JPH06313840A - Photometric device and photometric method - Google Patents

Abstract

PURPOSE:To enable application even in the case of unsteady light such as stroboscopic light by discharging the charge, accumulated in a capacitor by a photocurrent, at the constant current, and measuring the charge quantity by the discharging time. CONSTITUTION:Switches SW1, SW2 are closed to charge a capacitor 2 up to voltage VREF. A switch SW4 is opened, and a switch SW 5 is opened to supply the input VCMP of a comparator 40 with discharge start potential VINT. Then with stroboscopic emission performed simultaneously with the opening of the switch SW2, a photodiode 1 charges the capacitor 2. In the high state of the output signal CMP of an optical sensor, the SW1 of the optical sensor is opened, the switch SW4 is opened, and the switch SW5 is closed to supply the input VCMP of the comparator 4 with reference potential VREF. The switch SW 3 is closed to discharge the charge of the capacitor 2 at a constant current source 3. The switch SW3 is closed, and a latch circuit 5 latches the count value at the low time of the signal CNP of the comparator 4 to obtain the charge quantity.

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 Currently, an active method and a passive method are put into practical use as a method for automatically focusing an optical instrument such as a camera.

The passive system is a system in which reflected light from a subject is detected to perform distance measurement. Therefore, a certain amount of light is required, and when the darkness is less than the reference value, distance measurement is impossible. A method of irradiating a subject with auxiliary light such as infrared rays is used to enable distance measurement even in such a dark place.

However, this method requires a light emitting device for infrared rays and the like, and the autofocus device becomes expensive. If a strobe can be used as a light source for this supplementary light, it is not necessary to prepare a special light source for distance measurement for automatic focusing, so that the cost of the automatic focusing device can be reduced.

FIG. 6A shows a conventional example (JP-A-2-603).
Fig. 80 is a circuit diagram of a charge storage type photosensor according to No. The cathode of the photodiode 51 is connected to the power supply voltage V _DD , and the anode thereof is connected to the ground potential E through the switch 50 in the reverse bias direction.

The capacitor 52 is a photodiode 51.
Is the junction capacity of. 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.

To start the 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 deepen the potential well. At this time, the anode side 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 in the reverse direction through the photodiode 51, so that the capacitor 52 is discharged. The voltage V on the anode side of the photodiode rises as the capacitor 52 discharges.

This voltage V is given to one input (a non-inverting input terminal in the figure) of the comparator 53 and compared with the reference voltage Vr. Output S of this comparator 53
Is reset to the low state by closing switch 50. When the voltage V rises and reaches the reference voltage Vr,
Switch to high state.

The elapsed time from the time when the switch 50 is opened is t, and the photocurrent flowing through the photodiode 51 is In.
(T), the electrostatic capacity of the capacitor 52 is C, the potential on the anode side of the photodiode 51 is V (t), the capacitor 5
If the electric charge accumulated in 2 is Q (t),

[0011]

[Equation 1]

[0012] Here, since the direction in which In (t) charges the capacitor 52 is positive, the sign of In (t) is negative. Now, assuming that the light received by the photodiode 51 is stationary light, In (t) is considered to be constant and does not depend on time.

[0013]

## EQU00002 ## V (t) = In.t / C (2) can be transformed.

Therefore, the potential V (t) is equal to the reference potential Vr.
If 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) during which the output S of the comparator 53 is in the low state. The time Tn can be easily converted into a digital value by the clock counter.

FIG. 6B shows the time variation of the anode-side potential V (t) of the photodiode 51 when constant light is incident on the photosensor shown in FIG. 6A. As described above, when the stationary light is incident, the photocurrent can be approximated to be constant, so the potential V (t) changes in proportion to time.

The straight line p1 in FIG. 6B is strong light, and the straight line p3.
Is an example where weak light is incident, and the straight line p2 is an example when incident light having an intermediate intensity. As shown in FIG. 6B, 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 stroboscopic photography is performed on a person, stroboscopic light is reflected by the retina of the eye and the eye is photographed red, which is a so-called red-eye phenomenon. In order to prevent this red-eye phenomenon, a method has been considered in which preliminary light emission is performed immediately before shooting with a flash, and main light emission is performed after the pupil is closed before shooting.

