Patent ID: 8633737

Claim:
A two-stage post driver circuit for receiving a core output signal and generating a pad output signal to an output pad, the core output signal being in a range between a first source voltage and a ground voltage, the two-stage post driver circuit comprising: a controlling circuit for receiving the core output signal and the pad output signal, and generating a first pull-up controlling signal and a second pull-up controlling signal according to the core output signal; a pull-up unit comprising a first P-type transistor and a second P-type transistor, wherein the second P-type transistor has a source terminal connected to a second source voltage, and a gate terminal receiving the second pull-up controlling signal, wherein the first P-type transistor has a source terminal connected to a drain terminal of the second P-type transistor, a gate terminal receiving the first pull-up controlling signal, and a drain terminal connected to the output pad; and a pull-down unit connecting said output pad to a ground; wherein during a transient period of switching the pad output signal from the ground voltage to the second source voltage in response to the core output signal, the pad output signal is served as the first pull-up controlling signal by the controlling circuit, wherein during a steady period after the transient period, a constant voltage is served as the first pull-up controlling signal by the controlling circuit.