Oscillation circuit, electronic circuit using the same, and semiconductor device, electronic equipment, and timepiece using the same

Abstract

This invention relates to a crystal oscillation circuit that oscillates stably with a low power consumption. This crystal oscillation circuit comprises an inverting amplifier, a crystal oscillator, and a feedback circuit that inverts the phase of an output from this inverting amplifier and feeds it back as an input. The sum of the absolute value of the threshold voltage of a first semiconductor switching element and the absolute value of the threshold voltage of a second semiconductor switching element is set to be greater than or equal to the absolute value of the potential difference between first and second potentials, when said inverting amplifier includes the first and second semiconductor switching elements.

1. An oscillation circuit comprising:
 an inverting amplifier including a first semiconductor switching element and a second semiconductor switching element;  
 wherein said first and second semiconductor switching elements are prevented from being on simultaneously to limit a short-circuiting current flowing through said inverting amplifier when said oscillation circuit is driven, and  
 wherein a sum of an absolute value of a threshold voltage of said first semiconductor switching element and an absolute value of a threshold voltage of said second semiconductor switching element is set to be greater than or equal to an absolute value of a power voltage of said inverting amplifier, to limit a short-circuiting current flowing through said inverting amplifier.  
 
     
     
       2. The oscillation circuit as defined in  claim 1 ,
 further comprising a feedback circuit having a crystal oscillator connected between an output side and an input side of said inverting amplifier, for causing a phase of an output signal from said inverting amplifier to invert and feeding the inverted signal back to said inverting amplifier as an input;  
 wherein said inverting amplifier comprises a first circuit including said first semiconductor switching element, and a second circuit including said second semiconductor switching element;  
 wherein said first semiconductor switching element is connected to a side of a first potential and is driven to be turned on and off by said feedback input, to excite said crystal oscillator;  
 wherein said second semiconductor switching element is connected to a side of a second potential that differs from said first potential and is driven to be turned on and off by said feedback input at a timing that differs from that of said first semiconductor switching element, to excite said crystal oscillator.  
 
     
     
       3. The oscillation circuit as defined in  claim 1  wherein an OFF region in which said first and second semiconductor switching elements are turned off so that they are prevented from being on simultaneously includes a sub-threshold region in which a sub-threshold current flows. 
     
     
       4. The oscillation circuit as defined in  claim 1  wherein the sum of the absolute values of the threshold voltages of said first and second semiconductor switching elements is set to be greater than or equal to the absolute value of the power voltage of said inverting amplifier to satisfy the following formula
   |V reg |≦|V 1 +|V 2 ||V reg   |≦|V 1 |+|V 2 |   
 
       where the absolute value of the threshold voltage of said first semiconductor switching element is |V 1 |; the absolute value of the threshold voltage of said second semiconductor switching element is |V 2 |; and the absolute value of the power voltage of the inverting amplifier is |V reg |, and
 wherein the absolute values of the threshold voltages of said first and second semiconductor switching elements are set to be smaller than the absolute value of the power voltage of said inverting amplifier as represented by the following formulae 
   |V reg |>|V 1 | and  
   |V ref |>|V 2 |.  
 
 
     
     
       5. The oscillation circuit as defined in  claim 1 , further comprising a source of constant current being connected in parallel to at least one of said first and second semiconductor switching elements, wherein a shortage of power necessary for stabilizing oscillation is offset by power from said source. 
     
     
       6. The oscillation circuit as defined in  claim 5  wherein the absolute value of the power voltage of the inverting amplifier is set to be equal to a minimum value of power necessary for stabilizing oscillation. 
     
     
       7. The oscillation circuit as defined in  claim 1 , further comprising constant current sources connected in parallel with at least one of said first and second semiconductor switching elements, each constant current source supplying a different constant current, and a selection circuit for selecting a constant current source from said constant current sources, wherein a shortage of power necessary for stabilizing oscillation is offset by power from said selected source. 
     
