PWM Actuator Timing Around CDS Image Sensor Readout
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Solution Overview
Problem
Electromagnetic interference (EMI) caused by pulse width modulation (PWM) techniques in actuator assemblies, such as SMA wires, degrades image quality in image sensors, particularly in battery-operated devices like mobile phones, due to noise interference in captured images.
Innovation Solution
Implementing a computer-implemented method that generates PWM control signals at a frequency equal to an integer multiple of the reciprocal of the image sensor's sampling period, suspends signal generation during specific intervals, and schedules measurement pulses to avoid overlapping with image sensor reading periods, using correlated double sampling (CDS) to reduce EMI noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If PWM techniques are used to drive the actuator component, then power efficiency is improved, but EMI noise in the image sensor increases
Solution Approach 1:
The patent applies periodic action by synchronizing the PWM control signal frequency with the image sensor's sampling period. The PWM frequency is set to an integer multiple of the reciprocal of the sampling period, creating a periodic relationship that ensures EMI noise occurs only during specific intervals when the image sensor is not actively reading signals, thus maintaining power efficiency while reducing noise interference
Solution Approach 2:
The patent implements preliminary action by introducing a time delay between receiving the sync signal and starting the sensing interval. This delay is calculated to ensure that the sensing interval overlaps with both or neither of the reference signal and light-sensing signal reading durations, proactively preventing EMI noise from affecting image quality before the noise can interfere with the imaging process
2Measurement precision
If the sensing interval overlaps with the reference signal and light-sensing signal reading durations, then measurement of actuator electrical characteristics is improved, but image quality degrades due to EMI noise
Solution Approach 1:
The patent introduces a time delay between receiving the sync signal and starting the sensing interval to proactively position the sensing interval in a time window that avoids overlapping with critical image sensor reading operations. This preliminary timing adjustment ensures that electrical characteristic measurements can be taken without degrading image quality
Solution Approach 2:
The patent dynamically adjusts the timing of the sensing interval based on the sync signal from the image sensor. The controller modifies the start time and duration of the sensing interval in real-time to achieve optimal overlap conditions, allowing flexible coordination between actuator measurement and image capture operations
3Manufacturing precision
If PWM frequency is increased to improve control resolution, then actuator control precision is improved, but EMI interference with the image sensor increases
Solution Approach 1:
The patent uses periodic action by setting the PWM frequency to a specific relationship with the image sensor sampling period (integer multiple of the reciprocal of the sampling period). This creates a synchronized periodic pattern where high-frequency PWM control signals generate EMI noise only during intervals when the image sensor is not reading, thus achieving both high control precision and minimal interference
Data Source
AI summary
A computer-implemented method driving an actuator component that drives movement of a movable part relative to a support structure, an image sensor fixed relative to the movable part or the support structure. The image sensor carries out CDS so as to read, offset in time by a sampling period, a reference signal and a light-sensing signal, and outputs a sync signal prior to CDS. The method comprises receiving the sync signal; generating PWM control signals at a PWM frequency substantially equal to an integer multiple of the reciprocal of the sampling period; during a sensing interval, suspending generating PWM control signals to drive the actuator component; and scheduling the sensing interval to start a time delay after receiving the sync signal, such that the sensing interval overlaps with both or neither of a duration of reading the reference signal and a substantially equal duration of reading the light-sensing signal by the image sensor.