KR100226424B1 - Linear transmitting system using feedforward and cartesian loop linearization method - Google Patents

Abstract

The present invention relates to a linear transmission system in a wireless communication system, and an object thereof is to linearize the final power amplifier and the entire transmission system. Its features include input information supply means for supplying baseband analog input information, signal distortion means for distorting the original signal with an error signal, modulating the information signal with a first local oscillation signal and having a second local oscillation signal. A modulating means for raising the frequency of the modulated signal, a feedforward linear amplifying means for suppressing the intermodulation distortion characteristic of the power amplifier and linearizing the final stage power amplifier by a feedforward method, and sampling the feedforward linear amplifying means. Demodulation means for demodulating a signal with the first local oscillation signal and downgrading the frequency of the demodulated signal with the second local oscillation signal, comparing the baseband input data signal with a signal demodulated from the demodulation means; Error signal generating means for generating an error signal and supplying the signal distortion means; The first local oscillation signal is supplied to the modulation means and the demodulation means to modulate an information signal and to demodulate the signal sampled from the feedforward linear amplification means, and to raise the frequency of the modulated signal and to demodulate the demodulated signal. And a local oscillation means for supplying the local oscillation signal to the modulation means and the demodulation means to lower the frequency of the signal.

Description

Linear transmitting system using feedforward and Cartesian loop linearization method

The present invention relates to a linear transmission system in a wireless communication system, and more particularly, to a linear transmission system using a feedforward and a Cartesian loop linearization method.

In general, in a mobile communication system, in particular, a system using a linear modulation scheme, it is essential to reduce interference on adjacent channels.

The degree of adjacent channel interference is mainly determined by the intermodulation distortion characteristics of the power amplifier used in the final stage in a well designed system.

Linearization schemes used in a mobile communication system to reduce adjacent channel interference due to intermodulation distortion include feedback, predistortion, and feedforward.

Among these linearization methods, the feedforward linearization method outperforms other linearization methods in terms of the degree of linearization improvement or linearization bandwidth, but there are many components and the intermodulation distortion characteristics usually required only by precisely adjusting the characteristics of each component. A system satisfying 60 dBc can be implemented, but it is not easy to implement.

In addition, the original signal needs to be linearized as a whole because the intermodulation distortion characteristics deteriorate gradually from the baseband to the modulator and the frequency uplinker.

The characteristics of active devices are fundamentally nonlinear. In particular, in the case of a high output amplifier, as the operating point approaches the saturation region, the nonlinearity increases markedly, and the magnitude and phase of the output are distorted.

In addition, when two or more carriers are applied to a high power amplifier, the closer to the saturation region, the larger intermodulation components are generated and affect adjacent channels.

These intermodulation components act as a noise source in the adjacent channel, causing a deterioration in transmission quality, and affecting other bands by shifting to other carriers' frequency bands.

Recently, the digital mobile communication system uses a linear modulation scheme and multi-carrier scheme, which emphasizes the linearity of the amplifier which reduces phase distortion and intermodulation signals generated in the signal amplification process.

Class A amplifiers, which are known to have good linearity, can solve these problems, but they require significant backoff of the operating point in order to obtain the desired linearity, which is very uneconomical in terms of efficiency. .

Therefore, there is a lot of research to improve the nonlinearity of the amplifier externally by attaching a linearizer to the class AB amplifier, which is less linear than the class A amplifier, but has a high power efficiency, and this method includes predistortor and feedback ( There is a feedback method and a feedforward method.

The best improvement among the three methods is the feedforward method, but the circuit is quite complicated.

Thus, precise production is required for a satisfactory improvement effect.

For example, in the case of a mobile communication system, if a class AB amplifier having an intermodulation spurious specification of -60 dBc to other bands and a -30 dBc intermodulation characteristic is used, the feed forward linearization circuit should improve the -30 dBc to satisfy this. .

However, to satisfy this problem, there is a problem that mass production is difficult and the defect rate of the product is increased because it requires a very precise design and manufacturing.

In addition, when a signal is to be transmitted wirelessly in a communication system, the intermodulation distortion characteristic of the transmission system is mainly determined by the power amplifier used in the final stage.

In practical cases, however, since the original signal itself is applied to the transmission system and gradually undergoes a modulator, a frequency uplinker, etc., the intermodulation distortion characteristic deteriorates, so even if a high performance linear amplifier is used at the final stage, the entire system is intermodulated. It is not easy to satisfy the distortion characteristics, and even in a well-designed transmission system, there is a problem in that it is difficult to linearize the power amplifier used in the final stage to satisfy a desired system standard.

