JP2007333801A - Focus detecting device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a focus detecting device capable of more accurately detecting focus and further improving focus detection accuracy when luminance is low, in a multiple AF system having a charge holding section that temporarily holds charges output from a photoelectric conversion element. <P>SOLUTION: The focus detecting device calculates a first correction value for a fixed pattern noise (PD dark current) arising depending on the accumulation time of a photoelectric conversion element array itself. The focus detecting device also calculates a second correction value for a fixed pattern noise (ST dark current) arising depending on the charge holding time of the charge holding section that temporarily holds charges output from the photoelectric conversion element array. When focal point information is calculated based on a digital value acquired by converting an output from the photoelectric conversion element array by a converting section, a digital value corrected using the first and second correction values is used. This makes it possible to calculate focus information by compensating for all dark noises that may arise in the multiple AF system indispensable to the charge holding section. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a focus detection apparatus for a camera, for example.

  Conventionally, regarding a camera focus detection device, for example, according to Patent Document 1, when a CCD is used as a photoelectric conversion element, a method for improving focus detection accuracy at low luminance by correcting a dark current generated in the CCD is disclosed. Is disclosed.

  Patent Document 2 discloses a method for improving focus detection accuracy by correcting two types of fixed pattern noise when a MOS photoelectric conversion element is used as a photoelectric conversion element. In Patent Document 2, one fixed pattern noise to be corrected is a variation (noise) of an output signal generated regardless of the accumulation time of the photoelectric conversion element, and the other one fixed noise pattern is caused by the dark current of the element. This noise is generated and increases with accumulation time. Any fixed pattern noise is noise caused by the MOS photoelectric conversion element itself.

JP-A 63-279211 JP 2000-101932 A

  By the way, regarding the focus detection method of a camera, a TTL phase difference automatic that detects the defocus amount of the photographing lens by guiding the light flux that has passed through the photographing lens onto a pair of photoelectric conversion elements and performing focus detection calculation on the output thereof. In general, the focus detection (AF) method is widely used in single-lens reflex cameras. In addition, recent single-lens reflex cameras generally perform focus detection or distance measurement in a plurality of focus detection areas in a shooting area. A photoelectric conversion element array used in such a multi-AF focus detection apparatus or distance measuring apparatus having a plurality of focus detection areas is provided for each of the plurality of focus detection areas. Here, since the brightness of the subject differs for each region where focus detection is to be performed, if the photoelectric conversion element arrays are controlled in common in one accumulation time, a photoelectric conversion element array that cannot be controlled in an appropriate accumulation time occurs. However, since focus detection cannot be performed accurately unless the accumulation time is appropriate, accumulation control is performed independently for each photoelectric conversion element array.

  However, since the accumulation times of the photoelectric conversion element arrays are not the same, inconvenience occurs when the output of the photoelectric conversion element array is A / D converted by the A / D converter. That is, if an A / D converter is provided for each photoelectric conversion element array, the conversion operation by the A / D converter can be performed immediately after the accumulation operation of the photoelectric conversion element array is completed. As the number increases, the number of required A / D transformers also increases, leading to an increase in circuit scale. On the other hand, if one or two A / D converters are used for a plurality of photoelectric conversion element arrays, a charge holding unit that temporarily holds the output charges of the photoelectric conversion element arrays that have completed the accumulation operation is required. It becomes. Alternatively, the output obtained from the photoelectric conversion element array for all the focus detection regions is temporarily stored in the operation unit of the subsequent stage so that the output charge of the photoelectric conversion element array is temporarily held due to the structure of the CCD. It is important to hold it in the part in order to simplify the CCD chip configuration.

  Here, even in the charge holding unit that temporarily holds the output charge of the photoelectric conversion element array, dark current noise is independently generated, and the noise is superimposed on the output charge of the held photoelectric conversion element array, The focus detection accuracy, particularly the focus detection accuracy at low luminance, is deteriorated. Therefore, as shown in Patent Document 1, even if the influence of noise due to dark current due to the accumulation time of the photoelectric conversion element array is removed, it is insufficient to improve the focus detection accuracy at low luminance. Further, Patent Document 2 is a technique specialized for a CMOS sensor, and does not provide a solution to the above-described problem associated with a CCD chip.

  The present invention has been made in view of the above, and in a multi-AF method including a charge holding unit that temporarily holds the output charge of a photoelectric conversion element, more accurate focus detection is possible, and at low luminance. An object of the present invention is to provide a focus detection apparatus capable of further improving the focus detection accuracy.

