Laser Distance Module INL Compensation for Fast ADC Sampling
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Solution Overview
Problem
Fast analog-to-digital converters in distance measuring devices, such as laser trackers and scanners, suffer from integral nonlinearity errors (INL) that affect measurement accuracy and resolution, leading to periodic distance errors and signal distortion due to temperature and time variations.
Innovation Solution
A method involving the superposition of a bias signal with varying offset values onto the reception signals, which shifts the signal over a wide value range, allowing for averaging that minimizes local INL errors, and a calibration process using INL parameters to correct for ADC nonlinearity, particularly through the use of FPGA or microprocessor-based look-up tables for real-time compensation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If fast analog-to-digital converters are used for high-speed signal detection, then measurement speed and productivity are improved, but integral nonlinearity errors increase leading to reduced measurement precision
Solution Approach 1:
The patent applies preliminary action by performing a calibration process before actual measurements to determine INL parameters. These parameters are stored in lookup tables and used to pre-compensate for nonlinearity errors during fast measurements, allowing the system to maintain both high speed and high precision without real-time complex calculations
Solution Approach 2:
The patent changes the operational parameters of the ADC by applying different bias signals that shift the operating point of the converter. By measuring at multiple different bias levels and combining the results, the system compensates for INL errors and achieves higher measurement precision while maintaining fast conversion speeds
2Productivity
If ADC conversion stages are increased to achieve high sampling rate and resolution, then productivity is improved, but device complexity and INL errors worsen
Solution Approach 1:
The patent segments the measurement process into multiple independent ADC conversions performed at different bias levels. Instead of using a single complex high-resolution ADC, the system uses multiple simpler ADC stages with different operating points, combining their results to achieve the desired precision while maintaining high sampling rates
Solution Approach 2:
The patent introduces bias signals as intermediary elements that mediate between the simple ADC hardware and the precision measurement requirement. These bias signals shift the operating point of the ADC to different regions, allowing the system to extract multiple independent measurements that when combined compensate for the inherent nonlinearity of each individual ADC stage
3Measurement precision
If bias signal superposition is applied to shift signal over wide value range, then measurement precision is improved through averaging, but device complexity increases
Solution Approach 1:
The patent applies periodic action by systematically varying the bias signal across multiple measurement cycles. The bias signal is changed in a periodic manner to sweep through different operating regions, and measurements are taken at each stage. This periodic variation allows the system to average out INL errors while maintaining a structured and manageable signal processing approach
Data Source
AI summary
A distance measuring method and an electronic laser distance measuring module, in particular for use in a distance measuring apparatus, especially configured as a laser tracker, tachymeter, laser scanner, or profiler, for fast signal detection with an analog-to-digital converter, wherein conversion errors that arise in the context of a signal digitization, in particular timing, gain and offset errors of the ADC, are compensated for by means of variation of the sampling instants.