JP2895999B2 - Image sensor circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image sensor circuit for detecting an image of an object such as an object by focusing an optical instrument such as an autofocus camera on the object. Related to what can be detected.

[0002]

2. Description of the Related Art As is well known, methods for focusing an optical instrument on an object are roughly classified into an external light triangulation method using light passing outside the imaging lens and a TTL using light passing through the imaging lens.
In each case, at least one pair of image sensors is incorporated in the optical instrument, and the images of the object are spatially separated from each other by optical means or formed on each image sensor through different optical paths. Based on the relative positional deviation of the images received by both image sensors and the relationship between the positions, the distance to the target and the deviation from the focal point of the imaging lens are electrically detected, and then the position of the imaging lens is detected. The optical instrument is brought into a focused state by controlling so as to adjust the distance or eliminate the defocus. The present invention relates to an image sensor incorporated therein for focusing an optical instrument on a target by such an external light triangulation method or TTL method, and an image sensor circuit including a processing circuit for a light detection signal thereof.

In order to accurately detect the distance to an object serving as the basis for focusing and the defocus of the imaging lens, it is necessary to first increase the image detection accuracy of each image sensor. Since it varies within a very wide range of 10: ^6, it is common to use a charge storage type for a photosensor constituting an image sensor. At present, it is possible to detect from a very weak light to a very strong light in several tens to several hundreds of stages by using such an optical sensor.

After an image of an object is detected with high accuracy by an image sensor using such an optical sensor, it is necessary to accurately detect the distance to the object and defocus based on the detected image. Since it is inconvenient to detect the relative positional shift or positional relationship between the images received by a pair of image sensors if the analog light detection signal is used as it is, recently, a circuit having an AD conversion function has been combined with the image sensor, and In many cases, the detection signal of the optical sensor is digitized into video data of, for example, 4 to 8 bits. This image sensor circuit is usually incorporated into one integrated circuit device together with related circuits for handling the video data.

[0005]

By improving the image detection accuracy of the image sensor as described above, converting the detection signal into image data, and performing data processing suitable for the external light triangulation system or the TTL system. In almost all cases, the optical instrument can be precisely focused on the object, except that if the object is in a very bright backlit background, the effective accuracy of the image sensor that detects the image will be significantly reduced and the optical instrument There is a problem that focusing becomes difficult. The reason will be briefly described below with reference to FIG.

An object 1 such as a person in FIG. 3 (a) is exposed to a bright backlight BL indicated by an arrow in the figure, and the optical instrument is located at the center of the visual field of the image sensor 10 indicated by a thin line in the figure. Assume that one is captured. FIG. 3B shows the direction x in which the light sensors of the light received by the image sensor 10 are lined up at this time.
Is shown on a logarithmic scale, and the light intensity I is very high at both ends in the x direction corresponding to the left and right backgrounds of the object 1 as shown in FIG. In the department it will be much lower. For this reason, although the image sensor 10 has the capability of distinguishing and detecting the light intensity I within a wide range indicated by R in the drawing from dark light to bright light as described above, the image of the subject 1 is important. For detection, only the detection performance within the very narrow effective range Re shown in the figure can be used.

That is, if there is a large difference between the brightness of the back light BL of the object 1 and its background, no matter how high the image detection accuracy of the image sensor is, the performance of the angle is not utilized, and each light showing the image of the object 1 is not utilized. The contents of the video data by the sensors are all the same, at the very least, the content of the least significant 1 bit changes, and the lack of information in the video content makes it very uncertain or impossible to focus the optical instrument. Would.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an image sensor circuit with improved image detection accuracy for such objects so that the above problems can be solved and the optical instrument can be accurately focused even on objects in a bright backlit background. To improve.

[0009]

SUMMARY OF THE INVENTION According to the present invention, there is provided, in accordance with the present invention, a light for converting the intensity of light received by a charge storage type photosensor in an image sensor from an object into a time signal representing the charge storage time. A sensor circuit, a clock pulse generating circuit for generating a clock pulse for counting the charge storage time represented by the time signal, and a charge pulse counting the charge storage time represented by each time signal to convert the time signal into digital video data. Except for the image data circuit that performs image processing and the optical sensor that receives backlight in the image sensor, the time signal is received from the optical sensor circuit corresponding to the optical sensor that is arranged in the range that receives the target image. A count command circuit for issuing a count command in response to a time signal indicating the accumulation time is provided for the image sensor circuit, and the video data circuit is closed based on the count command. It is achieved by starting the operation of converting a time signal to the video data by Kkuparusu.

