System and method for power-efficient charging and discharging of a capacitive load from a single source

Abstract

A system and method for efficiently charging and discharging a capacitive load from a single voltage source. The system includes a brat switch for selectively connecting the voltage source to the load and a second switch for selectively providing a short across the load as may he common in the art. A particularly novel aspect of the invention resides in the provision of plural capacitive elements and a switching mechanism for selectively connecting each of the capacitive elements to the load whereby the load is gradually charged or discharged. In the illustrative embodiment, the switching mechanism includes a set of switches for selectively connecting each of the capacitive elements to the capacitive load and a switch control mechanism for selectively activating the switches.

1. A system for efficiently charging and discharging a capacitive lad from a single voltage source of a first potential consisting of:
 a first switch for selectively charging the load;    a second switch for selectively discharging the load;    plural capacitive elements; and    switch means for selectively connecting each of the capacitive elements to the capacitive load to gradually charge or discharge the capacitive load.    
     
     
       2. The invention of  claim 1  wherein said switch means includes plural third switches connected between said capacitive elements and said load. 
     
     
       3. The invention of  claim 2  wherein said switch means includes means for selectively activating the first, second and third switches. 
     
     
       4. The invention of  claim 3  wherein the capacitive load has a first terminal connected to the first switch and a second terminal connected to a source of a second potential. 
     
     
       5. The invention of  claim 4  wherein the second switch has a first terminal connected to the first terminal of the load and a second terminal connected to said source of a second potential. 
     
     
       6. The invention of  claim 5  wherein each of the third switches has a first terminal connected to the first terminal of the load and a second terminal connected to a first terminal of an associated one of the plural capacitive elements. 
     
     
       7. The invention of  claim 6  wherein the means for selectively activating the first, second and third switches includes a finite state machine. 
     
     
       8. The invention of  claim 7  wherein the finite state machine is designed to receive a clock signal and an input signal and provide selective activation signals for the first, second and third switches in response thereto. 
     
     
       9. The invention of  claim 8  wherein a second terminal of each of the plural capacitive elements is connected to said source of a second potential. 
     
     
       10. The invention of  claim 9  wherein each of the capacitive elements has a capacitance which is at least an order of magnitude greater than the capacitance of the load. 
     
     
       11. A method for efficiently charging and discharging a capacitive load from a single voltage source including the steps of:
 providing a flat switch for selectively connecting the voltage source to the load;    providing a second switch for selectively providing a short across the load;    providing plural capacitive elements;    providing plural third switches for selectively connecting each of the capacitive elements to the capacitive load; and    selectively activating the first, second and third switches to gradually charge or discharge the capacitive load.    
     
     
       12. An apparatus for driving a capacitive load, comprising:
   a voltage source; and        a switch network,        wherein the switch network is operable to electrically connect the capacitive load and the voltage source to drive the load to a first voltage level,        wherein the switch network is further operable to electrically connect the capacitive load and a capacitive storage system, and wherein when the capacitive storage system and the capacitive load are electrically connected by the switch network, a voltage level of the capacitive storage system tends to self stabilize to a second voltage level; and        wherein the switch network is further operable to cause charge to be transferred from the capacitive storage subsystem to the capacitive load and is still further operable to cause charge to be transferred from the capacitive load to the capacitive storage subsystem.     
     
     
       13. An apparatus as claimed in  claim 12 , wherein the capacitive load comprises a first capacitive element and the capacitive storage system comprises a second capacitive element. 
     
     
       14. An apparatus as claimed in  claim 12 , wherein the capacitive storage system comprises a plurality of capacitive elements. 
     
     
       15. An apparatus as claimed in  claim 12 , wherein when the capacitive storage system and the capacitive load are electrically connected by the switch network, the capacitive storage system and the capacitive load are electrically floating. 
     
     
       16. An apparatus as claimed in  claim 12 , wherein the capacitive load comprises a first capacitive element and the capacitive storage system comprises a second capacitive element, and wherein when the capacitive storage system and the capacitive load are electrically connected by the switch network, the first and second capacitive elements are electrically connected in parallel. 
     
