JPH05343929A - Power amplifier - Google Patents

Abstract

PURPOSE:To improve the voltage utilization factor of an amplifier element when an output power level is set small while increase in amplitude distortion is suppressed by keeping an operating point of the amplifier element within an active area at all times and keeping a voltage amplitude of an output signal obtained therefrom constant. CONSTITUTION:When a mobile station receives a transmission power control command from a radio base station, a control section 23 obtains control information and gives the information to a variable attenuator 43, a class A power amplifier 21, and variable reactance elements 241-243. That is, when the operating point of the amplifier 21 is constant, the current gain rate is proportional to an input power level, but an output signal with a voltage waveform of a maximum amplitude is obtained from an input signal whose level is set small and a voltage utilization factor is made constant. Furthermore, since the operating point of the amplifier 21 is set to a minimum value under the control of the control section 23 within a range of a no distortion maximum output, an average power consumption at each level of the reduced transmission power is reduced in response to the transmission power control command and the power efficiency is improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power amplifier that suppresses an increase in amplitude distortion, amplifies the power of an input signal, and can switch and set an output power level.

[0002]

2. Description of the Related Art In a digital mobile communication system such as a digital cordless telephone system, a digital car telephone system and a mobile telephone system, in order to form a number of stable radio channels at a desired transmission rate in a limited radio frequency band. In many cases, a phase amplitude modulation method is adopted in which the radio frequency can be effectively used by changing the phase and amplitude of a carrier signal according to transmission information.

In such a mobile communication system, as a power amplifier for setting a transmission power to a predetermined value in a radio base station or a mobile station, amplitude distortion of a transmission wave generated by a phase amplitude modulation method is suppressed to transmit transmission information. For faithful transmission, a class A power amplifier having linear input / output characteristics is often used.

FIG. 4 is a diagram showing an example of the configuration of a transmitter of a mobile station apparatus using a class A power amplifier. In the figure, a transmitting unit gives an oscillator 41 for generating a carrier signal, a modulator 42 for phase-amplitude modulating the carrier signal with transmission information, and gives a signal output from the modulator an attenuation amount according to a transmission power control signal. It comprises a variable attenuator 43 and a class A power amplifier 44 that amplifies the power of the signal output via the attenuator and feeds it to the antenna system. Note that the class A power amplifier 44 is composed of a circuit using a transistor as an amplifying element, and as shown in FIG. 5, the output characteristics are such that the instantaneous value i _c of the collector current of such a transistor and the collector −
It is represented by the instantaneous value v _{ce of the} voltage between the emitters.

In the transmitting section having such a configuration, the amount of attenuation of the variable attenuator 43 is varied to set the power level of the input signal of the class A power amplifier 44 to determine the transmission power. The transmission power control signal that determines the amount of attenuation is determined by the control unit of the mobile station device, which is transmitted when the radio base station recognizes that the level of the received wave from the mobile station is higher than a predetermined value. Is output from. Here, the power control command is transmitted by the radio base station in order to prevent the sensitivity of the receiver from being suppressed by the reception wave of a large level received from the mobile station located at the closest point to the radio base station. For example, it shows at which level among 6 levels of transmission power level is set evenly every 4 dB in a variable range of 20 dB according to the reception electric field level.

[0006]

By the way, in the class A power amplifier mounted on such a mobile station apparatus, the power consumption is constant regardless of the output power level, and the loss due to various circuit elements is reduced. The considered power efficiency was about 30%, which is less than 50% of the theoretical value. Further, the power efficiency is, for example, as shown in FIG. 5, when the output power level is 2 in accordance with the power control command described above.
In the state of being reduced by 0 dB, it was 0.3 (= 30 × 10 ^{− ( 20/10)} ) percent, which was remarkably decreased in accordance with the decrease of the output power level.

[0007] Therefore, in the mobile station apparatus, the decrease in power efficiency at the time of reducing the transmission power described above requires a large-capacity battery, which occupies a large amount of weight and volume, and is originally required depending on the operation mode. It was a factor that hindered the reduction in weight and size.

Further, in a transmitting apparatus which obtains a large transmission power, for example, a method of increasing the power efficiency while compensating for the amplitude distortion by using a class C amplifier to which a negative feedback circuit is added can be adopted. For portable mobile station devices with low power consumption, such a method can improve the overall power efficiency because the power consumption of the circuit implementing the method accounts for a large percentage of the power consumption of the entire device. I was not able to adopt it.

