KR20020093327A - Feedforward linearizer in a IMT-2000 system - Google Patents

Abstract

PURPOSE: A feed-forward linearizer in an IMT(International Mobile Telecommunication)-2000 system is provided to reduce the volume of the entire linearizer circuit by removing a delay line of a signal loop and a delay loop. CONSTITUTION: A power divider(101) divides an inputted RF(Radio Frequency), and outputs two carriers to a main path(102) and an auxiliary path(103), respectively. The first variable attenuator(104) variably attenuates the carrier outputted through the main path(102). An auxiliary amplifier(105) amplifies an output signal of the first variable attenuator(104) at a certain level. The first hybrid coupler(106) couples the carrier outputted from the auxiliary amplifier(105), attenuates a part of the carrier, and outputs the attenuated carrier to the main path(102). The first hybrid coupler(106) outputs the other part of the carrier having an attenuation and a phase difference. A main power amplifier(107) amplifies the carrier of the main path(102) outputted from the first hybrid coupler(106), and outputs the amplified carrier. The second hybrid coupler(108) couples the signal outputted from the first hybrid coupler(106), and outputs the signal having an attenuation and a phase difference. A cross modulation amplifier(109) amplifies the carrier outputted through the auxiliary path(103), and compensates a delay time generated in the auxiliary amplifier(105). The second variable attenuator(110) variably attenuates a signal outputted from the cross modulation amplifier(109). A power coupler(111) couples an output signal of the second variable attenuator(110) and an output signal of the second hybrid coupler(108), cancels the carrier signal, and outputs only a cross modulation signal. An error amplifier(112) amplifies a signal outputted from the power coupler(111). The third variable attenuator(113) variably attenuates an output signal of the error amplifier(112). A phase shifter(114) shifts a phase of a signal outputted from the third variable attenuator(113). A directional coupler(115) couples an output signal of the phase shifter(114) and an output signal of the main power amplifier(107), cancels the cross modulation signal, and outputs only the carrier.

Description

Feedforward linearizer in IMT-2000 system

The present invention relates to a feedforward linearizer in a mobile communication system (PCS, IMT-2000 system, WLL system, etc.), and in particular, a delay path of a signal loop and an error loop. The present invention relates to a feedforward linearizer in an IMT-2000 system in which the phases of main signal components and intermodulation components are automatically controlled.

In general, in communication systems such as personal mobile communication systems (PCS), next generation mobile communication systems (IMT-2000 systems), and wireless subscriber network systems (WLL systems) currently in use, high frequency (RF) and microwave circuits are used. Because of the nonlinearity of the device, it has the characteristics of a nonlinear circuit. In particular, the power amplifier operates a transistor, which is a main active element, in a saturation region with strong nonlinear characteristics to obtain maximum power, thereby causing gain and phase distortion, and generating an intermodulation (IMD) signal, thereby degrading transmission quality.

In general, when a single frequency input signal is applied to a power amplifier, the output gain decreases and a phase delay occurs. When multiple frequency signals are input, intermodulation having different nonlinear propagation characteristics in addition to the output signal having the same frequency as the input signal is obtained. Distortion components occur.

1 is an output waveform diagram of a power amplifier to which two carriers are applied in an RF processing part of a general IMT-2000 system.

Cross modulation components are generated because the consumption of energy in the power amplifier can degrade the output of the fundamental frequency, in particular the tertiary cross-modulation signal components which is located in the band _{(2f 1 -f 2, 2f 2} -f 1) is transmitted The biggest impact is on quality deterioration.

Therefore, in order to compensate for such nonlinear characteristics, a linearizer is used in conjunction with a power amplifier, and the conventional technologies developed to date are as follows.

1) Back-off method: This method reduces the input level of the amplifier to operate in a relatively linear region, but increases the volume of the entire power amplifier, reduces power efficiency, heat dissipation, and supplies large capacity power. There are disadvantages.

2) Predistortion method: A predistortion circuit having a reverse distortion characteristic in consideration of the distortion component to be produced by the power amplifier is added to the input side of the power amplifier in advance to attenuate the distortion component. This method requires a long operating point adjustment after fabrication and has a relatively small amount of improvement in nonlinearity.

3) Feedforward method: This method compares the input signal and output signal of the power amplifier, extracts the error signal of only the intermodulation noise component, synthesizes the output signal of the power amplifier, and finally generates a linear output signal. This is how you get it.

2 is a diagram illustrating a linearizer configuration of a conventional IMT-2000 system to which the feedforward scheme is applied.