     
       8. The oscillation circuit as defined in  claim 7  wherein the absolute value of the power voltage of the inverting amplifier is set to be equal to a minimum value of power necessary for stabilizing oscillation. 
     
     
       9. The oscillation circuit as defined in  claim 7  wherein a target absolute value of the power voltage of said inverting amplifier is set to be between an absolute value of a minimum power voltage of said inverting amplifier necessary for stabilizing oscillation and an absolute value of a first power voltage that is smaller than the absolute value of said minimum power voltage by a range of fluctuations of power voltages of inverting amplifiers in oscillation circuits which are produced in large quantities and wherein said selection circuit selects a constant current based on power voltages of inverting amplifiers in oscillation circuits which are produced in large quantities, and a shortage of power necessary for stabilizing oscillation is offset by power from said selected source. 
     
     
       10. The oscillation circuit as defined in  claim 7  wherein said constant current sources comprise a plurality of constant current sources connected in parallel to said first semiconductor switching element, each of said plurality of constant current sources supplying a different constant current and another plurality of constant current sources connected in parallel to said second semiconductor switching element, each of said another plurality of constant current sources supplying a different constant current and wherein said selection circuit selects a constant current source from said pluralities of constant current sources, and a shortage of power necessary for stabilizing oscillation is offset by power from said selected source. 
     
     
       11. The oscillation circuit as defined in  claim 1 , further comprising a power supply circuit for selectively outputting at least two types of power voltages V reg , one having a large absolute value for initiating oscillation and the other having a small absolute value for stabilizing oscillation and wherein the power voltage having said large absolute value for initiating oscillation is supplied to said inverting amplifier during a period of time between turning power on and stabilizing oscillation while the other power voltage having said small absolute value for stabilizing oscillation is supplied to said inverting amplifier during a period of time between stabilizing oscillation and terminating oscillation. 
     
     
       12. The oscillation circuit as defined in  claim 11 , further comprising a voltage control circuit for controlling said power supply circuit to output the power voltage having the large absolute value for initiating oscillation when a period of time between turning power on and stabilizing oscillation is detected, for controlling said power supply circuit to output the other power voltage having the small absolute value for stabilizing oscillation when a transition from turning power on to stabilizing oscillation is detected. 
     
     
       13. The oscillation circuit as defined in  claim 12  wherein said voltage control circuit comprises a power-on detecting circuit for detecting a power on of said oscillation circuit and a timer for detecting at transition from turning power on to stabilizing oscillation by measuring time passed since power is turned on, for controlling said power supply circuit to output the power voltage having the large absolute value for initiating oscillation at a time said power is turned on and for controlling said power supply circuit to output the other power voltage having the small absolute value for stabilizing oscillation when said timer detects a transition from turning power on to stabilizing oscillation. 
     
     
       14. The oscillation circuit as defined in  claim 1  wherein said inverting amplifier comprises a first inverting amplifier for initiating oscillation and a second inverting amplifier for stabilizing oscillation and wherein said first inverting amplifier provides oscillation during a period of time between turning power on and stabilizing oscillation while said second inverting amplifier provides oscillation during a period of time between stabilizing oscillation and terminating oscillation. 
     
     
       15. The oscillation circuit as defined in  claim 14 , further comprising an inverting-amplifier switching circuit for selecting said first inverting amplifier when a period of time between turning power on and stabilizing oscillation is detected and for selecting said second inverting amplifier after a transition from turning power on to stabilizing oscillation. 
     
     
       16. The oscillation circuit as defined in  claim 15  wherein said inverting-amplifier switching circuit comprises a power-on detecting circuit for detecting a power on of said oscillation circuit and a timer for detecting a transition from turning power on to stabilizing oscillation by measuring time passed since power is turned on and wherein said first inverting amplifier is selected at a time power is turned on while said second inverting amplifier is selected when said timer detects a transition from turning power on to stabilizing oscillation. 
     
