JP2610450B2 - Focus detection method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a static induction transistor (Static Inductor).
On-transistor (hereinafter simply abbreviated as SIT), a photoelectric conversion element capable of non-destructively reading out accumulated optical signal charges is used as a photo sensor so that focus detection can be performed with the minimum necessary integration time. Focus detection method.

[Conventional technology]

In general, in order to perform focus detection in an automatic focus control device such as a camera, a signal corresponding to the contrast of a subject is required. However, if the signal level is too low, noise and quantization errors due to A / D conversion are reduced. The effect becomes remarkable, which is not preferable. On the other hand, if this signal level is too large to exceed the dynamic range of A / D conversion, a correct detection signal cannot be obtained. Therefore, in order to perform accurate focus detection, it is necessary to control the integration time so that an output signal of an appropriate magnitude is obtained from the photo sensor regardless of the luminance of the subject.

In order to solve such a problem, in a conventional focus detection device using a photoelectric conversion element such as a CCD (Charge Coupled Device) as a photo sensor, once a signal is read out to confirm an output signal level, The integration time cannot be directly controlled by the output signal level of the photoelectric conversion element due to the destructive readout in which the signal charge stored until then is lost.

For this reason, conventionally, a separate photoelectric conversion element for monitoring the amount of light, for example, a photodiode is arranged in the vicinity of a row of photoelectric conversion elements such as a CCD for focus detection, and the output level of the photoelectric conversion element for monitoring is indirectly determined. Japanese Patent Laying-Open No. 57-64711 proposes a configuration in which the signal output of a focus detection photoelectric conversion element array is estimated and the integration time of the photoelectric conversion element array is controlled.

Japanese Patent Application Laid-Open No. Sho 59-140409 proposes a method of amplifying the output of a photosensor to increase the apparent integration time so that the focus is detected when the subject has low luminance. In this focus detection method, when the integration required to obtain a signal required for focus detection does not end within a predetermined time when the luminance is low, and the charge accumulation amount is lower than a predetermined value, the photo sensor is increased by one or more amplification factors. Focus detection is attempted by amplifying the output signal. This prevents the integration time from exceeding a predetermined time, prevents deterioration of responsiveness, and reduces the detection accuracy by amplifying the output signal of the photo sensor. We are trying to prevent it.

In JP 61-26016 discloses the integration time at a low luminance discontinued at predetermined time T _1, to determine the amplification factor of the photo sensor output signal by an output level of the monitor for a photoelectric conversion element at that time, Once the focus is determined, and if it is determined that the focus cannot be detected because the in-focus state cannot be obtained, a method of extending the integration time to T ₂ (> T ₁ ) and re-integrating again is used. Proposed.

[Problems to be solved by the invention]

By the way, as described above, the integration time is set for convenience depending on whether or not the output of the monitoring photoelectric conversion element separately provided in the vicinity of the photoelectric conversion element row such as a CCD has reached a predetermined reference value. In the conventional focus detection device described above, it cannot be said that a reasonable integration time is determined according to the state of the subject. For example, even for a subject having a high contrast and capable of focus detection even at relatively low luminance. In addition, since integration is continued until the output of the photoelectric conversion element for monitoring reaches a predetermined value, there is a disadvantage that it takes more time than necessary.

The disadvantage is that when the subject has high brightness, the integration time is originally short, so the effect is small when viewed from the overall time required for focus detection. In this case, this drawback becomes conspicuous and causes poor response and causes of camera shake.

Furthermore, this focus detection device requires a separate photoelectric conversion element for monitoring, a comparator for determining whether the output level of the photoelectric conversion element for monitoring has reached a reference value, a reference voltage generation circuit, and the like. However, there is a disadvantage that the circuit configuration is complicated and large.

In the case of the conventional focus detection method of amplifying the sensor output at low luminance, there is an irrationality that the amplification factor must be set according to the monitor output level instead of the sensor output level. In the focus detection method disclosed in the official gazette, once the amplification rate is set based on the monitor output level at a predetermined integration time, amplification is performed, and if the in-focus state still cannot be obtained, the integration time is extended. A wasteful and complicated operation of performing integration again is performed.

The present invention has been made in order to solve the above problems in the conventional focus detection method, and a photoelectric conversion element such as an SIT reads out a signal corresponding to the accumulated charge without destroying the accumulated photoelectric charge. Focusing on the fact that such a non-destructive photoelectric conversion element is used as a photosensor, focus detection can be performed with a reasonable integration time according to the state of the subject without using a photoelectric conversion element for monitoring. It is an object to provide a possible focus detection scheme.

