Photoelectric converter and a method of driving the same
View Patent ↗A photoelectric converter capable of reducing random noise comprises a photoelectric conversion circuit for generating an optical signal in correspondence to incident light, a reset circuit connected to an output terminal of the photoelectric conversion circuit, and an amplification circuit connected to output terminals of the photoelectric conversion circuit and the reset circuit. An electric charge transfer unit has one terminal connected to an output terminal of the amplification circuit and another terminal connected to a capacitor. A source follower amplifier has a gate connected to the electric charge transfer unit and the capacitor, and a channel selection circuit is connected to a source of the source follower amplifier. A common signal line is connected to an output terminal of the channel selection circuit, a first current source is connected to the common signal line, and a second current source is connected to the source of the source follower.
1. A photoelectric converter, comprising:
a photoelectric conversion circuit for generating an optical signal in correspondence to incident light;
a reset circuit connected to an output terminal of the photoelectric conversion circuit;
an amplification circuit connected to output terminals of the photoelectric conversion circuit and the reset circuit;
an electric charge transfer unit having a terminal connected to an output terminal of the amplification circuit;
a capacitor connected to the other terminal of the electric charge transfer unit;
a source follower amplifier having a gate connected to the electric charge transfer unit and the capacitor;
a channel selection circuit connected to a source of the source follower amplifier;
a common signal line to which an output terminal of the channel selection circuit is connected;
a first current source connected to the common signal line; and
a second current source connected to the source of the source follower amplifier;
wherein the capacitor holds a reference signal generated through resetting of the photoelectric conversion circuit by the reset circuit, and when the channel selection circuit is turned ON, the reference signal is read out from the capacitor to the common signal line, and then the electric charge transfer unit is turned ON to read out the optical signal to the common signal line.
2. A photoelectric converter according to claim 1 ; wherein after the reference signal and the optical signal are read out to the common signal line, the channel selection circuit is turned OFF, and the electric charge transfer unit is turned ON to read out to the capacitor a reference signal generated through resetting of the photoelectric conversion circuit by the reset circuit.
3. A photoelectric converter according to claim 1 ; wherein while the channel selection circuit is held in an ON state, the first current source is turned ON to cause a current to flow, and when the electric charge transfer unit is turned ON to read out the reference signal to the capacitor, the second current source is turned ON to cause a current to flow.
4. A photoelectric converter according to claim 1 ; wherein the current caused to flow through the second current source is substantially the same as that caused to flow through the first current source.
5. A photoelectric converter according to claim 1 ; wherein the first and second current sources are constituted by MOS transistors, respectively, and drains of the MOS transistors are connected to a source of the source follower amplifier, and control for turning ON and OFF of the first and second current sources is carried out by changing gate voltages of the MOS transistors.