PWM Increment Calibration for PVT-Accurate Pulse Timing
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Solution Overview
Problem
Pulse width modulation (PWM) signals with higher resolution increments experience variance due to process, voltage, and temperature variations, leading to inaccuracies in applications like LiDAR systems where precise distance measurements are critical, as existing calibration techniques do not account for increment-to-increment variation.
Innovation Solution
A method and system for calibrating PWM signals by generating two signals, one without and one with a commanded higher resolution increment, sampling both signals and the VDDIO rail, calculating the actual increment length, and compensating for the difference between commanded and actual lengths, using a microcontroller and ADCs to ensure accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If higher resolution increments are added to PWM signals to achieve finer control granularity, then the control precision is improved, but the variance due to process, voltage, and temperature increases leading to measurement inaccuracies
Solution Approach 1:
The patent applies preliminary action by performing calibration measurements before actual PWM operation. The system pre-determines calibration factors by measuring the actual duration of PWM increments at different duty cycles and storing these calibration data for later compensation during normal operation, thus eliminating the need for real-time calibration while maintaining high precision.
Solution Approach 2:
The patent implements feedback by using measured calibration data to compensate for process, voltage, and temperature variations. The system continuously monitors the relationship between commanded and actual PWM increment durations, and uses this feedback information to adjust and correct subsequent PWM signal generation, ensuring consistent accuracy despite environmental changes.
2Measurement precision
If runtime calibration techniques are employed to normalize the higher resolution increment, then the average increment size is improved, but the increment-to-increment variation is not accounted for
Solution Approach 1:
The patent applies segmentation by dividing the calibration process into multiple discrete measurements across different duty cycle points. Instead of relying on a single average calibration value, the system performs separate calibration measurements at multiple operating points (e.g., 10%, 50%, 90% duty cycle) and maintains separate calibration factors for each point, thus accounting for non-linear variations and ensuring consistent accuracy across the full operating range.
3Measurement precision
If multiple calibration measurements are performed at different duty cycles, then the calibration accuracy is improved, but the calibration time increases
Solution Approach 1:
The patent performs comprehensive multi-point calibration measurements in advance during the manufacturing or initialization phase, storing the calibration data in memory. This preliminary action ensures that all necessary calibration information is captured before normal operation begins, allowing the system to use pre-computed calibration factors during runtime without incurring additional calibration time during actual PWM operation.
Data Source
AI summary
A system and method for calibrating a pulse width modulation (PWM) signal that extends the on time by a higher resolution increment. The system comprises a PWM generator that receives a VDDIO rail to generate first and second PWM signals, the second PWM signal having an on time extended by the higher resolution increment having a commanded length. The system further comprises a VDDIO circuit that receives the VDDIO rail and outputs a VDDIO signal. First and second analog-to-digital converters are configured to generate a first and second sets of PWM samples and first and second sets of VDDIO samples. A microcontroller is configured to calculate an actual increment length based on the samples, and to compensate for a difference between the commanded length and the actual increment length.