JPH0115225B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to an imaging device that can effectively suppress blooming.

(Prior art) In general, in solid-state image sensors such as CCDs, an overflow drain is provided within the light receiving surface to prevent blooming, or surface recombination is used to eliminate excess carriers. ing.

In particular, the latter method has advantages such as high sensitivity because it does not sacrifice the aperture ratio in the light receiving surface, and horizontal resolution can be increased because the degree of integration can be improved.

1 to 3 are diagrams for explaining a blooming prevention method using such surface recombination, and FIG. 1 is a front view of a general frame transfer type CCD.

In the figure, reference numeral 1 denotes a light receiving section, which is composed of a plurality of photosensitive vertical transfer registers. Further, numeral 2 consists of a plurality of vertical transfer registers shielded from light by a storage section. Reference numeral 3 denotes a horizontal transfer register, which inputs the information in each vertical transfer register of the storage section 2 by shifting one bit at the same time to the horizontal transfer register, and then transfers the video signal from the output amplifier 4 by causing the register 3 to perform a horizontal transfer operation. You can get it.

Generally, the information formed in each vertical transfer register of the light receiving section 1 is vertically transferred to the storage section 2 during the vertical blanking period in the standard television system, and is transferred to the horizontal transfer register 3 within the next vertical scanning period. The data is sequentially read out line by line.

Here, it is assumed that the light receiving section 1, the storage section 2, and the horizontal transfer register 3 are each driven in two phases, and the respective transfer electrodes are set as P ₁ / P ₂ , P ₃ / P ₄ , P ₅ / P ₆ . , the transfer clocks are φp ₁・φp ₂ , φp ₃・φp ₄ , φp ₅・
Let φp ₆ be.

FIG. 2 is a diagram showing the potential profile under such transfer electrodes P ₁ to P ₆ . For example, under each electrode provided on a P-type silicon substrate 6 with an insulating layer 5 interposed therebetween, ion implantation, etc. For example, a low level voltage _-V1 is applied to electrodes _P2 , _P4 , and _P6 , and a high level voltage is applied to electrodes _P1 , _P3, and _P5 . When V ₂ is applied, a potential as shown by the solid line in the figure is formed, and a low level voltage V ₁ is applied to electrodes P ₁ , P ₃ , and P ₅ .
is applied, and a high level voltage V ₂ is applied to electrodes P ₂ , P ₄ , and P ₆ .
When the voltage is applied, a potential as indicated by the broken line in the figure is formed.

Therefore, by applying alternating voltages with opposite phases to electrodes P ₁ , P ₃ , and P ₅ and electrodes P ₂ , P ₄ , and P ₆ , carriers are sequentially transferred in one direction (toward the right in the figure). .

In addition, the dashed-dotted line in the figure indicates a large positive voltage V ₃ at the electrode.
This shows the potential when .

FIG. 3 is a diagram showing the shape of the electrode voltage and internal potential in the thickness direction of the semiconductor substrate 6. As shown in the figure, for the electrode voltage _V3 , the potential well becomes shallow and the excess carrier becomes shallow. A second state occurs in which it recombines with majority carriers at the interface with the insulating layer.

On the other hand, when the electrode voltage is _-V1 , the first state is an accumulation state, and a large number of carriers tend to gather around the interface, and for example, this large number of carriers is supplied from a channel stopper region (not shown). .

Therefore, for example, when a barrier is formed by applying voltage -V ₁ to electrode P ₂ , by alternately applying voltages -V ₁ and V ₃ to electrode P ₁ , the electrode
The minority carriers accumulated under _P1 are limited to a predetermined amount or less.

However, in order to effectively eliminate excess carriers, accumulation states and inverted states must be formed alternately and at high speed in the semiconductor substrate during the accumulation period, which reduces power consumption. There is a problem that is large. Furthermore, when such pulse control is performed at high speed, there is a problem that noise caused by the pulses is mixed into the signal.

