Switchless high efficiency amplifier

Amplifiers – With plural amplifier channels – Redundant amplifier circuits

Reexamination Certificate

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Details

C330S195000

Reexamination Certificate

active

06300828

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates generally to a method and apparatus for providing a switchless high efficiency amplifier, and in particular, to a method and apparatus for providing an amplifier that switches between an amplifier that handles typical lower loads and an amplifier that handles the higher peak loads.
BACKGROUND OF THE INVENTION
As is well known, an amplifier is a device that receives an input and applies a defined gain in order to produce an output that is greater than the input. For example, a voltage amplifier may receive a 10V input and produce an output of 20V, if the voltage amplifier has a gain of two. Amplifiers are able to apply the gain to produce an output up to a certain value. For example, a voltage amplifier can produce an output up to a value of the operational voltage applied to the amplifier. That is, a voltage amplifier with an operational voltage of 15V and a gain of three can produce the desired output as long as the input does not exceed 5V. If the voltage amplifier receives an input voltage of 6V it would attempt to produce an output of 18V, which is above the maximum that this voltage amplifier can produce. Therefore, the voltage amplifier would not have the potential to drive the load to the desired voltage. Thus, when designing a device utilizing an amplifier, assurances should be made that the amplifier can handle the maximum input that will be received. That is, if the typical range of input voltages is 3-5V but a peak voltage of between 6-8V is possible, the amplifier should be capable of handling an 8V input.
Amplifiers work best if they are producing outputs that are near the maximum output that the amplifier can handle. That is, a 15V amplifier works most efficiently when producing outputs around 15V. However, the typical outputs of a 15V amplifier are probably much lower since the 15V operating voltage (i.e., maximum output) was selected to handle peak input voltages. For example, the maximum input voltage (peak voltage) for a 15V amplifier with a gain of three is 5V, and a typical input voltage may be in the range of 1-3V. An example 15V amplifier is illustrated in
FIG. 1. A
voltage supply V
s
is connected to the amplifier A. The amplifier A is powered by an operational voltage of 15V. The gain of the amplifier A is three as defined by resistors R
1
and R
2
. The output voltage V
o
of the amplifier A is applied to the load R
L
. As the chart depicts the typical range of voltage inputs to the amplifier A from the voltage supply V
s
is between 1-3V so that the typical output voltage V
o
is between 3-9V. Therefore, the output voltage V
o
ranges between 20-60% of the peak output potential for the typical input. Thus, the amplifier A is typically very inefficient.
FIG. 1
depicts the amplifier A receiving a peak voltage from the voltage source V
s
at time t7, at which time the amplifier A is at 100% efficiency. The amplifier A runs at peak efficiency only at the periods of time when peak input voltages are being received by the amplifier A.
Thus, an inherent problem associated with standard amplifiers is the conflict between the desirability of providing large output potentials and the undesirability of providing lower potentials through a large potential drop. One solution proposed is to provide separate amplifiers which each operate efficiently within a range. One amplifier would be designed to handle the typical inputs, while the other amplifier would be designed to handle the peak inputs. Switching between these two amplifiers would provide both efficiency and the capability of handling peak inputs. However, this type of dual amplifier has seldom been utilized because a complex switching means is required. For example, as illustrated in
FIG. 2
, a switching circuit would be required to receive the input voltage and make a determination of which of the two amplifiers the voltage should be applied to.
Thus, there is a need for an amplifier that provides high efficiency and high potential capability that does not require a complex switching mechanism.
SUMMARY OF THE INVENTION
The present invention relates to an amplifier that can handle peak inputs while maintaining high efficiency. To accomplish this, an amplifier is provided that contains at least two separate amplifiers. One amplifier is used for the typical inputs that are received from an input source and a second amplifier is used solely for peak inputs. Utilizing the second amplifier to handle the peak inputs allows the first amplifier to concentrate solely on the typical inputs. Thus, for example, the operating voltage of a first voltage amplifier can be reduced so that the output voltage is a large percentage of the operating voltage and is operating at close to peak efficiently. Instead of using complex switching devices to switch between the first voltage amplifier and the second voltage amplifier, a small resistor is placed between the output of the second voltage amplifier and the load. The resistor reduces the output voltage of the second voltage amplifier available to be applied to the load. Thus, when the output of the first voltage amplifier and the output of the second voltage amplifier are the same, the first voltage amplifier will provide current to the load since the voltage available to be applied to the load is greater for the first voltage amplifier. When the input voltage exceeds the operational value for the first voltage amplifier the first voltage amplifier is of such a type that it becomes reverse biased and logically disconnects itself from the load. When this happens, the resistance connected to the output of the second voltage amplifier does not reduce the output voltage enough to prevent current from flowing from the second voltage amplifier to the load. Once the input voltage returns to a value within the limits of the first voltage amplifier, the first voltage amplifier becomes operational again, and the resistor again becomes a barrier to current flowing from the second voltage amplifier to the load. Thus, the inventive amplifier provides a simple design for producing an amplifier with high efficiency and high potential capability.


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Low-Power ADSL Central-Office Line Driver, Texas Instruments, product preview, 1999, 6 pgs.

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