JP3363591B2 - Imaging device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image pickup apparatus using a solid-state image pickup element.

[0002]

2. Description of the Related Art Many video cameras and electronic cameras using CCD as an image sensor have been developed and put on the market.

7, FIG. 8, FIG. 9 and FIG. 10 are drawings for explaining the structure and read-out operation of the CCD, and FIG.
8 and 9 are timing charts for driving the CCD, and FIG. 10 is a potential distribution directly below the photoelectric conversion portion of the CCD.

In FIG. 7, reference numeral 20 is a photoelectric conversion unit that converts subject light into an electric signal (signal charge), 21 is a vertical transfer unit that transfers each pixel charge, and 22 is each charge transferred by the vertical transfer unit 21. A horizontal transfer unit 23 for transferring in the vertical direction is an output amplifier 23 for converting the transferred charges into a signal voltage and outputting the signal voltage. As shown in FIG. 7, when reading the image pickup signal from the CCD, the signals of all pixels are simultaneously fetched into the vertical transfer unit, and signals of two pixels adjacent in the vertical direction are mixed and added and transferred in the vertical transfer unit. Field reading mode (hereinafter abbreviated as field mode) and a frame reading mode (hereinafter referred to as frame mode) in which the signals of the pixels on the odd and even rows are independently divided into two and transferred to the vertical transfer section. Abbreviated).

FIG. 8 is a diagram showing the waveforms of the four-phase vertical drive pulses V1 to V4 in the field mode. The read pulse is V during the blanking period for every V (vertical period).
1, V3 is superimposed. As a result, the odd-row signal and the even-row signal are simultaneously transferred to the corresponding vertical transfer units. After that, by supplying V1 to V4 every H (horizontal period), the signals in the odd rows and the signals in the even rows are added in a predetermined combination and then vertically transferred. The above combination is determined by the phase of the first transfer pulse V1 to V4 in the 1V period and is shifted by 1 pixel for each 1V. As a result, the interlace effect is obtained.

FIG. 9 shows V1 to V4 in the frame mode.
In the figure showing the drive pulse waveform of, the read pulse is added every 1V. That is, only the odd-row signals are transferred to the vertical transfer unit and read out for 1V period, and then the even-row signals are transferred to the vertical transfer unit and read for the subsequent 1V period.

Further, recently, the mainstream CCD has realized a high sensitivity and a wide dynamic range by a VOD structure which sweeps away unnecessary charges in the depth direction of a silicon substrate.

FIG. 10 is a diagram showing the principle thereof, and the limit of the amount of accumulated charges, which is shaded, is the capacity of the charge accumulation well determined by the voltage Vsub applied to the silicon substrate. Therefore, the amount of accumulated charges can be variably controlled by variably controlling Vsub.

In the image pickup device having the CCD as described above, the image quality of the image pickup greatly depends on the dynamic range determined by the CCD. That is, when an image pickup device having a narrow dynamic range is used, when a high-contrast subject is photographed, the saturation of the signal causes discoloration of the high-saturation subject portion or disappearance of the contrast in the high-luminance portion.

Since a CCD for a general-purpose video camera is premised on field reading, the dynamic range (hereinafter abbreviated as D range) is a field mode.
It is set to be optimal at the time of reading. That is, comparing the charge storage capacities of the photoelectric conversion unit 20 and the vertical transfer unit 21 in FIG. 7, the storable charge amount of each stage of the vertical transfer unit is set to twice the storable charge amount of the photoelectric conversion unit.

Therefore, when the frame mode is carried out by such an image pickup device, the vertical transfer unit 1 per pixel of the photoelectric conversion unit 1
Since the number of stages corresponds, the capacity of the vertical transfer unit 21 cannot be effectively utilized, and the D range of the CCD output must be narrower than that in the field mode. That is, since the maximum charge capacity of one pixel of the photoelectric conversion unit is smaller than that of one stage of the vertical transfer unit, the photoelectric conversion unit is saturated before the transfer unit in the frame mode, which is more than that in the field mode. The saturation level is low.

As described above, in the general-purpose CCD, the photoelectric conversion unit 2
Since the D range for one stage of the vertical transfer unit corresponds to the D range for pixels, it is not possible to secure the same D range as in field mode in frame mode.
The range will be almost halved.

