A piezoelectric actuator driver circuit for automatic focusing of mobile phone cameras

The analog front end (AFE) chip is presented to perform precise automatic focus operations with a piezoelectric actuator for mobile phone camera applications. In order to achieve the desired frequency response of a piezoelectric actuator, the frequency of a multi-vibrator oscillator can be swept in various manners such as the frequency step and the number of transitions between frequency changes. A novel method using the resistor ladder circuit is incorporated for a bridge-driving signal generator whose frequency can be linearly swept and controlled according to the input digital code. The AFE chip is implemented in a 0.35-mum 1-poly 4-metal CMOS technology and runs at the single supply voltage of 2.8 V.