Active switching star node and network of stations interconnected by such a star node
View Patent ↗In a network a star node (SN 1 ) interconnects a plurality of stations (ST 1 –ST 3 ). The star node (SN 1 ) has interfaces (I 1 –I 3 ), each having a connection terminal (BP) for connecting a selected one of the stations to the star node (SN 1 ) and each interface receives at a connection terminal (BP) a signal from the station associated with that interface and forwards the received signal to the connection terminal (BP) of the other interfaces. The star node (SN 1 ) further has a common terminal (RT 1 ) and each interface has a receiver (CMP 1 ) coupled to the connection terminal (BP) for receiving the signal from the associated station, a transmitter (TR) coupled to the connection terminal (BP), a first activity detector (A 1 ) for generating a first activity signal (AS 1 ) in response to signal transitions at an input (CIP 1 ) of the receiver (CMP 1 ), a second activity detector (A 2 ) for generating a second activity signal (AS 2 ) in response to signal transitions at the common terminal (RT 1 ), a first switch (SW 1 ) for disabling signal transfer from the receiver (CMP 1 ) to the common terminal (RT 1 ) in response to the second activity signal (AS 2 ), and a second switch (SW 2 ) for disabling signal transfer from the common terminal (RT 1 ) to the transmitter (TR) in response to the first activity signal (AS 1 ). The structure of the interface allows easy expansion of the number of interfaces within the star node (SN 1 ) and a data protocol without a preamble.
1. A star node for interconnecting a plurality of stations in a network, the star node comprising interfaces each having a connection terminal for connecting a selected one of the stations to the star node, each interface having means for accepting at the connection terminal a signal from the station associated with the interface and for forwarding said signal to the connection terminal of the other interfaces, characterized in that the star node comprises a common terminal and in that the interface comprises a receiver having an input coupled to the connection terminal for receiving the signal from the associated station, a transmitter having an output coupled to the connection terminal, a first activity detector for generating a first activity signal in response to signal transitions at the input of the receiver, a second activity detector for generating a second activity signal in response to signal transitions at the common terminal, a first switching means for disabling signal transfer from an output of the receiver to the common terminal in response to the second activity signal, and a second switching means for disabling signal transfer from the common terminal to an input of the transmitter in response to the first activity signal.
2. A star node as claimed in claim 1 , wherein the star node further comprises: a resistor for coupling the common terminal to a first supply voltage terminal, and wherein the first switching means comprises a driver having a driving input for receiving a driving signal for providing a conduction path between the common terminal and a second supply voltage terminal in response to the driving signal, and a first electronic switch responsive to the second activity signal, inserted between the output of the receiver and the driving input of the driver, and wherein the second switching means comprises a second electronic switch responsive to the first activity signal, inserted between the common terminal and the input of the transmitter.
3. A star node as claimed in claim 2 , wherein the first activity detector has an input connected to the driving input of the driver and the second activity detector has an input connected to the input of the transmitter, the first electronic switch being closed in response to a value of the second activity signal which is indicative of no signal transitions at the input of the second activity detector and the second electronic switch being closed in response to a value of the first activity signal which is indicative of no signal transitions at the input of the first activity detector.
4. A star node as claimed in claim 2 , wherein the driver is a transistor having its main current conduction path inserted between the common terminal and the second supply terminal and having its control electrode coupled to the driving input.
5. A star node as claimed in claim 4 , wherein the star node further comprises a further resistor for coupling a further common terminal to the first supply voltage terminal and wherein the interface comprises a further connection terminal and a termination resistor connected between the connection terminal and the further connection terminal, wherein the receiver comprises first and second comparators having corresponding inputs oppositely connected to the connection terminal and the further connection terminal and having respective comparator outputs, the first electronic switch being inserted between one of the comparator outputs and the control electrode of the transistor, wherein the first switching means comprises a further first electronic switch responsive to the second activity signal similarly to the first electronic switch, and a further transistor having its main current conduction path inserted between the further common terminal and the second supply terminal and having a control electrode, the further first electronic switch being inserted between the other one of the comparator outputs and the control electrode of the further transistor, wherein the transmitter has non-inverting and inverting inputs and balanced outputs, the balanced outputs of the transmitter being connected to a respective one of the connection terminal and the further terminal, the second electronic switch being inserted between the common terminal and one of the non-inverting and inverting inputs of the transmitter, wherein the second switching means comprises a further second electronic switch responsive to the first activity signal similarly to the second electronic switch, inserted between the further common terminal and the other one of the non-inverting and inverting inputs of the transmitter, and wherein the first activity detector has an additional input connected to the control electrode of the further transistor and the second activity detector has the input and an additional input connected to respective ones of the non-inverting and inverting inputs of the transmitter.
6. A star node as claimed in claim 2 , wherein the first activity detector has an input connected to the output of the receiver and the second activity detector has an input connected to the common terminals, the first electronic switch being closed in response to a value of the second activity signal which is indicative of no signal transitions at the input of the second activity detector and the second electronic switch being closed in response to a value of the first activity signal which is indicative of no signal transitions at the input of the first activity detector.
7. A star node as claimed in claim 2 , wherein the driver is a transistor having its main current conduction path inserted between the common terminal and the second supply terminal and having its control electrode coupled to the driving input.
8. A star node as claimed in claim 7 , wherein the star node further comprises a further resistor for coupling a further common terminal to the first supply voltage terminal and wherein the interface comprises a further connection terminal and a termination resistor connected between the connection terminal and the further connection terminal, wherein the receiver comprises first and second comparators having corresponding inputs oppositely connected to the connection terminal and the further connection terminal and having respective comparator outputs, the first electronic switch being inserted between one of the comparator outputs and the control electrode of the transistor, wherein the first switching means comprises a further first electronic switch responsive to the second activity signal similarly to the first electronic switch, and a further transistor having its main current conduction path inserted between the further common terminal and the second supply terminal and having a control electrode, the further first electronic switch being inserted between the other of the comparator outputs and the control electrode of the further transistor, wherein the transmitter has non-inverting and inverting inputs and balanced outputs, the balanced outputs of the transmitter being connected to a respective one of the connection terminal and the further terminal, the second electronic switch being inserted between the common terminal and one of the non-inverting and inverting inputs of the transmitter, wherein the second switching means comprises a further second electronic switch responsive to the first activity signal similarly to the second electronic switch, inserted between the further common terminal and the other one of the non-inverting and inverting inputs of the transmitter, and wherein the first activity detector has an additional input connected to the other one of the comparator outputs and the second activity detector has the input and an additional input connected to respective ones of the common terminal and the further common terminal.