In order to solve the above problems, the present invention uses a linearization method that is used to reduce the influence of adjacent channel interference, which should be considered important in a communication system using a linear modulation scheme. The purpose of this is to linearize the final power amplifier and transmission system apparatus to improve the intermodulation distortion characteristics and to easily accommodate the requirements of the required intermodulation distortion characteristics. have.

A feature of the present invention for achieving the above object is input information supply means for supplying baseband analog input information, signal distortion means for distorting the original signal with an error signal, and modulating the information signal with a first local oscillation signal; Modulating means for raising a frequency of the modulated signal with a second local oscillating signal, feed forward linear amplifying means for suppressing intermodulation distortion characteristics of a power amplifier and linearizing a final stage power amplifier by a feed forward method; Demodulation means for demodulating a signal sampled from the feedforward linear amplification means with the first local oscillation signal, and for lowering the frequency of the demodulated signal with the second local oscillation signal, and the baseband input data signal; Comparing the demodulated signal from the demodulation means to produce the error signal, Supplying the first local oscillation signal to the modulation means and the demodulation means for modulating the error signal generating means for supplying the means and the information signal and for demodulating the signal sampled from the feedforward linear amplifying means, And a local oscillation means for supplying the second local oscillation signal to the modulation means and the demodulation means to raise the frequency of the signal and to lower the frequency of the demodulated signal.

In the present invention, by linearizing the entire transmission system as well as the power amplifier used in the final stage, the linearization system reduces the linearization burden at the final stage and substantially amplifies and transmits only the original signal, thereby reducing the linearization burden at the final stage. As a result, it is easy to implement a linearizer of the final stage power amplifier and provides a linear transmission system that substantially amplifies only original signal information by linearizing the entire transmission system.

In addition, the power amplifier is linearized, and the output is sampled at the final stage, and the signal is lowered to the baseband to obtain the original signal information and the information on the intermodulation distortion characteristics of the entire transmission system.

By comparing the signal obtained through this process with the time-delayed original signal information, we extract only the information about the intermodulation distortion characteristics of the entire transmission system. Linearize the entire transmission system by pre-distorting to have characteristics.

1 is a block diagram of a linear transmission system,

2 is a detailed block diagram of a feedforward linear amplifier,

3 is a detailed block diagram of a linear transmission system.

Explanation of symbols for main parts of the drawings

10: signal source 11: baseband digital input data signal source

12: D / A converter 20: Distortor

30 modulator 31 modulator

32: frequency upr 40: local oscillator

41: first local oscillator 42: second local oscillator

50: feed-forward linear amplifier 51: signal divider

52: main amplifier 53: first signal converter

54 subtractor 55 first combiner

56: first delay circuit 57: second coupler

58: second signal converter 59: error amplifier

60: demodulator 61: demodulator

62: frequency down converter 63: third signal converter

70 estimator 71 second delay circuit

72: estimator 80: third signal combiner

Hereinafter, with reference to the accompanying drawings will be described in detail one of the preferred embodiments according to the present invention.

1 is a block diagram of a linear transmission system.

Referring to FIG. 1, a linear transmission system is as follows.

The signal source 10 generates baseband analog input information, the distorter 20 distorts the original signal with an error signal, the modulator 30 modulates the information signal with a local oscillation signal, and generates a local oscillator ( 40 is used to increase or decrease the frequency, the feed forward linear amplifier 50 suppresses the intermodulation distortion characteristics of the power amplifier to linearize the final stage power amplifier by the feed forward method, and the demodulator 60 feeds the feed. The sampled signal from the forward linear amplifier 50 is demodulated, and the estimator 70 compares the baseband input data signal with the demodulated signal from the demodulator 60 to produce an error signal.

Since the intermodulation distortion characteristics of the system in the entire transmission system are gradually deteriorated during the modulation and demodulation process at the baseband, the final stage output signal is sampled to improve the intermodulation distortion characteristics of the entire system. Demodulate back to the baseband signal, and compare the demodulated signal with the original information signal in the estimator 70 to produce an error signal.

The generated error signal is negatively added to the original signal through the baseband distortion 20 and applied to the modulator 30.

In this way, the intermodulation distortion characteristics of the entire transmission system can be improved by distorting the original signal so as to be opposite to the intermodulation distortion characteristics of the entire system.

The modulator 30 is applied to the feedforward linear amplifier 50 to modulate the local oscillation signal using the distorted original signal and then amplify it to a desired signal size.

Therefore, only the original signal applied to the transmission system is amplified and the intermodulation distortion generated in the transmission system is suppressed.

