KR0171024B1 - Linearization circuit - Google Patents

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a feedforward linearization circuit, which is a new circuit that combines a feedforward and a back-pass. Thus, when only the feedforward is used, the distortion signal is satisfactory. Although it required maintaining precision and time-consuming tuning to suppress it, the distortion of the distortion signal itself at the amplifier output through the back-pass can be reduced to some extent, thereby reducing the burden of improving the linearity of the feedforward circuit.

The present invention can be applied to the linearization of high power amplifiers as it is, and in particular, it can be applied to the signal amplification stage of a system using multiple channels such as mobile communication and satellite communication. In addition, when applied to a system using a phase modulation method, such as QPSK, there is an advantage that can reduce the phase distortion due to linear amplification.

Description

Feedforward Linear Circuit

FIG. 1A is a block diagram of a feedforward. FIG.

Figure 1b is the signal spectrum of the main point in Figure a.

Figure 2a is an overall block diagram according to the present invention.

Figure 2b is the spectrum of each point in Figure a.

FIG. 3a is a detailed block diagram of FIG. 2a. FIG.

Figure 3b is the signal spectrum of the main point in Figure a.

* Explanation of symbols for main parts of the drawings

1: amplifier path 2: linearization path

3: Back-pass path 11: Divider

12: first coupler (Coupler) 13: main amplifier

14 second coupler 15 first signal delay circuit

16: third coupler 17: second signal delay circuit

18. First Phase Conversion and Variable Attenuator 19: Subtraction Circuit

20: fourth coupler 22: second phase conversion and variable attenuator

22: third phase conversion and variable reducer 23: error amplifier

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a feedforward linearization circuit, and in particular, a back-pass is provided in a feedforward linearization circuit in a digital mobile communication system, thereby avoiding feedback of an original signal. The present invention relates to a feedforward linearization circuit for backpassing a signal.

In general, 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 significantly, resulting in distortion of the magnitude and phase of the output. In addition, when two or more carriers are applied to the high power amplifier, the closer the saturation region is, the larger the cross-over components occur, affecting adjacent channels. These intermodulation components act as a noise source in adjacent channels, reducing transmission quality and affecting other bands by shifting to other carriers' frequency bands.

Recently, the digital mobile communication system uses a phase modulation method and multi-carrier method, which emphasizes the linearity of the amplifier to reduce the phase distortion and the horn modulated signal generated in the signal amplification process.

Class A amplifiers, which are known to have good linearity, can solve the above problems, but in order to achieve the desired linearity, the operating point needs to be significantly backoff, which makes them very uneconomical in efficiency. Therefore, many studies have been conducted 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. Such methods include predistortor and feedback ( Feedback) and feedforward methods.

The most improved method among the three methods is the feedforward method.

This feedforward method is briefly described with reference to FIG. 1 as follows.

First, in FIG. 1A, the couplers 4a-4c have a function of combining with a function of distributing a signal, wherein a phase of a signal to be distributed or summed is 90 degrees apart. The amplifiers 5a and 5b are for amplifying the signal, the delay lines 6a and 6b are for delaying the time of the signal passing through, and the phase shifters and the variable attenuators 7a and 7b keep the signals in phase. It is a phase changer used for the purpose and an attenuator for adjusting the magnitude of the signal. The subtraction circuit is a circuit for extracting only a specific signal.

In this configuration, the spectrum of each major point is shown in Fig. 1b, where points A and B show only a signal, and point C shows a distortion and an original signal generated due to the nonlinear characteristics of the amplifier. Feedforward is one of the ways to remove this distortion. Point D is a signal obtained by adjusting the magnitude and phase of the original signal, which is inverted in phase by 180 degrees. Point E is the remaining distortion signal after subtracting only the original signal. If the distortion signal is equal in magnitude to the distortion signal shown in point G and the phase is inverted by 180 degrees, the distortion signal is removed and only the original signal is amplified and output as point H. do. In other words, the feedforward is a method of adding a signal again in a progressing direction while processing the same signal as the original signal at the same time.

The opposite concept is feedback.

Until now, when only the feedforward method was used, there was a problem that it was necessary to maintain and tune a lot of time in order to suppress the distortion signal to a satisfactory level.

