JP2001244828A - Power amplifier - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a transmission device which uses a high efficient power amplifier by optimizing the bias of the power amplifier at any time corresponding to saturated electric power and transmission electric power needed for the power amplifier in a transmitter. SOLUTION: This power amplifier controls its bias to an optimum value at any time corresponding to the saturated electric power and output electric power needed for the power amplifier.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power amplifier used for a transmission apparatus for performing wireless transmission and wired transmission using a linear modulation method.

[0002]

2. Description of the Related Art In a communication system such as digital mobile communication, it is indispensable to increase transmission speed and quality in order to diversify services. For this reason, the transmission method is switched according to the propagation path conditions under the condition that a certain transmission quality is maintained. That is, when the propagation path condition is bad, the transmission rate is reduced by lowering the number of modulation levels, and when the propagation path condition is good, the transmission rate is increased by increasing the modulation level. This allows for a fixed modulation scheme,
High-speed and high-quality transmission can be performed.

[0003] A conventional transmitter will be described with reference to FIG. FIG. 4 is a block diagram showing a configuration of a conventional transmitter. In FIG. 4, for example, two modulation schemes to be switched are 16 QAM (both roll-off rate α = 0.4) and π / 4 shift QPS.
Consider the case of K (both roll-off rates α = 0.4).
The initial setting is 16QAM.

[0004] A data signal input from an input terminal 1 is supplied to a modulation unit 2. The input signal is modulated by the modulation unit 2 and supplied to the D / A converter 3. The D / A converter 3 converts the 16QAM-modulated signal into an analog signal and supplies the analog signal to the mixer 4. The mixer 4 performs frequency conversion of the input analog signal to a predetermined (for example, radio frequency band) transmission frequency using a local oscillation signal given from the local oscillator 5,
Provided to the band pass filter (BPF) 6. The BPF 6 removes harmonic components from the signal whose frequency has been converted to a predetermined frequency and supplies the signal to a power amplifier (PA) 7. The power amplifier 7 amplifies the input signal and outputs the amplified signal via the antenna 8.
As described above, the data signal input from the input terminal 1 is
The signal is modulated by the transmitter, amplified to a predetermined power level, and transmitted from the antenna 8.

[0005] In FIG. 4, information of a modulation scheme determined by a propagation path state is transmitted from an information input terminal 9 to a modulation section 2.
The modulation unit 2 switches the modulation method of the signal input from the input terminal 1 according to the information. For example, when the propagation path condition is poor, the amount of information that can be transmitted per symbol decreases, but the information of the modulation method is changed so that the inter-code distance is long and the modulation method is switched to π / 4-shift QPSK, which is strong against noise. It is provided to the modulation scheme switching section 2. Also, for example, when the propagation path condition is good, the modulation method is switched to π / 4 shift QPSK, which is a modulation method in which the inter-symbol distance is short and weak to noise but the amount of information that can be transmitted per symbol is large. Is given to the modulation scheme switching section 2. in this way,
High-speed and high-quality transmission is possible by a method of judging the propagation path state and switching the modulation method.

Next, another conventional example will be described with reference to FIG. FIG. 5 is a block diagram showing a configuration of a transmitter that receives three data signals, modulates and combines them at different frequencies, and performs common amplification for transmission. Here, 16QAM is adopted as an example of the modulation method. Input terminal 11
Is input to the modulation unit 14. The modulation unit 14 performs predetermined mapping on the input signal,
Performs generation of the modulated wave, further, over the modulation to a predetermined frequency f _1, and supplies the signal to the adder 17. Similarly, the input terminal
The data signal input from 12 is provided to modulation section 15.
The modulator 15 performs predetermined mapping and generation of a modulated wave on the input signal, modulates the signal with a predetermined frequency f ₂ , and supplies the signal to the adder 17. Similarly,
The data signal input from input terminal 13 is provided to modulation section 16. The modulation unit 16 performs predetermined mapping and generation of a modulated wave on the input signal, and further performs predetermined frequency f ₃
And the signal is given to the adder 17.

