JP3979443B2 - Spatial information detection device using intensity-modulated light - Google Patents

Description

  The present invention relates to an apparatus for detecting spatial information using intensity-modulated light that detects various types of information related to space by receiving light from the space irradiated with intensity-modulated light.

  Conventionally, light whose intensity has been modulated is emitted from a light source to a space, and reflected light reflected by an object existing in the space is received by a photosensitive unit, and light emitted from the light source and light received by a photosensitive unit are A technique for detecting various information related to space based on the relationship is known. The information about the space means a distance to an object existing in the space, a change in received light amount due to reflection of the object existing in the space, and the like.

  To determine the distance to an object using intensity-modulated light, the received light intensity is detected multiple times at specific different phases synchronized with the modulation period, which is the reciprocal of the modulation frequency, and the detected light intensity and phase Thus, the phase difference between the light emitted from the light emitting source and the light received by the photosensitive portion is obtained. For example, if the intensity of light emitted from the light source is modulated with a sine wave, and the received light intensity at the photosensitive portion for a specific different phase at the time of modulation is detected three times or more (preferably four times or more), the phase difference can be calculated. Can be sought.

Now, it is assumed that the light emitted from the light emitting source is intensity-modulated as shown by a curve a in FIG. 18 and the received light intensity at the photosensitive portion changes as shown by a curve b in FIG. Here, the detected values corresponding to the received light intensity when the received light intensity is sampled at four points where the phase of the curve A is 0 degrees, 90 degrees, 180 degrees, and 270 degrees are A0, A1, A2, and A3, respectively. . However, the detected values A0, A1, A2, and A3 in each phase do not correspond to the incident light at the instantaneous time in each phase, but correspond to the incident light in the period shown as the integration time Tw in the drawing, for example. Here, the phase difference ψ does not change during the period when the detection values A0, A1, A2, and A3 are sampled, and the light attenuation rate from light emission to light reception (the attenuation is ignored in the figure) is also changed. If not, the detected values A0, A1, A2, and A3 are obtained every 90 degrees, and the relationship between the detected values A0, A1, A2, and A3 and the phase difference ψ is expressed by the following equation. Can do.
ψ = tan ⁻¹ {(A3-A1) / (A0-A2)}
When the phase difference ψ is obtained from the plurality of detection values A0, A1, A2, and A3 as described above, the modulation period T [s], the phase difference ψ [rad], and the speed of light c [m / s] are obtained. By using this, the distance L [m] to the object can be obtained as follows.
L ≒ cT (ψ / 4π)
As an apparatus for realizing the above technical idea, one photosensitive portion and four memory cells are provided for one pixel, and an electrical switch provided between each memory cell and the photosensitive portion in one pixel is provided. There has been proposed one in which each detection value A0, A1, A2, A3 is distributed and stored in each memory cell by being turned on during a period corresponding to the integration time Tw described above (see, for example, Patent Document 1). .
JP 10-508736 A (page 7-9, FIG. 1, FIG. 4)

  By the way, in the apparatus described in Patent Document 1, the detection values A0, A1, A2, and A3 are stored in the memory cell only by turning on and off the switch provided between the photosensitive portion and the memory cell. Among the charges generated in the portion, the charges not transferred to the memory cell remain in the photosensitive portion for a while. Such residual charge disappears by recombination inside the photosensitive portion, or is transferred to the memory cell when the switch is turned on next time.

  Here, it is assumed that the maximum measurable distance is 7.5 m, for example. In this case, since the modulation frequency is 20 MHz, the integration time Tw must be shorter than the modulation period of 50 ns. On the other hand, since the time required for the residual charge to disappear by recombination is usually longer than 100 μs, not only the charge generated by light reception in the integration period Tw but also the residual charge is transferred to the memory cell. That is, noise components due to residual charges are mixed into the charges accumulated in the memory cells in addition to the signal charges corresponding to the detection values A0, A1, A2, and A3. Since the light received by the photosensitive unit is intensity-modulated, the noise component also changes according to the detection values A0, A1, A2, and A3. If the phase difference ψ is obtained by the above-described calculation, the noise component is changed. May cause errors.

  The present invention has been made in view of the above-described reasons, and the object thereof is to discard a residual charge that is not used as a signal charge among the charges generated in the photosensitive portion, thereby mixing a noise component into the signal charge. An object of the present invention is to provide an apparatus for detecting spatial information using intensity-modulated light that is capable of suppressing and detecting spatial information with a high SN ratio.

The invention according to claim 1 is a structure in which a plurality of control electrodes are stacked on the main surface of the semiconductor layer via an insulating film, and from a space irradiated with light whose intensity is modulated by a modulation signal having a predetermined modulation frequency. Of the light generated by the photosensitive portion, the photosensitive portion that receives the light and generates a charge corresponding to the received light intensity, the charge accumulation portion that accumulates the signal charge among the charges generated by the photosensitive portion, and the waste electrode. A charge discarding unit in which the movement of charges discarded as unnecessary charges is controlled according to the discarding voltage applied to the discarding electrode, a charge extracting unit for taking out signal charges accumulated in the charge accumulating unit, and a plurality of adjacent specified pluralities By controlling the voltage applied to the control electrode as a group and timing synchronized with the period of the modulation signal, the depth of the potential well formed in the portion corresponding to each control electrode in the semiconductor layer is controlled. A control circuit unit, and an evaluation unit that evaluates information about the space using the charge extracted by the charge extraction unit. The control circuit unit is included in the storage period during which the charge generated by the photosensitive unit is stored. A potential well is formed in association with a plurality of control electrodes, and in the discard period in which unnecessary charges are discarded, the charge in the potential well corresponding to at least one control electrode among the charges accumulated in the accumulation period is used as a signal charge. The present invention is characterized in that it is left as it is, and unnecessary charges generated corresponding to the remaining control electrodes are discarded in the charge discarding unit by controlling in a direction in which the potential well of the portion corresponding to the control electrode becomes shallower.