  In order to solve the above-described problems and achieve the object, a focus detection apparatus according to the present invention includes a plurality of photoelectric conversion element arrays corresponding to a plurality of focus detection regions, and outputs from the photoelectric conversion element arrays as digital values. A conversion unit that converts the output of the photoelectric conversion element array into a photoelectric conversion element array, and temporarily stores the output charge of the photoelectric conversion element array until the accumulation operation of the photoelectric conversion element array ends and the operation of the conversion unit starts. The charge holding unit to hold, the first correction value for the fixed pattern noise generated depending on the accumulation time by the photoelectric conversion element array, and the fixed pattern noise generated depending on the charge holding time in the charge holding unit A second correction value for the first and second calculation values, and calculation means for calculating focus information for each focus detection area based on the digital values corrected using the first and second correction values. That And butterflies.

  The focus detection device according to the present invention includes a plurality of photoelectric conversion element arrays corresponding to a plurality of focus detection areas, a conversion unit that converts an output from the photoelectric conversion element array into a digital value, and the photoelectric conversion element array. A charge holding unit that temporarily holds the output charge of the photoelectric conversion element array until the accumulation operation of the photoelectric conversion element array ends and the operation of the conversion unit starts, and A storage unit that stores the first fixed pattern noise generated in the photoelectric conversion element array and the second fixed pattern noise generated in the charge holding unit, and calculates focus information for each focus detection region based on the digital value. Calculating means, and when calculating the focus information, the calculating means stores the time of accumulation operation of the photoelectric conversion element array and the first fixed pattern noise of the photoelectric conversion element array stored in the storage unit. And based A first correction value is calculated, and a second fixed pattern corresponding to the time that the output charge of the photoelectric conversion element array is held in the charge holding unit and the photoelectric conversion element row stored in the storage unit The second correction value is calculated based on the noise, and the focus information is calculated after correcting the digital value that is the output of the photoelectric conversion element array based on the first and second correction values. It is characterized by doing.

  In addition, the focus detection apparatus according to the present invention includes a plurality of photoelectric conversion element arrays corresponding to a plurality of focus detection areas, an accumulation control unit that controls accumulation operations of the photoelectric conversion element arrays, and the photoelectric conversion element arrays. And a charge holding section that temporarily holds the output charge when the accumulation operation of the photoelectric conversion element is completed, an accumulation time by the photoelectric conversion element array, and an output charge of the photoelectric conversion element array in the charge holding section A time measuring means for measuring the charge holding time in which the charge is held, a conversion unit for converting the output from the charge holding unit into a digital value, and measurement is performed under a predetermined condition and is generated in each photoelectric conversion element array A storage unit that stores the first fixed pattern noise and the second fixed pattern noise generated in each of the charge holding units; and a calculation unit that calculates focus information for each focus detection region based on the digital value. And the calculation means calculates the focus information of the desired focus detection region, and stores the corresponding photoelectric conversion element array storage time and the first fixed of the photoelectric conversion element array stored in the storage unit. A first correction value is calculated based on the pattern noise, and the charge holding time of the corresponding charge holding unit and the second fixed pattern of the charge holding unit corresponding to the photoelectric conversion element array stored in the storage unit The second correction value is calculated based on the noise, and the focus information is calculated after correcting the digital value that is the output of the photoelectric conversion element array based on the first and second correction values. It is characterized by doing.

  The focus detection apparatus according to the present invention further includes a temperature detection unit that detects an ambient temperature of the photoelectric conversion element array in the above invention, and the calculation unit includes a temperature output detected by the temperature detection unit. And calculating the first and second correction values.

  The focus detection apparatus according to the present invention further includes an amplifier that amplifies an output of the photoelectric conversion element array in the above invention, and the calculation means includes the first and second amplifiers including the amplification degree of the amplifier. The correction value is calculated.

  According to the focus detection apparatus of the present invention, together with the first correction value for the fixed pattern noise generated depending on the accumulation time of the photoelectric conversion element array itself, the charge that temporarily holds the output charge of the photoelectric conversion element array In calculating the second correction value for the fixed pattern noise generated depending on the charge holding time of the holding unit, and calculating the focus information based on the digital value obtained by converting the output from the photoelectric conversion element array by the conversion unit, Since the digital value corrected using the first and second correction values is used, all the dark noise that can be generated in the multi-AF method that requires the charge holding unit is canceled, and the focus information is obtained. It is possible to calculate, more accurate focus detection is possible, and there is an effect that the focus detection accuracy at low luminance can be further improved.

  Exemplary embodiments of a focus detection apparatus according to the present invention will be described below with reference to the accompanying drawings. The present invention is not limited to this embodiment, and various modifications can be made without departing from the spirit of the present invention.