Particularly in an electronic camera which performs frame mode in order to realize high image quality and high resolution, deterioration of the image quality is caused by the reduction of the saturation level, which is fatal.

On the other hand, recently, an image sensor capable of simultaneously reading out all pixels has been developed.

Since such an image pickup device is premised on reading out pixel by pixel from the beginning, the problem of imbalance between the photoelectric conversion unit and the transfer unit can be avoided. However, such an image pickup device is still expensive and cannot be used in an inexpensive image pickup device.

Further, paying attention to the change in the D range of the photoelectric conversion portion due to the Vsub potential shown in FIG. 10, and lowering the silicon substrate potential in the frame mode than in the field mode, the maximum accumulated charge of the photoelectric conversion portion is reduced. Expanding capacity has been conventional.

That is, FIG. 10 is a potential distribution diagram from directly under the photoelectric conversion portion of the image pickup device to the silicon substrate. The potential distribution shown by the solid line in FIG. 10 is a distribution when the substrate potential is set to Vsub1. In this case, the maximum value of the storage capacitance of the photoelectric conversion unit is determined by the depth of the well up to the level 1 in the figure. This is Vsub
This is the D range when set to 1. On the other hand, the potential distribution shown by the broken line is for the case where the substrate potential is determined by Vsub2, and the maximum value of the storage capacitance is determined by the depth of the potential well up to the level 2. That is, by changing the substrate potential from Vsub1 to Vsub2, the D range of the image sensor can be expanded.

Conventionally, by utilizing this characteristic of CCD, the D range is expanded in the frame mode by changing the setting of the substrate potential in the frame mode and the field mode. ing.

As described above, the level of the voltage Vsub supplied to the substrate potential of the CCD is set to Vs in the field mode.
By switching between ub1 and Vsub2 in frame mode, the D range in the frame mode of the photoelectric conversion unit can be made wider than in the field mode, and the photoelectric conversion unit in the frame mode is perpendicular to the vertical range. By improving the balance of the saturation level of the transfer unit, the total CCD
The output D range can be improved.

[0020]

However, in the above-mentioned conventional example, the D range cannot be fully expanded because only the CCD silicon substrate potential is controlled, and there is a problem such as blooming depending on the subject. There are cases where it will end up.

[0021]

In order to solve the above-mentioned problems, an image pickup apparatus according to one embodiment of the present invention has a photoelectric conversion section and a vertical transfer section, and an image pickup apparatus for converting an optical image into an electric signal. An element, a mode switching means for switching between the frame mode and the field mode, and a vertical transfer pulse having a first bias level when the frame mode is set by the mode switching means, and a field mode is set by the mode switching means. Since the vertical transfer pulse has a control means for switching the pulse to a second bias level higher than the first bias level, the dynamic range can be expanded and problems such as blooming can be prevented.

In particular, by changing the bias level in the frame mode and the field mode, the D range of the CCD in the frame mode can be appropriately expanded, so that a complicated circuit is not added. It can be realized by using a general-purpose image sensor. Therefore, the above problems can be achieved at low cost.

Further, by simultaneously switching the substrate potential, it is possible to achieve a wider dynamic range and prevent problems such as blooming.

Further, by making the level shift amounts of a plurality of vertical transfer pulses substantially equal, the D range can be expanded without lowering the efficiency of vertical transfer.
The performance is not deteriorated even for image quality other than the D range.

Further, by making the power supplies of the plurality of shift circuits common and making the temperature characteristics equal, it is possible to prevent the power supply fluctuation and the temperature characteristics from affecting the expansion of the D range and the transfer efficiency.

[0026]

[0027]

【Example】

(First Embodiment) FIG. 1 shows a system block of a digital camera according to a first embodiment of the present invention.