Further, the collector (drain) voltage of the amplifying transistor (FET) is lowered via the DC / DC converter in response to the lowering of the excitation power applied via the variable attenuator 43, thereby utilizing the voltage. It is also possible to use a method of suppressing the reduction of power efficiency by keeping the rate high, but such a method generally has a high speed operation that cannot be followed by the response characteristics of the DC / DC converter in a digital mobile communication system. Required and DC / D
It cannot be applied because the power conversion loss of the C converter causes a reduction in power efficiency.

Further, instead of the class A power amplifier, a class B power amplifier having a constant current utilization rate regardless of the input power level can be used. In such an amplifier, the voltage utilization rate is equal to the input power level. Since it changes in proportion to the level, sufficient power efficiency was not obtained in the state where the transmission power was reduced.

An object of the present invention is to provide a power amplifier which can reduce power consumption in a state where the output power level is set to a small value.

[0012]

FIG. 1 is a block diagram showing the principle of the present invention. The present invention relates to an amplification means 11 for amplifying the power of an input signal via an amplification element having an operating point set in an active region on the output characteristic, and the power of the input signal according to a target value of the output power level of the amplification means 11. A control means 13 for increasing / decreasing the level and the gradient of the load line of the amplification element is provided.

[0013]

In the present invention, the control means 13 sets the power level of the input signal to a smaller value as the target value of the power level to be obtained at the output of the amplification means 11 is smaller, and in parallel with such setting, the amplification element is set. The gradient of the load line is variably set in the direction in which the rate of change of the voltage with respect to the current increases in the output characteristic of.

That is, regardless of the power level of the input signal, since the operating point of the amplifying element is kept in the active region and the voltage amplitude of the output signal obtained through the amplifying element is kept substantially constant, The voltage utilization factor in the state where the output power level is set to a small value is increased while suppressing the increase of the amplitude distortion, and the power efficiency is improved as compared with the conventional example.

[0015]

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

In the figure, parts having the same functions and configurations as those shown in FIG. 4 are designated by the same reference numerals, and the description thereof will be omitted here. In the present embodiment, the characteristic configuration of the present invention is that the output of the variable attenuator 43 is connected to the antenna system via the class A power amplifier 21 whose operating point is variable and the variable matching device 22 cascade-connected to the class A power amplifier 21. The attenuation amount of the variable attenuator 43 that is connected and that is in accordance with the transmission power control command,
The point is that a control unit 23 that variably controls the operating point of the class A power amplifier 21 and the matching condition of the variable matching unit 22 is provided. The class A power amplifier 21 is composed of a circuit using a transistor as an amplification element.

In the variable matching device 22, the class A power amplifier 21
The output of is connected to the antenna system via a transmission line having a predetermined characteristic impedance. Three connection points are provided on such a transmission line at equal intervals. These coupling points are grounded via variable reactance elements 24 ₁ , 24 ₂ and 24 ₃ each composed of a varicap or the like, and reactance variable terminals of these variable reactance elements are connected to the control unit 23.

Regarding the correspondence between this embodiment and the block diagram shown in FIG. 1, the class A power amplifier 21 and the variable matching device 22 correspond to the amplifying means 11, and the control unit 23 and the variable attenuator 43 control. It corresponds to the means 13.

FIG. 3 is a diagram for explaining the operation of this embodiment. In the figure, _ic represents the instantaneous value of the collector current of the transistor that is the amplification element of the class A power amplifier 21, and v
_ce represents the instantaneous value of the collector-emitter voltage of the same transistor.

The operation of this embodiment will be described below with reference to FIGS. 2 and 3. In the following, for simplicity, it is assumed that the power amplifier 21 is mounted on the mobile station apparatus and is transmitting.

When the mobile station is located at a point sufficiently distant from the radio base station, the control unit 23 sets the attenuation amount of the variable attenuator 43 to 0 dB because the transmission power control command is not received from the radio base station. As shown in FIG. 3, the operating point of the class A power amplifier 21 is set to a point where the maximum output without distortion is obtained,
Furthermore, as shown in FIG. 3, the reactance values of the variable reactance elements 24 _{1 to} 24 ₃ of the variable matching device 22 are set to values that can achieve impedance matching between the antenna system and the class A power amplifier 21. Therefore, the antenna system is
A transmission wave is given from the class power amplifier 21 at a predetermined maximum power.

Further, in the control unit 23, the load at which the class A power amplifier 21 outputs a voltage waveform of the maximum amplitude without distortion for each level of the transmission power indicated by the transmission power control command received from the radio base station. The reactance values of the reactance elements 24 _{1 to} 24 ₃ for obtaining the gradient of the line, the attenuation amount of the variable attenuator 43 that can obtain a desired transmission power based on the power amplification degree of the class A power amplifier 21 in such a load line, Control information indicating each minimum operating point of the class A power amplifier 21 capable of obtaining the voltage waveform of the maximum amplitude without distortion while maintaining the gradient of the load line is obtained in advance based on actual measurement or design value. It is stored in memory as a table.

