Dynamic Latch SPAD Front End for Low Power Time-of-Flight Ranging
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Solution Overview
Problem
Time-of-flight ranging systems with large arrays of single photon avalanche diodes (SPADs) face excessive power consumption and accuracy issues due to continuous charging and discharging of capacitances, as well as sensitivity to supply and ground disturbances, which is undesirable in battery-powered or low-power applications.
Innovation Solution
A dynamic latch based system that asserts a photon received signal and uses differential timing references to latch data values, counting latching events to determine the phase of reflected laser light, thereby reducing power consumption and improving accuracy by only activating the latch when a detection event occurs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If full swing timing reference signals are driven continuously into and out of the SPAD array, then proper timing reference function is maintained, but excessive power is consumed due to continuous charging and discharging of capacitances
Solution Approach 1:
The patent applies periodic action by transitioning from continuous full-swing timing reference signals to event-triggered periodic latching operations. The dynamic latch circuit is activated only when photon detection events occur, rather than continuously charging and discharging capacitances. This periodic, event-driven approach maintains timing reference functionality while dramatically reducing power consumption in battery-powered or low-power TOF systems.
2Reliability
If full swing timing reference signals are used, then timing reference function is maintained, but the system becomes sensitive to supply and ground disturbances that alter timing references
Solution Approach 1:
The patent applies dynamics by using a dynamic latch circuit that adapts its operation based on detection events. The latch circuit dynamically captures timing reference values only when photons are detected, rather than continuously following full-swing signals. This dynamic approach makes the system less sensitive to supply and ground disturbances because the latch holds stable captured values between events, isolating the timing measurement from voltage fluctuations.
3Measurement precision
If a large array of SPADs is implemented, then detection capability is improved, but power consumption increases due to continuous operation of all timing references
Solution Approach 1:
The patent applies segmentation by dividing the timing reference operation into independent, event-triggered latching units rather than a continuous system operating all timing references simultaneously. Each detection event triggers localized latching operations only for the relevant SPAD channels, rather than continuously driving all timing references across the entire large array. This segmented, event-driven approach maintains detection capability while reducing overall power consumption.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution significantly reduces power consumption and enhances accuracy by minimizing unnecessary charging and discharging of capacitances, while maintaining system functionality even with supply and ground disturbances, making it suitable for battery-powered applications.
Implementation Method 1
single photon avalanche detector (SPAD) front end for counting detections of ranging light photons
Data Source
AI summary
A time-of-flight ranging system disclosed herein includes a receiver asserting a photon received signal in response to detection of light that has reflected off a target and returned to the time-of-flight ranging system. A first latch circuit has first and second data inputs receiving a first pair of differential timing references, the first latch circuit latching data values at its first and second data inputs to first and second data outputs based upon assertion of the photon received signal. A first counter counts latching events of the first latch circuit during which the first data output is asserted, and a second counter counts latching events of the first latch circuit during which the second data output is asserted. Processing circuitry determines distance to the target based upon counted latching events output from the first and second counters.