Pulse signal output circuit and shift register

摘要

To provide a pulse signal output circuit capable of operating stably and a shift register including the pulse signal output circuit. A pulse signal output circuit includes a plurality of transistors each including an oxide semiconductor. In accordance with operations of the pulse signal output circuit, the threshold voltage of the transistor including an oxide semiconductor is changed. A shift register including the pulse signal output circuit is formed. A pulse signal output circuit capable of operating stably and a shift register including the pulse signal output circuit can be provided.