JP2003115725A - High-frequency amplifier - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high-frequency amplifier which can perform efficiently multivalue modulation transmission through a satellite repeater by mounting on it an inexpensive digital processing circuit. SOLUTION: An amplitude-phase control portion 13 of a per-amp. portion 1 comprises an amplitude-phase sensing portion 131 for sensing the amplitude and phase of an input signal from the orthogonal signals obtained by transforming orthogonally the input signal; an amplitude-phase converting portion 132 for outputting based on the informations of the sensed amplitude and phase such amplitude and phase as to change the nonlinear characteristic of a nonlinear amplifier 2 to a linear characteristic; and an amplitude-phase/ orthogonal signal transforming portion 133 for transforming the converted amplitude and phase to orthogonal signals. Thereby, the amplitude-phase control portion 13 so converts the amplitude and phase of the input signal as to change the nonlinear characteristic of the nonlinear amplifier 2 to the linear characteristic, and outputs the converted amplitude and phase as the orthogonal signals.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high frequency amplifier, and more particularly to a high frequency amplifier for amplifying a signal which has been digitally modulated by a modulation method in which information is added to amplitude.

[0002]

2. Description of the Related Art Conventionally, communication satellites or broadcasting satellites have been
Traveling-Wave Tube Amp (TWTA)
High efficiency amplifier called lifier) is used. This amplifier has a characteristic that the output signal level does not increase linearly with the increase of the input signal level, the gain starts to decrease at the output saturation point, and then the gain gradually decreases. An example of this characteristic is shown in FIG.

Normally, the amplifier can be operated with the highest efficiency and the highest output at the output saturation point, so that in satellite broadcasting, the input signal is adjusted so as to be driven at the output saturation point.

In addition to analog broadcasting, satellite broadcasting currently being broadcast includes digital broadcasting using 8PSK (Phase Shift Keying) modulation. 8PSK is a 3-bit data, that is, (00
0), (001), (010), (011), (10
0), (101), (110), and (111) of 8 types of data are 0 to 45 degrees, 90 degrees, ... This is a modulation method in which data is transmitted by correspondingly switching the phase of the carrier wave according to the transmission data. FIG. 8 shows the relationship between the carrier wave phase and data.

As described above, some satellite broadcasts employ a modulation method in which information is not added to the amplitude in order to make it difficult for the traveling-wave tube amplifier used in the satellite repeater to undergo non-linear deterioration.

In addition, 32 of signal point arrangement as shown in FIG.
When using digital modulation, such as QAM (Quadrature Amplitude Moduration) modulation, which sends information by changing both the amplitude and phase of the carrier wave, the input signal level is made less susceptible to nonlinear deterioration of the traveling wave tube amplifier. Is narrowed down (back-off) for amplification using the highly linear region of the traveling wave tube amplifier.

For example, the output signal level is 3 above the saturation point.
dB lower (output back-off (OBO) = 3 dB) (at input amplitude where output amplitude is 0.71 in Fig. 7)
FIG. 10 shows the result obtained by simulating the reception signal point when the traveling wave tube amplifier is driven. In addition, the simulation conditions are the BSAT-2 currently in operation for the satellite repeater.
a was assumed. In addition, a grid with a crossing point at a point corresponding to an ideal signal point position is also shown by a dotted line.

Comparing this received signal point with the ideal signal point position, it can be estimated that the receiving point is distorted (particularly, the portion indicated by the arrow in the figure) and the bit error characteristic is greatly deteriorated. It turns out that the operation that took is necessary.

As described above, conventionally, in transmission using a satellite repeater, it is necessary to use a large back-off when using a modulation method in which information is not added to the amplitude or when using multilevel modulation. It was However, if a large back-off is taken, the efficiency of the traveling wave tube amplifier is deteriorated and power consumption is increased. Further, since it is necessary to adopt a high output traveling wave tube amplifier, the weight and cost of the satellite repeater increase.

Amplifiers for compensating for such non-linear characteristics have also been developed. For example, the 2000 IEICE General Conference, Lecture No. C-2-56, Proceedings Koguro et al. As discussed in "Consideration of Low Distortion", the high frequency was performed in an analog manner.

A method using a digital method is disclosed in, for example, Japanese Unexamined Patent Publication No. 2000-31869, which is the inverse of the amplitude / phase characteristic of the amplifier at the subsequent stage with respect to the quadrature baseband signal before transmission. It is designed to be preceded by a circuit with characteristics. However, it was not possible to compensate for the non-linear distortion in the high frequency amplification performed when relaying the signal transmitted at the high frequency.

