JPS61274475A - Electronic still camera - Google Patents

Abstract

PURPOSE:To obtain a reproduced picture with wide dynamic range and excellent picture quality by increasing the electric charge storage capacity of a photodetection storage section in the process from the shutter opening until closing point without reduction and giving sensitivity to a light signal with a wide range of intensity. CONSTITUTION:When a shutter opening time Tint is stored to a setting circuit 3, a clock pulse generating circuit 4 generates a clock pulse of a period T=Tint/ N (N is a positive integer). A control pulse generating circuit 5 receives the said clock pulse and a start pulse from a terminal 6 and is operated to count the clock pulse. A control voltage VG1 is fed to a control electrode 15 during a period from the count M (M is a positive integer and smaller than N) and a control voltage VG2 (VG2<VG1) is fed to the control electrode 15 during the period of the count from M+1 to N. When the voltage fed to the electrode 15 changes from the VG1 to the VG2, the charge storage capacity of the photo diode 11 is increased from Q1 to Q2 (Q2>Q1).

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to electronic still cameras, particularly those using solid-state image sensors.

[Technical background of the invention and its problems]

Electronic still cameras using solid-state image sensors are widely known. In this camera, a solid-state image sensor in which photosensitive pixels are arranged two-dimensionally is placed in the silver halide film portion of an ordinary camera, and image signals obtained from the sensor are recorded on a magnetic disk or the like. That is, an optical image of a subject is formed on a solid-state image sensor by an optical system, and the solid-state image sensor generates a signal charge according to the optical signal. This signal charge is generated during the shutter open period. When the shutter is closed, the signal charge is read out and transferred,
After predetermined signal processing, the signal is recorded on a magnetic disk or the like.

The brightness of the subject of an electronic still camera is usually 10 to 1.
It varies over a wide range of about 0.06. In contrast, the dynamic range of a typical solid-state image sensor is about 103. Therefore, in order to obtain an appropriate image of the subject, it is necessary to adjust the shutter opening time and the aperture group of the lens so that the image signal of the subject is obtained between the noise level and the saturation level of the solid-state image sensor. Must be.

FIG. 12 of the accompanying drawings is a photoelectric conversion characteristic diagram of the solid-state image sensor, in which the horizontal axis represents the amount of incident light and the vertical axis represents the signal output voltage. As shown in the figure, when the noise voltage of the solid-state image sensor is 8 and the saturation voltage is Vs, the dynamic range is V/8. Now, if we assume that the dynamic range of the solid-state image sensor is 103 and set the exposure conditions so that the average signal voltage of the subject is 100 ■o, then parts of the subject that are 10 times brighter than the average will be resolved by saturation. I can't. Furthermore, even if a reasonable image can be obtained for an object portion with a brightness of 1710 times or less, the S/N ratio will not be good. Therefore, the practical level at which the brightness and darkness of a subject can be resolved is about 100.

Furthermore, the shutter time and lens aperture settings are not always performed appropriately. For example, if there is an error of 2 times or 172 times in the exposure setting, the image will not be good in many cases. Unlike a video, a camera image is a single still image, so if the dynamic range is narrow as described above, its practicality will be significantly reduced.

[Purpose of the invention]

The present invention has been made to overcome the above-mentioned drawbacks of the prior art, and an object of the present invention is to provide an electronic still camera that has a wide dynamic range and can obtain bidirectional images of good quality.

[Summary of the invention]

In order to achieve the above object, the present invention reduces the charge storage capacity of a light reception storage section that generates and stores signal charges in response to a light signal from a subject in the process from the time when the shutter is opened to the time when it is closed. The objective is to provide an electronic still camera that is sensitive to a wide range of strong optical signals.

[Embodiments of the invention]

Hereinafter, some embodiments of the present invention will be described with reference to FIGS. 1 to 11 of the accompanying drawings. In addition, in the description of the drawings, the same elements are given the same reference numerals.

FIG. 1 is a block diagram showing the configuration of one embodiment, in which the shutter opening time is predetermined according to the illuminance measured by an exposure meter or the like. The solid-state image sensor 1 is driven by a drive circuit 2. The shutter time setting circuit 3 is for setting the shutter opening time "int" of the camera, and the clock generating circuit 4 is for generating a clock pulse having a pulse width corresponding to the shutter opening time "int". The control pulse generation circuit 5 operates upon receiving the clock pulse from the clock generation circuit 4 and the shutter operation signal, ie, the start pulse, from the terminal 6, and outputs the υIt[l pulse. Solid-state image sensor 1
An optical image of a subject is formed through an optical system and a shutter (not shown), and signal charges corresponding to the optical signals are generated and accumulated. After this signal charge is processed by the signal processing circuit 7, it is sent to the recording section 8 and recorded on a magnetic disk or the like.

