Mixed-Voltage I/O Buffer with Floating-Well Leakage Isolation

The patent introduces a level shifter circuit as an intermediary component between the low-voltage internal circuit and high-voltage external interface. This level shifter converts the high-voltage input signal to a compatible low-voltage level for internal processing, preventing direct exposure of the gate oxide layer to high voltages while maintaining voltage compatibility at the interface.

The buffer is divided into distinct voltage domains: a high-voltage input stage, a level-shifting intermediate stage, and a low-voltage internal stage. Each stage operates at its appropriate voltage level, with isolation mechanisms preventing high-voltage stress from reaching the sensitive gate oxide layers in the low-voltage domain.

The level shifter acts as an intermediary that blocks direct current paths between high and low voltage domains. By converting voltage levels through controlled stages rather than direct connection, it prevents the formation of undesired current leakage paths while maintaining proper voltage level interface.

The buffer incorporates feedback mechanisms that monitor voltage levels and control the switching states of transistors to ensure proper isolation between voltage domains. This feedback control prevents simultaneous conduction paths that would create current leakage.

The circuit is segmented into different voltage domains where only the high-voltage interface stage uses thick oxide layer devices, while the majority of the internal low-voltage circuitry uses standard thin oxide layer devices. This selective application maintains reliability where needed while minimizing manufacturing costs.

Thick oxide layer devices are applied locally only at the high-voltage interface where reliability is critical, rather than throughout the entire circuit. This localized approach provides necessary protection against high-voltage stress while avoiding the increased cost of using thick oxide devices everywhere.