Time-resolving sensor using spad + ppd or capacitors in pixel for range measurement

A three-dimensional (3D) imaging system, comprising:

• an array of single-photon avalanche diodes (SPADs), each SPAD being responsive to an active shutter signal to generate an output signal based on detecting one or more photons that are incident on the SPAD, the one or more photons being reflected from an object;
• at least one logic circuit, each logic circuit being coupled to the output signal of at least one SPAD and to generate a first enable signal and a second enable signal, the first enable signal being active in response to a beginning of the active shutter signal and being inactive in response to the output signal of the at least one SPAD, and the second enable signal being in active in response to the output signal of the at least one SPAD and being inactive in response to an end of the active shutter signal;
• and
• at least one time-resolving sensor, each time-resolving sensor comprising:
• a differential time-to-charge converter (DTCC) circuit coupled to the first and second enable signals of a corresponding logic circuit, the DTCC circuit comprising:
• a capacitor device having a first terminal and a second terminal, the second terminal being coupled to a ground voltage;
• a first switching device having first, second and third terminals, the first terminal of the first switching device being coupled to the first terminal of the capacitor device, the second terminal of the first switching device being coupled to a first floating diffusion, and the third terminal of the first switching device being coupled to the first enable signal, the first switching device being responsive to the first enable signal to transfer a first charge on the capacitor device to the first floating diffusion;
• a second switching device having first, second and third terminals, the first terminal of the second switching device being coupled to the first terminal of the capacitor device, the second terminal of the second switching device being coupled to a second floating diffusion, and the third terminal of the second switching device being coupled to the second enable signal, the second switching device being responsive to the second enable signal to transfer a remaining charge on the capacitor device to the second floating diffusion;
• and
• an output circuit to output a first voltage that is based on the first charge on the first floating diffusion and a second voltage that is based on the remaining charge on the second floating diffusion, a first ratio of the first voltage to a sum of the first voltage and the second voltage being proportional to a time of flight of the one or more photons, and a second ratio of the second voltage to the sum of the first voltage and the second voltage being proportional to the time of flight of the one or more photons.

A method to resolve time, comprising:

• generating an active shutter signal;
• detecting at at least one single-photon avalanche diode (SPAD) one or more photons that are incident on the at least one SPAD during the active shutter signal, the one or more photons being reflected from an object;
• generating an output signal based on the one or more photons;
• generating a first enable signal and a second enable signal based on the output signal, the first enable signal being active in response to a beginning of the active shutter signal and being inactive in response to the output signal, and the second enable signal being active in response to the output signal and being inactive in response to an end of the active shutter signal;
• transferring a charge on a capacitor device to a first floating diffusion to form a first charge on the first floating diffusion if the first enable signal is active;
• transferring a remaining charge on the capacitor device to a second floating diffusion to form a second charge on the second floating diffusion if the second enable signal is active;
• and
• outputting a first voltage based on the first charge and the second voltage based on the second charge, a first ratio of the first voltage to a sum of the first voltage and the second voltage being proportional to a time of flight of the one or more photons, and a second ratio of the second voltage to the sum of the first voltage and the second voltage being proportional to the time of flight of the one or more photons.