Patent ID: 8654485

Claim:
An interface circuit comprising: first and second input terminals; a line voltage protection circuit coupled to the first and second input terminals, the protection circuit effective to provide an input DC voltage across the first and second input terminals within a predetermined range, and further effective to prevent the application of an input line voltage across the first and second input terminals; a first current source circuit coupled to the protection circuit, the first current source circuit effective as a fixed current source and further to generate a fixed voltage offset with respect to the input voltage; an isolation circuit coupled to the first current source circuit; a second current source circuit coupled to the isolation circuit, the second current source circuit effective to cancel out the fixed voltage offset generated by the first current source circuit, the first and second current source circuits collectively effective to provide a linear output DC voltage with respect to the input DC voltage, at least one of the first and second current source circuit comprising a low temperature coefficient circuit wherein the linear conversion of the input DC voltage to the output DC voltage is independent of the temperature throughout a predetermined operating range.