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

Therefore, the reflected light of the strobe light is detected,
There is a demand for an optical sensor that can be extracted as a light amount signal. FIG. 6C shows a time change of the anode-side potential V (t) of the photodiode 51 when unsteady light is incident. For example, it is a case of pulsed light emission such as strobe light. The curve q1 in FIG. 6C is strong light, and the curve q3.
Indicates a weak light, and the curve q2 indicates a voltage V (t) when light having an intermediate intensity is incident.

In this case, the photocurrent In (t) is a function of time. When the intensity of strobe light is maximum,
Since the photocurrent In (t) becomes maximum, the slope of the graph V (t) becomes large. On the contrary, when the light intensity is weak, the photocurrent In (t) decreases, so that the slope of the graph V (t) decreases.

At t = 0 in FIG. 6C, strobe light emission starts,
t = T _E corresponds to the end of light emission. After t = T _E ,
Since only very weak light is incident on the optical sensor, the voltage V
The rise in (t) is very gradual.

As described above, when the strobe light is used, the voltage V (t) rapidly rises with the strobe light emission, and becomes almost constant when the light emission is completed. Curve q
In the case of 1, the voltage V (t) is t = T ₁ and the reference voltage Vr
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,
After that, the reference voltage Vr is reached at t = T ₂ by the photocurrent caused by the very weak light.

In such a case, the time length until the voltage V (t) reaches the reference voltage Vr is not proportional to the amount of incident light. In addition, as in the curve q3, the reference voltage Vr may not be reached forever.

Therefore, the charge storage type photosensor shown in FIG. 6A is not suitable for non-steady light such as strobe light.

[0027]

When the incident light is unsteady light such as strobe light, the photocurrent of the photodiode, that is, the accumulated charge current is not constant. for that reason,
The charge storage type photosensor that estimates the integrated light quantity by measuring the time until the voltage rise due to the photocurrent reaches the reference voltage is difficult to apply to unsteady light such as strobe light.

An object of the present invention is to provide a charge storage type photometric technique which can be applied even to non-steady light such as strobe light.

[0029]

A charge storage type photosensor according to the present invention comprises a light receiving element for generating a photocurrent according to the amount of light received and a capacitor connected in series, and means for applying a bias to the series connection. Means for charging the capacitor to the reference voltage before measuring the amount of received light, switch means for terminating the charging operation for charging the capacitor by the photocurrent generated by the light receiving element, and the charge accumulated in the capacitor by the photocurrent A photoelectric conversion circuit including a constant current source for discharging at a constant current, a terminal voltage of the capacitor and a determination voltage are compared, and a comparison circuit that generates a detection signal when both match, and a clock pulse A counter that receives and starts counting simultaneously with the start of discharging the capacitor,
The storage unit is connected to the comparison circuit and the counter, and stores a count value of the counter based on a detection signal of the comparison circuit.

[0030]

The photometric device of the present invention discharges the electric charge accumulated in the capacitor with a constant current by the photocurrent, and measures the electric charge amount by the discharging time. This discharge time is proportional to the accumulated charge amount, and the accumulated charge amount is proportional to the received light amount. Therefore, highly accurate photometry can be performed by measuring the discharge time.

Further, by arranging a plurality of light receiving elements and terminating the charging operation by the photocurrent of all the light receiving elements within a fixed time, it is possible to measure the amount of light received by each light receiving element. The end of the charging operation can be based on when the terminal voltage of the capacitor corresponding to the light receiving element receiving the maximum amount of light reaches a certain voltage.

When the amount of received light is small, a strobe can be used as auxiliary light, and the charging operation can be ended by the end of strobe light emission.

[0033]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A storage type optical sensor according to an embodiment of the present invention will be described below with reference to FIG.

