Method for reading an image sensor
An image sensor includes a pixel array where each pixel is formed in a portion of a substrate electrically insulated from other portions of the substrate. Each pixel includes a photodetector; a transfer transistor; and a readout circuit comprising one or a plurality of transistors. The transistors of the readout circuit are formed inside and on top of at least one well of the portion. The reading from the photodetector of a pixel of a current row uses at least one transistor of the readout circuit of a pixel of at least one previous row, the well of the pixel of the previous row being biased with a first voltage greater than a second bias voltage of the well of the pixel of the current row.
1 . A method for reading an image sensor that includes a plurality of pixels arranged in rows of a pixel array, wherein each pixel is formed in a portion of a substrate electrically insulated from other portions of the substrate, and each pixel comprises a photodetector, a transfer transistor and a readout circuit comprising one or more transistors, wherein the one or more transistors of the readout circuit are formed inside and on top of a well of said portion, the method comprising:
using at least one transistor of the readout circuit of a pixel of at least one previous row in the pixel array for reading from the photodetector of a pixel of a current row in the pixel array;
biasing the well of the pixel of the at least one previous row at a first bias voltage; and
biasing the well of the pixel of the current row at a second bias voltage;
wherein the first bias voltage is greater than the second bias voltage.
2 . The method according to claim 1 , wherein a difference between said first and second bias voltages is in a range from 0.25 to 1 V.
3 . The method according to claim 1 , comprising reading from the photodetector of the pixel of the at least one previous row before reading from the photodetector of the pixel of the current row.
4 . The method according to claim 1 , further comprising biasing the wells of the pixels of the array on a row by row basis.
5 . The method according to claim 1 , wherein said one or more transistors of the readout circuit are P-channel MOS transistors.
6 . The method according to claim 5 , wherein the substrate is P-type doped and the well is N-type doped.
7 . The method according to claim 1 :
wherein using comprises reading from the photodetector of a pixel of a row of rank i using at least one first transistor of the readout circuit of a pixel of a row of rank i−1 and at least one second transistor of the readout circuit of a pixel of a row of rank i−2; and
further comprising biasing the well of the pixel of the row of rank i−2 with a third bias voltage;
wherein the third bias voltage is greater than the second bias voltage of the well of the pixel of the row of rank i.
8 . The method according to claim 7 , wherein the third voltage is equal to the first voltage.
9 . An image sensor configured to implement the method for reading of claim 1 .