Solid state imaging device and differential circuit having an expanded dynamic range
A solid-state imaging device that is configurable into a small size appropriate for expanding dynamic range includes: a photodiode which is a photoelectric conversion unit that generates charge by incident light; a MOS transistor which is connected to the photodiode and transfers the charge; a floating diffusion region which is a first accumulation unit which accumulates the charge via the MOS transistor; a MOS transistor which is a second transfer unit connected to the floating diffusion region and connected in series to the MOS transistor; and a MOS transistor which is an output unit which outputs, via the MOS transistor, a signal voltage in accordance with an amount of the charge.
1. A solid-state imaging device including a plurality of pixel circuits two-dimensionally arranged on a semiconductor substrate, said solid-state imaging device comprising:
a photoelectric conversion unit configured to generate a charge from incident light;
a first transfer unit connected to said photoelectric conversion unit and configured to transfer the charge;
a first accumulation unit configured to accumulate the charge via said first transfer unit;
a second transfer unit connected to said first accumulation unit and connected in series to said first transfer unit;
an output unit configured to output a signal voltage that is a voltage according to an amount of the charge via said second transfer unit; and
a reset unit configured to set a voltage of a connection point between said second transfer unit and said output unit to a reset voltage,
wherein said output unit is configured to output a reference voltage in a state where the reset voltage is applied to the connection point,
said photoelectric conversion unit generates a first charge while the incident light enters said photoelectric conversion unit during a first accumulation time within a first frame period,
said photoelectric conversion unit generates a second charge while the incident light enters said photoelectric conversion unit during a second accumulation time within the first frame period,
the first accumulation time is different from the second accumulation time,
the first transfer unit is configured to transfer the first charge and the second charge to the first accumulation unit,
said first accumulation unit is configured to add and accumulate the first charge and the second charge, and
only one picture is generated during the first frame period based on the first charge and the second charge accumulated by the first accumulation unit.
2. The solid-state imaging device according to claim 1 , further comprising
a differential circuit which detects a difference between the signal voltage and the reference voltage,
wherein said differential circuit includes:
a first capacitor and a second capacitor that are connected in series; and
an initializing switch through which an initializing voltage that is predetermined is applied to a connection point between said first and second capacitors, and
in a state where the initializing voltage is applied to the connection point, said differential circuit holds a difference voltage in said first capacitor and the initializing voltage in said second capacitor, and subsequently divides the reference voltage between said first and second capacitors, the difference voltage being a difference between the signal voltage and the initializing voltage.
3. The solid-state imaging device according to claim 1 ,
wherein each of said first and second transfer units includes a MOS transistor, and
a drain of said first transfer unit is connected to a source of said second transfer unit.
4. The solid-state imaging device according to claim 1 ,
wherein said photoelectric conversion unit, said first transfer unit, said first accumulation unit, said second transfer unit, said output unit, and said reset unit are provided in each of said plurality of pixel circuits.
5. The solid-state imaging device according to claim 1 , wherein said second transfer unit includes a MOS transistor.
6. The solid-state imaging device according to claim 1 , wherein said first accumulation unit has no contact with a metal material.
7. The solid-state imaging device according to claim 1 ,
wherein the first accumulation unit includes a first region of a first conductivity type and a second region having a second conductivity type different from the first conductivity type, and
the second region is disposed on the first region.
8. The solid-state imaging device according to claim 2 ,
wherein said second capacitor includes a plurality of separate capacitors one of which can be selectively connected in series to said first capacitor, and all of which can be coupled in parallel, and
said differential circuit divides the reference voltage between said first capacitor and each of said plurality of separate capacitors, and subsequently couples all of said plurality of separate capacitors in parallel.
9. The solid-state imaging device according to claim 7 ,
wherein the photoelectric conversion unit includes a third region of the first conductivity type and a fourth region of the second conductivity type,
the fourth region is disposed on the third region, and
an impurity concentration of the first conductivity type in the first region is higher than an impurity concentration of the first conductivity type in the third region.