JP6272073B2 - Imaging device, control method thereof, and control program - Google Patents

Description

  The present invention relates to an imaging apparatus, a control method thereof, and a control program.

  In general, an image sensor that converts light into an electric signal is used in an image pickup apparatus such as a digital video camera or a digital still camera, and various electronic devices such as a facsimile. As this image sensor, for example, a complementary metal-oxide semiconductor (CMOS) type image sensor is known.

  In a CMOS type image sensor, an A / D (Analog / Digital) conversion unit provided with an electric signal (analog signal) read from a plurality of pixels arranged in a two-dimensional matrix for each column is converted into a digital signal. There is what converts and outputs (refer patent document 1).

  In the A / D converter described above, an analog signal corresponding to the amount of incident light is input from the vertical signal line for each column, and the time until the voltage of the vertical signal line becomes equal to the reference voltage (ramp signal) is counted. The analog signal is converted into a digital signal according to the count value.

JP 2008-118634 A

  Here, output degradation in the conventional imaging apparatus will be described.

  FIG. 6 is a diagram for explaining the relationship between the amount of incident light and the output in a conventional imaging apparatus. FIG. 6A is a diagram illustrating a relationship between an incident light amount and an output in an image sensor used in a conventional imaging device, and FIG. 6B illustrates a relationship between a ramp signal used in the image sensor and time. FIG. FIG. 6C is a diagram illustrating the output of the imaging device when the gain of the output of the imaging device is increased, and FIG. 6D is a diagram illustrating the relationship between the incident light amount and the output of the imaging device. is there.

  As described above, the image sensor A / D-converts an analog signal corresponding to the amount of incident light and outputs it as a digital signal. On the other hand, in recent years, with the increase in the speed of the image sensor, for example, as shown in FIG. And coloring may occur at a specific gradation.

  As shown in FIG. 6B, such linearity degradation is caused by degradation of the linearity of the ramp signal due to the transient response characteristic in the period y corresponding to the rise of the ramp signal. Such deterioration of linearity becomes more prominent as the slope of the ramp signal becomes steeper.

  In addition, the A / D conversion period needs to be shortened when the frame rate at the time of reading the image sensor increases or the amount of read data per hour increases. The shortening of the A / D conversion period and the deterioration of the linearity of the ramp signal are in a trade-off relationship.

  By the way, the digital signal output from the imaging device may be gain-adjusted (for example, increased) by a digital signal processor (DSP) provided in the imaging device. Some image pickup devices include a color filter for each pixel. In this type of image pickup device, white balance is adjusted by increasing the gain for each color filter (that is, for each pixel output). Furthermore, the gain is increased in order to obtain a high sensitivity that exceeds the upper limit sensitivity of the image sensor.

  As shown in FIG. 6C, although gain increase by the DSP ideally has linearity, degradation of linearity actually occurs. That is, as shown in FIG. 6D, when the gain of the output of the image sensor is increased by the DSP, the linearity is deteriorated in a wide region of the output range A.

  For example, when “DSP gain up x1” (1 × gain up), degradation of linearity occurs in the output range B of the imaging apparatus, and when “DSP gain up x2” (2 times gain up), Linearity degradation occurs in the corresponding output range A.

  As shown in FIG. 6A, in the output of the image sensor, the linearity is significantly deteriorated in the low output level portion (output region B) as compared with the high output level portion (output region C). On the other hand, in the output of the image pickup apparatus at “DSP gain up x2” shown in FIG. 6D, only the low output level portion (output region B shown in FIG. 6A) in which the linearity deterioration in the output of the image pickup device is remarkable. As a result, linearity degradation in the output of the imaging apparatus as described above occurs.

  As a result, in the output of the image pickup apparatus, coloring may occur in a specific gradation particularly when high sensitivity is set.

  An object of the present invention is to provide an imaging apparatus, a control method therefor, and a control program that can suppress coloring of a specific gradation even when high sensitivity is set.