The adder 17 receives the given frequencies f ₁ , f ₂ , f ₃
Are combined and given to the mixer 4. In the mixer 4, the signal synthesized by the adder 17 is frequency-converted to a predetermined (for example, radio frequency band) frequency by a local oscillation signal supplied from the local oscillator 5, and is provided to the power amplifier 7. The power amplifier 7 commonly amplifies the input signal up to a predetermined power and outputs the signal via the antenna 8.

[0008] Here, a peak factor when a signal having an AM (amplitude modulation) component of N waves is synthesized.
r) is described (N: a positive integer of 2 or more). The peak factor when one 16-QAM signal having a roll-off rate α = 0.4 is one wave is about 5 dB. This is because the envelope level fluctuates due to the state transition of the modulated wave, and the amplitude (peak) is about 1.7 times the average amplitude of the modulated wave when the signal pattern of the modulated wave is a random pattern such as pseudo noise. Value) occurs instantaneously. For power amplifiers,
Even for this peak value, a characteristic that can maintain a certain degree of linearity is required.

Here, considering the envelope fluctuation when N unmodulated carriers are combined, when N = 2, the peak value is obtained when the vector phases of the two carriers match, and
The power at this time is 6 dB higher than the power of one wave and 3 dB higher than the average power of two waves. When N = 3, the power is increased by 10 dB for one wave and 5 dB for the average power of three waves. Considering the same below, the difference between the average power of the N-wave unmodulated carrier and the peak power is 10 ·
Expressed as log N. When each carrier is modulated, a peak factor due to the modulation is added. However, if there is no correlation between the modulated data, the peak factor at the time of N-wave synthesis tends to be saturated. However, the peak factor when combining up to about four waves is approximately expressed as (peak factor due to modulation) + 10 · log N (dB) ‥‥‥ (1). If so, the peak factor of the composite signal of the three modulated waves is about 10 dB. As an example,
The output specification of the power amplifier shown in FIG.
Assuming that the wave is / 3, considering the peak factor, 6
A power amplifier capable of outputting 00 W is required.

[0010]

In the prior art described above, when the modulation method is changed depending on the propagation path condition, the bias value of the power amplifier is set to the optimum back-off amount for the modulation method having the largest peak factor. Therefore, when the modulation method is switched, the optimum bias value is not always obtained, and the efficiency is reduced. Also, when a plurality of carriers are commonly amplified in a certain frequency band, a bias is set for the case where the number of communication channels is maximized, and when the number of channels to be used is reduced, an optimum bias value is set. However, there is a disadvantage that the efficiency is reduced. An object of the present invention is to eliminate the above-mentioned drawbacks and to degrade transmission quality even with a change in maximum output power due to switching of a modulation scheme or a change in transmission power due to a change in the number of output carriers. It is another object of the present invention to provide a highly efficient power amplifier and a transmitting apparatus.

[0011]

SUMMARY OF THE INVENTION In order to achieve the above object, a transmitter according to the present invention has a required output power.
The bias point of the power amplifier is switched to an optimum point as needed. As a result, high efficiency of the power amplifier and the transmission device using the same are realized.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a block diagram showing the configuration of the transmitter of the present invention, and FIG. 2 is a diagram for explaining the operation of the transmitter of FIG. In FIG. 1, two modulation schemes to be switched according to the propagation path state are 16QAM and π / 4 shift QPSK, roll-off rate α = 0.4, the initial setting of the modulation scheme is 16QAM, and the average transmission power is 30 W, as in the conventional example. And

FIG. 1 has almost the same configuration as that of FIG.
1 is connected to an antenna 8 via a modulation unit 2, a D / A converter 3, a mixer 4, a bandpass filter 6, and a power amplifier (PA) 7. The local oscillator 5 is connected to the mixer 4. However, the power control unit 10 has been added, and the power control unit (PW.CONT)
10 supplies a bias voltage to the power amplifier 7. And
The information input terminal 9 is connected to a power control unit 10 in addition to the modulation unit 2.

The operation of FIG. 1 will be described below. The data signal is input from the input terminal 1, and is modulated and amplified by the components of the modulation unit 2, the D / A converter 3, the local oscillator 5, the mixer 4, the BPF 6, and the power amplifier 7, and is output from the antenna 8 The operation is as shown in FIG. Further, similarly to FIG. 4, information on the modulation scheme determined by the propagation path state is output from the information input terminal 9 and provided to the modulation scheme switching unit 2. Then, this information is further provided to the power supply control unit 10. As described above, the peak factor differs depending on the modulation method, and the required saturation power changes. Therefore, the power amplifier 10
Give 7 the optimal bias value.