[Means and actions for solving the problems]

In order to solve the above problems, a first invention of the present application is a non-destructive photoelectric conversion element array including a plurality of readable photoelectric conversion elements whose outputs correspond to the signal charges without destroying the accumulated optical signal charges, A / D conversion means for converting the analog output of the photoelectric conversion element array into a digital value, and focus detection calculation means for calculating the distance to the subject based on the digital output value of the A / D conversion means After a predetermined initial integration period T ₀ (T ₀ ≧ 0) has elapsed after the start of charge accumulation,
Non-destructive reading of output of the photoelectric conversion element array, A / D conversion,
The focus detection is performed by repeatedly executing a series of focus state detection operations of the focus detection calculation.

In order to perform focus detection in this manner, the signal corresponding to the accumulated photocharges up to each readout point is read nondestructively and A / D converted without interrupting the accumulation of photocharges. A series of operations of executing focus detection calculation based on digital signals are repeated until focus detection is completed, and without using a photoelectric conversion element for monitoring, it is necessary to make a rational decision according to the brightness and contrast of the subject. Focus detection becomes possible with a minimum integration time.

The second invention of the present application is also directed to a non-destructive photoelectric conversion element array composed of a plurality of readable photoelectric conversion elements capable of reading an output corresponding to a signal charge without destroying the accumulated optical signal charge, and an analog of the photoelectric conversion element row. Variable amplification means for amplifying the output according to the level of the output, A / D conversion means for converting an analog output from the variable amplification means to a digital value,
A focus detection calculating means for calculating a distance to a subject based on a digital output value of the A / D converting means, and a predetermined initial integration period T ₀ (T ₀ ≧ 0) elapses after the start of charge accumulation. After that, non-destructive readout of the output of the photoelectric conversion element row,
Focus detection is performed by repeatedly executing a series of focus state detection operations of A / D conversion and focus detection calculation of the non-amplified output, over a predetermined integration period T ₁ (T ₁ > T ₀ ) at low luminance. When the in-focus state cannot be detected, the output of the photoelectric conversion element array is amplified according to the level of the output, and focus detection is performed by repeatedly executing the above-described series of in-focus state detection operations. It is.

To do this way the focus detection, the effect of the first invention is conducted, while also exceeds a predetermined integration period T ₁ at low luminance focus state detection is impossible, the output of the photoelectric conversion element arrays, Amplification is performed at an amplification factor according to the level, and the above-described series of in-focus state detection operations are repeatedly executed, so that time loss due to re-integration in the conventional focus detection method can be prevented. Since the amplification factor is determined based on its own output, it is possible to determine the amplification factor rationally.

〔Example〕

Hereinafter, embodiments will be described. FIG. 1 is a block diagram of a configuration example of a focus detection device used for implementing a focus detection method according to the first invention of the present application. In the figure, 1 indicates a plurality of SIs.
This is an SIT image sensor provided with a line sensor composed of an array of T elements, and is configured so that light beams transmitted through a pair of lenses L ₁ and L ₂ are input. Note that, in this configuration example, the case where the focus detection method of the pupil division method is used is described.
L ₁ and L ₂ become unnecessary. 2 is a CPU, and the image sensor 1
Basic clock pulses phi ₀ for driving the _{non-destructive} read command signal phi _NDR the start of the reset signal phi _RESET accumulated photocharge source lines and the read transistors of SIT constituting each pixel of the line sensor, respectively S
It is configured to supply to the IT driver circuit 3. The driver circuit 3 supplies the SIT image sensor 1 with gate drive signals φ _G , a transfer pulse φ _T, and a read line reset pulse φ _R corresponding to readout, accumulation, and accumulated charge reset, which are drive signals for the SIT image sensor 1. Is supplied according to the control signal of CPU2,
The clock pulses phi ₁ for driving the scanning circuit 4 scanning start pulse phi _ST are supplied for scanning circuit 4. From the scanning circuit 4, a pulse φ _S1 for sequentially selecting output lines of the SIT image sensor 1,
φ _S2 ,... φ _Sn are supplied.