  FIG. 1 is a block diagram including a schematic mechanism showing an example of a configuration around an AF of a camera system to which the multi-AF type focus detection apparatus of the present embodiment is applied. Here, an example in which the TTL phase difference AF method is applied to a single-lens reflex camera is shown. Reference numeral 10 denotes an interchangeable lens that is detachably mounted on a camera body (not shown) and incorporates a photographing lens 11. An in-focus state is obtained by driving the photographing lens 11 in the optical axis direction by the motor driver 12. In the interchangeable lens 10, a lens CPU 13 that receives a defocus amount from the camera body side, calculates a driving amount of the photographing lens 11, and drives and controls the photographing lens 11 through the motor driver 12 by the driving amount. Is provided.

  On the other hand, in the camera body, a main mirror 14 is provided on the optical axis of the taking lens 11. The main mirror 14 has a movable mirror configuration, and is positioned at a down position as shown in the figure during AF, and splits the light beam that has passed through the photographing lens 11 into a finder optical system 16 and an AF optical system 19. When the subject is photographed, it is retracted upward, and the total luminous flux transmitted through the photographing lens 11 is guided to the image sensor 24. Here, as is well known, the finder optical system 16 is composed of an optical element such as a pentaprism, and a finder screen 15 is disposed in the preceding stage, and a finder eyepiece 17 that the photographer looks into is disposed in the subsequent stage. ing. A sub-mirror 18 is provided behind the main mirror 14 in the optical axis direction to totally reflect the light beam transmitted through the main mirror 14 toward the AF optical system 19 when the main mirror 14 is located at the down position. When the main mirror 14 is retracted up, the sub mirror 18 is retracted together at a position where the light flux to the image sensor 24 is not blocked.

  In addition, an AF sensor 20 is provided that generates a signal for focus detection by causing a light beam that has been split by the main mirror 14 and passed through the AF optical system 19 to enter a pair of internal photoelectric conversion elements. As will be described in detail later, the AF sensor 20 is a multi-AF sensor having a pair of photoelectric conversion element arrays for each of a plurality of focus detection areas.

  Further, a microcomputer (CPU) 21 that functions as a system controller that controls each part including AF-related control and image processing is provided in the camera body. The microcomputer (CPU) 21 transmits lens data necessary for the calculation prior to the calculation from the lens CPU 13, and transmits a defocus amount as an AF calculation result to the lens CPU 13. Between the AF sensor 20 and the microcomputer (CPU) 21, an AF controller 22 having an ASIC configuration that is controlled by the microcomputer (CPU) 21 and controls the AF sensor 20 is provided.

  In FIG. 1, a two-dimensional CCD device is used as the image sensor 24, but a film corresponds to a silver salt camera. A focal plane shutter 23 is provided in front of the image sensor 24.

  Next, configuration examples of the AF optical system 19 and the AF sensor 20 will be described. FIG. 2 is a schematic configuration diagram showing an example of the basic configuration of the AF optical system 19 including the AF sensor 20. Since the AF optical system 19 has a configuration of a known TTL phase difference AF optical system, it will be briefly described. When the photographic lens 11 is in focus, the light beam that has passed through the photographic lens 11 is focused on the imaging equivalent surface 31 that is a virtual surface on the front surface of the AF optical system 19, condensed and divided by the condenser lens 32, and paired. The light beam is narrowed by the separator diaphragm 33 and imaged by the pair of separator lenses 34 on the sensor arrays 35 </ b> A and 35 </ b> B that are a pair of photoelectric conversion element arrays in the AF sensor 20. Here, a known TTL phase difference AF method for measuring the defocus amount of the photographing lens 11 by measuring the imaging interval between the pair of sensor arrays 35A and 35B is constructed.

FIG. 3 is a schematic front view showing an arrangement of distance measuring points on the photographing screen 25 as an arrangement example of the multi-configuration AF sensor 20. The AF sensor 20 of the first embodiment shows an application example to a multi-AF sensor having 11 distance measuring points (focus detection areas) of 22 lines indicated by P _{1 to} P ₁₁ , for example, for horizontal lines. It is set as a combination of a horizontal sensor row and a vertical sensor row for vertical lines. Here, the distance measuring points P _{1 to} P ₃ are arranged in the upper stage, the distance measuring points P _{4 to} P ₈ are arranged in the middle stage, and the distance measuring points P _{9 to} P ₁₁ are arranged in the lower stage. Further, the distance measuring point P ₄ is arranged in the first vertical column, the distance measuring points P ₁ , P ₅ and P ₉ are arranged in the second vertical column, and the distance measuring points P ₂ , P ₆ and P ₁₀ are arranged in the vertical 3 direction. The distance measuring points P ₃ , P ₇ and P ₁₁ are arranged in the fourth column, and the distance measuring points P ₈ are arranged in the fifth column.

