JP2004356699A - Imaging apparatus and imaging element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an imaging apparatus and an imaging element capable of extracting only variations in an optical input analog signal without converting the analog signal. <P>SOLUTION: A differential image signal with a wide dynamic range can directly be obtained from the imaging apparatus and the imaging element through the circuit configuration wherein two sets of analog signal storage units are provided to one light receiving element and two sets of image signals stored in two sets of the analog signal storage units are compared to obtain the differential image signal. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an imaging apparatus and an imaging device that detect a difference image signal (hereinafter, referred to as a variation) of one frame of an optical input signal and outputs only the variation as an image.
[0002]
[Prior art]
A conventional system for extracting a variation of an optical input signal mainly performs signal processing by a digital device connected to the imaging apparatus 1 in order to detect the variation of the optical input signal. The A / D conversion circuit ADC2, which is enclosed by a dotted line, is output from the frame memories 3a and 3b, which have a memory capacity for two frames and obtain a delay signal for one frame, and the ADC2 and the frame memories 3a and 3b. The differential amplifier 4 detects the difference between the data and detects the variation.
[0003]
An example of the operation of the conventional digital device for extracting the variation of the optical input signal will be described below. First, an optical image of a subject as an optical input signal is captured by the imaging device 1 and converted into an analog electric signal S0. The analog electric signal S0 is sent to an A / D conversion circuit ADC2 to be converted into a digital signal S1, and then sent to the frame memories 3a and 3b. A digital signal S2 having a time difference of frames is output. The digital signal S2 is input to the differential amplifier 4 together with the digital signal S1 to obtain a differential image signal S3 (= S2-S1). The difference image signal S3 is input to the digital signal processor 5 to extract features of the difference image signal based on signal level, contour information, color information, and the like (described in Patent Document 1 below).
[0004]
FIG. 7 shows a schematic diagram of the imaging device 1 for obtaining an optical input signal. The imaging apparatus 1 includes a lens 7 for forming an optical image of a subject on the image sensor 6, an image sensor 6 for receiving the optical image of the subject and converting it into an analog electric signal S <b> 0, and a drive for supplying a pulse train for driving the image sensor 6. The imaging device 1 includes a circuit 9, an imaging element 6, and a power supply circuit 8 that supplies power to the driving circuit 9. The imaging apparatus 1 forms an optical image of a subject on the imaging element 6 by a lens 7, and the imaging device 6 forms an image. The subject optical image is converted into an analog electric signal S0 and output from the imaging device 1.
[0005]
Next, each signal waveform diagram in FIG. 6 is shown in FIG. The signal levels in (a) to (g) of FIG. 11 are shown with white as 100% and black as 0%.
FIG. 8A shows an analog electric signal S0 output from the imaging apparatus 1 in the order of one frame, S0a, S0b, S0c, S0d,. . , And the L1 and H1 portions of S0b include a variation. The analog electric signal output S0 from the imaging apparatus 1 prevents the signal output from being inverted (a phenomenon in which when there is an optical input exceeding 100%, the conversion to the electric signal becomes oversaturated and the signal output becomes 100% or less). The actual saturation level is set at 400% or more for the sake of safety. When used only for viewing image information, a signal level of 100% to 400% is compressed to about 120% for use. However, in order to accurately obtain a difference image signal as a variation from image information, it is common to use the image data without compression. Accordingly, the analog electric signal S0 output from the imaging apparatus 1 which has captured the optical input signal close to 100% in FIG. 8A as the subject optical image includes a variation exceeding 100% as shown in the H1 portion. Are not compressed or cut and sent to the next ADC 2 as they are.
[0006]
FIG. 8B is a diagram in which the analog electric signal S0 (S0a, S0b, S0c,...) Is converted into a digital signal S1 (S1a, S1b, S1c,...).
In the A / D conversion circuit ADC2, the input level is set to 100%. When a signal of a higher level is input, the output data is output at the time of output as shown by the shaded portion of H1 in S1b of FIG. 8B. It is cut and accurate fluctuations cannot be obtained.
