Zero-overhead class G amplifier with threshold detection

The present invention is generally related to the field of line driver devices, and more particularly to an apparatus and method for reducing the overhead power dissipation of an ADSL line driver amplifier.

Generally, line drivers used in Central Office (CO) operating Asymmetrical Digital Subscriber Line (ADSL) applications have been known to dissipate too much power. Although progress has been made in the last several years in reducing line driver power dissipation, the demand for increased circuit density in a fixed space with fixed thermal cooling capabilities requires that line driver power dissipation be decreased even further.

Conventional line driver amplifiers are typically Class G topology amplifiers which linearly and continuously transition between the upper and lower power supplies of the amplifier. These power supply voltages typically use varying amounts of current from both supplies depending on the amplitude of the signal being amplified. However, this requires the amplifier to generate an overhead voltage in its output stage so as to prevent distortion in the amplified signal. This overhead voltage significantly increases the power dissipation of the device.

Accordingly, there is needed a line driver device having reduced power dissipation that allows for higher density packaging of ADSL circuits.

The present invention achieves technical advantages as a line driver circuit that takes advantage of the “peaky” nature of an ADSL signal by running a line driver amplifier from a lower set of power supply voltages as a baseline, and from a higher set of voltages only when the amplitude of the signal being transmitted requires it. Advantageously, this reduces the power dissipation in the line driver by operating the line driver the majority of the time from the lower supply voltage.

In one embodiment, the invention is an ADSL line driver circuit with reduced power consumption capabilities. The line driver circuit includes an amplifier amplifying the input signal. Preferably, a switching circuit is adapted to selectively establish which power supply voltages are driving the line amplifier. This switching is initiated in response to detecting the voltage amplitude of the input signal reaching a predetermined threshold level.

In another embodiment, the invention is a method for reducing the power consumption of an ADSL line driver circuit, where the method includes the steps of receiving a input signal having a voltage amplitude, and amplifying the input signal using an amplifier in response to the detected amplitude of the input signal. The amplifier is discretely powered by a selected power supply voltage. Advantageously, the line driver amplifier is discretely switched between an upper and lower set of supply voltages in order to draw required current from either the upper or lower power supplies as a function of the input signal amplitude. A delay circuit issued to allow the switching of power supplies driving the amplifier.

For a more complete understanding of the present invention, reference is made to the following detailed description taken in conjunction with the accompanying drawings wherein:

FIG. 1 shows an ADSL line driver driven by multiple power supplies and responsive to a threshold detection circuit in accordance with the present invention; and

FIG. 2 illustrates an algorithm for reducing the power consumption of an ADSL line driver circuit in accordance with the exemplary embodiment of the present invention.

The numerous innovative teachings of the present application will be described with particular reference to the presently preferred exemplary embodiments. However, it should be understood that this class of embodiments provides only a few examples of the many advantageous uses and innovative teachings herein. Moreover, some statements may apply to some inventive features, but not to others.

FIG. 1 shows an ADSL line driver circuit 10 discretely operating from different power supplies and having a threshold detection circuit in accordance with the present invention. The line driver circuit 10 includes a delay circuit 14 , a D/A converter 16 , and a comparator 18 . The line driver circuit 10 is also seen to include a line driver amplifier 20 , as well as switches 22 and 24 which selectively couple one of the two sets of power supplies to the power supply terminals of the amplifier 20 as a function of the input signal amplitude. In operation, the present invention reduces the power dissipation in the line driver 20 by operating the line driver 20 from a lower set of power supply voltages (+/−VCCL) the majority of the time. By using switches 22 and 24 , the amplifier transitions between at least two power supplies, the line amplifier's 20 overhead voltage is reduced and its power dissipation is diminished.

As shown, the comparator 18 determines and controls when the switches 20 and 27 switch the line driver amplifier 20 between power supplies by comparing an input signal 12 to be amplified with a predetermined threshold value 17 . If, for example, the amplitude of the transmitted signal 12 is determined to exceed a predetermined threshold 17 and amplifier 20 needs a higher power supply voltage to support it, the line driver 20 is responsively and discretely switched to the higher supplies (+/−VCCH) by switches 22 and 24 . Conversely, the comparator 18 discretely returns the line driver 20 to the lower supplies (+/−VCCL) when the signal 12 determined by comparator 18 to be is less than the threshold 17 .

In this instance, although switching between two power supply voltages is illustrated, limitation on the number power supplies to which the line driver amplifier 20 may be switched is not to be inferred and more than two power supply sets could be utilized. Moreover, although the input signal 12 is illustrated as an ADSL signal, commonly a digital signal, it should be understood that any number of signals may be inputted through the line driver circuit 10 , such as an analog signal, for example according to the present invention.

In the selected embodiment, the invention is seen to include a delay circuit 14 having the input signal 12 passed therethrough. Delay circuit 14 is adapted to delay the input signal longer than the comparator processing time in order to allow time for the line driver power supply switches 22 and 24 to transition the corresponding voltage levels to the amplifier 20 . That is, when comparator 18 determines that the input signal 12 is to be amplified by line driver 20 operating from a different set of power supplies, the delay circuit 14 delays the input sufficiently long to allow both detection by comparator 18 and switching by switches 22 and 24 , such as 0.5 μsec.

In yet another embodiment, greater power reduction can be achieved by applying hysteresis to the switching thresholds of comparator 18 such that the falling edge threshold voltage is higher than the rising edge threshold, thus advantageously keeping the lower overhead power supply voltage on the output transistors of the line driver amplifier 20 lower during the falling edge.

Referring to FIG. 2, there is illustrated a line driver power reduction algorithm 200 in accordance with present invention. The power reduction algorithm 200 begins with a receiving act 210 where the input signal 12 , preferably an digital signal, is received by a delay circuit 14 , as depicted in FIG. 1 .

Next, a switching act 214 discretely transitions the amplifier 20 to operate from between a lower and a higher power supply, or vice versa, based on the amplitude of input signal 12 . Specifically, the switching act 214 comprises comparing the amplitude of the input signal 12 with the threshold value 17 . Delay act 216 momentarily delays the input signal 12 before it is coupled to D/A converter 16 , where a converting act 218 converts the input signal 12 to an analog signal 19 . The switching act 214 is followed by an amplifying act 212 which amplifies the analog signal 19 .

As such, in the preferred embodiment, the present invention is able to transition between the upper and lower power supplies of the amplifier 20 in response to a signal generated by comparator 18 . If, for example, the input signal 12 is less than the threshold value 17 , the comparator 18 responsively triggers switches 22 and 24 to operate the line amplifier 20 at the lower supply voltages. If, however, the comparator determines that the input signal 12 exceeds the predetermined threshold value 17 , the comparator 18 responsively triggers the switches 22 and 24 to operate the line amplifier 20 at the higher supply voltages and to draw a higher required current.

Accordingly, the invention advantageously monitors the changing voltage amplitude of the input signal 12 —which is normally amplified by line amplifier 20 running from a lower set power supply voltages—and discretely switches the line amplifier 20 to operate from a higher set of power supply voltages when the transmitted analog signal 19 needs it. By discretely transitioning between a plurality of power supply voltages, the invention reduces the power dissipation in the line driver circuit 10 by operating the line driver amplifier 20 the majority of the time from a lower supply voltage.

Though the invention has been described with respect to specific preferred embodiments, many variations and modifications will become apparent to those skilled in the art upon reading the present application. It is therefore the intention that the appended claims be interpreted as broadly as possible in view of the prior art to include all such variations and modifications.