FIG. 1A is a circuit diagram of an accumulated charge type photosensor according to an embodiment of the present invention, and FIG. 1B is a timing diagram. When used as a phase difference detection type distance measuring device for a camera, two sets of image sensors in which the accumulated charge type photosensors are arrayed are used.

The anode of the photodiode 1 is one electrode (positive electrode) of the capacitor 2 via the switch SW1.
It is connected to the. The other electrode (cathode) of the capacitor 2 is connected to the ground potential.

The positive electrode of the capacitor 2 is a switch SW2.
Connected to the reference potential V _REF via the switch S
By closing W2, the capacitor 2 is connected to the voltage V _REF.
Can be charged to.

Further, the positive electrode of the capacitor 2 is connected to the cathode of the constant current source 3 via the switch SW3. The anode of the constant current source 3 is connected to the ground potential. By closing the switch SW3, the electric charge charged in the capacitor 2 can be discharged at a constant current level.

The positive electrode of the capacitor 2 is connected to one input V _OUT of the comparator 4. The other input V _CMP of the comparator 4 is connected to the reference potential V _REF via the switch SW5 and is connected to the discharge start potential V _INT higher than the reference potential V _REF via the switch SW4.

The comparator 4 has a potential V _OUT of the positive electrode of the capacitor 2 and a reference potential V _REF , or a discharge start potential V
It compares with _INT and outputs the output signal CMP. The cathode of the photodiode 1 is connected to a potential higher than the discharge start potential V _INT , and the anode potential is set to the discharge start potential V _INT.
The reverse bias is applied even when it becomes.

The counter 7 closes the switch SW3,
The time from the start of charging the capacitor 2 is counted, and the count value is supplied to the latch circuit 5. The output signal CMP of the comparator 4 and the count value of the counter 7 are input to the latch circuit 5. The latch circuit 5 latches the count value when the output signal CMP of the comparator 4 becomes low.

A method of measuring the amount of light when strobe light is applied to a subject using the thus-stored charge type photosensor will be described below. The switches SW1 and SW2 are closed and the capacitor 2 is charged to the voltage V _REF . At this time, the reference potential V _REF is also supplied to the anode of the photodiode 1, and the photodiode 1 is reverse biased. Switch SW4 closed, switch SW5
_{Is released,} and the discharge start potential V _{INT is applied} to the input V _CMP of the comparator 4.

At this time, one input V of the comparator 4
_The reference potential V _REF is given to _OUT , and the other input V _CMP
Since the discharge start potential V _INT is applied to the output signal CMP, the output signal CMP is in the low state.

Next, the switch SW2 is opened. Figure 1
(B) shows each switch S after the switch SW2 is opened.
W1-SW4 state, positive electrode potential V of capacitor 2
FIG. 7 is a timing chart showing _OUT , the output signal CMP of the comparator 4, the elapsed time counting clock pulse CP, and the intensity of stroboscopic light emission. SW1 to SW4 are
The state "1" indicates that the switch is closed, and the state "0" indicates that the switch is open.

At the same time when the switch SW2 is opened, the strobe light is emitted. The photodiode 1 receives the reflected light L of the strobe light from the subject, generates a photocurrent, and charges the capacitor 2. When charging is started, the potential V _OUT of the positive electrode of the capacitor 2 rises from the reference voltage V _REF according to the amount of light incident on the photodiode 1.

The solid line shown at V _OUT in FIG. 1B shows the maximum amount of incident light among the photosensors constituting the image sensor, and the dotted line represents one of the other photosensors. ing.

The voltage V of the photosensor with the maximum amount of incident light
_{When OUT} reaches the discharge start potential V _INT , the output signal CMP of the comparator 4 of the photosensor becomes high. This is shown by the solid line of CMP in FIG.

Output signal CM of the photosensor with the maximum amount of incident light
When P is in the high state, the switches SW1 of all the optical sensors forming the image sensor are simultaneously opened.
This completes the charging operation of the capacitor 2 of the all-optical sensor.

[0048] At this time, positive electrode potential V _{OU T} of the capacitor 2 of the optical sensor incident light quantity is not at its maximum, as indicated by a dotted line in V _OUT in FIG. 1 (B), the reference potential V _REF and the discharge starting voltage V It has an intermediate potential to _INT .