Note that the clock pulse generation circuit changes in time and particularly increases in response to the time signal indicating the charge accumulation time of the light sensor from each light sensor circuit as described above. The configuration in which the clock pulse is generated is advantageous in that the optical sensor can easily detect a wide range of light intensity from weak light to strong light.

The range in which the time signal is to be given to the counting command circuit in the above configuration is most suitably a photosensor circuit corresponding to the photosensors arranged in the center of the image sensor. The number of light sensors in the image sensor should be set to 50 to 90% of the total number of light sensors in the image sensor, especially to 70 to 80% in order to avoid the adverse effects of backlight and make it easier to detect the target image. Is desirable. In some cases, it is advantageous to provide a time signal to the counting command circuit from a photosensor circuit corresponding to the photosensor in a range excluding one end of the image sensor. Also, if necessary, the range in which the time signal should be given to the counting command circuit can be adjusted, or the range in which the shortest charge accumulation time should be detected in order to determine the generation timing of the counting command from the time signal received by it can be adjusted. It can be.

In order to start the operation of converting the time signal into the video data by the video data circuit in accordance with the counting command,
Thereby, the clock pulse may be validated, or the clock pulse generating circuit may be activated thereby. Note that the image sensor and the image sensor circuit of the present invention require at least one pair in order to focus an optical instrument.
Three pairs of image sensor circuits are incorporated into the optical instrument.

[0013]

According to the present invention, first, a time signal representing the charge accumulation time of the light sensor is generated in the light sensor circuit, and the time signal is converted into the image data by dividing the charge accumulation time in a video data circuit receiving the clock signal by a clock pulse. After receiving the image of the target, except for the optical sensor that receives backlight.
The count command circuit detects the shortest charge accumulation time from only the time signal of the optical sensor circuit within the range to be generated and generates a counting command, and the video data circuit clocks the charge accumulation time represented by each time signal based on the counting command. By starting the operation of converting to video data by pulsing, the time signal is converted to video data most suitable for target video detection without being affected by bright backlight, improving the accuracy of target video detection It is to let.

In order to facilitate understanding of the above operation of the present invention, consider a case where the counting command circuit detects the shortest charge storage time of all the photosensors of the image sensor and generates a counting command. Of course, since the counting command is generated at the timing corresponding to the shortest bright backlight, the video data circuit immediately starts the operation of ticking the charge accumulation time represented by each time signal with a clock pulse, and the converted video data has An upper bit portion corresponding to a bright backlight is included. On the other hand, in the present invention, since the counting command is generated at the timing of the shortest charge accumulation time in the time signal excluding the range of the backlight, the video data converted from the time signal uses the above-described upper bit portion corresponding to the backlight. The present invention can improve the accuracy of detecting an image of an object, since it is not redundantly included, and almost all of the bits contain useful information for detecting an image of the object.

When the conversion into the video data is started by the counting command generated at the timing corresponding to the shortest charge accumulation time in the time signal of the optical sensor circuit excluding the range where the backlight enters, a bright backlight is generated. Since the charge accumulation time of the time signal of the optical sensor circuit in the entering range has already ended at this time, all the image data against the backlight have the same value, but there is no hindrance to the detection of the target image. Also, in the normal case where the background is not backlit, the time signal including the background is converted to video data in a form suitable for video detection in the other range, so the detection accuracy of the background will not decrease at all. However, there is no problem in detecting the target image.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows an embodiment of an image sensor circuit according to the present invention. FIG. 1 (a) is an entire circuit diagram including an image sensor 10, and FIG. 1 (b) is a partial circuit diagram of an optical sensor circuit 20 therein. . 2A and 2B show waveforms of main signals related thereto, FIG. 2A shows an operation start reset pulse RP, FIG. 2B shows an internal potential v of the optical sensor circuit 20, and FIG. Time signal TS
FIG. 4D is a waveform diagram of the clock pulse CP. As described above, at least one pair of the image sensor circuits shown in FIG. 1 is provided for focusing an optical instrument, and the image data IDs obtained by the image sensor circuits are processed according to the above-described external light triangulation or TTL method. Together with the associated circuitry, for example, in a common integrated circuit device and integrated into the optics.