  In order to achieve the above object, an imaging apparatus according to the present invention compares a plurality of pixels arranged in a two-dimensional matrix, an analog signal read from the plurality of pixels, and a ramp signal, and the comparison result. An imaging device having an A / D conversion unit that counts according to the analog signal and outputs a digital signal corresponding to the analog signal, and a gain adjustment unit that performs gain adjustment on the digital signal, Control means for controlling the operation of the A / D conversion means with an output dynamic range corresponding to the input dynamic range in the gain adjustment means, and a voltage corresponding to the difference between the output dynamic range and the input dynamic range to a maximum voltage The initial voltage of the ramp signal is changed as compared with the case where the gain adjustment is not performed. Characterized in that it has a setting means.

  According to the control method of the present invention, the plurality of pixels arranged in a two-dimensional matrix, the analog signal read from the plurality of pixels, and the ramp signal are compared, and counting is performed according to the comparison result. A method for controlling an imaging apparatus, comprising: an imaging device having an A / D conversion unit that outputs a digital signal corresponding to an analog signal; and a gain adjustment unit that performs gain adjustment on the digital signal. A control step of controlling the operation of the means with an output dynamic range corresponding to the input dynamic range in the gain adjusting means; and a voltage corresponding to a difference between the output dynamic range and the input dynamic range as a maximum voltage. A setting step for changing the setting of the initial voltage with respect to the case where the gain adjustment is not performed; Characterized in that it has.

  The control program according to the present invention compares a plurality of pixels arranged in a two-dimensional matrix, an analog signal read from the plurality of pixels, and a ramp signal, and performs counting according to the comparison result. A control program used in an imaging apparatus having an imaging device having an A / D conversion unit that outputs a digital signal corresponding to an analog signal, and a gain adjustment unit that performs gain adjustment on the digital signal. A control step of controlling the operation of the A / D conversion means in an output dynamic range corresponding to the input dynamic range in the gain adjusting means, and a computer according to a difference between the output dynamic range and the input dynamic range. The initial voltage of the ramp signal is set as the maximum voltage, and the gain adjustment is performed. A setting step of changing the setting for the case of not performing, characterized in that for the execution.

  According to the present invention, the operation of the A / D conversion unit is controlled by the output dynamic range corresponding to the input dynamic range in the gain adjustment unit, and the voltage corresponding to the difference between the output dynamic range and the input dynamic range is set as the maximum voltage. The setting of the initial voltage of the ramp signal is changed when gain adjustment is not performed. As a result, it is possible to suppress coloring of a specific gradation even when setting high sensitivity.

1 is a block diagram illustrating a configuration of an example of an imaging apparatus according to a first embodiment of the present invention. It is a block diagram which shows the example about the structure of the image pick-up element shown in FIG. 3 is a timing chart for explaining the operation of the AD converter shown in FIG. 2. It is a figure which shows the linear characteristic of the video signal which is the incident light quantity of the image pick-up element shown in FIG. 2, and the output of a camera. It is a timing chart for demonstrating operation | movement of the AD conversion part with which the image pick-up element used with the camera which concerns on the 2nd Embodiment of this invention was equipped. It is a figure for demonstrating the relationship between the incident light quantity and output in the conventional imaging device, (a) is a figure which shows the relationship between the incident light amount and output in the image pick-up element used with the conventional imaging device, (b) is. The figure which shows the relationship between the ramp signal used with an image pick-up element, and time, (c) is a figure which shows the output of an imaging device at the time of gain-up of the output of an image pick-up element, (d) is the incident light quantity, the output of an image pick-up device, and It is a figure which shows the relationship.

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

[First Embodiment]
FIG. 1 is a block diagram showing the configuration of an example of an imaging apparatus according to the first embodiment of the present invention.

  The illustrated imaging apparatus is, for example, a digital still camera (hereinafter simply referred to as a camera), and includes an imaging optical system (hereinafter simply referred to as an optical system) 1001. Although not shown, in this optical system 1001, a zoom lens, a diaphragm mechanism, and the like are arranged in a lens barrel. Then, the optical image (subject image) that has passed through the optical system 1001 is formed on the light receiving surface of the CMOS type image sensor 1002.

