JP6790665B2 - Calibration circuit, calibration method and program - Google Patents

Description

The present invention relates to calibration circuits, calibration methods and programs.

In mobile phone base stations, the active antenna function is realized by adjusting the phase and amplitude of signals in the transmission system for each antenna using a digital circuit. This is called a digital beam former. In order to form a beam that outputs in a desired direction from an antenna using a digital beam former, it is necessary to adjust the phase and amplitude at each antenna end to predetermined values in advance, and in the transmission system corresponding to each antenna. It is necessary to calibrate.
Patent Document 1 describes, as a related technique, a technique for compensating for a change in the characteristics of an amplifier caused by a change over time or a change in temperature.
Patent Document 2 describes a technique for correcting the characteristics of an amplifier as a related technique.

Japanese Unexamined Patent Publication No. 03-248612 Special Table 2013-515424

By the way, in order to perform calibration in the transmission system corresponding to each antenna, it is necessary to input a calibration signal having a fixed pattern known in advance from the calibration circuit to each transmission system. This signal is fed back via the calibration network immediately before the antenna (for example, a circuit in which a coupler is attached to each port of the transmission system), and the phase and amplitude are compared for each transmission system. Then, the deviation indicated by the comparison result is stored as an offset, and when the active antenna is operated, this offset is added by a digital circuit so that the phases and amplitudes of the antennas are aligned.
However, in the method using this related technique, it is necessary to transmit a calibration signal when performing calibration. Therefore, if the calibration is performed only once at the time of startup using the related technology, the calibration will be deviated due to the subsequent temperature change or aging change of the transmission system. In addition, in order to periodically perform calibration during operation using the related technology, it was necessary to temporarily stop the transmission signal and transmit the calibration signal.
Therefore, in a device using an active antenna used in a mobile phone base station or the like, there has been a demand for a technique capable of calibrating the phase and amplitude of the antenna according to a change with time or a change in temperature without stopping the signal.

An object of the present invention is to provide a calibration circuit, a calibration method, and a program capable of solving the above problems.

In order to achieve the above object, the present invention provides a means for using a digital predistortor for calibrating an active antenna device, the digital predistorter is provided with a register that functions as a delay offset adder circuit, and a plurality of AMP systems It is a calibration circuit that adjusts the delay of the above at the end of the antenna .

Further, the present invention is a calibration circuit including a DPD circuit having a lookup table and a delay offset addition circuit, and a distortion correction circuit, and the lookup table calibrates the amplitude and phase due to a change with time or a change in temperature. The delay offset addition circuit changes the designation of the address in the lookup table, the amplitude offset is added to the amplitude in the correction characteristic, and the phase offset is added to the phase in the correction characteristic. The correction characteristic after the offset addition to which is added is output from the lookup table to the distortion correction circuit, and the distortion correction circuit is output from the lookup table using the input OFDM modulation signal. This is a calibration circuit that calibrates the amplitude and phase based on the correction characteristics after the offset addition and adjusts the delays of a plurality of AMP systems at the antenna ends .

Further, the present invention is a calibration method of a calibration circuit including a DPD circuit having a lookup table and a delay offset addition circuit and a distortion correction circuit, and adjusting the delays of a plurality of AMP systems at the antenna ends. By storing the correction characteristics for calibrating the amplitude and phase due to temperature changes and changing the address designation in the lookup table that stores the correction characteristics, the amplitude offset is added to the amplitude in the correction characteristics. The correction characteristic after offset addition, in which the phase offset is added to the phase in the correction characteristic, is output from the lookup table to the distortion correction circuit, and the OFDM modulation signal input by the distortion correction circuit is used. It is a calibration method of a calibration circuit including calibrating the amplitude and phase due to the change with time or the change in temperature based on the correction characteristic after the offset addition .

Further, the present invention includes a DPD circuit having a lookup table and a delay offset addition circuit, and a distortion correction circuit, and a computer having a calibration circuit that adjusts the delays of a plurality of AMP systems at the antenna ends is subjected to a change over time or a change in temperature. By storing the correction characteristics for calibrating the amplitude and phase and changing the address designation in the lookup table that stores the correction characteristics, the amplitude offset is added to the amplitude in the correction characteristics, and the correction is performed. The correction characteristic after offset addition, in which the phase offset is added to the phase in the characteristic, is output from the lookup table to the distortion correction circuit, and the OFDM modulation signal input by the distortion correction circuit is used. This is a program for calibrating the amplitude and phase due to the change over time or the change in temperature based on the correction characteristics after the offset addition .

