Performance of an electronic apparatus (for example, computer) has been improved remarkably since a signal inside LSI (Large Scale Integration) and a signal between LSIs can transmit at a high speed. Meanwhile, attenuation of the signal through a transmission path inside the LSI becomes severely large, due to applying a fine rule to LSI. Moreover, since width of a printed wiring pattern of PWB (Printed Wiring Board) and a diameter of a signal wiring cable tend to become small to realize the high speed and high dense LSI, attenuation of the signal through the transmission paths of the PWB and the cable also becomes severely large. The increasing attenuation of the signal causes distortion of a signal waveform. Moreover, making transmission frequency high also causes the severe distortion of the signal waveform.
For this reason, it is very important to develop a technology to compensate for the distortion of the signal waveform. For example, a patent document 1 discloses a technology to receive an attenuated signal. The invention disclosed in the patent document 1 relates to a technology on a signal including a two-level signal and a repetitive signal (referred to as a CRI (clock run in) signal) which is allocated in front of the two-level signal and indicates phase and amplitude of the two-level signal. According to the invention of the patent document 1, after deciding whether the receiving CRI signal is a high-level signal or a low-level signal, a total of duration time of the high-level signal and a total of duration time of the low-level signal are measured respectively, and a reference voltage, which is used for deciding a level of the receiving two-level signal, is adjusted on the basis of a ratio of these duration times.    [Patent document 1] Japanese Patent Application Laid-Open No. 1994-244687