JPH07101819B2 - Distortion compensation circuit in multi-frequency simultaneous amplifier - Google Patents

Description

The present invention relates to a distortion compensation circuit in a multi-frequency simultaneous amplifier,
More specifically, a multi-frequency amplifier capable of performing low-distortion and efficient signal amplification by automatically compensating for non-linear distortion components generated when a large number of radio frequency signals having different frequencies are simultaneously amplified by feedback control. Distortion compensation circuit in.

[Background of the Invention] Recently, the use of multiple frequencies has been promoted along with the development of wireless communication, and the demand for wideband multifrequency simultaneous power amplifiers (hereinafter referred to as multifrequency simultaneous amplifiers) has increased accordingly.

When such a multi-frequency simultaneous amplifier simultaneously amplifies a signal composed of a large number of radio frequencies, such as a transmission signal of a base station of a car telephone or a signal of a television broadcast wave, a non-input / output characteristic of the amplifier is used. Due to the linearity, a cross-modulation component is generated due to mutual interference between a plurality of signals, and this cross-modulation component adversely affects the characteristics of the multi-frequency simultaneous amplifier.

In order to reduce the influence of non-linear distortion such as cross-modulation, a multi-frequency simultaneous amplifier having a large saturation output and good linearity is required. An amplifying element such as a transistor capable of extracting a large output power is indispensable for such a multi-frequency simultaneous amplifier, but it is extremely difficult to efficiently extract a large output power by a single transistor. Therefore,
Usually, multi-frequency simultaneous amplifiers that employ the following three types of distortion reduction methods have been proposed.

The first method, as shown in FIG. 1, different frequencies f ₁ to the signal S ₁ (f ₁₎ for carrying the f _n to S _n (f _n) respectively to the amplifier a ₁ for each signal of a _n of Is used separately and the respective output signals are combined by the antenna duplexer 2, which is the method used in the current transmitters of automobile telephone base stations and high-power television broadcasters. In this system, the amplifiers a _{1 to} a _n have a frequency f ₁
To f _n , one for each, and those amplifiers
Since the antenna duplexer 2 for synthesizing the output signals of a _{1 to} a _n is also required, the device is upsized, and the frequency used cannot be changed easily because the antenna duplexer 2 limits the frequency to be used. It exposes the drawback.

The second method is, as shown in FIG. 2a, a multi-frequency signal using a wide band low distortion amplifier 4 having improved distortion characteristics of the amplifier.
In this method, S ₁ (f ₁ ) to S _n (f _n ) are combined by the n-wave combiner 6 and then amplified simultaneously. In this method, the frequency to be used can be freely changed, but the signal output level of the wide band low distortion amplifier 4 is changed to the saturation output of the wide band low distortion amplifier 4 because of the requirement to reduce the distortion generated in the wide band low distortion amplifier 4. There is a problem that the signal must be used at a signal level that is sufficiently smaller than the level, and as a result, the overall power use efficiency becomes extremely low. In this case, for example, when the frequency channel intervals are assigned with the frequency width Δf as shown in FIG. 2b,
In this, the frequency f _3, f ₄ 2 two signals adjacent channel corresponding to S ₃ (f _3), when S ₄ (f ₄₎ are input to the wideband low-distortion amplifier 4, the wideband low-distortion amplifier 4 tertiary distortion in the output terminal 8 nonlinearities that correspond to spurious frequency f _2, f ₅ of the tertiary distortion component as shown in the frequency f _3, the first equation and the second equation in the vicinity of f ₄ follows A component (see FIG. 2c) is generated, and the lower channel of each frequency f ₃ {hereinafter, C
Labeled (f ₃ )} and interferes with channel C (f ₄ ) above frequency f ₄ .

2f ₃ −f ₄ = f ₃ −Δf = f ₂ (1) 2f ₄ −f ₃ = f ₄ + Δf = f ₅ (2) Therefore, in this method, the generation of such spurious in the use band is reduced to a low level. Since it has to be suppressed, the signal output level of the wide band low distortion amplifier 4 cannot be increased to a predetermined level or higher. Therefore, the power efficiency of the wide band low distortion amplifier 4 is deteriorated, and in practice, it is extremely difficult to realize the high power wide band low distortion amplifier 4 by this method.

