Power amplification system for radiofrequency communications

Abstract

Power amplification system for radio frequency communications, comprising a input port of an input radio frequency signal, an output port of an output radio frequency signal; a digital predistortion unit operatively interposed between the input port and the output port and quadrature modulation correction means operatively interposed between the digital predistortion unit and between at least one of the input port and the output port.

Claims

1. Power amplification system for radio frequency communications, comprising: at least one input port of an input radio frequency signal; at least one output port of an output radio frequency signal; at least one digital predistortion unit operatively interposed between said input port and said output port; at least one quadrature modulation correction unit operatively interposed between said digital predistortion unit and between at least one of said input port and said output port; at least one observation port connected to said output port and to said at least one quadrature modulation correction unit and adapted to receive an observed radio frequency signal; at least one intermediate frequency conversion unit connected to said input port and to said at least one quadrature modulation correction means and adapted to convert said input radio frequency signal into a respective intermediate frequency input signal; and at least one switch positionable between a first configuration, wherein it connects said input port to said IF conversion unit, and a second configuration, wherein it connects said observation port to said IF conversion unit.

2. System according to claim 1, wherein said at least one quadrature modulation correction unit comprises at least one input correction unit operatively interposed between said input port and said digital predistortion unit.

3. System according to claim 2, wherein said at least one quadrature modulation correction unit comprises at least one output correction unit operatively interposed between said digital predistortion unit and said output port.

4. System according to claim 3, wherein said at least one quadrature modulation correction unit comprises at least one observation correction unit operatively interposed between said observation port and said digital predistortion unit.

5. System according to claim 1, comprising at least one I/Q quadrature demodulation unit connected to said input port and to said at least one quadrature modulation correction unit and adapted to convert said input radio frequency signal into a respective I/Q input signal.

6. System according to claim 1, comprising at least one I/Q quadrature demodulation unit connected to said observation port and to said at least one quadrature modulation correction unit.

7. System according to claim 1, comprising at least one RF modulation unit connected to said at least one quadrature modulation correction unit and to said output port and adapted to convert an I/Q output signal into said output radio frequency signal.

8. System according to claim 1, comprising at least one amplification unit connected upstream of said output port.

9. System according to claim 1, wherein said intermediate frequency conversion unit is connected to said observation port and is adapted to convert said observed radio frequency signal into a respective observed intermediate frequency signal.

10. System according to claim 1, comprising at least one analog/digital conversion unit operatively interposed between said input port and/or said observation port and said at least one quadrature modulation correction unit.

11. System according to claim 1, comprising at least one digital/analog conversion unit operatively interposed between said at least one quadrature modulation correction unit and said output port.

12. System according to claim 1, wherein said digital predistortion unit and said at least one quadrature modulation correction unit are made by means of an electronic board of the Field Programmable Gate Array type.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Other characteristics and advantages of the present invention will become better evident from the description of a preferred, but not exclusive embodiment of a power amplification system for radiofrequency communications, illustrated by way of an indicative, but non-limiting example in the accompanying drawings wherein:

(2) FIG. 1 is a general block diagram illustrating an example of a digital predistortion algorithm of known type;

(3) FIG. 2 is a general block diagram illustrating an example of RFin to RFout amplifier of known type;

(4) FIG. 3 is a general block diagram illustrating a first possible embodiment of the system according to the invention;

(5) FIG. 4 is a general block diagram illustrating a second possible embodiment of the system according to the invention.

EMBODIMENTS OF THE INVENTION

(6) With particular reference to such illustrations, S globally indicates a power amplification system for radiofrequency communications.

(7) In particular, the system S is intended for base and repeater radio stations used in mobile technologies of third and fourth generation (3G/4G) and more. Applications of a different type cannot however be ruled out.

(8) FIG. 3 shows a first possible embodiment of the system according to the invention, described below.

(9) The system S comprises an IN input port of an RF IN input radio frequency signal received, an OUT output port of an RF OUT output radio frequency signal to be sent, an OBS observation port connected to the OUT output port by means of a feedback connection and adapted to receive an RF OBS observed radio frequency signal.

(10) Advantageously, the system S comprises a DPD digital predistortion unit operatively placed between the IN input port, the OUT output port and the OBS observation port and correction means of the modulation in quadrature QMC IN, QMC OUT and QMC OBS operatively placed between the DPD digital predistortion unit and the IN, OUT and OBS ports.

(11) In particular, the system S comprises: a QMC IN input correction unit operatively interposed between the IN input port and the DPD digital predistortion unit; a QMC OUT output correction unit operatively interposed between the DPD digital predistortion unit and the OUT output port; a QMC OBS observation correction unit operationally placed between the OBS observation port and the DPD digital predistortion unit.

(12) Consequently, as shown in FIG. 3, the proposed architecture envisages the use of two correction units QMC IN and QMC OBS on the receiving side, a DPD digital predistortion unit and a QMC OUT correction unit on the transmission side.

(13) The DPD digital predistortion unit implements the digital predistortion algorithm (in the same way as schematically shown in the example in FIG. 1) which estimates the coefficients of predistortion to be applied to the transmitted signal.

(14) The DPD digital predistortion unit makes a comparison between the RF IN signal corrected by means of the correction unit QMC IN and the RF OBS signal corrected by means of the correction unit QMC OBS in order to estimate the predistortion coefficients to be applied to the signal to be sent. The output signal of the DPD is then sent to the correction unit QMC OUT.

(15) The system S also comprises a first demodulation unit I/Q, indicated in the illustration by the reference DM1, connected to the input port IN and adapted to convert the RF IN input radio frequency signal into a respective input signal I/Q, indicated in the illustration as IQ IN. In practice therefore, IQ IN is the RF IN radiofrequency signal received and converted into the respective signals I and Q.

