Amplifying device and method for controlling the same

An amplifying device includes a first pre-distorter unit outputting a modulated signal obtained by adding a phase compensation amount and an amplitude adjustment amount to an input signal, a power amplifier inputting the modulated signal and outputting an output signal obtained by amplifying the modulated signal, a power supply voltage modulation unit modulating a power supply voltage, a second pre-distorter unit controlling the power supply voltage modulation unit on the basis of amplitude information on the input signal; and a control unit controlling an operation of the first pre-distorter unit and the second pre-distorter unit, wherein the control unit includes a phase control unit controlling the phase compensation amount by using a phase coefficient, a first amplitude control unit controlling the amplitude adjustment amount by using a first amplitude coefficient, and a second amplitude control unit controlling the operation of the second pre-distorter unit by using a second amplitude coefficient.

This application is a National Stage Entry of PCT/JP2011/079971 filed Dec. 16, 2011, which claims priority from Japanese Patent Application 2010-283133 filed Dec. 20, 2010, the contents of all of which are incorporated herein by reference, in their entirety.

TECHNICAL FIELD

The present invention relates to amplifying devices and methods for controlling the same, in particular, to an amplifying device and a method for controlling the same having highly-efficient and low distortion characteristics.

BACKGROUND ART

In a transmitter used in a base station of a radio communications system, an amplifying device having high power efficiency is required in order to miniaturize the transmitter and reduce its power consumption. As technologies to realize high efficiency of the amplifying device, technologies are known in which the power consumption can be reduced by controlling a power supply voltage depending on an input signal. A particularly effective system of them is an Envelope Tracking system.

The Envelope Tracking system is a system in which a power supply voltage of an amplifier such as a power amplifier and the like is changed depending on the amplitude of an input signal. Since the electric power supplied from a power supply decreases by this system in comparison with driving it by a constant power supply voltage, it becomes possible to amplify signals high efficiently. Here, if an output signal voltage exceeds the power supply voltage of the power amplifier, the linearity between the input signal and the output signal is lost due to the output saturation arising. Therefore, in general, the power supply voltage is designed so that the power supply voltage supplied to the power amplifier may always become higher than the output signal voltage.

Meanwhile, since low distortion characteristics are generally required for the amplifying device used in the transmitter, a distortion compensation system such as Digital Pre-distortion (DPD) system and the like is adopted. The digital pre-distortion system is a system in which the distortion caused by the power amplifier is cancelled by means of preliminarily distorting signals input into the power amplifier composing the amplifying device using a pre-distorter and consequently the low distortion characteristics of the amplifying device are realized. In the digital pre-distortion (DPD) system, a distortion model of the power amplifier is constructed by comparing an input signal and an output signal of the power amplifier, and inverse characteristics of the distortion model are set for the pre-distorter.

Configuration examples of the digital pre-distortion (DPD) system include a system using a look up table (LUT). A correction value corresponding to each of the amplitudes of the input signals has been preliminarily recorded in the look up table (LUT), and the correction value is updated sequentially so that the distortion of the power amplifier may be cancelled. There are two kinds of distortion which are compensated by using the look up table (LUT). One is a distortion due to non-linear characteristics in output amplitude characteristics to input amplitudes of the signal (hereinafter, referred to as “AM-AM characteristics”) and another is a distortion due to non-linear characteristics in output phase characteristics to input amplitudes (hereinafter, referred to as “AM-PM characteristics”). By correcting two kinds of distortion mentioned above, signal characteristics between the input signal and the output signal of the amplifying device become a linear relationship and consequently the distortion is suppressed. Here, the look up table (LUT) is not limited to the above-mentioned configuration which separately includes one for correcting the AM-AM characteristics and another for correcting the AM-PM characteristics. A system is also known which configures a look up table (LUT) including complex values by using input-output data stream of complex signals.

Configuration examples of the digital pre-distortion (DPD) system include another system approximating a correction amount of distortion for the power amplifier by using a polynomial. In this case, the non-linear characteristics of the power amplifier are cancelled by calculating coefficient values of the polynomial using the output signal and the input signal of the power amplifier, and by updating the coefficient values sequentially. Another system is also known in which the pre-distorter has filter characteristics, and a memory effect of the power amplifier is suppressed taking the past information into consideration by selecting the number of taps of the filter.

Although each amplifying device individually adopting either the Envelope Tracking system or the digital pre-distortion (DPD) system has been described above, it is also possible to configure an amplifying device which adopts both systems. An example of the above-mentioned amplifying device is disclosed in patent literature 1.

As shown inFIG. 12, a related amplifying device500described in patent literature 1 includes a power amplifier510, a power supply modulation unit520, a distortion compensation unit530, a first estimation unit540, and a second estimation unit550. The power supply modulation unit520supplies the power amplifier510with a power supply modulation voltage depending on an input signal, and the distortion compensation unit530compensates the distortion in the power amplifier510. The first estimation unit540estimates a first amplifier model which indicates the characteristics of the power amplifier510between input and output signals on the basis of the input signal and the output signal of the power amplifier510. The second estimation unit550estimates a second amplifier model which indicates the characteristics of the power amplifier510between the power supply modulation voltage and the output signal on the basis of the power supply modulation voltage and the output signal. The distortion compensation unit530compensates the distortion of the power amplifier510on the basis of the first amplifier model, and the power supply modulation unit520controls the power supply modulation voltage on the basis of the second amplifier model.

