JP2003142950A - Power amplifier - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a power amplifying device which performs high-precision distortion compensation by always holding at the optimum level an envelope detection output supplied to a control part which performs control for suppressing a distortion generated when a signal having envelope variation is amplified. SOLUTION: The power amplifying device includes a power amplifier which amplifies the signal having envelope variation, a prepositioned compensation part which performs distortion compensation for the signal so as to remove the distortion generated owing to the nonlinearity that the power amplifier has, a control part which controls the distortion compensation of the prepositioned compensation part, a detection part which generates the envelope detection output to be inputted to the control part from the signal, and a gain varying means which is inserted between the detection part and control part and varies the level of the envelope detection output to a specified value.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power amplifier suitable for application to a communication device that performs wireless transmission or wire transmission by a linear modulation method, or a communication device that simultaneously amplifies a plurality of signals having different frequencies.

[0002]

2. Description of the Related Art For example, Japanese Patent No. 2746130 discloses a technique of compensating for a distortion component due to the non-linearity of a power amplifier by means of a pre-compensation unit at the input of the power amplifier. Hereinafter, a conventional example of a power amplification device including such a front-end compensation unit will be described with reference to FIGS. 5 and 6.

QPSK (Quadrature Phase Shift Keyin
g), QAM (Quadrature Amplitude Modulation) or OFDM (Orthogonal Frequency Division Multiplexing)
A high-frequency signal whose modulated wave is modulated by a modulation method such as g) is accompanied by envelope fluctuation. A high-frequency signal accompanied by such envelope fluctuation is input from the input terminal 1 and distributed by the distributor 2 into two paths. One of the distributed signals is detected by the input signal detection unit 8 and input to the control unit 10. The other output of the distributor 2 is input to the power amplifier 5 via the delay element 3 and the pre-compensation unit 4. The signal amplified to the desired power by the power amplifier 5 is output from the output terminal 7 via the directional coupler 6.

In the power amplifier 5, the elements constituting the amplifier 5 usually have a characteristic that the amplification gain decreases as the input signal increases (hereinafter referred to as "AM-AM conversion"), and the phase increases as the input signal increases. Has a non-linearity such as a characteristic of changing (hereinafter referred to as "AM-PM conversion"). Therefore, when the above high frequency signal is input,
Intermodulation distortion occurs due to the envelope variation. Since this distortion causes a problem such as deterioration of signal quality or interference with other communication channels, the level of the distortion component is strictly limited by laws and regulations, especially in wireless communication and the like.

The front compensator 4 is for canceling and suppressing the distortion component generated in the power amplifier 5, and is inserted in front of the power amplifier 5. Hereinafter, the distortion suppression by the predistortion unit 4 will be described with reference to FIGS. 7 and 8. Figure 7 shows the amplifier
It is a vector diagram for explaining AM-AM conversion and AM-PM conversion characteristics.

Letting R be the magnitude of the vector of the signal after amplification assuming that the signal is amplified by an ideal power amplifier having no distortion, and its phase angle be θ, the signal amplified by the power amplifier having distortion. Will change the magnitude of the vector to R ′ by the AM-AM conversion, and further change the phase to θ ′ by the AM-PM conversion, resulting in a phase shift of Δθ.
The amount of deviation due to AM-AM conversion or AM-PM conversion depends on the input level, and the relationship between the output level and the phase with respect to the input level is as shown in FIG.

Therefore, by providing the input signal with a non-linear characteristic opposite to the non-linear characteristic of the power amplifier itself, that is, by realizing the characteristic shown by the broken line in FIG. 8, the distortion component is canceled. , That suppression is possible. Distortion compensation is given to the input signal by the inverse nonlinear characteristic.

The front compensator 4 is composed of a variable attenuator 41 and a variable phase shifter 42 in the example shown in FIG. 5, and the variable attenuator 41 generates an inverse characteristic to the AM-AM conversion characteristic of the power amplifier 5. Further, the inverse characteristic with respect to the AM-PM conversion characteristic is generated by the variable phase shifter 42.

At this time, as described above, since the nonlinear characteristic of the power amplifier 5 depends on the input level, the control unit 10
Generates a control signal corresponding to a change in the envelope level of the input signal, thereby setting the attenuation amount of the variable attenuator 41 and the phase amount of the variable phase shifter 42.