[0012]

As described above, there is no accurate digital method for amplifying a high frequency signal. Therefore, at present, a non-linear compensation method using an analog method, which is inferior in accuracy, or an operation in which a large output backoff is taken at the expense of efficiency has been performed.

Therefore, an object of the present invention is to provide a high frequency amplifier which can carry out multi-level modulation transmission by a satellite repeater efficiently by mounting an inexpensive digital processing circuit.

[0014]

As a means for solving the above problems, the present invention provides a non-linear amplifier having a non-linear characteristic,
A pre-circuit unit for converting the amplitude and phase of an input signal is provided in the preceding stage of the nonlinear amplifier, the pre-circuit unit includes an input frequency conversion unit for converting an input high frequency signal into a low frequency signal, and the input frequency conversion unit. A / D converter that converts the low-frequency signal converted by the frequency converter into a digital signal, and the amplitude and phase of the input signal detected from the digital signal converted by the A / D converter, and the detected amplitude and phase And an amplitude / phase control unit that converts the amplitude and the phase based on the above, converts and outputs the converted amplitude and phase into a quadrature signal, and D / that converts the quadrature signal output by the amplitude / phase control unit into an analog signal. A non-linear characteristic of the non-linear amplifier is compensated by having an A conversion section and an output frequency conversion section for converting an analog signal output from the D / A conversion section into a high frequency signal having the same center frequency as the input signal. amplifier Output is characterized in that to convert the amplitude and phase of the input signal to be linear.

As a result, the amplitude and phase of the input signal are converted so as to compensate for the non-linear characteristic of the non-linear amplifier, and the output of the non-linear amplifier becomes linear.

The non-linear amplifier is a traveling-wave tube amplifier, and the pre-circuit section has a characteristic in which the horizontal axis and the vertical axis of the amplitude characteristic of the traveling-wave tube amplifier are switched up to the output saturation point. In addition, with a characteristic that a constant amplitude is output for an input amplitude above the output saturation point, for the output phase, the phase shift amount when the output amplitude is input to the traveling wave tube amplifier is sign-inverted. It is preferable to convert the amplitude and phase of the input signal so as to obtain the above characteristics. As a result, the output of the traveling wave tube amplifier has a linear characteristic.

[0017]

DETAILED DESCRIPTION OF THE INVENTION The present invention will be described below with reference to the drawings. 1 to 6 are diagrams showing a high-frequency amplifier according to an embodiment of the present invention.

In FIG. 1, the high-frequency amplifier has a configuration in which a non-linear amplifier 2 such as a traveling-wave tube amplifier is preceded by a pre-circuit unit 1 for compensating the non-linear characteristic of the non-linear amplifier 2.

The front circuit section 1 includes an input frequency conversion section 11 for converting an input high frequency signal into a low frequency signal, an A / D conversion section 12a for converting an analog signal into a digital signal,
12b, an amplitude / phase control unit 13 for converting and outputting an amplitude / phase of an input signal, D / A conversion units 14a, 14b for converting a digital signal into an analog signal, and a low frequency signal into a high frequency signal. The output frequency conversion unit 15, an oscillator 16 that generates a signal having a preset frequency, and a 90-degree phase shifter 17 that changes the phase of the input signal by 90 degrees are provided.

The input frequency converter 11 includes a multiplier 111.
a, 111b and low-pass filters 112a, 112b are provided to convert an input signal into a quadrature signal (I signal, Q signal). Further, the amplitude / phase control unit 13 uses the I signal,
An amplitude / phase detector 131 that detects amplitude information and phase information from the Q signal, and an amplitude / phase detector 131 based on this amplitude information and phase information.
An amplitude / phase converter 132 for converting a phase and an amplitude / phase / quadrature signal converter 133 for converting the converted amplitude / phase into a quadrature signal are provided. The output frequency converter 15 includes a low-pass filter 151a and 151b and a multiplier 15
2a and 152b, an adder 153, and a band pass reactor wave unit 1
54, and converts the input quadrature signal into a high frequency signal.

In such a high frequency amplifier, the pre-circuit unit 1 has a function of improving the linearity of the non-linear amplifier 2.

For example, when the characteristic of the non-linear amplifier 2 is as shown in FIG. 7, in order to improve the linearity of the amplifier having such characteristic, a circuit having the input / output characteristic as shown in FIG. It can be installed in. The two dotted lines in the figure show the graph of the amplitude characteristic and the phase characteristic shown in FIG.