     
       17. An apparatus as claimed in  claim 12 , wherein the capacitive load comprises a first capacitive element and the capacitive storage system comprises a second capacitive element, and wherein when the capacitive storage system and the capacitive load are electrically connected by the switch network, the first and second capacitive elements are electrically connected such that a first terminal of the first capacitive element is electrically connected to a first terminal of the second capacitive element and a second terminal of the first capacitive element and a second terminal of the second capacitive element are electrically connected to a common potential. 
     
     
       18. An apparatus as claimed in  claim 12 , wherein the switch network comprises a plurality of switching elements. 
     
     
       19. An apparatus as claimed in  claim 12 , wherein the switch network comprises a plurality of MOS transistors. 
     
     
       20. An apparatus as claimed in  claim 12 , wherein a capacitance of the capacitive storage system is larger than a capacitance of the capacitive load. 
     
     
       21. An apparatus as claimed in  claim 12 , wherein a capacitance of the capacitive storage system is an order of magnitude larger than a capacitance of the capacitive load. 
     
     
       22. An apparatus as claimed in  claim 12 , wherein the apparatus is a driver. 
     
     
       23. An apparatus as claimed in  claim 12 , wherein the switch network is further operable to electrically connect the capacitive load and the voltage source to drive the capacitive load to a third voltage level wherein when the capacitive storage system and the capacitive load are electrically connected by the switch network the capacitive load settles at a second voltage level between the first and third voltage levels, and wherein during operation of the apparatus the capacitive load is first driven to the first voltage, then subsequently settles at the second voltage level and then is subsequently driven to the third voltage level. 
     
     
       24. An apparatus comprising:
   a capacitive load;        a voltage source;        a switch network; and        a capacitive storage system,        wherein the switch network is operable to electrically connect the capacitive load and the voltage source to drive the load to a first voltage level,        wherein the switch network is further operable to electrically connect the capacitive load and the capacitive storage system, and wherein when the capacitive storage system and the capacitive load are electrically connected by the switch network, a voltage level of the capacitive storage system tends to self stabilize to a second voltage level, and        wherein the switch network is further operable to cause charge to be transferred from the capacitive storage subsystem to the capacitive load and is still further operable to cause charge to be transferred from the capacitive load to the capacitive storage subsystem.     
     
     
       25. An apparatus as claimed in  claim 24 , wherein the capacitive load comprises a first capacitive element and the capacitive storage system comprises a second capacitive element. 
     
     
       26. An apparatus as claimed in  claim 24 , wherein the capacitive storage system comprises a plurality of capacitive elements. 
     
     
       27. An apparatus as claimed in  claim 24 , wherein when the capacitive storage system and the capacitive load are electrically connected by the switch network the capacitive storage system and the capacitive load are electrically floating. 
     
     
       28. An apparatus as claimed in  claim 24 , wherein the capacitive load comprises a first capacitive element and the capacitive storage system comprises a second capacitive element, and wherein when the capacitive storage system and the capacitive load are electrically connected by the switch network, the first and second capacitive elements are electrically connected in parallel. 
     
     
       29. An apparatus as claimed in  claim 24 , wherein the capacitive load comprises a first capacitive element and the capacitive storage system comprises a second capacitive element, and wherein when the capacitive storage system and the capacitive load are electrically connected by the switch network, the first and second capacitive elements are electrically connected such that a first terminal of the first capacitive element is electrically connected to a first terminal of the second capacitive element and a second terminal of the first capacitive element and a second terminal of the second capacitive element are electrically connected to a common potential. 
     
     
       30. An apparatus as claimed in  claim 24 , wherein the switch network comprises a plurality of switching elements. 
     
     
       31. An apparatus as claimed in  claim 24 , wherein the switch network comprises a plurality of MOS transistors. 
     
     
       32. An apparatus as claimed in  claim 24 , wherein a capacitance of the capacitive storage system is larger than a capacitance of the capacitive load. 
     
     
       33. An apparatus as claimed in  claim 24 , wherein a capacitance of the capacitive storage system is an order of magnitude larger than a capacitance of the capacitive load. 
     