Here, the relationship between the peak factor due to the difference in modulation scheme and the saturation output of the power amplifier 7 will be described. When the roll-off rate α = 0.4, the peak / factor of 16QAM is about 5 dB, and the peak factor of π / 4 shift QPSK is about 3
dB. Since the peak factor when 16QAM is selected is about 5 dB, the bias setting of the power amplifier 7 is such that a 95 W output is possible. In this state, it is assumed that switching to π / 4 shift QPSK is performed due to deterioration of the propagation path state. Since the peak factor of π / 4 shift QPSK is about 3 dB, the required maximum power of the power amplifier 7 is 60 W
If you operate with the bias value fixed at the initial value set for 16QAM, you will have an extra 35 W of back-off. Therefore, the modulation method is shifted by π / 4
When switching to QPSK, by setting the bias value so that the maximum saturation power of the power amplifier 7 becomes 60 W,
It is possible to give an optimum bias value to the required output power of the power amplifier 7. FIG. 2 shows input / output characteristics when the bias value of the power amplifier 7 is changed. FIG.
Is a diagram showing an example of the input / output characteristics of the power amplifier 7, where the horizontal axis is the input power and the vertical axis is the output power.

Next, another embodiment will be described with reference to FIG. FIG. 3 is a block diagram showing a configuration of one embodiment of the transmitter of the present invention. FIG. 3 shows that the modulation method is 16QAM with a roll-off rate α = 0.4, and the number of communication channels to be used is 3 waves / 60 W
(1 wave / 20 W), which is commonly amplified by the power amplifier 7. The voltage control unit (PW. CONT) 10 is added to the configuration of the present invention in FIG. .
Data signals are input from input terminals 11, 12, and 13, respectively.
The operation until output from the antenna 8 via the adder 17, the D / A converter 3, the mixer 4, the local oscillator 5, the BPF 6, and the power amplifier 7 via the modulators 14, 15, and 16 is shown in FIG. 5, the description is omitted.

On the other hand, information on the number of channels is provided to the power supply control unit 10 via the information input terminal 18. The power control unit 10 obtains the information on the number of channels to be input, and applies a predetermined bias voltage to the power amplifier 7 corresponding to the number. Here, the setting of the bias value of the power amplifier when the number of communication channels changes from three to two or one will be described.

First, 3 is used as a communication channel (carrier).
When using waves, the average power per wave is 20 W, so 60 W for three waves and, considering the peak factor, the output of 600 W is obtained from the equation (1) shown in the conventional technology. Set the bias value so that it becomes possible. Here, if the number of communication requests is reduced and the number of channels is reduced to two waves, the maximum power required for the power amplifier 7 is 250 W, and further, if the number of channels is one, it is 63 W. As described above, based on the information on the number of carriers input from the information input terminal 18, the power supply control unit 10 sets the optimum bias value for the output power and operates the power amplifier 7.

Next, an application example of the present invention will be described with reference to FIGS. FIG. 6 is a block diagram illustrating a configuration of an embodiment of a power amplifier (hereinafter, referred to as an FF amplifier) that performs feed-forward distortion compensation. FIG. 7 is a diagram illustrating spectra at points A to D in the block diagram shown in FIG.

The modulated wave input terminal 20 is connected to a variable attenuator 22 and a delay unit 25 via a power divider 21. The variable attenuator 22 is connected to a power distributor 26 via a phase shifter 23 and a main amplifier 24. The power divider 26 is connected to an output terminal 33 via a delay unit 28 and an adder 32. On the other hand, the power distributor 26 is also connected to the adder 27. Also, the delay unit
25 is connected to the adder 27, and the adder 27 is connected to the variable attenuator 2
9, and the adder 3 via the phase shifter 30 and the error amplifier 31
Connected to 2. Hereinafter, this operation will be described.

