JP4385384B2 - Photosensitive element sensitivity control method, spatial information detection device using intensity-modulated light - Google Patents

Description

  The present invention relates to a sensitivity control method for a light receiving element and a spatial information detection apparatus using intensity-modulated light.

  2. Description of the Related Art Conventionally, when the sensitivity of a light receiving element is to be controlled by an external signal, a configuration in which an optical member that can adjust the amount of light passing through an external signal is arranged in front of the light receiving element. This technology controls the amount of light incident on the light receiving element, but on the other hand, by controlling the proportion of the charge generated by the light receiving element corresponding to the received light intensity and actually taking it out as signal charge, A technique for controlling the sensitivity of the element is also employed.

  The technology to control the sensitivity of the light receiving element is, for example, that light whose intensity is modulated is emitted from the light source to the space, the reflected light reflected by the object existing in this space is received by the light receiving element, and the light emitted from the light source is emitted. This is employed when detecting various information related to space based on the relationship between the light received by the light receiving element and the light received by the light receiving element. Here, the information related to the space means a distance to an object existing in the space, a change in received light amount due to reflection by the object existing in the space, and the like. When determining the distance to the object, the light emitted from the light source to the space is intensity-modulated at a predetermined modulation frequency, and the photoelectric element receives the received light intensity multiple times in synchronization with the modulation period that is the reciprocal of the modulation frequency. A technique for detection is considered (for example, Patent Document 1).

That is, the intensity of light radiated from the light source to the space is modulated, and the received light intensity at the photoelectric element for the specific phase at the time of modulation is detected, and the received light intensity of the specific phase is measured three times in synchronization with the modulation period. If it calculates | requires above, the phase difference of the light radiated | emitted from the light emission source and the light received by the light receiving element can be calculated | required by the relationship of the calculated | required received light intensity. In the following description, it is assumed that the received light intensity is obtained four times or more. For example, when the intensity of light radiated from the light source to the space is modulated with a sine wave, the received light intensity is detected at four points where the phase of the modulation signal is 0 degrees, 90 degrees, 180 degrees, and 270 degrees. If the received light intensities at that time are A0, A1, A2, and A3, respectively, the phase difference ψ is expressed as follows using the received light intensities A0, A1, A2, and A3 at the respective phases.
ψ = tan ⁻¹ {(A3-A1) / (A0-A2)}
As described above, if the received light intensity of a specific phase is determined in accordance with the modulation period, it is necessary to control the sensitivity of the light receiving element. In the technique described in Patent Document 1, the light receiving element is integrated. A switch region is provided in a path for transferring the stored charge to the storage region, and the switch region is configured to accumulate the charge necessary for obtaining the received light intensity A0, A1, A2, A3 among the charges integrated by the light receiving element in the storage region. The structure which controls is adopted.
JP 10-508736 A (page 7-9, FIG. 1, FIG. 2)

  In the technique described in Patent Document 1 described above, there is a problem that the structure is relatively complicated because it is necessary to provide a switch area and a storage area separately from the photosensitive portion in the image sensor. There is also a problem that the aperture ratio is small and the sensitivity is low because the area occupied by the portion that needs light shielding in the image sensor is relatively large.

  The present invention has been made in view of the above-mentioned reasons, and an object of the present invention is to provide a sensitivity control method for a light receiving element having a relatively simple structure and a relatively large aperture ratio and excellent S / N. Another object of the present invention is to provide a spatial information detection device using intensity-modulated light using this method.

According to the first aspect of the present invention, there is provided a photosensitive portion that generates an amount of charge corresponding to the received light intensity, and at least one of the charges generated in the photosensitive portion formed in the photosensitive portion by applying a control voltage to a control electrode provided in the photosensitive portion. A method for controlling light reception sensitivity in a light receiving element including a charge integration unit that integrates a charge collecting unit and a charge extraction unit that extracts the charge accumulated in the charge integration unit as a light reception output, wherein the impurity concentration of a semiconductor layer in the photosensitive unit for, grant distribution corresponding to the distance from the control electrode along the light receiving surface, the magnitude of a control voltage to the control electrode so that the area of the charge accumulation portions in a plane along the light receiving surface of the photosensitive section changes is varied and a generation period to increase the area of the charge accumulation portion, between a holding period for holding the generated electric charges in the generation period by reducing the area of the charge accumulation portion, the area of the charge accumulation portion big Characterized in that the switching of the.

The invention of claim 2 is an apparatus for detecting spatial information using intensity-modulated light, and receives light from a space irradiated with light that has been intensity-modulated with a modulation signal having a predetermined modulation frequency to obtain a received light intensity. A photosensitive portion that generates a corresponding amount of charge, a charge accumulation portion that accumulates at least a portion of the charge generated in the photosensitive portion formed by applying a control voltage to a control electrode provided in the photosensitive portion, and a charge With the passage of time so that the area of the charge collection section in the plane along the light receiving surface of the photosensitive section changes with the passage of time a control circuit unit for outputting a control voltage magnitude varies, and a evaluation unit for evaluating the information related to the space using a charge removed by a charge take-out portion, the impurity concentration of the semiconductor layer in the photosensitive portion, the light-receiving surface In line with Grant distribution corresponding to the distance from the electrode, the control circuit section changes the magnitude of the control voltage to the control electrode so that the area of the charge accumulation portions in a plane along the light receiving surface of the photosensitive section changes Between the generation period for increasing the area of the charge integration portion and the holding period for holding charges generated in the generation period by reducing the area of the charge integration portion. It is characterized by switching.

