US 4,178,504 AGranted

Balanced termination for a transmission line

AssigneePhillips Petroleum Company

InventorRobert L. Farmer

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Abstract

Balancing of a "transmit" line and a "receive" line, which make up a half-duplex serial transmission line, is accomplished, where a first optical isolator is utilized to drive an electrical current signal over the "transmit" line and a second optical isolator is utilized to receive electrical current signals from the "receive" line, by adding a third optical isolator to the circuit. The third optical isolator is in an on condition when the first optical isolator is in an on condition and is in an off condition when the first optical isolator is in an off condition. The third optical isolator is used to make the "receive" and "transmit" lines both see a "signal ground", at the ends thereof connected to the first and second optical isolators, when current is flowing in the "transmit" line. The third optical isolator is used to make the "receive" and "transmit" lines both see the same resistive element, at the ends thereof connected to the first and second optical isolators, when no current is flowing in the "transmit" line. In this manner, a balanced transmission line is insured under all circumstances.

Claims9

Dependent claims

Apparatus comprising:

a first optical isolation means having an input stage and an output stage;
a transmission line means which is made up of a transmit line having first and second ends and a receive line having first and second ends, said transmit line and said receive line forming a current loop, the first end of said transmit line forming the input of said current loop and the first end of said receive line forming the output of said current loop, the second end of said transmit line being resistively connected to the second end of said receive line, the first end of said transmit line being electrically connected to the output stage of said first optical isolation means;
means for supplying a first digital signal to the input stage of said first optical isolation means in such a manner that said first digital signal will be transmitted as the presence or absence of electrical current flow on said transmit line;
a second optical isolation means having an input stage and an output stage;
means for electrically connecting the first end of said receive line to the input stage of said second optical isolation means;
a third optical isolation means having an input stage and an output stage, said third optical isolation means being in an on condition when said first optical isolation means is in an on condition and said third optical isolation means being in an off condition when said first optical isolation means is in an off condition;
means for electrically connecting the input stage of said second optical isolation means to the output stage of said third optical isolation means in such a manner that the first end of said transmit line and the first end of said receive line are electrically balanced when electrical current is flowing in said transmit line, and the first end of said transmit line and the first end of said receive line are also electrically balanced when electrical current is not flowing in said transmit line.

4 more elements

Apparatus comprising:

a first optical isolation means having an input stage made up of a first light emitting diode, having an anode and a cathode, and having an output stage made up of a first phototransistor having a base, emitter and a collector, and a first driving transistor, having a base, emitter and a collector, the emitter of said first phototransistor being electrically connected to the base of said first driving transistor;
a transmission line means which is made up of a transmit line having first and second ends and a receive line having first and second ends, said transmit line and said receive line forming a current loop, the first end of said transmit line forming the input of said current loop and the first end of said receive line forming the output of said current loop, the second end of said transmit line and the second end of said receive line being resistively connected, the first end of said transmit line being electrically connected to the emitter of said first driving transistor associated with said first optical isolation means;
means for supplying a first digital signal to the input stage of said first optical isolation means in such a manner that current flows from the anode side of said first light emitting diode to the cathode side of said first light emitting diode causing light to be emitted by said first light emitting diode, the light being emitted by said first light emitting diode being sensed by said first phototransistor in such a manner that said first phototransistor is turned on and said first driving transistor is also turned on;
a power supply means;
means for electrically connecting said power supply means to the collector of said driving transistor in such a manner that when said first driving transistor is turned on in response to light being emitted from said first light emitting diode, said first digital signal will be transmitted as the presence or absence of electrical current flow on said transmit line;
a second optical isolation means having an input stage made up of a second light emitting diode, having an anode and a cathode, and having an output stage made up of a second phototransistor, having a base, emitter and collector, and a second driving transistor, having a base, emitter and collector, the emitter of said second phototransistor being electrically connected to the base of said second driving transistor;
means for electrically connecting the first end of said receive line to the anode side of said second light emitting diode which forms the input stage of said second optical isolation means;
a third optical isolation means having an input stage made up of a third light emitting diode, having an anode and a cathode, and having an output stage made up of a third phototransistor, having a base, emitter and collector, and a third driving transistor, having a base, emitter, and collector, the emitter of said third phototransistor being electrically connected to the base of said third driving transistor, said third optical isolation means being in an on condition when said first optical isolation means is in an on condition, and said third optical isolation means being in an off condition when said first optical isolation means is in an off condition;
means for electrically connecting the cathode side of said second light emitting diode, which forms the input stage of said second optical isolation means, to the collector of said third driving transistor, associated with said third optical isolation means, in such a manner that the first end of said transmit line and the first end of said receive line are electrically balanced when electrical current is flowing in said transmit line and the first end of said transmit line and the first end of said receive line are also electrically balanced when electrical current is not flowing in said transmit line.

6 more elements

Dependencies are inferred from the claim text.

Facts

Application: 05/870,545Filed 18 Jan 1978
Granted: 11 Dec 1979
Term ends: Not estimatedThe source records don’t support an estimate.

Classification5 codes

H04L 12/40045
Architecture of a communication node: details regarding the feeding of energy to the node from the bus
H04L 5/1407
Two-way operation using the same type of signal, i.e. duplex: artificial lines or their setting
H04L 12/40032
Architecture of a communication node: details regarding a bus interface enhancer
H04L 25/26
Repeater circuits; Relay circuits: circuits with optical sensing means , i.e. using opto-couplers for isolation