KR20100090378A - Digital linearizer for transmitter using microwave frequency - Google Patents

Abstract

PURPOSE: A digital linear device for transmission using frequency microwave frequency is provided to reduce a Back-off margin, thereby gaining high power efficiency. CONSTITUTION: An input frequency down converter(110) performs converting frequency down about an IF(Intermediate Frequency) signal. A digital pre-distortion linear unit(130) removes a cross modulation signal by a signal feedback from a digital signal and an amplifier of a first A/D converter unit(120). A feedback processing unit(160) converts an output signal of the amplifier to the feedback signal. A frequency up converter(150) converts an IF signal of a D/A converter into microwave frequency.

Description

Digital Linearizer For Transmitter Using Microwave Frequency

The present invention relates to a digital linearization device that can be applied to a high power amplifier of a transmitter using a microwave frequency, and more particularly, to a digital linearization device that can improve high power efficiency and frequency use efficiency by improving the linearization characteristics of the amplifier. It is about.

In particular, the present invention is applicable to all microwave communication transmitters using C-Band, X-Band, Ku-Band, Ka-Band.

In general, microwave transmitters mainly use traveling wave tube amplifiers (TWTA) and solid state power amplifiers (SSPAs) using semiconductors for high power high frequency characteristics.

1 is a schematic diagram illustrating a microwave transmitter including a conventional high power amplifier.

Referring to FIG. 1, a conventional microwave transmitter increases a frequency up of an input IF signal (Typically L-Band) to a microwave frequency band (C-Band, X-Band, Ku-Band, Ka-Band) signal. An up-converter, a high output amplifier for amplifying the uplink frequency band signal, and an antenna for emitting the amplified signal are configured.

In addition, the conventional microwave transmitter is composed of a UPC formed in front of the frequency up-converter to amplify the transmission signal by weakening the attenuator mounted therein when the input IF signal is weakened by rain or the like.

Conventional microwave transmitters, however, typically amplify the high power amplifier up to the maximum power level and operate in the vicinity of saturation region with nonlinear characteristics. Intermodulation) occurs as a noise source of the amplifier, which reduces the transmission quality.

Therefore, in the conventional microwave transmitter to which a plurality of carriers are input, the microwave transmitter is controlled to operate in the linear region by reducing the output of several dB to several tens of dB to reduce intermodulation noise.

However, in order to operate in the linear region, it is necessary to lower the output from several dB to several tens of dB, so the efficiency of the transmitter is increased due to the low efficiency, high power consumption, and a power amplifier having a larger output capacity than the desired output. there was.

In order to solve the above problems, an object of the present invention is to improve the linearization characteristics of the high-power amplifier for microwave transmitter to reduce the back-off margin digital linearization device that can increase the high power efficiency and frequency use efficiency To provide.

In order to achieve the above object, a digital linearization apparatus according to the present invention down-converts a frequency for an input IF signal and automatically detects or sets a multicarrier, and an input frequency down converter and the converted IF signal as a digital signal. The signal output from the digital predistortion linearization unit and the amplifier to remove the intermodulation signal generated due to the non-linear characteristics by using the first A / D conversion unit for converting to the converted digital signal and the signal fed back from the amplifier A feedback processor for converting a feedback signal for input into a digital predistortion linearizer, a D / A converter for converting a digital signal processed by the digital predistortion linearizer into an IF signal, and an IF output from the D / A converter It includes a frequency up-converter for converting the signal into a microwave frequency and transmitting to the amplifier Characterized in that.

Here, the input frequency down converter automatically searches for an input signal processor for mixing and outputting an input signal and a selected frequency, an amplification path for outputting the signal output through the input signal processor, and a center frequency and bandwidth in use. An RF splitter for distributing signals to a detection path for outputting; an output signal processor for converting a signal output through the amplification path into an IF signal; and a frequency at a predetermined interval after frequency downconverting the signal output through the detection path; And a control unit for controlling the signal determination unit for measuring the power of the variable signal and the input signal processing unit, the RF divider, the output signal processing unit, and the signal determination unit.

The input signal processing unit may include a frequency block selection PLL for selecting an input frequency for each block and a mixer for mixing and outputting a frequency selected from the input signal and the frequency block selection PLL.