  According to the first aspect of the present invention, a light receiving element that uses a part of the photosensitive portion as a charge accumulation portion by applying a control voltage to a control electrode provided in the photosensitive portion that generates an amount of electric charge corresponding to the received light intensity. Since the control voltage to the control electrode is changed so that the area of the charge accumulation portion in the plane along the plane changes, the area of the part that generates charges according to the amount of received light in the light receiving element depends on the control voltage. It is possible to adjust the ratio of the electric charges generated in the photosensitive portion and taken out as signal charges through the charge accumulation portion by the control voltage. Furthermore, a charge accumulation unit corresponding to the photosensitive unit is provided, and a generation period for increasing the area of the charge integration unit by changing the area of the charge integration unit according to the control voltage to the control electrode provided in the photosensitive unit, and charge integration Since the area of the charge accumulation unit is switched between the holding period for holding the charge generated during the generation period by reducing the area of the unit, the sensitivity control and charge accumulation are performed within the surface of the photosensitive unit. Compared to a conventional configuration in which a switch area and a storage area are provided in a separate area from the photosensitive part, there is an advantage that the structure becomes simple, and while having functions for controlling sensitivity and collecting charge. Since it can be used without being shielded from light, the light receiving area can be made relatively large, the aperture ratio is large, and as a result, the signal charge can be taken out with high S / N.

  According to a second aspect of the present invention, there is provided a light receiving element that uses a part of the photosensitive portion as a charge accumulation portion by applying a control voltage to a control electrode provided in the photosensitive portion that generates an amount of charge corresponding to the received light intensity. Since the control voltage to the control electrode is changed so that the area of the charge accumulation portion in the plane along the plane changes, the area of the part that generates charges according to the amount of received light in the light receiving element depends on the control voltage. The ratio of the electric charge generated by the photosensitive portion and taken out as signal charge through the charge accumulation portion can be adjusted by the control voltage. In addition, it is possible to take out signal charges including information about the space by receiving light from the space irradiated with the intensity-modulated light by the light receiving element and adjusting the sensitivity of the light receiving element. Furthermore, a charge accumulation unit corresponding to the photosensitive unit is provided, and a generation period for increasing the area of the charge integration unit by changing the area of the charge integration unit according to the control voltage to the control electrode provided in the photosensitive unit, and charge integration Since the area of the charge accumulation unit is switched between the holding period for holding the charge generated during the generation period by reducing the area of the unit, the sensitivity control and charge accumulation are performed within the surface of the photosensitive unit. Compared to a conventional configuration in which a switch area and a storage area are provided in a separate area from the photosensitive part, there is an advantage that the structure becomes simple, and while having functions for controlling sensitivity and collecting charge. Since it can be used without being shielded from light, the light receiving area can be made relatively large, the aperture ratio is large, and as a result, the signal charge can be taken out with high S / N.

First, a configuration example using the light receiving element 1 having the configuration shown in FIG. 1 will be described. The light receiving element 1 includes a semiconductor layer 11 to which an impurity is added, the main surface of the semiconductor layer 11 is covered with an insulating film 12 made of an oxide film, and a control electrode 13 is provided on the semiconductor layer 11 via the insulating film 12. Have a configuration. The light receiving element 1 has a structure known as a MIS element. However, the light receiving element 1 has a plurality of (five in the illustrated example) control electrodes 13 in a region functioning as one light receiving element 1. Different. Materials are selected for the insulating film 12 and the control electrode 13 so that light can be transmitted. When light enters the semiconductor layer 11 through the insulating film 12, charges are generated inside the semiconductor layer 11. The conductivity type of the semiconductor layer 11 in the illustrated example is n-type, and electrons e are used as charges generated by light irradiation.

  In the light receiving element 1 having this structure, when a positive control voltage + V is applied to the control electrode 13, a potential well (depletion layer) 14 for accumulating electrons e is formed in the semiconductor layer 11 at a site corresponding to the control electrode 13. . That is, when light is applied to the semiconductor layer 11 with a control voltage applied to the control electrode 13 so as to form the potential well 14 in the semiconductor layer 11, a part of the electrons e generated in the vicinity of the potential well 14. Are captured in the potential well 14 and accumulated in the potential well 14, and the remaining electrons e disappear due to recombination in the deep part of the semiconductor layer 11. Further, the electrons e generated at a location away from the potential well 14 are also extinguished by recombination in the deep part of the semiconductor layer 11.

