JPH1117464A - Phase shifter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To execute the wide band conversion and high-stabilization of an amplitude characteristic in a phase shifter and to simplify adjustment work by providing a distributor, variable attenuators and a directional coupler and changing the respectively distributed signal levels so as to change the phases of signals. SOLUTION: An input terminal 1 is connected to a delay line 2 and the delay line 2 is connected to a power distributor 3. The first output of the power distributor 3 is connected to the first variable attenuator 4 and the second output of the power distributor 3 is connected to the variable attenuator 5. The first variable attenuator 4 is connected to the input of the directional coupler 6 and the second variable attenuator 5 is connected to the input of the directional coupler 6. The first output of the directional coupler 6 is connected to an output terminal 8 with an amplifier 7 and the second output of the directional coupler 6 is grounded. Then, the phases of the signals are changed by changing the respectively distributed signal levels in the phase shifter.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a linear compensating circuit for compensating for non-linearity of a power amplifier in a transmitting apparatus for performing radio transmission using digital data.

[0002]

2. Description of the Related Art As an example of the prior art, a phase shifter used in a feed-forward type linear compensation circuit of a power amplifier used for digital radio will be described. FIG. 4 is a block diagram of a feedforward linear compensation circuit, where 11 is an input terminal,
12 is a distributor, 13 is a power amplifier (PA), 14 is a phase shifter, 15
Is a power divider, 16 is a first adder, 17 is a delay unit, 18 is a linear amplifier (LA), 19 is a second adder, and 20 is an output terminal. The input terminal 11 is connected to a splitter 12, which is connected to a power amplifier 13 and a phase shifter 14. The power amplifier 13
Is connected to a power divider 15 which is a delay unit 17
And the first adder 16. The delay unit 17 is connected to a second adder 19. The phase shifter is connected to the first adder 16.
And the first adder 16 is connected to a linear amplifier 18. The linear amplifier 18 is connected to the second adder 19, which is connected to an output terminal 20.

Referring to FIG. 4, a feedforward type linear compensation circuit will be described. The modulated carrier is input from an input terminal 11 to a splitter 12, which transmits the input signal to a power amplifier 13 on the main signal path side and splits the signal to a phase shifter 14. The phase shifter 14 applies the same delay amount as the delay amount generated in the power amplifier 13 to the input signal, and adjusts the output signal of the power amplifier 13 so that the output signal has the opposite phase. The signal delayed by the phase shifter 14 and having the opposite phase is
Input to the first adder 16. The output of the power amplifier 13 is input to a power divider 15, which sends the input signal to a second adder 19 via a delay unit 17 and to the first adder 16. Distribute and send. Therefore, the output of the power amplifier 13 and the phase shifter 14 are added to the first adder 16.
Are input and added. The output of the power amplifier 13 has a distortion component due to its non-linearity.The output of the phase shifter 14 does not include the distortion component, and the output of the power amplifier 13 has a delay amount opposite to that of the output of the power amplifier 13. Are the same signal. Therefore, the two signals are added by the first adder 16, and only the distortion component generated from the power amplifier 13 is extracted. The distortion component output from the first adder 16 is input to a linear amplifier 18 and the linear amplifier 18
The output level of the second adder 19 is adjusted, and the output of the second adder 19 is output from the output terminal 20. The output of the power amplifier 13 is input to the second adder 19 with the same delay amount as that of the linear amplifier 18 given by the delay unit 17. Accordingly, in the second adder 19, the extracted distortion component is subtracted from the signal from the linear amplifier 18, and the distortion component included in the signal of the linear amplifier 18 is canceled to thereby reduce the nonlinear distortion. Compensation is provided. FIG. 3 shows a circuit configuration of the phase shifter 14 used in the linear compensation circuit.