According to the present invention, in a device using an active antenna, the phase and amplitude of the antenna can be calibrated according to changes over time and temperature without stopping the signal.

It is a figure which shows the structure of the active antenna apparatus by one Embodiment of this invention. It is a figure which shows the mode of the amplitude correction in one Embodiment of this invention. It is a figure which shows the state of the phase correction in one Embodiment of this invention. It is a figure which shows the example of the look-up table in one Embodiment of this invention. It is a figure which shows the minimum structure of the digital predistorter by embodiment of this invention.

<Embodiment>
The embodiments of the present invention will be described in detail with reference to the drawings.
(Constitution)
The calibration circuit of the active antenna device 100 according to the embodiment of the present invention is shown in FIG. In the example of the calibration circuit 1 shown in FIG. 1, three transmission circuits and an antenna are described for simplification, but they are composed of more systems in order to actually operate as an active antenna. After passing through the beam former 1, the signal of each transmission system is output from the antenna 13 via the phase amplitude correction circuit 2, the distortion correction circuit 4, and the transmission AMP 12. Further, a CAL signal generator 3 that generates a calibration signal is connected to the beam former 1. A DPD circuit 5 (digital predistorter) is connected to the distortion correction circuit 4, and the inside of the DPD circuit 5 is an amplitude conversion circuit 6, a delay circuit 7, a look-up table 8, a comparison circuit 9, and a delay offset addition. It is composed of a circuit 10 and a down converter 11. Further, the signal immediately before each antenna 13 is branched by the coupler 17, and then one system is selected by the selector 14 and input to the down converter unit 11 of the DPD circuit 5.
(Explanation of operation)
Next, the operation of the calibration circuit 200 of the active antenna device 100 according to the embodiment of the present invention will be described. Since the calibration circuit 200 of the active antenna device 100 of the present invention assumes a portable base station, a modulated wave signal such as OFDM (Orthogonal Frequency-Division Multiplexing) is input to each transmission system. This is because the distortion characteristics of the transmission AMP 12 are important in a mobile base station, and high efficiency of the AMP is required to reduce power consumption. The DPD circuit 5 is often adopted.
First, when the active antenna device 100 of the present invention is started, calibration is performed in order to match the phase and amplitude at the output of each antenna 13. At this time, the pilot signal is generated by the CAL signal generator 3 connected to the beam former 1 instead of the normal signal. The beam former 1 operates as a through circuit, and a calibration signal is sent to each transmission system as it is. Since the phase and amplitude of the pilot signal are known, the initial offset is set in the phase amplitude correction circuit 2 so that the amplitude phases of the respective transmission systems are aligned, and the phase amplitudes between the antennas in the initial state are aligned.
Subsequently, during operation, an OFDM-modulated transmission signal is input to each system. The operation of the DPD circuit 5 is used to correct the distortion of the modulated wave generated by the transmission AMP 12, but in a general digital predistorter, the phase is such that the transmission AMP 12 has the opposite characteristics depending on the input amplitude. And the amplitude are back-added in the previous stage of the transmission AMP 12, but the DPD circuit 5 of the present invention further detects the phase shift between the input and the output of the transmission AMP 12 and corrects the delay. The calibration circuit 200 using the DPD circuit 5 will be described. The modulated wave signal is first converted into amplitude by calculating the sum of squares of ich and qch in the amplitude conversion circuit 6. Using this amplitude as an index, the back calculation value of the amplitude and phase shift amount learned in advance in the lookup table 8 is extracted, and this value is input to the distortion correction circuit 4 and multiplied by the modulated wave signal to distort the transmission AMP 12. Produces a corrected signal. The value stored in the lookup table 8 is sequentially learned and updated by comparing the input signal with the output signal of the transmission AMP12. The output signal of the transmission AMP 12 is branched by the coupler 17, converted to the baseband by the down converter section 11, and the input signal is adjusted to the same timing as the output of the transmission AMP 12 through the delay circuit 7. Then, they are compared by the comparison circuit 9, and this is averaged to obtain the updated data of the lookup data. Here, the delay circuit 7 only adds a certain delay value, but the delay offset addition circuit 10 is also connected to the lookup table 8, and the delay when the delay amount of the transmission system changes can be adjusted. It has become like.
Here, the state of correction is shown in a graph in FIGS. 2 and 3. In FIG. 2, the amplitude of the input level is shown on the X-axis and the amplitude of the corrected output level is shown on the Y-axis. The transmission AMP 12 has a compression characteristic in which the gain drops when the input level is high as a general characteristic. In order to correct this characteristic, the look-up table 8 stores correction data that raises the output level as the input level having the opposite characteristic becomes higher. For reference, FIG. 4 shows a typical example of lookup data. Here, in the initial state, the correction curve is shown by a solid line, but when the gain of the transmission AMP 12 decreases due to a change over time, the data in the lookup table 8 is sequentially changed to a curve like a broken line. As a result, correction for increasing the gain is performed, and as a result, the output of the transmission AMP 12, that is, the output of the antenna 13 is kept constant. Next, the phase correction is as shown in FIG. 3, and the Y-axis shows the phase of the correction output level. Generally, in the transmission AMP 12, the phase is constant when the output level is low, and the phase changes rapidly when the output level rises. Therefore, the correction characteristics as shown by the solid line in FIG. 3 are stored in the loop-up table 8. The phase change in the distortion compensation of the normal transmission AMP12 is the same at the time of a small signal, and the phase is shifted only on the right side near saturation, but when the delay of the transmission AMP12 moves due to the change with time, it is a broken line. As shown, the curve is translated in the Y-axis direction. At this time, the data itself of the lookup table 8 does not change, and the phase offset is added by changing the address. The delay offset addition circuit 10 periodically patterns the input / output waveforms. Matching is performed, and the offset for the phase in which the input and output match is stored. In this active antenna device 100, an LTE (Long Term Evolution) OFDM modulated wave is used, and since the signal is random, pattern matching is possible and the phase difference between input and output can be detected. By correcting the amplitude and phase fluctuation of the transmission AMP 12 due to the change with time in this way, the phase and the amplitude of the output of the antenna 13 are kept constant.