  According to a second aspect of the present invention, in the first aspect of the present invention, the control circuit unit controls the control in the set in the accumulation period so that a potential well that leaves a signal charge in the discard period is deeper than the other potential wells. The voltage applied to the electrode is controlled.

  According to a third aspect of the present invention, in the second aspect of the present invention, the control circuit section controls the voltage applied to the control electrode in the set so that the potential well formed in the accumulation period is stepped. It is characterized by.

  According to a fourth aspect of the present invention, in the second or third aspect of the present invention, the charge discarding portion is an overflow drain, and the control circuit portion is a potential of a portion that forms a potential well that leaves a signal charge during the discarding period. The voltage applied to the control electrode in the set is controlled so that the potential of the potential well in the other part formed during the accumulation period is shallower than the potential of the overflow drain. It is characterized by that.

  According to a fifth aspect of the present invention, in the first to fourth aspects of the present invention, the control circuit unit may apply a potential barrier without applying a voltage to a control electrode adjacent to another group among the control electrodes in the group. It is characterized by forming.

  According to the configuration of the first aspect of the present invention, the storage period in which charges are stored in the plurality of potential wells in association with the plurality of control electrodes provided in the photosensitive portion, and the control electrode in which the potential wells are formed in the storage period are provided. Since the potential well of the corresponding part is controlled to become shallower and a disposal period for discarding unnecessary charges is provided in the charge disposal section, the sensitivity of the photosensitive section is substantially adjusted. Since the voltage applied to the control electrode is changed at the timing synchronized with the period of the modulation signal, it is possible to adjust the amount of the electric charge that becomes an unnecessary charge among the charges generated in the photosensitive portion at the timing synchronized with the period of the modulation signal. it can. That is, of the charges generated in the photosensitive portion, residual charges that are not used as signal charges are discarded as unnecessary charges, and there is an advantage that mixing of noise components into the signal charges is suppressed. In particular, since unnecessary charges are discarded at a timing synchronized with the period of the modulation signal, unnecessary charges that are desired to be prevented from being mixed into the signal charges can be discarded accurately, leading to an improvement in the SN ratio. Further, since the residual charge that is an unnecessary charge is quickly removed, it is possible to take out the signal charge at a relatively short time interval without waiting for the natural disappearance due to recombination of the residual charge.

  According to the second aspect of the invention, the potential is set so that the potential well where the signal charge is left is deeper than the other potential wells in the accumulation period. Therefore, the generated charge is deepest in the accumulation period. The charge is discarded except for the potential well that flows into the potential well and leaves the signal charge in the discard period, and the sensitivity between the accumulation period and the discard period can be changed. Further, even in the accumulation period as well as the discarding period, a potential barrier is formed adjacent to the potential well where the signal charge is left, and leakage of the signal charge can be prevented.

  According to the configuration of the invention of claim 3, since the stepwise potential well is formed in the accumulation period, the deepest potential well in the accumulation period even in a part away from the potential well where the signal charge is left in the discard period. A charge is induced in

  According to the configuration of the invention of claim 4, a configuration is adopted in which the charge is discarded using the overflow drain, and in the accumulation period, only the potential of the potential well where the signal charge is left in the discard period is made deeper than the potential of the overflow drain. Since the potential of the remaining potential well is shallower than the potential of the overflow drain, some charges are discarded even during the accumulation period, and some charges generated in the photosensitive part are discarded while being discarded to the overflow drain. Will be accumulated.

  According to the configuration of the fifth aspect of the present invention, since the potential barrier is formed in the adjacent texture, it is possible to prevent leakage of charges to other photosensitive portions.

  Hereinafter, an example in which the technology of the present invention is used for a distance measuring device that measures the distance using the phase difference between the light from the intensity-modulated light source and the light received by the photosensitive unit will be described. The idea can be applied not only to distance measurement, but also to devices that determine the phase difference between the original phase of intensity-modulated light and the light received by the photosensitive unit, and devices that determine the change in reflected light from an object. is there.

(Basic configuration)
First, the basic configuration is shown. As shown in FIG. 1, a light emitting source 2 that irradiates light to a space is provided, and the light emitted from the light emitting source 2 is intensity-modulated by a control circuit unit 3 at a constant modulation frequency. As the light emitting source 2, for example, a light emitting diode in which a large number of light emitting diodes are arranged on one plane or a combination of a semiconductor laser and a diverging lens is used. The control circuit unit 3 modulates the intensity of light emitted from the light source 2 with, for example, a 20 MHz sine wave.

  On the other hand, light from the space enters the photosensitive portion 11 of the image sensor 1 through the light receiving lens 4. The photosensitive portion 11 generates an amount of electric charge according to the received light intensity, and a photodiode is assumed here. However, as the structure of the photodiode constituting the photosensitive portion 11, in addition to a structure having a pn junction, various structures such as a pin structure and an MIS structure can be adopted. Here, an image sensor 1 is assumed in which a plurality of (for example, 100 × 100) photosensitive portions 11 are arranged in a matrix on a two-dimensional plane, and light is emitted to the two-dimensional plane that is the light receiving surface of the image sensor 1. A three-dimensional space irradiated with light from the source 2 is mapped through the light receiving lens 4. That is, since the object Ob existing in the field of view seen by the image sensor 1 through the light receiving lens 4 is mapped to the photosensitive portion 11, the phase difference between the light emitted from the light source 2 and the light received by each photosensitive portion 11 is calculated. If detected, the distance to each part of the object Ob corresponding to each photosensitive part 11 can be obtained.