When sufficient light does not enter the optical sensor, such as when the subject is far from the strobe light or when the ambient light is low in brightness, the voltage V of the optical sensor having the maximum amount of incident light is detected. _It takes a very long time for _OUT to reach the discharge start potential V _INT . Alternatively, the discharge start potential V
It may not reach _INT .

In such a case, the switch SW2 is opened and the switch SW1 is forcibly forced from the outside when a predetermined time elapses after the charging of the capacitor 2 is started.
To release the charging operation. For example, it is preferable to set the light emission time of the strobe to about 200 ms for the steady light and the strobe light emission time for the strobe light.

Next, the switch SW4 is opened and the switch SW5 is closed to apply the reference potential V _REF to the input V _{CMP of the} comparator 4. At this time, since the input V _OUT of the comparator 4 of each photosensor is higher than the reference potential V _REF , the output signal CMP of the comparator 4 becomes high. This state is shown by the dotted line of CMP in FIG.

The switch SW3 is closed, and the electric charge charged in the capacitor 2 is discharged by the constant current source 3. When the discharge is started, the positive electrode potential V _OUT of the capacitor 2 drops at a constant rate and eventually returns to the reference potential V _REF . When it becomes lower than the reference potential V _REF, the output signal CMP of the comparator 4 becomes low.

When the switch SW3 is closed and discharge is started, the counter 7 starts counting clock pulses CP at the same time. This count value is supplied to the latch circuit 5. The latch circuit 5 outputs the output signal C of the comparator 4.
Latch the count value when MP goes low.
The count value corresponding to this time corresponds to the charge amount charged in the capacitor 2 of each photosensor.

As described above, in the present embodiment, the charge charged in the capacitor 2 is discharged with a constant current and the discharge time is counted. Therefore, the light incident on the photodiode 1 is a stationary light or an unsteady light. Regardless of whether it is light or not, the actually accumulated charge amount is proportional to the count value.

Capacitor 2 of the above charge storage type photosensor
The electric charge stored in is very small. Therefore, in order to detect the accumulated charges with high sensitivity, a constant current source that allows a minute current to flow is necessary. Below is an example of the configuration of a constant current source for small currents.
This will be described with reference to FIGS.

FIG. 2 shows an n-channel MOS transistor 3
This is an example of a configuration in which individual devices are directly connected to form a CCD. When the switch SW3 is in an open state, it is in a low state, and when it is closed, it is in a high state. The potential V ₃ and the clock pulse CP are input to an AND circuit, and a logical product V _{TG of the} two
To form.

The drain of the transistor TR1 is connected to the positive electrode of the capacitor 2, and the transistors TR2, T
R3 is connected in series with the transistor TR1 in this order. The source of the transistor TR3 is connected to the constant potential V ₁ .

The output V _{TG of the} AND circuit is applied to the gate of the transistor TR1. Transistor TR2
A constant potential V ₂ intermediate between the reference potential V _REF and the constant potential V ₁ is always applied to the gate of the. The gate of the transistor TR3 is supplied with the pulse potential V _IG whose phase is delayed by about a half cycle with respect to the clock pulse CP.

3A to 3D show the transistor TR.
The potential figure of the channel region of 1-TR3 is shown. The shaded areas in the figure show that the electrons are full. The potential V ₂ ′ represents the potential of the channel region when the constant potential V ₂ is applied to the gate of the transistor TR2.

FIG. 3A shows the gate of the transistor TR3.
Pulse is applied to the_IGGoes high
Indicates the condition of the day. The source of the transistor TR3 is a constant voltage
Rank V ₁Connected to the energy level V₁Until
Full of electrons.

Therefore, the transistors TR3 and TR
Electrons are injected up to the channel region of 2. Since the gate potential of the transistor TR1 is low, electrons are not injected into the channel region of the transistor TR1.

FIG. 3B shows the state when the gate potential V _IG of the transistor TR3 returns to the low state. The potential well of the channel region of the transistor TR3 becomes high, and the electrons injected into the channel region of the transistor TR2 are isolated.

