ADSL Drivers and Receivers

ADSL drivers and receivers is a device for interfacing data between a processing system and DSL compatible telephone lines. Digital subscriber line (DSL) is a technology that enables fast data transmission on the copper telephone phone lines historically used for voice traffic. It does this by utilizing the higher frequencies that are above audio and not used by the telephone company for voice. Asynchronous DSL is so named because it optimizes the performance of the connection to provide higher downstream (towards the customers premises) bandwidth at the expense of upstream bandwidth.
ADSL drivers can be of two types: ADSL CPE line drivers that are optimized for the customer end of the telephone line and xDSL line drivers that support full ADSL performance at the central office (CO). The two differ in their performance specifications, the CO equipment tending to be higher power and more highly specified. The reason for this is to foster high downstream bandwidth. They have amplifiers with very high gain-bandwidths (in the region of 100MHz) to support the high-speed signaling.
Drivers typically need both positive and negative supply voltage rails, typically operate from a wide voltage range but ideally operate from +/-12V. CPE drivers can usually output around 350mA on approximately 43Vpp differential output swings while CO drivers typically can provide nearly double this. Being line drivers they are optimized to drive an isolating line transformer that connects to a 200 Ohm load. They usually require minimum external components—typically, some resistors and capacitors for the snub circuit, some supply decoupling, and matching resistors. There are also gain setting resistors to support differing transformer impedance.
ADSL receivers perform the opposite role to the drivers. They take the signal from a line transformer connected to the telephone line and convert it to a high-speed, low-noise differential low voltage signal for subsequent digital processing. They have programmable gain control on their amplifiers to allow the ADSL modem to adjust levels to compensate for line losses. Usually, this is a fairly course steps (6dB). Receivers have low noise characteristics (typically around 2nV/sqrt(Hz)) and high gain bandwidth.
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