In the image sensor 1, in addition to the photosensitive unit 11, a charge storage unit 12 that stores a signal charge for obtaining a phase difference among charges generated by the photosensitive unit 11, and a signal charge stored in the charge storage unit 12. A charge extraction unit 13 that is taken out of the image sensor 1 and a charge discarding unit 14 that discards unnecessary charges that are not used as signal charges among the charges generated by the photosensitive unit 11 are provided. The charge storage unit 12 includes a control electrode 12a. When the control voltage applied to the control electrode 12a is changed, the movement of charges from the photosensitive unit 11 to the charge storage unit 12 is controlled. In addition, the charge discarding unit 14 includes a discarding electrode 14a. When the discarding voltage applied to the discarding electrode 14a is changed, the movement of charges from the photosensitive unit 11 to the charge discarding unit 14 is controlled. The control circuit unit 3 controls the control voltage and the discard voltage. Here, the charge accumulating units 12 are provided so as to correspond one-to-one for each photosensitive unit 11, and the charge discarding units 14 are provided so as to correspond one-to-many with the plurality of photosensitive units 11. Here, it is assumed that one charge discarding unit 14 is provided for all the photosensitive units 11 of the image sensor 1. The signal charge extracted as the output of the image sensor 1 through the charge extraction unit 13 is input to the evaluation unit 5, which evaluates the phase difference between the light emitted from the light emitting source 2 and the light received by each photosensitive unit 11. Further, the distance to the object Ob is obtained based on the phase difference and output.

  As described in the conventional configuration, in order to obtain the distance to the object Ob, it is necessary to obtain the detection values A0, A1, A2, and A3 at a timing synchronized with the period of the modulation signal. Charge storage unit 12 using, as signal charges, charges corresponding to a certain time width Tw (see FIG. 18) corresponding to specific phases (for example, four phases of 0 degrees, 90 degrees, 180 degrees, and 270 degrees) of the modulation signal. It is necessary to accumulate in That is, the ratio of the signal charge stored in the charge storage unit 12 with respect to the intensity of light incident on the photosensitive unit 11 is increased during the period corresponding to the above-described time width Tw and decreased during other periods (ideal It is necessary to set it to 0. Since the ratio of generating signal charges with respect to the amount of light incident on the photosensitive portion 11 corresponds to sensitivity, in order to obtain the distance to the object Ob using the image sensor 1, it is necessary to control the sensitivity of the image sensor 1. It can be said that.

In order to control the sensitivity in the image sensor 1 having the above-described configuration, it is conceivable to control the magnitude of the control voltage applied to the control electrode 12a at an appropriate timing, but as described in the conventional configuration, By simply controlling the magnitude, unnecessary residual charges among the charges generated by the photosensitive portion 11 are mixed into the signal charges as noise components. Therefore, by keeping the control voltage applied to the control electrode 12a at a constant voltage, the charge generated in each photosensitive portion 11 is always taken into the charge storage portion 12 provided corresponding to each photosensitive portion 11, while for disposal electrodes 14a, in a period except for the period during which charges are generated to handle as the signal charges of the charges generated by the photosensitive unit 11, a waste voltage so that the charge is moved to the charge discarding unit 14 from the photosensitive portion 11 Apply. In short, the sensitivity of the image sensor 1 is controlled by changing the discard voltage at a timing synchronized with the period of the modulation signal, and the signal charge is stored in the charge storage unit 12.

  Now, it is assumed that the intensity of light emitted from the light source 2 to the space is modulated by the modulation signal as shown in FIG. The charge storage unit 12 stores one type of detection values A0, A1, A2, and A3 in a plurality of cycles (tens of thousands to hundreds of thousands) of the modulation signal, and stores each detection value A0, A1, A2, and A3. Then, the signal charges accumulated in (1) are taken out and the next detected values A0, A1, A2 and A3 are accumulated. For example, when the detection value A0 is accumulated for tens of thousands of cycles of the modulation signal, the signal charge corresponding to the detection value A0 is once taken out and then the detection value A1 is accumulated for tens of thousands of cycles of the modulation signal. To do. FIG. 2 shows a state in which signal charges corresponding to the detected value A0 are accumulated. As shown in FIG. 2B, the control voltage applied to the control electrode 12a is kept constant. Further, as the detection value A0, the charge generated by the photosensitive portion 11 during the period in which the phase of the modulation signal is 0 to 90 degrees (corresponding to the time width Tw in the conventional configuration shown in FIG. 18) is employed. That is, a waste voltage is applied to the waste electrode 14a so that the charge generated in the photosensitive portion 11 is an unnecessary charge during the period of 90 to 360 degrees of the modulation signal as shown in FIG. In short, the waste voltage is applied in a period other than the period corresponding to the period (0 to 90 degrees) in which the signal charges are accumulated in the period in which the charges move from the photosensitive portion 11 to the charge accumulation portion 12, and the desired detection value is obtained. Except for the period in which the signal charge for obtaining A0 is accumulated, the charge generated in the photosensitive part 11 is discarded as an unnecessary charge in the charge discarding part 14. Such control makes it possible to extract signal charges corresponding to a desired detection value A0 as shown in FIG. The processing shown in FIG. 2 is performed for tens of thousands to hundreds of thousands of cycles of the modulation signal, and the signal charge obtained in the charge storage unit 12 during this period is taken out by the charge extraction unit 13 to the evaluation unit 5 as a detection value A0, The evaluation unit 5 detects spatial information (in this example, the distance to the object Ob) based on the signal charge.

  In the above-described control, a control voltage that is a constant voltage is applied to the control electrode 12a during the period in which the waste voltage is applied to the waste electrode 14a, but the magnitude relationship between the waste voltage and the control voltage is appropriately determined. By setting, it is possible to prevent the accumulation of signal charges during the period when unnecessary charges are discarded. The reason why charges are accumulated for tens of thousands to hundreds of thousands of cycles of the modulation signal is to increase the sensitivity by increasing the amount of charges to be accumulated. Here, for example, the modulation signal is set to 20 MHz. Therefore, even if signal charges are taken out at 30 frames / second, accumulation of several hundred thousand cycles or more becomes possible.

  As described above, the charge discarding unit 14 including the disposal electrode 14a is provided, and unnecessary charges that are not used as signal charges out of the charges generated in the photosensitive unit 11 are actively discarded to the charge discarding unit 14. In the part 11, most of the charge generated in the photosensitive part 11 during the period when the signal charge is not given to the charge storage part 12 is discarded as unnecessary charge, and mixing of noise components into the signal charge is greatly suppressed. Will be.