  As described above, since the potential well 14 is formed at a portion corresponding to the control electrode 13 to which the control voltage is applied, the potential well 14 is formed on the main surface of the semiconductor layer 11 by changing the number of the control electrodes 13 to which the control voltage is applied. The area of the potential well 14 (in other words, the area of the charge accumulation portion in the light receiving surface) can be changed. If the area of the charge accumulation unit changes, the proportion of electrons e generated in the semiconductor layer 11 accumulated in the charge accumulation unit changes, so that the charge accumulated in the charge accumulation unit is taken out as a signal charge to the outside. In this case, the sensitivity of the light receiving element 1 is substantially adjusted. That is, the sensitivity of the light receiving element 1 can be controlled by controlling the application pattern of the control voltage to the control electrode 13. For example, when a control voltage is applied to three control electrodes 13 as shown in FIG. 1A and when a control voltage is applied to one control electrode 13 as shown in FIG. The area occupied by the potential well 14 which is an integrated portion changes in the light receiving surface, and the area of the potential well 14 is larger in the state of FIG. 1A than in the state of FIG. The ratio of the signal charge with respect to the light amount is increased, and the sensitivity of the light receiving element 1 is substantially increased.

  In order to take out the signal charge from the potential well 14 which is the charge accumulation portion in the light receiving element 1 described above, a technique similar to that of the frame transfer type CCD may be adopted. After the electron e is accumulated in the potential well 14, the control is performed. By controlling the voltage application pattern, the electrons e accumulated in the potential well 14 are transferred in one direction (right direction or left direction in the figure), and the electrons e are taken out from an electrode (not shown) provided in the semiconductor layer 11. Become.

  If the operation of each part of the light receiving element 1 is expressed by function, the semiconductor layer 11 includes a photosensitive part 1a (see FIG. 2) that generates electrons e upon incidence of light and a charge integration part that integrates the electrons e generated by the photosensitive part 1a. 1c (see FIG. 2), and the control electrode 13 functions as a sensitivity control unit 1b (see FIG. 2) by changing the application pattern of the control voltage during light reception. Further, the semiconductor layer 11 also functions as the charge extraction portion 1d (see FIG. 2) by controlling the application pattern of the control voltage to the control electrode 13. By making the sensitivity of the light receiving element 1 controllable by the above-described operation for controlling the application pattern of the control voltage, the apparatus shown in FIG. 2 can be realized using the light receiving element 1.

The illustrated apparatus is an apparatus that detects spatial information from a space irradiated with intensity-modulated light. Here, the spatial information means a distance to the object, a change in the amount of received light due to reflection by an object existing in the space, and the like. What information is extracted as spatial information from the output of the light receiving element 1 depends on the configuration of the evaluation unit 3. Here , the evaluation unit 3 obtains the phase difference between the original phase of the intensity-modulated light applied to the space and the light received by the photoelectric element 1, and from this phase difference to the object 5 existing in the space. The example which calculates | requires distance is shown.

  The apparatus shown in FIG. 2 includes a light emitting source 2 that irradiates light into a space in which a distance to the object 5 is to be obtained, and a light receiving element 1 that receives light reflected by the object 5. The light emission source 2 is driven by a modulation signal having a predetermined modulation frequency output from the control circuit unit 4, and the light emitted from the light emission source 2 is intensity-modulated at the 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 4 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 irradiated with light from the light emitting source 2 enters the light receiving element 1 through the light receiving optical system 6. The light receiving element 1 includes a plurality of (for example, 100 × 100) photosensitive portions 1a having the structure shown in FIG. 1, and the photosensitive portions 1a are arranged in a matrix or the like to constitute the image sensor 7. In this type of image sensor 7, for example, the photosensitive portions 1 a are arranged in a matrix on a single semiconductor substrate, and the semiconductor layers 11 that are integrally continuous in each column in the vertical direction of the photosensitive portions 1 a are shared and the semiconductor layers. 11 is used as a transfer path for charges (electrons e) in the vertical direction, and a CCD type horizontal transfer unit that receives the electrons e from one end of the semiconductor layer 11 in each column and transfers the electrons e in the horizontal direction is provided on the semiconductor substrate. The provided structure can be adopted. The image sensor 7 having this configuration is similar to a frame transfer type CCD image sensor.

  The light receiving optical system 6 maps a three-dimensional space in which light from the light source 2 is emitted onto a two-dimensional plane that is a light receiving surface of the image sensor 7. That is, the object 5 existing in the field of view viewed by the image sensor 7 through the light receiving optical system 6 is associated with the photosensitive portion 1a. Here, since the light receiving intensity of the light incident on the photosensitive portion 1a corresponding to the object 5 is modulated by the light from the light source 2, the light emitted from the light source 2 and the light received by the photosensitive portion 1a Is detected, the distance to each part of the object 5 corresponding to the photosensitive portion 1a can be obtained.

  In FIG. 2, in order to facilitate understanding of the function of the image sensor 7, the function of the light receiving element 1 is divided into the photosensitive portion 1a, the sensitivity control portion 1b, the charge accumulation portion 1c, and the charge extraction portion 1d as described above. It is described. The charge extraction unit 1 d in FIG. 2 includes not only the semiconductor layer 11 but also the horizontal transfer unit of the image sensor 7. The sensitivity control unit 1b and the charge extraction unit 1d share the control electrode 13 as described above, and the sensitivity is controlled by controlling the application pattern of the control voltage generated by the control circuit unit 4 and applied to the control voltage 13. Regulation and charge transfer are made.