First, regarding the amplitude characteristic, up to the output saturation point (point of output amplitude 1 [V] shown in FIG. 7), a curve in which the horizontal axis and the vertical axis of the amplitude characteristic graph of FIG. With respect to the amplitudes of the input signals described above, the characteristics are such that a constant amplitude is output.

Regarding the phase characteristic, the output amplitude with respect to the input amplitude is obtained from the amplitude characteristic obtained by the above method, and the phase shift amount when this output amplitude is input is obtained from the phase characteristic graph of FIG. It is obtained by inverting the sign of the obtained phase shift amount.

By providing the front-end circuit section 1 with such input / output characteristics, the input / output characteristics of the high-frequency amplifier are linear in amplitude characteristics and zero in phase shift as shown in FIG. With such comprehensive characteristics, amplification of multi-valued modulated waves can be ideally performed.

Next, the operation will be described. When a high frequency signal having a center frequency fc and a bandwidth fb is input to the high frequency amplifier, the input frequency conversion unit 11 multiplies this input signal by the multiplier 1
A signal generated by the oscillator 16 by 11a and 111b,
This signal is multiplied by a signal whose phase is changed by 90 degrees to be converted into a quadrature signal composed of I signal and Q signal, and each signal is converted into a low frequency signal having a center frequency fp by the low pass filtering sections 112a and 112b. Output each. Here, it is preferable to select the center frequency fp near 0 Hz because the clock frequency of the digital circuit can be reduced. The frequency of the signal generated by the oscillator 16 is set to a value close to the center frequency fc of the input signal.

I signal output from the input frequency converter 11,
The Q signal is input to the A / D conversion units 12a and 12b, respectively, A / D converted at a frequency of fb + fp or higher in the A / D conversion unit, and the I signal and the Q signal output from the Q signal are shown in FIGS. The orthogonal signal points as shown in are obtained. However,
When the center frequency fp is not 0, the values shown in FIGS.
A signal in which the orthogonal signal points are rotating at the frequency fp is obtained as shown in FIG.

The A / D-converted signal is input to the amplitude / phase control unit 13, and the amplitude / phase detection unit 131 outputs the signal shown in FIG.
A memory table for performing conversion as shown in FIG. 5 (a conversion table in which output data (conversion data) is stored in a memory in which an input value is indexed as an index) is used to convert the values of the input I signal and Q signal from FIG. Detects the amplitude and the phase shown in FIG. 5, and outputs the detected amplitude and phase as amplitude information and phase information, respectively.

The amplitude / phase converter 132 receives the amplitude information and phase information output from the amplitude / phase detector 131,
Based on the amplitude information and the phase information, the amplitude and phase are converted and output by the memory table set so as to have the input / output relationship of FIG.

By the above processing, the amplitude / phase of the input signal is converted to have the input / output characteristic of FIG. 2 according to the input amplitude and is output to the amplitude / phase / quadrature signal converter 133. .

The amplitude / phase / quadrature signal converter 133 receives the amplitude and phase output from the amplitude / phase converter 132, and converts this amplitude and phase into quadrature components (I signal, Q signal) on the quadrature phase plane. It is converted into orthogonal components by a memory table set to be converted and output as I signals and Q signals, respectively.

The I and Q signals output from the amplitude / phase control unit 13 are converted into analog signals by the D / A conversion units 14a and 14b, respectively, and the output frequency conversion unit 15 becomes the center frequency fc of the input signal. Thus, the frequency is converted and output, and becomes the input signal of the non-linear amplifier 2 in the subsequent stage.

In this way, the signal whose amplitude and phase are converted according to the input / output characteristics of FIG. 2 and converted into a high frequency signal is input to the non-linear amplifier 2.

In the non-linear amplifier 2, since the non-linear characteristic works so that the amplitude / phase characteristic given by the pre-circuit section 1 becomes the characteristic of FIG. 3, the total characteristic of the pre-circuit section 1 and the non-linear amplifier 2 combined. Is as shown in FIG. 3, which is a high-efficiency, highly linear high-frequency amplifier.

FIG. 6 shows the result obtained by simulating the received signal points according to this embodiment. The calculation condition was OBO = 3 dB as in FIG. Comparing FIG. 6 and FIG. 4, it can be seen that in FIG. 6, the difference from the ideal point is much smaller than in FIG. Therefore, at this time, a significant improvement in the bit error rate characteristic can be expected.

As described above, in the present embodiment, the amplitude and phase are converted so that the output of the non-linear amplifier 2 has a linear characteristic by compensating for the non-linear characteristic of the post-stage non-linear amplifier 2 in the front circuit section 1. Therefore, a high-efficiency and highly linear high frequency amplifier can be obtained.

