The sensor interface IC measures or calibrates a target resistance to be used as a gain resistor for a TIA amplifier in the sensor interface IC. One or more excitation currents are generated in response to different specified excitation voltages that are applied to an external calibration resistor having a specified calibration resistance value. Response voltages are measured across the target resistor, respectively in response to the corresponding different one or more excitation currents. The resistance value of the target resistor is determined using a difference between the measured response voltages, a difference between the specified excitation voltages, and the specified calibration resistance value.