[0007]
Next, the digital signal S1 converted into a digital signal by the ADC 2 is added to the frame memories 3a and 3b, and the memory having the capacity of the two frames is alternately used for Write / Read one frame at a time. S2 ((c) in FIG. 8) is formed and sent to the differential amplifier 4 together with the digital signal S1. In the differential amplifier 4, the digital signal S1 and the digital signal S2 having a time difference are subjected to subtraction such that S3 (= S2−S1) is formed and output as a differential image signal S3.
Also in this difference image signal S3, as shown in FIG. 8D, the H1 portion having a level of 100% or more is output in a cut state, so that only the difference image signal S3 lacking the fluctuation information is obtained. Absent.
[0008]
FIGS. 8A to 8D show the case where the signal level is set to nearly 100% in order to obtain as large a variation as possible. (E) to (g) of FIG. 8 described below are the cases where the optical input signal level is set to 50% so as not to cut off the variation, (e) is the digital signal S1, (f) is the digital signal S2, ( g) shows the difference image signal S3. When the optical input signal level is reduced in this manner, the difference image signal S3 is not cut because the variation is not 100% or more even if the variation is included. When the image signal level also decreases and is input to the ADC 2, the resolution of the differential image signal S3 is reduced to half.
[0009]
For this reason, if an optical input signal is converted from an analog electric signal to a digital signal and a digital image is used to detect a differential image signal, the amount of saturation may be cut or the resolution may be reduced due to the effect of the optical input signal level. In the digital signal processing 5, a sufficient fluctuation analysis could not be performed.
[0010]
Next, the configuration of the imaging device 6 in the imaging device 1 will be described in more detail with reference to the block diagram of FIG. The image sensor 6 has a vertical selection circuit 6a, a horizontal selection circuit 6b, and a pixel configuration section 6c.
The image pickup device 6 receives a subject optical image and converts it into an analog electric signal. A pixel configuration unit 6c in which a plurality of pixels are arranged in a matrix, and a vertical selection that sends a pulse sequence for selecting a pixel line of a vertical line to the pixel configuration unit 6c. The circuit 6a includes a horizontal selection circuit 6b composed of a row of switches for selecting horizontal pixels.
[0011]
The operation of the image sensor 6 includes pixels (0, 0), (0, 1),..., Which form an optical image of a subject and store charges corresponding to the light amount of the optical image of the subject. . . (N, m-1) and (n, m) are converted into pulse trains row0, row1,. . . row, a pixel column of a vertical line is selected, and Sout0, Sout1,. . . Soutm-1 and Soutm are sent to the horizontal selection circuit 5b, and the horizontal selection circuit Sout0, Sout1,. . . Soutm-1 and Soutm are sequentially selected and output from the image sensor 6 as an analog electric signal S0 of the subject optical image.
[0012]
FIG. 10 shows a circuit example of one pixel constituting the pixel configuration part 6c of the image sensor 6, and an operation example of this one pixel will be described. First, the transistor Tr1 is turned on by a reset pulse to reset the charge of the photodiode PD1. . Next, Tr1 is turned off. When light from the subject light image is formed on the photodiode PD1 in this state, electric charges are accumulated in the photodiode PD1 according to the light amount of the subject light image.
[0013]
After accumulating this electric charge for a predetermined time (for example, one frame), the transistor Tr11 is turned on by a row pulse supplied from the vertical selection circuit 6a, and the electric charge stored in the photodiode PD1 is transferred to the electric charge of the optical image of the subject via Tr10 and Tr11. The converted signal is taken out as the output signal Sout and is applied to the horizontal selection circuit 6b shown in FIG.
[0014]
The horizontal selection circuit 6b selects the output signal Sout of the pixel in the horizontal direction, removes a part of the noise by a CDS (Correlated Double Sampling: Correlated Double Sampling) circuit (not shown), and outputs the analog signal S0 from the image sensor 6. I do. The electric charge accumulated in the photodiode PD1 is released as an output signal at the same time when the transistor Tr11 is turned on, and thus disappears by one reading.
