Patent ID: 8817671

Claim:
A full duplex transmission circuit comprising: a first internal input terminal receiving a signal to be transmitted; a second internal input terminal receiving a signal having an amplitude equal to ½ times an amplitude of the signal to be transmitted and having a same phase as a phase of the signal to be transmitted; an external input/output terminal connected to a transmission line having a characteristic impedance Z; an internal output terminal being output a received signal from the external input/output terminal; a first metal oxide semiconductor transistor having a source thereof connected to a current source and the external input/output terminal, a gate thereof connected to the first internal input terminal, and a drain thereof connected to a source of a second metal oxide semiconductor transistor and the internal output terminal, wherein the received signal is amplified by the first metal oxide semiconductor transistor and output from the drain of the first metal oxide semiconductor transistor to the internal output terminal; and the second metal oxide semiconductor transistor having a source thereof connected to the drain of the first metal oxide semiconductor transistor and the internal output terminal, and a gate thereof connected to the second internal input terminal, wherein a current generated by the current source and sizes of the first and second metal oxide semiconductor transistors are set so that transconductances of the first and second metal oxide semiconductor transistors become equal to 1/Z.