In the third method, as shown in FIG. 3, when the second method is adopted, the distortion component generated at the time of amplification is corrected by the predistortion compensator.
This is a so-called feedforward control system in which compensation is performed in advance with 10. The problem with this method is that, firstly, when the output level of the signal to be amplified, the number of signals, and the frequency arrangement change, the distortion component also changes, so the distortion compensation amount of the predistortion compensator 10 is readjusted each time. It has to be complicated. Second
Since it is difficult to design the dynamic range of the predistortion compensator 10 to be large, the multi-frequency simultaneous amplifier used for the application in which the output signal level of the wideband low-distortion amplifier 4 and the number of input signals change significantly This is because it cannot be used in a stable state. That is, since it is necessary to widen the dynamic range of the predistortion compensator 10 by 6 dB every time the signal frequency is doubled, the predistortion compensator 10 is required.
However, the multi-frequency simultaneous amplifier that uses is extremely difficult to deal with changes in the output signal level and the number of input signals.

[Object of the Invention] The present invention has been made in order to solve the above technical problem, and detects a non-linear distortion component generated when a large number of radio frequency signals are simultaneously amplified by a multi-frequency simultaneous amplifier. , Non-linear distortion is automatically compensated by supplying a component for compensating for the distortion component to the input side of the wide band low distortion amplifier as a feedback signal, thereby wide band and low distortion, more power efficient, and in use condition It is an object of the present invention to provide a multi-frequency simultaneous amplifier having a high possibility corresponding to the above.

[Means for Achieving the Object] In order to achieve the above object, the present invention provides, for example, a fourth embodiment.
As shown in FIG. 5 and FIG. 5, in a distortion compensation circuit in a multi-frequency simultaneous amplifier in which a large number of radio frequency input signals having different frequencies are combined by a multi-frequency synthesizer 22 and then amplified by a wide band low distortion amplifier 24, The first combiner 26 for branching the output signal of the distortion amplifier 24, the distortion detector 28 for detecting a distortion component from the signal branched by the first combiner 26, and the output signal of the multi-frequency synthesizer 22 as the main line signal. A second coupler 34 that branches into a sample signal, a distortion amplifier 38 that generates a distortion component from the sample signal, and a variable attenuator connected in series with the distortion amplifier 38.
40 and a variable phase shifter 42, a third coupler 36 that couples the output signal of the variable phase shifter 42 and the main line signal from the second coupler 34 and supplies the combined signal to the input side of the wide band low distortion amplifier 24, and Attenuator
40 and a control unit 30 connected to the control input terminal of the variable phase shifter 42 and connected to the distortion detector 28.
30 is a plurality of frequency data f ₁ of the radio frequency of the input signal,
After calculating frequency channels f _-1 , f ₀ , f ₄ , f ₅ of spurious components that can be separated from the frequency of the input signal among the spurious components generated in the wide band low distortion amplifier 24 based on f ₂ and f _3. , The distortion detector 28 is controlled so that the distortion component detected by the distortion detector 28 becomes the distortion component of the frequency of the calculated spurious component, and the variable attenuator is set so that the distortion component detected by the distortion detector 28 is minimized. It is characterized in that the attenuation factor of 40 and the phase of the variable phase shifter 42 are controlled.

[Embodiment] Next, preferred embodiments of a multi-frequency simultaneous amplifier incorporating an automatic distortion compensation circuit according to the present invention will be described in detail below with reference to the accompanying drawings.

In FIG. 4, reference numeral 20 indicates a multi-frequency simultaneous amplifier incorporating the automatic distortion compensation circuit according to the present embodiment, and the multi-frequency simultaneous amplifier 20 is basically a signal S having different frequencies.
A multi-frequency synthesizer 22 (hereinafter, referred to as an n-wave synthesizer) that synthesizes ₁ (f ₁ ) to S _n (f _n ) and distortion compensation that compensates the multi-frequency synthesized signal Q ₂ of the n-wave synthesizer 22. Section 23 and the distortion compensating section 23
The wideband low-distortion amplifier 24 that amplifies the multifrequency combined signal Q ₄ that has passed through, and the sample signal Q ₈ is extracted from the multifrequency combined signal Q ₆ of the wideband low distortion amplifier 24 via the first combiner 26, and Distortion detector 28 for detecting a distortion signal from the sample signal Q _8, and a distortion compensation signal for the multi-frequency composite signal Q ₂ input to the wideband low distortion amplifier 24 according to the distortion level data detected by the distortion detector 28. Of the amplitude control signal S _A and the phase control signal S _P for controlling the phase.

