Miscellaneous active electrical nonlinear devices – circuits – and – Signal converting – shaping – or generating – Current driver
Reexamination Certificate
2001-11-29
2002-12-24
Ton, My-Trang Nu (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Signal converting, shaping, or generating
Current driver
C327S309000
Reexamination Certificate
active
06498521
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to digital subscriber line (DSL) technologies. More particularly, the present invention relates to a dynamic supply control for a line driver for use with digital subscriber line (DSL) and asymmetrical digital subscriber line (ADSL) systems.
BACKGROUND OF THE INVENTION
FIG. 1
schematically illustrates a conventional line driver system
1
with a single-ended line driver (LD)
3
. The line driver
3
is supplied with a fixed supply voltage V
cc
and drives a transmission line
5
with a load R
L
through a transformer
7
having a turns ratio of 1:n. In the traditional line driver system
1
, in order to prevent clipping of an output signal, the fixed supply voltage V
cc
is chosen high enough to handle the highest signal peak of an input signal. Discrete Multitone (DMT) signals are commonly used in DSL and ADSL systems, and the associated waveforms exhibit a high Peak-to-Average Ratio (PAR).
FIG. 2
illustrates a typical waveform of a DMT signal. As shown in
FIG. 2
, however, the DMT signal amplitude is relatively small for most of the time, and very high peaks occur only occasionally. However, in the conventional line driver system
1
, the line driver
3
must be always supplied with a high supply voltage higher than the highest peak expected. Since the average power consumption of the line driver
3
is substantially given by the average of (fixed supply voltage)×(line driver current), a high supply voltage increases the power consumption of the line driver system
1
. In other words, a fixed high supply voltage, which is actually needed only during occasional high peaks, results in wasting the valuable system power.
Using a Class-G amplifier for a line driver is one possible solution, which provides a dynamic supply control scheme so as to reduce the line driver power consumption. A Class-G amplifier basically employs switching between a low supply voltage and a high supply voltage based on the output signal strength. However, the Class-G scheme requires an extra voltage supply, and switching between two supply voltages introduces glitches and creates high frequency harmonics. Such glitches and high frequency harmonics are difficult eliminate, and/or require additional circuitry to reduce the undesirable effects. Therefore, this Class-G approach is less attractive in view of both performance and cost.
A Class-H high-output voltage level line driver can provide an output voltage swing larger than the supply voltage.
FIG. 3
schematically illustrates a supply voltage
9
and an output signal
11
of a conventional Class-H high-output voltage line driver for audio signals (up to 20 kHz). The conventional Class-H line driver typically operates as a non-inverting amplifier with a single-ended output. As shown in
FIG. 3
, in order to provide a higher output voltage, the supply voltage
9
is lifted as soon as the line driver output voltage
11
increases above-the DC output level (common mode voltage level CM). However, although the conventional high-output voltage level line driver allows reducing the gain of the amplifier and may increase the signal-to-noise ratio, lifting the supply voltage whenever the input audio signal crosses the common mode voltage level is not optimum to save the power of the line driver.
Accordingly, it would be desirable to provide a line driver circuit for DSL/ADSL applications with reduced power consumption without increasing the cost or complexity of the circuitry.
BRIEF DESCRIPTION OF THE INVENTION
A dynamic supply control circuit is provided for a line driver. The line driver has an amplification factor G, receives an input signal voltage, and drives a transmission line having a load R
L
via a transformer having a turns ratio of 1:n. The circuit includes an input node for receiving an input signal voltage, a supply node for supplying a driving voltage to the line driver, a lift diode coupled between a fixed supply voltage and the supply node, a lift capacitor coupled between the supply node and an output node, and a lift amplifier having the amplification factor G coupled between the input node and the output node. The lift amplifier drives the lift capacitor when the input signal voltage is greater than an input threshold voltage, the input threshold voltage having a value greater than a common mode voltage of the input signal voltage.
REFERENCES:
patent: 4466107 (1984-08-01), Stoner
patent: 5909135 (1999-06-01), Baldwin et al.
patent: 6275078 (2001-08-01), Zabroda
patent: 6411136 (2002-06-01), Nianxiong et al.
Bicakci Ara
Conroy Cormac S.
Lee Sang-Soo
LSI Logic Corporation
Nu Ton My-Trang
Thelen Reid & Priest LLP
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