Here , in order to obtain the phase difference between the light emitted from the light source 2 into the space and the light received by the photosensitive unit 1a, the sensitivity in the sensitivity control unit 1b is synchronized with the period of the modulation signal that drives the light source 2. An example of performing the control will be shown. That is, the sensitivity control unit 1b alternately repeats the high sensitivity state and the low sensitivity state, and synchronizes this repetition cycle with the modulation signal cycle.

Specifically, as shown in FIG. 3, if the change in intensity of light radiated from the light source 2 into the space is a curve a and the change in the received light intensity at the photosensitive portion 1a is a curve b, It can be seen that in order to obtain the phase difference ψ, the intensities at four points at different phases can be obtained for the curve b. For example, it is assumed that the received light intensity at curve B at the timing of 4 points with a phase of 0 degree, 90 degrees, 180 degrees, and 270 degrees for curve A is A0, A1, A2, and A3, respectively. Here, the received light intensities A0, A1, A2, and A3 in each phase are actually proportional to the amount of light incident within the time indicated by the time width Tw. Here, if the phase difference ψ does not change while the received light intensity A0, A1, A2, A3 is obtained, and the light attenuation rate from light emission to light reception does not change, the light reception intensity A0, A1. , A2 and A3 are obtained every 90 degrees, the relationship between each received light intensity A0, A1, A2 and A3 and the phase difference ψ can be expressed by the following equation.
ψ = tan ⁻¹ {(A3-A1) / (A0-A2)}
That is, if the sensitivity control unit 1b is set to be highly sensitive by the time width Tw at the timing for obtaining the above-described received light intensity A0, A1, A2, A3, the signal charge corresponding to the received light intensity A0, A1, A2, A3 at each timing. Is accumulated in the charge accumulation section 1c. The four signal charges obtained in this way are taken out to the evaluation unit 3 through the charge extraction unit 1d each time a signal charge is obtained, or four signal charges are associated with each of the different photosensitive units 1a. If the signal charges are obtained and then extracted to the evaluation unit 3 through the charge extraction unit 1d, the phase difference ψ can be obtained from the above equation, and the phase difference ψ can be obtained by using the modulation frequency and the phase difference ψ. Can be converted into a distance to the object 5.

  In the configuration described above, since the semiconductor layer 11 is shared by the photosensitive portion 1a and the charge integration portion 1c, even during a period other than the period in which the sensitivity control portion 1b is set to high sensitivity in order to extract signal charges, In order for the semiconductor layer 11 to function as the charge accumulation unit 1c, it is necessary to apply a control voltage to the control electrode 13 in a state where the sensitivity control unit 1b has low sensitivity. That is, charges other than signal charges are also mixed in the charge accumulation unit 1c. However, since the area of the charge accumulating portion 1c is small during the period of low sensitivity, and it is considered that charges other than the signal charge are mixed almost equally into the four signal charges, the light reception is performed as shown in the above equation. By the calculation for calculating the difference between the intensities A0, A1, A2, and A3 (the calculation for determining (A3-A1) and (A0-A2)), components due to charges other than the signal charges are removed together with the influence of disturbance light. Further, in order to suppress the mixing of charges other than the signal charge during the period in which the area of the charge accumulating portion 1c is reduced as shown in FIG. 1B, the control electrode 13 corresponding to the charge accumulating portion 1c in this period is suppressed. You may employ | adopt the structure which provides a light shielding film in the vicinity.

In the illustrated example, four signal charges (light receiving intensities A0, A1, A2, A3) are obtained every 90 degrees within one period of the modulation signal. If the phase of the signal is defined, it is not essential to extract every 90 degrees, and if no change occurs in the phase difference ψ or the light attenuation rate during the extraction of the four signal charges, 1 of the modulation signal is obtained. It is not essential to take out four signal charges within a period. Moreover, although the light radiated | emitted from the light emission source 2 is modulated with the sine wave, you may modulate intensity | strength with other waveforms, such as a triangular wave or a sawtooth wave. Further, when there is an influence of disturbance light such as sunlight or illumination light, it is desirable to dispose an optical filter that transmits only the wavelength of light emitted from the light source 2 in front of the photosensitive portion 1a. The same applies to the following configuration examples .

In the operation example shown in FIG. 3, since the signal charge is extracted in synchronization with the period of the modulation signal, for example, when the modulation frequency is 20 MHz, the accumulation time of the signal charge for one period of the modulation signal is several tens of ns. About short. In this case, the waveform distortion of the control voltage applied to the control electrode 13 directly affects the detection accuracy of the phase difference ψ. Further, the waveform distortion of the light emitted from the light emitting source 2 also directly affects the detection accuracy of the phase difference ψ.

Therefore, here , by controlling the sensitivity control unit 1b at a local frequency different from the modulation frequency, the sensitivity control unit 1b is used as a mixer for mixing the modulation frequency and the local frequency, and the beat signal obtained as a result of the mixing is used. To detect the phase difference ψ. In this configuration , as long as the periodicity of the waveform of the control voltage and the waveform of the modulation signal is maintained, the phase difference ψ can be detected without being affected by the waveform distortion. Here, the local oscillation signal of the local oscillation frequency is given from the control circuit unit 4. By adopting such a configuration, the charge accumulating unit 1c has an envelope component of the frequency difference between the charge (corresponding to the received light signal) corresponding to the amount of light received by the photosensitive unit 1a and the local oscillation signal. The signal charge corresponding to the beat signal is accumulated. The cycle of the beat signal depends on the frequency difference between the modulation frequency and the local frequency. For example, if the frequency difference is set to about 300 kHz, the cycle of the beat signal is about 3 μs.

