Solid-state image-sensing device having a plurality of controlled pixels, with each pixel having a transfer gate signal that is ternary-voltage signal switched among three levels, and method of operating same
By feeding an appropriate voltage as a signal φTX to a transfer gate TG, a MOS transistor T 1 is operated in a threshold region. A potential linearly or natural logarithmically converted by a buried photodiode PD is transferred to an N-type floating diffusion layer FD so as to be fed out, as an image signal, via MOS transistors T 3 and T 4.
1. A solid state image sensing device comprising:
a plurality of pixels, each pixel including:
a buried photodiode that generates and accumulates therewithin a photoelectric charge commensurate with an amount of incident light;
a transfer gate that transfers the photoelectric charge accumulated in the buried photodiode;
a floating diffusion layer that accumulates therewithin the photoelectric charge transferred from the buried photodiode via the transfer gate;
a reset gate that is electrically connected to the floating diffusion layer to reset the floating diffusion layer;
an amplifier that is electrically connected to the floating diffusion layer;
a read-out switch for reading out an output signal amplified by the amplifier; and
a transistor that has the transfer gate as a control electrode, that has the floating diffusion layer as a first electrode, and that has the buried photodiode as a second electrode;
a first voltage application circuit that applies to the transfer gate a voltage switched among a first, a second, and a third voltage, the first voltage bringing the transistor into a non-conducting state, the third voltage bringing the transistor into a conducting state, the second voltage lying between the first and third voltage; and
a second voltage application circuit that causes the reset gate to be in an on state or in an off state,
wherein
when the reset gate is in the on state, the first voltage application circuit applies the second voltage to the transfer gate so that the photoelectric charge commensurate with the amount of incident light is accumulated within the buried photodiode, and that the transistor operates in a subthreshold region at least in part of a brightness range of the light incident on the buried photodiode to make the buried photodiode and the transistor perform linear photoelectric conversion under a predetermined amount of incident light and logarithmic photoelectric conversion at or over the predetermined amount of incident light,
when the reset gate is in the off state, the first voltage application circuit applies the third voltage to the transfer gate to transfer the photoelectric charge accumulated in the buried photodiode to the floating diffusion layer,
when the reset gate is in the off state, the first voltage application circuit applies the first voltage to the transfer gate to inhibit transfer of the photoelectric charge from the buried photodiode, and a voltage signal commensurate with the photoelectric charge transferred to the floating diffusion layer is outputted, and
during an entire time period between accumulation of the photoelectric charge in the buried photodiode under application of the second voltage to the transfer gate and until a beginning of output of the voltage signal, the reset gate is switched once from the on state to the off state and is kept in the off state by the second voltage application circuit.
2. A method of operating a solid state image sensing device comprising a plurality of pixels, wherein each pixel comprises:
a buried photodiode that generates and accumulates therewithin a photoelectric charge commensurate with an amount of incident light;
a transfer gate that transfers the photoelectric charge accumulated in the buried photodiode;
a floating diffusion layer that accumulates therewithin the photoelectric charge transferred from the buried photodiode via the transfer gate;
a reset gate that is electrically connected to the floating diffusion layer to reset the floating diffusion layer;
an amplifier that is electrically connected to the floating diffusion layer;
a read-out switch for reading out an output signal amplified by the amplifier; and
a transistor that has the transfer gate as a control electrode, that has the floating diffusion layer as a first electrode, and that has the buried photodiode as a second electrode;
a first voltage application circuit that applies to the transfer gate a voltage switched among a first, a second, and a third voltage, the first voltage bringing the transistor into a non-conducting state, the third voltage bringing the transistor into a conducting state, the second voltage lying between the first and third voltage; and
a second voltage application circuit that causes the reset gate to be in an on state or in an off state,
the method comprising the following steps:
applying the second voltage to the transfer gate while the reset gate is in the on state, so that the photoelectric charge commensurate with the amount of incident light is accumulated within the buried photodiode, and that the transistor operates in a subthreshold region at least in part of a brightness range of the light incident on the buried photodiode to make the buried photodiode and the transistor perform linear photoelectric conversion under a predetermined amount of incident light and logarithmic photoelectric conversion at or over the predetermined amount of incident light;
applying the third voltage to the transfer gate to transfer the photoelectric charge accumulated in the buried photodiode to the floating diffusion layer while the reset gate is in the off state;
applying the first voltage to the transfer gate to inhibit transfer of the photoelectric charge from the buried photodiode; and
outputting a voltage signal commensurate with the photoelectric charge transferred to the floating diffusion layer,
wherein, during an entire time period between accumulation of the photoelectric charge in the buried photodiode under application of the second voltage to the transfer gate and until a beginning of output of the voltage signal, the reset gate is switched once from the on state to the off state and is kept in the off state.