     
       34. An apparatus as claimed in  claim 24 , wherein the switch network is further operable to electrically connect the capacitive load and the voltage source to drive the capacitive load to a third voltage level wherein when the capacitive storage system and the capacitive load are electrically connected by the switch network, the capacitive load settles at a second voltage level between the first and third voltage levels, and wherein during operation of the apparatus, the capacitive load is first driven to the first voltage, then subsequently settles at the second voltage level, and then is subsequently driven to the third voltage level. 
     
     
       35. An apparatus for driving a capacitive load, comprising:
   a voltage source; and        a switch network,        wherein the switch network is operable to electrically connect the capacitive load and the voltage source to drive the load to a first voltage level,        wherein the switch network is further operable to electrically connect the capacitive load and a capacitive storage system, and wherein when the capacitive storage system and the capacitive load are electrically connected by the switch network, the capacitive storage system is electrically isolated from the voltage source, and        wherein the switch network is further operable to cause charge to be transferred from the capacitive storage subsystem to the capacitive load and is still further operable to cause charge to be transferred from the capacitive load to the capacitive storage subsystem.     
     
     
       36. An apparatus as claimed in  claim 35 , wherein the capacitive load comprises a first capacitive element and the capacitive storage system comprises a second capacitive element. 
     
     
       37. An apparatus as claimed in  claim 35 , wherein the capacitive storage system comprises a plurality of capacitive elements. 
     
     
       38. An apparatus as claimed in  claim 35 , wherein when the capacitive storage system and the capacitive load are electrical connected by the switch network, the capacitive storage system and the capacitive load are electrically floating. 
     
     
       39. An apparatus as claimed in  claim 35 , wherein the capacitive load comprises a first capacitive element and the capacitive storage system comprises a second capacitive element, and wherein when the capacitive storage system and the capacitive load are electrically connected by the switch network, the first and second capacitive elements are electrically connected in parallel. 
     
     
       40. An apparatus as claimed in  claim 35 , wherein the capacitive load comprises a first capacitive element and the capacitive storage system comprises a second capacitive element, and wherein when the capacitive storage system and the capacitive load are electrically connected by the switch network, the first and second capacitive elements are electrically connected such that a first terminal of the first capacitive element is electrically connected to a first terminal of the second capacitive element and a second terminal of the first capacitive element and a second terminal of the second capacitive element are electrically connected to a common potential. 
     
     
       41. An apparatus as claimed in  claim 35 , wherein the switch network comprises a plurality of switching elements. 
     
     
       42. An apparatus as claimed in  claim 35 , wherein the switch network comprises a plurality of MOS transistors. 
     
     
       43. An apparatus as claimed in  claim 35 , wherein a capacitance of the capacitive storage system is larger than a capacitance of the capacitive load. 
     
     
       44. An apparatus as claimed in  claim 35 , wherein a capacitance of the capacitive storage system is an order of magnitude larger than a capacitance of the capacitive load. 
     
     
       45. An apparatus as claimed in  claim 35 , wherein the apparatus is a driver. 
     
     
       46. An apparatus as claimed in  claim 35 , wherein the switch network is further operable to electrically connect the capacitive load and the voltage source to drive the capacitive load to a third voltage level, wherein when the capacitive storage system and the capacitive load are electrically connected by the switch network, the capacitive load settles at a second voltage level between the first and third voltage levels, and wherein during operation of the apparatus, the capacitive load is first driven to the first voltage, then subsequently settles at the second voltage level, and then is subsequently driven to the third voltage level. 
     
     
       47. An apparatus comprising:
   a capacitive load;        a voltage source;        a switch network; and        a capacitive storage system,        wherein the switch network is operable to electrically connect the capacitive load and the voltage source to drive the load to a first voltage level,        wherein the switch network is further operable to electrically connect the capacitive load and the capacitive storage system, and wherein when the capacitive storage system and the capacitive load are electrically connected by the switch network, the capacitive storage system is electrically isolated from the voltage source, and        wherein the switch network is further operable to cause charge to be transferred from the capacitive storage subsystem to the capacitive load and is still further operable to cause charge to be transferred from the capacitive load to the capacitive storage subsystem.     
     
