JP3324825B2 - Charge storage type 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 a photometric technique, and more particularly to a photometric technique using a charge storage type light receiving element.

[0002]

2. Description of the Related Art At present, as a method for automatically focusing an optical instrument such as a camera, an active method and a passive method are in practical use.

[0003] The passive method is a method in which reflected light from a subject is detected and distance measurement is performed. Therefore, when a certain amount of light is required and the darkness is equal to or less than the reference value, the distance cannot be measured. In order to enable distance measurement even in such a dark case, a method of irradiating a subject with auxiliary light such as infrared rays is adopted.

However, in this method, a light emitting device for infrared rays or the like is required, and an automatic focusing device becomes expensive. If a strobe light can be used as a light source of the auxiliary light, it is not necessary to prepare a special light source for the auto-focusing distance measurement, so that the cost of the auto-focus device can be reduced.

FIG. 9A shows a conventional example (JP-A-2-603).
No. 80) is a circuit diagram of a charge storage type optical sensor. The cathode of the photodiode 51 is connected to the power supply voltage V _DD , and the anode is connected to the ground (ground) potential E via the switch 50 in the reverse bias direction.

The capacitor 52 includes a photodiode 51
Is the junction capacity. The anode of the photodiode 51 is connected to one input of the comparator 53, and the other input is connected to the reference voltage Vr.

At the start of measurement, the switch 50 is closed for a short time, and the capacitor 52 is charged to the power supply voltage V _DD . That is, a reverse bias is applied to the pn junction of the photodiode to expand the depletion layer and keep the potential well deep. At this time, the anode voltage V of the photodiode 51 is once reset to the ground potential E, that is, “0”.

After the switch 50 is opened, a photocurrent proportional to the intensity of the light L received by the photodiode 51 flows through the photodiode 51 in the reverse direction, so that the capacitor 52 is discharged. With the discharge of the capacitor 52, the anode voltage V of the photodiode increases.

The voltage V is applied to one input (a non-inverting input terminal in the case shown) of the comparator 53 and is compared with a reference voltage Vr. The output S of the comparator 53
Is reset to a low state by closing the switch 50. When the voltage V rises and reaches the reference voltage Vr,
Switches to a high state.

The time elapsed since the switch 50 was opened is represented by t, and the photocurrent flowing through the photodiode 51 is represented by In.
(T), the capacitance of the capacitor 52 is C, the potential on the anode side of the photodiode 51 is V (t),
Assuming that the charge stored in 2 is Q (t),

[0011]

(Equation 1)

## EQU1 ## Here, the sign of In (t) is negative because the direction in which the capacitor 52 is charged is positive. Now, assuming that the light received by the photodiode 51 is steady light, In (t) does not depend on time and is considered to be constant.

[0013]

V (t) = In · t / C (2)

Therefore, the potential V (t) becomes equal to the reference potential Vr
Assuming that the time until it becomes equal to is Tn,

[0015]

## EQU3 ## In = CVr / Tn (3)

That is, the photocurrent In can be obtained by measuring the time Tn (charge accumulation time) when the output S of the comparator 53 is in the low state. The time Tn can be easily converted to a digital value by a clock counter.

FIG. 9B shows a time change of the anode-side potential V (t) of the photodiode 51 when steady light enters the optical sensor shown in FIG. 9A. As described above, when stationary light is incident, the photocurrent can be approximated to be constant, so that the potential V (t) changes in proportion to time.

A straight line p1 in FIG. 9B is a strong light, and a straight line p3.
Represents an example in which weak light is incident, and a straight line p2 represents an example in which light having an intermediate intensity is incident. As shown in FIG. 9B, the straight line p1 is V
= When the time becomes Vr and T _1, T ₁ corresponds to the charge accumulation time Tn.

On the other hand, when a person is photographed with a strobe, the strobe light is reflected by the retina of the eye and the eye is photographed in red. In order to prevent this red-eye phenomenon, a method has been considered in which a preliminary light emission is performed immediately before photographing with a strobe, a main light is emitted after a pupil is closed, and photographing is performed.

If the automatic focusing can be performed at the time of the preliminary light emission, it is not necessary to perform a special auxiliary light emission for the automatic focusing, and the focusing can be performed efficiently.

