Texas Instruments Corporation

Subahashish Mukherjee

Donald Cook Richardson

Joseph T Nabicht

Kazi I Islam

Digital subscriber modems ( ) for use in Asynchronous Digital Subscriber Line (ADSL) communications are disclosed. The central office modem ( ) includes a digital transceiver function ( ) and an analog front end function ( ), where the analog front end function ( ) is integrated into a single integrated circuit. According to the disclosed embodiments, the analog front end function ( ) includes a transmit and a receive side. On the receive side, an impedance matching circuit ( ) is coupled to the input of a programmable gain amplifier ( C). The impedance matching circuit ( ) is controlled by the same control signals (C , C , C ) as used to select the gain of the programmable gain amplifier ( C), so that a constant input impedance is presented to the signal input (RXP), independent of the selected gain.

Impedance matching for programmable gain amplifiers

Digital subscriber modems (,) for use in Asynchronous Digital Subscriber Line (ADSL) communications are disclosed. Each modem includes a digital transceiver function (,) and an analog front end function (,), where the analog front end function (,) is integrated into a single integrated circuit. According to the disclosed embodiments, the analog front end functions (,) each include a transmit and a receive side. The transmit side includes oversampled registers (,C,,R) and digital filters (,C,,R) which serve to increase the sample rates of the digital data to be transmitted, so that the analog-to-digital converter (,C,,R) operates in an oversampled manner, and so that the downstream analog low pass filters (,C,,R) can be realized with relatively simple, low-order filters. On the receive side, digital filter functions (,C,,R) are included downstream from the analog-to-digital converters (,C,,R), to minimize the complexity of the receive-side analog filters (,C,,R). The remote DSL modem (,) also includes an equalizer function (,) to boost the signal amplitude with increasing frequency, to overcome the effects of line attenuation on the high frequency downstream transmissions.

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Banglalore, India

Subahashish Mukherjee