Patent ID: 6040711
Filing Date: 2000-03-21
Classification: H03K

Abstract:
A CMOS output buffer circuit comprising:a final amplifier stage including a pull-up transistor and a pull-down transistor connected between a voltage supply and ground and having a common output node, the pull-up transistor having a bulk electrode connected to a switchable bulk line;a control circuitry for driving the final amplifier stage including:a first logic gate supplied with an input data signal, the first logic gate driving the pull-up transistor; and a second logic gate supplied with said input data signal, the second logic gate driving the pull-down transistor,wherein a voltage supply terminal of the first logic gate is connected to said switchable bulk line;an auxiliary circuit to selectively couple said switchable bulk line to the voltage supply as long as a voltage of the output node is not higher than said voltage supply and to selectively decouple the switchable bulk line from the voltage supply when the voltage of the output node exceeds the supply voltage; andthe first logic gate including means for transferring the voltage on the output node to said voltage supply terminal, and thus to said switchable bulk line, when the voltage of the output node exceeds the supply voltage,wherein said auxiliary circuit includes switching means which as long as the voltage of the output node is not higher than the supply voltage are activated to connect said switchable bulk line to the supply voltage, and driving means which when the voltage of the output node exceeds the supply voltage deactivates said switching means, andwherein said switching means comprises a first transistor connected between the voltage supply and the switchable bulk line and having a bulk electrode connected to the switchable bulk line, and said driving means comprises a second transistor connected between the output node and a control electrode of the first transistor, and having a control electrode and a bulk electrode respectively connected to the voltage supply and to the switchable bulk line.