Simultaneous bidirectional transmission apparatus for transmitting and receiving differential signals

A simultaneous bidirectional transmission apparatus comprising at least one set of input/output devices interconnected by a first and a second transmission line, each of said input/output devices comprising:

• a transmitting circuit having a first and a second output terminal through which differential signals are sent out;
• a resistance circuit comprising a first, a second, a third, a fourth, a fifth and a sixth terminal, the first and the second terminal being connected to the first and the second output terminal of the transmitting circuit, respectively, the third and the fourth terminal being connected to a first and a second transmission line, respectively;
• a passive element circuit that receive signals applied to the fifth and the sixth terminal of the resistance circuit, and forms either a low-pass filter or an equalizing filter together with the resistance circuit;
• and
• a receiving circuit having a noninverting terminal and an inverting terminal connected to the first and the second output terminal, respectively, of the passive element circuit;
• wherein the resistance circuit of each input/output device comprises a first resistor and connected across the first and the third terminal;
• a second resistor connected across the second and the fourth terminal, a third resistor and connected across the first and the sixth terminal, a fourth resistor connected across the second and the fifth terminal, a fifth resistor connected across the third and the fifth terminal, and a sixth resistor connected across the fourth and the sixth terminal;
• said first to sixth resistors respectively having resistances R.sub.1, R.sub.1, R.sub.2, R.sub.2, R.sub.3 and R.sub.3 ;
• and the resistances R.sub.1, R.sub.2 and R.sub.3 approximately meet the following expressions:
• .GAMMA..sub.2 =(2.GAMMA..sub.1 +1).GAMMA..sub.3 +.GAMMA..sub.1 ( 1)
• .GAMMA..sub.3 ={1/2(.GAMMA..sub.1 +1)}{(2.GAMMA..sub.s +.GAMMA..sub.1 -.GAMMA..sub.s .GAMMA..sub.1)/(.GAMMA..sub.s +2.GAMMA..sub.1 -1)-1}(2)
• (1-.GAMMA..sub.s)/2<.GAMMA..sub.1 .ltoreq.1 (3)
• .GAMMA..sub.s =R.sub.s /Z.sub.0, .GAMMA..sub.1 =R.sub.1 /Z.sub.0, .GAMMA..sub.2 =R.sub.2 /Z.sub.0, .GAMMA..sub.3 =R.sub.3 /Z.sub.0 ( 4)
• where Z.sub.0 is the characteristic impedance of the transmission lines, and Rs is the output resistance of the transmitting circuit.