DC-DC Converter PWM Dithering for Stable Illumination Control
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Solution Overview
Problem
Existing digital loop control systems for illumination devices in ToF cameras face limitations in achieving precise control of emitted power due to fixed duty cycle steps, leading to phase/depth errors in image processing.
Innovation Solution
A digital controller with a duty cycle adjuster and dithering module generates PWM signals with finer duty cycles by combining multiple PWM signals of different duty cycles to stabilize the output of DC-DC converters, allowing for constant current drive.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If digital loop control is used to control the DC-DC converter, then the loop operating point remains stable between quadrants, but the duty cycle control precision is limited due to fixed step changes
Solution Approach 1:
The patent segments the duty cycle control into multiple discrete levels (first duty cycle, second duty cycle, third duty cycle) that can be selectively applied. Instead of using a single fixed-step PWM signal, the system divides the control into multiple manageable duty cycle segments that can be combined to achieve finer effective resolution while maintaining digital control stability.
Solution Approach 2:
The patent employs periodic switching between different duty cycle values over N PWM periods. By periodically alternating between first, second, and third duty cycles with different on-times, the system achieves an effective average duty cycle that falls between the discrete digital steps, thereby improving precision without compromising the stability provided by digital control.
2Measurement precision
If analog control is used for the DC-DC converter, then continuous duty cycle adjustment is possible, but the loop operating point changes between quadrants causing instability
Solution Approach 1:
The patent introduces dynamic behavior into the digital control system by varying the duty cycle across multiple PWM periods rather than maintaining a fixed duty cycle value. The controller dynamically selects between different duty cycle levels (first, second, third duty cycles) based on the target duty cycle requirement, enabling continuous-like adjustment while preserving digital control stability through structured periodic operation.
Solution Approach 2:
The patent changes the PWM signal parameter (duty cycle) in a controlled manner by using multiple discrete duty cycle values instead of a single fixed value. By adjusting which duty cycle level is applied during different PWM periods, the system achieves fine-grained control of the effective duty cycle while maintaining the stability benefits of digital control architecture.
3Measurement precision
If multiple PWM signals with different duty cycles are combined, then finer effective duty cycle control is achieved, but the control logic complexity increases
Solution Approach 1:
The patent uses a predetermined pattern of applying first, second, and third duty cycles over N PWM periods where the individual duty cycle applications may exceed or fall short of the target, but the average over the period achieves the desired precision. This partial action approach allows achieving fine resolution without requiring complex real-time calculation and adjustment logic for each individual PWM period.
Solution Approach 2:
The control system uses the natural accumulation effect of multiple PWM periods to self-average to the target duty cycle. By predeterminedly assigning different duty cycle values to different periods, the system allows the average output to self-correct to the desired level without requiring complex feedback adjustment logic, thereby reducing control complexity while maintaining precision.
Data Source
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AI summary
In described examples of a method (400) of controlling an illumination device by an output signal of a DC-DC converter, the output signal is controlled by a PWM signal. The method (400) includes receiving (405) a feedback signal corresponding to variation in the output signal with respect to a predetermined output signal, and determining (410) a target duty cycle of the PWM signal based on the feedback signal. The PWM signal of the target duty cycle is capable of enabling the DC-DC converter to generate the predetermined output signal. The method (400) includes providing (415) the PWM signal of an effective duty cycle equal to the target duty cycle over N switching pulses of the PWM signal to the DC-DC converter. The method (400) provides (415) the PWM signal by providing (420) M switching pulses of a first PWM signal of a first duty cycle, and by providing (425) N-M switching pulses of a second PWM signal of a second duty cycle.