Amplifiers – With plural amplifier channels – Redundant amplifier circuits
Reexamination Certificate
1999-09-30
2001-07-03
Pascal, Robert (Department: 2817)
Amplifiers
With plural amplifier channels
Redundant amplifier circuits
C330S051000, C330S149000
Reexamination Certificate
active
06255906
ABSTRACT:
BACKGROUND
1. Technical Field
The present invention relates generally to semiconductor devices; and, more particularly, it relates to power amplification circuitry.
2. Related Art
Many traditional power amplifiers feed signal with a non-constant envelope into a power amplifier array. One type of power amplifier is an envelope elimination and restoration (EER) power amplifier wherein the non-constant envelope is fed into the power amplifier so that the control of how to bias the power amplifier array is governed primarily by the non-constant envelope. One method of biasing the elimination and restoration (EER) power amplifier is to adjust the bias voltage as a function of the envelope of the electrical signal. This real time adjustment to the bias voltage presents a number of difficulties. The characteristic input impedance of the power amplifier tends to fluctuate as a function of the bias voltage provided to it. Also, the characteristic output impedance of the power amplifier tends to fluctuate as a function of the bias voltage provided to the power amplifier. In addition, the ambient environmental conditions in which the power amplifier is placed tend to affect its characteristic impedance. Absent some sophisticated compensation algorithms, conventional technologies that employ analog voltage biasing suffer from deleterious operation in dynamic environments.
There are significant problems with conventional power amplifiers in terms of efficiency of the feeding of a signal with a non-constant envelope to the power amplifier array. One particular problem is that a bias point is chosen for optimal operation at one (peak) power level. However, the non-constant envelope is inherently non-constant, therefore the power amplifier is only energy efficient at the designated peak level. In order to make the power amplifier efficient over a range of output power, its bias must be continually modified, which is substantially difficult to do. This is due largely to the real-time modification and varying of the voltage that is given to the power amplifier array which is very inefficient in terms of energy consumption.
One attempted solution to overcome the problems associated with conventional power amplifiers was the introduction in the 1950s of the elimination and restoration (EER) power amplifier. The elimination and restoration (EER) power amplifier adapts the voltage level of the voltage bias for the power amplifier array to the envelope power level of the non-constant envelope that is required at the output. This solution is one that does provide for optimal voltage bias at a variety of non-constant envelope levels, but it has many deficiencies itself. That is to say, although the solution of the elimination and restoration (EER) power amplifier does present a solution to some problems associated with conventional power amplifiers, it nevertheless introduces some undesirable problems. First, the efficiency of the bias adaptation technique employed by the elimination and restoration (EER) power amplifier inherently requires an additional amplifier. Also, the calibration of the elimination and restoration (EER) power amplifier is of utmost importance to ensure that the waveform fidelity of the waveform that is being amplified maintains its original shape including its spectral content.
The envelope digital to analog converter (DAC) power amplifier is a subset of the elimination and restoration (EER) power amplifier. Here, a power amplifier array of a power amplifier is treated as a purely digital device wherein each power amplifier within the power amplifier array is turned ON/OFF as required by the specific application. Various sizes of power amplifiers are employed within a power amplifier array to realize the required output levels within various applications. The envelope digital to analog converter (DAC) power amplifier is a very efficient technique to obtain adjustable optimal output power levels using a power amplifier. However, the deficiencies of the envelope digital to analog converter (DAC) power amplifier are great, similar to the deficiencies of the elimination and restoration (EER) power amplifier. For example, waveform fidelity of an original signal can easily be compromised without very good calibration of the envelope digital to analog converter (DAC) power amplifier. In addition, the input impedance of the envelope digital to analog converter (DAC) power amplifier tends to change as a function of the voltage that is used to bias the envelope digital to analog converter (DAC) power amplifier. Similarly, the output impedance of the envelope digital to analog converter (DAC) power amplifier tends to change as a function of the voltage that is used to bias the envelope digital to analog converter (DAC) power amplifier.
Further limitations and disadvantages of conventional and traditional systems will become apparent to one of skill in the art through comparison of such systems with the present invention as set forth in the remainder of the present application with reference to the drawings.
SUMMARY OF THE INVENTION
Various aspects of the present invention can be found in a power amplifier that amplifies an electrical signal. The power amplifier is operated as a completely digital device with a certain degree of digital pre-distortion compensation. The power amplifier contains, among other things, a number of power amplifiers connected in parallel and a control circuitry that switches on at least one power amplifier, selected from the number of power amplifiers. At least one power amplifier receives a voltage of saturation. That is to say, one of the power amplifiers is operated in a manner wherein it is fully ON or fully OFF. Either it receives a sufficient voltage that pushes it into saturation, or it receives no voltage whatsoever, i.e., cut-off. In addition, at least one additional power amplifier within the number of power amplifiers receives no voltage (cutoff) in certain embodiments of the invention.
In certain embodiments of the invention, the power amplifier amplifies an electrical signal having a magnitude and a phase. The magnitude passes through a first path as determined by the number of power amplifiers. The phase passes through a second path, also determined by the number of power amplifiers. The electrical signal is subsequently passed to an antenna. Certain embodiments of the invention also contain a time delay compensation circuitry that substantially minimizes any time delay mismatch between the first path and the second path through the number of power amplifiers, and a pre-distortion circuitry that substantially compensates for any impedance mismatch between the first path and the second path of the power amplifier and the antenna.
In certain embodiments of the invention, the first path is exclusively for an envelope and the second path is exclusively for a phase. The first path is sub-divided into parallel control word (similar to a digital to analog converter (DAC)) that enable parallel drivers which are analogous to the individual power amplifiers of a power amplifier array in the invention. The digital pre-distortion compensation compensates for gain and phase distortions that would result when the control word values change. For example, as the number of power amplifiers that are selected at any given time is changed, the input and output impedance of the power amplifier changes. The digital pre-distortion compensation, provided in accordance with the invention, provides a solution to minimize this undesirable effect and provide optimal performance.
The time delay compensation circuitry substantially minimizes any time delay mismatch between the first path and the second path performs the time delay compensation in real time. Time delay is introduced when the electrical distance between the first path and the second path (e.g. between an envelope path and a phase/RF path) are not the same. The abbreviation RF is a term of art for radio frequency and is well known in the art. Typically, these time delays are not the same because the RF components
Eidson Donald Brian
Grange Robert Edmund
Lindstrom Mats
Akin Gump Strauss Hauer & Feld L.L.P.
Conexant Systems Inc.
Nguyen Patricia T.
Pascal Robert
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