Circuit for joint transmitting voice and data over a telephone line
View Patent ↗The invention relates to an SLIC circuit ( 1 ), which is connected directly to a telephone line ( 2 ), for joint transmission of voice and data via the telephone line ( 2 ), with adequate echo attenuation achieved even at high data frequencies in that a first current which corresponds to the sum of the transmission and received currents (Ia, Ib), and a second current (Id) which corresponds to the current produced by the transmission power level (Vtx) at the data frequency, are produced, and the difference between the first current and the second current (Id) is emitted.
1. A circuit ( 1 ) for joint transmission of voice and data via a telephone line ( 2 ),
having a first and a second telephone line connection (TIP, RING) for connection to the telephone line ( 2 ),
having a data connection (ITD) for connection to a data line ( 3 ),
having first circuit means (T 1 -T 4 , R 3 , R 4 ), which are coupled to the telephone line connections (TIP, RING) for producing a first current which is composed of the sum of transmission and received currents (Ia, Ib) which flow via the telephone line ( 2 ) and are produced via a transmission power level (Vtx) and a received power level (Vrx), respectively, and
having second circuit means (T 5 , R 1 - 2 , C 1 -C 2 ) which are coupled to the telephone line connections (TIP, RING) for producing a second current (Id) which corresponds to the current produced solely by the transmission power level corresponding to the data,
with the outputs of the first circuit means (T 1 -T 4 , R 3 , R 4 ) and of the second circuit means (T 5 , R 1 -R 2 , C 1 -C 2 ) being coupled to the data connection (ITD) in such a manner that a current (Ic) which is emitted via the data connection (ITD) corresponds to the difference between the first current and the second current (Id).
2. The circuit as claimed in claim 1 ,
characterized
in that the first circuit means comprise a symmetrical arrangement of first and second drivers (T 2 , T 4 ) and first and second amplifiers (T 1 , T 3 ),
with the first and second drivers (T 2 , T 4 ) each receiving the transmission power level (Vtx) at one of their inputs and being connected by their other input via a first and second resistor (R 3 , R 4 ), respectively, to their output, and
with the first and second amplifiers (T 1 , T 3 ) amplifying the voltage drop across the first and second resistors (R 3 , R 4 ), respectively.
3. The circuit as claimed in claim 2 ,
characterized
in that the first and second amplifiers (T 1 , T 3 ) are each voltage/current amplifiers.
4. The circuit as claimed in claim 3 ,
characterized
in that the first resistor (R 3 ) is connected between a negative input and a positive input of the first amplifier (T 1 ), with the negative input of the first amplifier (T 1 ) being connected to the first telephone line connection (TIP), and
in that the second resistor (R 4 ) is connected between a positive input and a negative input of the second amplifier (T 3 ), with the positive input of the second amplifier (T 3 ) being connected to the second telephone line connection (RING).
5. The circuit as claimed in claim 2 ,
characterized
in that the first and second drivers (T 2 , T 4 ) are differential amplifiers, with the positive input, each receiving the transmission power level (Vtx), while the negative input is in each case connected via the corresponding resistor (R 3 , R 4 ) to the corresponding output of the driver (T 2 , T 4 ).
6. The circuit as claimed in claim 1 and claim 2 ,
characterized
in that the output of the amplifier (T 5 ) in the second circuit means is connected to the outputs of the first and second amplifiers (T 1 , T 3 ) in the first circuit means and to the data connection (ITD).
7. The circuit as claimed in claim 1 ,
characterized
in that the second circuit means comprise an amplifier (T 5 ) whose inputs are connected via respective high-pass filters (R 1 , C 1 ; R 2 , C 2 ) to the telephone line connections (TIP, RING).
8. The circuit as claimed in claim 7 ,
characterized
in that the amplifier (T 5 ) in the second circuit means is a voltage/current amplifier, a negative input of this amplifier (T 5 ) being connected via a first high-pass filter (R 1 , C 1 ) to the first telephone line connection (TIP), and a positive input of this amplifier (T 5 ) being connected via a second high-pass filter (R 2 , C 2 ) to the second telephone line connection (RING).
9. The circuit as claimed in claim 8 ,
characterized
in that the first and second high-pass filters (R 1 , C 1 ; R 2 , C 2 ) are designed such that the amplifier (T 5 ) in the second circuit means are supplied only with data current components of the currents (Ia, Ib) flowing in the transmission direction via the telephone line.
10. The circuit as claimed in claim 1 ,
characterized
in that the data connection (ITD) is coupled to a high-pass filter (R 6 , R 7 , C 3 ) via which the current signal (Ic) which is emitted via the data connection (ITD) is passed, the high-pass filter (R 6 , R 7 , C 3 ) being designed such that DC components and/or voice current components are filtered out of the current signal (Ic).