     
       17. The oscillation circuit as defined in  claim 14  wherein an absolute value of a threshold voltage of a semiconductor switching element that constitutes said first inverting amplifier is set to be smaller than an absolute value of a threshold voltage of a semiconductor switching element that constitutes said second inverting amplifier. 
     
     
       18. The oscillation circuit as defined in  claim 1  wherein said oscillation circuit uses a crystal oscillator having a high value of Q, the value Q being an index representing a degree of easiness in mechanical oscillation. 
     
     
       19. The oscillation circuit as defined in  claim 18  wherein said value Q is equal to or higher than 10,000 and is represented by the following
   Q=α/Rxt  
 
       where Rxt is a component of resistance in the crystal oscillator and α is a coefficient. 
     
     
       20. The oscillation circuit as defined in  claim 1  wherein said first and second semiconductor switching elements are configured by using field-effect transistor elements of differing conductivity types. 
     
     
       21. The oscillation circuit as defined in  claim 20  wherein said first and second semiconductor switching elements are configured by using field-effect transistor elements of differing conductivity types. 
     
     
       22. An oscillation circuit comprising:
 an inverting amplifier including a first semiconductor switching element and a second semiconductor switching element, said first and second semiconductor switching elements being prevented from being on simultaneously to limit a short- circuiting current flowing through said inverting amplifier when said oscillation circuit is driven; and    
   a bias circuit for applying a first direct current bias voltage and a second direct current bias voltage to gates of said first semiconductor switching element and said second semiconductor switching element, respectively;    
   said first and second direct current bias voltages shifting values of the direct current potentials of feedback inputs that are input from said inverting amplifier to said gates of said first and second semiconductor switching elements, to prevent said first and second semiconductor switching elements from being on simultaneously; and   
 a source of constant current being connected in parallel to at least one of said first and second semiconductor switching elements, wherein a shortage of power necessary for stabilizing oscillation is offset by power from said source.  
 
     
     
       23. The oscillation circuit as defined in  claim 22  wherein an absolute value of a power voltage of the inverting amplifier is set to be equal to a minimum value of power necessary for stabilizing oscillation. 
     
     
       24. An oscillation circuit comprising:
 an inverting amplifier including a first semiconductor switching element and a second semiconductor switching element, said first and second semiconductor switching elements being prevented from being on simultaneously to limit a short- circuiting current flowing through said inverting amplifier when said oscillation circuit is driven; and    
   a bias circuit for applying a first direct current bias voltage and a second direct current bias voltage to gates of said first semiconductor switching element and said second semiconductor switching element, respectively;    
   said first and second direct current bias voltages shifting values of the direct current potentials of feedback inputs that are input from said inverting amplifier to said gates of said first and second semiconductor switching elements, to prevent said first and second semiconductor switching elements from being on simultaneously; and   
 constant current sources being connected in parallel to at least one of said first and second semiconductor switching elements, each constant current source supplying a different constant current, and a selection circuit for selecting a constant current source from said constant current sources, wherein a shortage of power necessary for stabilizing oscillation is offset by power from said selected source.  
 
     
     
       25. The oscillation circuit as defined in  claim 24  wherein an absolute value of a power voltage of the inverting amplifier is set to be equal to a minimum value of power necessary for stabilizing oscillation. 
     
     
       26. The oscillation circuit as defined in  claim 24  wherein an absolute value of a target power voltage of said inverting amplifier is set to be between an absolute value of a minimum power voltage of said inverting amplifier necessary for stabilizing oscillation and an absolute value of a first power voltage that is smaller than the absolute value of said minimum power voltage by a range of fluctuations of power voltages of inverting amplifiers in oscillation circuits which are produced in large quantities and wherein said selection circuit selects a constant current based on power voltages of inverting amplifiers in oscillation circuits which are produced in large quantities, and a shortage of power necessary for stabilizing oscillation is offset by power from said selected source. 
     
