Equalizer Tap Coefficients for APD Distance Measurement
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Solution Overview
Problem
Existing distance measurement technologies using avalanche photo diodes (APDs) in Geiger mode face challenges in distinguishing between photons from light sources and ambient light, leading to inaccurate distance calculations due to transient responses and overlapping waveforms.
Innovation Solution
An electronic apparatus comprising a light source, detector, equalizer, and processing circuitry, where the equalizer uses tap coefficients based on the light source's output value and frequency response to generate an equalized signal, minimizing the impact of ambient light and improving distance measurement accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If photodetectors with high sensitivities (APDs in Geiger mode) are used to measure long distances, then detection capability is improved, but the ability to distinguish photons from light sources versus ambient light deteriorates
Solution Approach 1:
The system performs preliminary equalization of the detector response using stored tap coefficients before processing the received signal. By pre-characterizing the detector's frequency response and applying compensating filters, the system prepares the signal processing chain to better distinguish light source photons from ambient light photons, resolving the contradiction between high sensitivity and photon distinction accuracy
Solution Approach 2:
The system uses feedback from the known light source pulse shape and detector characteristics to adjust the equalization parameters. By continuously referencing the expected signal shape and comparing it with the actual detector output, the system can distinguish between genuine light source photons and ambient light photons even when using highly sensitive APDs in Geiger mode
2Measurement precision
If the detector operates in Geiger mode to detect individual photons, then sensitivity is improved, but transient responses occur causing waveform distortion
Solution Approach 1:
The system changes the parameter of the detector response by applying frequency-domain equalization. By storing the actual frequency response of the detector and applying compensating tap coefficients, the system transforms the distorted Geiger mode waveforms into shapes that more accurately represent the original light source pulse, thereby recovering waveform shape information while maintaining single-photon detection sensitivity
Solution Approach 2:
The system creates a reference copy of the expected pulse shape from the light source and uses it to guide the equalization process. By comparing the equalized detector output with the known pulse shape template, the system can identify and correct waveform distortions introduced by the Geiger mode operation, effectively copying the ideal waveform characteristics back onto the distorted signal
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 solution effectively reduces the impact of ambient light, allowing for accurate distance measurements by shaping the detector's output signal to match the light source's pulse shape, thereby enhancing the distinction between laser and ambient light photons.
Implementation Method 1
a detector 11, configured to detect a reflected wave of the pulse and convert the reflected wave to a first electric signal
Implementation Method 2
technology for measuring long distances by using photodetectors such as avalanche photo diodes (APDs) operating in Geiger mode
Data Source
AI summary
According to one embodiment, an electronic apparatus includes a light source, a detector, an equalizer and a processing circuitry. The light source is configured to emit a pulse having a first output value and a first frequency response. The detector is configured to detect a reflected wave of the pulse and convert the reflected wave to a first electric signal. The reflected wave of the pulse is received after the pulse is reflected by an object. The equalizer is configured to equalize the first electric signal using tap coefficients to generate a second electric signal. The tap coefficients are based on at least either one of the first output value and the first frequency response. The processing circuitry is configured to estimate a distance to the object based on the second electric signal.