  In the above-described example, the period during which the detection values A0, A1, A2, and A3 are sampled is set to ¼ period of the modulation signal, and one kind of detection values A0, A1, A2, and A3 in the tens of thousands to hundreds of thousands of periods of the modulation signal. In the case where the charge accumulating unit 12 and the charge discarding unit 14 are provided for each photosensitive unit 11, the detected values A0, A1, A2, and A3 are distributed to the respective photosensitive units 11. Therefore, four detection values A0, A1, A2, and A3 can be obtained within one period of the modulation signal. Further, the sampling timings of the detection values A0, A1, A2, and A3 need not be equal if the phase interval is known. Furthermore, although the example which modulated the intensity | strength of the light irradiated from the light emission source 2 with the sine wave was shown, you may modulate an intensity | strength with other waveforms, such as a triangular wave or a sawtooth wave. The light emitted from the light emitting source 2 is not limited to visible light, and infrared light or the like can be used. In order to obtain a distance image in which each pixel is associated with the distance to the object Ob, it is assumed that the image sensor 1 is a CCD image sensor, a CMOS image sensor, or the like and the photosensitive portion 11 is two-dimensionally arranged. A configuration in which the photosensitive portions 11 are arranged one-dimensionally may be employed. Further, when measuring a distance in only one direction in the space, or when irradiating the light beam from the light source 2 and scanning the light beam, a configuration in which only four photosensitive portions 11 are provided is adopted. The function of the image sensor 1 may be realized by an individual component instead of the image sensor 1 in which the photosensitive unit 11 is provided integrally with the charge storage unit 12 and the like.

  In the above-described example, as shown in FIG. 2, by applying a waste voltage to the waste electrode 14a during a period in which a control voltage that is a constant voltage is applied to the control electrode 12a, in a period in which no waste voltage is applied. Although an example in which the charge generated in the photosensitive portion 11 is used as a signal charge is shown, as shown in FIG. 3, the period in which the control voltage is applied to the control electrode 12a and the period in which the waste voltage is applied to the waste electrode 14a overlap. You may control so that it may not.

  Here, a case where signal charges corresponding to the detection value A0 are accumulated will be described as an example. Assume that the intensity of light emitted from the light source 2 to the space is modulated by a modulation signal as shown in FIG. Since the detection value A0 is extracted in the example shown in FIG. 3, the control voltage is applied to the control electrode 12a at the timing corresponding to the detection value A0 as shown in FIG. The period during which the control voltage is applied to the control electrode 12a is set from 0 degree to a certain period (0 to 90 degrees in the illustrated example) in the phase of the modulation signal. During this period, the charge from the photosensitive part 11 to the charge storage part 12 is transferred. It becomes possible to move. On the other hand, as shown in FIG. 3C, a discard voltage is applied to the waste electrode 14a in a period other than the period in which the signal charge corresponding to the detection value A0 is accumulated in the charge accumulation unit 12, and the period other than the period in which the signal charge is accumulated. The charges generated in the photosensitive unit 11 are discarded as unnecessary charges in the charge discarding unit 14. Such control makes it possible to extract signal charges corresponding to the detection value A0 as shown in FIG.

  In this control, the period during which the control voltage is applied to the control electrode 12a and the period during which the waste voltage is applied to the waste electrode 14a are separated, so that the magnitude relationship between the control voltage and the waste voltage is not considered. In both cases, the control voltage and the discard voltage can be controlled independently. As a result, the control voltage and the discard voltage can be easily controlled, and the ratio of the signal charge taken in with respect to the amount of light received by the photosensitive unit 11. This makes it easier to control the sensitivity, and also makes it easier to control the proportion of charges generated by the photosensitive portion 11 that are discarded as unnecessary charges.

  In the operation of FIG. 3, the period for accumulating the signal charge in the charge accumulating unit 12 is defined by the control voltage applied to the control electrode 12a, so that the period for applying the discard voltage to the discard electrode 14a can be shortened. For example, the waste voltage may be applied to the waste electrode 14a only during a predetermined period immediately before the control voltage is applied to the control electrode 12a.

  As described above, in the configuration in which the charge discarding unit 14 including the discard electrode 14a is provided and unnecessary charges that are not used as signal charges among the charges generated in the photosensitive unit 11 are actively discarded in the charge discarding unit 14, The charge generated in the photosensitive unit 11 can be discarded as an unnecessary charge during a period when the charge generated in the unit 11 is not stored as a signal charge in the charge storage unit 12, and noise components are greatly mixed into the signal charge. Will be suppressed.

  In the operation shown in FIG. 2, the waste voltage is applied to the waste electrode 14 a in an overlapping manner with the control voltage being applied to the control electrode 12 a, so that it is generated in the photosensitive portion 11 during the time when the waste voltage is not applied. Although an example in which the generated charge is used as a signal charge has been shown, as shown in FIG. 4, the waste voltage applied to the waste electrode 14a is kept constant and the charge generated in the photosensitive portion 11 is always discarded. In this period, the period during which the control voltage is applied to the control electrode 12a may be a period during which the signal charge is accumulated in the charge accumulation unit 12. That is, the conventional configuration is different from the conventional configuration in that a charge discarding unit 14 is provided and charges are always discarded from the photosensitive unit 11 to the charge discarding unit 14.

  The operation of FIG. 4 will also be described by taking as an example the case where signal charges corresponding to the detected value A0 are accumulated. Now, a case is assumed where the intensity of light emitted from the light source 2 to the space is modulated by the modulation signal as shown in FIG. As shown in FIG. 4B, the control electrode 12a provided in the charge storage unit 12 is used to store the charge generated in the photosensitive unit 11 in the charge storage unit 12 as a signal charge corresponding to the detection value A0. The control voltage is applied in a period corresponding to the detection value A0. That is, the period during which the control voltage is applied to the control electrode 12a is set from 0 degree to a certain period (0 to 90 degrees in the illustrated example) in the phase of the modulation signal. Charge transfer is possible. On the other hand, as shown in FIG. 4C, a constant voltage discard voltage, which is a DC voltage, is always applied to the waste electrode 14a, and a part of the charge generated by the photosensitive portion 11 is always used as an unnecessary charge. 14 to discard. In the above-described control, the control voltage is applied to the control electrode 12a only during the period in which the signal charge is accumulated in the charge accumulation unit 12, and thus the signal charge corresponding to the detection value A0 is extracted as shown in FIG. Is possible.

