Patent ID: 8107555

Claim:
A pre-emphasis automatic adjusting system for adjusting specified emphasis to be placed on a transmitting signal fed to a receiving device from a transmitting device based on a pre-emphasis adjusting signal transmitted via a signal transmission path and then returned back to the transmitting device by being reflected by the receiving device, the transmitting device comprising: a detecting unit which detects a degree of attenuation of said pre-emphasis adjusting signal returned back from said receiving device occurring in a mismatched portion of said signal transmission path; and an adjusting unit which adjusts the emphasis to be placed on said transmitting signal based on the degree of attenuation detected by said detecting unit, wherein said detecting unit comprises a reference voltage source which outputs a reference voltage to be set in advance and a comparison circuit connected to a connecting point between said transmitting device and said signal transmission path and to said reference voltage source to compare said reference voltage with said pre-emphasis adjusting signal inputted from said connecting point, wherein said reference voltage source comprises a first reference voltage source which outputs a first reference voltage to be set in advance, a second reference voltage source which outputs a second reference voltage to be set in advance being different from said first reference voltage, and wherein said comparison circuit comprises a first comparison circuit which compares said first reference voltage with said pre-emphasis adjusting signal inputted from said connecting point, and a second comparison circuit which compares said second reference voltage with said pre-emphasis adjusting signal to be input from said connecting point.