FIG. 3C shows a state when the clock pulse CP rises and the gate potential V _TG of the transistor TR1 becomes high. The potential well in the channel region of the transistor TR1 becomes deep, and the electrons isolated in the channel region of the transistor TR2 move to the drain region of the transistor TR1 having a deeper potential well. At this time, since the channel region of the transistor TR3 serves as a potential barrier, the transistor TR3
No new electrons are supplied from the source region of No. 3.

FIG. 3D shows the state when the clock pulse CP is in the low state. Electrons are not accumulated in the potential well of the channel region of the transistor TR2.

The amount of charge flowing in one cycle is equal to the amount of charge accumulated in the channel region of the transistor TR2. This charge amount is the constant potential V ₁ and the transistor TR.
It is defined by the difference in the potential V ₂ ′ of the _two channel regions.

In this way, a fixed charge moves in synchronization with the clock pulse CP, and a minute current flows in a pulsed manner. FIG. 3E shows a timing diagram of the output potential V ₃ of the switch SW3, the clock pulse CP, the gate potentials V _IG and V _{TG of} the transistors TR3 and TR1, and the minute current i (t).

The clock pulse CP supplied to the constant current source for the minute current and the counting clock pulse CP shown in FIG.
By synchronizing and, it is possible to obtain a digital value in which the amount of charge charged in the capacitor 2 by the photocurrent is quantized by the amount of charge that moves in one clock pulse. Note that even with such a pulsating current, a current having a constant amount of charge flowing in one cycle is referred to as a constant current in this specification.

FIG. 4 shows another configuration example of the constant current source for small current. A p-channel MOS transistor TR4 is connected in series to the small current constant current source shown in FIG. The drain of the transistor TR1 and the drain of the transistor TR4 are connected to the ground potential by a series circuit of the resistor 15 and the capacitor 16, and the potential divided by this series circuit is applied to the gate of the transistor TR4.

The p-channel MOS transistor TR5 and the n-channel MOS transistor TR6 are connected in series, and the source of the transistor TR6 is connected to the ground potential.

The gate of the transistor TR5 is connected to the gate of the transistor TR4 and constitutes a current mirror. The gate of the transistor TR6 is connected to the drain and operates in the saturation region.

The source of the n-channel MOS transistor TR7 is connected to the ground potential, and the gate thereof is connected to the gate of the transistor TR6 to form a current mirror.

Transistors TR1, TR2 and TR3
Is the same circuit as the constant current source for small current shown in FIG. 3, and has a pulsed current i (t) in synchronization with the clock pulse.
Shed. The drain current flowing through the transistor TR4 is i
_{If it is 4} , the gate potential of the transistor TR4 changes following the drain current i ₄ .

However, in the case of this embodiment, the capacitor 1 has the time constant defined by the resistor 15 and the capacitor 16.
Since 6 is charged and discharged, if the time constant is made larger than the cycle of the clock pulse, the gate potential of the transistor TR4 hardly changes. Therefore, the drain current i ₄ is almost constant regardless of time.

Assuming that the period of the clock pulse is T and the amount of charge moving in one period is Q, the drain current i ₄ is i ₄ =
Given by Q / T. For example, Q = 15fc, T = 1
When it is 5 μsec, i ₄ = 1nA.

The transistor TR5 is a transistor TR
Therefore, the drain current i ₅ of the transistor TR5 becomes a constant current proportional to the drain current i ₄ of the transistor TR4.

Drain current i of transistor TR6
₆ is equal to the drain current i ₅ of the transistor TR5. Therefore, the drain current i is applied to the transistor TR7 which forms a current mirror with the transistor TR6.
A drain current i ₇ proportional to ₅ flows.

Therefore, by appropriately setting the ratio of the channel length to the channel width of each of the transistors TR4 and TR5 (L / W ratio) and the L / W ratio of the transistors TR6 and TR7, the drain current i ₄ Can also obtain a minute desired minute current i ₇ .