FIG. 2 is a sectional view of a part of the interline transfer type solid-state image sensor used in the embodiment shown in the first factor. P
The type semiconductor substrate 10 includes an n-type impurity diffusion region tff111 that forms a photodiode for converting and storing optical signals into electrical signals, an n-type impurity region 12 that forms a drain for discharging excess charge, and a buried n-type impurity region 12 that forms a drain for discharging excess charge. An n-type impurity region 13 forming a deep channel is provided. The surface of the semiconductor substrate 10 is insulated 1t! It is covered with (Si02) 14, and a control electrode 15 and a transfer electrode 16 are formed thereon.

The control electrode 15 is connected from the photodiode 11 to the drain 12.
It is connected to the control pulse generation circuit 5 shown in FIG. 1. The transfer electrode 16 cooperates with the buried channel 13 to read and transfer signal charges, and constitutes a so-called vertical COD. This vertical C
The signal charges transferred to the OD are sent to the horizontal COD (not shown), and are transferred to the signal processing section 7 in synchronization with the clock from the drive circuit 2 shown in FIG. In addition, photo j ~ diode 11
The other parts are covered with a light shielding film 17, so that the optical signal from the subject reaches only the photodiode 11 part.

Next, the functions of each component of the embodiment shown in FIGS. 1 and 2 will be explained with reference to FIGS. 3 to 6. FIG. 3 shows the voltage value of the control pulse applied from the control pulse generation circuit 5 of FIG. 1 to the control electrode 15 of FIG.
FIG. 3 is a characteristic diagram showing the relationship between count values of pulses from First, the illuminance of the optical signal from the subject is measured by a not-shown exposure meter or the like, and the lens aperture and shutter opening time 'int' are determined based on this. This shutter opening time Tint is set and stored in the shutter time setting circuit 3. The operation of a shutter (not shown) is controlled by this setting circuit 3 or by another configuration. In this embodiment, the control electrode 15 is adjusted according to the shutter opening time.
Since the applied voltage is controlled, the shutter opening time is
It is an essential requirement of this embodiment that int be stored in the setting circuit 3.

When the shutter opening time Tint is stored in the setting circuit 3, the clock pulse generation circuit 4 has a period of TT, ot/N.
(N: positive integer) clock pulses are generated.

The control pulse generating circuit 5 operates upon receiving this clock pulse and the start pulse from the terminal 6, and counts the clock pulses. Then, during the period until the count value reaches M (MG, the main integer smaller than tN), a control voltage of 61 is applied to the control electrode 15, and the count value changes from M+1 to N.
Naruma Teno Period Ha■6□ (MG2〈v61) at
A pressure is applied to the m electrode 15. The waveform of such a control pulse is shown in FIG.

The voltage applied to the control IM pole 15 is V. When changing from 1 to v62, the charge storage capacity jlG of the photodiode 11
, tQ1 increases to 02' (Q2 > Ql). This is because the potential well of the photodiode 11 becomes substantially deeper, and this situation is illustrated in FIGS. 4 and 5.
As shown in the figure. Figure 4 shows the first diode 11 (
T in the control pulse generation circuit 5
This is a characteristic diagram showing the relationship between the count values of clock pulses of =T and nt/N, and FIG. 5 is an explanatory diagram of a potential well near the photodiode 11. As shown in FIG. 5, when the control tII voltage changes from V61 to MG2, the charge storage capacity of the photodiode 11 changes from Ql to Q2.

Therefore, the charge storage capacity changes as shown by the thick polygonal line L1 in FIG.

Next, a specific operation when photographing an image of a subject will be explained.

Before a shutter (not shown) is opened to photograph a subject, a predetermined voltage is applied to the drive circuit 2, shutter time setting circuit 3, clock generation circuit 4, control pulse generation circuit 5, signal processing circuit 7, and recording section 8. and the operation starts.

Furthermore, the solid-state image sensor 1 completes preparations for receiving the image of the subject.

At the same time as the shutter is opened, a start pulse (shutter operation signal) is applied to the terminal 6, and thereby a control voltage 61 is applied to the control a electrode 15. Further, the clock generation circuit 4 generates a clock pulse having a period of T-T, t/N, and this clock pulse is counted by the control pulse generation circuit 5.

