Photon-Counting Image Sensor Pulse Shaping for Glitch-Free Macropixels
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Solution Overview
Problem
Conventional image sensors with photon-counting detector elements, such as SPADs, often generate irregular pulses or glitches in their macropixel output lines, which can cause errors and malfunctions in downstream electronic modules.
Innovation Solution
The image sensor incorporates a first group of pulse shapers to convert signals into pulse shaper output streams with a minimum pulse length, and a connection unit to combine these streams into a macropixel stream. A monostable/astable circuit then processes the macropixel stream to create a pulse-free interval, ensuring that pulses are adequately spaced to prevent errors in subsequent electronics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If multiple pulse shaper output streams are combined into a macropixel stream using OR connection, then the aggregation of information from multiple SPADs is achieved, but irregular pulses and glitches are generated that can cause errors in downstream electronics
Solution Approach 1:
A deadtime generator circuit is introduced as an intermediary component between the connection unit and downstream electronic modules. This circuit generates a deadtime signal that temporarily disables downstream electronics during the OR connection operation, preventing irregular pulses and glitches from causing errors while allowing aggregated information to be processed safely
Solution Approach 2:
The deadtime generator circuit proactively generates a deadtime signal before potential glitches can affect downstream electronics. By anticipating the occurrence of irregular pulses during OR connection and preemptively disabling the downstream electronics, the system prevents errors before they occur
2Duration of action of stationary object
If electronic modules are swapped over time in double buffering fashion, then system continuity is maintained, but spurious pulses appear when switching coincides with photon arrival
Solution Approach 1:
The deadtime generator circuit acts as a mediator during bank switching operations. When a bank switch is detected, the circuit generates a deadtime signal that temporarily disables the downstream electronic module, preventing spurious pulses from occurring during the switching transition while maintaining system continuity through double buffering
Solution Approach 2:
The system applies preliminary anti-action by detecting bank switch events and proactively generating deadtime signals before spurious pulses can be generated. This counter-measure prevents the harmful effect of spurious pulses during bank switching while maintaining uninterrupted system operation
3Device complexity
If pulses from multiple SPADs are combined into a single macropixel signal, then the number of interconnection lines is reduced, but timing and intensity information is preserved while location information is lost
Solution Approach 1:
The system segments the macropixel output into multiple time bins, with each time bin preserving the timing information of photons from different SPADs. By dividing the temporal domain into discrete segments, the system maintains both the aggregated signal benefits and the ability to recover timing and location information through time-correlated single-photon counting
Data Source
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AI summary
An image sensor includes photon-counting detector elements (10) and a first group of pulse shapers (20) to convert signals (12) from the photon-counting detector elements (10) into pulse shaper output streams (22) in which pulses (23) have at minimum a first pulse length (t1). A connection unit (30) combines a plurality of the pulse shaper output streams (22) into at least one macropixel stream (32). The at least one macropixel stream (32) is processed by at least one monostable/astable circuit (40) which outputs a processed stream (42) in which pulses (43) have a second pulse length (t2). The second pulse length (t2) is shorter than the first pulse length (t1) by a time span t_PF and thus a pulse-free interval (PF) for at least the time span t_PF is created after each pulse (43) in the processed stream (42).