High speed voltage level shifter with a low input voltage

摘要

An input terminal of a voltage level shifter controls gates of thin oxide N-type MOS transistors with a relatively low threshold voltage. Consequently, the thin oxide N-type MOS transistor is still sufficiently turned on even when the input voltage is very low such that the voltage level shifter according to the present invention operates at high speed without distortion of the waveform of an output voltage. In order to protect the thin oxide N-type transistors, thick oxide N-type MOS transistors with gates controlled by a reference voltage level and thin oxide N-type MOS transistors with gates controlled by a relatively low voltage level are connected in series to drains of the thin oxide N-type MOS transistors to be protected. The reference voltage level is larger than the threshold voltage of the thick oxide N-type MOS transistor and equal to or smaller than a sum of twice of the relatively low voltage level and the threshold voltage of the thick oxide N-type MOS transistor.