A current source circuit comprising: a first variable resistor circuit, wherein the first variable resistor circuit includes a resistive material and a first plurality of tap inputs (TSN 1, TSN m) configured to set a resistance of the first variable resistor circuit; an output configured to provide a current, wherein the current is adjusted by varying the resistance of the first variable resistor circuit; a second variable resistor circuit, wherein: the second variable resistor circuit includes a resistive material of a same resistive material type as the resistive material of the first variable resistor circuit, the second variable resistor circuit includes a second plurality of tap inputs configured to set a resistance of the second variable resistor circuit, wherein each tap resistance of the second variable resistor circuit is proportional to a corresponding tap resistance of the first variable resistor circuit, and a first terminal of the second variable resistor circuit is coupled to a first test port and a second terminal of the second variable resistor circuit is coupled to a second test port to allow for a resistance measurement of the second variable resistor circuit during a test mode; and a non-volatile storage circuit configured to store a tap value generated during the test mode corresponding to a set of select signal values for the second plurality of tap inputs which provides a desired resistance of the second variable resistor circuit as determined during the test mode and to provide a set of select signal values for the first plurality of tap inputs based on the tap value stored in the non-volatile storage circuit; wherein the current source circuit is a transconductance current source. a first variable resistor circuit, wherein the first variable resistor circuit includes a resistive material and a first plurality of tap inputs (TSN 1, TSN m) configured to set a resistance of the first variable resistor circuit; an output configured to provide a current, wherein the current is adjusted by varying the resistance of the first variable resistor circuit; a second variable resistor circuit, wherein: the second variable resistor circuit includes a resistive material of a same resistive material type as the resistive material of the first variable resistor circuit, the second variable resistor circuit includes a second plurality of tap inputs configured to set a resistance of the second variable resistor circuit, wherein each tap resistance of the second variable resistor circuit is proportional to a corresponding tap resistance of the first variable resistor circuit, and a first terminal of the second variable resistor circuit is coupled to a first test port and a second terminal of the second variable resistor circuit is coupled to a second test port to allow for a resistance measurement of the second variable resistor circuit during a test mode; and the second variable resistor circuit includes a resistive material of a same resistive material type as the resistive material of the first variable resistor circuit, the second variable resistor circuit includes a second plurality of tap inputs configured to set a resistance of the second variable resistor circuit, wherein each tap resistance of the second variable resistor circuit is proportional to a corresponding tap resistance of the first variable resistor circuit, and a first terminal of the second variable resistor circuit is coupled to a first test port and a second terminal of the second variable resistor circuit is coupled to a second test port to allow for a resistance measurement of the second variable resistor circuit during a test mode; and a non-volatile storage circuit configured to store a tap value generated during the test mode corresponding to a set of select signal values for the second plurality of tap inputs which provides a desired resistance of the second variable resistor circuit as determined during the test mode and to provide a set of select signal values for the first plurality of tap inputs based on the tap value stored in the non-volatile storage circuit; wherein the current source circuit is a transconductance current source.