FIG. 2 is a detailed block diagram of a feedforward linear amplifier, which will be described below with reference to FIG. 2.

The signal divider 51 distributes the power of the signal, the main amplifier 52 amplifies the signal, the first signal converter 53 changes the delay time, magnitude and phase of the signal, and the subtractor 54 Only the mutual distortion information is generated by the nonlinear characteristics of the main amplifier, and the first combiner 55 samples the original signal amplified by the main amplifier 52 and the intermodulation distortion signal produced by the main amplifier, and the first delay circuit. 56 adjusts the delay time of the signal, and the second combiner 57 adds the error signal amplified by the error amplifier 59 and the signal from the main amplifier to obtain only the amplified original signal, and the second signal converter 58 ) Adjusts the magnitude and phase of the error signal, and the error amplifier 59 amplifies the intermodulation distortion characteristic error signal of the main amplifier made by the subtractor.

The input signal is divided into two due to the signal divider 51, one of which is input to the main amplifier path and the other to the linearization path.

The signal input to the main amplifier path is amplified by the main amplifier 52, and the distortion signal is also generated due to the nonlinearity of the main amplifier 52.

The amplified original signal and the distortion signal, which are outputs of the main amplifier 52, pass through the first combiner 55, and most of the power is transmitted to the first delay circuit 56, and the partial power is transmitted to the subtractor 54. do.

The signal transmitted by the signal divider 51 in the linearization path is passed through the variable attenuator 53 and the second signal converter via a time delay circuit 53 which causes a signal delay to cancel the time delay caused by the main amplifier 52. Forwarded to 53.

In the variable attenuator 53 and the second signal converter 58, amplification is performed among the signals (amplified signal including the intermodulated distortion characteristics of the amplified original signal and the main amplifier) transmitted to the subtractor through the first combiner 55. It is the same size as the original signal component, and serves to subtract 180 ° inverted phase signal into the subtraction circuit.

Therefore, the output of the subtractor 54 is only a distortion signal having information on the intermodulation distortion characteristics of the main amplifier.

The output signal of the subtractor 54 is 180 degrees in phase with the variable attenuator 58 for adjusting the error signal magnitude so that the second combiner 57 has the same magnitude as the intermodulation distortion signal of the main amplifier 52. To a second signal converter 58 for transmission.

The 180 ° phase-converted distortion signal in the second signal converter 58 is amplified in the error amplifier 59 and input to the main amplifier path through the second combiner 57.

The output signal of the first coupler 55 is provided with a first delay circuit 56 which delays the signal to offset the time delays generated by the error amplifier 59 and the variable attenuator and the second signal converter 58 of the linearization path. Input to the second coupler 57 via.

Among the two inputs of the second combiner 57, the signal input from the amplifier path is the amplified original input signal and the distortion signal, and the input signal in the linearization path is the distortion signal having the same magnitude but the opposite phase, and thus, the second combiner 57. Outputs only the amplified original input signal.

FIG. 3 is a detailed block diagram of the linear transmission system. Referring to FIG. 3, the linear transmission system will be described below.

The signal source 11 supplies baseband digital input data, the D / A converter 12 converts the digital signal into an analog signal, and the distorter 20 has an original signal with an error signal generated by the estimator. And modulator 31 modulates the local oscillation signal with the information signal, frequency upr 20 raises the frequency of the signal, and second local oscillator 42 and the frequency upr 20 The oscillation signal is supplied to the frequency downlinker 62, the feedforward linear amplifier 50 amplifies the signal by a desired intensity, and the demodulator 61 demodulates the intermodulation distortion characteristic of the information signal and the entire transmission system. The downlink 62 lowers the frequency of the final output signal, the third signal converter 63 changes the magnitude and phase of the sampled final output signal, and the second delay circuit 71 times the baseband analog signal. Delay, Estimator 72 compares the baseband delay signal with the signal applied from demodulator 61 to produce only an error signal, and third combiner 80 samples the final output signal and first local oscillator 41. Supplies an oscillation signal to the modulator 31 and the demodulator 61 to modulate and demodulate the information.

The digital information signal is converted into an analog signal through the digital-to-analog converter 72.

Sample a portion of the analog-converted signal, and after the remaining analog signal is amplified through the feedforward linear amplifier 50 used at the final stage, the signal combiner 80, the third signal converter 63, the frequency The time delay for returning to the estimator 72 through the scent 62 and the demodulator 61 is delayed using the delay circuit 21.