As described above, in the calibration circuit 200 of the active antenna device 100, the phase and amplitude of each antenna 13 are transmitted by providing the lookup table 8 of the DPD circuit 5 and the delay offset addition circuit 10 for correcting the delay. It can be kept constant even if it changes with time or changes in temperature. Therefore, it is possible to satisfy the condition that the phase and amplitude of the antenna 13 which are indispensable for digital beamforming are aligned. Since this phase and amplitude correction is always performed using a modulated signal such as OFDM, it is not necessary to stop the signal every time calibration is performed.

Next, the calibration circuit 200 having the minimum configuration according to the embodiment of the present invention will be described.
As shown in FIG. 5, the calibration circuit 200 having the minimum configuration according to the embodiment of the present invention includes a DPD circuit 5 and a distortion correction circuit 4.
The DPD circuit 5 includes a look-up table 8 and a delay offset addition circuit 10. The look-up table 8 houses correction characteristics for calibrating amplitude and phase due to aging or temperature changes. The delay offset addition circuit 10 changes the address designation in the lookup table 8, adds an offset to each of the amplitude and the phase in the correction characteristic, and distorts the correction characteristic to which the offset is added from the lookup table 8. Output to the correction circuit 4.
The distortion correction circuit 4 calibrates the amplitude and phase based on the correction characteristics output from the lookup table 8 using the input OFDM modulation signal.
In this way, in the active antenna device 1, it is possible to perform calibration for aligning the phase and amplitude output by each of the antennas 60 at startup to a predetermined phase and amplitude, and further, aging in the transmission system during operation. It is possible to correct the fluctuation of the phase and amplitude due to the change or the temperature change. As a result, in the active antenna device 1, it is possible to correct the fluctuation of the phase and amplitude that occurs in the transmission AMP without stopping the transmission of the transmission signal even during operation, and the phase and amplitude of the signal output by each of the antennas can be corrected. Can be aligned.

In the processing according to the embodiment of the present invention, the order of the processing may be changed as long as the appropriate processing is performed.