The image sensor shown in the upper part of FIG.
Reference numeral 10 denotes n, for example, 64, charge accumulation type optical sensors 11. In this embodiment, the optical sensor 11 is a photodiode to which a common power supply voltage V is applied in the reverse bias direction. The optical sensor circuit 20 indicated by a block below it
Are provided for each of the optical sensors 11, and in the figure, numerals 1 to n are given as their numbers for the convenience of the description below. An example of the circuit configuration of the optical sensor circuit 20 is shown in FIG. 1B together with the optical sensor 11. First, the circuit configuration and the operation of generating a time signal TS indicating the charge accumulation time of the optical sensor 11 will be described. This will be described with reference to FIG.

In this embodiment, since the junction capacitance 12 of the photodiode for the optical sensor 11 is used as a capacitor for storing electric charges, the optical sensor circuit 20 is connected in series with the optical sensor 11 as shown in FIG. It has a very simple configuration comprising a reset transistor 21 and a comparator 22 receiving a potential v at an interconnection point between the two. In order for the optical sensor 11 to start the light detection operation, a reset pulse RP shown in FIG. 2A is applied to the reset transistor 21 to turn it on within a short time, and the junction capacitor 12 is used to initialize the power supply voltage V and the operating point. While charging to a voltage difference from the voltage V0, the potential v applied to the comparator 22 is initialized to the voltage V0 as shown in FIG.

Thereafter, the junction capacitance is determined by the photocurrent of the optical sensor 11.
12 is discharged, and in response to this, the potential v rises with the lapse of time from the initial value V0 at an inclination corresponding to the intensity of light received by the optical sensor 11 as shown in FIG. 2 (b).
The comparator 22 compares this potential v received at one input with a reference voltage Vr received at the other input, and its output, the time signal TS in FIG.
At the same time, in the illustrated example, the voltage is reset to a low state, but rises to a high level when the voltage v reaches the reference voltage Vr. The time during which the time signal TS is in the low state after the reset pulse RP has disappeared represents the slope of the rise of the voltage v, that is, the light intensity received by the optical sensor 11, which is the charge accumulation time of the optical sensor 11. Ts. The charge storage time Ts is substantially inversely proportional to the light intensity.

The clock pulse generating circuit 30 at the lower right of FIG. 1A generates a clock pulse CP for digitizing the charge accumulation time Ts and digitizing the video data ID. In the example shown in FIG. Upon receiving the reset pulse RP at T, the operation starts simultaneously with its disappearance. In this embodiment, a clock pulse CP whose period increases with time as shown in the figure is generated. This period change is adjusted in accordance with the point that the charge accumulation time Ts is substantially inversely proportional to the light intensity received by the optical sensor 11 as described above, and thus, the light intensity that can vary within a wide range of several orders of magnitude. Can be represented by a relatively small number of bits of video data ID.

A video data circuit 40 enclosed by a dashed line in FIG. 1A converts the charge storage time Ts represented by the time signal TS output from the n photosensor circuits 20 into video data ID. In this embodiment, n latches 41 each receiving a time signal TS, a counter 43 connected to them via a bus 42, a transmission gate 44 for controlling the supply of a clock pulse CP thereto, latch
Output command circuit 45 that issues output command Si to 41 sequentially, and latch
An output bus 46 for video data ID connected to 41 is included in this.

In this embodiment, the latch 41 responds when the time signal TS rises from low to high at the end of the charge accumulation time Ts in FIG. 2C, and the counter 43 counts the clock pulse CP. Is read from the bus 42 and stored as a video data ID. The output command circuit 45 is, for example, a decoder circuit, and latches an output command Si (i = 1-n) according to an address AD that specifies the latch 41.
The video data ID is sequentially provided to the output 41 and the video data ID is output via the output bus 46.

In this embodiment, the counting command circuit 50 is constituted by a single OR gate, and receives the time signal TS only from the optical sensor circuits 20 corresponding to the optical sensors 11 arranged in the central area of the image sensor 10. That is, in this embodiment, the time signal TS generated by the optical sensor circuit 20 corresponding to each of the p optical sensors 11 within the range in which the backlight of the left and right sides in the image sensor 10 may enter is determined by the counting command circuit 50. Excluded from input to. As described above, when the total number of the optical sensors 11 in the image sensor 10 is 64, the exclusion number p is, for example, 8
Therefore, n-2p = 48 time signals TS are supplied to the count command circuit 50. In this example, the count command CS output from the count command circuit 50 is given to the transmission gate 44 in the video data circuit 40 to validate the clock pulse CP. Incidentally, the number of the optical sensor circuits 20 to 11 to which the time instruction TS is to be given to the counting instruction circuit 50 is set to 50 to 90% of the total number depending on the case, and from experience, it is set within the range of 70 to 80%. This is desirable in order to increase the amount of information on the target video as much as possible while eliminating the effects of backlight.

