Load adaptive class de driving amplifier for piezoelectric actuators

Abstract

An improved system and method for driving piezoelectric actuators for devices such as camera modules. The present invention replaces a conventional class D amplifier with a class DE amplifier. The class DE amplifier eliminates the switching losses that would otherwise occur when a class D amplifier is used. The present invention can also adjust the dead time of the amplifier based upon varying ambient temperature levels.

1 . A method of driving a piezoelectric actuator, comprising: 
 operatively connecting a class DE amplifier to a piezoelectric element, the class DE amplifier including first and second transistors;    applying a driving voltage the first and second transistors such that the duty cycle is 0<D<1; and    discharging a shunt capacitor associated with the first transistor when the first and second transistors are off, causing the first transistor to be turned on when the voltage across shunt capacitor is zero,    wherein application of the driving voltages alters the relative position of the piezoelectric element.    
   
   
       2 . The method of  claim 1 , further comprising:; 
 operatively connecting a temperature sensor to the class DE amplifier;    measuring the ambient temperature through the temperature sensor; and    adjusting dead time during which both transistors in the class DE amplifier are in an off state based upon the measured ambient temperature    
   
   
       3 . The method of  claim 2 , wherein the dead time is adjusted to correspond to one of a plurality of predefined fixed dead times based upon the measured ambient temperature.  
   
   
       4 . The method of  claim 2 , wherein the dead time is adjusted based upon an algorithm taking into account the measured ambient temperature  
   
   
       5 . The method of  claim 1 , wherein the piezoelectric element comprises a piezoceramic material.  
   
   
       6 . The method of  claim 1 , wherein the piezoelectric element is operatively connected to an actuator, and wherein the electrical state of the piezoelectric element affects the relative position of the actuator.  
   
   
       7 . The method of  claim 6 , wherein movement of the actuator caused by changes in the electrical state of the piezoelectric element causes a corresponding movement in a camera lens system.  
   
   
       8 . A method of driving a lens in a camera module, comprising: 
 positioning a piezoelectric element to engage an actuator for a lens in a camera module;    operatively connecting a class DE amplifier to the piezoelectric element, the class DE amplifier including first and second transistors;    driving the first and second transistors such that the duty cycle is 0<D<1; and    discharging a shunt capacitor associated with the first transistor when the first and second transistors are off, causing the associated transistor to be turned on when the voltage across shunt capacitor is zero,    wherein the input of voltage to the amplifier causes movement of the piezoelectric element, resulting in a corresponding movement in the actuator to move the lens.    
   
   
       9 . The method of  claim 8 , wherein the piezoelectric element comprises a piezoceramic material.  
   
   
       10 . The method of  claim 8 , further comprising: 
 operatively connecting a temperature sensor to the class DE amplifier;    measuring the ambient temperature through the temperature sensor; and    adjusting the dead time during which both transistors in the class DE amplifier are in an off state based upon the measured ambient temperature.    
   
   
       11 . The method of  claim 10 , wherein the dead time is adjusted to correspond to one of a plurality of predefined fixed dead times based upon the measured ambient temperature.  
   
   
       12 . The method of  claim 10 , wherein the dead time is adjusted based upon an algorithm taking into account the measured ambient temperature.  
   
   
       13 . The method of  claim 1 , further comprising charging a capacitor associated with the second transistor when the first and second transistors are off.  
   
   
       14 . A piezoelectric actuator system for a camera module, comprising: 
 a piezoelectric element in at least selective communication with a lens actuator; and    a class DE amplifier including first and second transistors, wherein discharging a shunt capacitor associated with the first transistor when the first and second transistors are off causes the first transistor to be turned on when the voltage across shunt capacitor is zero;    a piezoelectric element in electrical communication with the class DE amplifier; and    an actuator in at least selective contact with the piezoelectric element, wherein varying applied voltage to the class DE amplifier adjusts the relative position of the piezoelectric element, which alters the position of the actuator.    
   
   
       15 . The piezoelectric actuator system of  claim 14 , wherein the piezoelectric element comprises a piezoceramic material.  
   
   
       16 . The piezoelectric actuator system of  claim 14 , further comprising a temperature sensor operatively connected to the class DE amplifier, the temperature sensor measuring the ambient temperature, wherein the dead time during which both transistors in the class DE amplifier are in an off state is adjusted based upon the measured ambient temperature.  
   
   
       17 . The piezoelectric actuator system of  claim 16 , wherein the dead time is adjusted to correspond to one of a plurality of predefined fixed dead times based upon the measured ambient temperature.  
   
   
       18 . The piezoelectric actuator system of  claim 16 , wherein the dead time is adjusted based upon an algorithm taking into account the measured ambient temperature.  
   
   
       19 . The piezoelectric actuator system of  claim 16 , wherein the system maintains a gate control voltage to switch on a transistor of the class DE amplifier while the drain-source voltage is zero.  
   
   
       20 . A control circuit for piezoelectric actuation comprising: 
 a class DE amplifier including a first transistor and a second transistor, the first transistor including a first shunt capacitance and the second transistor including a second shunt capacitance;    a series resonant output circuit coupled to an output and operably connected to the class DE amplifier; and    a driving voltage applied to the first and second transistors having a duty cycle of 0<d<1 and discharging a shunt capacitor associated with the first transistor when the first and second transistors are off, causing the associated transistor to be turned on when the voltage across shunt capacitor is zero,    wherein application of the driving voltage causes the output to actuate a piezoelectric element.    
   
   
       21 . The control circuit of  claim 20 , further comprising a temperature sensor operatively connected to the class DE amplifier, wherein dead time for which the first and second transistors are simultaneously off is adjusted based upon ambient temperature monitored by the temperature sensor.  
   
   
       22 . The control circuit of  claim 20 , wherein the piezoelectric element comprises a piezoceramic material.  
   
   
       23 . The control circuit of  claim 20 , wherein the piezoelectric element comprises part of the series resonant output circuit.  
   
   
       24 . The control circuit of  claim 20 , wherein the control circuit maintains a gate control voltage to switch on a transistor of the class DE amplifier while the drain-source voltage is zero.  
   
   
       25 . An imaging device, comprising: 
 the control circuit of  claim 20;  and    a lens operatively connected to the control circuit,    wherein the actuation of the piezoelectric element causes a corresponding movement in the lens.    
   
   
       26 . A mobile telephone, comprising: 
 a processor;    a memory unit operatively connected to the processor; and    the imaging device of  claim 25  operatively connected to the processor.