The multi-frequency combined signal Q ₂ which is the output signal of the n-wave combiner 22 is passed through the second combiner 34 and the third combiner 36 constituting the distortion compensator 23 as a multi-frequency combined signal Q ₄ in a wide band low frequency range. Distortion amplifier
Introduced to 24 input terminals. The multi-frequency composite signal Q ₂ input to the second combiner 34 is branched into a main line signal Q ₃ and a sample signal Q ₅ , of which the sample signal Q ₅ is input to a distortion amplifier 38 and the output of the distortion amplifier 38. The signal is amplitude-controlled under the control of the control unit 30 in the variable attenuator 40, and then phase-controlled under the control of the control unit 30 in the variable phase shifter 42 in the same manner, and then the third combination is performed as the distortion compensation signal Q _10. Is introduced to the other input terminal of the device 36.

Multi-frequency composite signal Q ₆ which is the output signal of wide band low distortion amplifier 24
Is output to the output terminal 44 via the first combiner 26 by the multifrequency composite signal Q.
While being introduced as _12, as described above, a portion of the signal distortion detector unit as a sample signal Q ₈ of the multi-frequency combined signal Q ₆
It is introduced into one of the input terminals of the frequency mixer 46 that constitutes 28. In this case, the output signal of the local oscillator 48 to the other input terminal of the frequency mixer 46 whose oscillation frequency is varied by the frequency control signal S _F from the control unit 30 is introduced.

The amplitude of the signal of the specific frequency detected by the frequency mixer 46 is measured by the level measuring device 50, and the distortion level data S _D from the level measuring device 50 is introduced into the control unit 30.
The control unit 30 outputs a frequency control signal S _F for controlling the output signal frequency of the local oscillator 48 from the frequency data S _FD input from the frequency data input terminal 52, and the distortion level data S _D and the frequency data S _FD. From the amplitude control signal S _{A and the} phase control signal S _P to the variable attenuator that constitutes the distortion compensator 23.
40 and variable phase shifter 42, respectively.

The multi-frequency simultaneous amplifier according to this embodiment is basically configured as described above, and its operation and effect will be described next.

Therefore, first, in the multi-frequency simultaneous amplifier 20, as shown in the spectrum diagram of FIG.
f _1, f _2, f ₃ multi-frequency signals S ₁ which is _{(f 1), S 2 (} f 2), S 3
The three waves of (f ₃ ) are input to the n-wave combiner 22. In the initial state, the amplitude control signal S _A and the phase control signal S _P from the control unit 30
Are both 0 levels, the multi-frequency composite signal Q ₂ is input to the wide band low distortion amplifier 24 as the multi-frequency composite signal Q ₄ with the spectrum value as it is.

As a result, third-order distortion occurs due to the nonlinearity of the input / output characteristics of the wide band low distortion amplifier 24, and the frequency component of the multi-frequency composite signal Q ₄ of the wide band low distortion amplifier 24 is the spurious component shown in FIG. It will be a component containing. The multi-frequency composite signal Q ₆ of the wide band low distortion amplifier 24 including this distortion component is supplied to the main line by the first combiner 26.
The signal is branched from 54 and is introduced into one input terminal of the frequency mixer 46 in the distortion detector 28 as the sample signal Q ₈ .

The frequency component of the spurious component shown in Fig. 5b is the input signal.
Assuming that the frequencies of S ₁ (f ₁ ), S ₂ (f ₂ ) and S ₃ (f ₃ ) have the relations shown in the third and fourth equations, as shown in the following fifth and thirteenth equations, are categorized.

f ₂ = f ₁ + Δf (3) f ₃ = f ₁ + 2Δf (4) 2f ₁ −f ₂ = f ₁ −Δf (5) 2f ₁ −f ₃ = f ₁ −2Δf (6) 2f ₂ -F ₁ = f ₃ (7) 2f ₂ -f ₃ = f ₁ (8) 2f ₃ -f ₁ = f ₃ + 2Δf (9) 2f ₃ -f ₂ = f ₃ + Δf (10) f ₁ + F ₂ −f ₃ = f ₁ −Δf… (11) f ₃ + f ₁ −f ₂ = f ₂ … (12) f ₂ + f ₃ −f ₁ = f ₃ + Δf… (13) Spurious classified in this way Of the components, the spurious components shown in equations 7, 8 and 12 correspond to the channel frequencies f ₁ , f ₂ and f ₃ currently in use, and adversely affect the signal, while other spurious components are used. Channel C
Corresponding to the frequencies of the channels near (f ₁ ), C (f ₂ ) and C (f ₃ ), they are mixed in the vacant channels as an interfering signal.