  The optical system 1001 is controlled by a CPU 1004 to be described later, and the CPU 1004 performs drive control of the optical system 1001 to perform autofocus (AF) control and the like.

  The image sensor 1002 outputs a digital signal corresponding to the optical image. That is, the illustrated image sensor 1002 performs OB (optical black) clamping and A / D conversion, and outputs a digital signal. The digital signal is sent to a digital signal processor (DSP) 1007 as an imaging signal.

  The CPU 1004 controls the entire camera. The CPU 1004 develops the program recorded in the ROM 1005 in the RAM 1006 and controls the camera. In addition, the CPU 1004 instructs the image sensor 1002 by using a signal DRAMGE, an input range necessary for an input signal (that is, an image signal) of the DSP 1007.

  The ROM 1005 stores a program such as firmware for controlling the camera, and the RAM 1006 is used as a memory for temporarily storing control information related to the camera.

  The above-described DSP 1007 performs various types of signal processing on the imaging signal that is the output of the imaging device 1002 to generate a still image or moving image video signal (for example, a YUV signal) in a predetermined format. The external interface 1008 includes various encoders and D / A converters, and transmits and receives various control signals and data to and from external elements (here, the display 1012, the memory medium controller 1010, and the operation panel 1011).

  The display 1012 displays an image corresponding to a video signal (image data) sent from the external interface 1008. Although the display 1012 is incorporated in the camera, in addition to the display 1012, image data may be transmitted from an external interface 1008 to an external display device (not shown) to display an image.

  A memory medium 1009 is attached to the memory medium controller 1010. The memory medium 1009 is, for example, a memory card, and the memory medium controller 1010 stores image data in the memory medium 1009. Further, the memory medium controller 1010 reads the image data stored in the memory medium 1009 under the control of the CPU 1004.

  In addition to the memory card, for example, a disk medium using magnetism or light can be used as the memory medium 1009.

  The operation panel 1011 is operated by a user at the time of shooting, and the user gives various instructions using the operation panel 1011. The CPU 1004 controls the camera in response to an instruction input from the operation panel 1011.

  FIG. 2 is a block diagram showing an example of the configuration of the image sensor 1002 shown in FIG.

  The illustrated image sensor 1002 is a CMOS type image sensor as described above. The image sensor 1002 includes a pixel array 2001, a vertical scanning unit 2002, an A / D conversion unit 2003, a reference voltage generation unit (ramp signal generation unit) 2004, a horizontal scanning unit 2005, a horizontal output line 2006, a timing control unit 2007, A vertical output line 2015 and an amplifier reference voltage generation unit 2016 are provided.

  The A / D conversion unit 2003 includes an amplifier 2014 and an A / D conversion circuit 2013 for each column signal line (that is, the vertical output line 2015). Each of the A / D conversion circuits 2013 includes a comparator 2009 and an up / down counter 2011.

  A timing control unit 2007 controls operation timings of the vertical scanning unit 2002, the A / D conversion unit 2003, the reference voltage generation unit 2004, and the horizontal scanning unit 2005 under the control of the CPU 1004. Note that the timing control unit 2007 is supplied with a timing control clock MCLK from the CPU 1004.

  In the operation timing control, the timing control unit 2007 supplies an operation clock ADCLK for operating the up / down counter 2011 to the up / down counter 2011, and a switching signal for switching between the up count and the down count in the up / down counter 2011. Down select is given to the up / down counter 2011. The operation clock ADCLK is also supplied to the reference voltage generation unit 2004.

  The timing control unit 2007 receives the signal DRANGE from the CPU 1004 and sends an offset setting value related to the output voltage of the amplifier 2014 to the amplifier reference voltage generation unit 2016. Note that the signal DRANGE is a signal indicating the input range of the DSP 1007.

  The pixel array 2001 has a plurality of unit pixels (hereinafter simply referred to as pixels) 2008 arranged in a two-dimensional matrix. Each of the pixels 2008 converts the received light into a signal voltage, and outputs the signal voltage to a column signal line (that is, a vertical output line 2015) provided for each column.