Then, by detecting the reflected light of the strobe light,
There is a demand for an optical sensor that can be extracted as a light intensity signal. FIG. 9C shows a time change of the anode-side potential V (t) of the photodiode 51 when the non-stationary light is incident. For example, this is a case of pulse light emission such as a strobe light. Curve q1 in FIG. 9C is a strong light, curve q3.
Represents weak voltage, and curve q2 represents voltage V (t) when light of intermediate intensity is incident.

In this case, the photocurrent In (t) is a function of time. When the intensity of the strobe light is maximum,
Since the photocurrent In (t) becomes maximum, the slope of the graph V (t) increases. Conversely, when the light intensity is low, the photocurrent In (t) decreases, and the slope of the graph V (t) decreases.

At t = 0 in FIG. 9C, the strobe light emission starts,
t = T _E corresponds to the light-emitting end. t = T _E after is,
Since only very weak light enters the optical sensor, the voltage V
The rise in (t) is very slow.

As described above, when the strobe light is used, the voltage V (t) rises rapidly with the strobe light emission, and becomes almost constant when the light emission ends. Curve q
1, then the reference voltage Vr at the voltage V (t) is t = T ₁
Reach In the case of the curve q2, the voltage V (t) does not reach the reference voltage Vr when the strobe light emission ends, and
Thereafter, the reference voltage Vr is reached at t = T ₂ by the photocurrent due to the very weak light.

In such a case, the length of time until the voltage V (t) reaches the reference voltage Vr is not proportional to the amount of incident light. Further, there may be a case where the reference voltage Vr does not reach the reference voltage Vr forever, as indicated by the curve q3.

Therefore, the charge storage type optical sensor shown in FIG. 9A is not suitable for non-stationary light such as strobe light.

[0027]

When the incident light is non-stationary light such as strobe light, the photocurrent of the optical sensor, that is, the discharge current of the accumulated charge is not constant. Therefore, it is not easy to estimate the amount of light by measuring the time until the voltage rise due to the photocurrent reaches the reference voltage. It is difficult to apply a charge storage type image sensor by such a method to non-stationary light such as strobe light.

An object of the present invention is to provide a charge storage type image sensor circuit which can be applied to non-stationary light such as strobe light.

[0029]

According to the present invention, there is provided a charge storage type image sensor circuit comprising: a strobe clock generating means for generating a strobe clock having a strobe trigger function;
A strobe light emitting means (2) for continuously emitting strobe light in one operation in synchronization with the strobe clock;
A counting means (8) connected to the strobe clock generating means for counting the number of pulses of an input signal; and a plurality of photoelectric conversion means (CV) for receiving light from an object and converting the received light into an electric signal. ), A plurality of comparison means (CP) for comparing the electric signal converted by each of the photoelectric conversion means with a predetermined reference voltage and outputting a comparison result signal, and counting when the comparison result signal changes Means for storing the number of pulses of the means, normal mode clock generating means (4) for starting generation of a counter pulse in response to the first change of the comparison result signal output from the plurality of comparing means, and the strobe. Switching means (3) for selectively connecting to the clock generation means or the normal mode clock generation means.

[0030]

In the charge storage type image sensor, the strobe light is continuously emitted during one operation, so that the reflected light can be incident on the optical sensor in a number of times. This makes it possible to measure the number of light emissions until the voltage rise of the optical sensor reaches the reference voltage, and detect the amount of light. If a charge storage type image sensor according to this method is used, the amount of light can be detected in the case of strobe light as well as in the case of steady light.

[0031]

FIG. 1 is a configuration diagram of an image sensor circuit according to an embodiment of the present invention. This image sensor circuit is used for an automatic distance measuring device such as a camera. The image sensor has n pixels and detects the amount of light incident on each pixel.

In this embodiment, there are two modes for detecting the amount of light. One is a normal mode, which is used when light incident on each pixel can be regarded as stationary light. The normal mode is a passive mode, and can be configured using a conventional technique.

The other mode is a strobe mode, which is used when a strobe light is emitted for a subject to be measured for distance detection and its reflected light is detected. In the normal mode described above,
If a sufficient amount of light cannot be obtained from the subject to be measured, the strobe light of the auxiliary light is emitted in the strobe mode, and the reflected light from the subject is detected. For example, in a situation where a sufficient amount of light cannot be obtained, such as on a bad weather day or at night, the strobe mode is used. That is, in operation,
The normal mode is a passive mode, and the strobe mode is an active mode.