If the distance to the object 5 does not change with time, the phase of the beat signal is the phase of the light emitted from the light source 2, the phase of the local signal output from the control circuit unit 4, and the photosensitive unit 1a. It is determined by the relationship with the phase of the received light signal output from. That is, if the angular frequency corresponding to the modulation frequency is ω1, and the phase difference between the phase of the light emitted from the light source 2 and the phase of the received light signal is ψ, the signal intensity Y1 of the received light signal is expressed by the following equation. The However, a1 and b1 are constants, a1 corresponds to the amplitude of the received light signal, and b1 corresponds to dark current or external light (time change is ignored).
Y1 = b1 + a1 · cos (ω1 · t + ψ)
If the angular frequency of the local oscillation signal is ω2, the signal intensity Y2 of the local oscillation signal is expressed by the following equation. However, a2 and b2 are constants, a2 corresponds to the amplitude of the local oscillation signal, and b2 corresponds to the DC bias.
Y2 = b2 + a2 · cos (ω2 · t)
Here, since the signal obtained by mixing the received light signal and the local oscillation signal is (Y1 · Y2), a beat signal having an envelope component corresponding to the frequency difference between the modulation frequency and the frequency of the local oscillation signal is obtained. In addition, the phase difference ψ is directly reflected in the phase of the envelope component. That is, the signal charge for obtaining the phase difference ψ may be taken out in synchronization with the cycle of the beat signal. However, since the beat signal includes a fluctuation component of the light amount due to the modulation signal, it is necessary to extract the envelope component of the beat signal in order to extract the signal charge. In the example shown in FIG. 4, a configuration is adopted in which charges generated in the time width Ti shown in FIG. 4 are accumulated in the charge accumulating unit 1c in synchronization with the cycle of the beat signal (that is, a period corresponding to the time width Ti). Controls the sensitivity of the sensitivity control unit 1b with a local signal, and makes the sensitivity control unit 1b low in other periods). Therefore, in the charge accumulation unit 1c, the beat signal in the time width Ti is integrated, the fluctuation component due to the modulation signal is removed, and an amount of signal charge proportional to the envelope component of the beat signal is accumulated in the charge accumulation unit 1c. Will be. In other words, the charge accumulating unit 1c has envelope-detected the beat signal.

For example, signal charges are accumulated in the charge accumulating unit 1c at four points (for example, timings of 0 °, 90 °, 180 °, and 270 °) synchronized with the cycle of the beat signal. The integrated values A0 ′, A1 ′, A2 ′, and A3 ′ are integrated by the time width Ti. These integrated values A0 ', A1', A2 ', A3' can be handled in the same manner as the received light intensity A0, A1, A2, A3 shown in FIG. 3, and the phase difference ψ can be obtained by the following equation.
ψ = tan ⁻¹ {(A3′−A1 ′) / (A0′−A2 ′)}
In the example shown in FIG. 4, since the phase difference ψ is obtained using the four integrated values obtained in synchronization with the cycle of the beat signal, if the modulation frequency and the local frequency are managed so as not to cause a frequency error, Even if the local oscillation signal is generated without being synchronized with the light emitted from the light emitting source 2, the phase difference ψ can be obtained.

  As described above, when the phase difference ψ is obtained, a beat signal that is sufficiently lower than the modulation frequency is used, and the beat signal integration values A0 ′, A1 ′, A2 ′, and A3 ′ are used. The SN ratio can be made sufficiently large with respect to noise components due to current and external light.

In the example shown in FIG. 4, four integral values A0 ′, A1 ′, A2 ′, A3 ′ are obtained for each quarter cycle of the beat signal within one cycle of the beat signal. If the phase is defined, the timing for obtaining the integral values A0 ', A1', A2 ', A3' is not essential every quarter cycle, and it is not necessary to be within one cycle of the beat signal. . Other configurations and operations are similar to the operation example shown in FIG.

In the example shown in FIG. 4, four integrated values A0 ′, A1 ′, A2 ′, A3 ′ for obtaining the phase difference ψ are taken out at different timings. Here, a plurality of integrated values A0 ′, A1 ', A2' and A3 'can be taken out simultaneously . Here, an example is shown in which two integral values A0 ′, A1 ′, A2 ′, and A3 ′ having phases different from each other by 180 degrees in the beat signal are obtained simultaneously.

Integral value of two by two A0 ', A1', A2 ' , A3' in order to obtain at the same time, to form the one pixel by now in a set of two photosensitive portions 1a, have the opposite phase to the control circuit unit 4 Two kinds of local oscillation signals are generated, and local oscillation signals having opposite phases are given to the sensitivity control section 1b corresponding to the two photosensitive sections 1a. Although the two types of local oscillation signals are in opposite phases, the local oscillation frequencies are set equal. In this way, by providing the local control signal having the opposite phase to the sensitivity control unit 1b, the beat signals obtained as the outputs of the sensitivity control units 1b have the opposite phases.

