Directional receiver coupling arrangement with frequency selectivity and gain control for DSL
First Claim
1. A modem comprising:
- a) a communications circuit for coupling a signal source of the modem to a telecommunications network, the communications circuit comprising a signal line adapted to simultaneously carry a transmit (Tx) signal and a receive (Rx) signal and a compensation network connected to the signal line for balancing an impedance of the signal line; and
b) a directional coupler for coupling a signal receiver of the modem to the communications circuit, the directional coupler circuit comprising;
i) a primary network connected to the communications circuit, the primary network being tuned to attenuate frequencies in a frequency band of the Tx signal, and having a respective primary network output;
ii) an amplifier having a respective amplifier input connected to the primary network output, and a respective amplifier output connected to the receiver; and
iii) a feedback network tuned to attenuate frequencies in a frequency band of the Tx signal, and connected between the amplifier input and the amplifier output;
wherein the primary network, the amplifier, and feedback network are arranged to provide a virtual ground at the amplifier input.
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Accused Products
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.
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Citations
21 Claims
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1. A modem comprising:
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a) a communications circuit for coupling a signal source of the modem to a telecommunications network, the communications circuit comprising a signal line adapted to simultaneously carry a transmit (Tx) signal and a receive (Rx) signal and a compensation network connected to the signal line for balancing an impedance of the signal line; and b) a directional coupler for coupling a signal receiver of the modem to the communications circuit, the directional coupler circuit comprising; i) a primary network connected to the communications circuit, the primary network being tuned to attenuate frequencies in a frequency band of the Tx signal, and having a respective primary network output; ii) an amplifier having a respective amplifier input connected to the primary network output, and a respective amplifier output connected to the receiver; and iii) a feedback network tuned to attenuate frequencies in a frequency band of the Tx signal, and connected between the amplifier input and the amplifier output; wherein the primary network, the amplifier, and feedback network are arranged to provide a virtual ground at the amplifier input. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21)
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Specification