Here, reference numeral 11 denotes a power divider for power distribution of an input high frequency (RF) signal to two carriers, and reference numeral 12 denotes a power amplifier for power amplifying a carrier of a main path among carriers distributed by the power divider 11. 13 denotes a delay line for delaying a carrier on the main path, and reference numeral 14 denotes a delay line for delaying a carrier of an auxiliary path among carriers distributed by the power divider 11.

Further, reference numeral 15 denotes a first variable attenuator for variably attenuating a carrier wave on the auxiliary path through the delay line 15, and reference numeral 16 denotes a first phase shifting output signal of the first variable attenuator 15. A phase shifter, reference numeral 17 denotes a first combiner 17 for coupling a carrier wave output from the power amplifier 12, and reference numeral 18 denotes a second attenuating the combined signal from the combiner 17. Variable attenuator is shown.

Further, reference numeral 19 denotes a power combiner for coupling the output signal of the first phase shifter 16 and the output signal of the second variable attenuator 18, and reference numeral 20 denotes an output from the power combiner 19. An amplifier for amplifying the signal to be a predetermined level, reference numeral 21 denotes a third variable attenuator for variably attenuating the output signal of the amplifier 20, reference numeral 22 denotes an output signal of the third variable attenuator 21; Denotes a second phase shifter for phase shifting, and reference numeral 23 denotes a second phase shifter combining the output signal of the second phase shifter 22 with the carrier on the main path and outputting the resulting signal at a final RF out. A two bond group is shown.

The linearizer applied to the conventional IMT-2000 system configured as described above, first divides the high frequency signal input from the power divider 11 and outputs two main carriers and two secondary carriers.

The power amplifier 12 outputs power by amplifying the carrier of the main path output from the power divider 11, and the delay line 13 delays and outputs the carrier on the main path.

Next, the delay line 14 delays the carrier on the auxiliary path, and the first variable attenuator 15 variably attenuates the carrier delayed by the delay line 14, and the first phase shifter 16. Is a 90 degree phase shift and outputs the carrier wave output from the first variable attenuator 15.

In addition, the first combiner 17 couples the carrier wave flowing on the main path after being output from the power amplifier 12, and the second variable attenuator 18 receives the signal coupled by the first combiner 17. Variable attenuation.

Next, the power combiner 19 combines and outputs the signal output from the second variable attenuator 18 and the signal output from the first phase shifter 16, and the amplifier 20 outputs the power combiner ( The signal output from 19 is amplified to a predetermined level.

In addition, the third variable attenuator 21 variably attenuates the signal output from the amplifier 20 to a predetermined level, and the second phase shifter 22 is a phase of the signal output from the third variable attenuator 21. The second combiner 23 combines the signal output from the third variable attenuator 22 and the carrier on the main path passing through the delay line 13 to finalize the resultant signal. It will output as a signal.

That is, in the conventional IMT-2000 system as described above, the linearizer extracts only the carrier and intermodulation components obtained from the output of the power amplifier, and combines them in the reverse phase to the output of the power amplifier to cancel the intermodulation signal. Improve the Carrier to Intermodulation Ratio (C / I).

Although the improvement of IMD characteristics of the feedforward linearizer is superior to other methods, a delay line is configured in the auxiliary path to compensate the power amplifier operation time of the main path in the signal loop. The volume occupied was quite large, resulting in loss of signal, difficulty in adjusting phase and magnitude.

In other words, the conventional feedforward linearizer uses a coaxial cable or a micro strip line as a delay line in the auxiliary path to compensate for the operation time of the power amplifier in the main path. In addition, there are many difficulties in controlling the phase and the magnitude, and also various disadvantages such as loss of signal.

Accordingly, the present invention has been proposed to solve various problems occurring in the linearizer applied to the conventional IMT-2000 system as described above.

SUMMARY OF THE INVENTION An object of the present invention is to provide a feedforward linearizer in an IMT-2000 system in which a delay path of a signal loop and an error loop is unnecessary, and the phases of main signal components and intermodulation components are controlled automatically. There is.