Further, there is a problem in that dark current unevenness is likely to occur due to such pulses.

(Objective) It is an object of the present invention to provide an imaging device that can overcome the drawbacks of the prior art.

Another object of the present invention is to provide an imaging device that can effectively prevent blooming and has a high power saving effect.

(Example) The present invention will be explained below based on Examples.

FIG. 4 is a block diagram showing a first embodiment of the imaging apparatus of the present invention. The light from the object that enters through the optical system shown in 7 in the figure and the aperture 8 placed in its optical path is transmitted to a CCD as shown in the first figure.
The light is imaged on an image sensor 10 such as , etc., and is incident on a photometric light receiving element 14 via a beam splitter 9 and a deflection mirror 13 .

The light receiving element 14, the operational amplifier 27, and the resistor 26 form a known photoelectric conversion circuit. Also, operational amplifier 2
a resistor 28 and a resistor 29 connected to the output of 7;
The operational amplifier 31 and the reference voltage source 30 form an inverting amplifier that compares and inverts the output from the operational amplifier 27 with the reference voltage source 30, and its output is connected to one of the inputs of the OR gate 22 and drives the aperture. It is connected to a drive coil 32 for The aperture drive coil 32 is driven by the operational amplifier 31 to open the aperture 8 when a positive voltage is applied thereto, and to close the aperture 8 when a negative voltage is applied. Image sensor 10
The output of is connected to a luminance separation circuit 11, and further connected to an integration circuit 12 and a peak hold circuit 18. The output of the integrating circuit 12 is connected to an inverting input of a comparator 16, the non-inverting input of the comparator 16 is connected to a reference voltage source 17, and its output is connected to one input of an AND gate 21. Incidentally, the integrating circuit may be a smoothing circuit, an average value circuit, or a low-pass filter. The output of peak hold circuit 18 is connected to the inverting input of comparator 19, the non-inverting input of comparator 19 is connected to reference voltage source 20, and its output is connected to the other input of AND gate 21. and gate 21
The output of is connected to the other input of OR gate 22. The output of OR gate 22 is connected to a control terminal of switch circuit 36. Peak hold circuit 18
The output of is connected to the voltage controlled oscillator 24 via the switch circuit 36, and the output of the voltage controlled oscillator 24 is
It is connected to a driver 34 for forming driving pulses for the CCD 10. 35 is a clock generator which outputs various pulse timing signals for driving the CCD 10.

The driver 34 outputs pulses φp ₁ to φp ₆ based on this timing signal.

Furthermore, based on the output of the voltage controlled oscillator 24,
The driver 34 is connected to the voltages −V ₁ and + in FIG.
An alternating pulse φ _AB varying between V ₃ and V 3 is formed and supplied to the CCD.

37 is a set value circuit connected to the b side of the switch circuit 36, and while the OR gate 22 is outputting a high level, the contact of the switch circuit 36 is switched to the b side, and the voltage controlled oscillator 24 is turned off. A predetermined set value V ₀ is input to the input terminal. The setting value is
For example, the voltage is 0 (volt), and the oscillator 24 is configured to have zero oscillation frequency, that is, stop oscillation, in response to a 0 volt input.

Next, the operation of the configuration shown in the fourth figure will be explained. When the amount of light entering the light receiving element 14 is smaller than the appropriate value, the output of the photoelectric conversion circuit becomes a low voltage and the inverting amplifier 3
The output of 1 is a positive high voltage. Therefore, a positive voltage is applied to the aperture drive coil 32, and the aperture is driven in the opening direction. On the other hand, when the amount of light incident on the light-receiving element 14 is larger than the appropriate value, the operation opposite to the above is performed, and a current flows in the diaphragm drive coil 32 in the direction of closing the diaphragm, trying to reduce the amount of incident light.