FIG. 4 is a schematic front view showing an arrangement example of the AF sensor 20 on the sensor chip 26 corresponding to the distance measuring points P _{1 to} P ₁₁ as shown in FIG. The sensor chip 26 is a pair of a reference portion and a reference portion corresponding to a pair of sensor arrays 35A and 35B, and includes reference portion horizontal sensor rows 41 _UA for upper, middle, and lower horizontal lines. 41 _CA , 41 _DA , reference portion horizontal sensor row 41 _UB , 41 _CB , 41 _DB for the upper, middle and lower horizontal lines, and vertical reference portion for the vertical lines of the first to fifth columns The sensor rows 41 _{1A to} 41 _5A and the vertical portion reference sensor vertical sensor rows 41 _{1B to} 41 _5B for the first vertical column to the fifth vertical column. Sensor chips corresponding to the distance measuring point P1 shown in FIG. 3 for example, on the sensor board 26 shown in FIG. 4, as shown by the thick and P _1, the reference unit horizontal sensor array 41 _UA, and reference It is assigned to the left side of the unit horizontal sensor column 41 _UB , the reference unit vertical sensor column 41 _2A , and the reference unit vertical sensor column 41 _2B .

Here, a configuration example for one line of each sensor row will be described with reference to a blowing portion in FIG.該吹out moieties are those showing the enlarged one line, for example, reference unit horizontal sensor array 41 _CB. The reference portion horizontal sensor row 41 _CB is divided into n islands for one line, here, five islands (ISLAND) n = 1 to 5 for the first to fifth rows, and each island n = 1 to 5 are assigned in order (the number of islands in the entire AF sensor 20 is N = 11). Here, the island is a plurality of pixel rows corresponding to the distance measuring points shown in FIG. 3, and in the case of the reference portion horizontal sensor row 41 _CB , each corresponds to the distance measuring points P _{4 to} P ₈ . . The pixels in the same island are controlled so as to have the same accumulation time. In addition, the sensor array is normally configured with one line per island, but in this embodiment, as shown by k = 1, 2 in order to improve accuracy, the sensor array of two lines per island is one. The configuration is a staggered arrangement with a / 2 pitch shift (in practice, a monitor PD is interposed between the lines as shown in FIG. 5). Correlation is calculated in each of the sensor lines for the two lines arranged in a staggered manner, the image shift amount is calculated, and the average value of the two image shift amounts is taken to obtain sensor noise (mainly shot noise). In addition to being able to reduce to 1 / (√2) times, it is possible to reduce the amount of error that appears in one pixel period. Similarly, the sensor rows other than the reference portion horizontal sensor row 41 _CB are each divided into a plurality of islands and have a staggered arrangement for two lines.

Next, a configuration example of the sensor circuit in the AF sensor 20 will be described with reference to FIG. FIG. 5 is a block diagram illustrating a configuration example of a sensor circuit in the AF sensor 20. In FIG. 5, for example, the configuration of the reference portion horizontal sensor row 41 _UA and the reference portion horizontal sensor row 41 _UB for a pair of horizontal lines is shown in detail. For example, the reference unit horizontal sensor row 41 _UB for the distance measuring points P _{1 to} P ₃ (islands n = 1 to 3) will be described as an example. The sensor row includes a monitor PD (photodiode) 411, 4 includes a PD unit 412 serving as a photoelectric conversion element array, a transfer switch unit 413, an ST unit 414 serving as a charge holding unit, a transfer switch unit 415, and a CCD unit 416 for charge transfer output. According to the configuration shown in the part, two lines of k = 1 and k = 2 are provided with the monitor PD 411 interposed therebetween.

Here, the monitor PD 411 performs a monitoring operation for controlling the accumulation time of the PD unit 412 of each island (ranging point), and the pixels within the same island (ranging point) have the same accumulation time. Therefore, it is provided in units of islands (ranging points). In the case of the reference unit horizontal sensor row 41 _UB , three monitor PDs 411 are provided for the distance measuring points P _{1 to} P ₃ (islands n = 1 to 3).

Further, as shown in FIG. 6, the PD unit 412 includes a plurality of PDs (photodiodes) 412a, 412b,... For each pixel, and accumulates charges according to the amount of received light. As shown in FIG. 7, when the pulse signal TG1 _n generated at the accumulation end timing of the PD unit 412 of each island n is input based on the output of the monitor PD 411, the transfer switch unit 413 receives the PD unit in the same island. The output charge accumulated in each PD 412a, 412b,... 412 is moved to the corresponding island ST section 414. The ST unit 414 temporarily holds the output charge of the PD unit 412 until the accumulation operation of the corresponding PD unit 412 ends and the operation of the A / D converter described later starts. As shown in FIGS. 6 and 7, the charge held in the ST unit 414 is output to the CCD unit 416 all at once when a pulse signal TG2 _n instructing transfer output is input to the transfer switch unit 415. It is output to an FDA (floating diffusion amplifier) 42 _UB at a timing according to the clock signals φ1 and φ2.