In FIG. 1, 1 is an image pickup device such as a CCD for converting the reflected light from a subject into an electric signal, and 2 is a timing signal generation circuit (hereinafter TG) for generating a timing signal necessary for operating the image pickup device 1. 3) is a drive voltage setting circuit that generates a voltage for driving the image pickup device 1, 4 is an image pickup device drive circuit that amplifies the signal from the timing signal generation circuit 2 to a level at which the image pickup signal can be driven, and 5 is A preprocessing circuit equipped with a CDS (correlation double sampling) circuit and an AGC (automatic gain control) circuit for removing output noise of the image sensor 1, 6 is an A / D converter, and 7 is A / D converted. An image pickup signal processing circuit for processing a digital signal as an image pickup signal, 8 is a recording medium I / F (interface) circuit for performing modulation or the like for recording a signal on a recording medium 9, and 10 is for starting image pickup by a camera Remumo - De field mode - operation unit for external photographer to control de, 11 operation unit 10
Is a setting switching circuit that outputs a signal for changing the drive voltage according to the mode setting set by.

The first embodiment will be described below with reference to FIG.

First, the photographer controls the operation unit 10 to start the image pickup operation, and the image pickup element is exposed by an electronic shutter operation by a diaphragm (not shown) and a timing signal generator to read the output of the image pickup element. The preprocessing circuit 5 performs signal processing such as CDS processing and gain control on the read imaging output. At this time, the gain of the gain control circuit is determined at the time of manufacturing the image pickup device because it is determined by the sensitivity of the image pickup device. The output of the front-end circuit 5 is A /
The digital signal is converted by the D converter 6 and input to the image pickup signal processing circuit 7. The output of the image pickup signal processing circuit 7 is converted into a specific format (modulation) by the recording medium I / F and then recorded on the recording medium 9.

Now, in the above photographing, the operation unit 1
By setting 0, it is possible to set whether the image is picked up in the frame mode or the field mode. That is, when the setting of the camera is changed to the field mode imaging by the operation unit 10, the setting switching circuit 11 sets the setting value of the driving voltage setting circuit to the value of the field mode.

FIG. 2 shows the signal waveforms of the vertical transfer pulses V1 and V3 in this embodiment. In the figure, the pulses V1 and V3 in the frame mode are described.

In the present embodiment, the TG mode is switched by the frame mode / field mode signal from the setting switching circuit 11 to change the read pulse width of the vertical transfer pulse shown in FIG. In other words, as shown in the figure, the field mode
The switching is performed so that the pulse width becomes wider in the frame mode than in the frame mode.

As described above, since a wider read pulse can be used in the frame mode, when the storage capacity of the photoelectric conversion section is increased by operating the Vsub potential in the frame mode as shown in the conventional example. However, it becomes possible to reliably carry out the charge transfer from the photoelectric conversion section to the vertical transfer section.

(Second Embodiment) FIGS. 3 and 4 are drawings for explaining a second embodiment of the present invention, FIG. 3 is an example of the drive voltage setting circuit of FIG. 1, and FIG. It is a potential distribution diagram of a conversion part and a vertical transfer part. In FIG. 3, R1 to R5 are resistors, Tr1 to Tr2 are transistors, and V1 is a reference voltage source.

The VM 13 set by R1 to R5 and Tr1 to Tr2 is a signal that determines the level of the intermediate value in the vertical transfer pulses V1 and V3 of the ternary signal shown in FIGS.

In the VM 13 shown in FIG. 3, the frame mode / field mode signal becomes Low level in the field mode, so that Tr1 is turned off and the base level of Tr2 is determined by V1, R3 and R4. . This base potential is lowered by the level Vbe between the base and emitter of Tr2 and is output as the VM13 voltage. This level is, for example, the level of the VM 13 (field) in FIG. On the other hand, in frame mode, frame mode / field mode
Since the drive signal becomes High level and Tr1 is turned on, the base potential of Tr2 is V2, R3, R4, and other Tr1.
And R2, and the resistance value between the base grounds becomes small, so that the level becomes lower than that in the field mode.
Therefore, the emitter level VM13 of Tr2 is also lower than that in the field mode. This level is shown in Figure 4.
VM 13 (frame).

When the DC level of the VM 13 decreases in the frame mode, the potential barriers of the CCD photoelectric conversion section and the vertical transfer section during photoelectric conversion are as shown in FIG. The setting of VM13 in frame mode (setting of dotted line in FIG. 5) is higher than that of setting (solid line in FIG. 5), and therefore the capacity of the signal charge accumulated in the photoelectric conversion unit is higher. Is level 1 in field mode, and level 2 in frame mode
Therefore, it is possible to prevent the charges accumulated in the photoelectric conversion unit from leaking to the vertical transfer unit, and as a result, the capacity of the signal charges accumulated in the photoelectric conversion unit is the frame mode compared to the level 1 in the field mode. It can be increased to level 2 of the hour.