  The vertical operation unit 2002 performs vertical scanning for sequentially selecting the rows in the image array 2001. An amplifier 2014 is connected to each of the vertical output lines 2015, and an amplifier reference voltage is given to the amplifier 2014 from the amplifier reference voltage generation unit 2016. The amplifier reference voltage generation unit 2016 sends an offset signal (OFFSET) corresponding to the offset setting value sent from the timing control unit 2007 to the amplifier 2014.

  This offset signal is a signal corresponding to the difference between the output range of the image sensor 1002 and the input range of the DSP. The amplifier 2014 changes the offset amount of the output voltage according to the offset signal.

  The amplifier 2014 amplifies the analog signal that is the output of the vertical output line 2015, and sends the amplified signal to the comparator 2009 as an amplified signal. A reference voltage (that is, a ramp signal) is supplied from the reference voltage generation unit 2004 to the comparator 2009, and the comparator 2009 compares the voltage (analog signal) of the vertical output line 2015 and the reference voltage (ramp signal). The comparator 2009 outputs a comparison result signal (a high level (H) signal or a low (H) level signal) corresponding to the comparison result.

  Although not shown in FIG. 2, the operation clock ADCLK described above is frequency-divided by the frequency dividing unit, and a plurality of clock signals are supplied to the up / down counter 2011. The up / down counter 2011 operates in response to the clock signal, counts the comparison result signal that is the output of the comparator 2009, and outputs the count value. The count value that is the output of the up / down counter 2011 is held in the memory (MEM) 2012. In this way, the A / D conversion unit 2003 outputs a digital signal corresponding to the signal voltage output to the plurality of column signal lines (vertical output lines 2015) by A / D conversion.

  The horizontal scanning unit 2005 sequentially reads out the memory (MEM) 2012 under the control of the timing control unit 2007, and outputs a count value, that is, a digital signal, to the horizontal output line 2006.

  FIG. 3 is a timing chart for explaining the operation of the AD conversion unit 2003 shown in FIG.

  In FIG. 3, before the time t1, the ramp signal output from the reference voltage generation unit 2004 is set to an initial value (initial voltage: ramp signal reference voltage). Here, in the output of the image sensor 1002 (after A / D conversion), the width of the dynamic range is proportional to the bit length of the digital signal. Here, description will be made assuming that the accuracy of the up / down counter 2011 is 12 bits.

  It is assumed that the count speed of the up / down counter 2011 at the time of A / D conversion is always constant. Furthermore, when the slope of the ramp signal changes, the output of the image sensor 1002 changes. Specifically, the output of the image sensor 1002 decreases as the voltage change amount of the ramp signal per fixed time increases, and the output of the image sensor 1002 increases as the voltage change amount of the ramp signal per fixed time decreases. . Here, for convenience of explanation, it is assumed that the slope of the ramp signal set during A / D conversion is constant.

  Further, when the dynamic range (that is, output dynamic range) of the ramp signal in the image sensor 1002 is “a” and the input dynamic range of the DSP 1007 is “b”, the reference voltage of the ramp signal is set to the pixel output reference voltage. It is set upward by (ab) (that is, by (ab) as the maximum voltage). Thereby, the A / D conversion period of the S signal and the N signal falls within the linear period of the ramp signal (period in which the linearity does not deteriorate). However, in the actual ramp signal, the ratio between the linear period and the non-linear period (period in which the linearity deteriorates) changes due to the slope of the ramp signal and the stability of the peripheral circuit such as the power source.

  In the following description, it is assumed that the A / D conversion period of the S signal and the N signal ideally falls within the linear period of the ramp signal, but a part of the A / D conversion period of the S signal and the N signal is the ramp signal. Even if it overlaps with the non-linear period, coloring in a specific gradation is improved as compared with the conventional case.

  First, the timing control unit 2007 controls the timing of the reference voltage generation unit 2004, and raises an A / D conversion ramp signal (referred to as an N signal AD conversion ramp signal) related to the N signal at time t1. Here, the N signal refers to, for example, a signal generated when the pixel 2008 is reset.

  Immediately after the rise, the N signal AD conversion ramp signal exhibits a transient response characteristic, and a non-linear non-linear period occurs (time t1 to t2). When A / D conversion is performed in this non-linear period, the output of the image sensor 1002 shows linearity degradation with respect to the amount of incident light.