Here, the unnecessary charge of the PD unit 412 is reset by outputting a pulse signal TG1 _n to the transfer switch unit 415 and sweeping the unnecessary charge to the ST unit 414. Further, the resetting of unnecessary charges in the ST unit 414 is performed by setting the reset signal φRS for the ST unit 414 to the H level. That is, as shown in FIG. 7, the reset signal φRS is always turned on (H level) before the accumulation operation starts, thereby sweeping out the charge of the ST unit 414 and off at the time of the accumulation operation start (L level). ).

The configuration of other sensor arrays is the same, and the output signal of the monitor PD unit 411 of each sensor array is input to an integration time control circuit 47 which is an accumulation control means via a multiplexer (MUX) 46. A pulse signal TG1 _n is output from the integration time control circuit 47 to the transfer switch unit 413 corresponding to each island.

  The signal output from the CCD unit 416 to the FDA 42 is subjected to a removal process of amplifier noise and reset noise by a CDS (correlated double sampling) circuit 43, and then the amplification degree (gain) is 1 time, 2 times, and 4 times. , Variable by 8 times, and amplified by an amplifier (amplifier) 44 for setting the amplification factor at the time of reading. The output signal amplified by the amplifier 44 is configured to be output to the AF controller 22 from the respective output terminals Vout1 and Vout2 through selection processing by the output selection unit 45 of each of the reference unit system and the reference unit system. ing.

  The temperature sensor 46 serving as a dark current correction temperature detection unit is disposed at an appropriate location on the sensor chip 26. As the temperature sensor 46 for detecting the ambient temperature of the sensor chip 26, a photodiode having a temperature characteristic similar to that of the PD unit 412 or the like is used. The signal line is used to output to the AF controller 22 side.

  FIG. 8 is a schematic block diagram illustrating a configuration example of the AF controller 22. The AF controller 22 includes a sequencer 51 that controls the operation of the AF sensor 20 under the control of the microcomputer (CPU) 21, an A / D converter 52, a data memory 53, an AF calculation unit 54, a timer 55, a register 56, flash ROM 57, and the like. The A / D converter 52 is for converting the CCD output output from the AF sensor 20 side and the output of the temperature sensor 46 into digital data. In this embodiment, for example, the reference unit output terminal Vout1 is referred to. Two A / D converters are provided corresponding to the output terminal Vout2. The data memory 53 stores the data A / D converted by the A / D converter 52 and provides it for the calculation of focus information.

  The timer 55 serving as a time measuring means counts the elapsed time when the accumulation operation is started, and holds the timer count value when the accumulation end signal for each island is received from the AF sensor 20 in the register 56 for each island. Thereby, the AF controller 22 uses the timer count value at the end of accumulation for each island held in the register 56, so that the accumulation time and the charge retention time at the time of dark output of the PD unit 412 and ST unit 414 for each island. Is calculated.

Here, the accumulation end determination of the PD unit 412 for each island is performed based on the output of the monitor PD 411. The reset signal φRM for the monitor PD 411 is common to the monitor PDs of all islands, and the monitor PD 411 is reset by switching the reset signal φRM from the H level to the L level as shown in FIG. When the output of the monitor PD 411 becomes equal to or lower than a preset threshold voltage V _TH for generating TG1, the pulse signal tg1 is output to the integration time control circuit 47, and the accumulation operation is terminated. Based on this pulse signal tg1, the integration time control circuit 47 outputs a pulse signal TG1 to the transfer switch 413 of the corresponding island.

That is, the accumulation operation for the PD unit 412 is started at the same timing for all the islands 1 to N as shown in FIG. 7, and when the output of the monitor PD 411 becomes equal to or higher than a predetermined value, integration in the sensor circuit The integration is automatically terminated under the control of the time control circuit 47. However, even if the output of the monitor PD 411 does not exceed a certain value, the integration operation is automatically terminated when it is detected that the preset maximum integration time has been reached in the sensor circuit. Alternatively, also in the AF controller 22, when the timer 55 detects that the maximum accumulation time has been reached, a read command is issued to the AF sensor 20 to forcibly terminate the accumulation operation. When the accumulation operation ends, a corresponding island accumulation end signal (pulse signal TG1 _N ) is output from the integration time control circuit 47. The accumulation time is obtained by detecting how long the accumulation end signal (pulse signal TG1 _N ) is output after the accumulation operation is started by the timer 55. Here, the time when the dark current is generated in the PD unit 412 and the ST unit 414 of each island depends on the accumulation time of each island and the charge transfer start timing of the CCD unit 415. By counting the generated timing with the timer 55, the dark current generation time can be grasped.

