Reduction of non-linearity errors in automotive pressure sensors
Methods and apparatus for reduction of non-linearity errors in automotive pressure sensors. A pressure sensor includes a pressure sensing element including a pair of parallel electrodes, a pair of ceramic plates, rigid glass seals and a connection between the pair of parallel electrodes and an integrated circuit (IC). The IC executes a linear mapping function of a 1/C X value after a C X value is captured from the pressure sensing element, C representing a capacitance, the linear mapping function reducing a non-linearity error to enable two point calibration of a relationship between pressure and capacitance.
1. A pressure sensor for determining pressure in an environment comprising:
a pressure sensing element comprising: a pair of opposing ceramic plates spaced apart by a gap; a pair of parallel electrodes mounted on the pair of ceramic plates so that the electrodes oppose each other across the gap; at least one rigid glass seal allowing the pressure sensing element to be effectively coupled to the environment; an integrated circuit (IC); and a connection between the pair of parallel electrodes and the IC,
wherein:
one of the ceramic plates is a flexible diaphragm, configured with respect to the other ceramic plate such that a physical change in the gap is linear with a change in applied pressure to the flexible diaphragm; the electrodes configured such that a capacitance C of the electrodes is inversely proportional to the physical change;
the pressure sensing element generates a signal indicative of pressure in the environment that is linear with the applied pressure; the IC receives the signal; the IC represents the signal as a C x value; the IC executes a linear mapping function of a 1/C x value; and the linear mapping function reduces a non-linearity error resulting from an arrangement of the pressure sensing element by two point calibration of a relationship between pressure and capacitance; and
wherein the linear mapping function comprises:
Out x =1/ M *[(1/ C x )−(1/ C L ]+Out L , where M =[((1/ C H )−(1/ C L ))/(Out H −Out L )] and C ( ) =CDC out *C ref +C zero , wherein:
C x is a CDC output value converted to capacitance;
C L is C x at a low calibration pressure;
Out L is a low calibration output
C H is C x at a high calibration pressure;
Out H is a high calibration output; and
Out x is an output from the transform.
2. A pressure sensor comprising:
a pressure sensing element comprising a ceramic diaphragm plate and a ceramic substrate plate spaced apart by a gap, a pair of parallel electrodes mounted on the ceramic diaphragm plate and the ceramic substrate plate opposing each other across the gap, at least one rigid glass seal, and a connection between the pair of parallel electrodes and an integrated circuit (IC),
wherein:
the ceramic diaphragm plate is a flexible diaphragm configured with respect to the ceramic substrate plate such that a physical change in the gap is linear with a change in applied pressure to the flexible diaphragm; the electrodes configured such that a capacitance C of the electrodes is inversely proportional to the physical change;
the pressure sensing element captures a signal that is linear with applied pressure; the IC receives the signal; the IC represents the signal as a C x value; the IC executes a linear mapping function of a 1/C x value; and the linear mapping function reduces a non-linearity error resulting from an arrangement of the pressure sensing element to enable two point calibration of a relationship between pressure and capacitance; and
the linear mapping function comprises:
Out x =1/ M *[(1/ C x )−(1/ C L ]+Out L , where M =[((1/ C H )−(1/ C L ))/(Out H −Out L )] and C ( ) =CDC out C ref +C zero , wherein:
C x is a CDC output value converted to capacitance;
C L is C x at a low calibration pressure;
Out L is a low calibration output;
C H is C x at a high calibration pressure;
Out H is a high calibration output; and
Out x is an output from the transform.