SIT image sensor 1 supplies an output signal V _OS of the output circuit corresponding to the accumulated charge of each pixel SIT of SIT image sensor 1 with respect to A / D converter 5. The SIT driver circuit 3 supplies the A / D converter 5 with a signal φ _AD indicating the dimming of the A / D conversion. The A / D converter 5 supplies the CPU 2 with the signal φ _AD of the SIT image sensor 1. Output signal of output circuit V _OS
, And a signal RDY indicating that the A / D conversion has been completed is supplied.

The lens drive circuit 6 is a circuit for rotating the motor 7 in accordance with the subject distance information calculated by the CPU 2 to drive the taking lens. The lens ROM 8 is built in the lens barrel, and stores data necessary for focus detection, such as the F number of the lens and a conversion coefficient for obtaining a defocus amount from an image shift amount. The display device 9 is a device that indicates whether the object is in focus or out of focus.

Normally, it is necessary to detect the distance to the subject and feed back the movement amount of the lens to the CPU 2 when driving the taking lens based on the distance. However, the rotation amount of the lens driving motor 7 is used as the movement amount of the lens. Is generally used, and the light emitting diode 10 and the phototransistor 11 in this configuration example are used for this purpose. That is, when the lens driving circuit 6 operates and the motor 7 rotates, the slits 12 provided at equal intervals in the rotating member of the lens barrel rotate, and the light emitting diode for rotation detection is sandwiched between the slits 12. The photointerrupter, consisting of the phototransistor 10 and the phototransistor 11 facing each other,
It counts 12 numbers. Then, the CPU 2 stores the count number of the slit 12 in the memory, and stops the rotation of the motor 7 when the count reaches a predetermined amount.

Next, the configuration of the SIT image sensor 1 having a line sensor composed of the pixels SIT and its readout circuit will be described with reference to FIG.

In FIG. 2, reference numerals 20-1,..., 20-n denote pixel SITs forming a line sensor, and each SIT has a configuration as shown in FIG. That is, 101 is an n ⁺ silicon substrate acting as a drain of the SIT, and an n ⁻ epitaxial layer 102 serving as a channel region is deposited on the substrate 101.
A shallow n ⁺ source region 103 is formed in the epitaxial layer 102, and the source region 103 is
In 02, it is surrounded by a p ⁺ gate region 104. A MOS capacitor 105 is formed on the gate region 104, and a pulse is supplied through the capacitor 105. When the gate region 104 is reverse-biased, a depletion layer is formed outside the gate region 104. When light is incident on the depletion layer to generate a hole-electron pair, electrons are swept out to the source region 103 and the drain region 101, and holes are accumulated in the gate region 104.
Therefore, the gate potential increases, and the current between the drain region 101 and the source region 103 is modulated by the change in the gate potential, so that a signal amplified depending on light is obtained. In the drawing, reference numeral 106 denotes a separation area for separating each pixel.

When the SIT configured as described above is used as a pixel of a line sensor, the potential applied to the gate via a capacitor provided in the gate unit accumulates the photocharge, reads and accumulates a signal corresponding to the accumulated photocharge. The photo charge can be reset.

Returning to FIG. 2, the pixels SIT20-1, 20-2,.
Each gate of n is be connected to the line 25 through the capacitor, the gate input signal phi _G is adapted to be applied. On the other hand, each source has a source line 26-1, 26-2, ...
.., 22-n via transfer switches 21-1, 21-2,..., 21-n each comprising a MOS transistor. _Are commonly connected to a power supply VD. The source lines 26-1, 26-2,..., 26-n are connected to the drains of reset transistors 24-1, 24-2,. Transfer switches 21-1, 21-2, ..., 21-n
To the gates of the MOS transistors forming it is designed so as the transfer pulse phi _T is applied readout pixel SIT20-1,20-2 at integration end, the source potential of the ...... 20-n transistor 22- 1, 22-2,..., 22-n, and source lines 26-1, 26-2,.
When n is reset, the transfer switches 21-1, 21-2,
...... Turn on 21-n, and set the read transistors 22-1,
22-2, ..... Reset transistor 24 up to the gate of 22-n
, 24-2,..., 24-n. Reset transistors 24-1, 24-2, ..., 24-n
Source is grounded, the gate is configured to reset pulse phi _R is applied.

Read transistor 22-1 and 22-2, the drain of the ...... 22-n is connected to the power supply AV _DD, the source pixel selection switch 23-1 and 23-2, ...... 23-n and the pixel output read line A source follower circuit is formed with the load resistor _RL via the reference numeral 27. Pixel selection switches 23-1, 23-2, 23
Each gate of -n is connected to the scanning circuit 4 so that a scanning pulse for selection φ _S1 , φ _{S2 ,.}

Next, the operation of the focus detection system using the focus detection device shown in FIGS. 1 and 2 will be described with reference to the waveform diagrams showing the signal timings in FIG.