[0015]
[Patent Document 1]
"Japanese Patent Publication No. 2000-32347"
[0016]
[Problems to be solved by the invention]
By the way, in the case where the fluctuation of the conventional optical input signal is mainly extracted by the digital signal processing, the setting of the optical input signal when there is no fluctuation is set to 100%, for example, by increasing the illumination amount or opening the aperture of the imaging device. There is a method in which the fluctuation is set as close as possible to obtain as large a variation as possible.
According to this method, a large variation should be obtained. However, since the optical input signal level is set to around 100%, if the variation occurs in a brighter direction exceeding 100%, the A / D conversion is performed. The digital signal output is saturated in the section, and as a result, there is a problem that the variation cannot be extracted.
[0017]
Conversely, reduce the amount of illumination or lower the aperture and gain of the imaging device so that the entire input signal level when there is no fluctuation is 50% or less so that the optical input signal level including the fluctuation does not exceed 100%. There is a way to set it lower.
However, according to this method, since the input signal level is lowered, only a small variation is obtained, and there is a problem that the resolution when converting into a digital signal by the A / D converter decreases.
[0018]
The present invention has been made in view of the above points, and has as its object to solve the above problem, for example, by using an imaging device and an imaging device that can extract only a variation of an optical input signal as an analog signal.
[0019]
[Means for Solving the Problems]
A first means for achieving the above-mentioned object comprises a first imaging signal for one frame obtained by imaging an optical image of a subject and a first imaging signal for one frame existing immediately before the first imaging signal. Imaging that detects a difference between the first imaging signal and the second imaging signal having a time difference of one frame and outputs only the imaging signal related to the difference. A light receiving unit (photodiode PD1) in which a number of pixels for receiving the optical image of the subject and performing photoelectric conversion and output are arranged in a matrix, and connected to each of the pixels of the light receiving unit. And the photoelectric conversion outputs related to the set of the first and second imaging signals output from the respective pixels are sequentially and alternately rewritten with a time difference of one frame within a blanking period of one frame. Remember and write as possible Storage means (floating capacitances C1 and C2) which store the data so as to be interchangeable and simultaneously read out the photoelectric conversion outputs of the set of the first and second imaging signals having a time difference of one frame, and the storage means Generating the set of the first and second imaging signals from the photoelectric conversion output simultaneously read out from the storage device, and relating a difference between the generated first imaging signal and the generated second imaging signal to the difference. An imaging apparatus comprising: a differential unit (differential AMP 10d) that outputs an image signal.
[0020]
Further, a second means for achieving the above object is an imaging element used in the imaging device according to claim 1, comprising: the light receiving means; and the storage means. The means is connected to each of the pixels of the light receiving means, and stores rewritable photoelectric conversion outputs of the set of the first and second imaging signals output from each of the pixels. An image pickup device comprising two memories.
[0021]
BEST MODE FOR CARRYING OUT THE INVENTION
Embodiments of the present invention will be described with reference to the drawings with the most preferred embodiments. The imaging device and the imaging device according to the present invention capture an optical image of a subject by increasing the amount of illumination or opening the aperture of the imaging device so that the setting of the optical input signal when there is no fluctuation is set to around 100%. The difference between the imaging signal for each frame obtained as described above and the imaging signal for the immediately preceding frame is detected as a variation without saturation, and an image of only this variation is output.
[0022]
FIG. 1 shows a basic circuit configuration diagram of an imaging device and an imaging device according to the present invention. This basic circuit configuration diagram includes a pixel + memory section 10c, a CDS section 10b (correlated double sampling circuit included in the horizontal selection circuit), and a differential amplifier section 10d.
[0023]
The pixel + memory section 10c has a configuration corresponding to one pixel in the image sensor 10. The pixel + memory section 10c mainly includes a photodiode PD1 that accumulates electric charge corresponding to the light amount of the subject optical image, and floating capacitances C1 and C2 used as two analog memories. Become.
[0024]
To explain this operation, first, the transistor Tr1 is turned on by a reset pulse to reset the charge of the photodiode PD1. Next, the reset pulse is turned off, and the electric charge corresponding to the light amount of the subject light image is accumulated in the photodiode PD1 for the first frame. Immediately before the end of the charge accumulation for the first frame, the transistor Tr8 is momentarily turned on by the pulse orst to reset the charge of the floating capacitance C1.
