CAPACITIVE DETECTOR

• US 20090095080A1
• Filed: 09/10/2008
• Published: 04/16/2009
• Est. Priority Date: 10/15/2007
• Status: Abandoned Application

• Current Assignee: Freescale Semiconductor, Inc. (NXP Semiconductors NV)
• Original Assignee: Freescale Semiconductor, Inc. (NXP Semiconductors NV)
• Inventors: SASAKI, Hiroaki, Shikata, Eiji
• Application Number:
  US12/207,513
• Publication Number:
  US 20090095080A1
• Time in Patent Office: Days
• US Class Current: 73/514.32
• CPC Class Codes: G01D 5/24 by varying capacitance
• CPC Class Codes: G01D 5/2417 by varying separation
• CPC Class Codes: G01P 15/125 by capacitive pick-up
• CPC Class Codes: G01P 21/00 Testing or calibrating of apparatus or devices covered by the preceding groups

Abstract

A capacitive detector that accurately detects a physical quantity with a simple circuitry. An acceleration sensor includes a capacitance converter, an amplifier, a detection element unit, and a signal controller. The capacitor converter, which includes an operational amplifier, a switch, and a capacitor, converts a change in differential capacitance, which is obtained by fixed electrodes and a movable electrode, to voltage. The operational amplifier has a non-inversion input terminal, which receives a reference voltage. The signal controller supplies voltage that is applied to the fixed electrodes of the detection element unit. The signal controller includes a bias supply unit, which applies a predetermined bias voltage to the fixed electrodes during a test mode.

Claims

1. A capacitive detector for measuring a physical quantity, the capacitive detector comprising:

a movable electrode that moves in accordance with a change in a physical quantity;

first and second fixed electrodes that face the movable electrode;

a signal controller that applies voltages in a cycle including a first phase and a second phase, with the signal controller applying a first voltage to the first fixed electrode and a second voltage to the second fixed electrode during the first phase and applying the second voltage to the first fixed electrode and the first voltage to the second fixed electrode during the second phase;

a capacitance converter that outputs voltage corresponding to a change in capacitance calculated from a measurement of an amount of change in charge accumulated in the movable electrode from the first phase to the second phase; and

a bias supply unit that supplies a common direct current voltage to the first and second fixed electrodes.

2. The capacitive detector according to claim 1, wherein the second phase is shorter than an inverse of a resonant frequency of the movable electrode.

3. The capacitive detector according to claim 1, wherein the bias supply unit supplies a direct current voltage for correcting a predetermined physical quantity when measuring the physical quantity.

4. The capacitive detector according to claim 1, wherein the bias supply unit supplies a direct current voltage when receiving a test signal.

5. The capacitive detector according to claim 1, wherein the physical quantity is acceleration.