Autofocus Driver Calibration Using Current Replica Feedback
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Solution Overview
Problem
Autofocus systems in imaging devices face challenges due to offset voltage in operational amplifiers, leading to variations in the driver's output current from the ideal current, which affects image quality.
Innovation Solution
The implementation of a current comparator circuit and a replica circuit that work together to monitor the drive current, provide feedback, and adjust the drive current to minimize offset, thereby improving the accuracy of the drive current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If an operational amplifier is used in the driver circuit, then signal propagation is facilitated, but offset voltage causes the output current to deviate from the ideal current
Solution Approach 1:
A feedback circuit is implemented that monitors the actual output current of the driver and compares it with the ideal current. The difference (offset) is detected and fed back to adjust the driver's operation, thereby compensating for the offset voltage effect and improving output current accuracy while maintaining signal propagation capability
Solution Approach 2:
The patent replaces the purely operational amplifier-based current control with an electronic feedback mechanism that uses current sensing and comparison circuits. This substitution allows for precise measurement and correction of output current deviations without relying solely on the operational amplifier's inherent characteristics
2Measurement precision
If high performance drivers are used to reduce offset, then output current accuracy is improved, but device complexity increases
Solution Approach 1:
The driver circuit is segmented into distinct functional blocks: the operational amplifier for signal propagation, a current sensing circuit for monitoring output current, a comparison circuit for detecting offset, and a feedback circuit for correction. This segmentation allows each component to perform its specific function efficiently without requiring the entire system to be overly complex
Solution Approach 2:
An intermediary feedback circuit is introduced between the driver output and the operational amplifier input. This intermediary component monitors the output current and provides correction signals, acting as a mediator that improves accuracy without requiring the operational amplifier itself to be replaced with a more complex high-performance device
Data Source
AI summary
Driver circuits, systems for driving actuators, and imaging systems with actuators. The driver circuit includes a current comparator circuit, a driver, and a replica circuit. The current comparator circuit includes a first node having a first voltage. The current comparator circuit also includes a second node having a second voltage. The driver includes a first terminal responsive to the second voltage. The driver also includes a second terminal connected to a reference voltage. The replica circuit includes a third terminal connected to the first node. The replica circuit also includes a fourth terminal connected to the second terminal of the driver. The replica circuit also includes a fifth terminal connected to the first terminal of the driver.