JP3160081B2 - Distortion compensation circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a feed-forward type distortion compensating circuit for compensating for nonlinear distortion generated in a high-frequency power amplifier.

[0002]

2. Description of the Related Art In a microwave band transmitting apparatus which is required to transmit at a specified power while suppressing power efficiency, a power amplifier capable of producing a high output power with little non-linear distortion at its final stage. Is used.

[0003] Among the methods for realizing such a power amplifier, the output back-off system generally has a high power efficiency because an operating point of the amplifier is set lower than a saturation output because an input signal is modulated by transmission information. Cannot be obtained, and an amplifier having a sufficiently high saturation output level cannot be obtained. further,
In the negative feedback amplification system used in the region below the VHF band, stable operation cannot be expected at frequencies above the microwave band because the phase rotation of the feedback path increases. Therefore,
In a microwave band power amplifier, a distortion compensation circuit for compensating for intermodulation, AM-PM conversion, and other nonlinear distortion generated in the amplifier is added.

FIG. 3 is a diagram showing a configuration example of a conventional distortion compensation circuit. In the figure, an input signal S ₁ is provided to an input of a power divider (H) 41, one output of which is connected to an input of a power divider (H) 43 via a power amplifier 42. One output of the power divider 43 is connected to one input of a power combiner (H) 45 via a delay line 44, and its output is connected to an antenna system and a band-pass filter (BPF).
Connected to 46 inputs. The other output of the power divider 41 is connected to one input of a power combiner 49 via a variable phase shifter (Φ) 47 and a variable attenuator 48, and its output is connected to the input of a detector 50 and a variable phase shifter. (Φ) 51 is connected to the input. The output of the variable phase shifter 51 is connected to the other input of the power combiner 45 via a variable attenuator 52 and a compensation amplifier 53. The other output of the power divider 43 is connected to the other input of the power combiner 49 via the attenuator 54. The output of the band-pass filter 46 is connected to one input of a control unit 56 via a detector 55, and the output of the detector 50 is connected to the other input. A first output of the control unit 56 is connected to a control input of the variable phase shifter 47, and a second output of the control unit 56 is connected to a control input of the variable attenuator 48. A third output of the control unit 56 is connected to a control input of the variable phase shifter 51, and a fourth output of the control unit 56 is connected to a control input of the variable attenuator 52.

In the distortion compensating circuit having such a configuration, the power amplifier 42 amplifies the power of the input signal S ₁ (FIG. 4 (a)) supplied through the power divider 41, and obtains the power obtained by such amplification. The output signal S ₂ (FIG. 4B) is supplied to the power combiner 45 via the power distributor 43 and the delay line 44.

On the other hand, in the course of the initialization process started at the time of turning on the power, the control unit 56 controls the power combiner for all combinations of the phase shift amount of the variable phase shifter 47 and the attenuation amount of the variable attenuator 47. Signal S ₃ obtained at the output of 49 (FIG. 4 (c))
Is monitored via the detector 50, and the phase shift amount (hereinafter, referred to as “first initial phase shift amount”) and the attenuation amount (hereinafter, “first initial attenuation amount”) at which the power level is minimized. ) Are set in the variable phase shifter 47 and the variable attenuator 48, respectively.

The first initial phase shift amount set in this manner is determined by the power divider 41, the power amplifier 42, and the power divider 4
3. The amount of phase shift of the first signal path to the output end of the power combiner 49 via the attenuator 54, and the power combiner 49 via the power distributor 41, the variable phase shifter 47, and the variable attenuator 48. Are set to values at which the phase shift amount of the second signal path reaching the output end of the second signal path is substantially opposite in phase. Further, the first initial attenuation is set to a value at which the total gain of the first signal path is substantially equal to the total gain of the second signal path. Therefore, the output of the power combiner 49 cancels out the components of the input signal and the power amplifier 42
Is obtained. Hereinafter, a loop formed from the first signal path and the second signal path is referred to as a distortion extraction loop.