Multi-frequency composite signal Q ₆ which is the output signal of wide band low distortion amplifier 24
Is split by the first combiner 26 and is distorted (spurious) by the distortion detector 28.
In the case of measuring the level of
The spurious component shown in the equation is difficult to detect because it is superimposed on the signal frequencies f _{1 to} f ₃ , but the spurious component shown in the first, fifth, sixth, ninth, tenth, eleventh, and thirteenth equations is the input signal S ₁ ,
Since the frequency is different from S ₂ and S _3, it can be easily detected.

That is, the control unit 30 controls the signals S ₁ (f ₁ ) and S ₁ currently input to the n-wave synthesizer 22 from the frequency data input terminal 52.
₂ (f ₂ ), S ₃ (f ₃ ) corresponding frequency data S _FD representing the frequencies f ₁ , f ₂ , f ₃ and measurable spurious frequency channels C (f ₋₁ ), C (f ₀ ), C (f ₄ ), C
By calculating (f ₅ ) and controlling the frequency of the local oscillator 48, the frequency channels C (f ₋₁ ), C (f ₀ ), C
The spurious levels of (f ₄ ) and C (f ₅ ) are measured and the distortion level data S _D is taken into the control unit 30. Control unit
Reference numeral 30 controls the amplitude and phase of the distortion component generated in the distortion amplifier 38 as shown in FIG. 5c, and applies it to one input terminal of the third coupler 36. In this case, the main line signal Q ₃ from the second coupler 34 is introduced to the other input terminal of the third coupler 36.

Therefore, the multi-frequency composite signal Q ₄ including the distortion component applied to the wide band low distortion amplifier 24 becomes a signal in which the signal component S _X and the distortion compensation component S _Y are combined as shown in FIG. The multi-frequency composite signal Q _{6 that} has passed through the amplifier 24 is represented as a signal to which the distortion compensation component S _Y is newly added, as shown in FIG. Therefore, in the distortion detector 28, the distortion level data
The frequency channel C (f _-1 ) so that S _D is minimized
Through the amplitude control and the phase control corresponding to C (f ₅ ) to C (f ₅ ), it is possible to remove the distortion of the output multi-frequency combined signal Q ₁₂ as shown in FIG.

As described above, the multi-frequency simultaneous amplifier 20 including the distortion compensation circuit according to the present invention has a spurious signal that can be detected by the distortion detection unit 28 under the control of the control unit 30 even when the number of input signals or the frequency arrangement changes. The feedback control is performed at high speed so that the component is detected and the amount of distortion detected by the distortion detector 28 is minimized. Therefore, by using the multi-frequency simultaneous amplifier 20, the number of signals that can be amplified and the frequency arrangement can be freely changed and used.

Further, by adopting the automatic distortion compensation circuit according to the present invention, it is possible to downsize the amplifier main body, reduce power consumption, and reduce cost. The reason will be described below.

Generally, in a class A amplifier, the relationship between the signal output level of the amplifier and the spurious level of the third-order distortion component of the amplifier output has a property that the spurious level increases by 3 dB every time the signal output level increases by 1 dB. For example, in the multi-frequency simultaneous amplifier, when the output levels of the signals S ₁ (f ₁ ) and S ₂ (f ₂ ) are +30 dBm (1 W), the level of the distortion component of the output corresponding to this is −30 dBm, that is, Signal S ₁ (f ₁ ), S ₂ (f
Assuming that the output level of ₂ ) is -60 dB, the output levels of the signals S ₁ (f ₁ ) and S ₂ (f ₂ ) of this amplifier are respectively
When increasing by 10 dB to +40 dBm (10 W), the level of the distortion component of the output corresponding to this is 0 dBm, that is, the input signal S ₁
The output level of (f ₁ ) and S ₂ (f ₂ ) becomes −40 dB, and eventually the output signal level increases by 10 dB, resulting in a 20 dB deterioration in the signal-to-spurious ratio. When the number of output signals is doubled, the output peak power is increased by 6 dB and the signal-to-spurious ratio is deteriorated by 12 dB.