The selection of the two modes, the normal mode and the strobe mode, is performed by the switch 3. Mode signal MD
The signal in either mode is sent and input to the switch 3. When the mode signal MD is in the normal mode, the switch 3 is connected to the terminal 3a. Also, the mode signal M
When D is in the strobe mode, switch 3 is connected to terminal 3b.

First, the circuit operation of the light amount detection in the normal mode will be described. The image sensor circuit includes n photoelectric conversion units CV corresponding to the number of pixels and n comparators CP.
And n latches LT.

The photoelectric conversion unit CV has an optical sensor for receiving light incident on each pixel, and receives an optical signal from a subject whose distance is to be measured. The optical signal input to the photoelectric conversion unit CV is
It is converted into an electric signal by an internal light sensor. Charges corresponding to the light intensity are accumulated in the optical sensor, and a voltage value corresponding to the charge amount is output from the photoelectric conversion unit CV. The electric signal output from the photoelectric conversion unit CV is
It is input to the + input terminal of P and compared with the reference voltage Vr input to the-input terminal of the comparator CP.

After the output electric signal of the photoelectric conversion unit CV is cleared by the RESET signal for initializing the optical sensor, it increases with the passage of time in accordance with the amount of incident light. Eventually, when the output electric signal reaches the reference voltage Vr, the output of the comparator CP changes from a low state to a high state. Therefore, the time until the output electric signal changes is proportional to the reciprocal of the amount of incident light. Therefore, the time until the output electric signal changes is proportional to the reciprocal of the incident light intensity.

The OR gate 7 has comparators CP1 to CP1.
The output signal of CPn is input. The output of the OR gate 7 changes from the low state to the high state if any one of the output voltages of the photoelectric conversion units CV1 to CVn reaches the reference voltage Vr. That is, after the electric signal of the pixel having the highest light intensity among the n pixels in the image sensor reaches the reference voltage Vr, the output of the OR gate 7 becomes high.

The output of the OR gate 7 and the clock pulse generated by the clock generator 5 are input to the AND gate 6. As long as the output of the OR gate 7 is in the high state, the clock pulse is supplied from the clock generator 5 to the normal mode clock generation circuit 4 via the AND gate 6.

The normal mode clock generating circuit 4 is based on the clock pulse generated by the clock generator 5,
A counter pulse for measuring a time until the output electric signal of the photoelectric conversion unit CV reaches the reference voltage is generated. This counter pulse can be configured in various ways. For example, it is possible to generate a counter pulse whose period becomes longer as time elapses. This makes it possible to provide a count suitable for measuring the amount of incident light.

The normal mode clock generation circuit 4 starts generating counter pulses when the output of the OR gate 7 changes from a low state to a high state. Then, the counter pulse is counted by the counter 8 via the switch 3.

The output terminal of the comparator CP is a latch L
T to supply a latch command signal. When the latch command signal is generated, the count value counted by the counter 8 is stored in the latch LT. The count value stored in the latch LT indicates the time until the output electric signal of each photoelectric conversion unit CV reaches the reference voltage Vr.

The shift register 9 is connected to the latch LT and supplies a read signal to a target one of the latches LT1 to LTn. Thus, the desired count value in the latches LT1 to LTn is equal to the sensor data S.
Read as D. From the sensor data SD, the light intensity incident on each pixel can be calculated.

FIG. 2 shows sensor characteristics when steady light is input to the image sensor. In the image sensor, a plurality of pixels are arranged one-dimensionally. FIG. 2A is a signal waveform showing the measurement time. When this signal is high,
This is a period for counting pulses. When the sensor output corresponding to the electric charge accumulated in the optical sensor corresponding to each pixel reaches the reference voltage, the light intensity incident on the pixel can be calculated from the accumulation time up to that point.

In any one of the pixels in the image sensor, when the charge stored in the photosensor reaches the reference voltage, the signal goes high. In addition, in all the pixels in the image sensor, when the charge accumulated in the photosensor reaches the reference voltage, the signal falls to a low state. The duration of the high state at this time is about 10 ms.

