Back to results
US 9,313,434 B2Granted
Pixel circuit with capacitor discharge indicative of number of events
AssigneeSTMicroelectronics (Research & Development) Limited
InventorsNeale Dutton, Robert Kerr Henderson
Life of this patent
Estimating the term…
Abstract
A pixel circuit includes a single photon avalanche diode (SPAD) and a measurement circuit including a capacitance. The circuit is operable to discharge a known portion of the charge on the capacitance upon each detection of a SPAD event within a time period, such that the charge remaining on the capacitance at the end of the time period corresponds to the number of SPAD events detected within the time period. A time resolved imaging apparatus includes an array of such pixel circuits. A method of counting photon detection includes sensing photons with a SPAD device and discharging a known portion of the charge on a capacitance upon each detection of a SPAD event within a time period.
Claims24
A pixel circuit, comprising:
- a single photon avalanche diode (SPAD) configured to detect SPAD events;
- a measurement circuit comprising a capacitance,
- wherein said measurement circuit is operable to discharge a portion of the charge on said capacitance upon each SPAD event detection within a time period, such that the charge remaining on said capacitance at the end of the time period corresponds to the number of SPAD events detected within the time period;
- and
- a time gating stage operable to begin sensing operation on reception of an enable signal and comprising:
- a switch operable to selectively connect the SPAD output to the measurement circuit on reception of said enable signal;
- and
- two further switches operable to disable the pixel circuit on reception of a disable signal.
5 more elements
A time resolved imaging apparatus, comprising:
- an array of pixel circuits, each pixel circuit comprising:
- a single photon avalanche diode (SPAD) configured to detect SPAD events;
- a measurement circuit comprising a capacitance,
- wherein said measurement circuit is operable to discharge a portion of the charge on said capacitance upon each SPAD event detection within a time period, such that the charge remaining on said capacitance at the end of the time period corresponds to the number of SPAD events detected within the time period, and
- a radiation source for providing radiation incident on said SPAD;
- wherein the time resolved imaging apparatus is operable to modulate said radiation source and to switch between counting using a first statistical bin and counting using a second statistical bin, said switching being in phase with the modulation of said radiation source.
3 more elements
A method of measuring the time of flight of a photon, comprising:
- activating a radiation source to emit photons;
- detecting photons using a single photon avalanche diode (SPAD);
- discharging a known portion of the charge on a capacitance upon each detection of a photon within a time period, such that the charge remaining on said capacitance at the end of the time period corresponds to the number of photons detected within the time period;
- and
- dividing said time period between a plurality of statistical bins, such that periodically repeating portions of said time period are exclusively assigned to one of said statistical bins.
2 more elements
A pixel circuit, comprising:
- a single photon avalanche diode (SPAD) configured to detect SPAD events;
- a measurement circuit comprising a capacitance,
- wherein said measurement circuit is operable to discharge a portion of the charge on said capacitance upon each SPAD event detection within a time period, such that the charge remaining on said capacitance at the end of the time period corresponds to the number of SPAD events detected within the time period;
- a plurality of measurement circuits, each having a capacitance, wherein each measurement circuit defines a statistical bin;
- and
- wherein the pixel circuit is operable such that:
- said time period is divided between the statistical bins, such that periodically repeating portions of said time period are exclusively assigned to one of said statistical bins;
- and
- wherein each of said measurement circuits is operable to discharge a known portion of the charge on its respective capacitance upon each detection of a SPAD event only during the portion of said time period exclusively assigned to that measurement circuit.
6 more elements
A pixel circuit, comprising:
- a single photon avalanche diode (SPAD) configured to detect SPAD events;
- a measurement circuit comprising a capacitance,
- wherein said measurement circuit is operable to discharge a portion of the charge on said capacitance upon each SPAD event detection within a time period, such that the charge remaining on said capacitance at the end of the time period corresponds to the number of SPAD events detected within the time period;
- comprising a plurality of measurement circuits, each having a capacitance, wherein each measurement circuit defines a statistical bin;
- wherein the photon originates with a modulated radiation source;
- wherein the pixel circuit is operable to:
- define a first statistical bin to coincide with the portion of said time period during which said modulated radiation source is on;
- define a second statistical bin to coincide with the portion of said time period during which said modulated radiation source is off;
- count the number of SPAD events received in each of said first and second statistical bins,
- calculate a phase change in radiation incident on said SPAD compared to radiation having been emitted by said modulated radiation source, from the ratio of the number of SPAD events received in one of said first and second statistical bins to the number of SPAD events received in the other of said first and second statistical bins, and
- calculate from said phase change, the time of flight of radiation emitted by said radiation source and incident on said SPAD.
8 more elements
Dependencies are inferred from the claim text.