Line driver for an adaptive hybrid circuit
View Patent ↗A second output transmission signal (“TX 2 ”) added to a line driver is a scaled version of the main output transmission signal (“TX 1 ”). TX 2 is scaled from TX 1 by a variable scale factor K. An adaptive hybrid circuit subtracts TX 1 and TX 2 from a line signal carrying both a line transmission signal and a line received signal (“RX”). A programmable impedance Z tune is coupled between the TX 2 output of the line driver and the RX output of the adaptive hybrid circuit. A transmission echo in the output RX signal is measured. K and Z tune are then adaptively tuned to minimize the transmission echo. The hybrid in this case becomes a 4-port network, one port specifically added to adaptively cancel the transmission echo in the RX output of the adaptive hybrid circuit. Alternatively, the hybrid may be a 3-port hybrid including variable impedances to cancel the line transmission signal.
1. A circuit for a signal transmission system, comprising:
a hybrid circuit that extracts a line received signal from a line signal;
a first transmission input port to the hybrid circuit configured to receive a first transmission signal from a first transmission path;
a second transmission input port to the hybrid circuit configured to receive a second transmission signal from a second transmission path having an impedance; and
an output port configured to output the line received signal, wherein the impedance is configured to minimize a transmission echo produced when the hybrid circuit extracts the line received signal.
2. The circuit of claim 1 , wherein the impedance is variable.
3. The circuit of claim 2 , wherein the impedance adapts to a changing line impedance without user intervention.
4. The circuit of claim 2 , wherein the impedance is manually programmable.
5. The circuit of claim 1 , wherein the second transmission signal is a scaled version of the first transmission signal.
6. The circuit of claim 5 , wherein the second transmission signal is scaled from the first transmission signal by a factor K so as to minimize the transmission echo.
7. The circuit of claim 5 , wherein the impedance is fixed.
8. The circuit of claim 5 , wherein the impedance is variable.
9. The circuit of claim 1 , further comprising:
a line input to the hybrid circuit configured to receive the line signal, wherein the line signal includes the line received signal and a line transmission signal; and
a receive output from the hybrid circuit configured to output the line received signal along a receive path after the line received signal is extracted from the line signal.
10. The circuit of claim 9 , wherein the hybrid circuit comprises:
a positive transmission input node configured to receive a positive component of the first transmission signal;
a negative transmission input node configured to receive a negative component of the first transmission signal;
a positive line input node configured to receive a positive component of the line signal;
a negative line input node configured to receive a negative component of the line signal;
a positive output node configured to output a positive component of the line received signal; and
a negative output node configured to output a negative component of the line received signal.
11. The circuit of claim 10 , wherein the positive output node is further configured to receive a negative component of the second transmission signal, and wherein the negative output node is further configured to receive a positive component of the second transmission signal.
12. The circuit of claim 10 , wherein the hybrid circuit further comprises:
a first impedance located between the positive transmission input node and the negative output node;
a second impedance located between the negative transmission input node and the positive output node;
a third impedance located between the positive line input node and the positive output node; and
a fourth impedance located between the negative line input node and the negative output node.
13. The circuit of claim 12 , wherein:
the first and second impedances are approximately equal to each other; and
the third and fourth impedances are approximately equal to each other.
14. A duplex transmission system, comprising:
a line driver having a first transmission output and a second transmission output;
a hybrid circuit, comprising:
a first transmission input port coupled along a first transmission path to the first transmission output of the line driver, wherein the first transmission input port is configured to receive a first transmission signal; and
a second transmission input port coupled along a second transmission path to the second transmission output of the line driver, wherein the second transmission input port is configured to receive a second transmission signal; and
a transformer coupled to the hybrid circuit.
15. The duplex transmission system of claim 14 , wherein the second transmission signal is a scaled version of the first transmission signal.
16. The duplex transmission system of claim 15 , wherein the second transmission signal is scaled from the first transmission signal by a factor K so as to minimize a transmission echo produced when the adaptive hybrid circuit outputs a line received signal.
17. The duplex transmission system of claim 14 , further comprising:
an impedance located in the second transmission path.
18. The duplex transmission system of claim 17 , wherein the impedance is a variable impedance.
19. The duplex transmission system of claim 18 , wherein the variable impedance is adjustable to reduce a transmission echo produced when the hybrid circuit outputs a line received signal.
20. The duplex transmission system of claim 14 , wherein the adaptive hybrid circuit further comprises:
a line input port coupled to the transformer along a line signal path, wherein the line input port is configured to receive a line signal carrying a line transmission signal and a line received signal; and
a receive output port configured to output the line received signal along a receive path.
21. The duplex transmission system of claim 20 , wherein the second transmission input port and the receive port are co-located.
22. The duplex transmission system of claim 14 , wherein the transformer is coupled to a communications device.
23. A method of extracting a received signal from a line signal carrying both a line received signal and a line transmission signal, the method comprising:
substantially canceling a primary transmission signal from the line signal to produce a received signal;
inputting a secondary transmission signal of a line driver to substantially cancel a residual transmission signal from the received signal;
measuring a residual transmission echo in the received signal;
varying the secondary transmission signal of the line driver so as to minimize the residual transmission echo; and
outputting the received signal.
24. The method of claim 23 , wherein the varying step comprises:
changing an impedance of a secondary transmission path carrying the secondary transmission signal so as to minimize the residual transmission echo.
25. The method of claim 23 , wherein the varying step comprises:
changing a scale factor of the secondary transmission signal so as to minimize the residual transmission echo.
26. The method of claim 23 , wherein the canceling step comprises:
receiving an input transmission signal;
amplifying the input transmission signal to create the primary transmission signal; and
subtracting the primary transmission signal from the line signal.
27. The method of claim 26 , wherein the inputting step comprises:
scaling the primary transmission signal to produce the secondary transmission signal; and
subtracting the secondary transmission signal from the received signal.