Avalanche Photodiode Voltage Control for Distance Measurement
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Solution Overview
Problem
Measuring devices using avalanche photodiodes for distance measurement are temperature-sensitive, leading to reduced sensitivity and accuracy due to voltage fluctuations near the breakdown voltage, requiring frequent calibration and potentially damaging the diodes.
Innovation Solution
The device employs two comparators connected in parallel to monitor and adjust the operating voltage of the avalanche photodiode, ensuring it remains within the optimal range by checking voltage values during a staggered interval, independent of object approach, and adjusting the voltage to maintain sensitivity and prevent noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the operating voltage is increased to improve measuring sensitivity, then the sensitivity increases, but noise voltage increases and the diode may be damaged
Solution Approach 1:
The patent implements dynamic voltage adjustment by continuously adapting the operating voltage of the avalanche photodiode based on real-time temperature measurements. The voltage is adjusted within a range around the breakdown voltage to maintain optimal sensitivity while preventing excessive noise and damage, transforming the static voltage setup into a dynamic control system that responds to environmental changes.
Solution Approach 2:
The patent employs a feedback mechanism where the operating voltage is continuously adjusted based on the measured temperature and the resulting noise level. The control system monitors the voltage and modifies it to maintain optimal operating conditions, creating a closed-loop control that balances sensitivity and noise suppression.
2Object-generated harmful factors
If the operating voltage is set below the breakdown voltage to reduce noise, then noise decreases, but measuring sensitivity is reduced
Solution Approach 1:
The system dynamically adjusts the operating voltage to operate in a narrow range just below the breakdown voltage, optimizing the balance between sensitivity and noise. This dynamic adjustment allows the system to maintain high sensitivity while preventing excessive noise generation.
Solution Approach 2:
The patent changes the operating parameter (voltage) as a function of temperature. By adjusting the voltage based on temperature measurements, the system maintains optimal operating conditions across different environmental conditions, ensuring both sensitivity and low noise performance.
3Measurement precision
If a voltage query is performed before each measurement to calibrate the receiving diode, then the optimal operating voltage is achieved, but the measurement process time increases
Solution Approach 1:
The patent performs preliminary calibration by determining the optimal operating voltage characteristics during an initial phase or during manufacturing. This preliminary action stores the voltage-temperature relationship, allowing the system to skip repeated voltage queries during actual measurements and directly apply the pre-determined optimal voltage based on real-time temperature sensing.
Solution Approach 2:
The system uses its own temperature sensing capability to self-adjust the operating voltage without requiring external calibration equipment or time-consuming query procedures. The avalanche photodiode's temperature dependence is utilized as a feedback signal for automatic voltage adjustment.
4Measurement precision
If the receiving diode is operated near the breakdown voltage to maximize sensitivity, then sensitivity is optimized, but the diode becomes extremely temperature-sensitive and requires frequent calibration
Solution Approach 1:
The patent implements a feedback control system that continuously monitors temperature and adjusts the operating voltage accordingly. When temperature increases, the voltage is reduced to compensate for the increased sensitivity to thermal effects, maintaining stable operation without requiring frequent manual calibration.
Solution Approach 2:
The operating voltage is changed as a function of temperature to compensate for thermal effects. By dynamically adjusting the voltage parameter based on temperature measurements, the system maintains optimal sensitivity while compensating for temperature-induced variations in the avalanche photodiode's characteristics.
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 ensures consistent measuring accuracy and extended service life by maintaining the operating voltage within the breakdown voltage range, reducing noise and temperature-induced fluctuations, and eliminating the need for pre-measurement calibration.
Implementation Method 1
Such avalanche photodiodes generate a very high internal amplification when the laser waves emitted by the transmitter diode are reflected from the object onto the receiver diode, because impact ionization occurs in the barrier layer of the receiver diode.
Implementation Method 2
The time required for the light to travel from the transmitter diode to the object and from there to the receiver diode is measured. Since the speed of light is constant and known, the distance between the object and the measuring device can be calculated by the physical formula s=v*t.
Data Source
Figure 1
Figure 2
AI summary
In a measuring device (1) for determining the distance between itself and an object (2), comprising a first electrical circuit (3) by which a light-wave-emitting transmitting diode (5) can be pulse-controlled, a second electrical circuit (4) by which a receiving diode (6) arranged adjacent to the transmitting diode (5) is supplied with voltage, and a first comparator (10) connected in series with the receiving diode (6) by which the voltage changes detectable at the receiving diode (6) when the object (2) approaches can be measured, the measuring device (1) should, firstly, reliably determine the distance between an object (2) approaching the measuring device (1) and the device itself, and secondly, operate in a sensitivity range for distance determination that is permanently within the range of the breakdown voltage of the receiving diode (6) used.to optimize their measurement accuracy. This is achieved by using a second comparator (11) to determine the voltage change of the receiving diode (6) with a time delay relative to the transmitting pulse of the transmitting diode (5), and by using the second comparator (11) to regulate the operating voltage of the receiving diode (6) depending on the voltage change detected by the comparator (11) at the receiving diode (6) during the verification interval.