When the control unit 10 has the configuration shown in FIG.
The envelope signal detected by the input signal detection unit 8 is input terminal
After being input from 102, it is converted into a digital signal by an AD (Analog to Digital) converter 106. The control unit 10
On the other hand, a distortion component is extracted from the output signal of the power amplifier 5 that is input from the output signal detector 9 and converted into a digital signal by the AD converter 108, and a control signal that minimizes this distortion component level. Is calculated by the calculation unit (CALC) 107, and the calculated control signal is calculated by the DA (Digital to Analog) converters 109, 11
Output via 0. The delay element 3 is inserted in the input section of the pre-compensation section 4 so as to cancel the delay due to the processing time in the control section 10.

[0011]

In the above-mentioned conventional example,
When converting the envelope detection output on the input side to a digital signal,
It is necessary to adjust the dynamic range of the AD converter to be optimum. That is, such adjustment is required when the maximum value of the envelope signal constantly exceeds the dynamic range of the AD converter, or conversely, the maximum value of the envelope signal can be handled by the AD converter. This is to relieve that the required compensation accuracy cannot be obtained when the level is significantly lower than the signal level. In addition, even if adjustments are made at the time of shipment and optimization is performed, the correct detection result for the input power may not be obtained due to changes in the temperature of the detection unit and changes over time, which causes the problem of deterioration of compensation accuracy. It was

An object of the present invention is to provide a power amplifying device which carries out highly accurate distortion compensation by always keeping the envelope detection output at an optimum level.

[0013]

In order to achieve the above object, a power amplification device of the present invention is provided with a power amplifier for amplifying a signal accompanied by envelope fluctuation, and a distortion caused by non-linearity of the power amplifier. A pre-compensation unit that applies distortion compensation to the signal to remove it, a control unit that controls the distortion compensation amount of the pre-compensation unit, and an envelope detection output that is input to the control unit are generated from the signal. And a gain varying means for changing the level of the envelope detection output to a predetermined value, which is inserted between the detecting section and the control section. By the operation of the gain varying means, the envelope detection output can always be set to the optimum level, and highly accurate distortion compensation can be performed.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, a power amplifier device according to the present invention will be described in more detail with reference to the embodiments of the invention shown in FIGS.

In FIG. 1, the input signal from the input terminal 1 is divided into two paths by the distributor 2. One of the distributors 2
It is connected to the directional coupler 6 via the delay element 3, the pre-compensation section 4 and the power amplifier 5, and the other side of the divider 2 is connected to the control section 10 via the input signal detection section 8 and the variable gain element 11.
Connected with. The output signal of the power amplifier 5 is divided into two paths by the directional coupler 6, one of the directional couplers 6 is connected to the output terminal 7, and the other one is connected via the output signal detector 9 to the controller. Connected with 10. The control unit 10 includes a variable attenuator 41 and a variable phase shifter 42 that form the front-end compensation unit 4.
Is also connected to the variable gain element 11.

The operation of the power amplifier of this embodiment will be described below. A modulated wave which has an envelope variation such as QAM or OFDM and which is modulated by a linear modulation method is input to the input terminal 1 as an input signal. The input signal is distributed by the distributor 2, and one of the signals is input to the power amplifier 5 via the delay element 3 and the pre-compensation unit 4.

The power amplifier 5 has a non-linear characteristic and generates intermodulation distortion when there is no distortion compensation. This distortion component is
As mentioned above, the level is strictly restricted by laws and standards. Therefore, the pre-compensation unit 4 has the power amplifier 5
The distortion component generated at is suppressed by cancellation, and distortion compensation is performed. The variable attenuator 41 of the pre-compensation unit 4 receives the control signal from the control unit 10 and gives a characteristic opposite to the AM-AM conversion characteristic of the power amplifier 5 to the input signal to the power amplifier 5, The variable phase shifter 42 of the compensator 4 receives the control signal from the controller 10 and gives a characteristic opposite to the AM-PM conversion characteristic of the power amplifier 5 to the input signal to the power amplifier 5. As described above, distortion compensation is given to the input signal.

