Capacitance difference detecting circuit and MEMS sensor

A capacitance difference detecting circuit comprising:

• a pair of oscillators having capacitors whose capacitances chance according to an external force and generating first oscillating signals according to the capacitances, respectively;
• a detecting unit detecting a relative difference between the capacitances as a difference between frequencies of the first oscillating signals;
• a frequency comparator comparing the frequencies of the first oscillating signals in magnitude, wherein
• said detecting unit includes a mixer receiving a pair of first oscillating signals and outputting a frequency difference signal with a frequency equal to a difference between frequencies of the received pair of first oscillating signals.

A capacitance difference detecting circuit comprising:

• a pair of oscillators having capacitors whose capacitances chance according to an external force and generating first oscillating signals according to the capacitances, respectively;
• a detecting unit detecting a relative difference between the capacitances as a difference between frequencies of the first oscillating signals;
• and
• a mask control unit that activates a mask signal when the difference between the frequencies of the pair of first oscillating signals is smaller than a preset value, wherein
• said detecting unit includes a mixer receiving a pair of first oscillating signals and outputting a frequency difference signal with a frequency equal to a difference between frequencies of the received pair of first oscillating signals, and
• while receiving the activated mask signal, said mixer outputs the frequency difference signal indicating that the difference between the frequencies of the first oscillating signals is zero.

A capacitance difference detecting circuit comprising:

• a pair of oscillators having capacitors whose capacitances chance according to an external force and generating first oscillating signals according to the capacitances, respectively;
• a detecting unit detecting a relative difference between the capacitances as a difference between frequencies of the first oscillating signals;
• and
• a pair of PLL circuits disposed between said oscillators and said mixer, respectively, receiving the first oscillating signals from said oscillators to generate second oscillating signals having frequencies that are higher than the frequencies of the first oscillating signals, respectively, and outputting the generated second oscillating signals to said mixer as the first oscillating signals, wherein
• said detecting unit includes a mixer receiving a pair of first oscillating signals and outputting a frequency difference signal with a frequency equal to a difference between frequencies of the received pair of first oscillating signals.

A capacitance difference detecting circuit comprising:

• a pair of oscillators having capacitors whose capacitances chance according to an external force and generating first oscillating signals according to the capacitances, respectively;
• a detecting unit detecting a relative difference between the capacitances as a difference between frequencies of the first oscillating signals;
• a PLL circuit having a frequency divider disposed between one of said oscillators and said mixer, receiving one of the first oscillating signals from the one of said oscillators, generating a second oscillating signal with a frequency that is higher than a frequency of the one of said first oscillating signals, and outputting to said mixer the generated second oscillating signal as the one of said first oscillating signals;
• and
• a dividing control unit that changes a frequency division ratio of said frequency divider in order to make a frequency of the second oscillating signal coincide with a frequency of the other one of said first oscillating signals in an initial state in which the external force is not applied, wherein
• said detecting unit includes a mixer receiving a pair of first oscillating signals and outputting a frequency difference signal with a frequency equal to a difference between frequencies of the received pair of first oscillating signals.

A capacitance difference detecting circuit comprising:

• a pair of oscillators having capacitors whose capacitances change according to an external force and generating first oscillating signals according to the capacitances, respectively;
• a pair of PLL circuits having voltage controlled oscillators, and receiving the first oscillating signals from said oscillators to output second oscillating signals from the voltage controlled oscillators, respectively;
• and
• a detecting unit that receives input voltages to be inputted to the voltage controlled oscillators of said PLL circuits, respectively, the input voltages being adjusted according to frequencies of the first oscillating signals and the second oscillating signals, and that detects a difference between the received input voltages as a relative difference between the capacitances.

A MEMS sensor comprising:

• a substrate;
• a pair of first electrodes formed on said substrate;
• a mass body displaceably disposed to face said substrate, oscillating in a direction perpendicular to said substrate, and displaced by an angular speed or acceleration applied in a direction perpendicular to the direction of the oscillation;
• second electrodes formed on said mass body at positions to face said first electrodes, respectively;
• a pair of oscillators having a pair of capacitors each formed of the first electrode and the second electrode facing to each other, and generating the first oscillating signals according to capacitances of the capacitors, respectively;
• a detecting unit that detects a relative difference between the capacitances as a change in frequencies of the first oscillating signals;
• and
• a main control unit that calculates the angular speed or acceleration applied in a horizontal direction of said substrate according to the chance in the frequencies detected by said detecting unit;
• and
• a mask control unit that activates a mask signal when the difference between the frequencies of the pair of first oscillating signals is smaller than a preset value, wherein
• said detecting unit includes a mixer receiving a pair of first oscillating signals and outputting a frequency difference signal with a frequency equal to a difference between frequencies of the received pair of first oscillating signals, and a frequency/voltage converting unit that converts the frequency of the frequency differences signal to a detection voltage indicating the relative difference between the capacitances and
• while receiving the activated mask signal, said frequency/voltage converting unit outputs the detection voltage indicating that the difference between the capacitances is zero.

A MEMS sensor comprising:

• a substrate;
• a pair of first electrodes formed on said substrate;
• a mass body displaceably disposed to face said substrate, oscillating in a direction perpendicular to said substrate, and displaced by an angular speed or acceleration applied in a direction perpendicular to the direction of the oscillation;
• second electrodes formed on said mass body at positions to face said first electrodes, respectively;
• a pair of oscillators having a pair of capacitors each formed of the first electrode and the second electrode facing to each other, and generating the first oscillating signals according to capacitances of the capacitors, respectively;
• a detecting unit that detects a relative difference between the capacitances as a change in frequencies of the first oscillating signals;
• a main control unit that calculates the angular speed or acceleration applied in a horizontal direction of said substrate according to the change in the frequencies detected by said detecting unit;
• and
• a frequency comparator comparing the frequencies of the first oscillating signals in magnitude, wherein
• said detecting unit includes a mixer receiving a pair of first oscillating signals and outputting a frequency difference signal with a frequency equal to a difference between frequencies of the received pair of first oscillating signals.

