GB1586410A

GB1586410A - Hybrid circuits

Info

Publication number: GB1586410A
Application number: GB2459278A
Authority: GB
Original assignee: Plessey Co Ltd
Current assignee: Plessey Co Ltd
Priority date: 1978-05-30
Filing date: 1978-05-30
Publication date: 1981-03-18

Description

(54) IMPROVEMENTS IN OR RELATING TO HYBRID CIRCUITS (71) We, THE PLESSEY COMPANY LIMITED, a British Company, of Vicarage Lane, Ilford, Essex, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following state ment:- The present invention relates to hybrid circuit arrangements for coupling two wire to four wire transmission paths such as are used in telephone or other audio circuits where a subscribers telephone may be connected to a radio transmitter and a receiver.

Traditionally in telephony the connection of a 2 wire path a four wire path has been achieved by using a magnetic hybrid transformer which is a bulky and costly component. More recently operational amplifier circuit arrangements have been used but these arrangements are susceptible to interference from noise and also require the input voltages to be between fixed levels.

It is an object of the present invention to provide a hybrid circuit arrangement for coupling a two wire transmission path to a four wire transmission path which has a greater immunity from interference than the above previously known circuit arrangements.

The present invention therefore provides a hybrid circuit arrangement for coupling a two wire to a four wire transmission path including a first voltage to current converter whose input is connected to the receiving path of the four wire transmission path and whose output is connected to the two way transmission path. a second voltage to current converter whose input is connected to the two way transmission path and whose output is connected to the transmitting path of the four wire path and a third voltage to current converter whose input is connected to the receiving path and whose output is connected to the transmitting path.

Preferably, each path has a terminating conductance to provide a matched termination for each of the paths and preferably the conductance in the receiving path of the four way path has a centre tap which is connected to a predetermined potential to define the common mode potential of the balanced signal feed to the one way transmitting path.

Embodiments of the present invention will now be described, by way of example with reference to the accompanying drawings in which: Figure 1 shows a voltage to current converter for use in the hybrid circuit arrangement according to the present invention, and Figure 2 shows a block diagram of a hybrid circuit arrangement according to the present invention.

Referring now to Figure 1, the circuit of a voltage to current converter is shown with two input terminals 1, 2. two output terminals 1, 2 and positive, negative voltage supplies +HUT. A bias current is supplied at a BIAS input and this regulates the current output of the transactor.

The characteristic of the converter is that for a given voltage input the converter gives a constant current output. The input and output impedances are very high. The ratio between voltage input and current output is set by the external resistance R i.e. Iout = K 1/R Vin (in which K is a constant of any value within design limits).

The converter requires no additional feedback for stability and the input and output terminals are totally floating providing a true four terminal device.

Referring now to Figure 2, there is shown a hybrid circuit arrangement for coupling a two wire transmission line T to a four wire transmission line comprising a two wire receive path R and a two wire transmit path G. A first voltage to current converter A is connected between the receive path R and the transmission path T, a second B between the transmission path R and the transmit path G and a third C between the receive R and the transmit path G of the four way transmission path. Each converter A, B or C is shown as receiving a voltage input and converting this to a constant current output. Each converter A, B, C has a respective value of transfer conductance gA, gB, gC.

Converter A transfers a signal from the one way path R to the two way path T.

Converter B transfers a signal from the two way path T to the one way path G.

Converter C is connected between the one way paths G and R to cancel the signal fed to the path G by varactors A and B and originating from a signal at R. The condition required for cancellation is described by an equation: ga.gb ga = Cit +02 where G1 is the value of conductance 1 and G2 is the source conductance of the two way path at T.

The values of the conductances 1. 2 and 3 are arbitrary, but may be selected to provide matched terminations for transmission lines at T, G and R respectively. The conductance 2 has a centre tap (not shown) connected to a potential V (which will usually be earth potential). which defines to the one-way path G. Alternatively the conductance 2 may be connected at one end to a potential which then provides an unbalanced signal fed to the one-way path G.

The signal originating at the one-way path R may be balanced or unbalanced. The conductance 1 has a centre-tap connected to earth potential. but it is envisaged that in some circumstances this centre-tap may be omitted.

The invention therefore provides a hybrid circuit for coupling two way transmission path to a four way transmission path in which all three parts are balanced bv virtue of the fully floating inputs and outputs of the voltage to current converters.

WHAT WE CLAIM IS: l. A hybrid circuit arrangement for cou- pling a two wire to a four wire transmission path including a first voltage to current converter whose input is connected to the receiving path of the four wire transmission path and whose output is connected to the two way transmission path. a second voltage to current converter whose input is con nected to the two way transmission path and whose output is connected to the transmitting path of the four wire path. and a third voltage to current converter whose input is connected to the receiving path and whose output is connected to the transmitting path.

2. A hybrid circuit arrangement as claimed in claim 1 in which each path has a terminating conductance to provide a matched termination for each of the paths and in which the conductance in the receiving path of the four wire path has a centre tap which is connected to a predetermined potential to define the common mode potential of the balanced signal feed to the one way transmitting path.

3. A hybrid current arrangement for coupling a two wire to a four wire transmission path substantially as described with reference to the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **.

connected between the receive path R and the transmission path T, a second B between the transmission path R and the transmit path G and a third C between the receive R and the transmit path G of the four way transmission path. Each converter A, B or C is shown as receiving a voltage input and converting this to a constant current output. Each converter A, B, C has a respective value of transfer conductance gA, gB, gC.

Converter A transfers a signal from the one way path R to the two way path T.

Converter B transfers a signal from the two way path T to the one way path G.

Converter C is connected between the one way paths G and R to cancel the signal fed to the path G by varactors A and B and originating from a signal at R. The condition required for cancellation is described by an equation: ga.gb ga = Cit +02 where G1 is the value of conductance 1 and G2 is the source conductance of the two way path at T.

The values of the conductances 1. 2 and 3 are arbitrary, but may be selected to provide matched terminations for transmission lines at T, G and R respectively. The conductance 2 has a centre tap (not shown) connected to a potential V (which will usually be earth potential). which defines to the one-way path G. Alternatively the conductance 2 may be connected at one end to a potential which then provides an unbalanced signal fed to the one-way path G.

The signal originating at the one-way path R may be balanced or unbalanced. The conductance 1 has a centre-tap connected to earth potential. but it is envisaged that in some circumstances this centre-tap may be omitted.

The invention therefore provides a hybrid circuit for coupling two way transmission path to a four way transmission path in which all three parts are balanced bv virtue of the fully floating inputs and outputs of the voltage to current converters.

WHAT WE CLAIM IS: l. A hybrid circuit arrangement for cou- pling a two wire to a four wire transmission path including a first voltage to current converter whose input is connected to the receiving path of the four wire transmission path and whose output is connected to the two way transmission path. a second voltage to current converter whose input is con nected to the two way transmission path and whose output is connected to the transmitting path of the four wire path. and a third voltage to current converter whose input is connected to the receiving path and whose output is connected to the transmitting path.
2. A hybrid circuit arrangement as claimed in claim 1 in which each path has a terminating conductance to provide a matched termination for each of the paths and in which the conductance in the receiving path of the four wire path has a centre tap which is connected to a predetermined potential to define the common mode potential of the balanced signal feed to the one way transmitting path.
3. A hybrid current arrangement for coupling a two wire to a four wire transmission path substantially as described with reference to the accompanying drawings.