The elapsed R interval t from the shutter opening point (1=0> is Q<
When t<MT, the control voltage is ■. 1, the charge storage capacity a is Ql. When the illuminance of the subject at a certain photodiode 11 is low (the increase rate of the accumulated signal charge is the fourth
When it is below the straight line 11 in the figure, the charge will not pass under the limiting WZ pole 15 and be discharged to the drain 12. However, when the increase rate is higher than the straight line f11 and is like a broken straight line 12 (when the illuminance is high), the excess charge is treated as excess charge after the accumulated charge transfer reaches 01 as shown in Fig. 5 (C
) is discharged to the drain 12.

When the elapsed time t from the time of shutter opening is t=MT, the count value of the control pulse generation circuit 5 is M1. :
12, therefore the control voltage decreases from V61 to MG2'
The charge storage capacity increases from Ql to 02.

Therefore, during mti where MT<t<NT, charge is accumulated even when the rate of increase in accumulated charge is equal to or higher than straight line 11 in FIG. 4 (when the illuminance is high). Figure 5 (d
) shows this situation.

l! 13tWhen the count value of the pulse generation circuit 5 reaches N, the elapsed time from the shutter opening is t-NX (T/N>=Tio.

nt, the shutter is closed. Therefore, the generation of the signal charge ends, and the accumulated charge (2) at that time becomes image data and is read out by the transfer electrode 16.

The above operation can be summarized as follows. That is, in the photodiode 11 where the illuminance from the subject is low and the rate of increase in the accumulated charge a is less than the straight line 11 in FIG. 4, the signal charge amount Qsig when the shutter is closed is proportional to the illuminance (2).

When the illuminance from the subject is high, the rate of increase in accumulated charge is the straight line in Figure 4! In the photodiode 11 between J1 and the broken straight line 12, the signal charge M Q when the shutter is closed is
sig is a value obtained by adding a signal charge with effectively low sensitivity to Ql. Further, in the photodiode 11 where the illuminance from the object is quite high and the rate of increase in the accumulated charge amount is equal to or higher than the straight line 12 in FIG. 4, the signal charge amount Qsig becomes equal to the signal charge amount Qsig when the shutter is closed.

Here, if M/N=415 and Q2/Q1-2, the relationship between the signal charge IQS, g and the illuminance I when the shutter is closed is as follows: Q・=−T・・I (0≦I≦11 ) Sl
(1int Q ・ = −T・ ・I15+Q2/2sB
int (I≦■≦l2) Q・ =Q2 (I2≦1)1g. However, K is a constant, 11=5Q2/(-T in 8,
ot), l2=5Q2/ (2 to −T, o, ”).

The above photoelectric conversion characteristics are shown in FIG. Therefore, the output signal of the solid-state image sensor also has a knee characteristic similar to that shown in FIG. Note that the amount of light at which the signal charge is saturated is I ”int
(=502/2K), and the light intensity at the white point is I”
int (=5Q2/8K), and both do not depend on the shutter opening time "int".

Therefore, even if the shutter time is changed, the same knee characteristics can always be obtained, so the signal processing in the signal processing circuit 7 may be the same as conventional ones.

In this way, in the above example, M/N=415, Q/Q1
-2, the saturated light m becomes 12=502/ (2 to -"rnt), so it is possible to obtain a dynamic range 2.5 times that of the conventional example. Furthermore, M/N is brought closer to 1. , a larger dynamic range can be obtained.

The present invention is not limited to the above embodiments, and various modifications are possible. For example, as shown in FIG. 7(a), the knee characteristic may have a bending point at light amount - (illuminance) x (shiset ivy opening time) corresponding to the inclinations of lines l1Ij3, fJ4, and j5.

Furthermore, the storage charge capacity can be changed in a curved manner as shown in FIG. 7(b). Here, the curve L is Q (
It can be expressed as t/T, nt). The saturation light amount when Invention 3 (3) is not applied is QI(1)/(K・”1
nt), and the necessary condition to realize a dynamic range greater than this value is that the straight line j6 connecting the origin O and the point on the t-"int') curve L3 crosses the upper side of the curve L3 (point A -C).This is because the slope of the straight line 17 passing through the dot and touching the curve L3 between points A and C corresponds to the illuminance at saturation, which is greater than the slope of the straight line p6.

