Semiconductor devices with single-photon avalanche diode pixels
A semiconductor device may include an array of single-photon avalanche diode pixels. The single-photon avalanche diode (SPAD) pixels may include a SPAD coupled to a supply voltage terminal via first and second reset paths. The first reset path may be a fast reset path that provides the SPAD with a short recovery time. The second reset path may be a slower reset path that provides the SPAD with a longer recovery time, but is used to ensure the SPAD is quenched even when the quench resistance associated with the first reset path is low. Logic circuitry may selectively activate the first or the second resets to quench and reset the SPAD. A SPAD pixel may also include one or more switches that keep nodes in the SPAD pixel at a constant voltage when the SPAD pixel is inactive.
1. An image pixel, comprising:
a single-photon avalanche diode coupled between first and second supply voltage terminals;
a first reset path coupling the single-photon avalanche diode to the second supply voltage terminal;
a second reset path coupling the single-photon avalanche diode to the second supply voltage terminal;
a first transistor coupled along the first reset path;
a second transistor coupled along the second reset path; and
logic circuitry configured to generate a first control signal for a gate terminal of the first transistor and a second control signal for a gate terminal of the second transistor.
2. The image pixel defined in claim 1 , wherein the first supply voltage terminal is configured to provide a positive supply voltage and the second supply voltage terminal is configured to provide a grounding voltage.
3. The image pixel defined in claim 2 , wherein the single-photon avalanche diode has a first terminal coupled to the first supply voltage terminal and a second terminal that is coupled to a node and wherein the first and second transistors are coupled in parallel between the node and the second supply voltage terminal.
4. The image pixel defined in claim 1 , wherein the first control signal is an inverted version of the second control signal.
5. The image pixel defined in claim 1 , further comprising:
a readout path coupling the single-photon avalanche diode to readout circuitry; and
delay circuitry coupled along the readout path, wherein the delay circuitry has an input that is coupled to the logic circuitry.
6. The image pixel defined in claim 5 , further comprising:
buffer circuitry coupled along the readout path between the delay circuitry and the readout circuitry, wherein the buffer circuitry has an output that is coupled to the logic circuitry.
7. The image pixel defined in claim 6 , wherein the logic circuitry is configured to generate the first and second control signals based on signals received from the input of the delay circuitry and the output of the buffer circuitry.
8. The image pixel defined in claim 7 , further comprising:
a third transistor coupled in series with the first transistor along the first reset path, wherein an output of the delay circuitry is coupled to a gate terminal of the third transistor.
9. The image pixel defined in claim 5 , further comprising:
switching circuitry operable to couple the input of the delay circuitry to a third supply voltage terminal and operable to couple an output of the delay circuitry to the second supply voltage terminal.
10. A semiconductor device comprising:
a pixel that includes:
a single-photon avalanche diode having a first terminal coupled a supply voltage terminal and a second terminal coupled to a node, wherein the node is pulled to a first voltage in response to an incident photon;
a first transistor that is coupled to the node;
a second transistor that is coupled to the node and that is operable to pull the node to a second voltage;
a third transistor that is coupled in series with the first transistor, wherein the first and third transistors are operable to pull the node to the second voltage; and
a readout path, wherein the first, second, and third transistors are controlled based on a set of signals generated along the readout path.
11. The semiconductor device defined in claim 10 , wherein the pixel includes:
readout circuitry coupled to the node using the readout path; and
delay circuitry interposed between the node and the readout circuitry.
12. The semiconductor device defined in claim 11 , wherein the pixel includes:
a pull-up transistor coupling the node to a first additional supply voltage terminal; and
a pull-down transistor coupling an output of the delay circuitry to a second additional supply voltage terminal.
13. The semiconductor device defined in claim 12 , wherein the pull-up transistor and pull-down transistor are enabled when the pixel is inactive.
14. The semiconductor device defined in claim 10 , wherein the first transistor is controlled based on a first signal generated along the readout path and wherein the second and third transistors are controlled based on second and third signals generated along the readout path.
15. A semiconductor device comprising:
a single-photon avalanche diode coupled between first and second supply voltage terminals;
a first transistor coupling the single-photon avalanche diode to the second supply voltage terminal, the first transistor having a first gate terminal configured to receive a first control signal; and
a second transistor coupling the single-photon avalanche diode to the second supply voltage terminal, the second transistor having a second gate terminal configured to receive a second control signal that is an inverted version of the first control signal.