An AF calculation unit 54 serving as a calculation means performs a correlation calculation according to a TTL phase difference method based on a digital value which is a CCD output A / D converted by the A / D converter 52 and stored in the data memory 53, and a distance measuring point P calculating a focus information for each ₁ to P _11. In this calculation, noise (kTc noise) and amplifier noise generated due to thermal noise by the CDS circuit 44 in the sensor circuit are substantially reduced, but the CCD output includes a noise component due to dark current. Therefore, it is necessary to delete the dark current noise component by offset correction.

  Here, the dark current is generated not only in the PD unit 412 itself but also in the charge holding unit 414 that temporarily holds the output charge of the PD unit 412, and in the PD unit 412 as shown in FIG. Therefore, it is necessary to individually calculate and correct the dark current component generated in each of the storage time and the charge holding time in the charge holding unit 414. In particular, as shown in FIG. 10, the influence of the ST part dark current is more dominant than the PD part dark current.

  Therefore, in the AF calculation unit 54 of the present embodiment, the first correction value for the dark current noise that is fixed pattern noise generated depending on the accumulation time by the PD unit 412 and the charge holding time of 414 in the ST unit. The second correction value for dark current noise, which is a fixed pattern noise that occurs depending on the calculation, is calculated separately, and the focus for each island based on the digital value corrected using the first and second correction values. Compute information.

  In order to perform this correction processing, in this embodiment, the first fixed pattern noise FPN1 generated in the PD unit 412 and generated in the ST unit 414, which is measured in advance at the time of shipment from the factory, and the second fixed pattern generated in the ST unit 414. The noise FPN2 is stored in the flash ROM 57 for each island (for each distance measuring point), and when the AF calculation unit 54 calculates the focus information of the desired island (range measuring point), the corresponding PD unit 412 Based on the accumulation time and the first fixed pattern noise FPN1 of the PD unit 412 stored in the flash ROM 57, a first correction value (black data (PD unit)) is calculated, and the charge of the corresponding ST unit 414 is calculated. The second correction value (black data (ST section)) based on the holding time and the second fixed pattern noise FPN2 of the ST section 414 stored in the flash ROM 57 After calculating and correcting the CCD output based on the first and second correction values (black data (PD part)) + (black data (ST part)), the focus information is obtained. Calculate.

  Here, acquisition of the first fixed pattern noise FPN1 and the second fixed pattern noise FPN2 will be described with reference to FIGS. FIG. 11 is a schematic flowchart showing a processing procedure for acquiring fixed pattern noise data, FIG. 12 is a timing chart showing an example of a waveform when acquiring the second fixed pattern noise FPN2 data, and FIG. It is a timing chart which shows the example of a waveform at the time of fixed pattern noise FPN1 data acquisition.

  This process is executed by starting up the CPU 21 and the AF controller 22 in the test mode. In general, by outputting the CCD sensor output data in the dark at the factory, the dark output data of the PD unit 412 and the ST unit 414 after a lapse of a certain time is acquired, and the data is stored in a non-volatile flash. Write to ROM57. First, the dark output data of the ST unit 414 is acquired with the accumulation time of the PD unit 412 set to 0 msec, the charge holding time of the ST unit 414 set to 300 msec, and the gain of the amplifier 44 set to 8 times (step S101). Here, the charge holding time 300 msec of the ST unit 414 is set as an example of the maximum time in a range where the output is not saturated in the actual use environment so that other error factors can be reduced. In the process of step S101, as shown in FIG. 12, the PD units 412 of the islands 1 to N end the accumulation immediately after the accumulation starts because the accumulation time is 0 msec.

Then, when 300 msec has elapsed from the start of accumulation, the pulse signal TG2 is turned on to start transfer by the CCD unit 416 (step S102). At this time, since the transfer for each island is completed and the pulse signals TG2 _{1 to} TG2 _N are sequentially output and cannot be transferred at the same time, the CCD transfer start timing for each island, and hence the charge holding time for each ST unit 414 Causes a shift of + α (for example, 3 msec at the maximum), so that a process for correcting the shift amount of the charge retention time of the acquired data is performed (step S103). That is, a process of normalizing the error amount of α deviating from the set charge holding time of 300 msec by 300 msec is performed. Then, the charge retention time, which is the acquired data of the ST unit 414 for each island with the amount of deviation corrected, is written in the flash ROM 57 as the second fixed pattern noise FPN2 (factory reference value) (step S104).

