Avalanche Photodiode Array Non-Uniformity Correction
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Solution Overview
Problem
Multi-pixel time-of-flight (ToF) receivers with linear mode avalanche photodiode (APD) sensing elements suffer from gain mismatch due to manufacturing process variations, leading to non-uniform optical sensitivity across the photodiode array, which affects the accuracy of distance measurements in laser ranging systems.
Innovation Solution
Implementing a non-uniformity correction (NUC) method that allows the receiver to operate in a passive mode, where the direct current (DC) photocurrent is measured across APD elements, enabling individual control of reverse bias voltages to equalize gain and improve sensitivity uniformity, using techniques such as direct injection (DI) or buffered direct injection (BDI) structures and integration with current/voltage converters.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional APD-based multi-pixel ToF receivers are used, then the system can perform time-of-flight measurements, but gain mismatch and non-uniform optical sensitivity occur across pixels due to manufacturing variations
Solution Approach 1:
The patent applies preliminary action by performing non-uniformity correction (NUC) measurements and calculations before actual time-of-flight imaging operations. The system measures DC photocurrent levels across all pixels in advance, calculates correction factors to equalize gains, and stores these factors for subsequent use during normal operation, thereby eliminating sensitivity variations before they affect measurement precision
Solution Approach 2:
The patent implements parameter changes by adjusting the reverse bias voltage applied to individual APD elements based on measured photocurrent variations. By varying the bias voltage parameter for each pixel, the system compensates for manufacturing-induced gain differences and achieves uniform optical sensitivity across the array
2Measurement precision
If individual reverse bias control is implemented for each APD element, then gain uniformity can be equalized, but device complexity increases due to additional control circuits
Solution Approach 1:
The patent merges the non-uniformity correction functionality with the existing readout circuitry of the APD array. The DC photocurrent measurements are performed using the same pixel circuits and readout paths already present in the ToF receiver, eliminating the need for separate dedicated measurement circuits and reducing overall device complexity
Solution Approach 2:
The patent implements multi-functionality by enabling the APD array and associated electronics to perform multiple functions: during NUC mode, the system measures DC photocurrent levels for gain equalization, and during normal ToF mode, the same hardware performs time-resolved distance measurements. This universal design avoids duplicating circuitry for different operational modes
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 NUC method effectively reduces response non-uniformity among APD elements, enhancing the uniformity of sensitivity across the receiver and improving the accuracy of distance measurements in laser ranging systems.
Implementation Method 1
avalanche photodiode (APD) sensing elements
Implementation Method 2
linear mode avalanche photodiode (APD) sensing elements
Data Source
AI summary
Methods and apparatus for nonuniformity correction (NUC) for a sensor having an avalanche photodiode (APD) array and an integrated circuit. The sensor can include anode bias control module, a passive mode module, and an active mode module. DC photocurrent from the APD array can be measured and used for controlling an anode reverse bias voltage to each element in the APD to achieve a nonuniformity correction level less than a selected threshold.