By the way, normally, in order to improve the distortion characteristic of the amplifier, the means for enlarging the amplifying element is adopted as described above, but the enlarging of the amplifying element also increases the power consumption. For example, when trying to reduce the output signal-to-spurious ratio to −60 dB or less, the allowable output level of the amplifier becomes 1 W without distortion compensation.

On the other hand, the output signal-to-spurious ratio is -40 dB by the multi-frequency simultaneous amplifier adopting the automatic distortion compensation circuit according to the present invention.
Can be improved to -60dB and the allowable output level can be expanded to 10W, which is 10 times. If the multi-frequency simultaneous amplifier according to the present invention is used for the purpose of using it within the allowable output level of 1 W, as described above, the number of signals that can be handled by the distortion compensation effect of 20 dB is about It can be tripled.

In other words, by implementing the automatic distortion compensation according to the present invention, it is possible to realize an amplifier having an allowable output level higher than that of a conventional one with a small amplifying element, and to reduce the size of the amplifier, reduce the power consumption, and effectively use the frequency. It is possible to plan.

In the present embodiment, the radio frequency signal input to the n-wave synthesizer 22 has been described as a three-frequency signal, but it goes without saying that the same can be applied to an input signal exceeding three frequencies.

[Advantages of the Invention] As described above, according to the present invention, in a multi-frequency simultaneous amplifier that simultaneously amplifies multi-frequency signals, the amount of non-linear distortion that occurs during simultaneous amplification is detected for each frequency, and amplitude compensation is performed. Phase compensation is implemented. Therefore, it is possible to reduce the non-linear distortion component that occurs when a multi-frequency signal is simultaneously amplified. Therefore, when allowing the same distortion component as the multi-frequency simultaneous amplifier according to the related art, it is possible to simultaneously realize downsizing, simplification, effective use of frequency, etc. of the multi-frequency simultaneous amplifier.

Although the present invention has been described with reference to the preferred embodiment, the present invention is not limited to this embodiment,
It goes without saying that various improvements and design changes can be made without departing from the scope of the present invention.

[Brief description of drawings]

FIG. 1 is a block diagram of a multi-frequency simultaneous amplifier according to the related art, FIG. 2 is an explanatory view of a multi-frequency simultaneous amplifier according to another conventional technology and its operation, and FIG. 3 is a multi-frequency simultaneous amplifier according to another conventional technology. 4 is a schematic block diagram of a multi-frequency simultaneous amplifier including a distortion compensation circuit according to the present invention, and FIGS. 5a to 5f are multi-frequency simultaneous amplifiers including the distortion compensation circuit. 3 is a frequency spectrum diagram for explaining the action of FIG. 20 ... Multi-frequency simultaneous amplifier, 22 ... n-wave synthesizer 24 ... Wide band low distortion amplifier, 28 ... Distortion detection section 30 ... Control section Q ₂ , Q ₄ , Q ₆ ... Multi-frequency synthesized signal Q ₃ … Main line signal, Q ₅ , Q ₈ … Sample signal S _A … Amplitude control signal, S _D … Distortion level data S _F … Frequency control signal, S _FD … Frequency data S _P … Phase control signal

Claims (1)

[Claims] 1. A distortion compensating circuit in a multi-frequency simultaneous amplifier which synthesizes a large number of radio frequency input signals having different frequencies by a multi-frequency synthesizer and then amplifies it by a wide band low distortion amplifier. A first combiner for branching, a distortion detector for detecting a distortion component from the signal branched by the first combiner, and a second combiner for branching an output signal of the multi-frequency synthesizer into a main line signal and a sample signal. A combiner, a distortion amplifier that generates a distortion component from the sampled signal, a variable attenuator and a variable phaser connected in series with the distortion amplifier, an output signal of the variable phaser, and the second combiner. A third combiner for combining the main line signal and supplying it to the input side of the wideband low-distortion amplifier, connected to the control input terminals of the variable attenuator and variable phaser, and connected to the distortion detector. System And a control unit, based on a plurality of frequency data of radio frequencies of the input signal, a spurious component separable from the frequency of the input signal among spurious components generated in the wideband low distortion amplifier. After calculating the frequency channel of, the distortion component is controlled so that the distortion component detected by the distortion detector becomes the distortion component of the frequency of the calculated spurious component, and the distortion component detected by the distortion detector is A distortion compensating circuit in a multi-frequency simultaneous amplifier, wherein an attenuation factor of the variable attenuator and a phase of the variable phase shifter are controlled so as to be a minimum.