SPAD Turn-Off Voltage Regulation to Prevent Avalanche and Transistor Damage
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Solution Overview
Problem
Fully depleted single photon avalanche diodes (SPADs) face challenges in being kept off without damaging transistors due to the high anode voltage required, which is necessary to prevent avalanching.
Innovation Solution
A turn-off circuit is introduced, including a sense circuit and a regulation circuit that maintains a constant voltage at the turn-off voltage node by sinking current proportional to the photocurrent, using an amplifier and transistor configuration to manage the photocurrent and prevent avalanching.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the anode voltage is kept high (5-7 volts) to keep the SPAD off, then the SPAD remains non-avalanching, but the transistors T1 and T2 are damaged
Solution Approach 1:
The patent introduces a turn-off circuit as an intermediary between the SPAD anode and the high voltage source. This circuit includes a transistor that actively regulates the anode voltage, allowing the SPAD to be kept off without directly exposing the SPAD and transistors to damaging high voltages. The intermediary circuit manages the voltage distribution to protect sensitive components.
Solution Approach 2:
The patent dynamically changes the voltage parameter at the SPAD anode from a fixed high voltage (5-7V) to a regulated voltage level. By using a turn-off circuit with a transistor, the anode voltage is adjusted to a safe level that prevents avalanching while protecting the transistors from damage. This parameter change resolves the contradiction between maintaining SPAD off-state and preventing transistor damage.
2Reliability
If a clamp diode is used to set the turn-off voltage, then the SPAD can be kept off, but the circuit complexity increases
Solution Approach 1:
The turn-off circuit in the patent serves multiple functions: it acts as a clamp to prevent avalanching, regulates the anode voltage to protect transistors, and provides a controlled off-state for the SPAD. By combining these functions into a single circuit block, the patent reduces overall circuit complexity compared to using separate components for each function.
Solution Approach 2:
The patent merges the clamp diode functionality with the voltage regulation function into a single turn-off circuit. Instead of using a standalone clamp diode that would require additional protection circuits, the patent integrates both functions in one circuit block, thereby reducing component count and simplifying the overall circuit architecture.
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 solution effectively keeps the SPAD off while reducing area and power consumption, enhancing efficiency and suitability for applications like time-of-flight ranging and LiDAR.
Implementation Method 1
When a photon-generated carrier (via the internal photoelectric effect) is injected into the depletion region of the PN junction, a self-sustaining avalanche ensues
Implementation Method 2
a self-sustaining avalanche ensues, and detection of current output as a result of this avalanche can be used to indicate detection of the photon
Implementation Method 3
a regulation circuit configured to sink current from the turn-off voltage node to ground based upon the feedback voltage such that a voltage at the turn-off voltage node maintains generally constant
Data Source
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AI summary
Described herein is an electronic device, including a pixel and a turn-off circuit. The pixel includes a single photon avalanche diode (SPAD) having a cathode coupled to a high voltage node and an anode selectively coupled to ground through an enable circuit, and a clamp diode having an anode coupled to the anode of the SPAD and a cathode coupled to a turn-off voltage node. The turn-off circuit includes a sense circuit coupled between the turn-off voltage node and ground and configured to generate a feedback voltage, and a regulation circuit configured to sink current from the turn-off voltage node to ground based upon the feedback voltage such that a voltage at the turn-off voltage node maintains generally constant.