Abstract: A directional coupler for a modem has a high common mode noise rejection characteristic with low transmit signal leakage, and reduced distortion of components mixed with a received signal. A primary filter network is connected to a communications circuit. The primary filter network has an output connected to an input of an amplifier. A feedback network is connected between the input and output of the amplifier. The primary filter network, the amplifier and the feedback network are arranged to provide a virtual ground at the input of the amplifier, and a filter characteristic which attenuates frequencies in the transmit signal band. The advantage is reduced component count while providing excellent transmit signal rejection and reducing received signal distortion.

Abstract: A DSL modem comprises an additional transformer and additional coils on a coupling transformer to couple a received signal on a transmission line to a receive path without loss due to an active impedance. The ratio of windings on the coils allows gain to be introduced to improve the signal to noise ratio.

Abstract: A directional coupler for a modem has a high common mode noise rejection characteristic with low transmit signal leakage, and reduced distortion of components mixed with a received signal. A primary filter network is connected to a communications circuit. The primary filter network has an output connected to an input of an amplifier. A feedback network is connected between the input and output of the amplifier. The primary filter network, the amplifier and the feedback network are arranged to provide a virtual ground at the input of the amplifier, and a filter characteristic which attenuates frequencies in the transmit signal band. The advantage is reduced component count while providing excellent transmit signal rejection and reducing received signal distortion.

Abstract: The current technology involved with overlaying any type of digital subscriber loop (xDSL) service with plain old telephone service (POTS) makes use of two separate transformers, one for POTS and another for xDSL. This invention provides a transformer which combines the POTS transformer and the xDSL transformer into one transformer. This considerably reduces the weight volume and cost of the overlaid POTS and xDSL circuits. In combining the two transformers the magnetic coupling between any one of the windings used for POTS and any one of those used for xDSL must remain weak despite their close proximity. In addition, any two windings of the same type of service, either POTS or xDSL, must remain strongly coupled. This is achieved by choosing a special geometric form for the core and choosing strategic locations for the windings. A portion of the core is dedicated to serve as a shunt for each component of the magnetic field produced by the windings.

Abstract: A receiver which may be an xDSL receiver has improved dynamic range. The receiver has a first amplifier, a network of four impedances and a variable gain second amplifier. The variable gain second amplifier has an input connected to an ouput of the first amplifier, an output connected to the first amplifier, and a variable gain control input. The gain of the variable gain second amplifier is 1 K , and the pass-band gain of the receiver is K. By controlling the gain of the receiver with an AGC (automatic gain control), the receiver can amplify and filter inputs over a wide dynamic range with lower distortion and without saturation. Alternatively, the gain of the variable gain second amplifier is - 1 K . The four impedances can be arranged to realise low-pass or high-pass filters.

Abstract: A directional coupler for a modem has a high common mode noise rejection characteristic with low transmit signal leakage, and reduced distortion of components mixed with a received signal. A primary filter network is connected to a communications circuit. The primary filter network has an output connected to an input of an amplifier. A feedback network is connected between the input and output of the amplifier. The primary filter network, the amplifier and the feedback network are arranged to provide a virtual ground at the input of the amplifier, and a filter characteristic which attenuates frequencies in the transmit signal band. The advantage is reduced component count while providing excellent transmit signal rejection and reducing received signal distortion.

Abstract: A line driver combining active impedance and filter in one stage for connection to a transmission line having a characteristic impedance. The line driver comprises an amplifier, a transformer with a primary to secondary winding ratio of 1:n, a reference impedance, an input impedance and two feedback impedances. The primary winding of the transformer has a first end connected to the output of the amplifier and the secondary winding is connectable to the transmission line. The reference resistor has an end connected to the second end of the first winding at a junction node and the feedback circuit is connected to the input and output of the amplifier and also to the junction node. The reference impedance has a value equal to n 2 K times the characteristic impedance of the transmission line.

Abstract: Generation of a compensation signal for canceling the distortion component of a distorted signal at an affected node, where the distortion component is caused by electro-magnetic coupling from a distortion-causing signal source. The distortion-causing signal is coupled into a distortion cancellation system using capacitive or electro-magnetic coupling techniques, resulting in the generation of an induced voltage. The induced voltage is fed to an impedance network and then to a plurality of cells, one for each of the affected nodes. The compensation signal appearing at the output of the cell is combined with the distorted signal at the corresponding affected node. By appropriately selecting the impedance values of the components in the corresponding cell, substantial cancellation of the distortion from the distortion-causing signal source can be achieved. The system can be simplified if the degree to which the distortion-causing signal source couples into the distorted signal is determined ahead of time.

Abstract: A line driver combining active impedance and filter in one stage for connection to a transmission line having a characteristic impedance. The line driver comprises an amplifier, a transformer with a primary to secondary winding ratio of 1:n, a reference impedance, an input impedance and two feedback impedances. The primary winding of the transformer has a first end connected to the output of the amplifier and the secondary winding is connectable to the transmission line. The reference resistor has an end connected to the second end of the first winding at a junction node and the feedback circuit is connected to the input and output of the amplifier and also to the junction node. The reference impedance has a value equal to n2 /K times the characteristic impedance of the transmission line. The feedback circuit is arranged to produce a voltage at the output of the amplifier substantially equal to (K+1) times the voltage at the junction node, for a predetermined value of K.

Abstract: An receiver having improved dynamic range. The receiver comprises an opamp (operational amplifier), network of four impedances and a variable gain amplifier. The first impedance is connected from the input of the xDSL receiver to a first junction node, the second impedance is connected from the first junction node to a second junction node, the third impedance is connected from the second junction node to a ground reference, the fourth impedance is connected from the first junction node to a third junction node, the opamp has a non-inverting input connected to the second junction node, the opamp also has an inverting input connected to the third junction node, the opamp also has an output connected to the output of the xDSL receiver, the variable gain amplifier has an input connected to the output of the xDSL receiver, the variable gain receiver also has an output connected to the third junction node and the variable gain amplifier also has variable gain control input.

Abstract: A power amplifier receives an input analog signal and generates a corresponding power amplified output analog signal. The power amplifier includes first and second power supply rails, an amplifier circuit, and a switch circuit. The first and second power supply rails are capable of supplying power having respective first and second predetermined levels, and a single predetermined polarity. The amplifier circuit is connected to receive the input analog signal and adapted to generate the output analog signal. Finally, the switch circuit is adapted to selectively connect one of the first and second power supply rails to the amplifier circuit.