Distance Sensor Asynchronous Clock TDC Precision
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Solution Overview
Problem
Existing distance sensors face challenges in achieving high precision for time-of-flight measurements, particularly in determining small distances in the millimeter or centimeter range, due to limitations in the accuracy of pulse propagation time measurement.
Innovation Solution
The proposed distance sensor employs two independently operating asynchronous oscillators to generate clock signals for transmitter and evaluation unit operations. It includes a TDC unit with a coarse measuring unit and two fine measuring units, each with a delay line, allowing for precise measurement of the time intervals between transmission and reception pulses. Additionally, multiple TDC units with different phase clock signals are used to avoid measurement errors caused by pulse alignment with clock cycles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single clock signal is used for both transmitter and evaluation unit, then the device complexity is reduced, but measurement precision deteriorates due to pulse alignment errors with clock cycles
Solution Approach 1:
The patent divides the clock signal generation into two independent asynchronous oscillators: one for the transmitter and one for the evaluation unit. This segmentation prevents systematic alignment errors that would occur with a single shared clock signal, thereby improving measurement precision while accepting increased device complexity.
Solution Approach 2:
The patent changes the temporal parameter relationship between transmitter and evaluation unit by using asynchronous oscillators with different frequencies and phases. This parameter change eliminates periodic alignment errors that would occur with synchronous operation, improving measurement accuracy through statistical averaging of uncorrelated timing errors.
2Device complexity
If the clock signal is synchronized with transmission pulses, then the device complexity is reduced, but measurement precision deteriorates due to inability to accurately determine pulse arrival relative to clock start
Solution Approach 1:
Instead of synchronizing the clock with the transmission pulse (conventional approach), the patent inverts the relationship by using an asynchronous clock and measuring the transmission pulse timing relative to the clock cycles. This inversion allows accurate determination of pulse timing by counting complete clock cycles and measuring the residual time within the last cycle.
Solution Approach 2:
The patent introduces a residual time measurement mechanism as an intermediary between the asynchronous transmission pulse and the clock signal. This intermediary component (the fine measurement unit measuring time within the last clock cycle) enables precise timing determination without requiring direct synchronization between transmitter and evaluation unit clocks.
3Measurement precision
If two tapped delay lines are used to determine remaining signal propagation time, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The patent uses two tapped delay lines providing a conservative margin of precision for the residual time measurement. This partial redundancy ensures that the fine measurement capability exceeds the minimum requirement, allowing robust operation even with variations in clock frequency and phase, thereby improving reliability without excessive complexity.
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 enables highly accurate and reproducible distance measurements by precisely determining the time of flight of pulses, effectively overcoming previous limitations in precision and reducing measurement errors.
Implementation Method 1
The evaluation unit determines the signal propagation time between the transmission of a transmission signal and the reception of a remitted transmission signal
Data Source
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AI summary
The invention relates to a distance sensor (1) for determining the distance of objects (5) in a monitoring area, comprising a transmitter (3) and a receiver (4), wherein transmit pulses emitted by the transmitter (3) are directed to the object (5) and reflected by the object (5) as a receive pulse to the receiver (4), and with an evaluation unit in which the distance of the object (5) to the distance sensor (1) is determined from the transit time (6) of the transmit pulses to the object (5). A clock generator is provided, which generates a clock signal (11) that is asynchronous to the transmit pulse. The evaluation unit comprises at least one TDC unit (17), which has a coarse measuring unit (21) and two fine measuring units (20, 20') each with a delay line (31). The coarse measuring unit (21) is configured to count whole clock cycles (a) of the clock signal (11).A transmit pulse starts a first fine measurement unit (20), which in turn starts the coarse measurement unit (21) and measures the time interval (c) between the transmission of the transmit pulse and the subsequent start of a clock cycle (a) of the clock signal (11). The receive pulse following the transmit pulse starts the second fine measurement unit (20'), which stops the coarse measurement unit (21) and measures the time interval (c) between receiving the receive pulse and the subsequent start of a clock cycle of the clock signal (11).