FIG. 2B shows the change in the amount of charge accumulated with the passage of time. The horizontal axis represents time, and the vertical axis represents the amount of charge stored in the optical sensor. In stationary light,
The amount of charge stored in the optical sensor increases in proportion to the passage of time.

FIG. 2C shows the distribution of light intensity in each pixel. The horizontal axis represents the positions of the pixels arranged one-dimensionally,
The vertical axis represents the light intensity of 0 to 255 levels. The intensity of light incident on each pixel is obtained by measuring the time until a predetermined charge is accumulated in the pixel in the image sensor. The light intensity in each pixel is decomposed into fine gradations.

The case of the stationary light described above shows the characteristic in the light amount detection of the passive system. If a sufficient amount of light can be obtained from the subject for which distance measurement is performed, highly accurate light amount detection can be performed as described above. However, in light amount detection at night, active light amount detection is effective. Therefore, next, detection of light amount using strobe light will be described.

FIG. 3 shows sensor characteristics when reflected light of a single flash light is input to an image sensor. The strobe provided in the camera was emitted only once, and the reflected light from the subject was incident on the image sensor.

FIG. 3A shows a signal indicating the measurement time similarly to FIG. 2A. Even in any one of the pixels in the image sensor, the electric charge accumulated in the optical sensor reaches the reference voltage. If it does, the signal rises and goes high. In addition, in all the pixels in the image sensor, when the electric charge accumulated in the optical sensor reaches the reference voltage, the signal falls,
It becomes low state. The duration of the high state at this time is several μs.
This is an extremely short time as compared with the stationary light shown in FIG.

FIG. 3B shows the change in the amount of charge accumulated with the passage of time. The horizontal axis represents time, and the vertical axis represents the amount of charge stored in the optical sensor. In single-flash strobe light, the amount of charge stored in the photosensor is not proportional to the passage of time, but increases with unique characteristics corresponding to the strobe light-emitting characteristics. Then, the amount of charge accumulated in a short time is saturated.

FIG. 3C shows the distribution of light intensity in each pixel. The horizontal axis represents the positions of the pixels arranged one-dimensionally,
The vertical axis represents the light intensity of 0 to 255 levels. Since the subject used in FIG. 3C is the same as that in FIG. 2C, the characteristic shown in FIG. 2C is originally desired. However, in the case of single flash light emission, the light intensity at each pixel has not been resolved to a sufficiently fine gradation.

This is due to the characteristic that the flash emits light instantaneously with a rapid rise in a very short time. For this reason, the measurement time is as short as several μs, during which only a few counter pulses are generated. For this reason, a sufficient resolution of the gradation of the light intensity cannot be obtained.

Next, a method of realizing a high gradation characteristic of light intensity using strobe light will be described. To do so, instead of emitting a large amount of light in a short period of time, the strobe emits light in a plurality of times.

FIG. 4 shows the sensor characteristics when the reflected light of strobe continuous emission (1) is input to the image sensor.
The strobe provided in the camera was continuously emitted a plurality of times, and the reflected light from the subject was incident on the image sensor.

FIG. 4A is a waveform showing the measurement time. In any one of the pixels in the image sensor, when the charge accumulated in the photosensor reaches the reference voltage, the signal rises and goes to a high state. In addition, in all the pixels in the image sensor, when the charge accumulated in the photo sensor reaches the reference voltage, the signal falls and goes to a low state.
At this time, the duration of the high state is longer than that of the single flash light emission of FIG.

FIG. 4B shows the change in the amount of charge accumulated with the passage of time. The horizontal axis represents time, and the vertical axis represents the amount of charge stored in the optical sensor. In the continuous light emission of the strobe, the amount of electric charge accumulated in the optical sensor increases in a stepwise manner as many times as the number of times of continuous light emission of the strobe.

FIG. 4C shows the distribution of light intensity in each pixel. The horizontal axis represents the positions of the pixels arranged one-dimensionally,
The vertical axis represents the light intensity of 0 to 255 levels. The subject used in FIG. 4C is the same as that in FIG. As compared with the case of the stationary light shown in FIG. 2C, the distribution of the light intensity can be sufficiently recognized although the gradation is low. The light intensity in this case is represented by approximately four gradations, corresponding to four strobe light emission during the measurement time.

