Avalanche Photodiode Noise Elimination via Digital Signal Processing
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Solution Overview
Problem
Conventional methods for eliminating pulse noise in photo detecting devices require subtraction circuits with coils or operational amplifiers, limiting speed and bandwidth, and necessitate equalizing APD characteristics, which increases cost and complexity.
Innovation Solution
Generating a pulse noise mask signal based on timing signals to eliminate pulse noise without the need for subtraction or differential circuits, allowing for high-speed noise elimination regardless of APD characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If subtraction circuits (hybrid coupler or operational amplifier) are used to eliminate pulse noise, then pulse noise can be eliminated from the output signal, but the processing speed is limited and bandwidth cannot be widened
Solution Approach 1:
The patent replaces the mechanical/electronic subtraction circuit system (hybrid coupler with coils or operational amplifier circuit) with a digital signal processing system. The output signal is sampled at a rate of 2 GS/s or higher, and pulse noise is eliminated through digital subtraction of the average waveform from the original signal, achieving high-speed processing without the bandwidth limitations of analog circuits.
Solution Approach 2:
The patent changes the processing approach from analog continuous processing to digital discrete processing. By sampling the output signal at high speed (2 GS/s or higher) and performing digital averaging and subtraction operations, the system achieves both high processing speed and effective pulse noise elimination, overcoming the speed-bandwidth tradeoff of analog circuits.
2Reliability
If subtraction circuits are used for pulse noise elimination, then pulse noise can be removed, but the circuit complexity increases due to requirement of coils or operational amplifiers
Solution Approach 1:
The patent eliminates the need for complex analog circuits (hybrid coupler with multiple coils or operational amplifier circuits) by replacing them with a digital signal processing system. The pulse noise elimination is achieved through software-based digital subtraction of the average waveform from the original signal, significantly reducing hardware complexity while maintaining effective noise removal.
Solution Approach 2:
The patent creates a digital copy of the pulse noise waveform by calculating the average of multiple output signals. This average waveform serves as a template that is then subtracted from the original signal to eliminate pulse noise, replacing the need for physical circuit copies and reducing overall system complexity.
3Reliability
If conventional pulse noise elimination methods are used, then pulse noise can be eliminated, but equalization of APD characteristics is required which increases manufacturing cost
Solution Approach 1:
The patent changes from requiring precise matching of physical parameters (parasitic capacitance equalization of APDs) to a parameter-free digital processing approach. The digital signal processing method automatically adapts to any APD characteristics by calculating the average waveform from the actual output signals, eliminating the need for costly manufacturing equalization processes.
Solution Approach 2:
The system performs self-characterization by automatically calculating the average waveform from its own output signals. This self-service approach eliminates the need for external equalization of APD characteristics during manufacturing, as the digital processing adapts to the specific characteristics of each device automatically.
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 efficient pulse noise elimination at high speeds without the need for specialized circuits, accommodating differences in APD characteristics and improving photon detection performance.
Implementation Method 1
A reverse-bias voltage not less than an APD breakdown voltage (VBd) is applied to an APD so that the multiplication factor of the APD is increased to an extremely large value, whereby a photocurrent triggered by a single photon is amplified
Implementation Method 2
a photocurrent triggered by a single photon is amplified
Data Source
AI summary
In a photo detecting circuit using an avalanche photodiode (APD), a pulse noise mask signal indicating the timing of occurrence of a pulse noise is generated by XORing a reverse-bias-pulse application timing signal and its delayed signal. Pulse noises are eliminated by ANDing an output signal of the APD and the pulse noise mask signal. Alternatively, a pulse noise is estimated by taking the average for the output current signal a given number of times. Pulse noises are eliminated by subtracting the estimated pulse noise from the APD output signal.