FIG. 3 is a diagram showing a circuit configuration of a phase shifter used in a linear compensation circuit, wherein 1 is an input terminal, 2 is a delay line, 9 is a resonator, 10 is a variable attenuator (ATT), and 7 is an amplifier. , 8 are output terminals. In FIG. 3, the signal input from the input terminal 1 passes through the delay line 2 and is delayed by the delay generated by the power amplifier when output from the output terminal 8, and then transmitted from the resonator 9 to the variable attenuator 10. Is entered. The variable attenuator 10
The signal whose level has been adjusted is output from the output terminal 8 via the amplifier 7. That is, the phase is adjusted by the resonator 9,
By adjusting the level with the variable attenuator 10, distortion of the power amplifier is compensated. The resonator 9 is a bandpass filter, and the phase can be changed by changing the constants of the inductance L and the capacitance C in the resonator 9 with respect to the center frequency of the transmission carrier.
Regarding the change in amplitude due to the amplitude characteristic of the resonator 9,
The adjustment is performed by adjusting the amount of attenuation of the variable attenuator 10 at the subsequent stage. Regarding the state of the signals at the points A to D shown in FIG. 4, a single-frequency CW (Continuous Wave) is used as an input signal.
FIG. 5 is a vector diagram when e) is input from the input terminal 11.
Shown in In FIG. 5, the horizontal axis is the real axis (Re) when the signal component is displayed in a complex form, and the vertical axis is the imaginary axis (Im). Vector A
Is an output signal of the power amplifier 13, which is a signal distorted by the power amplifier 13, and includes a main signal component D output from the second adder 19 and a distortion component C extracted from the first adder 16.
Is a composite vector of By adding an inverse vector B of the main signal component D to this composite vector, a distortion component C
By taking out only the distortion component C from the output of the power amplifier, compensation is performed.

[0005]

In the above-mentioned conventional example,
Since the phase shifter has an amplitude characteristic (band characteristic) of 6 dB / Oct, if the spectrum of a transmission wave is widened due to modulation, the compensation amount varies due to the band characteristic. In particular, it becomes a problem when performing large-capacity transmission such as a video signal or wideband transmission such as spread spectrum. Also,
In order to secure a constant amount of compensation over a wide temperature range, it is necessary to use high-precision L or C or to add a temperature compensation circuit. Further, in the high frequency region, for example,
In the case of performing microwave transmission, it is necessary to configure the resonator with a distributed constant circuit, and there has been a problem that it takes a lot of time to adjust the phase shift amount to an optimum value.

SUMMARY OF THE INVENTION It is an object of the present invention to widen and stabilize the amplitude characteristic of a phase shifter and to simplify an adjustment operation.

[0007]

In order to achieve the above object, the present invention provides a phase shifter having a distributor and a directional coupler so as to adjust the level of each orthogonal signal. It was done.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIG. FIG. 1 is a block diagram illustrating a configuration example of a phase shifter according to the present invention, wherein 1 is an input terminal, 2 is a delay line, 3 is a power divider (PWR SPLT), and 4 is a first variable attenuator (ATT). ) And 5 are second variable attenuators (AT
T) and 6 are directional couplers composed of hybrid rings, 7 is an amplifier, and 8 is an output terminal. In FIG. 1, an input terminal 1 is connected to a delay line 2, which is connected to a power distributor 3. A first output of the power divider 3 is connected to a first variable attenuator 4, and a second output of the power divider 3 is a second output.
The first variable attenuator 4 is connected to a first input A of a directional coupler 6, and the second variable attenuator 5 is connected to a variable attenuator 5 of the directional coupler 6. It is connected to the second input B. A first output terminal of the directional coupler 6 is connected to an output terminal 8 via an amplifier 7, and a second output terminal of the directional coupler 6 is grounded. Hereinafter, this operation will be described. For simplicity, the delay time of delay line 2 is set to zero (τ =
0), and the attenuation of the first variable attenuator 4 and the second variable attenuator 5 is set to zero (AT = 0 (dB)). At this time, the state of the output signal from the directional coupler 6 constituted by a λ / 4 distributed constant circuit (hybrid ring) is represented by a vector diagram at the output point S as shown in FIG. It is output as a composite vector S of two orthogonal vectors P1 and P2 output from the distributor 3. At this time, since the amounts of attenuation of the first variable attenuator 4 and the second variable attenuator 5 are equalized, the phase angle of the composite vector S is 45 °. next,
Consider a case where the first variable attenuator 4 and the second variable attenuator 5 are set to arbitrary attenuation amounts. FIG. 2B shows a vector diagram when the attenuation amounts of the first variable attenuator 4 and the second variable attenuator 5 inserted in the two paths are set to different values. As shown in this figure, the phase angle of the combined vector S is different from the case of FIG. 2A (phase angle ≠ 45 °).
As described above, by setting the two variable attenuators to arbitrary values, it is possible to set an arbitrary phase angle from 0 ° to 90 °. The signal level after the synthesis is adjusted by the amplifier 7 at the subsequent stage. When the directional coupler 6 is formed of two parallel lines, a hybrid ring, a circular ring, or the like with an Au film on a dielectric substrate, the directional coupler 6 generally has a frequency of up to about 10 GHz when formed with a thick film, and a higher frequency when formed with a thin film. It can be used up to the band, has a wide band characteristic, and can change the phase very easily by changing the level of the two inputs with the variable attenuator as described above. Further, when this phase shift amount is made to correspond to all regions from 0 ° to 360 °, the delay amount of the delay line 2 is adjusted, the directional coupler 6 is connected in multiple stages, and the present invention is applied. Can be realized by connecting the phase shifters in multiple stages.