  Here, as shown in FIG. 5, it is assumed that three control electrodes 13 are provided for each of the two photosensitive portions 1a in the set. In the following description, in order to distinguish each control electrode 13 of one pixel, the numbers (1) to (6) are assigned to each control electrode 13 as shown in FIG. That is, one of the two photosensitive portions 1a in the set includes control electrodes (1) to (3), and the other includes control electrodes (4) to (6). It is desirable to provide an overflow drain in association with each photosensitive portion 1a.

As described with reference to FIG. 1, in the sensitivity control unit 1b, the area of the potential well 14 occupying the light receiving surface is changed, and the phase is opposite to the control electrode 13 of the photosensitive unit 1a which becomes one pixel by one set. Giving a local oscillation signal corresponds to alternately switching the area of the potential well 14 formed corresponding to each pair of adjacent photosensitive portions 1a in two steps.

  That is, as shown in FIG. 5A, in order to increase the area of the potential well 14 corresponding to the control electrodes (1) to (3), three control electrodes corresponding to one photosensitive portion 1a in one pixel. The control voltage which is the same voltage is applied to all of (1) to (3), and the central control among the three control electrodes (4) to (6) corresponding to the other photosensitive portion 1a is applied during this period. A voltage is applied only to the electrode (5) to reduce the area of the potential well. In other words, the region corresponding to the control electrodes (1) to (3) is a state in which the sensitivity control unit 1b is set to high sensitivity, and the region corresponding to the control electrodes (4) to (6) has a new charge due to light reception. Almost no (electrons e) are generated. In this state, out of the four interval integral values A0 ′, A1 ′, A2 ′, A3 ′ used for obtaining the phase difference ψ, the charge (electron e) corresponding to the integral value A0 ′ or the integral value A2 ′ is potential. It can be accumulated in the well 14.

  Further, as shown in FIG. 5B, in order to increase the area of the potential well 14 corresponding to the control electrodes (4) to (6), three control electrodes corresponding to one photosensitive portion 1a in one pixel. The control voltage which is the same voltage is applied to all of (4) to (6), and the central control among the three control electrodes (1) to (3) corresponding to the other photosensitive portion 1a is applied during this period. A voltage is applied only to the electrode (2) to reduce the area of the potential well 14. That is, the region corresponding to the control electrodes (4) to (6) is in a state in which the sensitivity control unit 1b is set to high sensitivity, and in the region corresponding to the control electrodes (1) to (3), new charges due to light reception are Almost no generation. In this state, out of the four interval integral values A0 ′, A1 ′, A2 ′, A3 ′ used for obtaining the phase difference ψ, the charge (electron e) corresponding to the integral value A1 ′ or the integral value A3 ′ is potential. It can be accumulated in the well 14.

  Both the states of FIG. 5A and FIG. 5B are alternately repeated in a period in which the integral values A0 ′ and A1 ′ can be obtained and in a period in which the integral values A2 ′ and A3 ′ can be obtained. It is. That is, by alternately repeating the state of FIG. 5A and the state of FIG. 5B within the period for obtaining the integral value A0 ′ shown in FIG. 4, the integral value A0 ′ and the integral value A1 ′ are obtained. Corresponding signal charges are accumulated in the potential well 14 corresponding to each photosensitive portion 1a, and the state shown in FIG. 5A and the state shown in FIG. 5B are obtained within the period for obtaining the integral value A2 ′ in FIG. By repeating alternately, signal charges corresponding to the integral value A2 'and the integral value A3' are accumulated in each potential well 14 corresponding to the photosensitive portion 1a.

Here , the voltage applied simultaneously to each of the three control electrodes (1) to (3) or (4) to (6) in both the state of FIG. 5A and the state of FIG. The voltage applied to only one control electrode (2) or (5) is set substantially equal.

  As described above, the signal charge corresponding to the integral value A0 ′ in the state of FIG. 5A is accumulated in the potential well 14 corresponding to the control electrodes (1) to (3), and as shown in FIG. When signal charges corresponding to the integration value A1 ′ are accumulated in the potential well 14 corresponding to the control electrodes (4) to (6) in the state, these integration values A0 ′ and A1 ′ are once taken out to the outside. Next, the signal charge corresponding to the integral value A2 ′ in the state of FIG. 5A is accumulated in the potential well 14 corresponding to the control electrodes (1) to (3), and is integrated in the state of FIG. 5B. Signal charges corresponding to the value A3 ′ are accumulated in the potential well 14 corresponding to the control electrodes (4) to (6), and these integrated values A2 ′ and A3 ′ are taken out to the outside. By repeating such an operation, signal charges corresponding to the integration values A0 ′, A1 ′, A2 ′, A3 ′ in the four sections can be obtained by two read operations, and the signal charges are used to change the signal charges. The phase difference ψ can be obtained.