The signal input from the modulation wave input terminal 20 is
The power is divided by a power divider 21, one of which is supplied to a main amplifier 24 via a variable attenuator 22 and a phase shifter 23, and the other is a delay unit.
Given to 25. In the main amplifier 24, the power is amplified to a predetermined power. However, the output (point A) is caused by the non-linearity of the amplifier.
Contains a distortion component other than the main signal component. On the other hand, the output (point B) of the delay unit 25 is a distortion-free output because it does not pass through the main amplifier 24. Adder 27 adds these two signals in opposite phases.
Thus, only the distortion component generated by the main amplifier 24 is extracted from the output (point C) of the adder 27. Also,
At this time, in order to match the phases of the two signals added in the adder 27, the delay unit 25 gives the same delay amount as the delay generated in the other path including the main amplifier 24.
A change in the amplitude level or phase due to a temperature change or the like is finely adjusted by the variable attenuator 22 and the phase shifter 23, respectively.

The extracted distortion component is amplified by an error amplifier 31 and provided to an adder 32. On the other hand, the main amplifier
The output of 24 is given the same delay amount as the delay generated on the path side of the error amplifier 31 by the delay unit 28, and is given to the adder 32. Also, fine adjustment of the signal level and phase is performed by the variable attenuator 29.
By the phase shifter 30. Then, by the adder 32,
By adding the two input signal components in opposite phases, a signal from which the distortion component of the output of the main amplifier 24 has been removed is taken out at the output (point D) of the adder 32, and output via an output terminal 33. The resulting signal is compensated for nonlinear distortion.

FIG. 7 shows the spectrum of points A to D shown in FIG. 6 for the operation described above. The horizontal axis represents the frequency f and the vertical axis represents the power P. At the point AA, both the main signal and the distortion component appear, and at the point B, only the main signal has no distortion component. Also, at point C, the main signal is canceled, so only the distortion component appears.At point D, the distortion component extracted at point C is subtracted from the main signal and distortion component that appear at point A, so only the main signal is subtracted. Be taken out. In the main amplifier 24 shown in FIG. 6, a method is used in which the bias value described above is set to an optimum value at any time by changing the saturation power of the FF amplifier and the transmission power according to the modulation method or the number of communication channels. .

The operation when the above-described embodiment is applied to the error amplifier with the same configuration as that of FIG. 6 will be described below. The modulation method is switched, that is, the back-off amount of the main amplifier 24 is relatively changed by the change of the peak factor, and the power of the distortion is also changed, so that according to the change of the distortion power input to the error amplifier 31, The bias of the error amplifier 31 is optimized. In addition, since the amount of distortion generated by changing the output power of the main amplifier 24 according to the number of communication channels also changes, the bias value of the error amplifier 31 is controlled.
Further, the above-described embodiment can be used for each of the main amplifier 24 and the error amplifier 31.

Next, another transmitter of the present invention will be described with reference to FIG.
This will be described with reference to the block diagram of FIG. FIG. 8 is a block diagram showing the configuration of the transmitter according to the present invention. In the example of FIG. 8, 16QAM modulation is used as a modulation method. Input terminal 1
1 'is a modulator 34, a mixer 35, a band-pass filter (BP
F) It is connected to an antenna 40 via a preamplifier 38 and a power amplifier (PA) 39. The local oscillator 36 is a mixer 35
Connected to Hereinafter, this operation will be described.

The serial data input from the input terminal 11 'is subjected to serial / parallel conversion and multi-level conversion by the modulator 34, signal points are arranged according to a predetermined mapping, and a 16QAM modulated wave is generated. The modulated wave output from the modulator 34 is
The mixer 35 frequency-converts the signal from the local oscillator 36 into a radio frequency band. The signal after frequency conversion is BPF37
Harmonic components are removed by the
Amplified to predetermined transmission power by PA39 and antenna
Output via 40.

In digital radio transmission, when using a multi-level QAM modulation such as 16QAM or a modulation scheme such as QPSK, the linearity of the power amplifier is required to secure transmission quality and to limit power to adjacent channels. However, on the other hand, improvement in power supply efficiency is required. Therefore, by using the above-described power amplifier, the DC power can be minimized and operated.

