This article presents a control method for a tiny ultrasonic linear actuator for a camera module. The actuator is operated by a smooth impact driving method and an inertia displacement principle, and the structure of the actuator is very simple and lightweight. To precisely control the actuator, an actuator driver circuit has been developed that uses a small and inexpensive magneto-resistive sensor. The magneto-resistive sensor measures the changing magnetic field from a magnet attached to a mobile element and has a period of 400 m, which is scaled by 400 divisions, resulting in 1 m resolution. A proportional-integral-derivative control is used for controlling precise position. Finally, to verify the movement characteristics of the tiny ultrasonic linear actuator using a magneto-resistive sensor, a laser Doppler vibrometer (Polytec) was used Generally, the autofocus function of a camera module needs a 10 m resolution with a 1-mm stroke. The experimental results show that the actuator with the magneto-resistive sensor is suitable for the camera autofocus function.
This paper proposes a built-in self-test (BIST) scheme for noise-tolerant testing of a digital-to-analogue converter (DAC). The proposed BIST calculates the differences in output voltages between a DAC and test modules. These differences are used as the inputs of an integrator that determines integral nonlinearity (INL). The proposed method has an advantage of random noise cancelation and achieves a higher test accuracy than do the conventional BIST methods. The simulation results show high standard noise-immunity and fault coverage for the proposed method.
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