To solve a problem that a digital signal detection circuit at a receiver side is made complicated in the case that a transmission side apparatus connected to a network system outputs a biphase modulation digital signal.
An interface apparatus 4 interposed between the transmission side apparatus and a communication path 6 converts transmission data S subjected to the biphase modulation into a transmission signal subjected to amplitude shift modulation and transmits the transmission signal to the communication path 6. An amplitude system conversion circuit 12 of the interface apparatus 4 converts the transmission data S into a digital signal subjected to NRZ modulation, and an amplitude modulation circuit 14 modulates the amplitude of carriers in response to the NRZ signal to produce the transmission signal. A detection circuit 22 of the interface apparatus 4 at a receiver side detects the transmission signal to extract the NRZ-modulated digital signal. A modulation system inverse conversion circuit 24 converts the NRZ signal into a biphase signal and provides an output of the biphase signal to a receiver side apparatus.
SUZUKI HIROHISA