FIG. 5 shows another sensor characteristic when the reflected light of the continuous stroboscopic light emission (2) is input to the image sensor. The strobe provided in the camera was continuously emitted a plurality of times, and the reflected light from the subject was incident on the image sensor. The stroboscopic light emission (2) has a smaller amount of light emission per flash than the continuous stroboscopic light emission (1) of FIG.

FIG. 5A is a waveform showing the measurement time. In any one of the pixels in the image sensor, when the charge accumulated in the photosensor reaches the reference voltage, the signal rises and goes to a high state. In addition, in all the pixels in the image sensor, when the charge accumulated in the photo sensor reaches the reference voltage, the signal falls and goes to a low state.
At this time, the duration of the high state is longer than the continuous strobe light emission (1) of FIG.

FIG. 5B shows the change in the amount of charge accumulated with the passage of time. The horizontal axis represents time, and the vertical axis represents the amount of charge stored in the optical sensor. In the continuous light emission of the strobe, the amount of electric charge accumulated in the optical sensor increases in a stepwise manner as many times as the number of times of continuous light emission of the strobe. This step-like characteristic has a finer step-like shape than the continuous stroboscopic light emission (1) of FIG.

FIG. 5C shows the distribution of light intensity in each pixel. The horizontal axis represents the positions of the pixels arranged one-dimensionally,
The vertical axis represents the light intensity of 0 to 255 levels. The subject used in FIG. 5C is the same as that in FIG. This characteristic has a higher gradation as compared with the case of strobe continuous light emission (1) shown in FIG. The light intensity in this case is represented by six gradations. That is, if the amount of strobe light emission per time is reduced and a predetermined amount of light is obtained by performing strobe light emission many times, light intensity of a high gradation can be detected accordingly.

Referring to FIG. 1, the circuit operation of light amount detection in the strobe mode will be described. When the mode signal MD is in the strobe mode, the active light amount detection by the above-described strobe continuous emission is performed. In the strobe mode, the switch 3 is connected to the terminal 3b.

The strobe clock generation circuit 1 generates a strobe clock. In response to the RESET signal, the optical sensor in the photoelectric conversion unit CV is cleared, and at the same time, pulse generation of a strobe clock signal is started. The strobe clock is input to the counter 8 as a counter pulse via the switch 3 and counted.

The comparator CP supplies a latch command signal to the latch LT. At that time, the count value counted by the counter 8 is stored in the latch LT. Since the count value stored in the latch LT is the count value of the strobe pulse, the number of light emission pulses from when the strobe starts continuous light emission until the output electric signal of each photoelectric conversion unit CV reaches the reference voltage Vr is calculated. Represent. Then, the shift register 9 reads out a desired count value in the latches LT1 to LTn as sensor data SD.

The strobe clock generated by the strobe clock generating circuit 1 also has the function of a strobe trigger. The strobe clock is input to the strobe light emitting circuit 2, and the strobe light is emitted according to the strobe clock.

FIG. 6 shows a timing waveform based on continuous stroboscopic light emission. The strobe clock is generated in the strobe clock generation circuit 1. For example, when it is desired to detect the light intensity gradation in 256 gradations from 0 to 255, if one light emission amount of the continuous strobe light emission is set to correspond to the light amount of one gradation, 255 gradations are set. Is sufficient.

Although FIG. 6 shows a case in which substantially the same strobe waveform is generated, the amount of strobe light emission per time may be initially large and gradually decreased. When the light intensity is low, the gradation is made fine, and when the light intensity is high, the gradation is made large. The gradation of the light intensity can be made close to the visibility of humans.

The -RESET signal is an initial setting signal that enables light amount detection, and clears the charge in the optical sensor that receives light from the subject. The strobe waveform is a current waveform that flows through the discharge tube of the strobe. Flash emission is performed in synchronization with a flash clock. -RE
After the SET signal, strobe light emission is started.

The accumulated charge waveform represents the amount of accumulated charges converted according to the light incident on the optical sensor. For the subject,
Light emitted from the strobe is irradiated, and the reflected light is incident on the optical sensor. That is, each time the strobe light is emitted, the reflected light is converted into electric charge by the optical sensor. By performing continuous stroboscopic light emission, the accumulated charge amount increases stepwise.

FIG. 7 shows a flash auxiliary light circuit for performing continuous flash emission. This corresponds to the strobe light emitting circuit 2 shown in FIG. The light emission of the strobe is originally used to increase the illuminance of the subject when shooting the subject. Before performing the main flash emission, continuous flash emission is performed as auxiliary flash emission in order to detect the amount of light.