  The length of the non-linear period depends on the magnitude of the slope of the N signal AD conversion ramp signal (corresponding to the amount of voltage change per unit time). The larger the slope, the longer the non-linear period in the A / D conversion period. The amount of deviation from an ideal ramp signal that maintains linearity (linearity) increases.

  It is assumed that the N signal AD conversion ramp signal enters the linear period at time t2. In order to obtain good linear characteristics with respect to the output of the image sensor 1002, it is necessary to perform A / D conversion after the N signal AD conversion ramp signal enters the linear period.

  Conventionally, the ramp signal reference voltage is constant regardless of the gain setting in the DSP 1007. Therefore, as described with reference to FIG. 6, when gain adjustment (gain increase) is performed in the DSP 1007, linearity deterioration becomes remarkable, and coloring occurs in a specific gradation.

  At time t <b> 3, under the control of the timing control unit 2007, the vertical scanning unit 2002 performs vertical scanning and reads the N signal in the pixel 2008 to the vertical signal line 2015. The N signal read out to the vertical output signal line 2015 is subjected to gain adjustment and offset adjustment in the amplifier 2014 and then input to the comparator 2009.

  Here, it is assumed that the offset amount in the offset adjustment is constant regardless of the gain increase setting of the DSP 1007. A signal input from the amplifier 2014 to the comparator 2009 is a pixel output.

  At time t4, the magnitudes of the N signal AD conversion ramp signal and the pixel output are inverted, and the output of the comparator 2009 becomes H level. The output control of the comparator 2009 is performed by the timing control unit 2007.

  When the output of the comparator 2009 becomes H level, the up / down counter 2011 starts counting the N signal by down-counting. The up / down counter 2011 counts N signals while the output of the comparator 2009 is at the H level.

  This period (that is, the H level period) is the N signal count period. The period from time t4 to time t6 when the N signal AD conversion ramp signal ends is the N signal A / D conversion period.

  At time t5, the relationship between the N signal AD conversion ramp signal and the pixel output is reversed, and the output of the comparator becomes L level. As a result, the up / down counter 2011 stops down-counting. Note that the stop of the downcount changes between times t4 and t6 according to the output of the N signal. At time t6, the N signal AD conversion period ends. At this time, the N signal AD conversion ramp signal is reset to the ramp signal reference voltage.

  Subsequently, under the control of the timing control unit 2007, the vertical scanning unit 2002 performs vertical scanning, and reads the S signal of the pixel 2008 to the vertical signal line 2015 during a period from time t7 to time t8. Note that the S signal is a signal by photoelectric conversion in the pixel 2008 (that is, an image signal).

  At time t <b> 9, the timing control unit 2007 controls the timing of the reference voltage generation unit 2004 to raise an A / D conversion ramp signal (referred to as an S signal AD conversion ramp signal) related to the S signal. Here, the period from time t9 to t10 is a non-linear period of the S signal AD conversion ramp signal.

  At time t11, the up / down counter 2011 starts counting the S signal under the control of the timing control unit 2007. At this time, the timing control unit 2007 sets the switching signal Down select to L level and performs up-counting by the up / down counter 2011. Further, at the same timing, the magnitudes of the S signal AD conversion ramp signal and the pixel output are inverted, and the output of the comparator 2009 becomes H level.

  When the output of the comparator 2009 becomes H level, the up / down counter 2011 starts counting the S signal by up-counting. The up / down counter 2011 counts the S signal while the output of the comparator 2009 is at the H level.

  This period (that is, the H level period) is the S signal count period, and the period from time t11 to time t13 when the S signal AD conversion ramp signal ends is the S signal AD conversion period.

  At time t12, the relationship between the S signal AD conversion ramp signal and the pixel output is reversed, and the output of the comparator 2009 becomes L level. As a result, the up / down counter 2011 stops the up-counting. Note that the stop of the up-count changes between time t11 and time t13 according to the output of the S signal.