As described above, the D range in the frame mode of the photoelectric conversion unit can be made wider than that in the field mode, and the saturation level of the photoelectric conversion unit and the vertical transfer unit in the frame mode can be increased. By improving the balance, it is possible to improve the total D range of the CCD output.

(Third Embodiment) In the second embodiment, the VM is used.
The level of 13 is switched, but in this case, only the intermediate potential between V1 and V3 of the vertical transfer pulse is switched. On the other hand, the efficiency of vertical transfer is affected by the relative value of each potential of the vertical transfer pulses V1 to V4.
If only 3 is switched, the vertical transfer efficiency will be reduced. Therefore, in this embodiment, the level of the VM 24 in FIGS. 8 and 9 is switched at the same time as the switching of the VM 13 so that the vertical transfer efficiency is not lowered by switching the VM 13.

FIG. 5 is a circuit diagram for explaining this embodiment, which is another embodiment of the drive voltage setting circuit of FIG. R5
-R10, VM3 set by Tr3 to Tr4 is the level of the vertical transfer pulses V2 and V4 which are binary signals (see FIG. 8,
9 is a signal for determining the VM 24).

With the circuit shown in FIG. 5, in the frame mode, the amount of VM which is almost equal to the amount of change in which the level of VM 13 is lowered is set.
I also tried to lower the level of 24. As a result, the D range of the photoelectric conversion section can be expanded and the efficiency of the vertical transfer section can be prevented from lowering as compared with the field mode.

Further, as shown in FIG. 5, V1 is commonly used as the power supply voltage, and the voltage between the base and the emitter of the transistor, which greatly affects the temperature characteristics of the circuit, is affected by one Vbe at both outputs. In this way, by making the power supply voltages of the circuits for deriving the VM13 and VM24 common and arranging the temperature characteristics that the circuits give to the outputs in this way, it is possible to prevent fluctuations in power supply and temperature changes. It is possible to prevent the transfer efficiency from deteriorating.

In the above embodiment, the intermediate level VM 13,
Only the VM24 was switched, but in this case another High
In some cases, the relative values of the h level and the Low level change, which affects the drive characteristics. So VM13, VM24
High level, Low corresponding to the level change amount of
You may switch so that a bell may be shifted.

(Fourth Embodiment) FIG. 6 is a circuit diagram showing a fourth embodiment of the present invention, in which R1 to R15 are resistors and Tr1 to T.
r6 is a transistor, and V1 and V2 are reference voltage sources.
In particular, V2 is a negative reference voltage source, and VM13, VM2
4, it is possible to output a negative level. In this embodiment, Vsub, VM13, and VM24 are all switched at the same time when the field mode and the frame mode are read and changed, thereby further expanding the D range of the photoelectric conversion unit in the frame mode and performing vertical transfer. It is also possible to secure efficiency. Further, by preparing the voltage source and temperature characteristics of each voltage generation circuit, it is possible to secure the characteristics without changing the relative value of each set voltage even when the power source changes or the temperature changes.

As described above, the silicon substrate potential is switched, the vertical transfer pulse level is switched, and the vertical transfer pulse width is switched at the same time to maximize the D range in the frame mode. In addition, the anti-blooming ability, which is lowered only by changing the substrate potential, can be driven without lowering. In other words, if only the Vsub potential is changed, the charges in the photoelectric conversion section where the potential well has become deep overflow and flow into the vertical transfer section, where they are mixed with the charges of adjacent pixels in the vertical transfer section. However, since the potential barrier with the vertical transfer section becomes high, the above problem can be avoided.

[0047]

In the image pickup apparatus of the present invention, an image pickup device having a photoelectric conversion unit and a vertical transfer unit for converting an optical image into an electric signal, a mode switching means for switching between a frame mode and a field mode, and the mode switching. The vertical transfer pulse has a first bias level when the frame mode is set by the means, and the vertical transfer pulse has a second bias level higher than the first bias level when the field mode is set by the mode switching means. Since it has a control means for switching so as to become, it is possible to achieve expansion of the dynamic range and prevention of occurrence of problems such as blooming.

