Charge control of micro-electromechanical device

Abstract

A charge control circuit for controlling a micro-electromechanical system (MEMS) device having variable capacitor formed by first conductive plate and a second conductive plate separated by a variable gap distance. The charge control circuit comprises a switch circuit configured to receive a reference voltage having a selected voltage level and configured to respond to an enable signal having a duration at least as long as an electrical time constant constant of the MEMS device, but shorter than a mechanical time constant of the MEMS device, to apply the selected voltage level across the first and second plates for the duration to thereby cause a stored charge having a desired magnitude to accumulate on the variable capacitor, wherein the variable gap distance is a function of the magnitude of the stored charge.

1 - 12 . (cancelled).  
   
   
       13 . A micro-electromechanical system comprising: 
 an M-row by N-column array of a micro-electromechanical cells, wherein each cell comprises: 
 a micro-electromechanical system (MEMS) device having a variable capacitor formed by a movable first conductive plate and a fixed second conductive plate separated by a variable gap distance; and  
 a switch circuit configured to receive a reference voltage having a selected voltage level and configured to respond to an enable signal having a duration at least as long as an electrical time constant of the MEMS device, but shorter than a mechanical time constant of the MEMS device, to apply the selected voltage level across the first and second plates for the duration to thereby cause a stored charge having a desired magnitude to accumulate on the variable capacitor, wherein the variable gap distance is a function of the magnitude of the stored charge.  
   
   
   
       14 . The micro-electromechanical system of  claim 13 , wherein each of the M rows receives a separate enable signal and all N switch circuits of a given row receive a same enable signal.  
   
   
       15 . The micro-electromechanical system of  claim 13 , wherein each of the N columns receives a separate reference voltage and all M switch circuits of a given column receive a same reference voltage, wherein each separate reference voltage can have a different selected voltage level.  
   
   
       16 . The micro-electromechanical system of  claim 13 , wherein each switch circuit comprises: 
 a first switch coupled to the micro-electromechanical device and configured to provide the reference voltage to the micro-electromechanical device for the duration of, and in response to, the enable signal.    
   
   
       17 . The micro-electromechanical system of  claim 16 , wherein the first switch comprises: 
 a p-channel metal-oxide-semiconductor (PMOS) device having a source configured to receive the reference voltage, a gate configured to receive the enable signal, and a drain configured to provide the reference voltage to the micro-electromechanical device based on the enable signal.    
   
   
       18 . The micro-electromechanical system of  claim 13 , further comprising: 
 a variable power supply configured to provide the reference voltages to the N columns of the array; and    a controller configured to provide the enable signals to the M rows of the array and to control the selected voltage level of the reference voltages provided by the variable power supply to the N columns of the array.    
   
   
       19 . The micro-electromechanical system of  claim 13 , wherein each switch circuit is further configured to discharge a stored charge on the variable capacitor in response to a clear signal.  
   
   
       20 . The micro-electromechanical system of  claim 19 , wherein each of the M rows receives a separate clear signal and all N switch circuits of a given row receive a same clear signal.  
   
   
       21 . The micro-electromechanical system of  claim 19 , wherein each switch circuit further comprises: 
 a second switch coupled across the first and second conductive plates and configured to discharge the stored charge from the variable capacitor in response to a clear signal.    
   
   
       22 . The micro-electromechanical system of  claim 21 , wherein the second switch comprises: 
 an n-channel metal-oxide-semiconductor (NMOS) device having a gate configured to receive the clear signal and a drain and source coupled across the first and second conductive plates.    
   
   
       23 . The micro-electromechanical system of  claim 19 , further comprising: 
 a variable power supply configured to provide the reference voltages to the N columns of the array; and    a controller configured to provide the enable signals and the clear signal to the M rows of the array and to control the selected voltage level of the reference voltages provided by the variable power supply to the N columns of the array.    
   
   
       24 - 32 . (Cancelled).  
   
   
       33 . A micro-electromechanical system comprising: 
 an M-row by N-column array of a micro-electromechanical cells, wherein each cell comprises:    a micro-electromechanical system (MEMS) device having a variable capacitor formed by a movable first conductive plate and a fixed second conductive plate separated by a restoring force providing a variable gap distance; and    a circuit configured to receive a reference voltage having a selected voltage level and configured to apply the reference voltage for a duration shorter than a mechanical time constant of the MEMS device to thereby cause a desired charge to accumulate on the variable capacitor before the reference voltage is removed, wherein the variable gap distance is a function of the magnitude of the stored charge.    
   
   
       34 . The micro-electromechanical system of  claim 33 , wherein each of the M rows receives a separate enable signal to apply the reference voltage and all N switch circuits of a given row receive a same enable signal.  
   
   
       35 . The micro-electromechanical system of  claim 33 , wherein each of the N columns receives a separate reference voltage and all M switch circuits of a given column receive a same reference voltage, wherein each separate reference voltage can have a different selected voltage level.  
   
   
       36 . The micro-electromechanical system of  claim 33 , wherein each circuit comprises: 
 a first switch coupled to the micro-electromechanical device and configured to provide the reference voltage to the micro-electromechanical device for the duration of, and in response to, an enable signal.    
   
   
       37 . The micro-electromechanical system of  claim 36 , wherein the first switch comprises: 
 a p-channel metal-oxide-semiconductor (PMOS) device having a source configured to receive the reference voltage, a gate configured to receive the enable signal, and a drain configured to provide the reference voltage to the micro-electromechanical device based on the enable signal.    
   
   
       38 . The micro-electromechanical system of  claim 33 , further comprising: 
 a variable power supply configured to provide the reference voltages to the N columns of the array; and    a controller configured to provide a set of enable signals to the M rows of the array and to control the selected voltage level of the reference voltages provided by the variable power supply to the N columns of the array.    
   
   
       39 . The micro-electromechanical system of  claim 33 , wherein each circuit is further configured to discharge a stored charge on the variable capacitor in response to a clear signal.  
   
   
       40 . The micro-electromechanical system of  claim 39 , wherein each of the M rows receives a separate clear signal and all N switch circuits of a given row receive a same clear signal.  
   
   
       41 . The micro-electromechanical system of  claim 39 , wherein each circuit further comprises: 
 a switch coupled across the first and second conductive plates and configured to discharge the stored charge from the variable capacitor in response to a clear signal.    
   
   
       42 . The micro-electromechanical system of  claim 41 , wherein the switch comprises: 
 an n-channel metal-oxide-semiconductor (NMOS) device having a gate configured to receive the clear signal and a drain and source coupled across the first and second conductive plates.    
   
   
       43 . The micro-electromechanical system of  claim 39 , further comprising: 
 a variable power supply configured to provide the reference voltages to the N columns of the array; and    a controller configured to provide a set of enable signals and the clear signal to the M rows of the array and to control the selected voltage level of the reference voltages provided by the variable power supply to the N columns of the array.