  Now, when the gain increase in the DSP 1007 is “× 1” (1 ×) and the accuracy of the up / down counter 2011 is 12 bits, the maximum count value is 4095 LSB. When the DSP 1007 gain is “× 2” (doubled), when the S signal is counted until time t13 shown in FIG. 3, the maximum count value is 2047LSB.

  The maximum count value when gain is increased by the DSP 1007 is equal to a value obtained by multiplying the maximum count value without gain increase by the ratio of the dynamic range a and the input dynamic range b of the DSP 1007. Further, if the power supply of the comparator is turned off after the count value of the up / down counter 2011 reaches the input dynamic range maximum value of the DSP 1007, it leads to power saving. That is, here, the A / D conversion period corresponding to the input dynamic range of the DSP 1007 is minimized, and when a predetermined period has elapsed from the start of the A / D conversion period, the reference voltage generation unit 2004 is turned off and the comparator 2009 is turned on. Stop.

  When the count period of the ramp signal is A and the count period corresponding to the dynamic range of the DSP 1007 is B, the N signal count period start time and the S signal count period start time are respectively from the rising edge of the N signal AD conversion ramp signal ( After AB and after the rising of the S signal AD conversion ramp signal (AB). The reason why the N signal count period start time and the S signal count period start time are defined in this way is that the count period B corresponding to the dynamic range of the DSP 1007 does not have to be in a non-linear period.

  Further, the difference between the ramp reference voltage and the pixel output reference voltage is reduced, and the start time of the N signal count period and the S signal count period is set to the front side after the passage of the ramp signal (A−B). Thus, the timing at which the S signal count value reaches the maximum value can be advanced. As a result, the power supply of the comparator 2009 can be turned off earlier to realize further power saving.

  FIG. 4 is a diagram illustrating the linear characteristic of the video signal that is the output of the camera and the incident light amount of the image sensor shown in FIG.

  In FIG. 4, the horizontal axis indicates the normalized light amount level obtained by normalizing the light amount incident on the pixel 2008, and the vertical axis indicates the output level (device output level) of the camera. The device output level is an output obtained by multiplying the output (S signal-N signal) of the image sensor 1002 by a gain in the DSP 1007. In FIG. 4, the linearity characteristic of gain × 1 (1 time) in the DSP 1007 is equal to the linearity characteristic shown in FIG.

  In the following description, two characteristics when the gain of the DSP 1007 is “× 1” and “× 2” will be described.

  First, when the gain of the DSP 1007 is set to “× 1”, the output range of the apparatus output is A with respect to the dynamic range of the incident light quantity x with respect to the pixel 2008. In this case, linearity deterioration is observed in the output range B on the low output side.

  Here, the linearity degradation region occurs in the output range B of the image sensor 1002. This is because the range B of the ramp signal shown in FIG. 6B is used in the A / D conversion.

  Further, there is no linearity degradation in the output range C of the imaging output on the high output level side. This is because the range C of the ramp signal shown in FIG. 6B is used in the A / D conversion.

  When the gain of the DSP 1007 is “× 2”, as described with reference to FIG. 3, the ramp signal is output for a period corresponding to the difference between the input range of the DSP 1007 and the A / D conversion range of the image sensor 1002. The start of the S signal AD conversion period is delayed from the start of (that is, the count start timing is delayed). As a result, it is possible to use the range C of the ramp signal shown in FIG. 6B where there is no linearity degradation of the ramp signal.

  As a result, the output range of the apparatus output is “A” with respect to the dynamic range of the incident light amount y with respect to the pixel 2008. As a result, the DSP 1007 can convert the S signal and the N signal during the linear period of the ramp signal, and in particular, can suppress the deterioration of linearity when the sensitivity is high.

[Second Embodiment]
Subsequently, a camera according to a second embodiment of the present invention will be described.

  The configuration of the camera according to the second embodiment is the same as that of the camera shown in FIG. The configuration of the image sensor used in the camera according to the second embodiment is the same as that of the image sensor shown in FIG. Therefore, the description of the configuration of the camera and the image sensor is omitted here.

