Amplifiers – Hum or noise or distortion bucking introduced into signal...
Reexamination Certificate
2001-06-15
2002-10-15
Pascal, Robert (Department: 2817)
Amplifiers
Hum or noise or distortion bucking introduced into signal...
C330S136000, C375S297000
Reexamination Certificate
active
06466092
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a distortion compensation apparatus. More particularly, it relates to a method and apparatus applicable to a high frequency power amplifier for transmission usable in particular in a portable telephone set.
2. Description of Related Art
In keeping up with increasing speed and increasing capacity in communication, the demand for linearity in a transmission power amplifier in a digital radio communication equipment is becoming more and more strict. This, however, obstructs improvement in the power efficiency in the power amplifier.
On the other hand, the continuous call time of a digital portable telephone set now in widespread use in general is becoming longer. Thus, in offering a new digital radio communication equipment to the market, its using time cannot be discounted in view of the competition power proper to a product. With this in view, the trend towards introducing the technique of distortion compensation for improving the efficiency is becoming brisk.
However, this technique is in need of a voluminous circuit scale and is extremely difficult to realize in a portable telephone set which features small size and lightness in weight. Moreover, because of the properties of the portable terminal, the environment in which the set is used id changed significantly, such that it is imperative to realize this distortion compensation by adaptive distortion compensation in order to follow up with these changes in environment. This poses a serious problem in conjunction with the demand for reduction in size. As a device for distortion compensation, there is known a technique of pre-distortion employing compensation means having opposite characteristics to those of the distortion of the power amplifier.
As this technique of pre-distortion, there are several reports as to adaptations of pre-distortion and adaptations of feedforward techniques. Several conventional techniques in the field of the adaptive secondary cell device used for the pre-distortion are hereinafter explained.
As a first conventional stricture,
FIG. 1
shows a block diagram of a technique introduced e.g., in 1992. European Microwave Conference Vol. 22, pp. 1125 to pp. 1130, “Power Amplifier Adaptive Linearization Using Predistortion with Polynominal”.
Referring to
FIG. 1
, if non-linear input/output characteristics of a power amplifier (PA)
114
, the distortion of which is to be compensated, are given by Vout=A(Vin), in-phase and quadrature signals I, Q of the input baseband to be input at an input terminal
111
may be calculated by a linearization comparator circuit
112
using a function H(I, Q) which linearizes A(Vin). The resulting I, Q signals are fed to a digital to analog converter (DAC)
113
and thereby analogized, while being converted into high frequency band signals which are input to a power amplifier
114
. An output Vout of the power amplifier
114
is detected and output from an output terminal
115
, at the same time as it is converted in a demodulator circuit
116
into baseband signals If and Qf. As for adaptive compensation for coping with changes in temperature, the linearization comparator circuit
112
compares the input signals I, Q to detection signals If, Qf to adjust a constant in a linearization function H so that a difference therebetween will be equal to zero. This operation is repeated until the difference is correctly equal to zero to set the constant in the function H (I, Q) ultimately to a proper value.
As another conventional structure, there is, for example, a technique disclosed in IEEE Transaction on Vehicular Technologies, Vol. 43, No. 2, May 1994, pp. 323 to pp. 332, “Adaptive Linearization Using Predistortion”.
FIG. 2
herein shows a block diagram disclosed in this publication. In
FIG. 2
, those parts or components corresponding to those shown in
FIG. 1
are denoted by the same reference numerals. A conversion table
124
, such as a memory, is accessed for the input signals I and Q to effect data conversion to derive data I′, Q′ capable of linearizing the power amplifier
114
. These data I′, Q′ are input to the power amplifier
114
. An output Vout of the power amplifier
114
is detected and converted in a demodulator
116
to produce signals If, Qf. For adaptive compensation, there is provided an address generator
123
for comparing the input signals I, Q to detection signals If, Qf from the demodulator
116
to adjust the address for accessing the conversion table
124
so that a difference en will be zero. The address generator
123
is repeatedly adjusted until the difference en is correctly zero to optimize the address value which accesses the conversion table
124
.
In the above-described conventional structures, the constant included in the linearization function or the address for accessing the linearization table is optimized. However, in these structures, repetitive operations are carried out using a feedback loop to reduce the difference. However, the feedback loop suffers a serious problem that the loop contains characteristics of the power amplifier
114
such that there is no guarantee that the convergence to an optimum value in stability will be realized at all times.
Moreover, the above-described conventional structures are in need of a demodulator in order to effect conversion of the power amplifier output into the baseband output. Since this demodulator is in general a quadrature demodulator, the circuit scale is voluminous.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a method and apparatus for distortion compensation whereby the distortion component of a device such as a power amplifier can be compensated extremely readily.
It is another object of the present invention to provide a method and apparatus which is not in need of the demodulator to simplify the structure.
In one aspect, the present invention provides a distortion compensation apparatus for compensating distortion components generated in a device, including adaptive amplitude distortion compensation means for finding an amplitude difference between an envelope signal of an input signal supplied to the device and an envelope signal of an output signal of the device, outputting adaptive correction data of amplitude distortion against temperature fluctuations in the device based on cumulative results of integration of the amplitude difference and for adaptively compensating the amplitude distortion of the device using the adaptive correction data.
Preferably, the distortion compensation apparatus includes amplitude distortion correcting means for outputting correction data for correcting the amplitude distortion of the device based on the envelope signal of the input signal supplied to the device, and for controlling the gain changing processing of the device responsive to the correction data to correct the amplitude distortion of the device.
Preferably, the adaptive amplitude distortion compensation means sums the adaptive correction data to the correction data used in the amplitude distortion correcting means to effect adaptive compensation of the amplitude distortion of the device.
Preferably, the adaptive amplitude distortion compensation means includes first envelope detection means for detecting an envelope signal of an input signal supplied to the device, second envelope detection means for detecting the envelope component of an output signal of the device, subtraction means for finding an amplitude difference between the envelope component of the input signal as detected by the first envelope detection means and the envelope component of the output signal as detected by the second envelope detection means, cumulating means for integrating and cumulating the amplitude difference as obtained by the subtraction means and adaptive correction data outputting means for outputting adaptive correction data against temperature fluctuations in the device based on the cumulated results in the cumulating means.
Preferably, the distortion co
Choe Henry
Maioli Jay H.
Pascal Robert
Sony Corporation
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