A MEMS sensor comprising:

• a substrate;
• a pair of first electrodes formed on said substrate;
• a mass body displaceably disposed to face said substrate, oscillating in a direction perpendicular to said substrate, and displaced by an angular speed or acceleration applied in a direction perpendicular to the direction of the oscillation;
• second electrodes formed on said mass body at positions to face said first electrodes, respectively;
• a pair of oscillators having a pair of capacitors each formed of the first electrode and the second electrode facing to each other, and generating the first oscillating signals according to capacitances of the capacitors, respectively;
• a detecting unit that detects a relative difference between the capacitances as a change in frequencies of the first oscillating signals;
• a main control unit that calculates the angular speed or acceleration applied in a horizontal direction of said substrate according to the change in the frequencies detected by said detecting unit;
• and
• a mask control unit that activates a mask signal when the difference between the frequencies of the pair of first oscillating signals is smaller than a preset value, wherein
• said detecting unit includes a mixer receiving a pair of first oscillating signals and outputting a frequency difference signal with a frequency equal to a difference between frequencies of the received pair of first oscillating signals, and
• while receiving the activated mask signal, said mixer outputs the frequency difference signal indicating that the difference between the frequencies of the first oscillating signals is zero.

A MEMS sensor comprising:

• a substrate;
• a pair of first electrodes formed on said substrate;
• a mass body displaceably disposed to face said substrate, oscillating in a direction perpendicular to said substrate, and displaced by an angular speed or acceleration applied in a direction perpendicular to the direction of the oscillation;
• second electrodes formed on said mass body at positions to face said first electrodes, respectively;
• a pair of oscillators having a pair of capacitors each formed of the first electrode and the second electrode facing to each other, and generating the first oscillating signals according to capacitances of the capacitors, respectively;
• a detecting unit that detects a relative difference between the capacitances as a change in frequencies of the first oscillating signals;
• a main control unit that calculates the angular speed or acceleration applied in a horizontal direction of said substrate according to the chance in the frequencies detected by said detecting unit;
• and
• a pair of PLL circuits disposed between said oscillators and said mixer, respectively, receiving the first oscillating signals from said oscillators to generate second oscillating signals having frequencies that are higher than the frequencies of the first oscillating signals, respectively, and outputting the generated second oscillating signals to said mixer as the first oscillating signals, wherein
• said detecting unit includes a mixer receiving a pair of first oscillating signals and outputting a frequency difference signal with a frequency equal to a difference between frequencies of the received pair of first oscillating signals.

A MEMS sensor comprising:

• a substrate;
• a pair of first electrodes formed on said substrate;
• a mass body displaceably disposed to face said substrate, oscillating in a direction perpendicular to said substrate, and displaced by an angular speed or acceleration applied in a direction perpendicular to the direction of the oscillation;
• second electrodes formed on said mass body at positions to face said first electrodes, respectively;
• a pair of oscillators having a pair of capacitors each formed of the first electrode and the second electrode facing to each other, and generating the first oscillating signals according to capacitances of the capacitors, respectively;
• a detecting unit that detects a relative difference between the capacitances as a chance in frequencies of the first oscillating signals;
• and
• a main control unit that calculates the angular speed or acceleration applied in a horizontal direction of said substrate according to the chance in the frequencies detected by said detecting unit;
• and
• a PLL circuit having a frequency divider disposed between one of said oscillators and said mixer, receiving one of the first oscillating signals from the one of said oscillators, generating a second oscillating signal with a frequency that is higher than a frequency of the one of said first oscillating signals, and outputting to said mixer the generated second oscillating signal as the one of said first oscillating signals;
• and
• a dividing control unit that changes a frequency division ratio of said frequency divider in order to make a frequency of the second oscillating signal coincide with a frequency of the other one of said first oscillating signals in an initial state in which the external force is not applied, wherein
• said detecting unit includes a mixer receiving a pair of first oscillating signals and outputting a frequency difference signal with a frequency equal to a difference between frequencies of the received pair of first oscillating signals.

A MEMS sensor comprising:

• a substrate;
• a pair of first electrodes formed on said substrate;
• a mass body displaceably disposed to face said substrate, oscillating in a direction perpendicular to said substrate, and displaced by an angular speed or acceleration applied in a direction perpendicular to the direction of the oscillation;
• second electrodes formed on said mass body at positions to face said first electrodes, respectively;
• a pair of oscillators having a pair of capacitors each formed of the first electrode and the second electrode facing to each other, and generating the first oscillating signals according to capacitances of the capacitors, respectively;
• a pair of PLL circuits having voltage controlled oscillators, and receiving the first oscillating signals from said oscillators to output second oscillating signals from the voltage controlled oscillators, respectively;
• and
• a detecting unit that receives input voltages to be inputted to the voltage controlled oscillators of said PLL circuits, respectively, the input voltages being adjusted according to frequencies of the first oscillating signals and the second oscillating signals, and that detects a difference between the received input voltages as a relative difference between the capacitances;
• and
• a main control unit that calculates the angular speed or acceleration applied in a horizontal direction of said substrate according to the change in the frequencies detected by said detecting unit.