  In the operation shown in FIG. 4, a constant voltage discarding voltage is applied to the disposal electrode 14 a regardless of whether or not a control voltage is applied to the control electrode 12 a. Unnecessary charges that have not been stored as signal charges in the storage unit 12 are discarded in the charge discarding unit 14 as discarded charges. Here, even during a period in which a part of the charge generated in the photosensitive unit 11 is accumulated in the charge storage unit 12 as a signal charge, the disposal of the charge from the photosensitive unit 11 to the charge discarding unit 14 continues. In order to properly store the voltage in the charge storage unit 12, it is necessary to consider the magnitude relationship between the control voltage and the discard voltage. However, since the discard voltage is a constant voltage and is always applied to the discard electrode 14a, only the control voltage is actually controlled, and the control itself is easy.

  As described above, in the operation of FIG. 4, the charge discarding unit 14 including the discard electrode 14 a is provided, and unnecessary charges that are not used as signal charges out of the charges generated in the photosensitive unit 11 are actively discarded in the charge discarding unit 14. Therefore, the mixing of noise components into the signal charge is greatly suppressed.

(Reference Example 1)
Hereinafter, as the image sensor 1 described in the basic configuration described above, a frame transfer type CCD having a vertical overflow drain on the market is used.

  As shown in FIG. 5, the image sensor 1 is a two-dimensional image sensor in which a plurality of photodiodes 21 (4 × 4 in the illustrated example) are arranged in the horizontal direction and the vertical direction, as the photosensitive portion 11. The storage unit D2 is provided with an imaging unit D1 that allows the photodiodes 21 arranged in the vertical direction to function as a vertical transfer CCD, and further a vertical transfer CCD that does not have a photoelectric conversion function is continuously formed in each column of photodiodes 21 in the vertical direction. Is provided. In addition, a horizontal transfer unit 23 including a horizontal transfer CCD serving as a charge extraction unit is provided at the lower end of each column of the vertical transfer CCDs in the storage unit D2. In the illustrated example, both the photodiode 21 and the vertical transfer CCD have a function of accumulating charges and transferring the charges in the vertical direction, and the imaging unit D1 and the accumulation unit D2 include the charge accumulation unit 12 and the charge extraction unit. 13 functions.

  Each photodiode 21 includes three control electrodes 21 a to 21 c arranged in the vertical direction on the light receiving surface, and each column of the vertical transfer CCDs in the storage unit D <b> 2 includes three control electrodes provided in each photodiode 21. Three control electrodes 28a to 28c having the same arrangement as 21a to 21c are provided as a set. In the illustrated example, four photodiodes 21 are provided for each vertical column in the imaging unit D1, and two sets of six control electrodes 28a to 28c are provided in the storage unit D2. Further, the horizontal transfer unit 23 includes two control electrodes 23a and 23b for each column. The control electrodes 21a to 21c provided on the photodiode 21 are driven in six phases by six-phase control voltages V1 to V6, and the control electrodes 28a to 28e are driven in three phases by three-phase control voltages VV1 to VV3. 23a and 23b are driven in two phases by two-phase control voltages VH1 and VH2. The horizontal transfer unit 23 extracts signal charges for each horizontal line from the storage unit D2, and outputs the signal charges for each horizontal line to the outside. This type of drive technique is well known in the field of CCDs and will not be described in detail here.

  The imaging unit D1, the storage unit D2, and the horizontal transfer unit 23 are formed on a single substrate 50, and an overflow electrode 24, which is an aluminum electrode, is provided on the substrate 50 so as to be in direct contact with no insulating film interposed therebetween. That is, the substrate 50 functions as an overflow drain. The overflow electrode 24 is formed on the surface of the substrate 50 so as to surround the entire imaging unit D1, the storage unit D2, and the horizontal transfer unit 23. The surface of the substrate 50 is covered with a light shielding film (not shown) except for the portion corresponding to the photodiode 21. Here, the overflow drain functions as the charge discarding unit 14 because unnecessary charges out of the charges generated in the photodiode 21 which is the photosensitive unit 11 function, and the amount of charges discarded in the overflow drain is applied to the overflow electrode 24. Since it is controlled by the voltage (discard voltage), the overflow electrode 24 functions as the discard electrode 14a.

A structure of a portion related to one photodiode 21 will be described with reference to FIG. Here, an n-type semiconductor is used as the substrate 50, a p-type semiconductor layer 51 is formed on the main surface of the substrate 50, and an n-well 52 made of an n-type semiconductor is formed on the main surface of the p-type semiconductor layer 51. Is done. Further, three control electrodes 21 a to 21 c are overlaid on the surface of a portion straddling the p-type semiconductor layer 51 and the n-well 52 via an insulating film 53 made of SiO ₂ . That is, the n well 52, the insulating film 53, and the control electrodes 21a to 21c form the MIS photodiode 21. Control electrodes 21a-21c are formed of polysilicon. The n-well 52 is formed continuously in the imaging unit D1 and the storage unit D2, and charges are stored and transferred in the n-well 52. That is, the imaging unit D1 performs charge generation, accumulation, and transfer in the n-well 52, and the accumulation unit D2 performs charge accumulation and transfer in the n-well 52.

  Next, a technique for driving the above-described image sensor 1 will be described. In the image sensor 1 described above, when light enters the photodiode 21, charges are generated in the photodiode 21. Here, if an appropriate voltage is applied to the control electrodes 21a to 21c, a potential well as a charge storage portion is formed in the n-well 52, and the generated charges can be stored in the potential well. Further, by controlling the voltage applied to the control electrodes 21a to 21c, the charge can be transferred by changing the depth of the potential well. On the other hand, if an appropriate waste voltage Vs is applied to the overflow electrode 24, the charge generated by the photodiode 21 is discarded through the substrate 50, and therefore, the voltage applied to the overflow electrode 24 and the time for applying the voltage are controlled. Thus, it is possible to change the ratio of the signal charge accumulated in the potential well of the n-well 52 among the charges generated by the photodiode 21.

