Nowadays, the demand for mobile phone camera functions is changing with each passing day, which raises higher and more complex requirements for the number and quality of mobile phone cameras. In the field of mobile phone camera driving, how to control the lens to achieve fast and stable focus is essential. The device that controls the lens focus in the phone is a voice coil motor (VCM).
The voice coil motor (VCM) works on the ampere theorem, that is, when the coil is electrically conductive, the force generated by the current pushes the lens movement fixed on the carrier to change the focusing distance. It can be seen that the control of the focus distance by the voice coil motor (VCM) device is actually achieved by controlling the current in the coil. A common voice coil motor (VCM) drive circuit.
The voice coil motor (VCM) drive circuit is actually a DAC circuit with a control algorithm. It converts the DAC code containing the digital position information uploaded from the I2C bus into the corresponding output current (output current corresponding to the DAC code); then converts the output current into the focusing distance through the voice coil motor (VCM) device. Different output currents form a loop through the voice coil motor, producing different amperage forces that drive the Lens motion above the voice coil motor. The movement of the Lens lens on the voice coil motor produces a damped oscillation before stopping, and the magnitude of the damped oscillation directly affects the stability of the Lens. The greater the damping oscillation, the worse the stability of the Lens, so the lens is not easy to capture sharp points during the focusing process, and it is easy to produce defocus. Conversely, the smaller the damping oscillation, the better the stability of the Lens, so that the lens is more easily stabilized at the focus during the focusing process. If the lens is free to dampen oscillations, the focus will be quite long. In order to achieve fast and stable focus, an algorithm for suppressing damped oscillations is added to the digital system of the VCM drive circuit. This algorithm is very important for the effect of the mobile phone camera. Only the optimized focus fast and stable control algorithm can ensure fast and accurate camera focus.