Circuit to improve sensing efficiency of pixels
There is provided a circuit to improve the sensing efficiency of pixels that uses the induction effect of a capacitor to duplicate a voltage deviation caused by additional electrons and uses a circuit to cancel out the voltage deviation during reading pixel data thereby improving the sensing efficiency.
1. A sensor circuit, comprising:
a photodiode;
a first voltage source having a first reset voltage;
a second voltage source having a second reset voltage;
a capacitor having a first electrode and a second electrode, the first electrode coupled to a floating diffusion node and having a sensing voltage generated by the photodiode at a start time of a storage interval, and the second electrode having the second reset voltage at the start time of the storage interval, wherein the first and second electrodes have an identical physical characteristic to induce an identical influence at the first and second electrodes when a variation is triggered by sensing noises in the storage interval;
a rear reset transistor connected between the second voltage source and the second electrode of the capacitor;
a readout circuit configured to
read, after the storage interval and when the first electrode of the capacitor is connected to the first voltage source, a first readout voltage on the second electrode of the capacitor,
read, after the first readout voltage is read and when the second electrode of the capacitor is connected to the second voltage source, a second readout voltage on the second electrode of the capacitor, and
calculate a voltage difference between the first readout voltage and the second readout voltage to cancel out a noise voltage generated within the storage interval; and
a source follower transistor, having a gate coupled to the second electrode of the capacitor, and having a source and a drain connected between the first voltage source and the readout circuit.
2. The sensor circuit as claimed in claim 1 , further comprising a reset transistor connected between the first voltage source and the photodiode.
3. The sensor circuit as claimed in claim 2 , further comprising:
a third voltage source; and
a transfer control transistor connected between the first electrode of the capacitor and the photodiode; and
a dump transistor connected between the third voltage source and the first electrode of the capacitor.
4. The sensor circuit as claimed in claim 1 , wherein when the first electrode of the capacitor is connected to the first voltage source, the second electrode of the capacitor is floated till the first readout voltage on the second electrode is read.
5. The sensor circuit as claimed in claim 1 , wherein the first and second electrodes have an identical area.
6. The sensor circuit as claimed in claim 1 , wherein the first and second electrodes have an identical shape.
7. The sensor circuit as claimed in claim 1 , wherein the first and second electrodes have an identical doping concentration.
8. The sensor circuit as claimed in claim 1 , wherein the first and second electrodes have an identical manufacturing procedure.
9. The sensor circuit as claimed in claim 1 , wherein the readout circuit is configured to
read the first readout voltage before the second electrode of the capacitor is reset by the second voltage source via the rear reset transistor after the storage interval, and
read the second readout voltage after the second electrode of the capacitor is reset by the second voltage source via the rear reset transistor after the storage interval.