  FIG. 5 is a timing chart for explaining the operation of the A / D conversion unit 2003 provided in the image sensor used in the camera according to the second embodiment of the present invention.

  In the timing chart shown in FIG. 5, the operation in the normal output region of the A / D converter 2003 is shown. Here, before the time t1, the pixel output reference voltage is set substantially equal to the ramp signal reference voltage that is the output of the reference voltage generation unit 2004. Then, a predetermined offset is set for the pixel output from the pixel output reference voltage.

  For this reason, when the gain is increased by the DSP 1007, when the dynamic range of the ramp signal in the image sensor 1002 is “a” and the input dynamic range in the DSP 1007 is “b”, the pixel output with respect to the pixel output reference voltage ( Set downward by a-b).

  As a result, the A / D conversion period of the S signal and the N signal falls within the linear period of the ramp signal. However, in the actual ramp signal, the ratio between the linear period and the non-linear period changes due to the slope of the ramp signal and the stability of peripheral circuits such as the power supply.

  In the following description, it is assumed that the A / D conversion period of the S signal and the N signal ideally falls within the linear period of the ramp signal. However, a part of the A / D conversion period of the S signal and the N signal is a part of the ramp signal. Even if it overlaps with the non-linear period, coloring in a specific gradation is improved as compared with the conventional case.

  The operation from time t1 to t13 is the same as that in the timing chart described with reference to FIG.

  As described above, in the second embodiment of the present invention, the DSP 1007 can convert the S signal and the N signal in the linear period of the ramp signal, and particularly suppresses the linearity degradation at the time of high sensitivity. be able to.

[Third Embodiment]
Next, a camera according to a third embodiment of the present invention will be described.

  The configuration of the camera according to the third embodiment is the same as that of the camera shown in FIG. The configuration of the image sensor used in the camera according to the third embodiment is the same as that of the image sensor shown in FIG. Therefore, the description of the configuration of the camera and the image sensor is omitted here.

  Here, the pixel output reference voltage is measured in advance and set so that the A / D conversion period is outside the non-linear period region. As a result, the usable area of the ramp signal is narrowed, the upper limit value of the count value of the up / down counter 2011 is lowered, and the output range of the image sensor 1002 is narrowed.

  With respect to the output of the image sensor 1002, the DSP 1007 can increase the gain, so that the camera can obtain the maximum output. Further, the slope of the ramp signal may be changed so as to compensate for the count that cannot be used as a result of the narrowing of the range. Thereby, the output range in the camera can be maintained.

  Specifically, using FIG. 5, the output range after narrowing the usable area of the ramp signal with respect to the output range “a” of the image sensor 1002 corresponds to “b”. Then, the change amount of the ramp signal corresponding to the passage of time is reduced by the ratio b / a. This makes it possible to compensate for the count that cannot be used by changing the pixel output reference voltage.

  As a result, in the third embodiment of the present invention, it is possible to ensure a dynamic range while eliminating degradation of linearity.

  As described above, according to the embodiment of the present invention, the A / D conversion circuit is provided for each column, and the A / D conversion circuit compares the output value for each column with the ramp waveform, and according to the result. When counting and converting to a digital signal, it is possible to avoid linearity deterioration due to transient characteristics at the rise of the ramp signal and to suppress coloring of a specific gradation at the time of setting high sensitivity.

  As is clear from the above description, in the example shown in FIGS. 1 and 2, the CPU 1004 and the DSP 1007 function as gain adjusting means. Further, the CPU 1004 and the timing control unit 2007 function as a control unit, a first setting unit, a second setting unit, and a third setting unit. Further, the CPU 1004 and the timing control unit 2007 function as power-off means.

  As mentioned above, although this invention was demonstrated based on embodiment, this invention is not limited to these embodiment, Various forms of the range which does not deviate from the summary of this invention are also contained in this invention. .

  For example, the function of the above embodiment may be used as a control method, and this control method may be executed by the imaging apparatus. Further, a program having the functions of the above-described embodiments may be used as a control program, and the control program may be executed by a computer included in the imaging apparatus. The control program is recorded on a computer-readable recording medium, for example.

  Each of the above control method and control program has at least a control step and a setting step.

