JPH0140287B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an accumulation time control method for a photoelectric conversion device that uses a charge storage type photoelectric element array to convert an optical image projected thereon into an electrical signal.

This type of accumulation time control method was published in Japanese Patent Application Laid-open No. 53-
It has already been disclosed in Publication No. 15131. In this publication, the output signal of a photoelectric conversion element is generally proportional to the amount of incident light, but due to the operating characteristics of the element, the output is not proportional to the amount of incident light and saturates above a certain range of light amount, and below a certain amount of light, the output signal is Cannot be obtained due to dark current etc. Therefore, in devices using photoelectric conversion elements, the range in which the element operates with linear characteristics (dynamic range) is generally limited, and the amount of light received by the element must be adjusted to stay within this range. be. Focusing on this point, a method has been described in which the accumulation time is controlled by detecting the peak value of the photoelectric output that occurs over time. Also disclosed is a case where the storage time is controlled by obtaining brightness information from another photometric circuit instead of the peak value.

However, for specific image processing purposes, it is not necessarily optimal to control the accumulation time using brightness information (peak value or average value) on the photoelectric conversion element. In other words, when controlling the storage time using brightness information, there will be a significant difference in the amount of information depending on whether the contrast of the subject is high or low, and by using such an incorrect amount of information, the responsiveness of the control will be reduced. There are problems in that this leads to a decrease in performance and also causes erroneous control.

Therefore, in order to solve such problems, the applicant has proposed that when the contrast is high, sufficient information for image processing can be obtained in a shorter accumulation time, so the accumulation time can be shortened to improve responsiveness. It is possible to optimize the detection to improve the image quality, and even if the response is poor in cases of low contrast, it is possible to detect such objects by increasing the storage time. We focused on the fact that optimization is possible.

From the above points of view, the applicant has decided to control the normal charge accumulation time using brightness information (peak value or average value).
Instead, the charge accumulation time is usually controlled according to the amount of contrast, and the accumulation time is limited based on brightness information so that the accumulation time does not become unnecessarily prolonged only for subjects with extremely low contrast. The purpose of this invention is to prevent the saturation of charge accumulation in a photoelectric element array, and to provide a balanced and efficient photoelectric conversion device with wide responsiveness and a wide detection range.

Embodiments illustrating the present invention will be described below. The illustrated example is a displacement detection photoelectric conversion device that extracts a specific spatial frequency component from an optical image projected onto a photoelectric element array and detects the displacement of the optical image in the array arrangement direction. This is an example in which the present invention is applied to.

In FIG. 1, a photodiode array 10
0 is provided, and the photoelectric output of each photodiode making up the array represents the illuminance distribution of the light image on the array. The charge accumulation time of each photodiode is the same, and this accumulation time is controlled based on the pulse output of the oscillation block 200. The photoelectric output of the array is amplified by amplifier 300.

The amplified photoelectric output is sent to a specific spatial frequency extraction circuit 400, which extracts a specific spatial frequency component having a spatial period of, for example, mm order or 0.1 mm order from the optical image. The AC output of this circuit is
The phase represents the relative positional relationship between the specific spatial frequency component in the optical image and the array. When the optical image is displaced in the arrangement direction of the array, this phase also changes accordingly, and by measuring this, the displacement of the optical image can be detected. However, if the same processing is applied to an optical image that contains many specific spatial frequency components or an optical image that contains only a small amount, the amplitude of the AC output of this circuit will depend on the amount of that component. If there are few components, the amplitude will be small. In this way, the extraction circuit 400
If the amplitude of the output changes greatly depending on various optical images, the phase measurement accuracy will deteriorate. Therefore, regardless of the amount of this specific spatial frequency component, in this embodiment, feedback is applied so that the amplitude is constant as described below.

A rectifying and smoothing circuit 500 is provided in the return path to rectify and smooth the output of the extraction circuit 400. The output of the rectifying and smoothing circuit 500 is sent to an error detector 600, which detects the difference between the output voltage of the rectifying and smoothing circuit 500 and the reference voltage of the reference voltage source 600a. The detection output of error detector 600 is given to V-F converter 700, which generates an output signal with a frequency corresponding to the error voltage. The output signal of V-F converter 700 is applied to oscillation block 200, which controls the storage time of each photodiode in array 100 based on the output frequency of V-F converter 700.