For example, transistors TR4 and TR
5, or by setting the current magnification of the two current mirrors composed of the transistors TR6 and TR7 to 1/10, a minute constant current of drain current i ₇ = 10 pA is obtained when the drain current i ₄ = 1 nA. be able to.

Next, an embodiment in which the photosensors shown in FIG. 1 are arranged in an array to form an image sensor will be described. FIG. 5 shows an embodiment in which the photosensors shown in FIG. 1 are arranged in an array to form an image sensor.

The photoelectric conversion circuit 12 includes the photodiode 1, the capacitor 2 and the constant current source 3 shown in FIG. The photoelectric conversion circuit 12, the comparator 4, and the latch circuit 5 constitute one optical sensor shown in FIG.

Switches SW1 and S in the photoelectric conversion circuit 12
W2 and SW3 are signals S from the control circuit 9, respectively.
It is controlled by IG1, SIG2, and SIG3. The input V _CMP of each comparator 4 is supplied with the discharge start potential V _INT via the switch SW4 or the reference potential V _REF via the switch SW5.

The strobe circuit 11 and the timer 10 include
A signal SIG2 for controlling the switch SW2 is supplied from the control circuit 9. The strobe circuit 11 has a switch SW2.
The flash fires at the same time as when the open signal is received. Timer 1
0 starts timing at the same time as receiving the opening signal of the switch SW2, and sets the output T1 to the high state at the end of flash light emission.

The output CMP of each comparator 4 is input to the OR circuit 13 to form a logical sum OR1. Logical sum O
R1 and the output T1 of the timer 10 are input to the OR circuit 14 to form a logical sum OR2. The logical sum OR2 is input to the control circuit 9.

With this two-stage OR circuit, if the output CMP of the comparator 4 of one photosensor becomes high,
The ORs OR1 and OR2 are in the high state, and the control circuit 9 is notified.

If the subject is far away and a sufficient amount of light does not enter the optical sensor, the output T of the timer 10
1, and the logical sum OR2 becomes high, and the control circuit 9 is notified of the end of strobe light emission.

The control circuit 9 detects that the output CMP of the comparator 4 of one photosensor is in a high state or the end of strobe light emission, and opens the switch SW5 and closes the switch SW4 to input each comparator. The discharge start voltage V _INT is supplied to V _CMP .

Next, the switch SW3 closing signal is transmitted,
The discharge of the capacitor 2 of each photosensor is started. at the same time,
Generates a clock pulse for counting the elapsed discharge time.
The counter 7 receives the clock pulse from the clock generation circuit 6. Further, the switch SW3 control signal SIG3 is received from the control circuit 9. The counter 7 is a switch S
When the W3 closing signal is received, counting of the clock pulse CP is started, and the count value is supplied to each latch circuit 5.

The latch circuit 5 outputs the output C of the comparator 4.
When MP changes from the high state to the low state, the count value of the clock pulse CP supplied by the counter 7 is latched.

Therefore, this count value represents the time from when the capacitor 2 of each photoelectric conversion circuit 12 starts discharging until the potential of the positive electrode returns to the reference potential V _REF . The latch circuit 5 designated by the shift register 8 outputs the count value to the data bus BUS1.

In this way, the count value corresponding to the amount of light incident on each photosensor can be sequentially obtained. Although the present invention has been described above with reference to the embodiments, the present invention is not limited thereto. For example, it will be apparent to those skilled in the art that various modifications, improvements, combinations, and the like can be made.

[0091]

As described above, the charge storage type photosensor according to the present invention can obtain a digital value corresponding to the amount of incident light even with unsteady light such as strobe light.

Therefore, by arranging the charge storage type photosensors in an array to form an image sensor, it is possible to perform distance measurement using an unsteady light such as strobe light in an optical instrument such as a camera.

[Brief description of drawings]

FIG. 1 is a circuit diagram and a timing diagram of a charge storage type photosensor according to an embodiment of the present invention.

FIG. 2 is a circuit diagram of a constant current source for minute current according to an embodiment of the present invention.

