Laser Pulse Timing Realignment for ADC Clock Error Suppression
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Solution Overview
Problem
Laser range finders face challenges in accurately measuring distances due to systematic noise introduced by Analog to Digital Converters (ADCs), which masks the detection of laser pulses, especially in long-range applications where PIN diodes are limited by noise and cost, and APDs are expensive.
Innovation Solution
A timing offset module shifts the timing reference of each laser pulse before firing, and the ASIC realigns digital codes to eliminate systematic clock errors, allowing for the identification of reflected returns by comparing ADC outputs over multiple clock pulses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If PIN diodes are used for detection, then cost is reduced, but systematic noise from ADC clocking limits long-range detection capability
Solution Approach 1:
The patent applies periodic action by using multiple ADC clock frequencies (different periods) to sample the same signal. By varying the clock period across multiple measurements and combining the results, the system eliminates systematic noise that is correlated with any single clock frequency, thereby enabling long-range detection with cost-effective PIN diodes
Solution Approach 2:
The patent changes the ADC clock frequency parameter across multiple measurements. By measuring the same signal with different clock frequencies and combining the measurements, the system removes systematic noise that depends on the clock frequency, achieving both low cost and high detection precision
2Measurement precision
If ADC resolution is increased to reduce quantization noise, then measurement precision improves, but systematic clock error becomes more significant
Solution Approach 1:
The patent converts the harmful systematic clock error into a beneficial filtering mechanism. By measuring with multiple clock frequencies and combining results, the system eliminates frequency-correlated noise, turning the previously problematic clock-dependent systematic error into an advantage where the combination process removes the error while preserving the signal
3Measurement precision
If multiple pulses are summed to improve signal-to-noise ratio, then random noise is reduced, but systematic clock error accumulates and masks detection
Solution Approach 1:
The patent uses periodic action with varying clock frequencies across multiple pulse measurements. By changing the clock period for each measurement and then combining the results, the system prevents systematic clock error from accumulating in the same way, allowing beneficial noise reduction while eliminating correlated noise
Solution Approach 2:
The patent performs preliminary action by varying the clock frequency before summing the measurements. By pre-conditioning the measurements with different clock frequencies, the system ensures that systematic errors do not align and accumulate during the summation process, enabling effective noise reduction without error accumulation
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 significantly reduces systematic noise errors, enabling more accurate distance measurements by distinguishing target returns from noise, even at long ranges, without the need for expensive APDs.
Implementation Method 1
a timing offset module shifts the timing reference of each laser pulse in the set of pulses prior to pulse firing
Implementation Method 2
the ASIC then realigns digital codes generated by the ADC from the returned or reflected detected laser pulses. This realignment eliminates systematic clock error introduced by clock driven operation of the ADC
Implementation Method 3
This approach significantly reduces systematic noise errors, enabling more accurate distance measurements by distinguishing target returns from noise
Data Source
AI summary
Error introduced by analog to digital conversion of a set of laser pulses can be reduced by shifting the clock reference time associated with the firing of the laser pulse. A timing offset module shifts the timing reference of each laser pulse. Digital codes generated by the ADC from the received signals are realigned and summed eliminating systematic error introduced by clock driven operations of the ADC. A comparison of the total ADC output of detected laser pulses over a select number of clock intervals enables a return signal to be distinguishable over the systematic error.