Method using a switch and memory to count events
A pulse data recorder system and method are provided. Upon the arrival or occurrence of an event or signal, the state of a digital switch is set. Upon receiving a pulse from a readout clock, the state of the switch is stored in a buffer memory, and the state of the switch is reset. As the readout clock is run, a time history of the state of the switch is obtained. The pulse data recorder can feature a plurality of unit cells, for use in imaging or other multiple pixel applications.
1. A method for counting events, comprising:
detecting a first event;
in response to detecting the first event, setting a state of a first switch;
at a first time, storing the state of the first switch at the first time in a first cell of a first memory;
resetting the state of the first switch; and
at a second time, moving the stored state of the first switch at the first time to a second cell of the first memory, and storing the state of the first switch at the second time in the first cell of the first memory, wherein the second time occurs after the first time and after resetting the state of the first switch.
2. The method of claim 1 , wherein the first time corresponds to a first clock pulse, and wherein the second time corresponds to a second clock pulse.
3. The method of claim 2 , wherein the first memory comprises a 1×M bit shift register.
4. The method of claim 3 , further comprising:
detecting a second event, wherein the second event is received after the first clock pulse and before the second clock pulse, and wherein the second event is received after the state of the first switch has been reset;
in response to detecting the second event and prior to the second clock pulse, setting the state of the first switch; and
in response to the second clock pulse, clocking the memory, wherein the state of the first switch at the first time is stored in a second cell of the memory, and wherein the state of the first switch at the second time is stored in the first cell of the memory.
5. The method of claim 4 , wherein the first switch is a latch, wherein in the absence of detecting an event after a clock pulse the latch is in a first state, wherein said detecting said first event sets the latch to a second state, and wherein resetting sets the latch to the first state.
6. The method of claim 4 , wherein the first event is the arrival of a first photon at a detector, wherein the second event is the arrival of a second photon at the detector, and wherein an elapsed time between said first clock pulse and said second clock pulse provides an intensity of a signal comprising the first and second events.
7. The method of claim 1 , wherein the first event is the arrival of a photon at a detector, wherein detecting the first event includes:
receiving at least a first photon at a first element; and
in response to receiving at least a first photon at a first element, generating a plurality of electrons, wherein the state of the first switch is set by the plurality of electrons.
8. The method of claim 1 , further comprising:
detecting a second event, wherein the first event is detected in association with a first area of a detector and the second event is detected in association with a second area of the detector;
in response to detecting the second event, setting a state of a second switch;
at the first time, storing the state of the second switch in a first cell of a second memory;
resetting the state of the second switch; and
at the second time, moving the stored state of the second switch at the first time to a second cell of the second memory, and storing the state of the second switch at the second time in the first cell of the second memory, wherein the first memory is a first 1×M bit memory, and wherein the second memory is a second 1×M bit memory.
9. The method of claim 8 , wherein the first area of the detector, the first switch, and the first memory comprise a first unit cell of an imaging photon-counting lidar, and wherein the second area of the detector, the second switch, and the second memory comprise a second unit cell of the imaging photon-counting lidar.
10. The method of claim 3 , further comprising:
reading out M bits of data from said 1×M bit shift register.