In addition, the output signal processing unit mixes the first variable PLL for supplying a specific frequency set in consideration of the center frequency and bandwidth searched by the controller, the signal output through the amplification path, and the specific frequency set in the first variable PLL. And a first narrowband bandpass filter for filtering according to a center frequency and a bandwidth selected to enable the linearization process through the digital predistortion linearization unit among the outputted mixer and the signal output to the mixer.

The signal determining unit frequency-converts the signal input to the detection path and then varies the frequency at a predetermined interval to search for a center frequency and a bandwidth, and a second variable PLL and a signal output to the detection path and the second variable. IF signal passed through the mixer and the second narrowband bandpass filter to remove the unwanted wave to measure the power of the variable signal at a predetermined interval to mix the variable frequency in the PLL It characterized in that it comprises a power detector for converting the power of the DC voltage value to transmit to the controller.

The controller shifts the frequency of the frequency block selection PLL to select an input frequency for each block, and shifts the frequency of the second variable PLL to detect the strength of the signal input to the detection path, and the power detector Detects the signal strength from the signal size output from the signal, and determines the presence or absence of the signal by determining the size of the signal, if the signal is detected to calculate the center frequency and bandwidth, if the signal is not detected, the frequency block selection PLL and the It is characterized by controlling to detect a signal by shifting the frequency of the two variable PLLs.

The controller calculates a center frequency and a bandwidth by calculating a second variable PLL frequency transition value and a signal magnitude value when calculating the center frequency and bandwidth, and when the calculated center frequency and bandwidth are larger than a set threshold, It is determined that there is a change in bandwidth, and the frequency shift of the second variable PLL is performed, and the frequency shift of the first variable PLL is performed to set the center frequency. It is characterized by maintaining the frequency of the variable PLL.

The digital predistortion linearization unit receives the feedback signal from the converted digital signal and the amplifier and generates a signal opposite to the nonlinear characteristic by using a crest factor reduction (CFR) function and a digital pre-distortion (DPD) function. To remove the intermodulation signal due to the nonlinear characteristic.

The feedback processor may include a recursive frequency down converter for converting a microwave signal output from the coupling terminal of the amplifier into an IF signal and a second A / for converting an IF signal converted from the recursive frequency down converter to a digital signal. It characterized in that it comprises a D conversion unit.

As described above, the digital linearizer according to the present invention has an excellent effect of obtaining high power efficiency by reducing the back-off margin by improving the linearization characteristics of the high power amplifier.

In addition, center frequency and bandwidth auto-discovery improves frequency usage efficiency and optimizes the performance of digital linearizers to maximize amplifier performance.

Hereinafter, specific embodiments of the present invention will be described in detail with reference to the drawings.

The digital linearization device according to the present invention is formed between an input signal and an amplifier, and is applied to a microwave communication transmitter as a device for improving linearization characteristics by removing nonlinear characteristics of the amplifier.

2 is a block diagram schematically showing a digital linearization device according to a preferred embodiment of the present invention.

Referring to FIG. 2, the digital linearization apparatus 10 according to the present invention is formed between an input signal and an amplifier, and down-converts an input frequency for converting an input IF signal and automatically detects or sets a multi-carrier. The intermodulation signal generated due to the nonlinear characteristic by using the 110 and the first A / D converter 120 for converting the converted IF signal into a digital signal and the signal fed back from the converted digital signal and the amplifier The digital predistortion linearization unit 130 for removing the signal and the feedback processor 160 for converting the signal output from the amplifier into a feedback signal for input to the digital predistortion linearization unit and the signal processed by the digital predistortion linearization unit D / A converter 140 for converting the IF signal and the IF signal output from the D / A converter converts the microwave frequency to the amplifier That may be configured to include a frequency up-converter 150.

Here, the input frequency down converter 110 has a role of down-converting the frequency so that the input IF signal can be converted into a digital signal by the first A / D converter.

In particular, the input frequency down-conversion unit 110 performs a function of automatically detecting and setting the center frequency and bandwidth of the multi-carrier used in the wideband transmitter so that the digital linearization characteristic can be optimized.

3 is a detailed block diagram of an input frequency down converter of FIG. 2.

Referring to FIG. 3, the input frequency down converter 110 mixes an input signal and a selected frequency and outputs the input signal processor 111 and an amplification path for outputting the signal output through the input signal processor. And an RF splitter 112 for distributing the signal to a detection path for automatically searching for the center frequency and bandwidth being used, and an output signal processor 113 for converting the signal output through the amplification path into an IF signal and the detection path. A control unit for controlling the signal decision unit 114 and the input signal processor, the RF divider, the output signal processor and the signal decision unit for varying the frequency at a predetermined interval after the frequency down-converted output signal, measuring the power of the variable signal And 115.

