A conventional VD circuit includes a bandgap reference,
resistor string and a comparator [3]. If the supply voltage is
larger than a certain setting value, the voltage at the positive
terminal of the comparator is greater than that at the negative
terminal; the output of the circuit becomes logic high, and vice
versa. This conventional VD circuit adopts voltage comparison
technology. To improve the precision and reduce the power
consumption, increasing the size of the resistor is a possible
solution, which causes a larger core area of the chip. Power
consumption of the voltage comparator limits the performance
as well. VD based on current comparison is an alternative
solution.