In the reset period T _RS shown in FIG. 4, the gate input signal φ _G becomes the reset level V _RS (> φ _B : built-in voltage between the gate and the source) and the reset pulse φ
When _R and transfer pulse phi _T becomes High level,
Pixel SIT20-1,20-2, the source potential V _S of ...... 20-n is reset to GND, the gate potential V _G becomes phi _B.

After the reset period _TRS ends, the first and second and subsequent integration periods T _INT1 , T _INT2 ,... Enter the gate input signal φ _G ,
Reset pulse phi _R, the transformer § pulse phi _T becomes GND level, the gate potential V _G becomes a reverse bias state given by the following equation (1), the start of optical integration.

Where C _G : SIT gate capacitor capacitance C _J = C _GS + C _GD C _GS : SIT gate-source parasitic C _GD : SIT gate-drain parasitic capacitance First, the first light integration period T _INT1 During this time, the charge Q _Ph (T _int1 ) generated by light irradiation is accumulated in the gate capacitance (C _G + C _J ) and is expressed by the following equation (2).

Q _Ph (T _int1 ) = _GL · A · P · T _int1 = _GL · A · E (2) where _GL is the generation rate (μA / μW) and A is the light receiving area (c
m ² ), P is irradiance of light (μW / cm ² ), T _int1 is integration time (sec), and E is exposure amount (E = P · T _int1 ).

The gate potential V _G is (1) and (2), Becomes

At time T _int1 , the first integration period T _INT1 ends,
When entering the reading period T _RD1 of the first pixel SIT is then gate input signal phi _G is read level V _RD, and the gate potential V _G is Becomes

However, the read level V _RD is set so that the output signal of the expression (6) described later is positive or 0 when Q _Ph = 0.

At this time, the potential between the gate and source of the pixel SIT is V
_GS is (are V _P is referred to as is the pinch-off voltage the potential difference between the gate and the source starts to flow the drain current of the pixel SIT.) V _GS> V _P, and therefore, the flow the drain current of the pixel SIT, the source line 26 -1,26-2,..., Charge the stray capacitance of 26-n. This charging continues until V _GS = V _P. Therefore, the source potential V _S becomes Becomes At this time, the transfer pulse φ _T
Is also at the high level, so the transfer switch
21-1 and 21-2, via the ...... 21-n, the source potential V _S is transmitted to the gate of the read Toranjisusuta 22-1,22-2, ...... 22-n.

Then read Toranjita 22-1 and 22-2, the gain of the source follower constituted by ...... 22-n and the load resistor R _L a (<
1), transfer switches 21-1 and 21-2, the efficiency of the ...... 21-n b, when the threshold voltage of the MOS transistors of the output circuit of the source follower and V _T, the light which is accumulated in each pixel SIT charge _{Q phi (i = 1, ......} n) output signal V _OSi represented by the following formula corresponding to (6), the selection pulse phi _S1 outputted from the scanning circuit 4, phi _S2, by ...... phi _Sn When the pixel selection switches 23-1, 232,..., 23-n are turned on sequentially, the output is successively performed for each selected pixel.

At this time, the source lines 26-1, 26-2,..., 26-n of the pixels SIT20-1, 20-2,..., 20-n and the readout transistors 22-1, 22-2,. The gate of the pixel SIT20−
1,20-2,..., The pixel is charged with a drain current of 20-n
Since the optical signal charges accumulated in the gate of the SIT are retained, the readout is performed nondestructively. When the transfer pulse phi _T and the reset pulse phi _R simultaneously High level while the read after the gate input signals φ _{G =} 0, accumulated in the gate of each pixel in timing SIT20-1,20-2, ...... 20-n The generated photocharges are not reset, and the source lines 26-1, 26-2,.
Only 1,22-2, ... 22-n are reset.

The output signal V _OS obtained as described above is subjected to A / D conversion and then input to the CPU 2, where focus detection calculation processing is executed, and focus detection is performed. If focus is achieved at this point,
The lens is driven via the lens driving circuit 6 according to the defocus amount obtained by the arithmetic processing.

