Patent ID: 7642818

Claim:
An input circuit, comprising: a diode, having an anode coupled to a ground voltage, and a cathode receiving an external input voltage; a resistor, having a first terminal coupled to the cathode; a first transistor, having a gate terminal receiving a first supply voltage, a first terminal coupled to a second terminal of the resistor, and a second terminal outputting an internal input voltage; a buffer, having an input terminal coupled to the second terminal of the first transistor, and an output terminal outputting an output voltage; a bulk voltage generating unit, having a first terminal coupled to the cathode, a second terminal receiving a control voltage, and a third terminal outputting a first bulk voltage when the external input voltage is less than or equal to the first supply voltage and outputting a second bulk voltage when the external input voltage is greater than the first supply voltage; and an enhancing unit, having a first terminal coupled to the second terminal of the resistor, a second terminal coupled to the input terminal of the buffer, a third terminal coupled to the input terminal or the output terminal of the buffer or the second terminal of the resistor, a fourth terminal outputting the control voltage, and a fifth terminal receiving the first bulk voltage or the second bulk voltage, for making the internal input voltage to be the same as the external input voltage when the external input voltage is less than or equal to the first supply voltage, and making the internal input voltage to be kept at a predetermined value which is less than the first supply voltage when the external input voltage is greater than the first supply voltage.