First, a normal flash circuit section will be described. The booster circuit 11 includes a resistor R4, a transistor Q2,
It has a switch S1, a transformer TR1, and a diode D1. The switch S1 is a switch for starting charging the capacitors C2 and C3. Transistor Q
Numeral 2 controls the operation of oscillation. The diode D1 is a rectifying diode.

The DC power supply VDD supplies power to the booster circuit 11. The booster circuit 11 receives the input DC voltage VDD
Is converted to AC, and after boosting by the transformer TR1, the diode D
The current is rectified by 1 to charge the capacitors C2 and C3.
The neon tube NE is a display lamp indicating that charging of the capacitors C2 and C3 has been completed, and is supplied with current through the resistor R5.

After the capacitors C2 and C3 have been charged, the strobe emits light by discharging the xenon tube Xe. Insulated gate bipolar transistor I
The GBT controls a current flowing through the xenon tube Xe. When the transistor IGBT is on, current flows through the xenon tube Xe, and when the transistor IGBT is off, no current flows.

When the transistor IGBT is turned on, the electric charge stored in the capacitor C3 is discharged, and a current flows through the primary coil of the transformer TR2. Then, a high voltage is generated in the secondary coil, and the xenon tube Xe
Is applied to the trigger electrode. Thereby, the xenon tube X
The xenon gas inside e is ionized, and the internal resistance of the xenon tube decreases. Then, the electric charge accumulated in the capacitor C2 is discharged between the electrodes of the xenon tube Xe.

The continuous emission of the strobe is performed by the transistor IG
It is controlled by the switching operation of the BT. Next, a control circuit for flash light emission including the transistor IGBT will be described. The strobe clock generated by the strobe clock generation circuit 1 of FIG.
Is input to That is, it is input as the strobe clock IN in FIG.

FIG. 8A shows a voltage waveform of the strobe clock IN. The horizontal axis represents time t. Strobe clock I
N is a pulse waveform composed of a low state of 0 [V] and a high state of 5 [V].

The capacitor C1 is connected to a DC power supply VCC via a resistor R1.
N is supplied. The capacitor C1 is charged according to the signal of the strobe clock IN. DC power supply VCC is +
5 [V].

FIG. 8B shows a voltage waveform at the emitter terminal ND1 of the transistor Q1. Emitter terminal ND1
Is connected to the capacitor C1. This voltage waveform represents a low state of 5 [V] and a high state of 10 [V].

The base terminal of the transistor Q1 is connected to a ground terminal via a Zener diode ZD1 and a resistor R3. The zener voltage of the zener diode ZD1 is set to about 6.2 [V] to limit the base current.

FIG. 8C shows a voltage waveform at the collector terminal ND2 of the transistor Q1. The collector terminal is connected to the ground terminal via the resistor R2. The collector terminal is connected to the gate terminal of the transistor IGBT. The voltage waveform is controlled with a Zener voltage of 6.2 [V] as a boundary, and has a low state of 0 [V] and a high state of 10 [V].

The transistor IGBT is a transistor having high input impedance characteristics and low saturation voltage characteristics. The gate terminal of the transistor IGBT is connected to the collector terminal of the transistor Q1, the collector terminal is connected to the xenon tube Xe, and the emitter terminal is connected to the ground terminal. When a high signal 10 [V] is supplied to the gate terminal, the transistor IGBT is turned on, and when a low signal 0 [V] is supplied, the transistor IGBT is turned off.

FIG. 8 (D) shows through a xenon tube Xe
4 shows a current waveform flowing into the collector terminal ND3 of the transistor IGBT. When the transistor IGBT is in the off state, no current flows, and during the on state, a current flows according to the discharge characteristics of the xenon tube Xe.

As described above, by changing the waveform of the strobe clock IN, the timing at which the strobe light is emitted can be controlled. If the cycle of the strobe clock IN is shortened, the interval of the strobe light emission is shortened, and if the cycle is lengthened, the interval of the strobe light emission is lengthened. Although the case has been described where the strobe clock IN is a pulse at regular intervals with respect to time, the strobe clock IN need not always be at regular intervals. The strobe clock IN can be changed to any signal shape.