Rectifier smoothing circuit 500, error detector 600, V-
The feedback circuit consisting of the F converter 700 applies feedback so that the amplitude of the AC output of the spatial frequency extraction circuit 400 is approximately constant.

Suppose that the irradiated light image changes from the state where this device is balanced and the above amplitude is a constant value, and an extracted spatial frequency component or a smaller light image is projected.
The difference between the photoelectric element outputs becomes smaller, and the amplitude of the AC output of the spatial frequency extraction circuit 400 becomes smaller than the above-mentioned constant value. Therefore, the DC output of the rectifying and smoothing circuit 500 also decreases and becomes smaller than the reference voltage, and the error detector 600 detects this difference. The output frequency of V-F converter 700 then decreases, and oscillation block 200 increases the storage time of the photodiodes of array 100 until the amplitude of the output of spatial frequency extraction circuit 400 reaches the constant value. When this constant value is reached, the output of the rectifying and smoothing circuit 500 matches the reference voltage, and the output of the error detector 600 is stabilized at this equilibrium point, and this state is maintained as long as the optical image does not change. Next, from this state, when an optical image containing a large number of extracted spatial frequencies is projected onto the array, the accumulation time is shortened due to the completely opposite effect described above, and the amplitude of the spatial frequency extraction circuit 400 remains at a constant value. controlled so that

In this way, whether there are many or few spatial frequency components to be extracted in the optical image, the amplitude of the output of the spatial frequency extraction circuit 400 can be made constant by controlling the accumulation time.

However, like the image of a white board, although it is bright, it contains almost no extracted spatial frequency components, and no matter how long the charge accumulation time of the photoelectric element is extended, the photoelectric output is saturated, so that the amplitude of the output of the spatial frequency extraction circuit 400 does not reach the desired value. When an image that has no value is projected onto the array, the output amplitude of the spatial frequency extraction circuit 400 is extremely small, so the output of the rectification and smoothing circuit 500 is also much smaller than the output of the reference voltage source 600a, and V-F The output frequency of converter 700 decreases. This increases the charge accumulation time and
The output of each photoelectric element also increases. Frequency fixed circuit 75
0 detects that the photoelectric output itself or the photoelectric output amplified by the amplifier 300 reaches a certain predetermined value, and as a result, it generates an output equal to the reference voltage of the reference voltage source 600a, and the output of the rectifying and smoothing circuit 500. The output frequency of a V-F converter 700 is fixed to the frequency at the time of detection regardless of the output. in this case,
Since the image is bright, the frequency fixing circuit 750 operates before the output frequency of the V-F converter 700 decreases much, thereby preventing the frequency from further decreasing unnecessarily.

Furthermore, even when a dark image containing almost no extracted spatial frequency components is projected onto the array, such as an image of a blackboard, the frequency fixing circuit 750 similarly causes the V-F converter to stop oscillating. It is not fixed at a certain frequency. Of course, since this optical image is dark, the photoelectric output or its amplified output reaches the predetermined value of the frequency fixing circuit 750 when the charge accumulation time becomes sufficiently longer than the previous example, so the fixed frequency at this time is Depending on the brightness of the image, it is lower than the previous one.

Note that even if the image becomes even darker and the output frequency is lowered to the extent that the V-F converter stops oscillating, the photoelectric output or its amplified output may not reach the predetermined value of the frequency fixing circuit 750. So,
It is desirable that the output characteristics of the V-F converter be saturated below a certain frequency.

Of course, even if the V-F converter is temporarily locked by the frequency fixing circuit 750, the next time an optical image containing sufficient extracted spatial frequency components is projected onto the array, the frequency fixing circuit 750 will lock the V-F converter. 7
50 becomes inactive or the output of the rectifying and smoothing circuit 500 increases, the V-F converter is unlocked, and the charge accumulation time is controlled so that the output amplitude of the spatial frequency extraction circuit 400 becomes a predetermined value. The level detection means of the present invention corresponds to the frequency fixing circuit 750 in this embodiment. Further, the contrast detection means corresponds to the extraction circuit 400 in this embodiment. Further, the control means corresponds to the detection circuit 600, the V-F converter 700, and the control circuit 200.

