Patent ID: 7907659

Claim:
A multiple tone modem, comprising: a line interface circuit having a hybrid circuit with both one or more transmit transformers and one or more receive transformers to interface the multiple tone modem to a communication line, wherein the hybrid circuit comprises: a lowpass transmit filter having lowpass functionality to confine a transmit signal through an output of the lowpass transmit filter to a first frequency band: a highpass transmit filter having highpass functionality to confine a transmit signal through an output of the highpass transmit filter to a second frequency band that is higher than the first frequency band, wherein the output of the lowpass transmit filter and the output of the highpass transmit filter are coupled on the communication line side of the hybrid circuit in a parallel configuration and an upper edge of the first frequency band confined to pass through the lowpass transmit filter and a lower edge of the second frequency band confined to pass through the highpass transmit filter are sufficiently separated to reduce interference effects between the two filters from the other frequency band; a first transmit transformer with device side windings coupled to a line driver and with communication line side windings coupled to the communication line; a second transmit transformer with device side windings coupled to the line driver and with communication line side windings coupled to the communication line; a first receive transformer for a receive signal with device side windings coupled to a receiver and with communication line side windings coupled to the communication line; and an impedance component coupled to the communication line side windings of the receive transformer and the communication line side windings of the first transmit transformer, wherein the impedance component substantially matches an impedance value of the line to cancel the transmit signal from the receive signal.