Semiconductor Photomultiplier Output Loads for Signal Overshoot Correction
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Solution Overview
Problem
Current semiconductor photomultipliers face performance limitations due to long signal rise and fall times, which compromise their effectiveness in applications like Positron Emission Tomography, Laser Ranging, and High Energy Physics, primarily because the bulk of the signal charge is released as an exponentially decaying current with a long time constant, and existing fast terminal readouts suffer from undesirable overshoot.
Innovation Solution
The semiconductor photomultiplier design incorporates a plurality of photosensitive elements with quench resistive elements and output loads in a parallel configuration, including capacitive and resistive loads, to correct overshoot and minimize time delay variations, allowing for improved signal processing and discrimination between neutron and gamma events.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If conventional readout circuitry is used, then device complexity is reduced, but signal rise and fall times become excessively long
Solution Approach 1:
The device is divided into multiple photosensitive elements (microcells) with individual quench resistive elements and output loads, allowing parallel signal processing that reduces overall signal rise and fall times while maintaining manageable complexity through modular architecture
Solution Approach 2:
A fast terminal signal path is introduced as an additional output dimension alongside the conventional summing node, enabling simultaneous fast and slow readout modes without increasing the complexity of existing circuitry
2Speed
If fast terminal readout is implemented, then signal rise time is improved, but overshoot occurs in the output signal
Solution Approach 1:
The overshoot phenomenon is converted into a useful feature by configuring the capacitive and resistive loads to generate a compensating negative overshoot that cancels the positive overshoot, thereby eliminating the harmful effect while maintaining the fast response benefit
Solution Approach 2:
The values of capacitive and resistive loads are optimized to control the timing and magnitude of the compensating signal, allowing precise adjustment of the overshoot cancellation while maintaining fast signal rise time
3Area of stationary object
If distributed biasing circuitry is used, then device area is reduced, but signal charge release time constant increases
Solution Approach 1:
The biasing function is segmented and distributed to individual photosensitive elements through separate biasing electrodes, reducing the need for large-area centralized biasing circuitry while maintaining fast signal response through localized charge collection
Solution Approach 2:
A third electrode providing a fast terminal output is introduced as an additional dimensional output path that bypasses the slow exponential decay through the distributed biasing circuitry, enabling fast readout without increasing device area
4Power
If Geiger mode APDs are used, then output amplitude is increased, but dark count rate increases
Solution Approach 1:
Each photosensitive element operates in Geiger mode with high gain for maximum output amplitude, while individual quench resistive elements locally control and limit the dark count rate of each microcell, achieving high overall signal amplitude with suppressed total dark count rate through localized control
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
This design enhances the output signal by fully or partially correcting overshoot, achieving faster rise and fall times, improved signal-to-noise ratio, and better discrimination between neutron and gamma events, matching the performance of traditional photomultipliers while reducing output capacitance and increasing the quench time constant for enhanced waveform fidelity.
Implementation Method 1
SPMs are semiconductor photon sensitive devices made up of an array of very small Geiger-mode avalanche photodiode (APD) cells
Implementation Method 2
APDs exhibit internal current gain effect of about 100-1000 due to impact ionization, or avalanche effect, when a high reverse bias voltage is applied
Data Source
AI summary
A semiconductor photomultiplier (SPM) device is described. The SPM comprises a plurality of photosensitive elements, a first electrode arranged to provide a bias voltage to the photosensitive elements, a second electrode arranged as a biasing electrode for the photosensitive elements, a plurality of quench resistive elements each associated with a corresponding photosensitive element, a plurality of output loads; a first node of each output load is common to one of the photosensitive elements and the corresponding quench element; and a third electrode provides an output signal from the photosensitive elements; the third electrode is coupled to a second node of the respective output loads; the outputs loads fully or partially correct an overshoot of the output signal on the third electrode.