     
       48. An apparatus as claimed in  claim 47 , wherein the capacitive load comprises a first capacitive element and the capacitive storage system comprises a second capacitive element. 
     
     
       49. An apparatus as claimed in  claim 47 , wherein the capacitive storage system comprises a plurality of capacitive elements. 
     
     
       50. An apparatus as claimed in  claim 47 , wherein when the capacitive storage system and the capacitive load are electrically connected by the switch network, the capacitive storage system and the capacitive load are electrically floating. 
     
     
       51. An apparatus as claimed in  claim 47 , wherein the capacitive load comprises a first capacitive element and the capacitive storage system comprises a second capacitive element, and wherein when the capacitive storage system and the capacitive load are electrically connected by the switch network, the first and second capacitive elements are electrically connected in parallel. 
     
     
       52. An apparatus as claimed in  claim 47 , wherein the capacitive load comprises a first capacitive element and the capacitive storage system comprises a second capacitive element, and wherein when the capacitive storage system and the capacitive load are electrically connected by the switch network, the first and second capacitive elements are electrically connected such that a first terminal of the first capacitive element is electrically connected to a first terminal of the second capacitive element and a second terminal of the first capacitive element and a second terminal of the second capacitive element are electrically connected to a common potential. 
     
     
       53. An apparatus as claimed in  claim 47 , wherein the switch network comprises a plurality of switching elements. 
     
     
       54. An apparatus as claimed in  claim 47 , wherein the switch network comprises a plurality of MOS transistors. 
     
     
       55. An apparatus as claimed in  claim 47 , wherein a capacitance of the capacitive storage system is larger than a capacitance of the capacitive load. 
     
     
       56. An apparatus as claimed in  claim 47 , wherein a capacitance of the capacitive storage system is an order of magnitude larger than a capacitance of the capacitive load. 
     
     
       57. An apparatus as claimed in  claim 47 , wherein the switch network is further operable to electrically connect the capacitive load and the voltage source to drive the capacitive load to a third voltage level, wherein when the capacitive storage system and the capacitive load are electrically connected by the switch network, the capacitive load settles at a second voltage level between the first and third voltage levels, and wherein during operation of the apparatus, the capacitive load is first driven to the first voltage, then subsequently settles at the second voltage level, and then is subsequently driven to the third voltage level. 
     
     
       58. An apparatus for driving a capacitive load, comprising:
   a voltage source; and        a switch network,        wherein the switch network is operable to electrically connect the capacitive load and the voltage source to drive the load to a first voltage level,        wherein the switch network is further operable to electrically connect the capacitive load and a capacitive storage system, and wherein when the capacitive storage system and the capacitive load are electrically connected by the switch network, the capacitive storage system and the capacitive load are electrically floating, and        wherein the switch network is further operable to cause charge to be transferred from the capacitive storage subsystem to the capacitive load and is still further operable to cause charge to be transferred from the capacitive load to the capacitive storage subsystem.     
     
     
       59. An apparatus as claimed in  claim 58 , wherein the capacitive load comprises a first capacitive element and the capacitive storage system comprises a second capacitive element. 
     
     
       60. An apparatus as claimed in  claim 58 , wherein the capacitive storage system comprises a plurality of capacitive elements. 
     
     
       61. An apparatus as claimed in  claim 58 , wherein when the capacitive storage system and the capacitive load are electrically connected by the switch network, the capacitive storage system and the capacitive load are electrically disconnected from the voltage source. 
     
     
       62. An apparatus as claimed in  claim 58 , wherein the capacitive load comprises a first capacitive element and the capacitive storage system comprises a second capacitive element, and wherein when the capacitive storage system and the capacitive load are electrically connected by the switch network the first and second capacitive elements are electrically connected in parallel. 
     
     
       63. An apparatus as claimed in  claim 58 , wherein the capacitive load comprises a first capacitive element and the capacitive storage system comprises a second capacitive element, and wherein when the capacitive storage system and the capacitive load are electrically connected by the switch network, the first and second capacitive elements are electrically connected such that a first terminal of the first capacitive element is electrically connected to a first terminal of the second capacitive element and a second terminal of the first capacitive element and a second terminal of the second capacitive element are electrically connected to a common potential. 
     
