VCM Driver Circuit PWM Current Control
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Solution Overview
Problem
Existing autofocus lens actuator voice coil motor driver circuits lack efficient current control mechanisms, particularly in small form factor devices like smartphones and tablets, which limits precise control over lens positioning for optimal image sharpness.
Innovation Solution
A driver circuit with a switch mode current control circuit and pulse width modulation (PWM) control, implemented in a six-pin integrated circuit package, that selectively conducts current through a voice coil motor (VCM) using power switches and a digital communications interface to achieve desired average current levels for precise lens positioning.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a linear current control circuit is used in the driver circuit, then the circuit structure is simple, but the current control precision is insufficient for accurate lens positioning
Solution Approach 1:
The patent replaces the linear current control circuit with a switch mode current control circuit that uses pulse width modulation (PWM) technology. This substitution enables precise current control through digital PWM signals while maintaining circuit simplicity through integrated implementation, directly resolving the contradiction between control precision and circuit complexity
Solution Approach 2:
The patent changes the control parameter from analog linear current control to digital PWM duty cycle control. By modulating the duty cycle of PWM signals, the average current through the VCM can be precisely controlled, achieving accurate lens positioning while keeping the circuit structure manageable through standard digital control techniques
2Volume of moving object
If the camera module is designed for small space applications, then the device size is reduced, but the power consumption increases due to less efficient current control
Solution Approach 1:
The patent implements periodic switching action through PWM control, where the power switches operate in periodic on-off cycles. This periodic action allows for efficient energy transfer to the VCM while maintaining small current ripple, reducing overall power consumption compared to linear control while enabling compact camera module design
Solution Approach 2:
The patent changes the operating mode from continuous linear current control to periodic switch mode control with PWM. This parameter change enables more efficient energy utilization by the VCM, reducing power consumption while allowing the camera module to be designed in a compact form factor suitable for mobile devices
3Area of stationary object
If a six-pin integrated circuit package is used, then the device footprint is minimized, but the current control capability is limited
Solution Approach 1:
The patent merges multiple functions including PWM generation, current control, and digital interface into a single six-pin integrated circuit package. This consolidation achieves minimal footprint while maintaining full current control capability through integrated switch mode control circuitry that provides both precision and versatility within the constrained pin count
Solution Approach 2:
The patent designs the six-pin driver circuit to perform multiple functions: PWM signal generation, current regulation, communication interface, and power management. This multi-functional integration ensures that despite the limited pin count, the driver circuit maintains adaptable and versatile current control capability for various lens actuation requirements
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enables precise and efficient control of VCM current, allowing for accurate autofocus and zoom lens actuation, reducing power consumption and enabling small form factor camera modules with improved image sharpness and reduced power usage.
Implementation Method 1
The lens actuator contains a voice coil motor (VCM) to which the lens is coupled
Implementation Method 2
A pulse width modulation (PWM) circuit is coupled to control the first and second power switches. The PWM circuit may be programmed to achieve a desired average current through the VCM
Data Source
AI summary
A driver circuit for a camera voice coil motor (VCM) is described. A first power switch selectively conducts current from a VCM node to a power supply node, and a second power switch selectively conducts current from the VCM node to a power return node. A pulse width modulation circuit controls the first and second power switches. In another embodiment, a switch mode current control circuit sources VCM current alternately from the power supply node and the power n node, into the VCM node. Other embodiments are also described and claimed.