transistors 57 and 56 are preferably manufactured on the same substrate and matched to have similar characteristics they would ordinarily turn on at the same gate to source voltage v gs but the circuit ensures that when the supply voltage is low but still high enough to turn on a transistor the transistor 56 will turn on before the transistor 57 thereby preventing the current from flowing to the patch 4 in the circuit because the source of the transistor 56 is grounded the transistor 56 can turn on as soon as the voltage at the node 62 which is the gate of the transistor 56 rises to the v gs turn on in contrast because the voltage at the source of the transistor 57 is raised above ground by the voltage across the resistor 48 v r48 the transistor 57 can not turn on until the voltage at the node 63 which is the gate of the transistor 57 rises to v gs turn on v r48 because the transistor 57 will not turn on until the voltage at the node 63 is v gs turn on v r48 and the transistor 56 will turn on when the voltage at the node 62 is v gs turn on the transistor 56 will always turn on before the transistor 57 when the supply voltage is.