This distortion compensation will be described in more detail. FIG. 2 shows an example of the configuration of the control unit 10 shown in FIG. The detection signal input terminal 102 for inputting the signal from the variable gain element 11 is connected to the data calculation unit (CALC) 107 via the AD converter 106 and at the same time connected to the gain control terminal 101 via the level detection unit 111. To be done. Further, the distortion signal input terminal 105 for inputting the signal from the detection unit 9 is the AD converter 1
It is connected to the data calculation unit 107 via 08. The data calculation unit 107 receives the variable attenuator control terminal 10 via the DA converter 109.
3 is connected to the variable phase shifter control terminal 104 via the DA converter 110.

The envelope detection output is input to the detection signal input terminal 102 from the detection unit 8 via the variable gain element 11. The envelope detection output is a signal capable of detecting the high frequency power of the input signal to the detection unit 8. The detected output is converted into digital data by the AD converter 106.

Since the distortion characteristic of the power amplifier 5 depends on the input power, the level of the input signal, that is, the input power is obtained from the data output from the AD converter 106, while the input from the detector 9 is further converted. The distortion component is extracted from the output signal of the power amplifier 5, which is converted into a digital signal by the device 108,
A control signal that minimizes the level of this distortion component is obtained by the calculation unit 107, and the obtained control signal is output via the DA converters 109 and 110.

At this time, the output level of the detector 8 is AD
It should be at the optimum level for the dynamic range of the converter 106. FIG. 3 is a diagram showing the relationship between the power of the input signal of the detection unit 8 and the output voltage. For example, let P1 be the average power of the modulation signal that is the input signal, and let V1 be the input of the AD converter 108 for giving the optimum compensation value at that time. When the characteristic of the detecting unit 8 is as shown by the dotted line in FIG. 3 due to the characteristic variation of the detecting unit 8 or the adjustment error, the output value becomes V1 ′, and thus an error may occur in the compensation value. Become. Further, in the vicinity of the maximum value of the input power, the AD converter 108 is saturated before the input power becomes the maximum and the output thereof overflows, so that correct compensation cannot be performed.

As described above, it is necessary to use a wide dynamic range as much as possible in order to prevent overflow even at the instantaneous maximum value of envelope fluctuation and to reduce the influence of quantization noise and the like. . Therefore, the level detection unit 111 monitors the state of each bit of the output of the AD converter 106 and controls the variable gain element 11 so that the input level of the AD converter 106 becomes optimum.

As a method for determining whether the input level to the AD converter 106 is appropriate, for example, in the case of an AD converter having a binary output (all "0" is the minimum value and all "1" is the maximum value). , All the bits of the AD converter 106 are monitored, and all the bits become 1 within a certain fixed time. If a certain number of times or more, it is judged that the input is excessive, and conversely within a certain specified time. If the most significant bit never becomes 1, the method of determining that the level is too low is adopted. When it is determined that the input is excessive, the gain of the variable gain element 11 is decreased, and when it is determined that the level is too low, the gain of the variable gain element 11 is increased. Note that some AD converters can detect an overflow, and in that case, an overflow detection signal may be used.

In the present invention, the pre-compensation unit 4 is shown in FIG.
The present invention is not limited to the configuration shown in FIG. 4 and can be realized by the configuration shown in FIG. 4, for example. The precompensation unit 4 configured as shown in FIG. 4 and its operation will be described below.

In FIG. 4, a modulated signal input terminal 401
Is connected to the multipliers 404 and 406 via the 90 ° distributor 402, and the multipliers 404 and 406 are connected to the adder 407,
The adder 407 is connected to the output terminal 408. In addition, the control signal input terminal 403 includes a multiplier 404 and another control signal input terminal 405.
Is connected to the multiplier 406. Input terminal 401 is connected to delay element 3 in FIG. 1, and output terminal 408 is connected to power amplifier 5 in FIG.

Next, the compensating operation of the front compensator 4 shown in FIG. 4 will be described. As described above, since the distortion generated in the power amplifier 5 is due to the AM-AM conversion characteristic and the AM-PM conversion characteristic of the power amplifier 5, the relationship between the input and output signals of the power amplifier having the non-linear characteristic is shown in FIG. It can be represented by a vector diagram of 7. From the relationship of this figure, the amplitude and phase of the signal input from the input terminal 401 may be changed so that the magnitude of the vector of the power amplifier input signal becomes R / R ′ and the phase becomes (θ + Δθ). This operation is realized by separating the same input signal into the in-phase component and the quadrature component, applying amplitude modulation corresponding to R / R 'and (θ + Δθ) to each of the separated signals, and then adding both. can do.