  The present invention can also be realized by executing the following processing. That is, software (program) that realizes the functions of the above-described embodiments is supplied to a system or apparatus via a network or various recording media, and the computer (or CPU, MPU, etc.) of the system or apparatus reads the program. To be executed.

1002 Image sensor 1007 DSP
2001 Pixel array 2003 A / D conversion unit 2004 Reference voltage generation unit 2007 Timing control unit 2008 Unit pixel 2009 Comparator 2011 Up / down counter 2016 Amplifier reference voltage generation unit

Claims (11)

A plurality of pixels arranged in a two-dimensional matrix, and an analog signal read from the plurality of pixels and a ramp signal are compared and counted according to the comparison result, and a digital signal corresponding to the analog signal An image pickup device having an A / D conversion means for outputting and a gain adjustment means for performing gain adjustment on the digital signal,
Control means for controlling the operation of the A / D conversion means with an output dynamic range corresponding to an input dynamic range in the gain adjustment means;
A first setting means for changing the setting of the initial voltage of the ramp signal with respect to a case where the gain adjustment is not performed, with a voltage corresponding to a difference between the output dynamic range and the input dynamic range as a maximum voltage;
An imaging device comprising:   The imaging apparatus according to claim 1, wherein the control unit makes the output dynamic range substantially equal to the input dynamic range.   3. The imaging apparatus according to claim 1, wherein the first setting unit sets the initial voltage of the ramp signal to be higher than that in a case where the gain adjustment is not performed.   A second setting for changing a count start timing according to the comparison result with respect to a case where the gain adjustment is not performed, with a count value corresponding to a difference between the output dynamic range and the input dynamic range as a maximum count value. The image pickup apparatus according to claim 1, further comprising: means.   The imaging apparatus according to claim 4, wherein the second setting unit delays the start timing of the count as compared with a case where the gain adjustment is not performed.   The imaging apparatus according to claim 4, wherein the second setting unit makes the count start timing earlier than when the gain adjustment is not performed.   Instead of the first setting means, the initial voltage of the analog signal input to the comparison means for obtaining the comparison result with a voltage corresponding to the difference between the output dynamic range and the input dynamic range as a maximum voltage, The imaging apparatus according to claim 1, further comprising a third setting unit that changes the setting when the gain adjustment is not performed.   The imaging apparatus according to claim 7, wherein the third setting unit sets an initial voltage of the analog signal to be higher than that in a case where the gain adjustment is not performed.   When the A / D conversion period corresponding to the input dynamic range is minimized and a predetermined period elapses from the start of the A / D conversion period, power supplied to the ramp signal generating means for generating the ramp signal is supplied. The imaging apparatus according to claim 1, further comprising a power-off unit configured to turn off. A plurality of pixels arranged in a two-dimensional matrix, and an analog signal read from the plurality of pixels and a ramp signal are compared and counted according to the comparison result, and a digital signal corresponding to the analog signal An image pickup device having an A / D conversion unit that outputs a signal, and a gain adjustment unit that performs gain adjustment on the digital signal,
A control step of controlling the operation of the A / D conversion means with an output dynamic range corresponding to an input dynamic range in the gain adjustment means;
A setting step for changing the setting of the initial voltage of the ramp signal as a maximum voltage corresponding to a difference between the output dynamic range and the input dynamic range when the gain adjustment is not performed;
A control method characterized by comprising: A plurality of pixels arranged in a two-dimensional matrix, and an analog signal read from the plurality of pixels and a ramp signal are compared and counted according to the comparison result, and a digital signal corresponding to the analog signal A control program for use in an imaging apparatus having an image sensor having an A / D conversion means for outputting a signal and a gain adjustment means for performing gain adjustment on the digital signal,
In the computer provided in the imaging device,
A control step of controlling the operation of the A / D conversion means with an output dynamic range corresponding to an input dynamic range in the gain adjustment means;
A setting step for changing the setting of the initial voltage of the ramp signal as a maximum voltage corresponding to a difference between the output dynamic range and the input dynamic range when the gain adjustment is not performed;
A control program characterized by causing

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