A specific circuit diagram of the photoelectric conversion device shown in FIG. 1 is shown in FIG. In FIG. 2, photodiodes D ₁ -D ₄ constitute an array 100 and series switching elements S ₁ -S ₄ constitute a switch group 110. In FIG. Each switch S ₁ to _{S 4} of the switch group 110 is sequentially turned on by gate pulses Ga ₁ to _{Ga 4} in FIG. 3(a),
Input signal voltages e ₁ to _{e 4} due to the accumulated charges of photodiodes D ₁ to _{D 4} are sequentially input to the sample and hold circuit 300b in the amplifier 300 at a cycle period T ₁ and a predetermined time lag t ₁ . The FET switch 300a is turned on by the Gb gate pulse shown in FIG. 3(b) just before the inputs _e1 to _e4 from the photodiodes _D1 to _D4 enter the sample and hold circuit 300b, and resets the sample and hold circuit 300b. Then, e ₁ to _{e 4} are sampled and held in sequence and output. Since the FET switch 300f is only turned on by the gate pulse Gc ₁ in FIG. 3(c) immediately after the input e ₁ from the photodiode D ₁ is sampled and held, the value of the input e ₁ is stored in the capacitor 300c. is accumulated over a cycle period _T1 . Therefore, the output V of the amplifier circuit 300 is V
=G ₁・G ₂・Vr−(1+G ₁ )G ₂・V ₂ +(1+G ₂ )
V ₁ (However, G ₁ and G ₂ are the gains of the amplifiers 300d and 300e, respectively, R ₂ /R ₁ and R ₄ /R ₃ , V ₁ is the output voltage of the sample and hold circuit 300b, and V ₂ is the gain of the capacitor 300c. The accumulated voltage is e ₁ ), but if the resistance value is selected so that G ₁・ G ₂ = R ₂ R ₄ / R ₁ R ₃ = 1, then V = Vr + (1 + G ₂ ) (V ₁ −e ₁ ) Therefore, when the input signals e ₁ to _{e 4} from the photodiode array 100 are sequentially input, the outputs V ₁ to _{V 4} of the amplifier circuit are as follows.

V ₁ = Vr V ₂ = Vr + (1 + G ₂ ) (e ₂ − e ₁ ) V ₃ = Vr + (1 + G ₂ ) (e ₃ − e ₁ ) V ₄ = Vr + (1 + G ₂ ) (e ₄ − e ₁ ) V ₁ to _{V 4} are the gate pulses Dc ₁ to V 4 in FIG. 3(c).
Gc ₄ is applied to the FET switches S ₁₀ to _{S 40} of the extraction circuit 400, so that it is sequentially accumulated in the capacitors C ₁₀ to _{C 40} . In this way, the amplifier 300 stores a constant value Vr in the capacitor C ₁₀ regardless of the output e ₁ of the photodiode D ₁ , and stores the output e of the photodiodes D ₂ to _{D 4} in the capacitors C ₂₀ to C ₃₀ , respectively. The value obtained by subtracting the output e ₁ from each _{of 2} ~ e ₄ (e ₂ − e ₁ )
The amplified values of (e ₃ −e ₁ ) and (e ₄ −e ₁ ) and the addition of a constant value Vr are stored. Since the difference between the outputs of the photodiodes is required to extract the desired spatial frequency component, the amplifier 300 that amplifies only this difference is extremely preferable, as described above. In other words, each difference of each photodiode D ₁ to _{D 4} is calculated, and in the case of a high-contrast optical image (large difference between brightness and darkness), these differences or these differences are synthesized in various forms and output. has a high output, so this differential or composite output amplifies information related to contrast. The accumulated voltages V ₁ to V ₄ are generated by gate pulse generators as gate pulses Gd 1 to _{Gd 4 delayed} by T ₂ /4 hours with a period T ₂ (T ₂ < T ₁ ) shown in FIG. 80
0 is applied to FET switches S ₁₀₀ to _{S 400} , added and converted into a voltage in a current addition and current-voltage conversion circuit 400a, and a frequency component of 1/T ₂ is extracted by a bandpass filter 400b. Ru.