In the control described above, in the period in which the area of the potential well 14 corresponding to one of the two photosensitive portions 1a forming one pixel is increased, the potential well 14 is used to hold the signal charge in the portion corresponding to the other. The area is reduced. In short, one of the two photosensitive parts 1a is mainly a generation period for generating charges, and the other is a holding period for mainly holding charges. Here, since the charge due to the light reception is generated even in the potential well 14 having a small holding area during the holding period, the charge integrating unit 1c holding the signal charges corresponding to the integrated values A0 'and A1' is integrated. A part of the signal charge corresponding to the values A2 ′ and A3 ′ is mixed, and the charge accumulating unit 1c holding the signal charge corresponding to the integrated values A2 ′ and A3 ′ corresponds to the integrated values A0 ′ and A1 ′. A part of the signal charge is mixed. In this way, 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 rate with respect to signal charges. Since the subtraction process ((A3′-A1 ′) and (A0′-A2 ′)) for obtaining the phase difference ψ is almost eliminated, the influence of the noise component is reduced when obtaining the phase difference ψ. Other configurations and operations are the same as those in the example shown in FIG.

In the example shown in FIG. 5, only the control voltage applied simultaneously to each of the three control electrodes (1) to (3) or (4) to (6) and one control electrode (2) or (5). Since the control voltage to be applied to is set to be substantially equal, the area of the potential well 14 changes, but the depths of both the large area potential well 14 and the small area potential well 14 are substantially equal. Yes.

Here, as shown in FIG. 6, the basic configuration is the same as the example shown in FIG. 5, but each of the three control electrodes (1) to (3) or (4) to (6) is simultaneously applied. The control voltage to be applied is set to be lower than the control voltage to be applied only to one control electrode (2) or (5), and the depth of the small area potential well 14 is set to that of the large area potential well 14. It is characterized in that it is set smaller than the depth. For example, if the voltage applied simultaneously to each of the three control electrodes (1) to (3) or (4) to (6) when forming the large area potential well 14 is 7V, the small area potential well When forming 14, the voltage applied only to one control electrode (2) or (5) is set to 3V or the like. In this way, by making the potential well 14 that mainly generates charges (electrons e) deeper than the potential well 14 that holds charges, the control electrode (1) (3) or (3) or ( 4) The charge generated at the portion corresponding to (6) is likely to flow into the deeper potential well 14, and as a result, the noise component flowing into the potential well 14 holding the charge is reduced as compared with the example shown in FIG. can do. Other configurations and operations are the same as those of the example shown in FIG.

As shown in FIG. 7 , in addition to the configuration shown in FIG. 6, the center of the three control electrodes (1) to (3) or (4) to (6) corresponding to each photosensitive portion 1a. The light shielding film 15 may be overlaid on the control electrode (2) or (5) . That is, almost no electric charge (electrons e) is generated in the portion covered with the light shielding film 15 in the photosensitive portion 1a, and therefore, almost no electric charge is generated in the photosensitive portion 1a in the portion corresponding to the small-area potential well 14 for holding the electric charge. The possibility that a charge that becomes a noise component is mixed while the signal charge is not generated can be greatly reduced. Further, here, at the portion corresponding to the large-area potential well 14 generating the charge, the central control electrode (3) of the three control electrodes (1) to (3) or (4) to (6) is provided. The voltage applied to 2) or (5) is set higher than the voltage applied to the control electrodes (1), (3), (4), and (6) on both sides. By making the voltage applied to the control electrodes (1) to (6) in such a relationship, the voltage generated in the portion corresponding to the control electrodes (1), (3), (4), and (6) in the photosensitive portion 1a. The electric charge flows into the portion corresponding to the control electrodes (2) and (5) and is accumulated.

By the way, in the example shown in FIG. 6, the potential well 14 formed in the part corresponding to the control electrodes (1) to (3) or (4) to (6) is constant during the generation period in which charges are generated. Here , as shown in FIG. 7, the potential well 14 formed in the generation period in which charges are generated here is the control electrode (1) (3) or (4) ( The part corresponding to 6) has a shallower step than the part corresponding to the control electrode (2) or (5).

Therefore, in the example shown in FIG. 6, if the state in which charges are generated (generation period) and the state in which charges are held (holding period) are switched in a short time of several ns or less, the generation period in which charges are generated A portion of the charge generated at the portion corresponding to the control electrode (1), (3), (4), or (6) in FIG. 5 corresponds to the control electrode (2) or (5) in the holding period for holding the charge. There is a risk of being left behind without moving to. As a result, the remaining charge flows into the potential well 14 formed corresponding to the adjacent photosensitive portion 1a, and the signal charge may be mixed between the adjacent charge accumulation portions 1c (potential well 14). . That is, the noise component contained in the signal charge increases.

On the other hand, by controlling so that the stepped potential well 14 is formed as in the example shown in FIG. 7, at the portion corresponding to the control electrode (1) (3) or (4) (6). The generated electric charges (electrons e) move to a portion corresponding to the control electrode (2) or (5) simultaneously with the generation. That is, even when the generation period for generating the charge and the holding period for holding the charge are switched in a short time of several ns or less, the charge accumulation unit 1c (potential that is formed corresponding to the adjacent photosensitive unit 1a. The possibility of mixing signal charges between the wells 14) is reduced. A technique for forming the potential well 14 in a stepped manner can be employed regardless of the presence or absence of the light shielding film 15. Other configurations and operations are the same as those of the example shown in FIG.