     
       64. An apparatus as claimed in  claim 58 , wherein the switch network comprises a plurality of switching elements. 
     
     
       65. An apparatus as claimed in  claim 58 , wherein the switch network comprises a plurality of MOS transistors. 
     
     
       66. An apparatus as claimed in  claim 58 , wherein a capacitance of the capacitive storage system is larger than a capacitance of the capacitive load. 
     
     
       67. An apparatus as claimed in  claim 58 , wherein a capacitance of the capacitive storage system is an order of magnitude larger than a capacitance of the capacitive load. 
     
     
       68. An apparatus as claimed in  claim 58 , wherein the apparatus is a driver. 
     
     
       69. An apparatus as claimed in  claim 58 , wherein the switch network is further operable to electrically connect the capacitive load and the voltage source to drive the capacitive load to a third voltage level, wherein when the capacitive storage system and the capacitive load are electrically connected by the switch network, the capacitive load settles at a second voltage level between the first and third voltage levels, and wherein during operation of the apparatus, the capacitive load is first driven to the first voltage, then subsequently settles at the second voltage level, and then is subsequently driven to the third voltage level. 
     
     
       70. An apparatus comprising:
   a capacitive load;        a voltage source;        a switch network; and        a capacitive storage system,        wherein the switch network is operable to electrically connect the capacitive load and the voltage source to drive the load to a first voltage level,        wherein the switch network is further operable to electrically connect the capacitive load and the capacitive storage system, and wherein when the capacitive storage system and the capacitive load are electrically connected by the switch network, the capacitive storage system and the capacitive load are electrically floating, and        wherein the switch network is further operable to cause charge to be transferred from the capacitive storage subsystem to the capacitive load and is still further operable to cause charge to be transferred from the capacitive load to the capacitive storage subsystem.     
     
     
       71. An apparatus as claimed in  claim 70 , wherein the capacitive load comprises a first capacitive element and the capacitive storage system comprises a second capacitive element. 
     
     
       72. An apparatus as claimed in  claim 70 , wherein the capacitive storage system comprises a plurality of capacitive elements. 
     
     
       73. An apparatus as claimed in  claim 70 , wherein when the capacitive storage system and the capacitive load are electrically connected by the switch network, the capacitive storage system and the capacitive load are electrically disconnected from the voltage source. 
     
     
       74. An apparatus as claimed in  claim 70 , wherein the capacitive load comprises a first capacitive element and the capacitive storage system comprises a second capacitive element, and wherein when the capacitive storage system and the capacitive load are electrically connected by the switch network, the first and second capacitive elements are electrically connected in parallel. 
     
     
       75. An apparatus as claimed in  claim 70 , wherein the capacitive load comprises a first capacitive element and the capacitive storage system comprises a second capacitive element, and wherein when the capacitive storage system and the capacitive load are electrically connected by the switch network, the first and second capacitive elements are electrically connected such that a first terminal of the first capacitive element is electrically connected to a first terminal of the second capacitive element and a second terminal of the first capacitive element and a second terminal of the second capacitive element are electrically connected to a common potential. 
     
     
       76. An apparatus as claimed in  claim 70 , wherein the switch network comprises a plurality of switching elements. 
     
     
       77. An apparatus as claimed in  claim 70 , wherein the switch network comprises a plurality of MOS transistors. 
     
     
       78. An apparatus as claimed in  claim 70 , wherein a capacitance of the capacitive storage system is larger than a capacitance of the capacitive load. 
     
     
       79. An apparatus as claimed in  claim 70 , wherein a capacitance of the capacitive storage system is an order of magnitude larger than a capacitance of the capacitive load. 
     
     
       80. An apparatus as claimed in  claim 70 , wherein the switch network is further operable to electrically connect the capacitive load and the voltage source to drive the capacitive load to a third voltage level, wherein when the capacitive storage system and the capacitive load are electrically connected by the switch network, the capacitive load settles at a second voltage level between the first and third voltage levels, and wherein during operation of the apparatus, the capacitive load is first driven to the first voltage, then subsequently settles at the second voltage level and then is subsequently driven to the third voltage level.