Furthermore, as shown in FIG. 7(C), the time when the shutter is opened (t=
Curve L4 such that the charge capacity is Ql(.)=O at
You may make it so that

FIG. 8 is a block diagram showing the configuration of another embodiment of the present invention, in which the shutter opening time is not predetermined. The light amount detector 20 detects the amount of incident light while the shutter is open, and an appropriate amount of light is set in advance. The clock pulse generation circuit 21 starts operating in response to a shutter operation signal (start pulse) from a terminal 22, and generates a clock pulse of a constant frequency. The control pulse generation circuit 23 has a function of counting clock pulses and a detection peak of the light amount detector 20 is 1/R (1/R) of the appropriate light amount.
However, until R > 1 (preset in advance) is reached, a constant potential control pressure is output, and after reaching 1/R of the appropriate light m, the potential becomes a function of (t/R・11>). It has a function of outputting a control voltage.However, tl is the time from when the shutter is opened until it reaches 1/R of the appropriate light amount.And,
The charge storage capacity of the photosensitive pixels constituting the solid-state image sensor 1 is controlled by this control m+ voltage.

FIG. 9 is a characteristic diagram showing the charge storage capacity of the photosensitive pixels constituting the solid-state image sensor of FIG. 8, and the operation of the embodiment shown in FIG. 8 will be explained with reference to this. When a shutter (not shown) is opened at time t=Q, a part of the optical signal incident on the solid-state image sensor 1 has its optical path changed by a half mirror or the like, and is sent to the light amount detector 20. At the same time, a start pulse is applied to the clock pulse generation circuit 21 via the terminal 22, and the clock pulses are counted by the control pulse generation circuit 23. In addition, a predetermined value of the control WZ pressure is sent from the control pulse generation circuit 23 to each photosensitive pixel of the solid-state image sensor 1, thereby increasing the charge storage capacity to a QC (constant value).
is maintained.

After the detection light aperture becomes 1/R of the appropriate light amount with 1=11,
A control pulse generating circuit 23 outputs a control pulse voltage such that the charge storage capacity of the photosensitive pixel becomes a function of (t/R·11).

At t/R-tl, the shutter is automatically closed and the charge storage capacity becomes equal to Q, (saturated light m). In this way, the knee characteristic of photoelectric conversion is obtained. - Note that the present invention is not limited to the above two embodiments and their modifications. For example, regarding solid-state image sensors, there are frame transfer type CCD5MO8 type image sensors, and charge readout using an amorphous silicon film as a photosensitive part.
Various types of image sensors such as the one used in D can be used.

Furthermore, the limitation of the charge storage capacity is not limited to that shown in FIG. In FIG. 2, a control electrode is provided adjacent to a photodiode, which is a photosensitive pixel, and the threshold value of excess charge is determined by applying a control voltage fl'Il to this electrode.
A transparent electrode (control electrode) may be provided on the photosensitive pixel, and the potential well state of the charge storage region may be determined by applying a control voltage to the transparent electrode (control electrode). FIG. 10 is a cross-sectional view of such a solid-state image sensor. As shown in the figure, a transparent electrode 31 is provided in the opening of the light shield film 17, and a control pressure of 1 m is applied thereto. And the photosensitive pixel and drain 1
An electrode 32 to which a constant potential is applied is provided between the electrodes 20 and 20.

FIG. 11 is an explanatory diagram of the potential well in FIG. 10. For transparent, the control voltage applied to the control I electrode 31 is 61
When , the capacitance for accumulating charge is Ql, but
When the control voltage changes from VGl to vG2, the capacitance changes from Ql to 0.
Increased to 2.