[0025]
Next, the transistor Tr2 is turned on by the pulse gxlo at the same time when the charge accumulation in the PD1 in the first one frame period ends, and the charge for the first one frame accumulated in the photodiode PD1 is moved to the floating capacitance C1. Next, the transistor Tr2 is turned off for a period of two frames by the pulse gxlo. As described above, the charges for the first one frame are accumulated in the floating capacitance C1 for two frame periods.
[0026]
The transistor Tr1 is turned on again by the reset pulse to reset the charge of the photodiode PD1. After the reset is completed, the charge based on the light amount of the subject light image is accumulated in the photodiode PD1 as the second frame. Immediately before the end of the second one-frame charge accumulation, the transistor Tr9 is momentarily turned on by the pulse erst to reset the charge of the floating capacitance C2.
[0027]
Next, the transistor Tr3 is turned on at the same time when the charge accumulation in the second one-frame period is completed by the pulse gxle, and the electric charge for the second one-frame accumulated in the photodiode PD1 is moved to the floating capacitance C2. Next, the transistor Tr3 is turned off by the pulse gxle. As described above, the charges for the second one frame are accumulated in the floating capacitance C2.
[0028]
In this way, the charge for the first one frame is stored in the floating capacitance C1, and the charge for the second one frame is stored in the floating capacitance C2. Then, Tr6 and Tr7 are respectively turned ON by the pulse row, and the electric charge of the floating capacitance C1 is passed through the transistors Tr4 and Tr6, and the electric charge of the floating capacitance C2 is passed through the transistors Tr5 and Tr7. Output signals Souta and Soutb obtained by converting the optical image into electric signals are output.
[0029]
The output signals Souta and Soutb are sent to the CDS unit 10b (CDS: Correlated Double Sampling ... correlated double sampling). In the CDS section 10b, currents corresponding to the input Souta and Soutb are supplied to the current sources I1 and I2, and a change in current generated at this time is transmitted as charges to the capacitors C3 and C4. The switches S1 and S2 are turned on before supplying signal components to the current sources I1 and I2, and the charges remaining in the capacitors C3 and C4 are reset. Next, the switches S1 and S2 are turned off, and the switches S3 and S4 are turned on to transmit the charge of the current change to the capacitors C5 and C6 via the capacitors C3 and C4. When the switches S3 and S4 are turned off, the electric charge due to the current change is accumulated in the capacitors C5 and C6. If the electric charges are amplified by the amplifiers AMPA1 and A2, the signals Sa and Sb from which a part of the DC noise is removed are obtained.
[0030]
The signals Sa and Sb output from the CDS unit 10b are applied to the switches S5 and S6 of the differential amplifier unit 10d. Since the signal Sa and the signal Sb have different input time of the optical signal stored for each frame, the switch positions of the switches S5 and S6 are switched so that the later stored time is always subtracted from the earlier stored signal, and the differential amplifier A3 is switched. To the differential image signal Sd.
In this way, a differential component as an analog electric signal can be obtained.
[0031]
Next, an example in which the extracted difference image signal Sd is applied to an A / D conversion circuit ADC2 having a circuit configuration as shown by a dotted line in FIG. 1 and converted into a digital signal will be described. By adding the differential image signal Sd extracted by the differential amplifier 10d to the ADC 2, a digital signal S1 of the differential image signal Sd is obtained. Since the differential image signal Sd in the analog state has a constant voltage when there is no fluctuation, the A / D conversion of the constant voltage is adjusted by the control voltage Ref1 so as to become the central level value of the digital signal S1.
[0032]
An example in which the image pickup device and the basic circuit of the image pickup device according to the present invention are incorporated in the image pickup device 10 is shown in an image sensor block diagram of FIG. 2 and a signal waveform diagram is shown in FIG.