"Feedforward linearizer in the IMT-2000 system" according to the present invention for achieving the above object,

In the feed forward loop type linearizer in the IMT-2000 system,

A power divider configured to distribute the input high frequency RF to output two carrier waves to the primary path and the secondary path, respectively;

A first variable attenuator configured to variably attenuate the carrier wave output through the main path;

An auxiliary amplifier for amplifying the output signal of the first variable attenuator to a predetermined level;

A first hybrid combiner which combines a carrier wave output from the auxiliary amplifier, attenuates a part of the carrier wave, and outputs a part of the main path, and a part of the subcarrier has a phase difference with attenuation;

A main power amplifier for amplifying and outputting a carrier of a main path output from the first hybrid coupler;

A second hybrid combiner configured to combine the signal output from the first hybrid combiner to have attenuation and a phase difference and output the combined signal;

A cross modulation amplifier for amplifying a carrier wave output through the auxiliary path to compensate for a delay time generated by the auxiliary amplifier;

A second variable attenuator configured to variably attenuate the signal output from the intermodulation amplifier;

A power combiner for combining the output signal of the second variable attenuator and the output signal of the second hybrid combiner to remove a carrier signal and output only a mixed modulated signal;

An error amplifier for amplifying the signal output from the power combiner;

A third variable attenuator configured to variably attenuate the output signal of the error amplifier;

A phase shifter for shifting the phase of the signal output from the third variable attenuator;

The directional coupler combines the output signal of the phase shifter and the output signal of the main power amplifier to remove the intermodulation signal and output only a carrier wave.

1 is an output waveform diagram of a power amplifier to which two carriers are applied in an RF processing part of a general IMT-2000 system.

2 is a configuration diagram of a feedforward linearizer applied to a conventional IMT-2000 system,

3 is a circuit diagram showing the configuration of a feedforward linearizer in the IMT-2000 system according to the present invention.

<Explanation of symbols for the main parts of the drawings>

104, 110, 113 ..... 1st, 2nd, 3rd variable damper

105 ..... Auxiliary Amplifier

106, 108 ..... First and second hybrid couplers

107 ..... Main Power Amplifier

109 ..... intermodulation amplifier

112 ..... error amplifier

114 ..... Phase Shifter

115 ..... Directional Coupler

Hereinafter, described in detail with reference to the accompanying drawings, preferred embodiments of the present invention according to the technical spirit as described above.

3 is a circuit diagram showing the configuration of a feedforward linearizer in the IMT-2000 system according to the present invention.

Here, reference numeral 101 denotes a power divider for outputting two carriers to the primary path 102 and the secondary path 103 by power distribution of the input high frequency RF, and reference numeral 104 denotes the main path 102. A first variable attenuator for variably attenuating an output carrier wave, a reference numeral 105 denotes an auxiliary amplifier for amplifying the output signal of the first variable attenuator 104 to a predetermined level, and reference numeral 106 denotes the auxiliary amplifier 105 The first hybrid coupler combines a carrier wave output from the attenuator and a part of the attenuator outputs the main path, and a part outputs the main path with attenuation and a phase difference. Reference numeral 107 denotes an output from the first hybrid coupler 106. Represents a main power amplifier for power amplifying and outputting the carrier of the main path, and reference numeral 108 denotes a scene output from the first hybrid coupler 106; A second hybrid coupler is outputted by combining arcs to have attenuation and phase difference.

Also, reference numeral 109 denotes a intermodulation amplifier that amplifies a carrier wave output to the auxiliary path 103 to compensate for the delay time generated by the auxiliary amplifier 105, and reference numeral 110 denotes the intermodulation amplifier 109. A second variable attenuator for variably attenuating the output signal. Reference numeral 111 denotes a combination of the output signal of the second variable attenuator 110 and the output signal of the second hybrid combiner 108 to remove the carrier signal. The power combiner outputs only the intermodulation signal, reference numeral 112 denotes an error amplifier for amplifying the signal output from the power combiner 111, and reference numeral 113 variably attenuates the output signal of the error amplifier 112. The third variable attenuator 113 denotes a phase shifter for shifting the phase of the signal output from the third variable attenuator 113. Out, and reference numeral 115 denotes a directional coupler which combines the output signal of the output signal to the main power amplifier 107 of the phase shifter 114, the cross-modulation signal is removed, and outputs only the carrier wave.

In the IMT-2000 system according to the present invention configured as described above, the feedforward linearizer first distributes power (RF) input from the power divider 101 to two carriers of the same size, and one of the distributed carriers. Output to the primary path 102 and the other to the secondary path 103.

The carrier output to the main path 102 is transmitted to the first variable attenuator 104, the first variable attenuator 104 variably attenuates the carrier to be transmitted to operate the auxiliary amplifier 105 of the rear stage linearly. Do it.

Next, the auxiliary amplifier 105 operates in the linear region to amplify and output the carrier wave passing through the first variable attenuator 104. Since the auxiliary amplifier 105 operates in the linear region, no intermodulation component is generated and only the carrier component is amplified and output.