Next, an example in which this phase shifter is applied to linear compensation of a power amplifier will be described. FIG. 9 is a block diagram of a feed-forward type linear compensation circuit, which can be implemented by using the phase shifter 14 'of the present invention in FIG.

Next, an example in which the phase shifter of the present invention is applied to a predistortion type linear compensation circuit will be described with reference to FIG. FIG. 6 is a block diagram of a predistortion type linear compensation circuit, in which 11 is an input terminal, 12 is a divider, 21 is a distortion generator (RDA), 14 'is a phase shifter, 15 is a power divider, and 16 is a 1 is an adder, 19 is a second adder, and 22 is a variable attenuator (AT
T), 17 is a delay unit, 18 is a linear amplifier (LA), 13 is a power amplifier (PA), and 20 is an output terminal. In FIG.
The input terminal 11 is connected to a distributor 12, which is connected to a distortion generator 21 and a phase shifter 14 '. The phase shifter 14 'is connected to a power divider 15, which is connected to a linear amplifier 18 and a first adder 16. The linear amplifier 18 is connected to a second adder 19. The distortion generator 21 is connected to the first adder 16, and the first adder 16 is connected to a variable attenuator 22.
Connected to. The variable attenuator 22 is connected to the delay unit 17,
The delay unit 17 is connected to the second adder 19. The second
Adder 19 is connected to the power amplifier 13 and the power amplifier 13
Is connected to the output terminal 20.

Hereinafter, this operation will be described. In FIG. 6, a signal input from an input terminal 11 is distributed by a distributor 12, one of which is input to a distortion generator 21, and the other is input to a phase shifter 14. The output signal of the distortion generator 21 includes a main signal component and a distortion component. For the sake of simplicity, the input / output characteristics of the distortion generator 21 are the same as the input / output characteristics of the power amplifier 13. Suppose you do. On the other hand, the phase shifter on the main signal path side
In 14 ', the same amount of delay as the amount of delay generated by the distortion generator 21 on the other path side is given to the input signal, and the output signal of the distortion generator 21 has a phase opposite to that of the main signal component. Adjust the amount of phase shift. The signal delayed by the phase shifter 14 ′ and having an inverted phase is input to the power divider 15 and sent to the first adder 16 and the linear amplifier 18. The first adder 16
From the output signal of the distortion generator 21, the phase shifter 14 '
By subtracting the main signal component output from the first adder 16, only the distortion component is extracted as the output of the first adder 16. The level of the extracted distortion component is adjusted by the variable attenuator 22, and the other path (main signal path) is set by the delay unit 17.
After being given the same delay amount as that generated by the linear amplifier 18 on the side, it is input to the second adder 19. The second adder 19 subtracts the signal from the delay unit 17 from the main signal component that is the output of the linear amplifier 18 so that the inverse characteristic of the distortion generated in the power amplifier 13 at the subsequent stage becomes It will be added to the main signal in advance. When this signal is amplified by the power amplifier 13, distortion occurs due to non-linearity. However, the distortion component is canceled by a distortion component previously added to the input signal of the power amplifier 13, and as a result, the power amplifier
The distortion component generated in 13 is compensated. FIG. 7 shows a vector diagram when a single frequency CW (Continuous Wave) is input from the input terminal 11 as an input signal with respect to the state of the signals at the points E to H shown in FIG. In FIG. 7, the horizontal axis is the real axis (Re) when the signal component is displayed in a complex form, and the vertical axis is the imaginary axis (Im). A vector E is an output signal of the distortion generator 21 and is a signal including a distorted signal which is expected to be generated by the power amplifier 13 in the subsequent stage. The distortion component G extracted from the first adder 16 and a power amplifier It becomes a combined vector with the main signal component H output from 13. By adding the inverse vector F of the main signal component H to the combined vector, only the distortion component G is extracted, and the distortion component G is subtracted from the input of the power amplifier 13 to perform compensation.