Here, the input signal processing unit 111 is selected by a frequency block selection phase lock loop (PLL) 111a for selecting an input frequency for each block, an input IF signal, and the frequency block selection PLL. It may be configured to include a mixer (111b) for mixing the input frequency.

The output signal processor 113 may include a first variable PLL 113a for supplying a specific frequency set in consideration of the center frequency and bandwidth searched by the controller, a signal output through the amplification path, and the first variable PLL. A mixer 113b for mixing and outputting a predetermined specific frequency and a first narrowband bandpass filter 113c for filtering to a center frequency and a bandwidth selected for linearization processing through a digital predistortion linearization unit among the signals output to the mixer It may be configured to include.

The signal determiner 114 converts the signal input to the detection path down to a frequency and then moves to the second variable PLL 114a and the detection path that vary a frequency at a predetermined interval to search for a center frequency and a bandwidth. A mixer 114b for mixing the output signal with the variable frequency in the second variable PLL, a second narrowband band pass filter 114c for removing the unwanted wave to measure the power of the variable signal at a predetermined interval, and It may include a power detector 114d for converting the power of the IF signal passed through the second narrowband bandpass filter to a DC voltage value and transmits it to the control unit.

 4 is a flowchart schematically illustrating an operation algorithm of a controller of an input frequency down converter of the present invention.

Referring to FIG. 4, first, the controller shifts the frequency of the frequency block selection PLL to select the input frequency for each block.

The frequency of the second variable PLL is then shifted to detect the strength of the signal input into the detection path.

Next, the information on the signal magnitude output from the power detector is output as a voltage value, and the value is detected using the A / D changer inside the controller.

When the signal strength is detected, it is determined whether the signal is present by determining the magnitude of the signal. At this time, when the signal is detected, the center frequency and the bandwidth are calculated, and when the signal is not detected, the signal is fed back to shift the frequencies of the frequency block selection PLL and the second variable PLL.

The center frequency and bandwidth are calculated by calculating a second variable PLL frequency transition value and a signal magnitude value when calculating the center frequency and bandwidth.

If the calculated value of the center frequency and the bandwidth is larger than the set threshold value, it is determined that there is a change in the center frequency and the bandwidth, and the frequency of the second variable PLL is shifted. And feed back to the frequency block selection PLL frequency shifting block.

Here, when the calculated values of the center frequency and the bandwidth are larger than the threshold value, the center frequency is set by executing the frequency shift of the first variable PLL.

 As described above, when the center frequency and the bandwidth of the input signal are calculated through the input frequency down converter, the first A / D converter converts the digital signal into a digital signal and inputs the digital predistortion linearizer.

The digital predistortion linearization unit receives a signal output from the first A / D converter and a signal fed back from the amplifier through a feedback processor to remove the intermodulation signal generated by the nonlinear characteristics of the amplifier.

Here, the feedback processor is a recursive frequency down converter for converting a microwave signal output from the coupling terminal of the amplifier to an IF signal and a second A for converting the IF signal converted from the recursive frequency down converter to a digital signal. It may be configured to include a / D conversion unit.

More specifically, a digital pre-distortion (DPD) function that receives a signal output from the first A / D converter and a signal fed back through a feedback processor from a amplifier and performs a crest factor reduction (CFR) function and an adaptive algorithm By generating the signal opposite to the nonlinear characteristics of the amplifier to remove the intermodulation signal caused by the nonlinear characteristics, and outputs only the linear signal to the amplifier.

Here, the CFR function and the DPD function may be implemented using an FPGA, a digital signal processor (DSP), a dedicated ASIC, or a mixed structure, and an algorithm for implementing the CFR function and the DPD function is voluntary to the general knowledge of the present invention. As it is obvious to the child, the detailed explanation is omitted.

Accordingly, the power efficiency of the amplifier can be improved by removing the intermodulation signal due to the nonlinear characteristic of the high output amplifier and improving the linearization characteristic to reduce the back-off margin.

While the present invention has been described in connection with what is presently considered to be practical exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, It will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention.

1 is a schematic diagram illustrating a microwave transmitter including a conventional high power amplifier.

