Auto Focus is to move the position of the entire lens by a small distance, control the focal length of the lens, and achieve a clear image, it is a common used method in mobile phone camera, and the auto focus is achieved by the working of VCM.
VCMFull Name: Voice Coil Montor working principle is that in a permanent magnetic field, the stretching position of the spring is controlled by changing the DC current of the coil in the motor, thereby driving the lens up and down movement.
It has the advantages of small size, high precision, good integration, high reliability, and can support high power, which significantly reduces the size and volume of the finished product and reduces the cost of the whole machine.
VCM can be roughly divided into three categories from the structure:
VCM can be roughly divided into five categories in terms of functions:
The VCM of the mobile phone camera needs the driver IC to complete the focusing. The driver IC controls the power supply current of the VCM to determine the moving distance of the lens mounted on the VCM, so as to adjust to the appropriate position to capture a clear image.
After entering the auto-focusing mode, the Driver moves from 0 to the maximum value, so that the lens moves from the original position to the maximum displacement. At this time, the sensor imaging surface automatically captures pictures and saves them in the DSP. The DSP calculates each picture through these pictures. MTF (Modulation transfer function) value, so as to find the maximum value in this MTF curve, and through the algorithm, get the current size corresponding to this point, once again instruct the Driver to provide this current to the voice coil, and stabilize the lens on this imaging surface , so that automatic focus is achieved.
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