Digital subscriber loop or line technology (xDSL) has enabled digital data, such as web pages and computer files to be transmitted at high speeds over telephone wires used for local phone service. Data in xDSL systems is typically transmitted over these telephone wires through voltage signal fluctuations.
In most circumstances, the voltage fluctuations used fall within a fixed range, but occasionally data may be transmitted through voltage fluctuations that exceed the fixed range. Since xDSL systems use amplifiers to boost voltage signals before transmitting them, an issue arises relating to the amount of supply voltage that is used to power the amplifiers that are processing these signals. For example, an amplifier with sufficient supply voltage to boost or amplify voltage signals solely to encompass voltage fluctuations within the fixed range, will in most instances accurately transmit data. However, in the occasional instances where the voltage fluctuations exceed the fixed range, the amplifier will not be able to accurately reproduce the voltage signal, since the voltage fluctuations exceed the amplification ability of the amplifier, resulting in data loss (“clipping”).
To overcome this limitation, supply voltages will be selected to properly supply the amplifier so that it will accurately amplify xDSL voltage signals in all instances, including the occasional instance when the voltage fluctuation exceeds the fixed range. While this amplifier will accurately transmit data in all instances, the overall system is inefficient and wastes power because in most instances the voltage fluctuations will be within the fixed range and not the occasional voltage fluctuation range that the system is designed to accurately amplify. Many xDSL systems today use this type of non-efficient amplifier system.
One technique for improving amplifier efficiency in these circumstances is described in U.S. Pat. No. 6,636,103, commonly owned with this application by Analog Devices, Inc. The contents of U.S. Pat. No. 6,636,103 are incorporated by reference herein. The '103 patent discloses an amplifier system for a single input channel that uses a charge pump to increase the voltage applied to the amplifier beyond the fixed range in the occasional instances when the voltage fluctuation exceeds the fixed range. However, using the system disclosed in this patent to amplify signals in a multi-channel xDSL system may also result in inefficiencies, as each input channel may have its own amplifier and charge pump to independently amplify voltage signals on each channel. This system is also only geared toward a single xDSL application.
Thus, there is a need for an efficient multi-channel xDSL signal amplification system supporting instantaneous amplifier power supply needs in response to a fluctuating input signal.