Effective signal detection circuit device of serial transmission apparatus using bi-phase code

An effective signal detection circuit device included in a receiver circuit device of a serial transmission apparatus that transmits data using bi-phase codes consisted of two half bits, the effective signal detection circuit device comprising:

• a shift register for converting every half bit of the bi-phase codes to a parallel signal by using a clock signal having a frequency obtained by multiplying a bit frequency of the bi-phase codes by an even number;
• and
• a determining circuit for receiving parallel signals corresponding to at least three consecutive half bits that are output from the shift register and determining existence or non-existence of an effective transmitted signal;
• wherein the determining circuit comprises:
• a first determining part for detecting one of the parallel signals corresponding to at least three consecutive half bits, the one of the parallel signals having a signal level different from the signal level of the other parallel signals, to thereby determine existence of an effective transmitted signal;
• a second determining part for detecting the parallel signals corresponding to at least three consecutive half bits, the parallel signals having a same signal level, to thereby determine non-existence of an effective transmitted signal;
• and
• a flip flop circuit having a reset terminal and a set terminal, the flip flop circuit being set by the output signal of the first determining part input to the set terminal thereof, the flip flop circuit being reset by the output signal of the second determining part input to the reset terminal thereof, and the flip flop circuit outputting an output signal as an output signal of the determining circuit.