[0008] The band-pass filter 46 and the detector 55 are used to output signals of the power combiner 45.
The above-described power component S ₄ in the occupied band of the input signal S ₁ (FIG. 4
(d)) is extracted. The control unit 56 monitors such a power component S ₄ for all combinations of the phase shift amount of the variable phase shifter 51 and the attenuation amount of the variable attenuator 52 in the course of the above-described initialization processing, and Are obtained, and the variable phase shifter 51 and the variable attenuator are respectively obtained by calculating the phase shift amount (hereinafter, referred to as “second initial phase shift amount”) and the attenuation amount (hereinafter, referred to as “second initial attenuation amount”). Set to 52.

The second initial phase shift amount set in this way is determined by the phase shift amount of the third signal path to the output terminal of the power combiner 45 via the power divider 43 and the delay line 44, and the power shift amount. The amount of phase shift of the fourth signal path to the output terminal of the power combiner 45 via the distributor 43, the attenuator 54, the power combiner 49, the variable phase shifter 51, the variable attenuator 52, and the compensation amplifier 53 is The values are set to values that are almost opposite in phase. Further, the second initial attenuation is set to a value at which the total gain of the third signal path is substantially equal to the total gain of the fourth signal path. Therefore, the output of the power combiner 45, as indicated by a dotted line in FIG. 4 (d), the non-linear distortion components of the output signal S ₂ of the power amplifier 42 is contained in the signal is outputted is offset. Hereinafter, a loop formed by the third signal path and the fourth signal path is referred to as a distortion removal loop.

Further, even after completing such initialization processing, the control unit 56 controls the power level of the output signal S ₃ of the power combiner 49 provided via the detector 50 and the power level of the output signal S ₃ via the detector 55. Given output signal S ₄ of power combiner 45
The power levels of the variable phase shifters 47 and 51 and the attenuation amounts of the variable attenuators 48 and 52 are variably set by sequentially monitoring the power levels of the variable attenuators and the perturbation method.
Therefore, the output of the power combiner 45 includes the power amplifier 4
Signal suppressed component of the linear distortion contained in the second output signal S ₂ is obtained.

[0011]

By the way, in such a conventional distortion compensating circuit, the component of the nonlinear distortion S ₃ obtained at the output of the detector 50 and the output signal S ₄ obtained at the output of the detector 55 are different from each other. , The input signal S ₁ at these power levels
Is used as a reference of the perturbation method for variably controlling the phase shift amounts of the variable phase shifters 47 and 51 and the attenuation amounts of the variable attenuators 48 and 52 despite the superimposition of the level variation of When the level of the input signal fluctuates, the accuracy of distortion compensation decreases.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a distortion compensating circuit capable of accurately performing distortion compensation on an input signal having a level fluctuation.

[0013]

FIG. 1 is a block diagram showing the principle of the present invention. The present invention relates to an input signal processing means for shifting a power level and a phase of an input signal branched from a signal path for providing an input signal to a power amplifier, an output signal of the power amplifier, and a power supply through the input signal processing means. A distortion extraction unit for extracting a distortion component included in the output signal by synthesizing the input signal whose level and phase are shifted; and for the output signal, the output signal and the distortion component extracted by the distortion extraction unit are In a distortion compensating circuit comprising a distortion compensating means 15 for synthesizing in the opposite phase and suppressing the distortion component, a distortion compensating means 15 is used to calculate a product of the input signal and the output signal whose power level and phase are shifted via the input signal processing means 11 Detects the phase difference between these signals and reduces the phase difference
Phase control means 17 for varying the amount of phase shift by the input signal processing means 11;
1 to detect a difference in power level between the input signal and the output signal whose power level and phase are shifted, and reduce the difference .
Power control means 19 for varying the amount of shift of the power level to be shifted by the input signal processing means 11 in the direction .