The output of the extraction circuit 400 obtained in this way is an optical image with a spatial frequency of 1/d lines/mm, where the width of the image sensor ₁ , that is, the length in the array direction of the four photodiodes D1 to _D4 is dmm. The extracted output amplitude indicates the magnitude of the optical image component, and the phase indicates the relative position of the optical image and the image sensor.

The output of the extraction circuit 400 is input to a phase difference measuring device 900. As mentioned above _, the phase of the AC output of the extraction circuit ₄₀₀ represents the relative positional relationship between the optical image and the array. The displacement of the optical image is detected by measuring the phase difference between the signal _{No. 2} and the output signal of the extraction circuit 400 using the phase difference measuring device 900.

On the other hand, the output of the extraction circuit 400 is fed back for frequency control and input to the rectification and smoothing circuit 500.
Since the circuit configuration of the embodiment of the rectifying and smoothing circuit 500 is well known, the explanation thereof will be omitted.

The frequency fixing circuit 750 consists of a diode 750a and a Tsuzner diode 750b. The input is the output of an OP amplifier 300d that amplifies the photoelectric output of the photodiode _D1 , and the output is the error detector 6.
00 input.

Error detector 600 is an integrator consisting of an OP amplifier and its feedback capacitor 600c. The difference voltage between the output from the rectifying and smoothing circuit 500 and the reference voltage Vc is integrated and output. The integrated amount of this detected differential voltage controls the V-F converter 700 to vary the frequency.

The V-F converter 700 generates an output signal of the following frequency depending on the input voltage. That is, f=Ae ^c 〓 Here, f: Output frequency υ: Input voltage, i.e., the output of the error detector 600 c: Constant The exponential characteristic of the output frequency with respect to the input voltage is expressed at the input section of the V-F converter 700. The diode 700c converts the input voltage into a charging current that is an exponential function of the input voltage, thereby charging the integrating capacitor 7.
Charging 00b. Other configurations are known V-
It is similar to the F converter.

Regarding the operation of the V-F converter 700, a current corresponding to the output voltage of the error detector 600 flows through the integrating capacitor 700b and the plurality of diodes 70.
Flow through 0c charges 700b. Therefore,
The output voltage of this OP amplifier 700a gradually increases. This voltage is the reference voltage of the comparator circuit 700d.
When Vth is exceeded, the output capacitor 700e is turned on and supplies an output pulse to the oscillation block 200. By turning on the output transistor 700e, the current supply circuit 700f operates, and the feedback capacitor 7
Instantly reverse charge or discharge 00b. As a result, the output voltage of 700a instantly returns to its initial state, starts charging the above-described output transistor 700e again, and repeats the above-described operation.

Next, the operation of the device shown in Fig. 2 will be explained.
For example, when an optical image with fewer specific spatial frequency components to be extracted is projected onto the array 100 while this device is operating normally, the rectifying and smoothing circuit 50
The output of 0 is the reference voltage of the error detector 600 +VC
Since it becomes smaller, the negative output -V of the error detector 600 increases, ie, V becomes smaller. Therefore V-
The output frequency f of the F converter 700 becomes smaller, and the oscillation block 200 has a scanning period of S ₁ to S ₄ .
T ₁ , that is, the accumulation period T ₁ of D ₁ to _{D 4} , is
Increase the output of 00 until it equals +VC.
Of course, at this time, the reset capacitor 350 and
The conduction period of S ₁₀ to S ₄₀ has been increased as well.

On the other hand, for an optical image in which more spatial frequency components are extracted than before, the output frequency increases by the completely opposite effect to the above, bringing the output amplitude of the spatial frequency extraction circuit 400 to a predetermined value.