  In order to explain how the electric charge generated by the photodiode 21 moves, the potential of electrons along the broken line L3 in FIG. 6 is shown in FIG. In FIG. 7, the right part indicates a region corresponding to the photodiode 21, and the left part indicates a region corresponding to the substrate 50. In addition, when no voltage is applied to the overflow electrode 24, a potential barrier B <b> 3 is formed by the p-type semiconductor layer 51 between the photodiode 21 (n well 52) and the substrate 50. In the photodiode 21 (n-well 52), a potential barrier B4 is formed by the p-type semiconductor layer 51 at a portion not facing the substrate 50, and charges (electrons e) formed by the photodiode 21 do not leak to the outside. It is like that. The height of the potential barrier B3 can be controlled according to the voltage applied to the overflow electrode 24.

  On the other hand, the amount of charge accumulated in the potential well formed in the n-well 52 by applying a voltage to the control electrodes 21a to 21c is determined by the depth of the potential well determined by the applied voltage to the control electrodes 21a to 21c. . That is, when the voltage applied to the central control electrode 21b among the three control electrodes 21a to 21c is higher than the voltage applied to the control electrodes 21a and 21c on both sides, the central portion becomes deepest as shown in FIG. A potential well 27 is formed. Here, by applying an appropriate voltage to the overflow electrode 24, the potential of the substrate 50 is lowered below the n-well 52, and the central control electrode 21b applies a voltage so that the potential barrier B3 remains, If a voltage is applied to the control electrodes 21a and 21c so that the potential barrier B3 is removed, most of the electrons e are accumulated in the central portion shown in FIG. 9B among the regions corresponding to the control electrodes 21a to 21c. Electric charges are discarded through the substrate 50 at both sides shown in FIGS.

  Here, in the potential well 27 corresponding to the central control electrode 21b, a part of the charge generated by the control electrodes 21a and 21c on both sides flows during the period in which the photodiode 21 generates charge. A part of electric charges generated by the electrodes 21a and 21c are mixed as a noise component. Further, since the signal charge is transferred every time one of the four detection values A0, A1, A2, and A3 is obtained, the charge generated by the photodiode 21 during the transfer of the signal charge is detected by the detection value A0, It will be mixed as a noise component in A1, A2 and A3. However, since these noise components are averaged by integration and almost eliminated by subtraction when obtaining the phase difference ψ, the influence of the noise components is reduced. That is, the phase difference ψ can be obtained with high accuracy while using a frame transfer type CCD.

  In the above example, three control electrodes 21 a to 21 c are associated with one photodiode 21, but the number of control electrodes associated with one photodiode 21 is not particularly limited.

(Reference Example 2)
In this example, a frame transfer type CCD is used as in Reference Example 1, but a horizontal overflow drain is provided instead of a vertical overflow drain.

  As shown in FIG. 10, the image sensor 1 is provided with an overflow drain 61 made of an n-type semiconductor on the right side of each column of photodiodes 21 arranged in the vertical direction. In the illustrated example, since four photodiodes 21 are arranged in the horizontal direction and four in the vertical direction, the overflow drains 61 are arranged in four rows, and the upper ends of the overflow drains 61 are aluminum electrodes arranged in the left-right direction. It is connected via the overflow electrode 24. The imaging unit D1, the storage unit D2, and the horizontal transfer unit 23 have the same functions as the image sensor 1 used in Reference Example 1.

  The structure of the image sensor 1 will be described with reference to FIG. 11 in which a portion related to one photodiode 21 is cut out. In this example, a p-type semiconductor substrate 60 is used. A p-type semiconductor layer 62 is formed on the main surface of the substrate 60, and an n-well 63 made of an n-type semiconductor is formed on the p-type semiconductor layer 62. The photodiode 21 is formed by the semiconductor layer 62 and the n-well 63. In the p-type semiconductor layer 62, a p + well 64 made of p + semiconductor is formed at a portion adjacent to the n well 63, and an overflow drain 61 made of n-type semiconductor is formed on the surface side of the p + well 64. The basic structure of the image sensor 1 is the same as that of the reference example 1 except that the conductivity type of the substrate 60 is different and the overflow drain 61 is provided.

  The operation of this example is the same as that of Reference Example 1, and as can be seen by comparing FIG. 12 showing the potential of electrons along the broken line L4 in FIG. 11 with FIG. The only difference is that the charge discarding unit for discarding the charge is the overflow drain 61 in the present example compared to the substrate 50 in the first reference example. The amount of charge accumulated in the potential well formed in the n-well 63 by applying a voltage to the control electrodes 21a to 21c is determined by the depth of the potential well determined by the applied voltage to the control electrodes 21a to 21c. That is, if the voltage applied to the central control electrode 21b among the three control electrodes 21a to 21c is higher than the voltage applied to the control electrodes 21a and 21c on both sides, the potential well corresponding to the central control electrode 21b is the most. Deepen. Here, if an appropriate voltage is applied to the overflow electrode 24 and the potential barrier B3 is lowered, the central control electrode shown in FIG. 13B among the regions corresponding to the control electrodes 21a to 21c. Charges are left in the potential well corresponding to 21b, and the charges generated in the regions corresponding to the control electrodes 21a and 21c on both sides shown in FIGS. 13A and 13C can be discarded in the overflow drain 61. Other configurations and operations are the same as those in Reference Example 1.

(First embodiment)
In the configuration in which the frame transfer type CCD described in the reference example 1 and the reference example 2 is used for the image sensor 1, the example in which the three control electrodes 21a to 21c are provided in each photodiode 21 has been described. The number of control electrodes provided in each photodiode 21 is not limited to three.

