Optoelectronic Sensor Time Base Unit for Sub-Picosecond Distance Measurement
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Solution Overview
Problem
Conventional optoelectronic sensors face challenges in achieving high time precision for distance measurement using the light transit time principle, particularly in achieving sub-picosecond resolution, which is essential for precise distance measurement, due to the high cost of advanced electronics and limitations in existing methods such as direct digital synthesis and sampling rate limitations.
Innovation Solution
The solution involves generating two slightly different frequencies with a difference period, where the time intervals are decoupled to achieve higher precision, utilizing a time base unit with PLLs to derive these frequencies from a master clock, and implementing a digital logic component like an FPGA to generate time shifts and histograms for precise transmission and reception time determination, allowing for fine adjustment of transmission times with sub-picosecond resolution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional electronics with high operating frequencies are used to achieve high time precision, then measurement precision is improved, but device cost increases significantly
Solution Approach 1:
The patent employs dynamic frequency switching between two frequencies (f1 and f2) to achieve time precision beyond the operating frequency of conventional electronics. By dynamically alternating between frequencies and using the difference period (TDIFF), the system achieves picosecond-level resolution without requiring electronics to operate at corresponding high frequencies, thus avoiding the cost penalty of high-frequency components.
Solution Approach 2:
The system changes the operating parameter from a single fixed frequency to two different frequencies with a specific difference period. This parameter change enables the use of lower-frequency, cost-effective electronics while achieving higher time precision through the frequency difference mechanism. The difference period TDIFF = 1/|f1-f2| provides the fine time resolution needed without requiring the main electronics to operate at that frequency.
2Measurement precision
If direct digital synthesis with high resolution is used, then time precision is improved, but component cost increases
Solution Approach 1:
The patent introduces an intermediary mechanism using two frequencies f1 and f2 with a difference period TDIFF. This intermediary approach allows the system to achieve high-resolution time measurements without requiring expensive high-resolution DDS components. The difference period acts as a mediator that translates lower-frequency operations into high-precision time measurements.
3Measurement precision
If sampling rate is increased to improve time resolution, then measurement precision is improved, but device complexity and cost increase
Solution Approach 1:
The system uses periodic switching between two frequencies f1 and f2, where each frequency operates at a manageable sampling rate. The periodic alternation creates a difference period TDIFF that provides the fine time resolution needed. This periodic action allows the use of lower sampling rate electronics while achieving high time resolution through the frequency switching mechanism, avoiding the need for extremely high sampling rates.
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 approach enhances measurement precision to the picosecond range or below, achieving higher resolution and cost-effectiveness by using simpler circuits and software, overcoming the limitations of conventional systems, and enabling precise distance measurement with improved signal-to-noise ratio.
Implementation Method 1
a light transmitter (12) transmits light pulses (86) to a monitored zone and a light receiver (16) surrounding the light transmitter (12) receives reflected light pulses (82)
Data Source
AI summary
An optoelectronic sensor (10) for the measurement of distances or distance changes in accordance with the light transit time principle is provided having a light transmitter (12) for the transmission of a light signal and having a light receiver (16) for the reception of the remitted or reflected light signal, wherein an evaluation unit (18) is provided which is made to fix the transmission time for the light signal relative to a reference time and to digitize the received light signal on a sampling pattern (108) having a sampling period to determine the reception time of the light signal, and wherein a time base unit (38) is provided by means of which the transmission time can be shifted relative to the sampling pattern (108) with a time precision below the sampling period. In this respect, the time base unit (38) is made to derive the time shift from a first time signal having a first frequency (f1) and a second time signal having a second frequency (f2) different from the first frequency (f1) and to provide any desired time shifts with a time resolution given by the difference period belonging to the first and second frequencies (f1, f2).