In particular, by changing the bias level in the frame mode and the field mode, the D range of the CCD in the frame mode can be appropriately expanded, so that a complicated circuit is not added. It can be realized by using a general-purpose image sensor. Therefore, low cost can be achieved.

Furthermore, by simultaneously switching the substrate potential, it is possible to achieve a wider dynamic range and prevent the occurrence of problems such as blooming.

Further, by making the level shift amounts of a plurality of vertical transfer pulses substantially equal, the D range can be expanded without lowering the efficiency of vertical transfer.
The performance is not deteriorated even for image quality other than the D range.

Further, by making the power supplies of the plurality of shift circuits common and making the temperature characteristics equal, it is possible to prevent the power supply fluctuation and the temperature characteristics from affecting the expansion of the D range and the transfer efficiency.

[0052]

[Brief description of drawings]

FIG. 1 is a block diagram of the configuration of a first embodiment of the present invention.

FIG. 2 is a timing chart for explaining the first embodiment of the present invention.

FIG. 3 is a circuit diagram showing a second embodiment of the present invention.

FIG. 4 is a potential distribution diagram of a CCD for explaining a second embodiment of the present invention.

FIG. 5 is a circuit diagram showing a third embodiment of the present invention.

FIG. 6 is a circuit diagram showing a fourth embodiment of the present invention.

FIG. 7 is a diagram illustrating a basic configuration of a CCD.

FIG. 8 is a basic vertical transfer pulse timing chart of the CCD in the field mode.

FIG. 9 is a basic vertical transfer pulse timing chart of a CCD in frame mode.

FIG. 10 is a potential distribution diagram immediately below the photoelectric conversion unit of the CCD.

[Explanation of symbols]

1 Image sensor 2 Timing signal generation circuit 3 Drive voltage setting circuit 4 Image sensor drive circuit 5 Preprocessing circuit 6 A / D converter 7 Imaging signal processing circuit 8 Recording medium I / F 9 recording media 10 Operation part 11 Setting switching circuit

Claims (7)

(57) [Claims] 1. An image sensor having a photoelectric conversion unit and a vertical transfer unit for converting an optical image into an electric signal, a mode switching unit for switching between a frame mode and a field mode, and a frame mode set by the mode switching unit. In this case, the vertical transfer pulse becomes the first bias level, and when the field mode is set by the mode switching means, the vertical transfer pulse is switched so as to become the second bias level higher than the first bias level. An imaging device comprising: 2. The image pickup apparatus according to claim 1, wherein the control unit switches an intermediate potential level of the vertical transfer pulse. 3. Two stages of the hanging lamp adjacent to the photoelectric conversion section.
A direct transfer unit is provided, and the control unit is responsive to the mode switching by the mode switching unit to select one of the two vertical transfer units.
At the same time a predetermined amount shifted intermediate potential level of the first vertical transfer pulse supplied to one of the vertical transfer portion of the 2-stage
The image pickup apparatus according to claim 1, wherein the intermediate potential level of the second vertical transfer pulse supplied to the other of the two is shifted by the predetermined amount. 4. The control means determines a shift amount of an intermediate level of the first vertical transfer pulse, and a first shift circuit determines a shift amount of an intermediate level of the second vertical transfer pulse. 4. The image pickup apparatus according to claim 3, further comprising two shift circuits, wherein the first shift circuit and the second shift circuit have a common power source. 5. The effect of the temperature characteristic of the first shift circuit on its output and the effect of the temperature characteristic of the second shift circuit on its output are substantially equal to each other. The imaging device described. 6. The control means shifts the intermediate potential level of the vertical transfer pulse in response to the mode switching by the mode switching means, and simultaneously shifts the high potential level and the low potential level by the same level. The image pickup apparatus according to claim 2. 7. The control means is based on the mode switching means .
The substrate potential of the image sensor is lowered in response to switching to the frame mode compared to the case of the field mode.
The image pickup apparatus according to claim 1, wherein the image pickup apparatus is changed as follows.