An Enhanced Inductance-to-Digital Converter for Single-Element and Differential-Type Inductive Sensors With Automatic Offset Eliminator

A novel inductance-to-digital converter (LDC) that outputs a digital value corresponding to the change in inductance ( \Delta L ) independent of offset inductance ( L_{01} , L_{02} , L_{03} ), mismatch in offset inductance ( L_{01} \neq L_{02} ), and series coil resistance ( R_{C1} , R_{C2} , R_{C3} ) is presented in this work. In most cases, the change in sensor inductance \Delta L due to the measurand will be very small as compared with L_{0} . Thus, the existing architectures that measure the sensor inductance L_{Xi} (=\!\!L_{0i} \pm \Delta L; i=1,2,3 ) leads to underutilization of the output range. The proposed scheme is effective in measuring \Delta L insensitive to L_{0i} for both single-element type inductive sensor (SIS) and differential-type inductive sensor (DIS). For most of the DIS, in practice, it is very difficult to obtain the matched offset inductance L_{01} = L_{02} for the differential pair L_{X1} and L_{X2} . This will introduce a noticeable error in the output for existing DIS readout schemes. Whereas, for the proposed LDC's automatic offset elimination (AOE) mechanism ensure that digital output is made independent of the offset inductance L_{03} (for SIS) and as