     
       27. The oscillation circuit as defined in  claim 24  wherein said constant current sources comprise a plurality of constant current sources connected in parallel to said first semiconductor switching element, each of said plurality of constant current sources supplying a different constant current and another plurality of constant current sources connected in parallel to said second semiconductor switching element, each of said another plurality of constant current sources supplying a different constant current and wherein said selection circuit selects a constant current source from said pluralities of constant current sources, and a shortage of power necessary for stabilizing oscillation is offset by power from said selected source. 
     
     
       28. The oscillation circuit as defined in  claim 22 , further comprising a power supply circuit for outputting at least two types of power voltages V reg , one having a large absolute value for initiating oscillation and the other having a small absolute value for stabilizing oscillation and wherein the power voltage having said large absolute value for initiating oscillation is supplied to said inverting amplifier during a period of time between turning power on and stabilizing oscillation while the other power voltage having said small absolute value for stabilizing oscillation is supplied to said inverting amplifier during a period of time between stabilizing oscillation and terminating oscillation. 
     
     
       29. The oscillation circuit as defined in  claim 28 , further comprising a voltage control circuit for controlling said power supply circuit to output the power voltage having the large absolute value for initiating oscillation when a period of time between turning power on and stabilizing oscillation is detected and for controlling said power supply circuit to output the other power voltage having the small absolute value for stabilizing oscillation when a transition from turning power on to stabilizing oscillation is detected. 
     
     
       30. The oscillation circuit as defined in  claim 29  wherein said voltage control circuit comprises a power-on detecting circuit for detecting a power on of said oscillation circuit and a timer for detecting a transition from turning power on to stabilizing oscillation by measuring time passed since power is turned on and for controlling said power supply circuit to output the power voltage having the large absolute value for initiating oscillation at a time said power is turned on and for controlling said power supply circuit to output the other power voltage having the small absolute value for stabilizing oscillation when said timer detects a transition from turning power on to the stabilizing oscillation. 
     
     
       31. The oscillation circuit as defined in  claim 22  wherein said inverting amplifier comprises a first inverting amplifier for initiating oscillation and a second inverting amplifier for stabilizing oscillation and wherein said first inverting amplifier provides oscillation during a period of time between turning power on and stabilizing oscillation while said second inverting amplifier provides oscillation during a period of time between stabilizing oscillation and terminating oscillation. 
     
     
       32. The oscillation circuit as defined in  claim 31 , further comprising an inverting-amplifier switching circuit for selecting said first inverting amplifier when a period of time between turning power on and stabilizing oscillation is detected and for selecting said second inverting amplifier after a transition from turning power on to stabilizing oscillation. 
     
     
       33. The oscillation circuit as defined in  claim 32  wherein said inverting-amplifier switching circuit comprises a power-on detecting circuit for detecting a power on of said oscillation circuit and a timer for detecting a transition from turning power on to stabilizing oscillation by measuring time passed since power is turned on and wherein said first inverting amplifier is selected when said power is turned on while said second inverting amplifier is selected when said timer detects a transition from turning power on to stabilizing oscillation. 
     
     
       34. The oscillation circuit as defined in  claim 31  wherein an absolute value of a threshold voltage of a semiconductor switching element that constitutes said first inverting amplifier is set to be smaller than an absolute value of a threshold voltage of a semiconductor switching element that constitutes said second inverting amplifier. 
     
     
       35. The oscillation circuit as defined in  claim 22  wherein said oscillation circuit uses a crystal oscillator having a high value of threshold, the value Q being an index representing the degree of easiness in mechanical oscillation. 
     
     
       36. The oscillation circuit as defined in  claim 35  wherein said value Q is equal to or higher than 10,000 and represented by the following
   Q=α/Rxt  
 
       where Rxt is a component of resistance in the crystal oscillator and α is a coefficient. 
     
