SPAD Array Readout Using Latched Position and Time Channels
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Achieving high spatial and temporal resolution with silicon photomultiplier (SPAD) arrays is challenging due to the complexity and cost of individualized readout circuitry for each detector, making it impractical to provide both high spatial and temporal resolution simultaneously.
Innovation Solution
A silicon-based photon detector array with a single (x,y) position channel and a single time output channel, utilizing a logical 'OR' connection of SPAD detectors with trigger circuitry and silicon-based readout latches, allowing for high spatial and temporal resolution with relatively simple readout circuitry.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If individualized readout circuitry is provided for each SPAD detector, then spatial resolution is improved, but device complexity and cost increase
Solution Approach 1:
The detector array is segmented into multiple independent SPAD detectors arranged in a two-dimensional grid, with each detector capable of independent photon detection. This segmentation allows spatial resolution to be improved by having many small detection elements while managing complexity through shared readout resources.
Solution Approach 2:
A single shared readout channel is designed to serve multiple SPAD detectors through time-multiplexed operation. The readout circuitry can sequentially or concurrently read out position and timing information from multiple detectors, making one channel perform the function of multiple channels and reducing overall system complexity.
2Measurement precision
If individualized time stamping is provided for each SPAD detector, then temporal resolution is improved, but device complexity and cost increase
Solution Approach 1:
Time stamping information is captured and stored in latches at the moment of photon detection, before the shared readout channel becomes busy. This preliminary action ensures that temporal information is preserved with high resolution even though the readout occurs later through a single channel.
Solution Approach 2:
Latches serve as intermediary storage elements between the SPAD detectors and the shared readout channel. These latches temporarily hold position and timing information, allowing the readout channel to process data from multiple detectors sequentially while maintaining the temporal precision of each detection event.
3Device complexity
If a single readout channel is used for the SPAD array, then device complexity is reduced, but spatial resolution capability is limited
Solution Approach 1:
The single readout channel operates in a periodic or sequential manner, cycling through multiple SPAD detectors in a systematic pattern. This allows the channel to extract position information from multiple detectors over time, achieving spatial resolution capabilities comparable to having individual readout channels for each detector.
Solution Approach 2:
The system transitions from a single spatial dimension of detection to two spatial dimensions by arranging SPAD detectors in a two-dimensional array. The shared readout channel reads out position information corresponding to both x and y coordinates, enabling spatial resolution in two dimensions despite using a single readout channel.
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
Enables high spatial and temporal resolution photon detection with a single readout channel, effectively addressing the complexity and cost issues of existing SPAD array designs, suitable for applications like time-of-flight PET imaging.
Implementation Method 1
When biased above its breakdown voltage, the avalanche diode goes into break down responsive to impingement of a single photon. Such a device is sometimes called a single photon avalanche diode (SPAD) detector. Impingement of a single photon causes the p-n junction to break down in a multiplicative (i.e., 'avalanche') cascade of electrons
Implementation Method 2
In a typical SPAD detector, the avalanche photodiode is reverse biased above its break down voltage and is in series with a quenching resistor. This current is quenched relatively quickly as voltage over the resistor due to the current flow lowers the reverse bias across the avalanche diode to a level below its break down voltage
Data Source
Figure 1
Figure 2
Figure 3
AI summary
A photon detector (10) includes a detector array (12) comprising single photon avalanche diode (SPAD) detectors (14) configured to break down responsive to impingement of a photon. Trigger circuitry (34) is configured to generate a trigger signal responsive to break down of a SPAD detector of the detector array. Latches (20, 22) are configured to store position coordinates of SPAD detectors of the detector array that are in break down. The latches are configured to latch responsive to a trigger signal generated by the trigger circuitry.The latches may include row latches (22) each connecting with a logical "OR" combination of SPAD detectors of a corresponding row of the detector array, and column latches (20) each connecting with a logical "OR" combination of SPAD detectors of a corresponding column of the detector array. Time to digital converter (TDC) circuitry (28) may generate a digital time stamp for the trigger signal.