Pre-distortion apparatus of power amplifier and method thereof

A pre-distortion apparatus of a power amplifier includes: a pre-distortion unit configured to generate a pre-distorted signal of an input signal by calculating a magnitude of the input signal and outputting a complex correction coefficient corresponding to the calculated magnitude of the input signal, and provide the generated pre-distorted signal as an input of the power amplifier; and a complex correct coefficient update unit configured to generate an error signal by comparing an output signal of the power amplifier with the input signal and updating the complex correction coefficient to minimize a magnitude of the generated error signal, wherein the pre-distortion unit provides a constant bias value corresponding to the magnitude of the input signal as a bias of the power amplifier while updating the complex correction coefficient.

CROSS-REFERENCES TO RELATED APPLICATIONS

The present application claims priority of Korean Patent Application Nos. 10-2009-0088208 and 10-2010-0062781, filed on Sep. 17, 2009, and Jun. 30, 2010, respectively, which are incorporated herein by reference in their entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

Exemplary embodiments of the present invention relate to a pre-distortion apparatus and a method thereof; and, more particularly, to a pre-distortion apparatus for minimizing distortion of an output signal output from a power amplifier and a method thereof.

2. Description of Related Art

In wired/wireless communication system, a transmitter amplifies a power of a transmission signal to be reached at a receiver because the transmission signal is attenuated in a wired/wireless channel. The transmitter commonly employs a power amplifier for amplifying the power of the transmission signal.

The power amplifier must maintain linearity of an input signal and an output signal to improve efficiency. However, the power amplifier has a non-linearity property.

Many methods have been introduced to linearize the non-linearity property of the power amplifier. Among them, a digital pre-distortion method was introduced to improve the non-linearity property of the power amplifier. The digital pre-distortion method distorts an input signal in advance to linearize a relation between an input signal and an output signal of a power amplifier.

Particularly, the digital pre-distortion method includes a complex gain type digital pre-distortion method and a polynomial type digital pre-distortion method. The complex gain type digital pre-distortion method calculates a complex correction value according to a magnitude of an input signal by adaptively comparing the input signal with a non-linear distorted signal and corrects the input signal in real time based on the complex correction value. The polynomial type digital pre-distortion method approximates a non-linear property of a power amplifier to a polynomial expression, adaptively calculates a coefficient of the polynomial expression from input and output signals, calculates an inverse transfer function of the power amplifier, and corrects a transmission signal based on the inverse transfer function.

A complex gain type digital pre-distortion apparatus provides a linearization method when a property of a power amplifier is not changed due to a constant bias voltage. Lately, a high power amplifier is commonly used. The high power amplifier has a bias voltage dynamically changing according to an input signal. Accordingly, the property of the high power amplifier is changed according to a magnitude of an input signal. Therefore, it is difficult to linearize the high power amplifier using the digital pre-distortion apparatus.

When a communication system employs a pre-distortion apparatus with a high power amplifier having a bias varying according to an input signal, a bias voltage of the high power amplifier is changed while updating a complex correction coefficient. Therefore, a convergence property of an adaptive algorithm is deteriorated.

SUMMARY OF THE INVENTION

An embodiment of the present invention is directed to a pre-distortion apparatus for minimizing distortion of an output signal by linearizing a power amplifier, and a method thereof.

Another embodiment of the present invention is directed to a pre-distortion apparatus for fixing a bias voltage of a power amplifier while updating a complex correction coefficient, and a method thereof.

In accordance with an embodiment of the present invention, a pre-distortion apparatus of a power amplifier includes: a pre-distortion unit configured to generate a pre-distorted signal of an input signal by calculating a magnitude of the input signal and outputting a complex correction coefficient corresponding to the calculated magnitude of the input signal, and provide the generated pre-distorted signal as an input of the power amplifier; and a complex correct coefficient update unit configured to generate an error signal by comparing an output signal of the power amplifier with the input signal and updating the complex correction coefficient to minimize a magnitude of the generated error signal, wherein the pre-distortion unit provides a constant bias value corresponding to the magnitude of the input signal as a bias of the power amplifier while updating the complex correction coefficient.

