In this paper a CMOS temperature-to-current converter is presented of which the output current is the difference between a PTC current and an NTC current. The PTC current is derived from a PTAT cell, while the NTC current is derived from a threshold voltage reference source. It is shown that this way of current subtraction diminishes to a certain extent the effects of the thermal dependence of the resistors used.
Kolling, A., Kölling, A., Bak, F., Bergveld, P., Seevinck, E., & Seevinck, E. (1990). Design of a CMOS temperature sensor with current output. Sensors and actuators. A: Physical, 0(A21), 645-649. https://doi.org/10.1016/0924-4247(89)80050-0