If the in-focus state is not detected at the time of the first reading, the operation steps of the second reading, A / D conversion, and focus detection calculation are started. In the second reading time T _int2, but is initiated by a level V _RD read gate input signal phi _G a transfer pulse phi _T High level, first time read performed in non-destructive reading manner , 20-n, the integration of the optical signal charges is continued even during the readout period, and therefore, the integration period T in the second readout.
_INT2 is from the start of the first integration to the time _Tint2 .

The second readout period T _RD2 includes the second integration period
An output signal corresponding to the optical signal charge that has increased from the first time stored in _TINT2 is read nondestructively. Then, an in-focus state detection operation is performed based on the increased output signal. Hereinafter, the above-described series of operations is continued until the in-focus state is detected.

Next, an algorithm of a focus detection example using the configuration example shown in FIGS. 1 and 2 is shown in a flowchart of FIG. In this focus detection example, after a predetermined initial integration time T ₀ (T ₀ ≧ 0) has elapsed after the start of integration for focus detection, non-destructive readout → A / D conversion → focus detection calculation → focus determination A series of operations is repeated until focusing is achieved. That is, if the determination is negative in the focusing determination step, the process returns to the non-destructive reading step.

Then, as this series of operations is repeated from the start of integration, the accumulated charge amount increases, and a focus state is detected at a point in time when the level exceeds a minimum level of a focus detectable signal determined by luminance and contrast of the subject. Then, at the time of focusing, focusing display is performed, and the lens is driven according to the obtained defocus amount. It should be noted that the integration time T _int is too long, because that usually causes of camera shake, integration time T _int
For previously set upper limit T _max for example 200 msec, it can not be obtained determination of focus even after the integration control time T _max is adapted to display a focus undetectable.

A conventional focus detection method that determines the integration time by comparing the light intensity monitor output with a predetermined reference value.The reference value does not depend on the brightness or contrast of the subject, and the dynamic range of the A / D converter and the saturation of the photoelectric conversion element The voltage is set to a constant value. Therefore, it cannot be said that the integration time is optimal for various states of the subject. This disadvantage has a significant effect particularly when a low-luminance subject is targeted. That is, even when the focus can be detected with a relatively high integration time and a relatively short integration time even at a low luminance, useless integration time occurs in which integration is continued until the monitor output reaches a predetermined reference value. Is a rational focus detection method that integrates only the time required for focus detection.
Generation of useless integration time as in the related art is reliably avoided.

FIG. 6 is a block diagram showing one configuration example of a focus detection device used for implementing the focus detection method according to the second invention of the present application. This configuration example is obtained by adding to the configuration example used for the implementation of the first invention shown in FIG. 1, the amplification factor control circuit 13 for amplifying the output signal V _OS of SIT image sensor 1 at the time of low luminance. As shown in FIG. 7, this amplification factor control circuit 13
An input terminal 14 to the output signal V _OS of SIT image sensor 1 is supplied, an output terminal 15 connected to the A / D converter 5, CPU 2
Input terminals 16-1, 16- of the amplification factor control signals AMP1, AMP2
2 is provided. Between the input terminal 14 and the output terminal 15, a circuit via only the analog switch SW1, a circuit via the amplifier circuit 17-1 with an amplification factor of 2 and the analog switch SW2, and a circuit via an amplification circuit 17-2 with an amplification factor of 4 And analog switch SW
3 is connected to an amplifier circuit 17-3 having an amplification factor of 8 and a circuit via an analog switch SW4. One gain control signal input terminal 16-1 is connected to an AND
One input terminal of the circuits 19-1 and 19-3 is connected to the inverter 18
-1 is connected to one input terminal of each of AND circuits 19-2 and 19-4, and the other gain control signal input terminal 16-2 is connected to the other of the AND circuits 19-1 and 19-2. And AND circuits 19-3 and 19 via an inverter 18-2.
-4 are connected to the other input terminals. .., And SW4 are controlled by outputs of the AND circuits 19-1,..., 19-4.

If the in-focus state cannot be detected for more than a predetermined time described later at low luminance, the CPU 2 determines the image expansion rate according to the level of the output signal of the SIT image sensor 1,
Supply the amplification factor control signals AMP1 and AMP2 to the amplification factor control circuit 13, and use the control signals AMP1 and AMP2 to control the amplification factor control circuit 13.
In, a predetermined analog switch is selected and the CPU 2
An amplification circuit having a predetermined amplification rate determined by the above is inserted. As a result, the output signal V _OS of the SIT image sensor 1 is amplified at a predetermined amplification rate and output as an output signal V _OS ′. Table 1 shows the output terminals a, of the AND circuits 19-1,..., 19-4 for the combinations of the levels of the amplification factor control signals AMP1, AMP2.
The levels of b, c, and d and the amplification factor of the amplification factor control circuit 13 are shown.