  In the present embodiment, a case where four control electrodes are provided for one photodiode 21 will be described. In FIG. 14, the numbers 1 to 4 correspond to the respective control electrodes, and one repetition period of the numbers 1 to 4 that are repeatedly described corresponds to the region of one photodiode 21. FIG. 14A shows a period in which charges generated by the photodiode 21 are accumulated, and FIG. 14B shows a period in which unnecessary charges are discarded. Furthermore, the threshold value Th1 indicates the potential of the overflow drain.

  As shown in FIG. 14 (a), adjacent photodiodes without applying a voltage to the control electrode (1) so that the charges generated by the photodiodes 21 are not mixed during the charge accumulation period. A potential barrier is formed between 21. Further, the voltage applied to the control electrodes (2) to (4) is lowered stepwise to form the stepped potential well 27. Here, the potential of the part corresponding to the control electrodes (3) and (4) is set higher than the threshold value Th1. Since the potential well 27 is deepest at the portion corresponding to the control electrode (2) and the potential is lower than the threshold Th1, the charge (electrons e) generated by light irradiation to the photodiode 21 is mainly the control electrode. Accumulated in the part corresponding to (2).

  As shown in FIG. 14B, in the discarding period in which charges are discarded, the control electrode is arranged so that the charge accumulated in the portion corresponding to the control electrode (2) having the lowest potential in the accumulation period does not leak to the outside. (3) Raise the potential of the part corresponding to (4). By this operation, the charge generated corresponding to the control electrodes (1), (3), and (4) during the accumulation period flows separately to the portion corresponding to the control electrode (2) and the overflow drain. Therefore, by appropriately adjusting the ratio between the charge accumulation period and the discard period, the amount of charges that become unnecessary charges among the charges generated by the photodiode 21 can be adjusted, and as a result, the sensitivity is adjusted. can do. Other configurations and operations are the same as those in Reference Example 1 or Reference Example 2.

(Second Embodiment)
This embodiment is an example in which six control electrodes (1) to (6) are provided for one photodiode 21 as shown in FIG. In FIG. 15, numerals 1 to 6 correspond to the control electrodes. Similarly to the example shown in FIG. 14, FIG. 15A shows a period for accumulating charges, and FIG. 15B shows a period for discarding charges.

  As shown in FIG. 15A, in the period for accumulating charges, adjacent photodiodes without applying voltage to the control electrode (1) so that the charges generated by the photodiodes 21 are not mixed. A potential barrier is formed between 21. Further, among the control electrodes (2) to (6), the potential of the portion corresponding to the control electrode (4) is made the lowest, and the portions corresponding to the remaining control electrodes (2), (3), (5) and (6) are set. Increase the potential step by step. Further, the potential of the portion corresponding to the control electrodes (2), (3), (5), and (6) is set higher than the threshold value Th2 that is the potential of the overflow drain. The potential corresponding to the control electrode (4) is the lowest, and this potential is lower than the threshold value Th2. Therefore, the charges (electrons e) generated by the light irradiation to the photodiode 21 are mainly controlled by the control electrode (4 ).

  As shown in FIG. 15B, in the period for discarding the charge, the control electrode (in order to prevent the charge accumulated in the portion corresponding to the control electrode (4) having the lowest potential in the accumulation period from leaking outside). 2) Increase the potential of the parts corresponding to (3), (5) and (6). By this operation, the charge generated corresponding to the control electrodes (1), (2), (3), (5), and (6) in the accumulation period flows separately into the portion corresponding to the control electrode (4) and the overflow drain. . Therefore, in the present embodiment as well, as in the first embodiment, the amount of charges that become unnecessary charges among the charges generated by the photodiode 21 is adjusted by appropriately adjusting the ratio between the charge accumulation period and the discard period. Can be adjusted and consequently the sensitivity can be adjusted. Other configurations and operations are the same as those in Reference Example 1 or Reference Example 2.

(Third embodiment)
As described above, when the frame transfer type CCD is used, the charge generated by the photodiode 21 is mixed into the signal charge as a noise component during a period other than the period for obtaining the detection values A0, A1, A2, and A3. Such a noise component is substantially constant and is averaged by accumulating charges during the period for obtaining the detection values A0, A1, A2, and A3. It is possible to remove. However, if there is a noise component, the signal-to-noise ratio is lowered, so that it is required to increase the dynamic range in a portion related to charge accumulation and transfer, resulting in high cost.

  Therefore, in the present embodiment, as shown in FIG. 16, the light shielding film 65 is provided in the vicinity of the region in which the signal charge is accumulated in the photodiode 21 and in the region not involved in the generation of the charge. The illustrated example is a configuration example in which six control electrodes are provided for one photodiode 21 as in the second embodiment, and specifically corresponds to the control electrodes (1) and (4). By providing the light shielding film 65 at the portion to be processed, electric charges (electrons e) are generated at the portions corresponding to the control electrodes (2), (3), (5), and (6) in the photodiode 21. With this configuration, charge generation is performed mainly at portions corresponding to the control electrodes (2), (3), (5), and (6), and the control electrode (4) hardly contributes to charge generation. That is, no noise component is generated in the control electrode (4), and the SN ratio can be improved as compared with the case where the light shielding film 65 is not formed. Other configurations and functions are the same as those of the second embodiment.

  In the first to third embodiments, the operation of FIG. 2 has been described as an example of the control timing of the control voltage and the discard voltage. However, it is needless to say that the operations of FIGS. 3 and 4 may be applied. That is.

  In each of the above-described embodiments, a configuration is adopted in which charge is extracted every time one of the four detection values A0, A1, A2, and A3 is obtained. However, in the image sensor 1 described below, a plurality of values are used. Detection values A0, A1, A2 and A3 can be obtained and extracted at once.

(Fourth embodiment)
This embodiment uses an image sensor 1 in which a partial configuration of a frame transfer type CCD having a horizontal overflow drain shown in FIG. 10 is changed. That is, as shown in FIG. 17, a configuration in which overflow drains 61a and 61b are provided for each photodiode 21 is adopted, and the charges generated by each photodiode 21 can be individually discarded. In this configuration, by applying a discard voltage synchronized with the period of the modulation signal to the overflow drains 61a and 61b, the ratio of the signal charge that moves to the potential well that is the charge storage portion among the charges generated by the photodiode 21 Adjust. However, in this embodiment, the timing at which the discard voltages φ1 and φ2 are applied to each pair of overflow drains 61a and 61b adjacent to each other in the direction in which the signal charge is transferred out of the overflow drains 61a and 61b has a phase in the modulation signal. The timing is different by 180 degrees. By applying discard voltages φ1 and φ2 to the two photosensitive portions 11 at a timing that is 180 degrees different in phase, signal charges corresponding to timings that are 180 degrees different in phase in the modulation signal correspond to each photosensitive portion 11. It can be accumulated in the formed potential well. That is, signal charges corresponding to different phases in the modulation signal can be accumulated in the potential wells formed respectively in the two adjacent photosensitive portions 11, and the four detection values A0 necessary for obtaining the phase difference ψ. , A1, A2 and A3 can be taken out collectively. In this way, the detection value A0 and the detection value A2 can be extracted at once, and the detection value A1 and the detection value A3 can be extracted at once.

  In the configuration of the present embodiment, noise components are generated because unintended charges are mixed with signal charges, but the noise components are small compared to the amount of signal charges, and are mixed at a substantially constant ratio with respect to signal charges. Therefore, the influence of the noise component is reduced when obtaining the phase difference ψ. Other configurations and operations are the same as those in Reference Example 2.

  In the present embodiment, three control electrodes 21a to 21c are associated with each of the overflow drains 61a and 61b, but four or more may be provided. In addition, a configuration is adopted in which discard voltages φ1 and φ2 with different timings of 180 degrees in the phase of the modulation signal are applied to different overflow drains. If it is the structure given to (4), it is also possible to take out four detection values A0, A1, A2, A3 collectively. Furthermore, the application timing of the discard voltage may be a specific phase synchronized with the period of the modulation signal, and the interval can be set appropriately.

It is a block diagram which shows a basic structure. It is operation | movement explanatory drawing which shows one operation example same as the above. It is operation | movement explanatory drawing which shows the other operation example same as the above. It is operation | movement explanatory drawing which shows the other operation example same as the above. 6 is a plan view showing an image sensor used in Reference Example 1. FIG. It is a principal part perspective view same as the above. It is operation | movement explanatory drawing same as the above. It is operation | movement explanatory drawing same as the above. It is operation | movement explanatory drawing same as the above. It is a top view which shows the image sensor used for the reference example 2. FIG. It is a principal part perspective view same as the above. It is operation | movement explanatory drawing same as the above. It is operation | movement explanatory drawing same as the above. It is operation | movement explanatory drawing which shows 1st Embodiment. It is operation | movement explanatory drawing which shows 2nd Embodiment. It is operation | movement explanatory drawing which shows 3rd Embodiment. It is a principal part perspective view which shows 4th Embodiment. It is operation | movement explanatory drawing which shows a prior art example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image sensor 2 Light emission source 3 Control circuit part 4 Light reception lens 5 Evaluation part 11 Photosensitive part 12 Charge storage part 12a Control electrode 13 Charge extraction part 14 Charge discard part 14a Discard electrode 21 Photodiode 21a-21c Control electrode 23 Horizontal transfer part 24 Overflow electrode 50 Substrate 60 Substrate 61 Overflow drain

Claims (5)

A structure in which a plurality of control electrodes are stacked on the main surface of a semiconductor layer via an insulating film, and receives light from a space irradiated with light whose intensity is modulated by a modulation signal of a predetermined modulation frequency and receives light intensity. A charge accumulating unit that generates an amount of charge corresponding to the charge, a charge accumulating unit that accumulates a signal charge out of the charges generated in the photosensitive unit, and a charge that is disposed as an unnecessary charge out of the charges generated in the photosensitive unit with a disposal electrode . Control is performed by combining a charge discarding unit whose movement is controlled according to a discarding voltage applied to the discarding electrode, a charge extracting unit for extracting signal charges accumulated in the charge accumulating unit, and a plurality of adjacent specified control electrodes. A control circuit unit for controlling the depth of a potential well formed in a portion corresponding to each control electrode in the semiconductor layer by controlling the voltage applied to the electrode at a timing synchronized with the unit and the period of the modulation signal; And an evaluation unit that evaluates information related to the space using the electric charge extracted by the unloading unit, and the control circuit unit includes a plurality of control electrodes in the set during the accumulation period for accumulating the electric charge generated by the photosensitive unit. The potential well is formed in correspondence with the remaining charge, and in the discarding period in which unnecessary charges are discarded, the charge of the potential well corresponding to at least one control electrode among the charges accumulated in the accumulation period is left as a signal charge, and the remaining Spatial information using intensity-modulated light, characterized in that unnecessary charges generated corresponding to the control electrode are discarded in the charge discarding part by controlling the potential well of the part corresponding to the control electrode to become shallower Detection device. The control circuit unit controls an applied voltage to the control electrode in the set in the accumulation period so that a potential well that retains signal charges in the discard period is deeper than other potential wells in the accumulation period. The spatial information detection device using the intensity-modulated light according to claim 1. 3. The intensity-modulated light according to claim 2, wherein the control circuit unit controls a voltage applied to the control electrode in the set so that a potential well formed in an accumulation period is stepped. Spatial information detection device. The charge discarding part is an overflow drain, and the control circuit part makes the potential of the part forming the potential well for leaving the signal charge in the discarding period deeper than the potential of the overflow drain, and the other part formed in the accumulation period 4. The intensity-modulated light according to claim 2, wherein the voltage applied to the control electrode in the set is controlled so that the potential of the partial potential well is shallower than the potential of the overflow drain. Spatial information detection device used. 5. The control circuit unit according to claim 1, wherein the control circuit unit forms a potential barrier without applying a voltage to a control electrode adjacent to another group among the control electrodes in the group. An apparatus for detecting spatial information using the intensity-modulated light according to item 1.

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