Digital Equipment Corporation

Compaq Computer Corporation, Inc.

David Benjamin Krakauer

Hamid Partovi

Kaizad R Mistry

Steven W Butler

William A McGee

An electrostatic discharge protection device for protecting a mixed voltage integrated circuit against damage is provided which includes at least on pair of NMOS transistors connected in a cascode configuration. Each NMOS transistor pair includes a first transistor, having a drain region coupled to and I/O stage of the mixed voltage integrated circuit, and a gate region coupled to the mixed voltage integrated circuit's low power supply. The second NMOS transistor of the pair is merged into the same active area as the first transistor and has a gate region and a source region coupled to the ground plane of the mixed voltage integrated circuit. The source region of the first transistor and the drain region of the second transistor are constructed of a shared NMOS diffusion region. This shared diffusion region is also the common node electrically coupling the first transistor's source to the second transistor's drain region, and is a further benefit of the invention because its length controls the trigger voltage and holding voltage of the cascode transistor pair. This electrostatic discharge protection device can be used either as a self protection pull-down portion of a mixed voltage I/O stage, or in a further aspect of the present invention, as a separate electrostatic discharge clamp.

ESD protection clamp for mixed voltage I/O stages using NMOS transistors

A circuit which protects an integrated circuit (IC) device from damage due to electrostatic discharge (ESD). The protection circuit includes an N-channel metal oxide semiconductor field effect transistor (MOSFET) clamping device and a gate modulation circuit. The source and drain of the MOSFET clamp are connected between an input/output (I/O) pad of the IC and a ground reference voltage. During normal operation of the IC, the gate modulation circuit disables the MOSFET clamp by connecting its gate terminal to a ground reference voltage. This permits signal voltages to pass between the I/O pad and any operating circuits connected to the pad. During an ESD event, the gate modulation circuit connects the gate to the I/O pad, which enables the MOSFET clamp, causing any ESD voltages and resulting currents to be shunted through the MOSFET clamp to ground. As a result, the ESD clamp reaches its clamped-to snapback voltage via an increase in MOSFET channel current, and not via junction breakdown. This insures that the ESD clamp reaches its snapback voltage before the onset of junction breakdown in the operating circuits. The circuit is especially useful in integrated circuits where the gate oxide of a standard ESD clamp transistor is too thin to protect the operating logic from I/O signal voltages that are greater than the supply voltage used for the operating logic circuits.

Electro-static discharge protection device having a modulated control

An electrostatic discharge protection device for protecting a mixed voltage integrated circuit against damage is provided which includes at least one pair of NMOS transistors connected in a cascode configuration. Each NMOS transistor pair includes a first transistor, having a drain region coupled to an I/O stage of the mixed voltage integrated circuit, and a gate region coupled to the mixed voltage integrated circuit's low power supply. The protection device also includes a second NMOS transistor, merged into the same active area as the first transistor, having a gate region and source region coupled to the ground plane of the mixed voltage integrated circuit. The drain region of the second transistor and the source region of the first transistor is constructed by a shared NMOS diffusion region. This shared diffusion region also constructs the common node coupling the source region of the first transistor to the drain region of the second. The shared diffusion area is a further benefit of the invention because its length controls the trigger voltage and the holding voltage of each cascode configured transistor pair. This electrostatic discharge protection device can be used either as a self protecting pull-down portion of a mixed voltage I/O stage or, in a further aspect of the present invention, as a separate electrostatic discharge clamp.

An ESD protection device is provided which includes a self referencing modulation circuit for controlling its operation. The modulation circuit includes a diode stack coupled to a resistor and further coupled to an inverter powered by the signal pad voltage in one embodiment, or an odd plurality of series connected inverters powered by the signal pad voltage in an alternate embodiment. The inverter chain is coupled to the ESD clamp. The modulation circuit requires no reference supply voltage to operate. The ESD protection circuit shunts currents associated with ESD events away from ICs as well as clamping I/O pad voltages to acceptable levels during an ESD event.

Growing community of inventors

Cambridge, MA, United States of America

David Benjamin Krakauer