Method and apparatus for variable time pulse sampling
Methods and apparatus for variable time sampling of optical pulses by a unit cell are disclosed. The methods may include detecting whether an amplitude of an optical pulse incident on one or more photo-detecting elements exceeds a sampling threshold, and while the pulse amplitude remains above the sampling threshold, iteratively sampling the optical pulse at a sampling rate that varies based on changes in the pulse amplitude.
1. A method of variable time sampling, by a unit cell, of optical pulses incident on one or more photo-detecting elements, the method comprising:
the unit cell detecting whether an amplitude of an optical pulse signal, received from and corresponding to an optical pulse incident on one or more of the photo-detecting elements, exceeds a sampling threshold; and
while the optical pulse signal amplitude remains above the sampling threshold, iteratively sampling the optical pulse signal at a sampling rate that varies based on changes in the optical pulse signal amplitude.
2. The method of claim 1 , wherein iteratively sampling the optical pulse signal comprises resetting an interval of the sampling rate upon each discrete detection of a change in the optical pulse signal amplitude exceeding at least one amplitude change threshold.
3. The method of claim 2 , further comprising setting the at least one amplitude change threshold prior to iteratively sampling the optical pulse signal.
4. The method of claim 2 , further comprising dynamically setting the at least one amplitude change threshold in response to an input.
5. The method of claim 1 , wherein the sampling rate varies in proportion to changes in an integral of the optical pulse signal amplitude.
6. The method of claim 5 , wherein iteratively sampling the optical pulse signal comprises resetting an interval of the sampling rate upon each discrete detection of a change in the optical pulse signal amplitude integral exceeding at least one amplitude integral change threshold.
7. The method of claim 1 , further comprising increasing the sampling rate with increasing optical pulse signal amplitude, and decimating the sampling rate with decreasing optical pulse signal amplitude.
8. The method of claim 1 , further comprising capturing a peak amplitude of the optical pulse signal when a time interval of the sampling rate is at a minimum.
9. The method of claim 1 , further comprising reconstructing a pulse shape of the optical pulse signal from sampled data for the optical pulse signal, including a peak amplitude of the optical pulse signal.
10. The method of claim 1 , wherein iteratively sampling the optical pulse signal further comprises:
enabling pulse detection logic to simultaneously gate the pulse amplitude to a first integrator, enabling the first integrator and a sample time integrator, wherein if the pulse detection logic is disabled, the first integrator and sample time integrator are held in a reset state;
comparing an integrated optical pulse signal amplitude output from the first integrator to a Δ-amplitude threshold that effectively determines the sampling rate; and
if the integrated optical pulse signal amplitude output exceeds the Δ-amplitude threshold, capturing a Δt output of the sample time integrator associated with the integrated optical pulse signal amplitude output exceeding the Δ-amplitude threshold, and then resetting the sample time integrator and first integrator.
11. The method of claim 10 , further comprising:
when the pulse amplitude falls back below the sampling threshold, disabling the pulse detection logic, thereby resetting the first integrator and sample time integrator, and causing a sample controller to signal externally that optical pulse sampling data is available for reading.
12. The method of claim 10 , further comprising feeding the sample time integrator a sample timing value T s that controls a time resolution of the sample time integrator.
13. The method of claim 10 , further comprising enabling the pulse detection logic in response to control logic from a neighboring unit cell.
14. The method of claim 1 , wherein the one or more photo-detecting elements comprises a plurality of adjacent pixels, and the method further comprising computing an angle of arrival of the optical pulse from changes in respective peak amplitudes measured by the plurality of adjacent pixels.
15. The method of claim 1 , further comprising:
when the pulse amplitude falls back below the sampling threshold, signaling externally that optical pulse sampling data is available for reading.
16. The method of claim 1 , further comprising capturing a time of arrival for the incident optical pulse when the optical pulse signal amplitude exceeds the sampling threshold.