[0014]

According to the present invention, the phase control means 17 controls the input signal whose power level and phase are shifted via the input signal processing means 11 and the output signal of the power amplifier corresponding to the input signal without such shift. And the phase difference included in the result of the multiplication is detected, and the phase shift amount of the input signal processing means 11 is varied in a direction in which the phase difference decreases. In parallel with the operation of the phase control unit 17, the power control unit 19 detects the difference between the power levels of the two signals described above, and adjusts the power level of the input signal processing unit 11 in a direction in which the difference decreases. Variable shift amount.

The result of the above-mentioned multiplication includes a first signal path from the signal path providing the input signal to the output of the distortion extracting means 13 via the power amplifier, and a power amplifier from the branch point of the signal path described above. Instead, the difference in the amount of phase shift from the second signal path leading to the output of the distortion extracting means 13 is uniformly included even if the power level of the input signal or the amplification of the power amplifier fluctuates.

That is, in the input signal processing means 11, even if the power level of the input signal or the amplification of the power amplifier fluctuates, the difference in the phase shift amount between the first signal path and the second signal path described above Since the difference of the total gain is corrected stably and accurately, the distortion component included in the output signal is accurately extracted at the output of the distortion extraction unit 13, and the distortion component is stably detected at the output of the distortion compensation unit 15. A compensated output signal is obtained.

[0017]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 2 is a diagram showing one embodiment of the present invention.

In the figure, components having the same functions and configurations as those shown in FIG. 3 are denoted by the same reference numerals, and description thereof is omitted here. In the present embodiment, the characteristic feature of the present invention is that the control unit 5 is provided between the control input of the variable phase shifter 51 and the variable attenuator 52 and the output of the detector 55.
A control unit 21 in place of 6, instead of the variable phase shifter 47 includes a variable phase shifter 22, a power distributor 23 ₁ between the one input and the output of the power combiner 49 of the variable attenuator 48 provided, comprising a power divider 23 ₂ between the input other outputs and the power combiner 49 of the attenuator 54, power divider 23 _1, 2
3 and ₂ of the not connected to the power combiner 49 output lies in having a distortion extraction control unit 24 between the control input of the variable phase shifter 22 and the variable attenuator 48.

In the variable phase shifter 22, in addition to the power distributor 41,
Output is 90 degree hybrid (HYB) 25₁Entering
Connected to power. 90 degree hybrid 25₁One out of
Power is multiplier 26₁Connected to one input of the
90 degree hybrid 25_TwoConnected to one input of
90 degree hybrid 25₁Is output from the multiplier 26 _Two
Is connected to one input of the
C25_TwoIs connected to the other input. Multiplier 26₁, 2
6_TwoIs input to the other input of the phase shift amount control of the distortion extraction control unit 24.
Connected to output, 90 degree hybrid 25_TwoOutput is acceptable
It is connected to the input of a variable attenuator 48.

In the distortion extraction control unit 24, the power distributor 23
Input corresponding to ₁ is connected to one input of the multiplier 28 through the AGC amplifier 27 _1, the input corresponding to the power distributor 23 ₂ connected to the other input of the multiplier 28 through the AGC amplifier 27 ₂ Is done. The output of the multiplier 28 is connected to the input of a voltage comparator 29 (CMP), and its non-inverted output and inverted output are connected to the input of an up-down counter (UDC) 30. The count output of the up / down counter 30 is connected to an address input of a read only memory (ROM) 31, and its output is a D / A converter (D / A) 32
Connected to the input of Two outputs of the D / A converter 32 are respectively connected to the other inputs of the multipliers 26 ₁ and 26 ₂ . The AGC voltage outputs of the AGC amplifiers 27 ₁ and 27 ₂ are connected to the input of the control circuit 33 (CNT), and the output is connected to the control input of the variable attenuator 48.