This feedforward method requires precise manufacturing for satisfactory improvement effect. For example, in the case of a mobile communication system, if a class AB amplifier with intermodulation spurious specification of -60dBc and intermodulation characteristic -30dBc is used, the feedforward circuit must improve -30dBc. However, to meet this requirement requires very precise design and fabrication, making mass production difficult and increasing the defective rate of the product. However, if the distortion signal from the linearization path is partially fed back and then adjusted to be 180 degrees to the phase of the amplifier input signal and pre-input to the class AB amplifier, the nonlinearity of the amplifier can be improved to some extent. If the output from -30dBc was improved only by -40dBc, then the linearization path would be much easier because only -20dBc could be improved.

Accordingly, an object of the present invention is based on a feedforward linearizer, and a feedforward linearization circuit can obtain a satisfactory distortion component by easily adding a simple back-pass and improving a feedback scheme. The purpose is to provide.

Technical features of the present invention for achieving the above object is a feedforward linearization circuit including an amplifier circuit and a linearization circuit including a main amplifier having a non-linearity, when the back-pass is added to the linearization path A back-pass circuit for back-passing only an unnecessary signal and outputting the signal to the amplifier circuit without feedback is provided. Here, the back-pass is similar to the feedback, but essentially the feedback samples the entire signal while in the present invention only the partial signal is sampled.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

2 is an overall block configuration according to the present invention, and as shown in A, an amplifier path 1 having a main amplifier having nonlinearity, and an input signal and an output signal of the amplifier path 1 are used for the nonlinearity of the amplifier. A linearization path (2) that cancels signal distortion due to gender, and a back-pass path that introduces a 180-degree inverted predistortion signal into the amplifier input using the signal in the linearization path to improve the nonlinearity of the amplifier to some degree. It consists of (3).

In this configuration, the spectrum of each point will be described with reference to FIG. 2b.

That is, the back-pass path 3 receiving the distortion signal point a in the linearization path 2 pre-inputs a signal such as point b to the input terminal of the amplifier. The amplifier amplifies the signal point d, which is the sum of the original input signal point C and the pre-input signal point b. The result is an output signal with improved linearity as in point e. The dotted line at Point e represents an improved amount of distortion signal components.

3 is a detailed configuration of FIG. 2 and the description thereof is as follows.

The configuration of the present invention, as shown in Figure 3a, divider 11 for dividing the input signal into the amplifier path and the linearization path, and the first coupler for mixing the signal from the back-pass to the amplifier path (12), a main amplifier 13 for amplifying the mixed signal through the first coupler 12, and for coupling a portion of the output signal (main signal + distortion signal) of the main amplifier 13 A signal delayed through the second coupler 14, the first signal delay circuit 15 to cancel the signal delay caused by the error amplifier of the linearization path, and the first signal delay circuit 15 of the linearization circuit amplifier The third coupler 16 for mixing in the path, the second signal delay circuit 17 for canceling the signal delay caused by the main amplifier 13 in the amplifier path, and 180 the phase of the input signal in the linearization path. Adjust phase shift and signal level to invert The first phase shifter and the variable attenuator 18, and the signal output from the second coupler 14 of the amplifier path and the first phase shifter and the variable attenuator 18 of the linearization path. A subtraction circuit 19 for subtracting only the distortion signal, a fourth coupler 20 for sending a portion of the distortion signal output from the subtraction circuit 19 to the back-pass, and a back-passed signal The phase of the signal output through the second phase conversion and variable attenuator 21 and the fourth coupler 20 for inverting the phase of the signal by 180 degrees and adjusting the signal level, and adjusting the signal level. And a third phase conversion and variable attenuator 22, and an error amplifier 23 for amplifying a distortion signal among the signals output from the variable attenuator 22.

The operation of the present invention having such a configuration will be described with reference to FIGS. 2 and 3b as follows.

The input signal is split into two due to the divider 11, one of which is point a to the amplifier path 1 and the other to point b is the linearization path 2. The signal input to the amplifier path 1 is amplified by the main amplifier 13, whereby a distortion signal is also generated due to the nonlinearity of the main amplifier (point e). The amplified and distorted signal, which is the output point e of the main amplifier 13, passes through the second coupler 14, and most of the power is passed to the first signal delay circuit 15. To the subtraction circuit (19). On the other hand, the signal point b transmitted by the divider 11 to the linearization path 2 passes through the second signal delay circuit 17 which delays the signal to cancel the time delay caused by the main amplifier 13. 1 phase shift and variable attenuator 18.