When the mobile station receives the transmission power control command from the radio base station, the control section 23 refers to the above-mentioned table based on the level of the transmission power indicated by the command to obtain the control information. Variable attenuator 43,
Class A power amplifier 21 and variable reactance element 24 ₁
Give to ~ 24 ₃ .

That is, in the class A power amplifier 21, when the operating point is constant, the current utilization rate becomes smaller as the input power level decreases in the same manner as in the conventional example (for example, the voltage level is 0.2 times higher). Then, the current utilization factor is 0.2 times.), But as shown in FIG. 3, the output signal is obtained with the voltage waveform of the maximum amplitude with respect to the input signal set to the small level via the variable attenuator 43. Therefore, the voltage utilization rate is kept substantially constant.

Further, in the class A power amplifier 21, the operating point is set to the minimum value under the control of the control section 23 within the range where the above-mentioned distortion-free maximum output can be obtained (FIG. 3). The average power consumption at each level of the transmission power reduced according to the power control command is reduced, and the power efficiency is significantly improved compared to the conventional example.

In the present embodiment, the present invention is applied to the mobile station device of the mobile communication system in order to switch the transmission power level according to the transmission power control command given from the radio base station. However, the device is not limited to such a mobile station device, and if the device needs to perform power amplification while suppressing an increase in amplitude distortion and switch the output power level, the modulation method of the signal to be amplified and the occupied bandwidth It is applicable regardless.

Further, in this embodiment, the class A power amplifier 21
Although the variable matching box 22 is arranged between the output end of the amplifier and the antenna system in order to change the gradient of the load line of the present invention, the present invention is not limited to such a method, and is used in, for example, an amplifier. A method of changing the impedance of the circuit on the output side of the amplification element may be adopted.

Further, in the present invention, the power level of the power fed to the antenna system is changed by changing the power level of the input signal of the class A power amplifier 21 via the variable attenuator 43. Is not limited to such a method, and for example, a variable gain amplifier is provided in front of the class A power amplifier 21 to change the gain of the amplifier, or the oscillator 41 is used.
Alternatively, a method of changing the level of the output signal or the modulation sensitivity of the modulator 42 may be used.

Further, according to the present invention, the amount of attenuation of the variable attenuator 43 corresponding to a desired transmission power level and the reactances of the variable reactance elements 24 _{1 to} 24 ₃ are based on the information previously stored in the memory of the controller 23. Although the value and the operating point of the class A power amplifier 21 are set, the present invention is not limited to such a method, and for example, the response time associated with the switching setting of the level of the power fed to the antenna system is allowed. If so, feedback control according to the level of the output power may be performed and the same setting may be performed.

Further, in this embodiment, the class A power amplifier 2
Although the bipolar type transistor is used as the amplifying element which constitutes No. 1, the present invention is not limited to such an amplifying element. For example, the operating point is set in the active region in the output characteristics such as FET, and amplification is performed. Any element may be used as long as it can obtain the action.

[0031]

As described above, according to the present invention, when the output power level of the amplifying means is set to a small value, the amplifying means is set in parallel with the variable setting of the power level of the input signal according to the value. The operating point of the amplifying element used in 1) is kept within the active region in the output characteristics, and the gradient of the load line of the amplifying element is varied to suppress the decrease in voltage utilization rate.

That is, since the power efficiency in the state where the output power level is set to a small value can be improved while suppressing the increase in the amplitude distortion of the input signal, in the device to which the present invention is applied, the capacity of the battery for supplying the driving power is increased. To reduce the weight and size, and to increase the performance by continuously operating a battery of the same capacity as before for a long time.

[Brief description of drawings]

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

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

FIG. 3 is a diagram for explaining the operation of this embodiment.

FIG. 4 is a diagram illustrating a configuration example of a transmission unit of a mobile station device using a class A power amplifier.

FIG. 5 is a diagram illustrating a decrease in power efficiency of a class A power amplifier.

[Explanation of symbols]

 11 Amplifying Means 13 Control Means 21, 44 Class A Power Amplifier 22 Variable Matching Device 23 Control Unit 24 Variable Reactance Element 41 Oscillator 42 Modulator 43 Variable Attenuator

Claims (1)

[Claims] 1. An amplifying means (11) for amplifying the power of an input signal through an amplifying element having an operating point set in an active region on the output characteristic, and an output power level target value of the amplifying means (11). A power amplifier comprising: a control means (13) for increasing / decreasing a power level of the input signal and a gradient of a load line of the amplification element in response thereto.