To use a different trigger point for the negative and positive
I − T dependence regions, the temperature dependence can be
determined using the system in Fig. 1. The system compares
the outputs of a delay-tracking temperature sensor operating
at the same voltage as the circuit being monitored VOP and
a reference temperature sensor at a voltage VREF that will
maintain the sign of its I − T slope despite process or voltage
variations [16]. VREF is a static voltage and may be generated
externally or by an internal level shifter or dc–dc converter. If
temperature changes cause the two sensor outputs to change
in the same direction, the dependence at VOP matches the
known dependence at VREF; if the readings change in opposite
directions, the dependence is the opposite of that at VREF