In addition, the first hybrid coupler 106 combines a carrier wave output from the auxiliary amplifier 105, and a part of the first hybrid coupler 106 transfers the result to the main power amplifier 107 having a 3 dB attenuation, and a part produces a 3 dB attenuation and a 90 ° phase difference. To the second hybrid coupler 108.

The second hybrid coupler 108 combines the carrier wave having the 90 ° phase difference to be delivered to the power combiner 111 to have a 3dB attenuation and 90 ° phase difference again. Therefore, the carrier transmitted to the power combiner 111 is 180 ° out of phase with respect to the original carrier.

In addition, the carrier wave output from the first hybrid coupler 106 is power amplified by the power amplifier 107 and transferred to the directional coupler 115. The signal passing through the power amplifier 107 is a signal in which the amplified carrier and the intermodulation component are mixed.

On the other hand, the intermodulation amplifier 109 of the auxiliary path 103 amplifies a carrier wave output to the auxiliary path 103 to a predetermined level to compensate for the time delay generated in the auxiliary amplifier 105. Since the intermodulation amplifier 109 operates in the nonlinear region, the output signal has both the amplified carrier component and the intermodulation component.

The signal passing through the intermodulation amplifier 109 is attenuated to a predetermined level in the second variable attenuator 110 and then transmitted to the power combiner 111, and the power combiner 111 transmits the auxiliary path 103. ) And a carrier having a 180 ° phase difference output from the second hybrid coupler 108 to remove the carrier and output only the intermodulation signal.

The intermodulated signal output as described above is transmitted to the error amplifier 112, and the error amplifier 112 amplifies it to a predetermined level and outputs it. The error amplifier 112 serves to compensate for the operation time of the main power amplifier 107 of the main path 102.

Next, the third variable attenuator 113 attenuates the intermodulated signal output from the error amplifier 112 to a predetermined level, and the phase shifter 114 passes the intermodulated modulator 113 through the third variable attenuator 113. The phase of the signal is shifted 180 ° and transferred to the directional coupler 115. Here, the intermodulation signal output from the phase shifter 114 is the same in magnitude and 180 degrees out of phase with respect to the intermodulation component output from the main power amplifier 107.

Finally, the directional coupler 115 combines the output signal of the phase shifter 114 and the output signal of the main power amplifier 107, eliminating intermodulation components and only pure carrier as the final output signal (RF out). Will print.

According to the present invention "feed forward linearizer in the IMT-2000 system" described above, since the delay lines of the signal loop and the delay loop, which occupy a large volume in the conventional linearizer circuit, can be eliminated, the volume of the overall linearizer circuit is reduced. There is an advantage that can be reduced.

In addition, the 90 ° hybrid coupler has an advantage that it is possible to solve the problem that it is difficult to control the signal because the conventional delay time does not match.

Claims (3)

In the feed forward loop type linearizer in the IMT-2000 system, A power divider configured to distribute the input high frequency RF to output two carriers of the same size to the primary path and the secondary path, respectively; A first variable attenuator configured to variably attenuate the carrier wave output through the main path; An auxiliary amplifier for amplifying the output signal of the first variable attenuator to a predetermined level; A first hybrid combiner which combines a carrier wave output from the auxiliary amplifier, attenuates a part of the carrier wave, and outputs a part of the main path, and a part of the subcarrier has a phase difference with attenuation; A main power amplifier for amplifying and outputting a carrier of a main path output from the first hybrid coupler; A second hybrid combiner configured to combine the signal output from the first hybrid combiner to have attenuation and a phase difference and output the combined signal; A cross modulation amplifier for amplifying a carrier wave output through the auxiliary path to compensate for a delay time generated by the auxiliary amplifier; A second variable attenuator configured to variably attenuate the signal output from the intermodulation amplifier; A power combiner for combining the output signal of the second variable attenuator and the output signal of the second hybrid combiner to remove a carrier signal and output only a mixed modulated signal; An error amplifier for amplifying the signal output from the power combiner; A third variable attenuator configured to variably attenuate the output signal of the error amplifier; A phase shifter for shifting a phase of a signal output from the third variable attenuator; And a directional coupler for combining the output signal of the phase shifter and the output signal of the main power amplifier to remove the intermodulation signal and output only a carrier wave. 2. The feed forward linearizer of claim 1, wherein the first and second hybrid couplers are configured as 90 ° hybrid couplers, each 90 ° phase shifted output of the carrier wave output to the auxiliary path side. . The feedforward linearizer of claim 1, wherein the phase shifter outputs the intermodulation signal output from the third variable attenuator 180 ° out of phase to the directional coupler.