Next, the dark output data of the PD unit 412 is acquired with the accumulation time of the PD unit 412 set to 300 msec, the charge holding time of the ST unit 414 set to 300 msec, and the gain of the amplifier 44 set to 8 times (step S105). When 300 msec has elapsed from the start of accumulation, the pulse signals TG1 _{1 to} TG1 _N are turned on to end the accumulation operation of the PD unit 412 and the pulse signal TG2 is turned on to start transfer by the CCD unit 416. (Step S106). At this time, since the transfer for each island is completed and the pulse signals TG2 _{1 to} TG2 _N are sequentially output and cannot be transferred at the same time, the CCD transfer start timing for each island, and hence the charge holding time for each ST unit 414 Causes a shift of + α (for example, 3 msec at the maximum), so that dark current data of only the PD unit 412 is calculated and a process for correcting the shift amount of the charge holding time is performed (step S107). That is,
PD part dark current (i) = (PD part + ST part) Dark current (i) -ST part dark current (i)
As described above, dark current data of the PD unit 412 is calculated. Here, i indicates the pixel position, and the ST portion dark current (i) value is a value that has already been obtained by the above-described processing. Then, the storage time, which is the acquired data of the PD unit 412 for each island in which the deviation amount of the ST unit is corrected, is written in the flash ROM 57 as the first fixed pattern noise FPN1 (factory reference value) (step S108).

In the AF calculation unit 54, the accumulation time of the PD unit 412 for each island (current time) measured using the timer 55 or the like, the charge holding time of the ST unit 414 (current time), and the temperature acquired from the temperature sensor 46 (current time). And the offset correction value (i) for each pixel based on the set gain of the amplifier 44,
Offset correction value (i)
= First correction value + second correction value = black data (PD portion) (i) + black data (ST portion) (i)
Black data (PD part) (i)
= Factory standard value (i) x {accumulation time (current) / accumulation time (factory)}
× 2 ^ {(Temperature (current) -Temperature (factory)) / 8 ° C} × Setting gain = FPN1 (i) × (Accumulation time (current) / 300 msec)
× 2 ^ {(Temperature (current) -Temperature (factory)) / 8 ℃} × Set gain Black data (ST section) (i)
= Factory reference value (i) × {charge retention time (current) / charge retention time (factory)}
× 2 ^ {(Temperature (current) -Temperature (factory)) / 8 ° C} × Setting gain = FPN2 (i) × (Charge holding time (current) / 300 msec)
* 2 ^ {(Temperature (current) -Temperature (factory)) / 8 [deg.] C. * Calculated based on the set gain. 2 ^ {(Temperature (current) -Temperature (factory)) / 8 ° C.} is performed because the calculation is doubled every 8 ° C. The reason why the setting gain of the amplifier 44 is multiplied is that the dark current value varies according to the value of the setting gain.

The AF calculation unit 54 corrects the uncorrected value (i), which is a digital value obtained from the A / D converter 52 as CCD data, by correcting the offset correction value (i).
Value after correction (i) = Value before correction (i) −Offset correction value (i)
Is used to perform processing for calculating focus information such as subsequent correlation calculation.

  FIG. 14 is a schematic flowchart showing an example of focus detection / focus correction operation with dark current correction executed by the CPU 21 control. First, with the first release (step S201; Yes), an accumulation operation for each PD unit 412 is started (step S202). When an accumulation end island is generated under the monitoring by the monitor PD 411, the accumulation time (current time) of the PD unit 412 of the target island is detected by the timer 55 (step S203). That is, the accumulation time (current) is the dark output generation time of the PD unit 412 shown in FIG. This process is repeated until the accumulation is completed for all islands (step S204).

Next, by sequentially outputting the pulse signals TG2 _{1 to} TG2 _N , transfer by the CCD unit 416 is started (step S206). Prior to the start of transfer, the dark output generation time in the ST unit 414 is set as the charge holding time (current time). ) And the offset correction value (i) is calculated by the FA calculation unit 54 (step S205). Then, the FA computing unit 54 performs offset correction of the digital value using the calculated offset correction value (i) (step S207), and after performing illuminance correction using the offset corrected digital value (step S208). ), A correlation calculation is performed according to the TTL phase difference method (step S209), and a defocus amount is calculated as focus information (step S210). A distance measuring point to be employed is selected in accordance with the calculated defocus amount (step S211), and the CPU 21 outputs the defocus amount at the distance measuring point to the lens CPU 13, whereby the lens CPU 13 causes the motor driver 12 to operate. The focus lens 11 is controlled to drive the lens in a focused state (step S212). As a result, it becomes possible to capture an image, and the process proceeds to an imaging operation.

