FIG. 1 is a configuration diagram of a CCD solid-state imaging device 1 according to an embodiment of the present invention. The CCD solid-state imaging device 10 includes an imaging chip 20, a CDS / multiplexing circuit chip 30, and an output circuit chip 40. These semiconductor chips 20, 30, 40 are housed in one package and connected by wire bonding. The circuit chips 30 and 40 may be integrated into one chip.

  The imaging chip 20 includes a plurality of photodiodes (PD) formed in a two-dimensional array on the surface of a semiconductor substrate and a plurality of vertical charge transfer paths (VCCD) formed along each photodiode column. In the imaging chip 20 of this embodiment, these PDs and VCCDs are divided into n image areas 20a, 20b,..., 20n in a strip shape in the horizontal direction, and each image area is an output charge transfer path. Horizontal charge transfer paths 21a, 21b,..., 21n are provided.

  Therefore, floating diffusion amplifiers 22a to 22n that output voltage value signals corresponding to the transferred signal charge amount as captured image signals are provided at the output ends of the horizontal charge transfer paths 21a to 21n. The output of the amplifier 22a is OSa, the output of the amplifier 22b is OSb,..., And the output of the amplifier 22n is OSn.

  The CDS / multiplexing circuit chip 30 takes in the output signals of the CDS (correlated double sampling) circuits 31a to 31n corresponding to the amplifiers 22a to 22n and the respective CDS circuits 31a to 31n, and multiplexes them into one column of signals. And a multiplexing circuit 32 composed of an output multiplexer.

  The output circuit chip 40 captures a signal (analog captured image signal) output from the multiplexing circuit 32 and converts it into a digital signal, and a digital image output from the A / D conversion circuit 41. A correction circuit 42 that performs correction processing on the image signal and outputs the captured image signal after correction to the outside, and a storage element 43 that stores correction values used when the correction circuit 42 performs correction processing.

  The storage element 43 is provided with a look-up table that stores correction values for compensating for the characteristic differences between the amplifiers 22a to 22n. The correction circuit 42 receives the captured image signal captured from the A / D conversion circuit 41. Which amplifier 22i is the output signal is identified, the corresponding correction value is obtained from the lookup table, and the captured image signal is corrected with this correction value.

  The same synchronizing signal (SYNC signal) and clock signal (CLK signal) are input to the multiplexing circuit 32, the A / D conversion circuit 41, and the correction circuit 42. These circuits 32, 41, and 42 are synchronized with each other. Operates based on. Further, the drive pulse Vi for the vertical charge transfer path and the drive pulse Hi for the horizontal charge transfer paths 21a to 22n are generated by a timing generator (not shown) based on these synchronization signals and clock signals.

  FIG. 2 is an internal configuration diagram of the CDS / multiplexing circuit chip 30. CDS circuits 31a to 31n that receive the output signals OSa to OSn from the amplifiers 22a to 22n, respectively, and perform correlated double sampling processing are provided in parallel. The buffer amplifier 33 is connected to one buffer amplifier 33 via 32n, and the output of the buffer amplifier 33 becomes an output signal of the circuit chip 30.

  A multiplexer control circuit 34 is provided in the circuit chip 30. The control circuit 34 outputs selector signals 34a to 34n to any one of the open / close switches based on the synchronization signal and the clock signal. When the selector signal 34 i is output, the open / close switch 32 i with the same i number is closed, and the output of the CDS circuit 31 i with this i number is output through the buffer amplifier 33.

  FIG. 3 is an explanatory diagram of multiplexing performed in the multiplexing circuit chip 30. In FIG. For the sake of simplicity, it is assumed that the light receiving area of the solid-state imaging device is divided into three image areas a, b, and c. The captured image signals for one row are a1, a2, a3, a4, a5 in the region a, b1, b2, b3, b4, b5 in the region b, and c1, c2, c3 in the region c. Let c4 and c5.

Pixel (PD) that detects signal a1, pixel that detects signal a2,... Pixel that detects signal a5, pixel that detects signal b1,... Pixel that detects signal b5, pixel that detects signal c1,. Pixels for detecting are arranged in a horizontal row. Therefore, the captured image signal for this line is
a1, a2, ..., a5, b1, b2, ..., b5, c1, c2, ... c5
If the signal arrangement is not obtained, the image of the subject cannot be obtained.

  However, the amplifier output signal OSa = a1-a2-a3-a4-a5 in the image area a, the amplifier output signal OSb = b1-b2-b3-b4-b5 in the image area b, and the amplifier output signal OSc in the image area c. = C1−c2−c3−c4−c5 are output in parallel, and thus do not have the above signal arrangement in time.

Therefore, in this embodiment, the controller 34 of the multiplexing circuit 32 controls the selector signal, and a1, b1, c1, a2, b2, c2,..., A5, b5, c5 in order of output time.
The A / D conversion circuit 41 converts the signal into a digital signal with this signal arrangement, and the correction circuit 42 corrects the amplifier characteristic difference and outputs it externally.

  An image processing apparatus (not shown) that receives an externally output signal stores the signals in the frame memory in the order in which they are received. Since these signals are digitized, the signal arrangement is instantaneously shown in FIG. Can be converted into the original signal array. The correction circuit 42 may be provided with this signal array conversion processing function.