Focus detection is performed as follows using the focus detection device configured as described above. First, after the start of integration, focus detection is performed by repeatedly executing a series of focus state detection operations of non-destructive readout of the output of the pixel SIT, A / D conversion, and focus detection calculation, as in the first invention. In the second invention, the in-focus state detection operation is repeatedly performed, and even if a predetermined integration time T ₁ within the integration limit time T _max , for example, 100 msec, the focus state is determined because the subject has low luminance. If is not, to determine the amplification factor of the CPU2 output signal in response to the level of the output signal V _OS of SIT image sensor 1, the amplification factor control signal AMP1, AMP
2 is output to the amplification factor control circuit 13.

As a result, in the amplification factor control circuit 13, an amplification circuit having a predetermined amplification factor is set, the output signal V _OS of the SIT image sensor 1 is amplified, and similarly based on the amplified output signal V _OS ′, the amplification is performed. The focus state detection operation is repeatedly performed to perform focus detection. Also in this case, if the in-focus state cannot be detected even after the integration limit time _Tmax has been exceeded, it is determined that the focus cannot be detected.

FIG. 8 is a flowchart showing the algorithm of the focus detection example of the second invention. In this focus detection example, first, the amplification factor of the amplification factor control circuit 13 is set to 1 and integration is started.
Once the initial integration time T ₀ elapses, reading nondestructive output pixel SIT, A / D conversion of the output is not amplified, focus determination is performed by the focus detection operation is performed. When the in-focus state is obtained, the in-focus state is displayed, and the lens is driven according to the obtained defocus amount.

When the in-focus state cannot be determined in the first in-focus state detecting operation, low luminance and the integration time T _int are equal to the predetermined time T ₁ (100 ms
If the condition exceeding c) is not satisfied, the in-focus state detecting operation is repeatedly executed until the in-focus state detection operation is obtained until the integration limit time _Tmax is reached with the amplification factor being 1.

On the other hand, if and integration time T _int of low intensity satisfies a condition that exceeds a predetermined time T ₁ is determined a predetermined amplification factor based on the output signal level by the CPU 2, a non-destructive read output signal is amplified The in-focus state detection operation is repeatedly executed until the in-focus state is obtained similarly. In any case, when the in-focus state cannot be determined even after the integration limit time has elapsed, a display indicating that the focus cannot be detected is displayed.

The reasons for the inability to detect the focus are as follows: (1) it is impossible to make an accurate judgment because the signal level is sufficient but there is no contrast; and (2) it is not possible to make an accurate judgment because the signal level is low due to low luminance. In the case (2), it is effective to amplify the output signal as described above. However, in the case (1), the amplification may exceed the range of the A / D converter. Therefore, the maximum value of the output signal of the pixel SIT is determined by the CPU, and the magnitude of the output signal is determined based on the maximum value, and the amplification magnification is determined along with the determination. These determinations are performed together with the focus determination, and the maximum value of the output signal is determined by comparing the first data and the second data, and the larger one is set as V _OSmax, and then the V _OSmax and the third data are set. And it is obtained that the larger one is set again as V _OSmax by repeating the processing up to the n-th.

FIG. 9 is a diagram showing an example of the relationship between the brightness of the subject and the integration time. The output signal of the pixel SIT (500 mV in this example) is shown in FIG.
By performing amplification of 2, 4, and 8 times, the luminance range of the subject in which a predetermined output level can be obtained within the integration limit time T _max is set to 3 times.
This shows an aspect that can be extended to the low luminance side over stages.

In the conventional focus detection method that amplifies the output signal, the amplification rate is determined based on the monitor output level, and the focus is determined once.
When focus cannot be obtained at low brightness, the integration time is extended and integration is performed again.
In the present invention, since the non-destructive readout mode is used using a photoelectric conversion element capable of nondestructive readout, there is no waste of re-integration, and the amplification factor is not a monitor output but a sensor output rather than a monitor output. Is set rationally based on

Note in the above example each component used in the practice of the present inventions, each termination nondestructive readout, and the reset pulse phi _R to the High level, showed that configured to reset the readout circuit, a non-destructive read end Even if the readout circuit is not reset every time, the nondestructive readout of the signal output can be repeatedly executed in the same manner.

