Bidirectional digital signal transmission system

A transmission system for transmitting and receiving digital signals on a transmission line from a transmit connection to a termination connection thereof comprising

• an input terminal for receiving digital signals of a first voltage level or of a second voltage level;
• transmit inverter means including a first transmit switching transistor and a first transmit resistance connected in series between a transmit source of operating potential and the transmit connection of the transmission line, and including a second transmit switching transistor, complementary to said first transmit switching transistor, and a second transmit resistance connected in series between said transmit connection and a transmit point of reference potential;
• said first transmit switching transistor and said second transmit switching transistor each having a control electrode connected to said input terminal;
• said first transmit switching transistor being in an open condition and said second transmit switching transistor being in a closed condition when said first voltage level is present at said input terminal;
• said first transmit switching transistor being in a closed condition and said second transmit switching transistor being in an open condition when said second voltage level is present at said input terminal;
• an output terminal connected to the termination connection of the transmission line;
• termination inverter means including a first termination switching transistor and a first termination resistance connected in series between a termination source of operating potential and the termination connection of the transmission line, and including a second termination switching transistor, complementary to said first termination switching transistor, and a second termination resistance connected in series between said termination connection and a termination point of reference potential;
• said first termination switching transistor and said second termination switching transistor each having a control electrode connected in common to an input connection thereto;
• said first termination switching transistor being in an open condition and said second termination switching transistor being in a closed condition when a first input condition is present at said input connection thereto;
• said first termination switching transistor being in a closed condition and said second termination switching transistor being in an open condition when a second input condition is present at said input connection thereto;
• each of said resistances having approximately the same resistive value, and the a.c. impedance of the transmission line between the transmit connection and the termination connection being approximately the same as the impedance of each of said resistances;
• control means coupled to the termination connection of the transmission line and to said input connection to the first and second termination switching transistors;
• said control means being operable to change the input condition at said input connection to the first and second termination switching transistors from the first input condition to the second input condition in response to the potential at the termination connection being in a predetermined range approximately midway between the potential of the transmit source of operating potential and the potential of the termination point of reference potential when the digital signal at the input terminal changes from the first voltage level to the second voltage level changing the first transmit switching transistor from the open condition to the closed condition and changing the second transmit switching transistor from the closed condition to the open condition thereby causing transition current to flow through the first transmit resistance and the transmission line producing a potential within said range at the transmit connection which is propagated along the transmission line to the termination connection;
• and
• said control means being operable to change the input condition at said input connection to the first and second termination switching transistors from the second input condition to the first input condition in response to the potential at the termination connection being within said range when the digital signal at the input terminal changes from the second voltage level to the first voltage level changing the first transmit switching transistor from the closed condition to the open condition and changing the second transmit switching transistor from the open condition to the closed condition thereby causing transition current to flow through the first termination resistance and the transmission line producing a potential within said range at the termination connection.

A bidirectional transmission system for transmitting and receiving digital signals in both directions over a transmission line between a first connection and a second connection thereof comprising

• a first input terminal for receiving digital signals of a first voltage level or of a second voltage level;
• first driver means connected between a first source of operating potential and a first point of reference potential, said first driver means having an input coupled to said first input terminal and an output coupled to said first connection of the transmission line;
• said first driver means being operable to change the potential at said first connection of the transmission line from the potential of the first point of reference potential to the potential of the first source of operating potential when the digital signal at the first input terminal changes from the first voltage level to the second voltage level, and said first driver means being operable to change the potential at said first connection of the transmission line from the potential of the first source of operating potential to the potential of the first point of reference potential when the digital signal at the first input terminal changes from the second voltage level to the first voltage level;
• a first output terminal connected to said first connection of the transmission line;
• a second input terminal for receiving digital signals of the first voltage level or of the second voltage level;
• second driver means connected between a second source of operating potential and a second point of reference potential, said second driver means having an input coupled to said second input terminal and an output coupled to said second connection of the transmission line;
• said second driver means being operable to change the potential at said second connection of the transmission line from the potential of the second point of reference potential to the potential of the second source of operating potential when the digital signal at the second input terminal changes from the first voltage level to the second voltage level, and said second driver means being operable to change the potential at said second connection of the transmission line from the potential of the second source of operating potential to the potential of the second point of reference potential when the digital signal at the second input terminal changes from the second voltage level to the first voltage level;
• a second output terminal connected to said second connection of the transmission line;
• first control means coupled to said first connection of the transmission line and to the input of the first driver means;
• said first control means being operable in response to the potential at the second connection of the transmission line changing from the potential of the second point of reference potential to the potential of the second source of operating potential to change the voltage at the input of the first driver means from the first voltage level to the second voltage level whereby said first driver means produces a potential at the first output terminal equal to the potential of the first source of operating potential;
• and
• said first control means being operable in response to the potential at the second connection of the transmission line changing from the potential of the second source of operating potential to the potential of the second point of reference potential to change the voltage at the input of of the first driver means from the second voltage level to the first voltage level whereby said first driver means produces a potential at the first output terminal equal to the potential of the first point of reference potential;
• second control means coupled to said second connection of the transmission line and to the input of the second driver means;
• said second means being operable in response to the potential at the first connection of the transmission line changing from the potential of the first point of reference potential to the potential of the first source of operating potential to change the voltage at the input of the second driver means from the first voltage level to the second voltage level whereby said second driver means produces a potential at the second output terminal equal to the potential of the second source of operating potential;
• and
• said second control means being operable in response to the potential at the first connection of the transmission line changing from the potential of the first source of operating potential to the potential of the first point of reference potential to change the voltage at the input of the second driver means from the second voltage level to the first voltage level whereby said second driver means produces a potential at the second output terminal equal to the potential of the second point of reference potential;
• first enabling means coupled between said first input terminal and the input of the first driver means and between said first control means and the input of the first driver means;
• second enabling means coupled between said second input terminal and the input of the second driver means and between said second control means and the input of the second driver means;
• said first enabling means being operable during a first enabling condition to connect said first input terminal to the input of the first driver means and to disconnect said first control means from the input of the first driver means;
• said second enabling means being operable during said first enabling condition to disconnect said second input terminal from the input of the second driver means and to connect said second control means to the input of the second driver means;
• said first enabling means being operable during a second enabling condition to disconnect said first input terminal from the input of the first driver means and to connect said first control means to the input of the first driver means;
• and
• said second enabling means being operable during said second enabling condition to connect said second input terminal to the input of the second driver means and to disconnect said second control means from the input of the second driver means;
• whereby during said first enabling condition digital signals are transmitted from said first input terminal to said second output terminal over the transmission line;
• and whereby during said second enabling condition digital signals are transmitted from said second input terminal to said first output terminal over the transmission line.