2 is a block diagram schematically showing a digital linearization device according to a preferred embodiment of the present invention.

3 is a detailed block diagram of an input frequency down converter of FIG. 2.

4 is a flowchart schematically illustrating an operation algorithm of a controller of an input frequency down converter of the present invention.

* Description of the symbols for the main parts of the drawings *

10: digital linearizer 110: input frequency down converter

120: first A / D conversion unit 130: digital predistortion linearization unit

140: D / A converter 150: frequency up converter

160: feedback processing unit

Claims (9)

An input frequency down converter configured to down convert a frequency of an input IF signal and automatically detect or set a center frequency and a bandwidth of a multicarrier; A first A / D converter converting the converted IF signal into a digital signal; A digital predistortion linearization unit for removing intermodulation signals generated due to nonlinear characteristics by using the converted digital signal and the signal fed back from the amplifier; A feedback processor for converting a signal output from an amplifier into a feedback signal for input to the digital predistortion linearization unit; A D / A converter converting the signal processed by the digital predistortion linearizer into an IF signal; And a frequency up converter for converting the IF signal output from the D / A converter into a microwave frequency and transmitting the microwave signal to an amplifier. The method of claim 1, The input frequency down converter is An input signal processor for mixing and outputting an input signal and a selected frequency; An RF splitter for distributing the signal into an amplification path for outputting the signal output through the input signal processor to an amplifier and a detection path for automatically searching for a center frequency and bandwidth in use; An output signal processor converting the signal output through the amplification path into an IF signal; A signal determination unit for varying a frequency at a predetermined interval after frequency down-converting the signal output through the detection path and measuring power of the variable signal; And a controller for controlling the input signal processor, the RF divider, the output signal processor, and the new decision unit. 3. The method of claim 2, The input signal processor A frequency block selection PLL for selecting an input frequency for each block; And a mixer for mixing and outputting the input signal and the frequency selected by the frequency block selection PLL. 3. The method of claim 2, The output signal processing unit A first variable PLL for supplying a specific frequency set in consideration of the center frequency and bandwidth searched by the controller; A mixer for mixing and outputting a signal output through the amplification path and a specific frequency set in the first variable PLL; And a first narrowband bandpass filter for filtering according to the center frequency and the bandwidth so as to perform the linearization process through the digital predistortion linearization unit among the signals output to the mixer. 3. The method of claim 2, The signal determination unit A second variable PLL for frequency downconverting the signal output through the detection path and varying the frequency at a predetermined interval to search for a center frequency and a bandwidth; A mixer for mixing the signal output to the detection path and the frequency varied in the second variable PLL; A second narrowband bandpass filter for removing the unwanted wave to measure the power of the variable signal at regular intervals; And a power detector for converting the power of the IF signal passing through the second narrowband band pass filter into a DC voltage value and transmitting the converted power to a controller. 3. The method of claim 2, The control unit Shifting the frequency of the frequency block selection PLL to select an input frequency for each block, shifting the frequency of the second variable PLL to detect the strength of the signal input to the detection path, and outputting the signal magnitude from the power detector Detects the signal strength from the signal, and determines the presence of the signal by determining the magnitude of the signal, if the signal is detected, calculate the center frequency and bandwidth, if the signal is not detected, the frequency of the frequency block selection PLL and the second variable PLL And control to detect a signal by transitioning. The method of claim 6, The control unit When calculating the center frequency and bandwidth Compute the center frequency and the bandwidth by calculating the second variable PLL frequency transition value and the signal magnitude value, and if the calculated center frequency and the bandwidth value are larger than the set threshold, it is determined that there is a change in the center frequency and the bandwidth. And setting the center frequency by executing the frequency shift of the first variable PLL and performing the frequency shift of the first variable PLL, and determining that there is no change in the center frequency and the bandwidth when it is smaller than the threshold value. The method of claim 1, The digital predistortion linearization unit Receives the feedback signal from the converted digital signal and the amplifier and generates a signal opposite to the nonlinear characteristic by using a CFR (Crest Factor Reduction) function and a digital pre-distortion (DPD) function to generate a cross-modulated signal by the nonlinear characteristic. Digital linearizer, characterized in that the removal. The method of claim 1, The feedback processing unit A recursive frequency down converter for converting a microwave signal output from the coupling terminal of the amplifier into an IF signal;  And a second A / D converter for converting the IF signal converted from the recursive frequency down converter into a digital signal.

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