  In this paper we present a simple and efficient built-in temperature sensor
for thermal monitoring of standard-cell based VLSI circuits. The proposed smart
temperature sensor uses a ring-oscillator composed of complex gates instead of
inverters to optimize their linearity. Simulation results from a 0.18$\mu$m
CMOS technology show that the non-linearity error of the sensor can be reduced
when an adequate set of standard logic gates is selected.