  The order of the signal arrangement (the upper arrangement in FIG. 3B) is determined for the multiplexed signals. For this reason, which signal is the signal output from which amplifier 22i (image region 20i) can be easily identified by counting the operation clock.

  Therefore, in the case of a signal output from the amplifier 22a, the correction value for the amplifier 22a of the storage element 43 is read from the lookup table, and the captured image signal is corrected based on this correction value. In the case of a signal output from the amplifier 22i, the correction value for the amplifier 22i is read from the lookup table, and the captured image signal is corrected based on this correction value.

  Thereby, even if the characteristics of the amplifiers 22i do not match, it is possible to obtain high-quality subject image data without unevenness.

  The lookup table provided in the storage element 43 preferably inputs data (correction value) in the inspection process of the production line of the solid-state imaging device and the adjustment process of the assembly line of the imaging device. In each process, with the correction processing using the lookup table disabled, uniformly illuminate the solid-state image sensor with light of a predetermined illuminance, drive the vertical charge transfer path and horizontal charge transfer path, and output the captured image signal Let Then, a correction value is determined so that each captured image signal has the same value, and is registered as lookup table data.

  Since how much the correction value is registered differs depending on the assembly maker of the imaging device or the like, a sufficient size is secured so that variable-length data can be registered as the capacity of the storage element 43. For example, it is possible to cope with not only the case where three points of measurement data of low illuminance, medium illuminance and high illuminance are obtained and registered correction values, but also the case where ten points of measurement data are obtained and correction values are registered. Keep it. Since the relationship between the illuminance and the output signal value is not linear, the more accurate the measurement data, the higher the accuracy of correction.

  When correction is performed using the look-up table data, if the number of points in the measurement data is small, the correction value is obtained by interpolating the measurement data in between. This interpolation calculation may be performed based on the measurement data when correcting the characteristic difference, or a correction value obtained by performing an interpolation calculation in advance may be registered in the lookup table.

The interpolation calculation is performed by linear interpolation, for example. FIG. 4 is an explanatory diagram of an example of interpolation calculation. Assume that the output value when the input value of the lookup table (LUT) is A10 = 10 is B10 = 20, and the output value when the input value is A20 = 20 is B20 = 40. Then, when the value of the output value B12 when the input value is A12 = 12, the interpolation output C12 is obtained instead of the output value B12. This C12 is
C12 = (B20-B10) / (A20-A10) * (A12-A10) + B10
= (40-20) / (20-10) * (12-10) +20
= 24
Can be calculated as

  The look-up table is not limited to the correction of the output value of the floating diffusion amplifier, but may be used for correction including the characteristic differences of other parts of the solid-state imaging device and all systems.

  As described above, according to the present embodiment, it is possible to obtain a high-quality image by correcting a picked-up image signal for a solid-state image pickup device that has conventionally had a difference in characteristics among a plurality of amplifiers as a defective product. Therefore, the manufacturing yield of the solid-state imaging device is increased, and it is possible to provide a solid-state imaging device in which the output charge transfer path is divided into a plurality of parts at low cost.

  In the above-described embodiment, since only one A / D conversion circuit 41 needs to be provided, it is necessary to deal with a characteristic difference between A / D conversion circuits that occurs when a plurality of A / D conversion circuits are provided. In addition, the cost can be reduced.

  The CCD solid-state imaging device according to the present invention is useful as a solid-state imaging device mounted on a digital camera or the like because it can read a captured image signal at high speed at low cost.

1 is a configuration diagram of a CCD solid-state imaging device according to an embodiment of the present invention. It is a block diagram of the CDS / multiplex circuit chip shown in FIG. It is explanatory drawing of the method of multiplexing in the multiplexing circuit shown in FIG. It is explanatory drawing of an example of an interpolation calculation.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 CCD type solid-state image sensor 20 Imaging chip 20a-20n Image area 21a-21n Horizontal charge transfer path 22a-22n Floating diffusion amplifier 30 CDS / multiplex circuit chip 31a-31n CDS circuit 32 Multiplex circuit 40 Output circuit chip 41 A / D conversion circuit 42 Correction circuit 43 Memory element (look-up table)

Claims (4)

  In a CCD solid-state imaging device having a charge transfer path for output having a floating diffusion amplifier for each divided region, the light receiving surface for receiving incident light from a subject is divided into a plurality of regions, and a characteristic difference between the plurality of floating diffusion amplifiers A storage element that stores a correction value for correcting the image, and a correction unit that corrects the captured image signal read from each divided region and output from the floating diffusion amplifier corresponding to the divided region with the correction value. A CCD type solid-state imaging device.   2. The CCD solid-state image pickup device according to claim 1, wherein the storage element has a capacity for storing measurement data having a variable length.   3. The CCD solid-state imaging device according to claim 1, wherein the correction unit performs the correction using a correction value obtained by performing an interpolation operation on the correction value stored in the storage element. 4. .   In a method for correcting an output signal of a CCD type solid-state imaging device comprising a light-receiving surface that receives incident light from a subject divided into a plurality of regions and an output charge transfer path having a floating diffusion amplifier in each divided region, the plurality of floating signals A correction value for correcting a characteristic difference of the diffusion amplifier is read from the storage element, and a captured image signal read from each divided area and output from the floating diffusion amplifier corresponding to the divided area is corrected with the correction value. An output signal correction method for a CCD solid-state imaging device.

Images