Active hybrid circuit

• US 3,970,805 A
• Filed: 02/22/1974
• Issued: 07/20/1976
• Est. Priority Date: 02/22/1974
• Status: Expired due to Term

• Current Assignee: Microtel Limited-Microtel Limitee
• Original Assignee: GTE Automatic Electric Incorporated (Verizon Communications Inc.)
• Inventors: Thomas, Robert M.
• Primary Examiner(s): Claffy, Kathleen H.
• Assistant Examiner(s): Myers, Randall P.
• Application Number:
  US05/444,889
• Time in Patent Office: 879 Days
• Field of Search: 179/170 R, 179/170 NC
• US Class Current: 379/405
• CPC Class Codes: H04B 1/586 using an electronic circuit
• CPC Class Codes: H04M 19/005 Feeding arrangements without the use of line transformers

Abstract

An active hybrid circuit for providing isolation between a signal receiving line and a signal transmitting line coupled to a two-wire telephone subset. The receiving line is coupled to a receiving amplifier having a differential output coupled to a pair of common terminals. The telephone subset is also connected to the two common terminals. The two common terminals are connected to the two inputs of a transmitting operational amplifier. The transmitting signal line is coupled to the output of the transmitting amplifier. A compensating network is connected between the input to the receiving amplifier and one of the inputs to the transmitting amplifier. The reflected signal produced at the output of the transmitting amplifier due to a received signal at the input to the receiving amplifier passing through the receiving amplifier and then through the transmitting amplifier is cancelled by an equal and opposite compensating signal occurring at the output of the transmitting amplifier by virtue of the received signal passing through the compensating network and the transmitting amplifier.

Claims

1. An active hybrid circuit comprising

an input terminal for receiving input signals;

receiving amplifier means having an input connection coupled to said input terminal and having two output connections for producing therebetween a differential output of the signals applied at the input connection;

two common terminals for connecting a transmitting and receiving unit thereto;

said output connections of the receiving amplifier means being coupled to said common terminals, whereby input signals received at the input terminal and amplified to produce a differential output by the receiving amplifier means are applied to the transmitting and receiving unit;

transmitting amplifier means having two input connections for receiving a differential input and having an output connection;

said input connections of the transmitting amplifier means being coupled to said common terminals, whereby signals being transmitted by the transmitting and receiving unit are applied to the transmitting amplifier means and amplified transmitted signals are produced at the output connection of the transmitting amplifier means; and

compensating means coupled to the input terminal and directly to a first of said two input connections of the transmitting amplifier means;

said compensating means including

first circuit means including impedance means connected between said input terminal and a connection point,

second circuit means including impedance means connected between said connection point and said first input connection of the transmitting amplifier means, and

third circuit means including impedance means connected between said connection point and a point of reference potential;

said compensating means being operable in response to a signal at the input terminal to produce a signal at said first input connection of the transmitting amplifier means causing the transmitting amplifier means to produce at its output connection a signal which is substantially equal and of opposite polarity to the signal produced at its output connection in response to the same input signal amplified by the receiving amplifier means, coupled to the transmitting amplifier means, and amplified by the transmitting amplifier means, whereby substantially none of a signal received at the input terminal appears at the output connection of the transmitting amplifier means.

2. An active hybrid circuit comprising

receiving input signals;

an input terminal for receiving amplifier means having an input connection coupled to said input terminal and having two output connections for producing therebetween a differential output of the signals applied at the input connection;

two common terminals for connecting a transmitting and receiving unit thereto;

said output connections of the receiving amplifier means being coupled to said common terminals, whereby input signals received at the input terminal and amplified to produce a differential output by the receiving amplifier means are applied to the transmitting and receiving unit;

transmitting amplifier means having two input connections for receiving a differential input and having an output connection;

said input connections of the transmitting amplifier means being coupled to said common terminals, whereby signals being transmitted by the transmitting and receiving unit are applied to the transmitting amplifier means and amplified transmitted signals are produced at the output connection of the transmitting amplifier meas; and

compensating means coupled to the input terminal and directly to a first of said two input connections of the transmitting amplifier means, said compensating means being operable in response to a signal at the input terminal to produce a signal at said first input connection means;

the transmitting amplifier means causing the transmitting amplifier means to produce at its output connection a signal which is substantially equal and of opposite polarity to the signal produced at its output connection in response to the same input signal amplified by the receiving amplifier means, coupled to the transmitting amplifier means, and amplified by the transmitting amplifier means, whereby substantially none of a signal received at the input terminal appears at the output connection of the transmitting amplifier means;

said receiving amplifier means being a differential amplifier means having a first input connection coupled to said input terminal and a second input connection coupled to a point of reference potential; and

said transmitting amplifier means being an operational amplifier having two input connections, an inverting input connection and a non-inverting input connection, a first of said two input connections being directly connected to said compensating means and the second of said two input connections being connected to said point of reference potential through a resistance.

3. An active hybrid circuit in accordance with claim 2 wherein said compensating means includes

first circuit means including impedance means connected between said input terminal and a connection point,

second circuit means including impedance means connected between said connection point and said first input connection of the transmitting amplifier means, and

third circuit means including impedance means connected between said connection point and said point of reference potential.

4. An active hybrid circuit in accordance with claim 3 including

means having capacitive impedance coupling one output connection of the receiving amplifier means to one of said common terminals;

means having capacitive impedance coupling the other output connection of the receiving amplifier means to the other of said common terminals;

means having capacitive impedance coupling the one of said common terminals to the first input connection of the transmitting amplifier means; and

means having capacitive impedance coupling the other of said common terminals to the second input connection of the transmitting amplifier means.

5. An active hybrid circuit in accordance with claim 4 wherein

said point of reference potential is at ground potential;

said first input connection of said transmitting amplifier means is the inverting input connection; and

said second input connection of said transmitting amplifier means is the non-inverting input connection.