In this embodiment, a memory table is prepared and processed for each of the amplitude detection, phase detection, amplitude / phase conversion, and amplitude / phase / quadrature signal conversion of the amplitude / phase control unit 13. However, all of these may be converted by a single memory table.

[0038]

According to the present invention, since the non-linear characteristic of the non-linear amplifier is compensated by the pre-circuit section and the amplitude and phase of the input signal are converted so that the output of the non-linear amplifier becomes linear, The output of the amplifier can be made to have a linear characteristic, and multilevel modulation transmission can be efficiently performed.

If a traveling-wave tube amplifier is used as the non-linear amplifier and the front-end circuit section is set so as to compensate for the non-linearity of the traveling-wave tube amplifier, the linearity can be achieved without impairing the high efficiency of the traveling-wave tube amplifier. Can be amplified.

[Brief description of drawings]

FIG. 1 is a diagram showing a high frequency amplifier according to an embodiment of the present invention, and is a schematic block diagram thereof.

FIG. 2 is a diagram showing an input / output characteristic of the front circuit unit.

FIG. 3 is a diagram showing the total input / output characteristics.

FIG. 4 is a diagram showing the amplitude detection memory table.

FIG. 5 is a diagram showing a phase detection memory table.

FIG. 6 is a diagram showing a result obtained by simulating a reception signal point when a 32QAM modulated signal is received through the high frequency amplifier.

FIG. 7 is a diagram showing input / output characteristics of a conventional nonlinear amplifier.

FIG. 8 is a signal point arrangement diagram of conventional 8PSK modulation.

FIG. 9 is a signal point constellation diagram of conventional 32QAM modulation.

FIG. 10 is a diagram showing a result of simulating reception signal points when a 32QAM modulated signal is received through a conventional satellite repeater.

[Explanation of symbols]

1 Front circuit part 11 Input frequency converter 111a, 111b multiplier 112a, 112b Low-pass filter 12a, 12b A / D converter 13 Amplitude / phase control unit 131 Amplitude / phase detector 132 Amplitude / phase converter 133 Amplitude / Phase / Quadrature signal converter 14a, 14b D / A converter 15 Output frequency converter 151a, 151b Low-pass filter 152a, 152b Multiplier 153 adder 154 Bandpass Reactor 16 oscillators 17 90 degree phase shifter 2 Non-linear amplifier

Continued front page    F term (reference) 5J067 AA01 AA34 CA21 CA87 FA01                       FA19 HA48 KA00 KA16 KA26                       KA32 KA34 KA42 KA44 SA13                       TA01 TA02                 5J090 AA01 AA34 CA21 CA87 FA01                       FA19 HA48 KA00 KA16 KA26                       KA32 KA34 KA42 KA44 SA13                       TA01 TA02                 5J500 AA01 AA34 AC21 AC87 AF01                       AF19 AH48 AK00 AK16 AK26                       AK32 AK34 AK42 AK44 AS13                       AT01 AT02

Claims (2)

[Claims] 1. A non-linear amplifier having a non-linear characteristic, and a pre-circuit unit for converting an amplitude and a phase of an input signal in a front stage of the non-linear amplifier, the pre-circuit unit reducing a high-frequency signal to be input. An input frequency conversion section for converting into a frequency signal, an A / D conversion section for converting the low frequency signal converted by the input frequency conversion section into a digital signal, and an input signal from the digital signal converted by the A / D conversion section Amplitude / phase control unit that detects the amplitude and phase of the signal, converts the amplitude and phase based on the detected amplitude and phase, and converts the converted amplitude and phase into a quadrature signal for output, and the amplitude / phase control unit. A D / A converter for converting the quadrature signal output by the converter into an analog signal, and an output frequency converter for converting the analog signal output by the D / A converter into a high frequency signal having the same center frequency as the input signal. , Said non-linear A high-frequency amplifier, characterized in that the amplitude and phase of an input signal are converted so that the nonlinear characteristic of the amplifier is compensated and the output of the nonlinear amplifier becomes linear. 2. The non-linear amplifier is a traveling-wave tube amplifier, and the front-end circuit section replaces the horizontal axis and the vertical axis of the amplitude characteristic of the traveling-wave tube amplifier up to an output saturation point. In addition to the characteristics, it is a characteristic that outputs a constant amplitude with respect to the input amplitude above the output saturation point, and regarding the output phase, the phase shift amount when the output amplitude is input to the traveling wave tube amplifier is coded. The high frequency amplifier according to claim 1, wherein the amplitude and the phase of the input signal are converted so as to have the inverted characteristics.