On the other hand, when an optical image with very few extracted spatial frequencies is projected, the output of the OP amplifier 300d exceeds the sum of the Zener voltage of the Zener diode 750b, the conduction voltage of the diode 750a, and the reference voltage +Vc of the reference voltage source 600a. , the frequency fixing circuit 750 operates to prevent the V-F converter 700 from lowering the frequency at this point in time.

FIG. 5 shows an embodiment in which a part of the apparatus shown in FIG. 2 is modified.

In the embodiment shown in FIG. 2, the frequency fixing circuit 7
50 detects the photoelectric output of only one photodiode _D1 constituting the photodiode array. However, this photodiode D ₁
In the case of a special optical image in which the intensity of light incident on the photodiode is significantly different from the intensity of light incident on the remaining photodiodes, the frequency fixing circuit 750 of the first embodiment shown in FIG. 2 does not operate correctly. There is a fear.

The second embodiment shown in FIG. 5 is an improvement on this.

The amplifier circuit 300 generates an output obtained by amplifying the photoelectric outputs as they are, rather than the difference between the respective photoelectric outputs. Therefore, the amplified photoelectric output of each photodiode is held in the hold circuit via the switching elements _S10 to _S40 .

The output terminals of each hold circuit are commonly connected through the same resistor R. As a result, the frequency fixing circuit 750 receives the total output of all photodiodes of the photoarray.

In this embodiment, the frequency fixing circuit 7
Since 50 controls the V-F converter based on the sum of the photoelectric outputs of all photodiodes, it can operate correctly even for extremely special optical images as described above. Of course, even if the frequency fixing circuit 750 is based on the average photoelectric output of all photodiodes,
Further, the same effect can be obtained by controlling the V-F converter 700 based on the photoelectric outputs of a plurality of appropriate photodiodes in the photodiode array. As described above, according to the present invention, by detecting information regarding the contrast of an optical image and controlling the charge accumulation time, the charge accumulation time can be shortened for a high contrast optical image, thereby improving the responsiveness of the photoelectric conversion device. Furthermore, since the charge accumulation time is set to a predetermined time by detecting that the value related to the output of the photoelectric element array exceeds a predetermined level, the charge accumulation time is unnecessarily long even for an optical image with extremely low contrast. This also prevents false detection.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a photoelectric conversion device of the present invention.
2 is a circuit diagram showing a specific example of the device shown in FIG. 1, FIGS. 3 and 4 are waveform diagrams of pulses generated in each part of the circuit shown in FIG. 2, and FIG. FIG. 3 is a circuit diagram of another embodiment in which a part of the embodiment is modified. [Explanation of symbols of main parts], 100...Photoelectric element array, 600...Detection circuit, 700...V-
F converter, 750... frequency fixed circuit.

Claims (1)

[Scope of Claims] 1. A charge storage type photoelectric element array comprising charge storage type photoelectric conversion elements arranged to generate a photoelectric output according to a light image projected thereon; and an output of the charge storage type photoelectric element array. level detection means for detecting that a value of the optical image exceeds a predetermined level and outputting a detection signal; and contrast detection means for detecting information regarding the contrast of the optical image based on the output of the charge storage type photoelectric element array. When the detection signal of the detection means is not output, the charge accumulation time of the photoelectric element array is controlled based on the information regarding the contrast of the contrast detection means, and when the detection signal of the detection means is output, A photoelectric conversion device using a charge accumulation type photoelectric element array, comprising: a control means for setting and controlling a charge accumulation time of the photoelectric element array to a predetermined time. 2. The method according to claim 1, wherein the level detection means detects that the photoelectric output of one of the charge storage type photoelectric elements in the charge storage type photoelectric element array exceeds a predetermined level. A photoelectric conversion device using a charge storage type photoelectric element array. 3. The charge storage type photoelectric device according to claim 1, wherein the contrast detection means detects information related to an added output obtained by adding difference outputs of photoelectric outputs of the different charge storage type photoelectric elements. A photoelectric conversion device using an element array. 4. Using the charge storage type photoelectric element array according to claim 1, wherein the contrast detection means detects information related to the differential output of photoelectric outputs of the different charge storage type photoelectric elements. Photoelectric conversion device.