340 and the source of transistor 360 is also coupled to the shunt 370 a more detailed description of these components is given below power is supplied to the asic by a power supply not shown at the supply voltage v dd as discussed above when the power supply begins generating a supply voltage the supply voltage ramps from zero volts to the operating voltage e g v dd of the asic in order to ensure that the internal logic within the asic is properly initialized the asic does not use the supply voltage until the supply voltage exceeds a minimum voltage this minimum voltage is predetermined by the design engineer when designing the asic for example if the operating voltage of the asic is 3 3 volts the design engineer programs the por circuit 300 to operate in a 3 3 volt asic by coupling node 302 to a 34 low 34 voltage v dd i e a voltage representing a logical zero 0 if the operating voltage of the asic is 2 0 volts the design engineer programs the por circuit 300 to operate in a 2 0 volt asic by coupling node 302 to v dd i e a voltage representing a logical one 1 a detailed description of the operation of the por circuit 300 for two asic operating voltages i e 3 3 volts and 2 0 volts is given below as described above fig3 illustrates a por circuit.