The signal passed through this delay circuit and the final stage output (output of the feedforward linear amplifier 50) are sampled by the signal combiner 80 and then demodulated by the demodulator 61 (this demodulated signal includes the nonlinear characteristics of the transmission system). Information on the intermodulation distortion and the original signal information together) to compare the signal to produce an error signal in the estimator 72, and the error signal generated in the estimator 72 to the original signal in the distorter 20 Add to and negative values.

Therefore, the distorter 20 removes the intermodulation distortion characteristic from the final output signal by generating a signal reflecting the intermodulation distortion characteristic of the entire transmission system as a negative value.

The modulator 31 modulates the signal of the local oscillator 41 by using a signal obtained by distorting the original signal into an error signal in order to remove the intermodulation distortion characteristic of the entire transmission system.

The modulated signal converts the frequency of the signal into a radio frequency through the frequency uplinker 20.

The local oscillator 42 is used for frequency up and frequency down, and the frequency up signal is applied to the feedforward linear amplifier 50 and amplified to the size of the signal required by the system.

As described above, in the mobile communication system, especially in the case of a system using a linear modulation scheme, intermodulation distortion in which the influence of adjacent channel interference due to intermodulation distortion of a transmission system greatly affects the capacity of the entire mobile communication system The capacity of the system can be increased by reducing adjacent channel interference due to characteristics, and it can be used in a linear transmission system required in the field of adaptive antenna, a technique used for increasing the capacity.

Claims (7)

Input information supply means for supplying baseband analog input information; Signal distortion means for distorting the original signal with an error signal; Modulating means for modulating an information signal with a first local oscillating signal and for raising a frequency of said modulated signal with a second local oscillating signal; Feedforward linear amplification means for suppressing the intermodulation distortion characteristic of the power amplifier and linearizing the final stage power amplifier in a feedforward manner; Demodulation means for demodulating a signal sampled from the feedforward linear amplification means with the first local oscillation signal, and for lowering the frequency of the demodulated signal with the second local oscillation signal; Error signal generation means for comparing the baseband input data signal with the demodulated signal from the demodulation means to produce the error signal and supply the error signal to the signal distortion means; And supplying the first local oscillation signal to the modulation means and the demodulation means to modulate the information signal and to demodulate a sample sampled from the feedforward linear amplification means, and to raise the frequency of the modulated signal and demodulate the demodulation means. And a local oscillation means for supplying the second local oscillation signal to the modulation means and the demodulation means to lower the frequency of the received signal. 2. The apparatus of claim 1, wherein said input information supply means comprises: a signal source for generating baseband digital input data; And a digital-to-analog converter for converting the digital signal into an analog signal. 2. The apparatus of claim 1, wherein said modulating means comprises: a modulator for modulating said information signal with said first local oscillation signal; And a frequency uplinker configured to increase the frequency of the modulated signal with the second local oscillation signal. 2. The apparatus of claim 1, wherein the feedforward linear amplifying means comprises: a signal distributor for distributing power of an input signal to two paths; A main amplifier for amplifying the distributed signal; A first combiner for sampling the original signal amplified by the main amplifier and the intermodulation distortion signal produced by the main amplifier; A first signal converter for varying the delay time, magnitude and phase of the divided signal; A subtractor which receives the output of the first combiner and the output of the first signal converter and extracts only the interdistortion information due to the nonlinear characteristics of the main amplifier; An error amplifier for amplifying the interdistortion information produced by the subtractor; A second signal converter for adjusting the magnitude and phase of the amplified interdistortion information; A first delay circuit for adjusting a delay time of the output signal of the main amplifier; And a second combiner which combines the mutual distortion information amplified by the error amplifier and a signal from the main amplifier and obtains only the amplified original signal. 2. The apparatus of claim 1, wherein the demodulation means comprises: a third combiner for sampling the final output of the feedforward amplifier; A third signal converter for converting a magnitude and a phase of the final output signal; A frequency downlinker for downgrading the frequency of the signal converted by the third signal converter with the second local oscillation signal; And a demodulator for demodulating the frequency down-signal and the intermodulation distortion characteristics of the entire transmission system. 2. The apparatus according to claim 1, wherein said local oscillation means supplies said first local oscillation signal to said modulation means and said demodulation means for modulating said information signal and demodulating said signal sampled from said feedforward linear amplification means. A first local oscillator; And a local oscillating means for supplying the second local oscillating signal to the modulating means and the demodulating means to raise the frequency of the modulated signal and to lower the frequency of the demodulated signal. A linear transmission system using a feedforward and Cartesian loop linearization method. 2. The apparatus of claim 1, wherein said error signal generating means comprises: a second delayer for time delaying a baseband analog signal; And an error signal generator for generating only an error signal by comparing the time delayed baseband signal with the output signal of the demodulation means.