The correspondence between the present embodiment and the block diagram shown in FIG.
2 and the variable attenuator 48 correspond to the input signal processing means 11, the power dividers 23 ₁ and 23 ₂ and the power combiner 49 correspond to the distortion extractor 13, and the delay line 44, the power combiner 4
5, variable phase shifter 51, variable attenuator 52, compensation amplifier 5
3. The band pass filter 46, the detector 55, and the control unit 21 correspond to the distortion compensating means 15, and the AGC amplifier 2
7 ₁ , 27 ₂ , multiplier 28, voltage comparator 29, up / down counter 30, read-only memory 31 and D /
The A converter 32 corresponds to the phase control means 17 and has an AGC
The amplifiers 27 ₁ and 27 ₂ and the control circuit 33 correspond to the power control unit 19.

The operation of this embodiment will be described below. The setting and variable control of the phase shift amount of the variable phase shifter 51 and the attenuation amount of the variable attenuator 52 are similarly performed by the control unit 21 instead of the conventional control unit 56, and therefore, the description thereof is omitted here. .

In the distortion extraction control unit 24, the AGC amplifier 2
7 ₁ amplifies a constant level signal input via the second signal path to the power combiner 49 is taken via a power divider 23 _1. AGC amplifier 27 ₂ amplifies the constant level signal input through the first signal path to the power combiner 49 is taken via a power distributor 23 _2. The multiplier 28 multiplies the two signals thus amplified to generate a voltage signal indicating a phase difference between these signals (the above-described first signal path and second signal path). I do. The voltage comparator 29 compares such a voltage signal with a predetermined threshold to obtain a difference in the amount of phase shift between the first signal path and the second signal path, and advances the phase according to the difference. It is output as a non-inverted output indicating (delay) and an inverted output indicating phase delay (advance). The up / down counter 30 integrates such a comparison result based on a predetermined clock and encodes the above-mentioned difference in the amount of phase shift. The read-only memory 31 stores control information to be given to the variable phase shifter 22 in advance corresponding to all possible values of such a difference in the phase shift amount.
Those corresponding to the difference in the phase shift amount given from the up / down counter 30 are sequentially read out and output. The D / A converter 32 converts the control information read in this way into voltage signals respectively corresponding to two orthogonal basebands and outputs them.

In the variable phase shifter 22, the 90-degree hybrid 25 ₁ branches the input signal S ₁ into two routes with a phase difference of 90 degrees. Multipliers 26 ₁ and 26 ₂ individually multiply the two voltage signals described above in each of these paths, and
Degrees hybrid 25 ₂ outputs a result of such multiplication recombined to. Thus, the variable phase shifter 22 corrects the difference in the amount of phase shift between the first signal path and the second signal path detected by the distortion extraction control unit 24. Here, regarding the gain control characteristics of the AGC amplifiers 27 ₁ and 27 ₂ , the amplitude and the phase of the two input signals of the multiplier 28 are balanced.
What is necessary is just to be able to set within a predetermined range according to the fluctuation of the level of the input signal or the amplification degree of the power amplifier 42.

In the distortion extraction control section 24, the AGC voltage outputs of the AGC amplifiers 27 ₁ and 27 ₂ are supplied to the power level of the input signal S ₁ passing through the second signal path and passing through the first signal path, respectively. voltage signal indicative of the power level of the output signal S ₂ of the power amplifier 42 to be obtained. The control circuit 33 calculates the difference between the voltage signals,
A voltage signal indicating a magnitude relationship between the total gain of the first signal path and the total gain of the second signal path is generated. Variable attenuator 4
8 corrects the difference in the total gain described above by varying the amount of attenuation according to the voltage signal generated by the control circuit 33 in this manner.

As described above, according to this embodiment, the difference in the amount of phase shift between the first signal path and the second signal path is uniformly detected and corrected by phase detection, and in parallel with the correction. Thus, the difference between the total gains of these signal paths can be reliably corrected. Therefore, as compared with the conventional method of correcting nonlinear distortion remains variation is remained in the amplification degree of the level variation and the power amplifier 42 of the input signals S ₁ which is not absorbed by the distortion extracting loop, compensation accuracy can be improved. In addition, the control of the phase shift amount of the variable phase shifter 51 and the control of the attenuation amount of the variable attenuator 52 are performed by the single control unit 56 in the conventional manner.
1 and the distortion extraction controller 24,
The balance of these target value control operations is enhanced.