In the image sensor circuit of this embodiment configured as described above, the light detection operation is started by the image sensor 10 and the light sensor circuit 20 by the reset pulse RP as described above, and at the same time, the latch of the video data circuit 40 is performed. The memory contents of 41 and the count value of the counter 43 are cleared, and the clock pulse generating circuit 30 is activated to generate the clock pulse CP shown in FIG. If the image sensor 10 includes the background image BL in addition to the image of the object 1 in FIG. 3A, the charge accumulation time Ts in most of the p light sensor circuits 20 corresponding to the left and right ends thereof. The earliest time elapses and the time signal TS rises from low to high, and the video data circuit 40
The corresponding latch 41 reads the count value in the counter 43 via the bus 42, but since the count command CS has not yet been issued from the count command circuit 50 and the counter 43 has not received the clock pulse CP, these In this embodiment, the latch 41 stores the count value of 0 as the video data ID.

When any of the time signals TS of the (p + 1) to (np) th photosensor circuits 20 in FIG. 1A received by the OR gate of the counting command circuit 50 becomes high, a counting command CS is generated and the transmission is performed. Since the gate 44 is turned on, the counter 43 starts counting upon receiving the clock pulse CP. In FIG. 2B, the waveform of the potential ve in the photosensor circuit 20 at which the time signal TS first goes high is shown by a broken line, and the corresponding waveform after the shortest charge accumulation time Te in FIG. Are counted in the counter 43. Therefore, the normal video data ID is stored in the latch 41 that receives the time signal TS whose charge storage time Ts is longer than the shortest charge storage time Te. Although the clock pulse CP in FIG. 2D is shown with a considerably long period for convenience of illustration, the clock pulse CP is actually made a short period so as to obtain a normal video data ID of 4 to 8 bits.

As described above, according to the present invention, the clock pulse CP for converting the charge storage time Ts into the video data ID is supplied to the optical sensor circuit in the range where the image sensor 10 receives bright backlight.
Since it is invalidated during the operation of 20 and is enabled only for the optical sensor circuit 20 in the range where the target image is received, the video data ID accurately representing the target image without the influence of the backlight with the desired number of bits Obtainable.

If the background of the object is not backlit, the image data ID representing the object and the background is obtained based on the range of receiving the image of the object in the image sensor as described above. Therefore, when the time signal TS having a charge accumulation time shorter than the shortest charge accumulation time Te in the range in which the target image is received comes out of the range in which the background is received, the corresponding video data ID is different from the actual one. Video data ID representing the video of
Is of course the same, so it does not hinder the focusing of the optical instrument. In any case, the image data ID obtained from the image sensor circuit of the present invention includes an accurate detection unit of the target image, and the external light triangulation or TTL method of the optical instrument is used in the same manner as in the related art. Can be used for focusing.

In the embodiment described above, the counting command circuit 50 fixes the number of the optical sensor circuits 20 receiving the time signal TS or the range in the image sensor 10. When the ratio between the object and the background greatly changes, it is advantageous to make the number or range adjustable. For this purpose, in addition to the OR gate of the counting command circuit 50 shown in FIG. 1A, a second OR gate which receives the time signal TS from each of the 1 to p optical sensor circuits 20 in the right and left ranges adjacent to the assigned range. Is provided to the output OR gate together with the output of the first OR gate, and the count command CS is extracted from the output OR gate. Then, the time signal TS of the count command circuit 50 is obtained by enabling and disabling the AND gate. Can be controlled or switched.

As can be seen, the present invention can be implemented in various embodiments other than the above-described embodiment. For example, depending on the type of the optical instrument, it is advantageous to set the range in which the time signal is supplied to the counting command circuit to a range excluding only one end of the image sensor. In the embodiment, the clock pulse is validated by the counting command. However, the clock pulse generating circuit may be activated by the counting command. The image sensor circuit of the present invention requires at least one pair for focusing an optical instrument.
３3 pairs are incorporated into the optics.