In the example shown in FIGS. 5 to 7, three control electrodes 13 are associated with each photosensitive portion 1a. However, four or more control electrodes 13 may be provided. Furthermore, although the number of control electrodes 13 to which the control voltage is applied is switched to two stages of one and three for the control electrodes 13 in a group, it is possible to switch to three or more stages. Further, a configuration is adopted in which local signals having opposite phases to each other are provided to the sensitivity control unit 1b of the different photosensitive units 1a. For example, local signals having different phases by 90 degrees are applied to four different photosensitive units 1a. If given, the integrated values A0 ′, A1 ′, A2 ′, A3 ′ of four sections can be obtained simultaneously.

Incidentally, the example shown in FIGS. 5 to 7 adopts the configuration in which the local oscillation signal is given to the sensitivity control unit 1b as in the example shown in FIG. On the other hand, a configuration in which signal charges corresponding to different phases synchronized with the modulation signal may be adopted. For example, when four photosensitive portions 1a are grouped, the charge accumulating portion 1c corresponding to each photosensitive portion 1a has received light intensity A0, A1, A2, A3 having different phases in synchronization with the period of the modulation signal. The signal charge corresponding to is integrated. In short, the signal charges of each phase are distributed and accumulated in the charge accumulating unit 1c corresponding to the plurality of photosensitive units 1a. If the plurality of signal charges accumulated in the plurality of charge accumulating sections 1c in this way are taken out collectively by the charge extracting section 1d, the received light intensity A0 is similar to the example shown in FIGS. , A1, A2, and A3, the phase difference ψ can be obtained based on the signal charges.

The image sensor 7 used in each of the configuration examples described above is assumed to be a two-dimensional array. However, the image sensor 7 may be a one-dimensional array . In the example shown in FIGS. Only one may be provided. Moreover, although the example which calculates | requires phase difference (psi) and calculates | requires distance was demonstrated as the evaluation part 3, the evaluation part 3 is not necessarily what calculates | requires distance, The structure which calculates | requires only phase difference (psi), integral value A0 ', A1', Other information about the space may be evaluated based on A2 ′ and A3 ′.

It provided with a plurality of control electrodes 13 to vary the area of the charge accumulation portion 1c in the configuration example described above above, but employs a configuration for changing the application pattern of the control voltage to the control electrode 13, photosensitive section The distribution of the impurity concentration of the semiconductor layer 11 in 1a is given according to the distance from the control electrode 13 along the light receiving surface, and the voltage applied to the control electrode 13 is also controlled to change the area of the charge accumulation portion 1c. It is possible.

It is principle explanatory drawing of a light receiving element . It is a block diagram which shows the structural example of the detection apparatus of spatial information . It is principle explanatory drawing which shows one operation example of the detection apparatus of spatial information . It is principle explanatory drawing which shows the other operation example of the detection apparatus of spatial information . It is operation | movement explanatory drawing which shows one operation example of a light receiving element . It is operation | movement explanatory drawing which shows the other operation example of a light receiving element . It is operation | movement explanatory drawing which shows another example of operation | movement of a light receiving element .

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Light receiving element 1a Photosensitive part 1b Sensitivity control part 1c Charge integration part 1d Charge extraction part 2 Light emission source 3 Evaluation part 4 Control circuit part 11 Semiconductor layer 12 Insulating film 13 Control electrode 14 Potential well

Claims (2)

A photosensitive portion that generates an amount of charge corresponding to the received light intensity, and a charge accumulation portion that accumulates at least a portion of the charges generated in the photosensitive portion by applying a control voltage to a control electrode provided in the photosensitive portion. And a charge extraction unit that takes out the charge accumulated in the charge accumulation unit as a light reception output, and controls the light reception sensitivity with respect to the impurity concentration of the semiconductor layer in the photosensitive unit along the light receiving surface. Charge distribution is given by giving a distribution according to the distance from the control electrode, and changing the control voltage magnitude to the control electrode so that the area of the charge accumulation part in the plane along the light receiving surface of the photosensitive part changes. Switching the area of the charge accumulation section between a generation period for increasing the area of the charge section and a holding period for holding charges generated in the generation period by reducing the area of the charge accumulation section Sensitivity control method of the light-receiving element characterized. Control of the photosensitive part that receives the light from the space irradiated with the light whose intensity is modulated by the modulation signal of the predetermined modulation frequency and generates an amount of charge corresponding to the received light intensity, and the control electrode provided in the photosensitive part A charge accumulating unit that accumulates at least a part of charges generated in the photosensitive unit by applying a voltage, a charge extraction unit that extracts the charges accumulated in the charge accumulating unit as a light receiving output, and a light receiving unit that receives the light. A control circuit unit that outputs a control voltage whose magnitude changes with time so that the area of the charge accumulation unit in the plane along the surface changes with time, and the charge that has been taken out by the charge extraction unit And an evaluation unit that evaluates information about the space using the sensor, the semiconductor layer in the photosensitive unit is provided with a distribution according to the distance from the control electrode along the light receiving surface, and the control circuit unit is a photosensitive unit Light reception Changing the magnitude of the control voltage to the control electrode so that the area of the charge accumulation portion varies in accordance with a plane, the smaller the generation period to increase the area of the charge accumulation section, the area of the charge accumulation portion detection equipment between, the spatial information with intensity modulated light, characterized in that for switching the magnitude of the area of the charge accumulation portion of the holding period for holding the generated electric charges in the generation period by.

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