Lattice Semiconductor Corporation

Ravi Lall

Keith Truong

Brad Sharpe-Geisler

John Schadt

William B Andrews

Giap H Tran

In one embodiment, an integrated circuit includes multiple I/O banks, each bank having multiple I/O-ESD tiles, each tile having one or more I/O circuits and electrostatic discharge (ESD) protection circuitry for the one or more I/O circuits in the tile. The ESD circuitry for one tile includes at least one RC-triggered clamp, whose resistance is provided by a resistor shared by one or more other RC-triggered clamps in one or more other tiles of the same bank and whose capacitance is provided by a combination of distributed capacitors, one for each of those two or more RC-triggered clamps. Each tile may have multiple instances of such RC-triggered clamps providing ESD protection for different (e.g., power supply and/or bus) nodes. The shared resistors are variable to allow different instances of the same ESD circuitry design to be implemented with the same time constant for different banks having different numbers of tiles.

ESD protection using shared RC trigger

In one embodiment, an integrated circuit has hot-socket circuitry to protect I/O drivers during hot-socket events. The hot-socket circuitry has (i) N-well-to-pad switcher circuitry that ties driver PMOS N-wells to pads when the pad voltages are greater than the power-supply voltage and (ii) N-well-to-power-supply switcher circuitry that ties the driver PMOS N-wells to the power supply when the pad voltages are less than the power-supply voltage. The hot-socket circuitry also has a special PMOS device connected between the pad and a gate of at least one other PMOS device in the N-well-to-power-supply switcher circuitry to turn off the N-well-to-power-supply switcher circuitry quickly whenever the pad voltage is greater than the power-supply voltage. Applying a reduced power-supply voltage level to the gate of the special PMOS device enables the hot-socket circuitry to be implemented without having to use low Vt devices and without having to implement substantially large drive strengths.

Hot-socket circuitry

In one embodiment of the invention, a programmable device, such as an FPGA, has a programmable input buffer with a VCCIO-powered buffer stage for high-voltage signaling and a VCC-powered buffer stage for low-voltage signaling. In addition to a main driver section, the VCCIO-powered buffer stage has a mixed-mode section for handling multiple different over-drive and multiple different under-drive conditions, a hysteresis section for providing multiple different trip-point hysteresis modes of operation, and a level-shifting section with look-ahead circuitry that enables the main driver section to be implemented with low-power, high-threshold devices, while still enabling the VCCIO-powered buffer stage to operate with low skew and high speed.

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Portland, OR, United States of America

Ravi Lall