The image pickup device 10 generates a pulse train (row = row0, row1, row2,..., Row) for selecting a vertical line of the pixel configuration unit 10c, and selects and illustrates horizontal pixels of the pixel configuration unit 10c. A pixel configuration unit 10c in which a plurality of pixels each including one horizontal line selection circuit A, B to which no CDS circuit is added, one photodiode PD1 and two analog memories (floating capacitors C1, C2) are arranged in a matrix; The differential AMP 10d detects a differential signal. (A / D conversion circuit ADC2 is added as necessary.)
[0033]
The image sensor 10 has a reset pulse (FIG. 3A) for resetting the photodiode PD1 for each frame, an orst pulse (FIG. 3B) for resetting the stray capacitance C1, and one frame of the photodiode PD1. Gxlo pulse ((c) in FIG. 3) for transferring the electric charge of the photodiode PD1 to the floating capacitance C1, an rst pulse ((d) in FIG. 3) for resetting the floating capacitance C2, and the charge for one frame of the photodiode PD1 by the floating capacitance C2 Gxle pulse ((e) in FIG. 3) to be transferred to the multiplexed signal is applied.
[0034]
All of these pulses are set to be turned on during the blanking period (BL1, 2, 3,...) Of the image sensor 10. As shown in (a) to (e) of FIG. 3, the order of ON is as follows: (b) reset the charge of the stray capacitance C1 by the orst pulse, and (c) store the charge in the photodiode PD1 by the gxlo pulse. The charge for the frame is transferred to the floating capacitance C1. After resetting the charge of the photodiode PD1 by the reset pulse (a), the charge corresponding to the light amount of the subject optical image is accumulated in the photodiode PD1 for the next one frame. When the charge for the next one frame is accumulated in the photodiode PD1, the rst pulse in (d) is turned on to reset the charge in the floating capacitance C2, and then the gxle pulse in (e) is turned on to turn on the next one. The charge for the frame is transferred to the floating capacitance C2. In this way, charges of the subject optical image having a time difference of one frame are accumulated in the floating capacitances C1 and C2 by the pulse train in the blanking period.
[0035]
The charges of the optical image of the subject stored in the floating capacitors C1 and C2 are the same signal for two frames as shown in FIGS. 3F and 3G (for example, Sa1, Sa1, Sb2, and Sb2). Is read out during the video signal period. (F), the charge of the subject optical image stored in the floating capacitor C1 is output as the signal Sa1 from the horizontal selection circuit A for two frame periods. (G) Next, the charge of the optical image of the subject accumulated in the floating capacitance C2 is output from the horizontal selection circuit B for two frame periods as Sb2. Subsequently, the charge of the third subject optical image is set to Sa3, and the charge of the fourth subject optical image is set to Sb4, and two frames are continuously output.
[0036]
Next, the signals output from the horizontal selection circuits A and B are converted into differential image signals by the differential AMP 10d. In the differential AMP 10d, Sd1 (= Sa1-Sb2), Sd2 (= Sb2-Sa3), and Sd3 (=) in FIG. 3H so that the signal of the subsequent frame is always subtracted from the signal of the previous frame in time. The signals output from the horizontal selection circuits A and B are alternately switched so as to be Sa3-Sb4). The difference image signals Sd1, sd2, Sd3,. . Is often small as indicated by the dotted line portion of (i), and if necessary, amplified and output to an output level close to 100% by the differential AMP 10d as indicated by the solid line of (i). (Sd2 '= Sd2xG0, Sd3' = Sd3xG0 ... G0: amplification factor).
[0037]
Next, as the maximum signal level of each part, 400% or more is secured from the pixel + memory section 10c of FIG. 1 to the differential amplifier section 10d via the CDS section 10b so that a sufficient differential signal can be obtained. . In this way, for example, even if the optical input signal is set to 100% and the fluctuation is superimposed on this by 100% and the maximum level becomes 200%, the differential image signal is cut as 100% level. Extracted without. In the differential amplifying unit 10d, the amplification factor G0 is set so that the maximum value becomes 100% in accordance with the level of the variation. Then, the difference image signal Sd is supplied to the A / D converter 2.
By doing so, for example, even if the optical input signal level is set to around 100%, the variation does not saturate, so that a differential image signal with a large variation can be obtained.