In accordance with an embodiment of the present invention, a pre-distortion method of a power amplifier includes: calculating a magnitude of an input signal; outputting a complex correction coefficient and a bias value of the power amplifier corresponding to the calculated magnitude of the input signal; providing the bias value as the a bias of the power amplifier while updating the complex correction coefficient; generating a pre-distorted signal by multiplying the complex correction coefficient with the input signal; generating an error signal by comparing the output signal and the input signal of the power amplifier; and updating the complex correction coefficient to minimize a magnitude of the generated error signal.

DESCRIPTION OF SPECIFIC EMBODIMENTS

Embodiments of the present invention relate to a pre-distortion apparatus for linearizing a high power amplifier having a non-linearity property decided according to a magnitude of an input signal and a method thereof. The pre-distortion apparatus in accordance with an embodiment of the present invention minimizes distortion of an output signal output from a high power amplifier by adaptively calculating a complex correction value according to a magnitude of an input signal and effectively compensating an input signal using the calculated complex correction value.

Hereinafter, the pre-distortion apparatus and method in accordance with an embodiment of the present invention will be described with reference to the accompanying drawings.

FIG. 1is a block diagram illustrating a complex gain type digital pre-distortion apparatus.

Referring toFIG. 1, the complex gain type digital pre-distortion apparatus includes a signal magnitude calculator101, a one-dimensional complex lookup table102, a multiplier103, a power amplifier104, an attenuator105, a delay filter106, an adder107, and an adaptive algorithm processor108.

The signal magnitude calculator101calculates a magnitude of a transmission signal x(n).

The one-dimensional complex lookup table102receives the calculated magnitude of the transmission signal from the signal magnitude calculator101. The one-dimensional complex lookup table102previously stores complex correction coefficients according to magnitudes of input signals. The one-dimensional lookup table102outputs a complex correction coefficient corresponding to the calculated magnitude of the transmission signal.

The multiplier103multiplies the complex correction coefficient outputted from the one-dimensional complex lookup table102with the transmission signal x(n) and outputs a pre-distortion signal z(n).

A digital-analog converter (not shown) and a frequency up-convertor (not shown) convert the pre-distortion signal z(n) output from the multiplexer103to a Radio Frequency (RF) signal. The RF signal is input to the non-linear power amplifier104.

An output signal of the power amplifier104is fed back to the attenuator105.

The attenuator105reduces the magnitude of the feedback signal as much as a gain of the power amplifier104.

The attenuated signal of the attenuator105is converted to a digital signal and is input to the comparator107.

The delay filter106generates a delayed signal by filtering the original transmission signal x(n). The comparator107receives the delayed signal from the delay filter106and compares the delayed signal with a digital output signal. The comparator107generates an error signal e(n) based on the comparison result.

The adaptive algorithm processor108updates the complex correction coefficients stored in the one-dimensional lookup table102using a least square method in order to minimize the magnitude of the error signal e(n) output from the comparator107.

As shown inFIG. 1, the complex gain type digital pre-distortion apparatus introduces a linearization method when the property of the power amplifier104is not changed by a constant bias voltage. However, a high power amplifier has been commonly used lately. The high power amplifier has a bias voltage changed according to an input signal. Therefore, the property of the high power amplifier is changed according to the magnitude of an input signal. As a result, it is difficult to linearize the high power amplifier using the typical digital pre-distortion apparatus shown inFIG. 1.

Further, when the pre-distortion apparatus ofFIG. 1is employed with a high power amplifier having a bias varying according to an input signal, a bias voltage of a high power amplifier is changed while updating a complex correction coefficient. Therefore, a convergence property of an adaptive algorithm becomes deteriorated.

In order to overcome the programs of the typical pre-distortion apparatus, an embodiment of the present invention relates to a pre-distortion apparatus for minimizing distortion of an output signal output from a power amplifier and a method thereof.

FIG. 2is a block diagram illustrating a pre-distortion apparatus in accordance with an embodiment of the present invention.