     
       37. The oscillation circuit as defined in  claim 1  wherein a threshold voltage V T  of each of said first and second semiconductor switching elements that functions as a gate voltage for inverting a conduction type of a silicon crystal surface is represented by the following
   V T =2φ E +[2·ε S ·q N A ·(2φ E )] 1/2 /(ε S /d)  
 
       where ε E  is a Fermi potential, ε S  is εSi (a relative dielectric constant of silicon) multiplied by ε0 (a dielectric constant of vacuum), q is an electron charge, N A  is a concentration of a substrate and d is a thickness of an oxide film. 
     
     
       38. An electronic circuit comprising the oscillation circuit as defined in  claim 1 . 
     
     
       39. A semiconductor device comprising the oscillation circuit as defined in  claim 1 . 
     
     
       40. An electronic equipment comprising the oscillation circuit as defined in  claim 1 . 
     
     
       41. A timepiece comprising the oscillation circuit as defined in  claim 1 . 
     
     
       42. The oscillation circuit as defined in  claim 24 , wherein said first and second semiconductor switching elements are configured by using field- effect transistor elements of differing conductivity types.   
     
     
       43. The oscillation circuit as defined in  claim 24 , further comprising a power supply circuit for outputting at least two types of power voltages V reg   , one having a large absolute value for initiating oscillation and the other having a small absolute value for stabilizing oscillation and wherein the power voltage having said large absolute value for initiating oscillation is supplied to said inverting amplifier during a period of time between turning power on and stabilizing oscillation while the other power voltage having said small absolute value for stabilizing oscillation is supplied to said inverting amplifier during a period of time between stabilizing oscillation and terminating oscillation.   
     
     
       44. The oscillation circuit as defined in  claim 43 , further comprising a voltage control circuit for controlling said power supply circuit to output the power voltage having the large absolute value for initiating oscillation when a period of time between turning power on and stabilizing oscillation is detected and for controlling said power supply circuit to output the other power voltage having the small absolute value for stabilizing oscillation when a transition from turning power on to stabilizing oscillation is detected. 
     
     
       45. The oscillation circuit as defined in  claim 44  wherein said voltage control circuit comprises a power- on detecting circuit for detecting a power on of said oscillation circuit and a timer for detecting a transition from turning power on to stabilizing oscillation by measuring time passed since power is turned on and for controlling said power supply circuit to output the power voltage having the large absolute value for initiating oscillation at a time said power is turned on and for controlling said power supply circuit to output the other power voltage having the small absolute value for stabilizing oscillation when said timer detects a transition from turning power on to the stabilizing oscillation.   
     
     
       46. The oscillation circuit as defined in  claim 24  wherein said inverting amplifier comprises a first inverting amplifier for initiating oscillation and a second inverting amplifier for stabilizing oscillation and wherein said first inverting amplifier provides oscillation during a period of time between turning power on and stabilizing oscillation while said second inverting amplifier provides oscillation during a period of time between stabilizing oscillation and terminating oscillation. 
     
     
       47. The oscillation circuit as defined in  claim 46 , further comprising an inverting- amplifier switching circuit for selecting said first inverting amplifier when a period of time between turning power on and stabilizing oscillation is detected and for selecting said second inverting amplifier after a transition from turning power on to stabilizing oscillation.   
     
     
       48. The oscillation circuit as defined in  claim 47  wherein said inverting- amplifier switching circuit comprises a power - on detecting circuit for detecting a power on of said oscillation circuit and a timer for detecting a transition from turning power on to stabilizing oscillation by measuring time passed since power is turned on and wherein said first inverting amplifier is selected when said power is turned on while said second inverting amplifier is selected when said timer detects a transition from turning power on to stabilizing oscillation.   
     
     
       49. The oscillation circuit as defined in  claim 46  wherein an absolute value of a threshold voltage of a semiconductor switching element that constitutes said first inverting amplifier is set to be smaller than an absolute value of a threshold voltage of a semiconductor switching element that constitutes said second inverting amplifier. 
     
     
       50. The oscillation circuit as defined in  claim 24  wherein said oscillation circuit uses a crystal oscillator having a high value of Q, the value Q being an index representing the degree of easiness in mechanical oscillation.