1 is a block diagram including a schematic mechanism showing an example of a configuration around an AF of a camera system to which a multi-AF focus detection apparatus according to an embodiment is applied. It is a schematic block diagram which shows the example of a fundamental structure of AF optical system including an AF sensor. It is a schematic front view which shows the ranging point arrangement | positioning on an imaging | photography screen. It is a schematic front view which shows the example of arrangement | positioning on the sensor chip of the AF sensor corresponding to the ranging point shown in FIG. It is a block diagram which shows the structural example of the sensor circuit in AF sensor. It is a schematic block diagram which shows a part of sensor structure. It is a timing chart which shows accumulation | storage operation | movement. 2 is a schematic block diagram illustrating a configuration example of an AF controller 22. FIG. It is a timing chart which shows operation | movement of monitor PD. It is a schematic diagram which shows the PD dark current in the reference | standard part and a reference part, ST dark current, and the data after correction | amendment. It is a schematic flowchart which shows the process sequence of fixed pattern noise data acquisition. It is a timing chart which shows the example of a waveform at the time of the 2nd fixed pattern noise FPN2 data acquisition. It is a timing chart which shows the example of a waveform at the time of the 1st fixed pattern noise FPN1 data acquisition. It is a schematic flowchart which shows the example of a focus detection and a focus correction operation | movement with dark current correction performed by CPU control.

Explanation of symbols

44 Amplifier 46 Temperature Sensor 47 Integration Time Control Circuit 52 A / D Converter 54 AF Operation Unit 55 Timer 57 Flash ROM
412 PD section (photoelectric conversion element array)
414 ST part (charge holding part)
P ₁ ~P ₁₁ distance measuring point

Claims (5)

A plurality of photoelectric conversion element arrays corresponding to a plurality of focus detection areas;
A conversion unit that converts an output from the photoelectric conversion element array into a digital value;
A charge holding unit that is provided for each photoelectric conversion element row, temporarily holds the output charge of the photoelectric conversion element row until the accumulation operation of the photoelectric conversion element row is finished and the operation of the conversion unit is started;
A first correction value for fixed pattern noise generated depending on the accumulation time by the photoelectric conversion element array, and a second correction value for fixed pattern noise generated depending on the charge holding time in the charge holding unit; Calculating means for calculating focus information for each focus detection region based on the digital values corrected using the first and second correction values,
A focus detection apparatus comprising: A plurality of photoelectric conversion element arrays corresponding to a plurality of focus detection areas;
A conversion unit that converts an output from the photoelectric conversion element array into a digital value;
A charge holding unit that is provided for each photoelectric conversion element row, temporarily holds the output charge of the photoelectric conversion element row until the accumulation operation of the photoelectric conversion element row is finished and the operation of the conversion unit is started;
A storage unit that stores first fixed pattern noise generated in the photoelectric conversion element array under a predetermined condition and second fixed pattern noise generated in the charge holding unit;
A calculation means for calculating focus information for each focus detection area based on the digital value;
With
The computing means is
When calculating the focus information, the first correction value is calculated based on the accumulation operation time of the photoelectric conversion element array and the first fixed pattern noise of the photoelectric conversion element array stored in the storage unit, Based on the time that the output charge of the photoelectric conversion element array is held in the charge holding section and the second fixed pattern noise corresponding to the photoelectric conversion element array stored in the storage section, a second correction value is obtained. A focus detection apparatus which calculates focus information after calculating and correcting the digital value which is an output of the photoelectric conversion element array based on the first and second correction values. A plurality of photoelectric conversion element arrays corresponding to a plurality of focus detection areas;
Accumulation control means for controlling the accumulation operation of the photoelectric conversion element arrays;
A charge holding unit that is provided for each photoelectric conversion element row and temporarily holds the output charge when the accumulation operation of the photoelectric conversion element is completed;
Time measuring means for measuring an accumulation time by the photoelectric conversion element array and a charge holding time in which the output charge of the photoelectric conversion element array is held in the charge holding unit;
A conversion unit that converts an output from the charge holding unit into a digital value;
A storage unit that stores first fixed pattern noise that is measured in a predetermined condition and is generated in each photoelectric conversion element array, and second fixed pattern noise that is generated in each charge holding unit, and
A calculation means for calculating focus information for each focus detection area based on the digital value;
With
The computing means is
When calculating the focus information of a desired focus detection region, the first fixed pattern noise of the photoelectric conversion element array stored in the storage unit and the first fixed pattern noise stored in the storage unit A correction value is calculated, and a second correction is performed based on the charge holding time of the corresponding charge holding unit and the second fixed pattern noise of the charge holding unit corresponding to the photoelectric conversion element array stored in the storage unit Focus detection is performed by calculating a focus value after calculating a value and correcting the digital value that is an output of the photoelectric conversion element array based on the first and second correction values. apparatus. A temperature detection unit that detects an ambient temperature of the photoelectric conversion element array;
The said calculating means performs calculation of said 1st and 2nd correction value including the temperature output detected by the said temperature detection part, The Claim 1 characterized by the above-mentioned. Focus detection device. An amplifier that amplifies the output of the photoelectric conversion element array;
The focus detection apparatus according to claim 1, wherein the calculation unit calculates the first and second correction values including an amplification degree of the amplifier.

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