Next, as an application example of the present invention, an application example to a transmitter in digital radio will be described. Fig. 8
FIG. 1 is a block diagram showing an example of a transmitter having a feedforward linear compensator using the present invention. 23 is a transmission data input terminal, 24 is a modulator (MOD), 25 is a mixer, 26 is a local oscillator, 27 is a bandpass filter, 28 is a preamplifier, 29 is a power amplifier (PA), 30 is an adder, 31 is a feed-forward type linear compensation circuit (FF), 32 is an antenna, and 33 is a directional coupler. The input terminal 23 is connected to a modulator 24, and the modulator 24 and the local oscillator 26 are
Connected to 25. The mixer 25 is a bandpass filter 27
, And the bandpass filter 27 is connected to a preamplifier 28. The preamplifier 28 is connected to a power amplifier 28 and to a feedforward linear compensation circuit 31 via a directional coupler 33. The power amplifier 29
And the feed-forward type linear compensation circuit 31
The adder 30 is connected to an antenna 31.

Hereinafter, this application example will be described. Serial data (transmission data) input from an input terminal 23 is input to a modulator 24. The modulator 24 performs serial-parallel conversion and multi-level conversion on the input signal, and arranges signal points according to a predetermined mapping. , 16QAM. The modulated wave output from the modulator 24 is input to a mixer 25, where the frequency is converted to a radio frequency band by a signal from a local oscillator 26. The frequency-converted signal passes through a band-pass filter 27 to remove harmonics, and is amplified by a preamplifier 28 and a power amplifier 29 to a predetermined transmission power. In digital radio transmission, when a modulation scheme such as multi-level QAM modulation such as 16QAM or QPSK is used, the linearity of a power amplifier is required in order to ensure transmission quality and to limit power leakage to adjacent channels. But,
On the other hand, improvement in power supply efficiency is required, and in order to satisfy both requirements, it is necessary to compensate for nonlinearity of the power amplifier. Further, as the capacity of transmission data, such as digital wireless transmission of video signals, increases, it is required to increase the transmission band and the transmission quality. Therefore, by using the linear compensator 31 using a wideband phase shifter as described in this embodiment, after compensating for the nonlinearity of the power amplifier 27,
This is transmitted from the transmission antenna 32.

[0014]

According to the present invention, a wideband and highly stable phase shifter can be realized with a relatively simple configuration, and a feedforward type and a predistortion type linear compensator are configured using this phase shifter. By doing so, it is possible to perform wideband digital transmission with high transmission quality and less unnecessary radiation.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention.

FIG. 2 is a phase vector diagram illustrating an example of the operation in FIG. 1;

FIG. 3 is a block diagram showing a conventional technique.

FIG. 4 is a block diagram illustrating a conventional feedforward linear compensation circuit.

FIG. 5 is a phase vector diagram illustrating an example of the operation of FIG. 4;

FIG. 6 is a block diagram showing another example of the operation of the linear compensation circuit of the present invention.

FIG. 7 is a phase vector diagram illustrating an example of the operation in FIG. 6;

FIG. 8 is a block diagram showing an example of a transmitter according to the present invention.

FIG. 9 is a block diagram illustrating an example of a feedforward linear compensation circuit according to the present invention.

[Explanation of symbols]

1: Input terminal, 2: Delay line, 3: Power divider (PWR
SPLT), 4: first variable attenuator (ATT), 5:
Second variable attenuator (ATT), 6: directional coupler,
7: amplifier, 8: output terminal, 9: resonator, 10: variable attenuator (ATT), 11: input terminal, 12: distributor,
13: Power amplifier (PA), 14, 14 ': Phase shifter, 15:
Power divider, 16: first adder, 17: delay, 1
8: linear amplifier (LA), 19: second adder, 20:
Output terminal, 21: Distortion generator (RDA), 22: Variable attenuator (ATT), 23: Input terminal, 24: Modulator (MO
D), 25: mixer, 26: local oscillator, 27: band-pass filter, 28: preamplifier, 29: power amplifier (PA), 30: adder, 31: feed-forward type linear compensation circuit (FF. ), 32: transmit antenna, 3
3: directional coupler,

Claims (4)

[Claims] 1. A phase shifter for changing a phase of a signal, a splitter for splitting the signal into two paths, a variable attenuator for changing a level of each signal distributed by the splitter, and a variable attenuator. A directional coupler for synthesizing the two signals attenuated by the phase shifter, wherein the phase of the signal is changed by changing the level of each of the distributed signals. 2. A feed-forward linear compensation circuit comprising the phase shifter according to claim 1. 3. A pre-distortion type linear compensation circuit comprising the phase shifter according to claim 1. 4. A digital wireless communication device having the linear compensation circuit according to claim 2.