On the other hand, the subject image formed on the image sensor 10 is photoelectrically converted to form charge information. A brightness component is separated from the output by a brightness separation circuit 11, and integrated by an integration circuit 12, thereby detecting the average brightness level of the subject.

The comparator 16 compares this level with a predetermined reference level, and if the output of the integrating circuit 12 is lower than the predetermined level, the comparator 16 outputs a high level signal.

That is, when the average brightness level of the object becomes lower than a certain level, a high level is obtained from the comparator.

On the other hand, the output of the luminance separation circuit 12 is connected to a peak hold circuit 18 to detect the peak in the luminance signal. The comparator 19 compares the detected peak with the voltage of the reference voltage source 20, and outputs a high level if the peak level is lower. The outputs of comparators 16 and 19 are both high level,
That is, only when the average luminance of the subject is low and the maximum luminance is also low, the AND gate 21 outputs a high level, the output of the OR gate 22 also becomes a high level, the switch 36 is switched to the b side, and the voltage controlled oscillation circuit 24 to stop the oscillation.

Note that the output of the integrating circuit 12 and the peak hold circuit 18 is delayed by the output scanning time of the image sensor 10 and is further delayed by the aperture operation, so for example, the aperture may be stopped down too much and the light incident on the light receiving element 14 may be weak. If the aperture drive coil 32 is overloaded, that is, if a positive voltage is applied to the diaphragm drive coil 32 and it is being driven in the opening direction, the input to the OR gate 22 becomes high level, so the output of the OR gate 22 becomes high level, and the oscillation of the oscillator 24 stops as described above. do.

Note that when this oscillation stops, the image sensor 10
is driven periodically by the pulses φp ₁ to φp ₆ shown in the first diagram.

Furthermore, the output of the peak hold circuit 18 is input to the voltage controlled oscillator 24, which generates a pulse train of a higher frequency as the peak value becomes larger according to the peak value, so that the image sensor 10 is supplied with a pulse φ _AB corresponding to the larger the peak value.

In this embodiment, when a power source (not shown) is turned on, the pulses φp ₁ to _{φp 6} are constantly supplied at a period according to the normal standard television system, and the pulse voltage is In the figure -
It is designed to vary between V ₁ +V ₂ .

Further, the pulse φ _AB is superimposed on the pulses φp ₁ to φp ₆ and is supplied to the transfer electrode of the image sensor.

Further, while the driver 34 vertically transfers the charge information in the light receiving section 1 of the image sensor 10 to the storage section 2, the pulse φ _AB is controlled to be at the 0 level. Therefore, φ _AB does not interfere with vertical transfer.

As described above, according to the embodiment of the present invention, a subject image is converted into charge information by the imaging means, a luminance signal is obtained by reading out this charge information, and a charge recombination pulse is generated according to the peak level of this luminance signal. Since the frequency is controlled, the power required for recombination can be used effectively.

Furthermore, in this embodiment, when the average level of the luminance signal is lower than a predetermined level and the peak level of the luminance signal is lower than a predetermined level, the formation of the pulse φ _AB for recombination is stopped, so that unnecessary pulses are generated. Power consumption can be effectively reduced.

Furthermore, if the photometric output of a photometric element other than the imaging means is smaller than a predetermined level, the pulse φ _AB
Therefore, even if the screen is suddenly switched from a bright object to a dark object, for example, the unnecessary pulse φ _AB can be omitted with good responsiveness.

In this embodiment, the oscillation frequency of the voltage controlled oscillator (VCO) 24 is changed depending on the output of the peak hold circuit 18, that is, the peak value of the luminance signal.
As a second embodiment, as shown in FIG. 5, the oscillation frequency of the VCO 24 may be controlled in accordance with the output level of the integrating circuit 12 shown in FIG. In that case, the frequency of the VCO 24 may be increased as the output of the circuit 12 increases.