[0028]

According to the present invention, the bias value of the power amplifier of the transmitter is optimized and operated according to the different maximum transmission power by changing the modulation method or changing the number of common amplification waves. Without deteriorating the quality, a highly efficient power amplifier and a transmitter using the same can be realized.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of an embodiment of a transmitter according to the present invention.

FIG. 2 is a view for explaining the operation of the transmitter in FIG. 1;

FIG. 3 is a block diagram showing a configuration of an embodiment of a transmitter according to the present invention.

FIG. 4 is a block diagram showing a configuration of a conventional transmitter.

FIG. 5 is a block diagram showing a configuration of a conventional transmitter that modulates three signals to different frequencies, amplifies the signals, and transmits the amplified signals.

FIG. 6 is a block diagram showing the configuration of an embodiment of the FF amplifier according to the present invention.

FIG. 7 is a view for explaining spectra at points A to D of the FF amplifier in FIG. 6;

FIG. 8 is a block diagram illustrating a configuration of a transmitter according to an embodiment of the present invention.

[Explanation of symbols]

1: Input terminal, 2: Modulation section, 3: D / A converter, 4: Mixer, 5: Local oscillator, 6: BPF, 7: Power amplifier,
8: Antenna, 9: Information input terminal, 11, 12, 13: Input terminal, 14, 15, 16: Modulator, 17: Adder, 18:
Information input terminal, 20: modulated wave input terminal, 21: power divider, 22: variable attenuator, 23: phase shifter, 24: main amplifier,
25: Delay device, 26: Power divider, 27: Adder, 28:
Delay device, 29: Variable attenuator, 30: Phase shifter, 31: Error amplifier, 32: Adder, 33: Output terminal, 34: Modulator, 35: Mixer, 36: Local oscillator, 37: BPF :,
38: Preamplifier, 39: PA, 40: Antenna.

 ──────────────────────────────────────────────────続 き Continued from the front page F term (reference) 5J090 AA01 AA41 CA21 CA36 FA10 GN02 GN07 HN03 KA00 KA15 KA16 KA23 KA26 KA32 KA34 KA44 KA53 MA10 MA14 SA14 TA01 TA02 TA03 5J091 AA01 AA41 CA21 CA36 KA16 KA00 KA23 KA00 KA53 MA10 MA14 SA14 TA01 TA02 TA03 5J092 AA01 AA41 CA21 CA36 FA10 KA00 KA15 KA16 KA23 KA26 KA32 KA34 KA44 KA53 MA10 MA14 SA14 TA01 TA02 TA03 VL08 5K060 BB07 HH06 KK06 LL01

Claims (5)

[Claims] 1. A power amplifier for use in a transmitter that communicates by switching between a plurality of modulation schemes, wherein a bias value of the power amplifier is optimized according to the modulation scheme. 2. A power amplifier for commonly amplifying N carriers (N is an integer of 2 or more), wherein a bias value of the power amplifier is optimized according to the number of carriers input. 3. A modulator for switching a modulation method in accordance with a user's instruction, a digital-to-analog converter for converting a signal modulated by the modulation into analog data, and a reference local signal oscillator for generating a predetermined frequency signal And a frequency signal generated by the reference local signal oscillator,
A mixer for frequency-converting the analog data, a band-pass filter for removing unnecessary frequency components of the signal frequency-converted by the mixer, and a power supply control unit for changing a setting of a bias value. And changing the setting of the bias value to amplify the input signal. 4. N input signals (N is an integer of 2 or more)
Are modulated to different frequencies, a plurality of modulated signals are combined, and in a power amplifier that amplifies the combined signal, N modulation units that modulate the input N signals to different frequencies are provided, An adder for combining the signals modulated by the N modulators; a digital-to-analog converter for converting the signal combined by the adder to analog data; a local signal for generating a signal having a predetermined reference frequency An oscillator; a mixer for converting the analog data to the reference frequency; a band-pass filter for removing unnecessary frequency components of a signal frequency-converted by the mixer; and a power supply control unit for changing a setting of a bias value. A power amplifier, comprising: changing the setting of the bias value according to the number of input signals. 5. A power amplifier that uses the power amplifier according to any one of claims 1 to 4 to perform a feedforward distortion compensation for removing a distortion component caused by nonlinearity of the amplifier.