Image-sensing apparatus
In a solid-state image-sensing device, when image sensing is performed, in each pixel, MOS transistors T 1 and T 5 are turned on and a MOS transistor T 6 is turned off so that a MOS transistor T 2 operates in a subthreshold region. When resetting is preformed, in each pixel, the MOS transistors T 1 and T 5 are turned off and the MOS transistor T 6 is turned on so that the gate voltage of the MOS transistor T 2 is kept constant. In this state, the MOS transistor T 2 is brought first into a conducting state and then, by turning a signal φVPS to a high level, into a cut-off state. This permits a signal proportional to the threshold value of the MOS transistor T 2 to be output as compensation data.
1. An image-sensing apparatus comprising:
a plurality of pixels, the pixels each including a photoelectric conversion portion that outputs an electric signal produced in accordance with amount of incident light and converted natural-logarithmically and a lead-out path by way of which the electric signal output from the photoelectric conversion portion is fed to an output signal line, the photoelectric conversion portion comprising:
a photosensitive element having a first electrode to which a direct-current voltage is applied and a second electrode;
a first switch having one contact connected to the second electrode of the photosensitive element;
a first transistor having a first electrode connected to another contact of the first switch, a second electrode, and a control electrode;
a second transistor having a first electrode to which a direct-current voltage is applied, a second electrode from which an electric signal is output, and a control electrode connected to the first electrode of the first transistor; and
a second switch connected between the first electrode and control electrode of the first transistor; and
a controller that makes the individual pixels perform image sensing by turning on the first and second switches and that detects variations in sensitivity of the individual pixels by turning off the first and second switches and varying a voltage fed to the control electrode and second electrode of the first transistor.
2. An image-sensing apparatus as claimed in claim 1 , wherein the first switch is a transistor.
3. An image-sensing apparatus as claimed in claim 1 , wherein the pixels are arranged in a matrix.
4. An image-sensing apparatus as claimed in claim 1 ,
wherein the pixels each further include a third switch having one contact connected to the control electrode of the first transistor and another contact to which a direct-current voltage is applied, and
wherein the controller turns off the third switch when making the individual pixels perform image sensing and turns on the third switch when detecting variations in sensitivity of the individual pixels.
5. An image-sensing apparatus as claimed in claim 4 ,
wherein the third switch is a transistor.
6. An image-sensing apparatus as claimed in claim 1 ,
wherein the second switch is a transistor.
7. An image-sensing apparatus comprising:
a plurality of pixels, the pixels each including:
a photodiode having two electrodes, the photodiode producing an electric signal in accordance with amount of incident light;
a first MOS transistor having a first electrode connected to one electrode of the photodiode, a second electrode, and a gate electrode;
a second MOS transistor having a first electrode connected to the second electrode of the first MOS transistor, a second electrode, and a gate electrode;
a third MOS transistor having a first electrode, a second electrode, and a gate electrode connected to the first electrode of the second MOS transistor;
a fourth MOS transistor having a first electrode connected to the first electrode of the second MOS transistor, a second electrode connected to the gate electrode of the second MOS transistor, and a gate electrode; and
a fifth MOS transistor having a first electrode connected to the gate electrode of the second MOS transistor, a second electrode to which a direct-current voltage is applied, and a gate electrode; and
a controller that makes the individual pixels perform image sensing by turning on the first and fourth MOS transistors and turning off the fifth MOS transistor so that the second MOS transistor operates in a subthreshold region below a threshold voltage thereof and that detects variations in sensitivity of the individual pixels due to variations in the threshold voltage of the second MOS transistors by turning off the first and fourth MOS transistors and turning on the fifth MOS transistor and then varying a voltage fed to the second electrode of the second MOS transistor.
8. An image-sensing apparatus as claimed in claim 7 ,
wherein the pixels each further include a seventh MOS transistor having a first electrode connected to the second electrode of the third MOS transistor, a second electrode connected to an output signal line, and a gate electrode connected to a line select line.
9. An image-sensing apparatus as claimed in claim 7 ,
wherein the pixels each further include a sixth MOS transistor having a first electrode to which a direct-current voltage is applied, a second electrode, and a gate electrode connected to the second electrode of the third MOS transistor, the sixth MOS transistor amplifying a signal output from the second electrode of the third MOS transistor.
10. An image-sensing apparatus as claimed in claim 9 ,
wherein the pixels each further include a seventh MOS transistor having a first electrode connected to the second electrode of the sixth MOS transistor, a second electrode connected to an output signal line, and a gate electrode connected to a line select line.
11. An image-sensing apparatus as claimed in claim 9 ,
wherein the third MOS transistor receives at the first electrode thereof a direct-current voltage, and
wherein the pixels each further include:
an eighth MOS transistor having a first electrode connected to the second electrode of the third MOS transistor, a second electrode connected to a direct-current voltage, and a gate electrode; and
a second capacitor having one end connected to the second electrode of the third MOS transistor, the second capacitor being reset through the eighth MOS transistor when a reset voltage is fed to the gate electrode of the eighth MOS transistor.
12. An image-sensing apparatus comprising:
a plurality of pixels, the pixels each including a photoelectric conversion portion that outputs an electric signal produced in accordance with amount of incident light and converted natural-logarithmically and a lead-out path by way of which the electric signal output from the photoelectric conversion portion is fed to an output signal line, the photoelectric conversion portion comprising:
a photosensitive element;
a circuit for producing a natural-logarithmically converted electric signal, said circuit including a first transistor having a first electrode, a second electrode and a control electrode;
a first switching element having a first terminal connected to the photosensitive element and second terminal connected to the first electrode of the first transistor;
a second transistor having a first electrode, a second electrode and a control electrode, said control electrode of the second transistor receiving an electric signal output from the circuit; and
a controller that makes the individual pixels perform image sensing by turning on the first switching element and feeding a first voltage to the second electrode of the first transistor so that the first transistor operates in a subthreshold region and that turns off the first switching element for resetting the individual pixels, said controller temporarily feeding a second voltage to the second electrode of the first transistor during the first switching element is turned off, said second voltage being different from the first voltage so that the individual pixels are brought into a substantially identical initial state.
13. An image-sensing apparatus as claimed in claim 12 ,
wherein the first electrode and the control electrode of the first transistor are electrically connected to the control electrode of the second transistor.
14. An image-sensing apparatus as claimed in claim 12 ,
wherein said photoelectric conversion portion further comprises a second switching element provided between the first electrode and the control electrode of the first transistor.
15. An image-sensing apparatus as claimed in claim 12 ,
wherein the control electrode of the first transistor is insulated with the control electrode of the second transistor.
16. An image-sensing apparatus as claimed in claim 12 , wherein said second voltage causes a higher current to flow through said first transistor than the current flow through said first transistor during said image sensing.