Further, in each of the above configuration examples, the SIT is used as the non-destructively readable photoelectric conversion element.
International Electron Devices Meeti
ng (IEDM) Proceedings, pages 353-356, “A NEW MOS IMAG
E SENSOR OPERATING IN A NON−DESTRUCTIVEREADOUT MO
CMD (Charge Modulat) shown in a paper entitled "DE"
ing Device) A light receiving element can be used instead of the SIT. This CMD light receiving element has an amplifying function for each pixel similarly to the SIT and is a non-destructive readout light receiving element.
The same operation and effect as when T is used can be obtained.

〔The invention's effect〕

As described above based on the embodiments, the present invention
Using a non-destructive readable photoelectric conversion element such as T or CCD as a photosensor, reads out the output signal depending on the accumulated charge without destroying the accumulated charge, and focuses on a series of A / D conversion and focus detection calculations. Since focus detection is repeatedly performed until the state detection operation is focused, the photoelectric conversion unit for monitoring is not required, and focus detection is performed with a minimum necessary and reasonable integration time according to the state of the subject. Can be. Also, when amplifying the output of the photoelectric conversion element for the sensor at the time of low luminance, the amplification factor can be rationally determined by the output of the photoelectric conversion element for the sensor itself.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an example of a configuration of an apparatus used for implementing a focus detection method according to the first invention of the present application, and FIG.
FIG. 3 is a circuit configuration diagram showing the SIT image sensor and its readout circuit shown in FIG. 1, FIG. 3 is a schematic sectional view showing the structure of the SIT, and FIG. 4 is a diagram showing the device shown in FIGS. FIG. 5 is a signal waveform diagram for explaining the focus detection method used, FIG. 5 is a flowchart showing an example of an algorithm of the focus detection method of the first invention, and FIG. FIG. 7 is a block diagram showing an example of a configuration of a device used, FIG. 7 is a diagram showing a configuration example of an amplification factor control circuit of the device shown in FIG. 6, and FIG. 8 is an algorithm of a focus detection method according to the second invention. FIG. 9 is a flowchart showing an example of
FIG. 4 is a diagram illustrating an example of a relationship between luminance of a subject and integration time. In the figure, 1 is a SIT image sensor, 2 is a CPU, 3 is SI
T driver circuit, 4 is a scanning circuit, 5 is an A / D converter, 6 is a lens drive circuit, 8 is a lens ROM, 9 is a display circuit, 10 is a light emitting diode, 11 is a photodiode, 12 is a slit,
13 is an amplification factor control circuit, 20-1, 20-2,..., 20-n are pixels SI
Indicates T.

Claims (2)

(57) [Claims] 1. A non-destructive photoelectric conversion element array comprising a plurality of readable photoelectric conversion elements capable of reading an output corresponding to a signal charge without destroying an accumulated optical signal charge, and an analog output of the photoelectric conversion element row. A / D conversion means for converting to a digital value, and focus detection calculation means for calculating the distance to the subject based on the digital output value of the A / D conversion means, and Initial integration period T ₀ (T ₀ ≧
0), focus detection is performed by repeatedly executing a series of in-focus state detection operations of non-destructive reading of output of the photoelectric conversion element array, A / D conversion, and focus detection calculation. Detection method. 2. A non-destructive photoelectric conversion element array comprising a plurality of readable photoelectric conversion elements capable of reading an output corresponding to a signal charge without destroying an accumulated optical signal charge, and an analog output of the photoelectric conversion element array. Variable amplification means for amplifying according to the level of the output, A / D conversion means for converting an analog output from the variable amplification means to a digital value, and a digital output value of the A / D conversion means. A focus detection calculating means for calculating a distance to a subject, and after a predetermined initial integration period T ₀ (T ₀ ≧ 0) has elapsed after the start of charge accumulation, non-destructive output of the photoelectric conversion element array is provided. The focus detection is performed by repeatedly executing a series of focus state detection operations of A / D conversion of the output which is not read out and amplified and focus detection calculation, and a predetermined integration period T ₁ (T ₁ > T ₀ ) at low luminance. If the focus state cannot be detected even if the Was amplified in accordance with the output of 換素Ko column to the level of output, the focus detection system and performs the focus detection by executing repeatedly the series of in-focus state detecting operation.