Distance measurement sensor with multiple memory nodes

A method for implementing a CMOS active-pixel image sensor with multiple memory nodes for indirect time-of-flight IToF distance measurement on a scene under observation,

• the image sensor (52) comprising:
• a set of a whole number Nk, greater than or equal to 1, of CMOS active pixels (102;
• 302) Pix#k, k varying from 1 to Nk, each having a photosensitive area PhDk and a whole number M, greater than or equal to 2, of memory nodes MNk,m, m varying from 1 to M;
• a subsystem (66) for the non-destructive fast readout of the Nk times M memory nodes MNk,m and for controlling the mechanism for inhibiting the exposure of the Nk pixels Pix#k, implemented during the acquisition of an image by the Nk pixels;
• an image readout subsystem (62) for the M memory nodes MNk,m of each pixel Pix#k, k varying from 1 to Nk;
• an image preprocessing subsystem (64);
• the method for implementing the image sensor during the acquisition of an image comprising steps in which:
• the image readout subsystem (62) reads the M memory nodes MNk,m of each pixel (102;
• 302) Pix#k, k varying from 1 to Nk, establishes, through analog-to-digital conversion, Nk times M digital values, representative of quantities of charges generated by the photosensitive areas PhDk, k varying from 1 to Nk, and integrated by the M memory nodes MNk,m during a pixel exposure image duration, less than or equal to a predetermined maximum exposure image duration Tmax_exp, and supplies the M times Nk read digital values at output;
• the image preprocessing subsystem (64) applies digital processing operations to said digital values supplied at output by the image readout subsystem (62) and sends preprocessed pixel-level image data to an application system for determining indirect times-of-flight IToF of a scene under observation;
• and
• the method for implementing the image sensor being characterized in that:
• the subsystem (66) for the non-destructive fast readout of the Nk times M memory nodes MNk,m and for controlling the mechanism for inhibiting the exposure of the Nk pixels Pix#k, on each of the Nk pixels Pix#k, k varying from 1 to Nk, performs, during a current cycle Cycle_acq#k,s of acquiring an image s, a predetermined whole number Nr of non-destructive fast read operations FCr, r varying from 0 to Nr-1, on the voltages present on the M memory nodes MNk,m, m varying from 1 to M, and after each fast read operation FCr, determines a signal for inhibiting the exposure of the pixel Pix#k, based on a decision criterion as to whether or not to continue the exposure of the pixel Pix#k, the decision criterion being dependent on the voltage values read non-destructively from the M memory nodes MNk,m after said fast read operation FCr and on one or more decision thresholds;
• and
• the signal for inhibiting each pixel Pix#k charges or discharges an inhibition memory point (IMk) of the pixel Pix#k in order to activate or deactivate the mechanism for inhibiting the pixel by driving at least one transistor (TIk, TIkm) for inhibiting the exposure of the pixel.