(16) Respective A/D analog/digital conversion units are operatively placed between the first demodulation unit DM1 and the correction unit QMC IN. Consequently, the D IF IN digital signal represents the RF IN signal converted into a relative IF signal.

(17) In practice therefore, the correction unit QMC IN corrects the modulation errors due to the first demodulation unit DM1 and to the A/D converter in reception.

(18) The system S also comprises an RF modulation unit, indicated in the illustration by the block M, connected downstream of the correction unit QMC OUT and upstream of the output port OUT and adapted to convert the IQ OUT output I/Q signal into the RF OUT radiofrequency output signal.

(19) Suitable D/A digital/analog conversion units are operatively placed between the correction unit QMC OUT and the modulation unit M.

(20) In practice, therefore, the correction unit QMC OUT corrects the modulation errors due to the modulation unit M and conversion errors D/A of the transmitted RF OUT signal.

(21) In addition, an amplification unit PA is connected upstream of the output port OUT and downstream of the modulation unit M.

(22) A second demodulation unit I/Q, indicated in the illustration by the reference DM2, is connected to said OBS observation port and is adapted to convert the RF OBS observed radiofrequency signal into a respective I/Q observed signal, indicated in the illustration as IQ OBS. In practice therefore, IQ OBS is the RF OBS radiofrequency signal observed and converted into the respective signals I and Q.

(23) Respective A/D analog/digital conversion units are operatively placed between the second demodulation unit DM2 and the correction unit QMC OBS. Consequently, the D IF OBS signal represents the RF OBS signal converted into a relative IF signal.

(24) In practice therefore, the QMC OBS correction unit corrects the errors due to the demodulation performed by the second demodulation unit DM2 and the A/D conversion of the RF OBS signal, which is also affected by the modulator M and the converter D/A of the RF OUT signal in the event of the QMC OUT being disabled.

(25) The system S comprises an intermediate-frequency conversion unit CNV IF connected to the input port IN with interposition of a first RF AMP1 amplifier and adapted to convert the FR IN input radiofrequency signal into a respective intermediate-frequency input signal IF IN. In practice therefore IF IN is the signal received and converted into the IF intermediate frequency.

(26) Moreover, the intermediate frequency conversion unit CNV IF is connected to the observation port OBS and is adapted to convert the RF OBS observed radio frequency signal into a respective IF OBS observed intermediate frequency signal. In practice, therefore, IF OBS is the signal observed and converted into the intermediate frequency IF.

(27) The conversion unit CNV IF therefore has a first IF IN output signal connected to the QMC IN correction unit with interposition of a respective A/D conversion unit.

(28) The CNV IF conversion unit also has a second IF OBS output signal connected to the QMC OBS correction unit and to the QMC OUT correction unit with interposition of respective A/D conversion units.

(29) The IF IN and IF OBS signals are required to allow the correction of the RF IN input, of the RF OUT output and of the RF OBS observed signal respectively. The signal used to correct the modulation errors is necessarily an IF signal so as to prevent the DC, offset and phase errors.

(30) Conveniently, the digital predistortion unit DPD and the quadrature modulation correction units QMC IN, QMC OUT and QMC OBS can be made by means of an electronic board of the Field Programmable Gate Array (FPGA) type.

(31) In particular, the digital part of the system S can be implemented on a baseband operating FPGA board so as to optimize the band amplitude of the input and output signals and so as to improve the DSP (Digital Signal Processing) algorithms of the DPD and of the QMC.

(32) With reference to a second possible embodiment, shown in FIG. 4, the system S comprises an RF switch connected to the CNV IF conversion unit and to the IN and OBS ports and positionable between a first configuration, wherein it connects the IN input port to the CNV IF conversion unit, and a second configuration, wherein it connects the OBS observation port to the CNV IF conversion unit.

(33) In this case, therefore, the system S has the RF SW switch that allows the selection of the feedback signal.

(34) In practice, the RF SW switch is positioned first of all in position C1 on the RF IN signal and, subsequently, in position C2 on the RF OBS signal. The switch is therefore repeated periodically according to a predefined and determinate period depending on the system requirements.

(35) In fact, by means of the use of the RF SW switch, the D IF FB signal in the FPGA circuit can represent the RF IN signal or the RF OBS signal converted into the respective IF signal.

(36) It has in practice been ascertained how the described invention achieves the proposed objects.

(37) In particular, the fact is underlined that in such innovative solution, the DPD algorithm and the QMC algorithm are suitably combined with one another, so as to permit better performance of the RF amplifiers.

(38) In particular, the predistortion permits offsetting the non-linear effects of a PA power amplifier produced during the transmission of a broad band signal. Furthermore, the DPD digital predistortion algorithm acts on baseband signals thereby obtaining all the advantages relating to the I/Q (half band, low-pass filtering).

(39) Three QMC sections are used, at input, output and along the observation path of the DPD block, respectively.

(40) Each QMC section has a respective feedback path of the same RF signal, converted into IF. Such feedback can be used by the QMC algorithm as reference to clean the IQ signal.

(41) The advantage of such method is that the IF feedback signal does not require a band width equal to five times the width of the input signal band. In fact, the QMC algorithm operates only on the input signal band.

(42) This is a combination of integrated software and hardware able to make a correction by means of modulation of quadrature in reception and in transmission and a correction by means of predistortion with characteristics that make the solution practical, completely engineerable, sturdy and independent. The proposed algorithm has been designed to operate with various mobile communication standards such as, e.g., WCDMA, WiMAX, CDMA2000, TD-SCDMA, LTE-FDD, LTE-TDD and any of their combinations in a multi-rate configuration.