[0038]
FIG. 4 shows an example of a system using the image pickup device and the image pickup device according to the present invention, and FIG. 6 shows an image pickup device 1 ′ incorporating the image sensor 10.
An example of a differential image signal detection system using an image pickup device and an image pickup device according to the present invention includes an image pickup device 1 'and an A / D conversion circuit ADC2. It became unnecessary because it was incorporated in For this reason, the number of digital devices can be significantly reduced, and a great effect on resource saving can be obtained. If the A / D conversion circuit ADC2 is incorporated in the image pickup device and the image pickup device, it is needless to say that the resource saving effect can be obtained.
[0039]
【The invention's effect】
As described above, according to the image pickup apparatus and the image pickup device of the present invention, even if an optical input signal is set near 100% when there is no variation, there is no saturation due to the variation, so that the illumination of the subject light image is performed. By increasing the amount, opening the aperture of the imaging device, and setting the optical input signal when there is no fluctuation to about 100%, the imaging signal for each frame obtained by imaging the subject optical image and the Can be obtained as an image of only a good variation.
[Brief description of the drawings]
FIG. 1 is a diagram showing a basic circuit configuration of an imaging device and an imaging device according to the present invention.
FIG. 2 is a diagram illustrating an example of a block diagram of an entire image sensor according to the present invention.
FIG. 3 is a diagram showing signal waveforms for explaining the operation of the present invention.
FIG. 4 is a diagram showing an example of a digital signal processing system according to the present invention.
FIG. 5 is a diagram showing an example of an imaging device according to the present invention.
FIG. 6 is a diagram showing an example of a conventional digital signal processing system.
FIG. 7 is a diagram illustrating an example of a conventional imaging apparatus.
FIG. 8 is a diagram showing signal waveforms for explaining a conventional operation.
FIG. 9 is a diagram illustrating an example of a block diagram of an entire conventional image sensor.
FIG. 10 is a diagram illustrating a circuit example of one pixel in a conventional image sensor.
[Explanation of symbols]
1 imaging device 2 ADC
3 Digital signal processing 4 Frame memory 5 Digital signal processing 6 Conventional image sensor 6a Vertical selection circuit 6b Horizontal selection circuit (including CDS section)
6c Pixel Configuration Unit 7 Lens 8 Power Supply Circuit 9 Drive Circuit 10 Image Sensor 10a Vertical Select Circuit 10b Horizontal Select Circuit (Including CDS Unit) According to the Present Invention
10c Pixel configuration part (pixel + memory part)
10d differential AMP (comparing means)
PD1 photodiode (light receiving means)
C1, C2 stray capacitance (storage means)

Claims (2)

One set of the first image pickup signal for one frame and the second image pickup signal for one frame existing immediately before the first image pickup signal obtained by imaging the subject optical image are taken as one set. An imaging device that detects a difference between the first imaging signal and the second imaging signal having a time difference of, and outputs only an imaging signal related to the difference,
Pixels for receiving the optical image of the subject and performing photoelectric conversion and output, a large number of light receiving means arranged in a matrix,
A blanking period for one frame, which is connected to each of the pixels of the light receiving means and outputs the photoelectric conversion outputs of the one set of the first and second imaging signals from each of the pixels, respectively. The first and second imaging signals are stored in such a manner that they can be rewritten alternately and sequentially with a time difference of one frame, and are stored so as to be rewritable and have a time difference of one frame. Storage means for simultaneously reading photoelectric conversion outputs;
The one set of the first and second imaging signals are generated from the photoelectric conversion outputs simultaneously read from the storage unit, and a difference between the generated first imaging signal and the generated second imaging signal is calculated by the An image pickup device comprising: a differential unit that outputs an image pickup signal related to a difference. An imaging device used in the imaging device according to claim 1,
Comprising the light receiving means and the storage means,
The storage means,
Two memories respectively connected to the respective pixels of the light receiving means and rewritably storing the photoelectric conversion outputs of the set of the first and second imaging signals output from the respective pixels; An imaging device, characterized in that:

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