Although one embodiment of the present invention has been described, the above-mentioned DPD circuit 5 and other control units may have a computer system inside. The process of the above-mentioned processing is stored in a computer-readable recording medium in the form of a program, and the above-mentioned processing is performed by the computer reading and executing this program. Here, the computer-readable recording medium refers to a magnetic disk, a magneto-optical disk, a CD-ROM, a DVD-ROM, a semiconductor memory, or the like. Further, this computer program may be distributed to a computer via a communication line, and the computer receiving the distribution may execute the program.

Further, the above program may realize a part of the above-mentioned functions. Further, the program may be a file that can realize the above-mentioned functions in combination with a program already recorded in the computer system, that is, a so-called difference file (difference program).

Although some embodiments of the present invention have been described, these embodiments are examples and do not limit the scope of the invention. These embodiments may be added, omitted, replaced, or modified without departing from the gist of the invention.

1 ... Beam former 2 (2a, 2b, 2c) ... Phase amplitude correction circuit 3 ... CAL signal generator 4 (4a, 4b, 4c) ... Distortion correction circuit 5 ... DPD circuit 6 ... Amplitude conversion circuit 7 ... Delay circuit 8 ... Lookup table 9 ... Comparison circuit 10 ... Delay offset addition circuit 11 ... Down converter section 2 (12a, 12b, 12c) ...・ Transmission AMP
13 (13a, 13b, 13c) ... Antenna 14 ... Selector 17 (17a, 17b, 17c) ... Coupler 100 ... Active antenna device

Claims (6)

A means of using a digital predistator to calibrate an active antenna device,
Equipped with a,
A register that functions as a delay offset addition circuit is provided in the digital predistorter, and delays of a plurality of AMP systems are adjusted at the antenna end by the delay offset addition circuit.
Calibration circuit. A means for using an OFDM modulated wave as a signal for calibration of the active antenna device ,
The calibration circuit according to claim 1. A means for correcting the deviation of the delay change of the transmission system as well as the phase compensation of the transmission AMP to the digital predistorter.
The calibration circuit according to claim 1 or 2. A calibration circuit including a DPD circuit having a look-up table and a delay offset addition circuit, and a distortion correction circuit.
The look-up table
Contains correction characteristics for calibrating amplitude and phase due to changes over time or temperature.
The delay offset addition circuit
By changing the address designation in the look-up table, the amplitude offset is added to the amplitude in the correction characteristic, and the phase offset is added to the phase in the correction characteristic. Output from the uptable to the distortion correction circuit
The distortion correction circuit
Using the input OFDM modulation signal, the amplitude and phase are calibrated based on the correction characteristics after the offset addition output from the lookup table .
A calibration circuit that adjusts the delays of multiple AMP systems at the antenna ends . A DPD circuit having a look-up table and the delay offset adding circuit, saw including a distortion correction circuit, a method of calibrating Awaseko Uncalibrated circuit delays plurality AMP systems in the antenna end,
Containing correction characteristics for calibrating amplitude and phase due to changes over time or temperature,
Correction after offset addition, in which the address designation in the lookup table that stores the correction characteristic is changed, the amplitude offset is added to the amplitude in the correction characteristic, and the phase offset is added to the phase in the correction characteristic. To output the characteristics from the look-up table to the distortion correction circuit,
Using the OFDM modulation signal input by the distortion correction circuit, the amplitude and phase due to the change over time or the change in temperature are calibrated based on the correction characteristics after the offset addition.
Calibration method of the calibration circuit including. A DPD circuit having a look-up table and the delay offset adding circuit, saw including a distortion correction circuit, a computer Awaseko Uncalibrated circuit at the antenna end delay of a plurality AMP systems,
Containing correction characteristics for calibrating amplitude and phase due to changes over time or temperature,
Correction after offset addition, in which the address designation in the lookup table that stores the correction characteristic is changed, the amplitude offset is added to the amplitude in the correction characteristic, and the phase offset is added to the phase in the correction characteristic. To output the characteristics from the look-up table to the distortion correction circuit,
Using the OFDM modulation signal input by the distortion correction circuit, the amplitude and phase due to the change over time or the change in temperature are calibrated based on the correction characteristics after the offset addition.
A program that executes.

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