Alternatively, as shown in FIG. 6 as a third embodiment, by connecting the light receiving element 14, the operational amplifier 27, and the diode 260 for logarithmic compression as shown in the figure, the amount of light incident on the light receiving element can be adjusted. The frequency of the pulse φ _AB may be controlled according to the logarithm of the amount of light incident on the light receiving element 14 by outputting a logarithmic compression value and inputting this output value to the VCO 24 .

Of course, as in the first and second embodiments, the frequency of φ _AB is controlled to increase as the amount of incident light increases.

Further, the light receiving element 14 may be one that measures TTL light or may be one that measures external light.

In the first to third embodiments, the oscillation frequency control of the VCO 24 may be performed continuously, or may be divided into several stages and the frequency may be changed stepwise.

In this way, if the configuration is adopted as in the second and third embodiments, the configuration becomes simpler.

FIG. 7 is a diagram showing a fourth embodiment of the present invention. In this embodiment, instead of the oscillator 24 shown in _FIG .
An oscillator 38 is provided for generating the fourth
The oscillator 38 is stopped while the output of the illustrated comparator 31 is at a high level.

In this case as well, although not shown in the figure, the output of the light receiving element 14 shown in the fourth figure is input to the comparator 31, and this light receiving element 14 may be one that performs external photometry.

FIG. 8 is a diagram showing a fifth embodiment of the present invention. In this embodiment, the oscillator 38 of the fourth embodiment is turned on and off by the comparator 16 shown in FIG. The oscillator 38 is turned off while outputting.

FIG. 9 shows a sixth embodiment, in which the oscillator 38 shown in FIG. 8 is turned off while the output of the comparator 19 shown in FIG. 4 is at a high level.

As described above, in the seventh to ninth illustrated embodiments, any one of the following cases occurs: when the light receiving element output is lower than the predetermined level, when the average value of the luminance signal is lower than the predetermined level, and when the peak value of the luminance signal is lower than the predetermined level. Since the oscillation of the pulse φ _AB is turned OFF in the case of 1, the power saving effect is high, and the circuit configuration is also simple.

(Effects) As explained above, according to the present invention, the oscillation frequency of the recombination pulse is reduced to zero according to the brightness state of the subject (for example, the output level of the light receiving element, the average level of the brightness signal, the peak value of the brightness signal, etc.) Since the control is performed within a predetermined range including , the power associated with the formation of the recombination pulse can be effectively saved, and blooming is less likely to occur. In other words, as the brightness level or the peak of a part thereof increases, the frequency of the pulse φ _AB increases, so the recombination speed of excess charges increases accordingly, making it possible to efficiently eliminate excess charges. be.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an example of an image sensor applicable to the present invention, FIG. 2 is a diagram showing its potential profile, FIG. 3 is a potential state diagram in the thickness direction of the image sensor, and FIG. FIG. 5 is a diagram of a second embodiment of the invention, FIG. 6 is a diagram of a third embodiment of the invention, FIG. 7 is a diagram of a fourth embodiment of the invention, and FIG. 8 is a diagram of a fourth embodiment of the invention. 9 is a diagram showing a fifth embodiment of the present invention, and FIG. 9 is a diagram showing a sixth embodiment of the present invention. DESCRIPTION OF SYMBOLS 1... Light receiving part, 5... Insulating layer, 6... Semiconductor substrate, 24... Voltage controlled oscillator, 38... Oscillator.

Claims (1)

[Scope of Claims] 1. An imaging means having a plurality of light receiving sections for converting an optical image into charge information, and repeatedly recombining at least a portion of the charge information in each of the light receiving sections with charges of other polarity. a signal supply means for applying a periodic signal to the electrodes in each light receiving section; a detection means for forming a detection signal corresponding to the brightness of the optical image incident on the imaging means; and a control means for variably controlling the frequency of the periodic signal by the signal supply means in accordance with the detection signal. 2. The imaging apparatus according to claim 1, wherein the control means stops the supply of the periodic signal by the signal supply means when the brightness of the optical image is lower than a predetermined level.