3A and 3B are a potential diagram and a timing diagram for explaining the operation of the constant current source for small current of FIG.

FIG. 4 is a circuit diagram of a constant current source for minute current according to another embodiment of the present invention.

5 is a block diagram of an image sensor using the charge storage type photosensor shown in FIG. 1. FIG.

6A and 6B are a circuit diagram of a charge storage type photosensor according to a conventional example and a graph showing a change over time of a charging voltage due to stored charges.

[Explanation of symbols]

 1 Photodiode 2 Capacitor 3 Constant Current Source 4 Comparator 5 Latch Circuit 6 Clock Generation Circuit 7 Counter 8 Shift Register 9 Control Circuit 10 Timer 11 Strobe Circuit 12 Photoelectric Conversion Circuit 13, 14 OR Circuit 15 Resistor 16 Capacitor 50 Switch 51 Photodiode 52 Capacitor 53 Comparator

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI Technical indication H04N 5/232 J

Claims (9)

[Claims] 1. A series connection of a light receiving element that generates a photocurrent according to the amount of received light and a capacitor, means for applying a bias to the series connection, and means for charging the capacitor to a reference voltage before measuring the amount of received light. A switch means for terminating the charging operation for charging the capacitor with a photocurrent generated by the light receiving element, and a constant current source for discharging the electric charge accumulated in the capacitor by the photocurrent with a constant current. Photoelectric conversion circuit;
A comparison circuit that compares the terminal voltage of the capacitor with a determination voltage and generates a detection signal when they match; a counter that receives a clock pulse and starts counting at the same time when the discharge of the capacitor starts; Connected to the circuit and the counter, based on the detection signal of the comparison circuit,
A photometric device having a storage unit for storing the count value of the counter. 2. The photometric device according to claim 1, wherein the determination voltage of the comparison circuit is connected to the reference voltage. 3. A changeover switch, wherein a plurality of sets of the photoelectric conversion circuit, the comparison circuit, and the storage means are provided, and the reference voltage and a discharge start voltage higher than the reference voltage are selectively applied as a determination voltage of the comparison circuit. 2. The photometric device according to claim 1, further comprising: means and a control means for detecting a first detection signal of the plurality of comparison circuits and notifying the switch means of the end of the charging operation. 4. A plurality of sets of the photoelectric conversion circuit, the comparison circuit, and the storage means are provided, and the strobe is caused to emit light at the same time as the start of charging by the photocurrent of the capacitor, and the switch means is charged at the end of the strobe light emission. The photometric device according to claim 1, further comprising other control means for notifying the end of the operation. 5. A photometric method of charging a capacitor with a photocurrent according to the amount of light received by a light receiving element and measuring the amount of accumulated charge, a step of charging the capacitor to a reference voltage before measuring the amount of received light, and The device includes a step of irradiating an element with light and a step of charging the capacitor with a generated photocurrent, and a step of measuring a charge amount by discharging time while discharging a charge accumulated in the capacitor with a constant current. Photometric method. 6. The photometric method according to claim 5, wherein in the charge amount measuring step, the time until the voltage across the capacitor reaches the reference voltage is measured. 7. A charge storage type photosensor for charging a capacitor by a photocurrent according to the amount of light received by a light receiving element and measuring the amount of stored charge is arranged for each pixel, and the amount of light for each pixel is measured. In the image detection method for detecting an image, a step of charging the capacitors of the photosensors of all pixels to a reference voltage, and a step of charging the capacitors with a photocurrent generated by irradiating the light receiving elements of the photosensors of all pixels with light. An image having a charge end step of ending the charge operation of all pixels at the same time, and a charge amount measurement step of discharging the charge accumulated in each capacitor with a constant current and measuring the charge amount for each pixel by the discharge time. Detection method. 8. The charging ending step ends the charging operation when the charging voltage of the capacitor of the photosensor of the pixel receiving the maximum amount of light reaches the discharge starting voltage. Image detection method. 9. The image detecting method according to claim 7, wherein in the charging ending step, the charging operation is ended when the stroboscopic light emission is ended.