Referring toFIG. 2, the pre-distortion apparatus in accordance with an embodiment of the present invention includes a pre-distortion unit210, and a complex correction coefficient update unit240.

The pre-distortion unit210generates a pre-distorted signal z(n) of an input signal x(n) by calculating a magnitude of the input signal x(n) and outputting a complex correction coefficient corresponding to the calculated magnitude of the input signal x(n). Then, the pre-distortion unit210provides the generated pre-distorted signal z(n) to an input terminal of a power amplifier (PA)220.

The pre-distortion unit210provides a constant bias voltage value corresponding to the magnitude of the input signal x(n) to a bias terminal of the power amplifier200while updating the outputted complex correct coefficient.

The pre-distortion unit210will be described in detail with reference toFIG. 2.

Referring toFIG. 2, the pre-distortion unit210includes an input signal magnitude calculator211, a quantization mapper213, a one-dimensional lookup table215, and a multiplier217.

The input signal magnitude calculator211receives the input signal x(n) and calculates the magnitude of the input signal x(n).

The quantization mapper213quantizes the calculated magnitude of the input signal x(n) from the input signal magnitude calculator211. The quantization mapper213maps the quantized data to one of memory addresses. The quantization mapper213outputs the mapped memory address to the one-dimensional lookup table215.

The one-dimensional lookup table215outputs a complex correction coefficient and a bias voltage value, which are indicated by the input memory address. Hereinafter, the one-dimensional lookup table215will be described with reference toFIG. 3.

FIG. 3is a block diagram illustrating the one-dimensional lookup table in the pre-distortion apparatus in accordance with an embodiment of the present invention.

Referring toFIG. 3, the signal magnitude calculator211receives an input signal x(n), divides a time (x-axis) by a plurality of predetermined samples and calculates the magnitude of the input signal x(n) of each sample.

The quantization mapper213receives the calculated magnitude data from the input signal magnitude calculator211, quantizes the magnitude data, and maps the quantized data to predetermined memory addresses. For example, the input signal magnitude is divided into eight levels (3-bits) and each level is mapped to a different memory address. If the magnitude of the input signal is in 0.25-0.31252, the input signal is mapped to a memory address Add3which is allocated to a level of 0.2˜50.31252. The quantization mapper213outputs the memory address Add3to the one-dimensional lookup table215.

The one-dimensional look table215receives the predetermined memory address Add3and outputs complex correction coefficients Mag3and Ang3and a bias value bias3, which are indicated by the received memory address Add3. The output complex correction coefficients Mag3and Ang3are input to the multiplier217shown inFIG. 2, and the bias value bias3is input to the bias provider230and used as a bias voltage of the power amplifier220. Although a magnitude of an input signal x(n) mapped to the memory address Add3is different, the one-dimensional lookup table215always outputs a Bias value corresponding to the address Add3to be used as a bias value of the power amplifier. Therefore, the bias of the power amplifier220can be fixed while the complex correction coefficients Mag3and Ang3are updated.

The multiplier217multiplies the complex correction coefficient output from the one-dimensional lookup table215with the input signal x(n) and outputs the multiplying result as the pre-distorted signal s(n).

The complex correction coefficient update unit240generates an error signal e(n) by comparing the output signal y(n) of the power amplifier220with the input signal x(n) and updates the complex correction coefficient output from the one-dimensional lookup table215in order to minimize the magnitude of the generated error signal e(n).

Particularly, the complex correction coefficient update unit240includes a delay filter241, a comparator243, and an adaptive algorithm processor245.

The delay filter241delays the input signal x(n) as long as a predetermined time for synchronizing an initial input signal x(n) with an output signal of the power amplifier220after passing through the pre-distortion unit210.

The attenuator250receives the output signal y(n) from the power amplifier220and attenuates the outputs signal. The comparator243receives an attenuated signal from the attenuator250and generates the error signal e(n) by subtracting the attenuated output signal from the delayed input signal from the delay filter241.

The adaptive algorithm processor245receives the generated error signal e(n) from the comparator243and updates the complex correction coefficients stored in the one-dimensional lookup table215using an adaptive algorithm such as the least square method in order to minimize the error signal e(n).

The bias provider230receives the bias voltage value from the one-dimensional lookup table215, converts the bias voltage value to an analog signal, modulates the analog signal, and outputs the modulated signal to the bias terminal of the power amplifier220.

The bias provider230may include a digital analog converter231and a bias modulator233. The digital analog converter231converts the digital bias value from the one-dimensional lookup table215to an analog bias value signal. The bias modulator233modulates the analog bias value signal o from the digital analog converter231and outputs the modulated signal to the bias terminal of the power amplifier220.

InFIG. 2, the digital frequency up-converter251converts the pre-distorted signal z(n) to an analog pre-distorted signal, up-converts the analog pre-distorted signal with reference to a local oscillation frequency of the local oscillator253to a RF signal, and outputs the RF signal. The RF signal output from the digital frequency up-converter251is input to an input terminal of the power amplifier220.

The attenuator260attenuates the output signal y(n) from the power amplifier220as much as a gain of the power amplifier220.

The digital frequency down-converter255converts the attenuated signal from the attenuator260to a digital signal and down-converts the digital signal with reference to a local oscillator frequency of the local oscillator253. The digital frequency down-converter255outputs the down-converted signal to the comparator243of the complex correction coefficient update unit240.

Hereinafter, a pre-distortion method in accordance with an embodiment of the present invention will be described with reference toFIG. 4.

Referring toFIG. 4, at step S410, a magnitude of a transmission signal such as an input signal x(n) is calculated. Particularly, a time is sampled as predetermined samples and calculates a representative value of each sample.

At step S420, magnitude data of the input signal for each sample is quantized and mapped. The magnitude data of the input signal is mapped to a predetermined memory address. For instance, an input signal magnitude is divided into eight levels (3-bits) and different memory addresses are allocated to each level. If the input signal magnitude is in between 0.25 to 0.31242, the input signal is mapped to a memory address Add3which is allocated to a 0.25-0.31252 level.

At step S430, a complex correction coefficient indicated by the predetermined memory address is output with reference to the one-dimensional lookup table. Further, a constant bias value is output too. As shown inFIG. 3, the one-dimensional lookup table stores different complex correction coefficients and bias values for each memory address. Therefore, the one-dimensional lookup table can output a complex correction coefficient and a bias value, which are indicated by the input memory address. For example, when the one-dimensional lookup table receives a memory address Add3, the one-dimensional lookup table outputs the complex correction coefficients Magi and Ang3and a bias value (bias3) which are indicated by the input address Add3.

At step S440, a pre-distorted signal is generated by multiplying the output complex correction coefficients with the input signal.

The output bias value is converted to an analog signal, modulated through a bias modulator, and used as a bias of a power amplifier.

The generated pre-distorted signal is converted to an analog signal and up-converted to a RF signal. The RF signal is input to an input terminal of the power amplifier.

The power amplifier amplifies the RF signal input using the bias value outputted at the previous step S420.

At step S450, an error signal of the input signal is generated by feeding back the output signal of the power amplifier and comparing the feedback signal with an initial input signal. Particularly, the error signal is generated by subtracting the down-converted output signal from the delayed input signal. The down-converted output signal is a signal down-converted after being attenuated as much as a gain of a power amplifier.

At step S460, the output complex correction coefficients are updated using an adaptive algorithm such as the least square method to minimize the generated error signal.

As shown inFIGS. 2 to 4, the pre-distortion apparatus and method in accordance with an embodiment of the present invention can prevent an output signal of a power amplifier from being distorted by fixing a bias while updating a complex correction coefficient in order that a property of a power amplifier is not to be changed although a magnitude of an input signal is changed. Further, the pre-distortion apparatus and method in accordance with an embodiment of the present invention prevents a convergence property of an adaptive algorithm from being deteriorated.

Also, using the pre-distortion apparatus and method in accordance with an embodiment of the present invention, a typical complex gain type pre-distortion apparatus may be simply and effectively combined with a high power amplifier having a variable bias.