Television – Camera – system and detail – Solid-state image sensor
Reexamination Certificate
1999-04-01
2004-12-28
Garber, Wendy R. (Department: 2712)
Television
Camera, system and detail
Solid-state image sensor
C348S302000, C348S308000
Reexamination Certificate
active
06836291
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a solid-state image pickup device and, more particularly, to a solid-state image pickup device comprising pixels arranged in two dimensions.
BACKGROUND OF THE INVENTION
A two-dimensional solid-state image pickup device in which pixels each including a photoelectric converting element such as a photodiode and means for drawing out photoelectric charges generated in the photoelectric converting element onto an output signal line are arranged to form a matrix (with rows and columns) has had a wide variety of applications. Such solid-state image pickup devices can be subdivided into CCD types and MOS types depending on the means for reading out (drawing out) the photoelectric charges generated in the photoelectric converting element. A CCD image pickup device has the drawback of a narrow dynamic range due to the photoelectric charges which are transferred while being accumulated in potential wells. In a MOS image pickup device, on the other hand, charges accumulated in the pn junction capacitance of a photodiode are read out via a MOS transistor.
Referring to
FIG. 24
, the structure of each pixel in a conventional MOS solid-state image pickup device will be described. In the drawing, a photodiode PD has a cathode connected to the gate of a MOS transistor T
1
and to the drain of a MOS transistor T
2
. The MOS transistor T
1
has a source connected to the drain of a MOS transistor T
3
which has a source connected to an output signal line Vout. A direct-current voltage VDD is applied to the drain of the MOS transistor T
1
, while a direct-current voltage Vss is applied to the source of the MOS transistor T
2
and to the anode of the photodiode. A reset pulse &PHgr;RS is applied to the gate of MOS transistor T
2
.
When the photodiode PD is irradiated with light, photoelectric charges are generated and accumulated in the gate of the MOS transistor T
1
. When the MOS transistor T
3
is turned ON with the application of a pulse &PHgr;V to the gate thereof, an electric current proportional to the charges in the gate of the MOS transistor T
1
is led out onto the output signal line Vout through the MOS transistors T
1
and T
3
, whereby an output current proportional to the quantity of incident light is read out. After the reading of a signal, the MOS transistor T
3
is turned OFF to turn the MOS transistor T
2
ON, which initializes the gate voltage of the MOS transistor T
1
.
Thus, in the conventional MOS solid-state image pickup device, the photoelectric charges generated in the photodiode and accumulated in the gate of the MOS transistor are read from each of the pixels without any alterations thereto so that the output signal has a narrow dynamic range and contains the variable component and noise component of light from the power source. Moreover, since the output signal is on a low level, the conventional MOS image pickup device is disadvantageous in that the S/N ratio is low and a high-quality image pickup signal cannot be obtained therefrom.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a solid-state image pickup device capable of producing a high output from a pixel. Another object of the present invention is to provide a solid-state image pickup device capable of generating an image pickup signal with an excellent S/N ratio. Still another object of the present invention is to provide a solid-state image pickup device with a wide dynamic range.
These and other objects of the present invention are achieved by a two-dimensional solid-state image pickup device comprising pixels arranged to form a matrix, each of the pixels including: a photoelectric converting element; logarithmic converting means for changing an output current from the photoelectric converting element into a logarithmically converted voltage; a transistor having a first electrode, a second electrode, and a control electrode to which an output voltage from the logarithmic converting means is applied; a capacitor having one terminal for receiving an output current from the second electrode of the transistor; an amplifier for amplifying an output from the capacitor; and a lead-out path for leading out an amplified signal onto an output signal line.
In this arrangement, the output signal from the photoelectric converting means is integrated in the capacitor so that the variable component and high frequency noise of light from the light source contained in the output signal is absorbed in the capacitor and removed from the output signal. The output signal from the photoelectric converting means from which the variable component and high frequency noise have been removed is further amplified by the amplifier to have a sufficient magnitude and then outputted, resulting in an image pickup signal with excellent sensitivity.
Moreover, logarithmic compression conversion achieves a wider dynamic range in the solid-state image pickup device in the arrangement. Furthermore, since each pixel is provided with the photoelectric converting means, the capacitor, the amplifier, and the lead-out means, a signal can be read more stably and more accurately.
The amplifier may include: an amplifier transistor having a first electrode, a second electrode, and a control electrode to which the output from the capacitor is applied; and a load resistor connected to an output line leading to the second electrode of the amplifier transistor. The load resistor may be used in common by several pixels. Hence, the load resistors may be smaller in total number than the pixels. In the case of using the amplifier transistor, the lead-out path is appropriately connected to the second electrode of the amplifier transistor such that a signal is led out from the second electrode.
A transistor having a first electrode connected to the second electrode of the amplifier transistor, a second electrode connected to a direct-current voltage, and a control electrode connected to a direct-current voltage may be used as the load resistor. A MOS transistor may be used as the amplifier transistor. In the case of using an n-channel MOS transistor, the direct-current voltage applied to the first electrode of the amplifier transistor is properly set higher in potential than the direct-current voltage connected to the second electrode of the resistor transistor.
In the case of using a p-channel MOS transistor as the amplifier transistor, the direct-current voltage applied to the first electrode of the amplifier transistor is properly set lower in potential than the direct-current voltage connected to the second electrode of the resistor transistor. The lead-out path to be used may include a switch for sequentially selecting a specified one of all the pixels and leading out the amplified voltage from the selected pixel onto the output signal line. The provision of a second capacitor for performing the subsequent integration while the output from the first capacitor is led out enables integration in the second capacitor simultaneously with the reading of the signal from the first capacitor and thereby provides compatibility with the shooting of a dynamic picture.
Additionally, a current input path to the capacitor may be provided with a switch to be controlled simultaneously in each of the pixels such that an integration time in each of the pixels is equal. In this case, there is no time lag between the reading of charges accumulated in the capacitors in one column and the reading of charges accumulated in the capacitors in another column so that the integration time in the capacitor (as well as the timing for integration) is equal in each of the pixels. Consequently, signals are free from any error due to a time lag between the reading of the signal from one pixel and the reading of the signal from another pixel.
These and other objects of the present invention may also be achieved by a two-dimensional solid-state image pickup device comprising pixels arranged to form a matrix, each of the pixels including: a photodiode; a first MOS transistor having a first electrode and a
Hagihara Yoshio
Miyatake Shigehiro
Nakamura Satoshi
Takada Kenji
Garber Wendy R.
Minolta Co. , Ltd.
Sidley Austin Brown & Wood LLP
Wilson Jacqueline
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