Continuous selftest for inertial sensors at 0 hz

Abstract

A sensor with continuous self test ( 101 ). An exemplary inertial sensor ( 106 ) may include one or more self test electrodes ( 208, 210 ) so that one or more test signals ( 402, 404 ) may be applied to the electrodes ( 208, 210 ) during normal operation of the sensor. Normal sensor output may be read and stored ( 316 ) during normal operation, when self test signals are typically not applied to the sensor. The normal sensor output provides a baseline for comparison to a sensor offset error detection signal ( 408 ) produced when a test signal may be applied to one self test electrode, and also to a sense error detection signal ( 406 ) produced when a test signal may be applied to both self test electrodes ( 208, 210 ).

1 . A system comprising:
 a sensing element having a continuous self test capability; and   a processing device directing continuous self test, coupled to the sensing element for providing the continuous self test of the system being performed during normal operation of the system, when g-forces are not present.   
     
     
         2 . The system of  claim 1  in which normal operation of the sensor is disabled when self test is actuated. 
     
     
         3 . The system of  claim 1 , in which continuous self test occurs in at least one time period of a plurality of time periods during normal operation of the sensor. 
     
     
         4 . The system of  claim 1 , in which the sensing element is an inertial sensor. 
     
     
         5 . The system of  claim 1 , in which the sensing element is a MEMS device having a movable electrode disposed between a pair of fixed electrodes. 
     
     
         6 . The system of  claim 1 , in which the processing device is a dedicated processor. 
     
     
         7 . The system of  claim 1 , in which the processing device is an ASIC. 
     
     
         8 . The system of  claim 7 , in which the processing device includes an interface circuit to format an output of the processing device for presentation to a data interface. 
     
     
         9 . The system of  claim 1 , in which the processing device further includes an offset error generation circuit, coupled to the sensing element, to generate an offset error test voltage. 
     
     
         10 . The system of  claim 9 , in which the processing device further comprises a sense error generation circuit coupled to the sensing element to generate a sense error test voltage. 
     
     
         11 . An inertial sensor circuit comprising:
 a sensing element having a movable electrode disposed between a first electrode and a second electrode of a pair of fixed electrodes providing a continuous self test capability; and   a processing device controlling continuous self test, coupled to the sensing element for directing and providing stimuli for the continuous self test of the system performed at any time while the inertial sensor circuit is operated under normal conditions and, when g-forces are not present.   
     
     
         12 . The inertial sensor circuit of  claim 11  in which an offset error test signal is coupled to the first electrode to create an offset change output from the sensing element. 
     
     
         13 . The inertial sensor circuit of  claim 12  in a sensor error test signal is coupled to the second electrode to create a gain change output from the sensing element. 
     
     
         14 . The inertial sensor circuit of  claim 13  in which the processing device includes a register array for comparing a previously recorded reference signal to the offset change output. 
     
     
         15 . The inertial sensor circuit of  claim 13  in which the processing device includes a register array for comparing a previously recorded reference signal to the gain change output. 
     
     
         16 . A method of providing continuous self test of an inertial sensor comprising:
 operating the sensor in a normal operating mode;   inhibiting the normal operating mode; and   operating the sensor in a continuous self test mode at any time during operation of the sensor.   
     
     
         17 . The method of providing continuous self test of a sensor of  claim 16 , in which operating the sensor in continuous self test mode includes creating a reference. 
     
     
         18 . The method of providing continuous self test of a sensor of  claim 16 , in which the continuous self test mode includes operating the sensor in an offset error detection mode. 
     
     
         19 . The method of providing continuous self test of a sensor of  claim 16 , in which the continuous self test mode includes operating the sensor in a sense error detection mode. 
     
     
         20 . The method of providing continuous self test of a sensor of  claim 16 , further comprising comparing an output from the sensor operating during the offset error detection mode and an output from the sensor operating in the sense error detection mode to a reference signal output from the sensor operating in the normal operating mode.