〔Effect of the invention〕

As described above, in the present invention, the charge storage capacity of the light reception and storage section that generates and stores signal charges in accordance with the optical signal from the subject is
Since the shutter increases without decreasing during the process from several points in time to the point in time when the shutter is closed, it has a wide dynamic range and can obtain ambidextrous images of good quality even when there is a large difference in intensity of illumination of the subject. Still cameras can be provided.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing the configuration of an embodiment of the present invention, Fig. 2 is a sectional view of a part of a solid-state image sensor used in this embodiment, and Fig. 3 is a voltage value of a control pulse in this embodiment. FIG. 4 is a characteristic diagram showing the relationship between the charge amount of the photosensitive pixel and the clock pulse count value in this embodiment, and FIG. 5 is a solid-state image shown in FIG. 2. An explanatory diagram of the potential well of the sensor, FIG. 6 is a diagram of photoelectric conversion characteristics according to this embodiment,
FIG. 7 is a characteristic diagram for explaining a modification of this embodiment,
FIG. 8 is a block diagram showing the configuration of another embodiment of the present invention;
FIG. 9 is a characteristic diagram showing the charge amount of the photosensitive pixel in this embodiment, FIG. 10 is a sectional view of a part of another example of a solid-state image sensor applicable to the present invention, and FIG. 11 is an explanation of the potential well. 12 are photoelectric conversion characteristic diagrams of the solid-state image sensor. DESCRIPTION OF SYMBOLS 1... P-type semiconductor substrate, 11... Photodiode, 12... Drain, 13... Buried channel, 14
...Insulating film, 15.31...Control electrode, 16...
Transfer electrode, 17... light shield film. Applicant's agent Kiyoshi Inomata Figure 2 Count number Count number Figure 4 Menu Figure 5 Party figure 6 Figure 7 (C) Figure 11

Claims (1)

[Claims] 1. An optical system that forms an optical image of a subject, a shutter that is placed in front or behind this optical system to block and pass light from the subject, and controls the opening time of this shutter. an opening time control means, a light receiving and accumulating section disposed at the imaging position of the optical image and generating and accumulating signal charges according to the optical signal; storage capacity control means for controlling the light receiving and accumulating section so that the signal charge accumulating capacity increases in the process according to a function of t/T_i_n_t, where t is a time;
An electronic still camera comprising: a readout means for reading out the signal charges in the light receiving and accumulating section; and means for processing and recording the signal charges read out from the readout means. 2. The opening time control means has means for outputting an opening time signal indicating the opening time of the shutter and an opening time signal indicating the time point at which the shutter is opened, and the storage capacity control means outputs the opening time signal. 2. The electronic still camera according to claim 1, wherein the storage capacity of the light reception storage section is controlled in response to the open time signal from the time when the light receiving and storage section receives the open time signal. 3. The opening time control means comprises intensity detection means for detecting the intensity of incident light from a subject, and means for setting the opening time of the shutter based on this detected value. The electronic still camera according to item 2. 4. The light receiving and accumulating section has a plurality of photosensitive pixels arranged two-dimensionally, and the storage capacity control means includes setting means for setting a threshold value for excess charge of the photosensitive pixels, and discharging this excess charge. The electronic device according to any one of claims 1 to 3, further comprising a discharge means, and wherein the threshold value by the setting means is controlled by applying a predetermined control voltage to the setting means. still camera. 5. The light receiving and accumulating section has a plurality of photosensitive pixels each including an insulating film formed on a semiconductor substrate and a conductive electrode arranged two-dimensionally thereon, and the charge accumulating capacity of the photosensitive pixel is The electronic still camera according to any one of claims 1 to 3, wherein the electronic still camera is controlled by applying a predetermined control voltage to the conductive electrode. 6. An optical system that forms an optical image of the subject, a shutter that is placed in front or behind this optical system to block and pass light from the subject, and light amount detection that detects the amount of incident light while the shutter is open. means, an opening time control means for controlling the opening time of the shutter so that the shutter is closed at a predetermined time after the detected light amount exceeds a predetermined value; a light receiving and accumulating section that is arranged to generate and accumulate signal charges in accordance with an optical signal, and a period from the time when the shutter is opened to the time when the amount of light detected by the light amount detecting means exceeds the predetermined value as T_1; In the process from the time when the value exceeds the value to the time when the shutter is closed, the storage capacity of the signal charge becomes t, where t is the time.
storage capacity control means for controlling the light receiving and accumulating section so as to increase as a function of /T_1; reading means for reading out the signal charges of the light receiving and accumulating section; and means for processing and recording the signal charges read from the reading means. An electronic still camera equipped with. 7. The light receiving and accumulating section has a plurality of photosensitive pixels arranged two-dimensionally, and the storage capacity control means includes setting means for setting a threshold value for excess charge of the photosensitive pixels, and discharging the excess charge. 7. The electronic still camera according to claim 6, further comprising a discharge means, and wherein the threshold value set by the setting means is controlled by applying a predetermined control voltage to the setting means. 8. The light receiving and accumulating section has a plurality of photosensitive pixels each including an insulating film formed on a semiconductor substrate and a conductor electrode arranged two-dimensionally thereon, and the charge accumulating capacity of the photosensitive pixel is 7. The electronic still camera according to claim 6, wherein the electronic still camera is controlled by applying a predetermined control voltage to the conductive electrode.