Therefore, the signal input from the input terminal 401 is separated into mutually orthogonal signal components by the 90 ° distributor,
The adder 40 controls the amplitude and amplitude ratio of each component by the signals input from the control signal input terminals 403 and 405.
By combining in 7, the operation as the predistortion unit 4 is performed. In this way, the pre-compensation unit 4 can be realized with a relatively simple circuit configuration.

[0028]

According to the present invention, the maximum value of the envelope of the input signal to the control unit for generating the control signal for compensating the distortion becomes the optimum value for the dynamic range of the AD converter of the control unit. Can be automatically adjusted to be. As a result, it is possible to eliminate the influence of the temperature change and the secular change of the detection section that outputs the envelope, and thus it is possible to always keep the envelope detection output at an optimum level and highly accurate distortion compensation is possible. A power amplification device can be realized.

[Brief description of drawings]

FIG. 1 is a block diagram for explaining an embodiment of the invention of a power amplification device according to the present invention.

FIG. 2 is a block diagram illustrating an example of a control unit used in the power amplification device in FIG.

FIG. 3 is a diagram showing the relationship between input power and detected output voltage.

FIG. 4 is a circuit diagram for explaining another example of the pre-compensation unit used in the power amplification device of FIG.

FIG. 5 is a block diagram for explaining a conventional power amplifier device.

6 is a block diagram for explaining a control unit used in the power amplification device in FIG.

FIG. 7 is a vector diagram for explaining the principle of distortion compensation.

FIG. 8 is a diagram for explaining input / output characteristics of a power amplifier.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Input terminal, 2 ... Distributor, 3 ... Delay element, 4 ... Pre-compensation part, 5 ... Power amplifier, 6 ... Directional coupler, 7 ... Output terminal, 8 ... Input signal detection part, 9 ... Output signal Detection unit, 10 ...
Control unit, 11 ... Variable gain element, 101 ... Gain control signal output terminal, 102, 105 ... Detection signal input terminal, 103, 104 ... Control signal output terminal, 106, 108 ... AD converter, 107 ... Control data calculation unit, 109, 110 ... DA converter.

   ─────────────────────────────────────────────────── ─── Continued front page    F-term (reference) 5J090 AA01 AA41 CA02 CA03 CA21                       FA01 FA19 GN01 KA15 KA16                       KA23 KA33 KA34 KA55 KA68                       SA13 TA01                 5J091 AA01 AA41 CA02 CA03 CA21                       FA01 FA19 KA15 KA16 KA23                       KA33 KA34 KA55 KA68 SA13                       TA01                 5J500 AA01 AA41 AC02 AC03 AC21                       AF01 AF19 AK15 AK16 AK23                       AK33 AK34 AK55 AK68 AS13                       AT01                 5K004 AA08 JF04

Claims (4)

[Claims] 1. A power amplifier for amplifying a signal accompanied by envelope fluctuation, a pre-compensation unit for compensating distortion of the signal in order to remove distortion caused by nonlinearity of the power amplifier, and the pre-compensator. A control unit for controlling the distortion compensation of the compensation unit,
A detection unit for generating an envelope detection output to be input to the control unit from the signal, and for changing the level of the envelope detection output inserted between the detection unit and the control unit to a predetermined value. A power amplification device comprising: a gain varying unit. 2. The front compensator has an amplitude changing means for changing the amplitude of the signal and a phase changing means for changing the phase,
The power amplification device according to claim 1, wherein the distortion compensation is given to the signal by the amplitude varying means and the phase varying means. 3. The pre-compensation unit divides the signal into an in-phase component and a quadrature component that are orthogonal to each other, and first and second multipliers that change the amplitudes of the in-phase component and the quadrature component, respectively. And an adder for adding the outputs of the first and second multipliers, and the distortion compensation is given to the signal by the distributor, the first and second multipliers and the adder. The power amplification device according to claim 1, wherein the power amplification device is provided. 4. The control unit has a control signal generation unit for generating a control signal for controlling the distortion compensation amount of the pre-compensation unit, and the control signal generation unit has a distortion of an output signal of the power amplifier. The power amplifier device according to claim 1, wherein the control signal is generated so as to minimize the component.