Offset error compensation systems and methods in sensors

Abstract

Embodiments relate to reducing offset error in sensor systems. In embodiments, the sensitivity and offset of a sensor depend differently on some parameter, e.g. voltage, such that operating the sensor at two different values of the parameter can cancel the offset error. Embodiments can have applicability to stress sensors, Hall plates, vertical Hall devices, magnetoresistive sensors and others.

What is claimed is: 
     
         1 . A sensor configured to sense a physical characteristic comprising:
 at least one sensor element having an output, wherein an output signal comprises an offset error in an absence of the physical characteristic;   an input quantity other than the physical characteristic that affects the offset error, wherein in a first phase of operation of the sensor a first input quantity produces a first output signal having a first offset error, and wherein in a second phase of operation of the sensor a second input quantity different from the first input quantity produces a second output signal having a second offset error; and   offset correction circuitry coupled to the output and configured to provide a sensor output signal comprising a sum of the first output signal and a product of the second output signal and a correction factor chosen to offset a difference between the first offset error and the second offset error.   
     
     
         2 . The sensor of  claim 1 , wherein the input quantity is selected from the group consisting of a voltage, a current or a bias magnetic field. 
     
     
         3 . The sensor of  claim 1 , wherein the at least one sensor is selected from the group consisting of a Hall-effect sensor, a vertical Hall sensor, a spinning current vertical Hall sensor, a magnetoresistive sensor, and a stress sensor. 
     
     
         4 . The sensor of  claim 1 , wherein the at least one sensor element comprises a plurality of sensor elements coupled in a sensor bridge. 
     
     
         5 . The sensor of  claim 1 , wherein the offset correction circuitry comprises a shift register coupled to the output, and wherein the first and second output signals are stored by the shift register. 
     
     
         6 . The sensor of  claim 1 , wherein the correction factor comprises −1*(the first offset error)/(the second offset error). 
     
     
         7 . A method comprising:
 operating a sensor in a first operating phase having a first sensor input quantity to obtain a first sensor output signal and a first sensor offset error;   operating the sensor in a second operating phase having a second sensor input quantity to obtain a second sensor output signal and a second sensor offset error; and   providing a total sensor output signal comprising the sum of the first and second sensor output signals adjusted by a offset correction factor related to the first and second sensor offset errors.   
     
     
         8 . The method of  claim 7 , further comprising determining the offset correction factor by dividing the first sensor offset error by the second sensor offset error and multiplying the result by −1. 
     
     
         9 . The method of  claim 7 , wherein providing a total output signal further comprises summing the first sensor output signal with a product of the offset correction factor and the second sensor output signal. 
     
     
         10 . The method of  claim 7 , wherein the offset correction factor is chosen to cancel an offset error of the sensor. 
     
     
         11 . The method of  claim 7 , wherein the first and second sensor input quantities are selected from the group consisting of a voltage, a current and a magnetic field. 
     
     
         12 . The method of  claim 7 , wherein the sensor has an offset error in the absence of a physical quantity to be sensed by the sensor. 
     
     
         13 . The method of  claim 12 , wherein the physical quantity comprises a magnetic field, a voltage, a current, or a temperature. 
     
     
         14 . A sensor comprising:
 at least one sensor element configured to sense a characteristic and having an input and an output; and   offset compensation circuitry coupled to the output and configured to cancel an offset error of the sensor by correcting an output signal of the at least one sensor by a correction factor related to an offset error of the sensor when operated in a first phase and an offset error of the sensor when operated in a second phase.   
     
     
         15 . The sensor of  claim 14 , wherein a signal at the input of the at least one sensor element is different in the first phase and the second phase. 
     
     
         16 . The sensor of  claim 15 , wherein a signal at the output of the at least one sensor element is different in the first phase and the second phase. 
     
     
         17 . The sensor of  claim 14 , wherein the correction factor comprises a result of dividing the offset error in the first phase by the offset error in the second phase and multiplying by −1. 
     
     
         18 . The sensor of  claim 14 , wherein the sensor comprises a magnetic field sensor, a stress sensor, or a current sensor. 
     
     
         19 . The sensor of  claim 14 , wherein a total output of the sensor comprises the sum of outputs of the sensor in the first and second phases adjusted by the correction factor. 
     
     
         20 . The sensor of  claim 19 , wherein the total output of the sensor comprises the sum of the output of the sensor in the first phase and a product of the output of the sensor in the second phase and the correction factor.