In this embodiment, in order to absorb the level fluctuation of the input signal and the fluctuation of the amplification degree of the power amplifier, and to detect the total gain of the first signal path and the second signal path. Although the AGC amplifiers 27 ₁ and 27 ₂ are used, the present invention is not limited to such a configuration.
The GC amplifier and the entire distortion extraction control unit 24 may be realized using a DSP that performs equivalent operations.

Further, in this embodiment, an example of application to a transmitter in the microwave band has been described. However, the present invention is not limited to such a device, and it is required to perform power amplification with low distortion. The present invention can be applied to any device as long as it is a device, and the frequency band of the input signal, the presence or absence of modulation, and the modulation method are not limited at all.

[0029]

As described above, according to the present invention, the signals input to the two inputs of the distortion extracting means are multiplied by the signals supplied from the signal path for supplying the input signals, and the phase difference between these signals is calculated by the power of the input signal. Even if the level or the amplification of the power amplifier fluctuates, it is uniformly detected and corrected.

That is, since the distortion component contained in the output signal of the amplifier can be obtained more stably and more accurately at the output of the distortion extracting means, the accuracy and stability of the distortion compensation can be improved.

The detection and correction of the phase difference are individually performed in parallel with the control of the power control means for absorbing the difference between the total gains of the two signal paths leading to the two inputs of the distortion detection means. In addition, since the processing is performed separately from the processing of the distortion compensating means, the balance and stability of the variable control of the phase and the gain necessary for maintaining the distortion compensation characteristics are improved.

Therefore, the performance of the power amplifier to which the distortion compensation circuit according to the present invention is added can be enhanced.

[Brief description of the drawings]

FIG. 1 is a principle block diagram of the present invention.

FIG. 2 is a diagram showing one embodiment of the present invention.

FIG. 3 is a diagram illustrating a configuration example of a conventional distortion compensation circuit.

FIG. 4 is a diagram illustrating a frequency spectrum of a signal in each section of the distortion compensation circuit.

[Explanation of symbols]

 Reference Signs List 11 input signal processing means 13 distortion extraction means 15 distortion compensation means 17 phase control means 19 power control means 21, 56 control unit 22, 47, 51 variable phase shifter (Φ) 23, 41, 43 power distributor (H) 24 Distortion extraction controller 25 90-degree hybrid (HYB) 26 multiplier 27 AGC amplifier 28 multiplier 29 voltage comparator (CMP) 30 up / down counter (UDC) 31 read-only memory (ROM) 32 D / A converter (D / A) 33 control circuit (CNT) 42 power amplifier 44 delay line 45, 49 power combiner (H) 46 band pass filter (BPF) 48, 52 variable attenuator 50, 55 detector 53 compensation amplifier 54 attenuator

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H03F 1/32

Claims (1)

(57) [Claims] 1. An input signal processing means for shifting a power level and a phase of an input signal branched from a signal path for supplying an input signal to a power amplifier, an output signal of the power amplifier, and the input signal processing means. (11) a distortion extraction unit (13) that combines an input signal whose power level and phase are shifted to extract a distortion component included in the output signal, and for the output signal, A distortion compensating means (15) for synthesizing the distortion component extracted by the distortion extracting means (13) in a reverse phase to suppress the distortion component, wherein the input signal processing means (11) through detecting a phase difference between these signals from the product of the input signal and the output signal and the power level and the phase was shifted, towards which the phase difference is reduced
Countercurrent, the input signal processing means (11) phase control means which varies the shift amount of the phase shifting (17), the input signal shifted and the power level and phase through the input signal processing means (11) And a power control means (19) for detecting a difference in power level between the input signal processing means and the output signal, and varying a shift amount of the power level shifted by the input signal processing means (11) in a direction in which the difference is reduced. A distortion compensation circuit.