[0030]

As described above, according to the present invention, the light intensity received by each optical sensor in the image sensor is converted into a time signal representing the charge accumulation time by the optical sensor circuit, and the light in the image sensor which receives bright backlight is obtained. Target image, excluding sensor
The time signal of the optical sensor circuit corresponding to the receiving range is given to the count command circuit, and the count command is generated at the timing of the shortest charge storage time, and the charge storage time represented by each time signal in the video data circuit accordingly. The following effects can be obtained by starting the operation of counting by the clock pulse and converting it into video data.

(A) The clock pulse for converting the charge accumulation time into video data is invalidated during the operation of the photosensor circuit in the range where the image sensor is receiving bright backlight, and the range in which the target video is received. Enabled only to convert the time signal of the optical sensor circuit to video data,
The video data accurately representing the target video can be extracted from the image sensor circuit without being disturbed by the backlight of the background. (b) When the background is not bright backlight, the time signals of all the photosensor circuits including the background range are almost normal to the video data based on the charge accumulation time of the photosensor circuit in the range where the target image in the image sensor is received. , Accurate video data is obtained for both the object and the background. (c) When the image sensor is incorporated into the optical instrument, slight misalignment or variation is likely to occur in the position relative to the optical axis. Since the time signal is converted into the video data based on the charge accumulation time of the photosensor circuit in the receiving range, the influence of the positional shift is reduced, and the incorporation of the image sensor can be facilitated.

As described above, the present invention has an effect of improving the detection accuracy of an image of a subject exposed to bright backlight without deteriorating the performance of an image sensor in a normal background. It can contribute to improvement of usability and expansion of the range of use by increasing the focusing accuracy of the object by the distance method or the TTL method.

[Brief description of the drawings]

FIG. 1 shows an embodiment of an image sensor circuit according to the present invention. FIG. 1 (a) is an overall circuit diagram including an image sensor, and FIG.
(b) is a partial circuit diagram of the optical sensor circuit.

FIG. 2 shows waveforms of main signals related to FIG.
(a) is a reset pulse, (b) is an internal potential of the photosensor circuit, (c) is a time signal, and (d) is a waveform diagram of a clock pulse.

FIG. 3 is a diagram for explaining a problem when an object of an image sensor receives backlight; FIG. 3 (a) is a diagram showing the relationship between the object and the background of the image sensor with respect to the background, and FIG. It is a distribution diagram of the received light intensity.

[Explanation of symbols]

 1 Image detection target 10 Image sensor 11 Optical sensor 20 Optical sensor circuit 30 Clock pulse generation circuit 40 Video data circuit 50 Count command circuit BL Backlight CP clock pulse CS Count command ID Video data TS Time signal Te Minimum charge accumulation time Ts Charge accumulation time v Internal potential of photosensor circuit

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-2-297514 (JP, A) JP-A-2-183123 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) G02B 7/28 G03B 13/36

Claims (4)

(57) [Claims] An image sensor circuit for detecting an image of an optical instrument for focusing on an object, wherein each light sensor in the image sensor converts the light intensity received from the object into a time signal representing its charge accumulation time. A photosensor circuit for converting, a clock pulse generating circuit for generating a clock pulse for counting a charge accumulation time represented by the time signal, and a charge control circuit for counting the charge accumulation time represented by each time signal by the clock pulse to convert the time signal into a digital image. Excludes the video data circuit that converts data and the optical sensor that receives back light in the image sensor.
A count command circuit for receiving a time signal from an optical sensor circuit corresponding to an optical sensor arranged in a range for receiving an image of an object, and issuing a count command in response to a time signal representing the shortest charge accumulation time among them. An image sensor circuit, wherein a video data circuit is started to convert a time signal into video data by a clock pulse based on a count command from a count command circuit. 2. The image sensor according to claim 1, wherein a time signal is supplied to the counting command circuit from an optical sensor circuit corresponding to an optical sensor arranged in the center of the image sensor. circuit. 3. The circuit according to claim 2, wherein the number of light sensors arranged in the center is 50 times the number of light sensors in the image sensor.
An image sensor circuit characterized by being set to ~ 90%. 4. A circuit according to claim 2 , wherein the range of the photosensors corresponding to the photosensor circuits to which the time signal is to be given to the counting command circuit is adjustable. An image sensor circuit comprising: