CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a national stage application of International Application No. PCT/JP2017/043479, entitled, “AMPLIFIER, CONFIGURATION METHOD OF AMPLIFIER, AND COMMUNICATION APPARATUS,” filed on Dec. 4, 2017, the disclosure of which is hereby incorporated by reference in its entirety.

TECHNICAL FIELD

The present invention relates to an amplifier, a configuration method of an amplifier, and a communication apparatus.

BACKGROUND ART

A power amplifier (PA) is an indispensable component for any communication system. For optimal performance, the PA is required to possess high linearity in wide range of power level. However, it is quite difficult to achieve such high linearity in real-world applications. Nonlinearity in the PA causes out-of-band spurious emissions, and thereby spectral expansion occurs and adjacent channel leakage ratio (ACLR) performance deteriorates.FIG. 12illustrates spectral expansion due to the nonlinearity in the PA. For solving the above-described problem, various linearization techniques ranging from analog solutions to digital solutions have been proposed. The digital predistortion (DPD) is one of the most effective solution to remove the nonlinearity of the PA. In the DPD, an original signal is predistorted before being fed into the PA to remove nonlinearity.

The envisioned 5G system handles signals with bandwidths in a range of hundreds of MHz. Compounded with PA nonlinearity, this necessitates the usage of analog to digital converters (ADCs) in the feedback loop of the DPD in order of Gbps, which are exorbitantly costly. In order to overcome this problem, bandlimited DPDs, which extract information on PA nonlinearity as a feedback from an in-band of PA output, have been proposed. This is configured by putting a bandpass filter (BPF) in the feedback loop to reduce the ADC's sampling rate. Configurations for downconverting from a high frequency (e.g. RF) to lower frequency (e.g. a baseband or intermediate frequency (IF) band) have been proposed (Patent Literature 1 and Non Patent Literature 1).

Further, a significant amount of information included in out-bands of PA output is thrown out and, hence, the performance is sub-optimal.

Patent Literature 1 discloses an embodiment in which the out-bands of PA output are also analyzed in addition to the in-bands of PA output. This makes it possible to scoop extra information available in the out-bands of PA output in order to improve the performance.

CITATION LIST

Patent Literature

PTL 1: US Patent Publication No. 2016/0065147

Non Patent Literature

NPTL 1: R. N. Braithwaite, “Closed-loop digital predistortion (DPD) using an observation path with limited bandwidth”, IEEE Trans. Microw. Theory Techn., vol. 63, no. 2, pp. 726-736, February 2015

SUMMARY OF INVENTION

Technical Problem

In PTL1, the out-bands extracted from either side (i.e., either of a low frequency side and high frequency side) of the in-band of PA output are processed separately for evaluation of model for the DPD. In this method, at each instant, only a solution path selected for searching optimized model for the DPD is performed so that only distortion in the selected side is corrected. Thus, performance of the other non-selected side deteriorates. As a result, this can lead to sub-optimal performance in the form of imbalance of ACLRs.

The present invention has been made in view of the above-mentioned problem, and an object of the present invention is to effectively improve linearity of an output signal of an amplifier.

Solution to Problem

An aspect of the present invention is an amplifier including: an in-band extraction unit configured to extract an in-band from an predistorted and amplified analog signal; an out-band extraction unit configured to extract at least one pair of out-bands including a low frequency side out-band and a high frequency side out-band from the predistorted and amplified analog signal; an analog to digital converter configured to convert the extracted in-band and out-bands to digital signals; and a signal processing unit configured to process information included in the digital signals converted by the analog to digital converter and adjust an operation of predistorting an input baseband digital signal to generate the predistorted and amplified analog signal.

An aspect of the present invention is a configuration method of an amplifier including: disposing an in-band extraction unit configured to extract an in-band from an predistorted and amplified analog signal; disposing an out-band extraction unit configured to extract at least one pair of out-bands including a low frequency side out-band and a high frequency side out-band from the predistorted and amplified analog signal; disposing an analog to digital converter configured to convert the extracted in-band and out-bands to digital signals; and disposing a signal processing unit configured to process information included in the digital signals converted by the analog to digital converter and adjust an operation of predistorting an input baseband digital signal to generate the predistorted and amplified analog signal.

Advantageous Effects of Invention

According to the present invention, it is possible to effectively improve linearity of an output signal of an amplifier.

