Off-chip driver circuit

Details Off-chip driver circuit Off-chip driver circuit

1995-07-25

1998-03-17

Westin, Edward P.

Electronic digital logic circuitry

Interface

Supply voltage level shifting

326 68, 326 83, H03K 190175, H03K 19094

Patent

active

057291578

ABSTRACT:
An off-chip driver circuit having circuitry for providing protection against high voltages when the off-chip driver circuit is disabled is described. The circuitry for providing protection against high voltages utilizes a minimum number of transistors and therefore minimizes the chip area utilized by the off-chip driver circuit. An off-chip driver circuit has an input terminal and an output terminal. A pull-up transistor has a controllable path connected between a first power supply voltage and the output terminal of the off-chip driver circuit, and a control terminal connected to the input terminal via a pass gate connected to isolate the input terminal from high voltages applied to the output terminal. A control transistor has a controllable path connected between the control terminal of the pull-up transistor and the output terminal, and a control terminal connected to a control potential. An auxiliary pass transistor has a control terminal and a controllable path connected between a reference terminal and the control terminal of the pull-up transistor. An auxiliary control transistor has a control terminal connected to receive the control potential, and a controllable path connected between the output terminal and the control terminal of the auxiliary pass transistor. Auxiliary circuitry holds the control terminal of the auxiliary pass transistor in a state determined by the auxiliary control transistor. The auxiliary circuitry may include an auxiliary pull-down transistor having a controllable path connected between the control terminal of the auxiliary pass transistor and a reference potential, and a control terminal connected to a voltage selected to maintain the auxiliary pull-down transistor on.

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