As described above, by providing the normal mode and the strobe mode in the image sensor circuit, even in a dark subject where a sufficient sensor output cannot be obtained in the normal mode, a good sensor output can be obtained by using the strobe mode. Obtainable. Further, by changing the number of times of continuous light emission of the strobe, the image sensor circuit can detect light intensity having a desired gradation.

The present invention has been described in connection with the preferred embodiments.
The present invention is not limited to these. For example,
It will be apparent to those skilled in the art that various modifications, improvements, combinations, and the like can be made.

[0087]

According to the present invention, by continuously emitting strobe light, reflected light can be incident on the optical sensor in a large number of times. Thus, even in a situation where a sufficient amount of light cannot be obtained, for example, on a bad weather day or at night, it is possible to perform light amount detection with a fine gradation level using a strobe. Also, by using strobe light as auxiliary light, no other special light source is required.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an image sensor circuit according to an embodiment of the present invention.

FIG. 2 is a graph showing sensor characteristics when stationary light is input to an image sensor. FIG. 2A is a waveform showing the measurement time, FIG. 2B shows the change in the amount of charge accumulated with the passage of time, and FIG. 2C shows the light intensity at each pixel.

FIG. 3 is a graph showing sensor characteristics when reflected light of a single flash light is input to an image sensor. FIG.
3A is a waveform showing the measurement time, and FIG. 3B shows the change in the amount of charge accumulated with the passage of time.
(C) shows the light intensity in each pixel.

FIG. 4 is a graph showing sensor characteristics when reflected light of strobe continuous emission (1) is input to an image sensor. . FIG. 4A is a waveform showing the measurement time.
4B shows a change in the amount of charge accumulated with the passage of time, and FIG. 4C shows the light intensity at each pixel.

FIG. 5 is a graph showing sensor characteristics when reflected light of continuous stroboscopic light emission (2) is input to an image sensor.
FIG. 5A is a waveform showing the measurement time, FIG. 5B shows the change in the amount of charge accumulated with the passage of time, and FIG. 5C shows the light intensity at each pixel.

FIG. 6 is a graph showing a timing waveform due to continuous stroboscopic light emission.

FIG. 7 is a circuit diagram of a strobe auxiliary light circuit that performs continuous strobe light emission.

FIG. 8 is a graph showing a circuit operation waveform in the strobe auxiliary light circuit.

FIG. 9 is a circuit diagram and a graph showing characteristics of a charge storage type optical sensor according to the related art. FIG. 9A is a circuit diagram of a charge storage type optical sensor, and FIG. 9B shows an anode potential of a photodiode when stationary light is incident.
(C) represents the anode potential of the photodiode when non-stationary light is incident.

[Explanation of symbols]

 CV photoelectric converter CP comparator LT latch MD mode signal SD sensor data Vr reference voltage 1 strobe clock generation circuit 2 strobe light emission circuit 3 switch 4 normal mode clock generation circuit 5 clock generator 6 AND gate 7 OR gate 8 counter 9 shift register

────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Jun Hasegawa 1-6-6 Matsuzakadaira, Yamato-cho, Kurokawa-gun, Miyagi Fujifilm Micro Devices Co., Ltd. In-house (56) References JP-A-58-113727 (JP, A) JP-A-56-52732 (JP, A) JP-A-62-96827 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G01J 1/00-1/60

Claims (1)

(57) [Claims] 1. A strobe clock generating means (1) for generating a strobe clock having a function of a strobe trigger, and a strobe light emitting means (2) for continuously emitting strobe light in one operation in synchronization with the strobe clock. A counting means (8) connected to the strobe clock generating means for counting the number of pulses of an input signal; and a plurality of photoelectric conversion means for receiving light from an object and converting the received light into an electric signal. (CV), a plurality of comparison means (CP) for comparing the electric signal converted by each of the photoelectric conversion means with a predetermined reference voltage, and outputting a comparison result signal, and when the comparison result signal changes Storage means for taking in the number of pulses of the counting means, and a normal mode clock for starting generation of a counter pulse in response to the first change of the comparison result signal output from the plurality of comparison means. A charge accumulation type image sensor circuit comprising: a clock generation means (4); and a switching means (3) for selectively connecting the counting means to the strobe clock generation means or the normal mode clock generation means.