| 摘要 |
Digital subscriber modems (8, 15) for use in Asynchronous Digital Subscriber Line (ADSL) communications are disclosed. The central office modem (8) includes a digital transceiver function (10) and an analog front end function (12), where the analog front end function (12) is integrated into a single integrated circuit. According to the disclosed embodiments, the analog front end function (12) includes a transmit and a receive side. On the receive side, an impedance matching circuit (56) is coupled to the input of a programmable gain amplifier (54C). The impedance matching circuit (56) is controlled by the same control signals (C1, C2, C3) as used to select the gain of the programmable gain amplifier (54C), so that a constant input impedance is presented to the signal input (RXP), independent of the selected gain.
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