Accordingly, in the first phase conversion and variable attenuator 18, the phase of the signal (amplified signal + distortion signal) of the signal (amplified signal + distortion signal) transmitted to the subtraction circuit 19 through the second coupler 14 is only 180 in phase. Also serves to input the inverted signal (point f) to the subtraction circuit (19). Therefore, the output point g of the subtraction circuit 19 is only a distortion signal. This distortion signal passes through the fourth coupler 20, and at the same time, the distortion signal transfers some power to the second phase shifter and the variable attenuator 21 of the back-pass path 3, and adjusts the remaining power to the signal level. A third phase shifter and a variable attenuator 22, which is a phase shifter for converting a phase 180 degrees with a variable attenuator for the second phase, are transferred. The distortion signal 180 degrees phase-converted by the phase shifter of the third phase shifter and the variable attenuator 22 is amplified (point h) by the error amplifier 23 which is a class-A amplifier, and is connected to the amplifier path (3) through the third coupler 16. Is entered in 1).

The output signal of the second coupler 14 passes through the first signal delay circuit 15 through the first signal delay circuit 15 to cancel the time delay generated by the error amplifier 23 of the linearization path to the third coupler 16. Is entered. Accordingly, the point e of the two inputs of the third coupler 16, which is input from the amplifier path, is an amplified input signal and a distortion signal, and the input signal point h in the linearization path is the same in magnitude but opposite in phase. Since the distortion signal, the third coupler 16 outputs only the amplified input signal point I.

However, in practice, it is very difficult to suppress the distortion signal to a level of about -60 dBc only by the feedforward linearization method described above because of the limitation of performance and precision in manufacturing each device. Therefore, this problem can be solved by adding a back-pass path and improving the linearity of the main amplifier to some extent. That is, the distortion signal (some power of the point g signal) transmitted through the fourth coupler 20 to the back-pass path is 180 degree phase shifted through the second phase shift and the variable attenuator 21 (point c). Input to the first coupler 12, this input distortion signal improves the output of the main amplifier 13 to a much better linearity. The main amplifier 13 generates a distortion signal while amplifying the input signal. At this time, the input signal itself is pre-inputted through a back-pass path having a phase opposite to the distortion signal generated by the main amplifier 13. Since point c) is included, the distortion signal is partially canceled and suppressed. The dotted line at Point e represents the amount of improvement in the linearity of the main amplifier under the influence of the pre-input distortion signal through the back-pass path. In this case, the overall gain reduction is small because the original signal is not directly back-passed.

According to the present invention, since the distortion signal of the main amplifier is improved, a feedforward linearization algorithm is applied, and thus, an output having higher linearization improvement can be obtained.

The present invention as described above can be applied as it is to linearization of a high power amplifier, and in particular, it can be applied to the signal amplification stage of a system using a plurality of channels, such as mobile communication, satellite communication. In addition, when applied to a system using a phase modulation method such as QPSK, the linear amplification can reduce the phase distortion. In addition, the back-pass reduces the distortion signal itself at the amplifier output to some extent, reducing the linearity improvement burden of the feedforward circuit.

Claims (2)

An amplifier circuit which receives an input signal through an amplifier path and amplifies it through a main amplifier having nonlinearity, delays it, and improves the distortion component by adding it to an output signal of a linearization circuit; After subtracting the output signal of the main amplifier from the subtractor through the first phase conversion and the gain attenuation converter, the subtracted error signal is passed through the second phase conversion and the gain attenuation converter and then amplified through the amplifier. A feedforward linearization circuit comprising a linearization circuit provided to sum with an output signal, wherein an error signal, which is an output signal of the subtractor, is detected through a coupler and inputted through a coupler to the front end of the main amplifier to improve distortion components. A feedforward linearization circuit, characterized in that a back-pass circuit is added. The linear feeder of claim 1, wherein the back-pass circuit comprises a phase shifter and a variable attenuator.