As mentioned above, in the related amplifying device500, the distortion compensation unit530and the power supply modulation unit520control independently the distortion compensation and the power supply modulation voltage on the basis of the first amplifier model and the second amplifier model, each of which is obtained by the estimation unit independently of each other. Therefore, it is said that it becomes possible to control suitably both of power supply modulation characteristics and distortion compensation characteristics depending on the characteristics of the power amplifier510, and that it is possible to simplify the calculation for carrying out these controls.Patent Literature 1: Japanese Patent Application Laid-Open Publication No. 2010-045508 (paragraphs [0014] and [0015], and FIG. 3)

DISCLOSURE OF INVENTION

Problem to be Solved by the Invention

It is said that the related amplifying device500mentioned above minimizes the distortion characteristics of the amplifying device by means of the distortion compensation unit530and maximizes efficiency in the amplifying device by means of the power supply modulation unit520. However, since the distortion compensation unit530and the power supply modulation unit520control the distortion compensation and the power supply modulation voltage independently of each other, there is a problem that each of them does not always converge at the optimum point. That is to say, if any one of parameters of the distortion compensation and the power supply modulation voltage is optimized and fixed, then the other parameter is optimized, the characteristics of the power amplifier vary according to the change of the other parameter. Therefore, since the optimum point of the previously-optimized parameter is moved, it is difficult to set both these parameters optimally.

As mentioned above, the related amplifying device has a problem that it is difficult to realize the low distortion characteristics and the highly-efficient operation of the amplifying device simultaneously.

The object of the present invention is to provide an amplifying device and a method for controlling the same which solve the problem mentioned above that it is difficult to realize the low distortion characteristics and the highly-efficient operation of the amplifying device simultaneously.

Means for Solving a Problem

An amplifying device according to an exemplary aspect of the invention includes a first pre-distorter unit outputting a modulated signal obtained by adding a phase compensation amount and an amplitude adjustment amount to an input signal; a power amplifier inputting the modulated signal and outputting an output signal obtained by amplifying the modulated signal; a power supply voltage modulation unit modulating a power supply voltage of the power amplifier; a second pre-distorter unit controlling the power supply voltage modulation unit on the basis of amplitude information on the input signal; and a control unit controlling an operation of the first pre-distorter unit and the second pre-distorter unit; wherein the control unit includes a phase control unit controlling the phase compensation amount by using a phase coefficient, a first amplitude control unit controlling the amplitude adjustment amount by using a first amplitude coefficient, and a second amplitude control unit controlling the operation of the second pre-distorter unit by using a second amplitude coefficient; and wherein the first amplitude control unit cooperates with the second amplitude control unit so that an amplitude amplification factor may become constant which is a ratio of an amplitude of the output signal to an amplitude of the input signal.

A control device for a power amplifier according to an exemplary aspect of the invention includes a first pre-distorter unit outputting, to the power amplifier, a modulated signal obtained by adding a phase compensation amount and an amplitude adjustment amount to an input signal; a second pre-distorter unit controlling the power supply voltage modulation unit on the basis of amplitude information on the input signal; and a control unit controlling an operation of the first pre-distorter unit and the second pre-distorter unit; wherein the control unit includes a phase control unit controlling the phase compensation amount by using a phase coefficient, a first amplitude control unit controlling the amplitude adjustment amount by using a first amplitude coefficient, and a second amplitude control unit controlling the operation of the second pre-distorter unit by using a second amplitude coefficient; and wherein the first amplitude control unit cooperates with the second amplitude control unit so that an amplitude amplification factor may become constant which is a ratio of an amplitude of an output signal of the power amplifier to an amplitude of the input signal.

A method for controlling an amplifying device according to an exemplary aspect of the invention includes the steps of updating a phase coefficient determining a phase compensation amount to an input signal of an amplifying device so that a phase difference between the input signal and an output signal of the amplifying device may be minimized; calculating a phase correction value which is a phase coefficient to minimize the phase difference; generating an input modulated signal by applying to the input signal a function whose output value is equal to or greater than an input value for every input value; updating a first amplitude coefficient determining an amplitude adjustment amount to the input signal so that an amplitude difference between the input modulated signal and the output signal may be minimized; calculating a first amplitude correction value which is the first amplitude coefficient to minimize an amplitude difference between the input modulated signal and the output signal; updating a second amplitude coefficient determining an amplitude of a power supply voltage of a power amplifier composing the amplifying device, under the condition that the first amplitude correction value is kept constant, on the basis of amplitude information on the input signal so as to supply a power supply voltage by which an output of the power amplifier becomes a saturated state; calculating, as a second amplitude correction value, the second amplitude coefficient at a time when an amplitude amplification factor becomes constant which is the ratio of an amplitude of the output signal to an amplitude of the input signal; and compensating phase difference between the input signal and the output signal by using the phase correction value and controlling the amplitude amplification factor to be kept constant by using the first amplitude correction value and the second amplitude correction value.

A program according to an exemplary aspect of the invention which makes a computer execute a procedure for updating a phase coefficient determining a phase compensation amount to an input signal of an amplifying device so that a phase difference between the input signal and an output signal of the amplifying device may be minimized; a procedure for calculating a phase correction value which is a phase coefficient to minimize the phase difference; a procedure for generating an input modulated signal by applying to the input signal a function whose output value is equal to or greater than an input value for every input value; a procedure for updating a first amplitude coefficient determining an amplitude adjustment amount to the input signal so that an amplitude difference between the input modulated signal and the output signal may be minimized; a procedure for calculating a first amplitude correction value which is the first amplitude coefficient to minimize an amplitude difference between the input modulated signal and the output signal; a procedure for updating a second amplitude coefficient determining an amplitude of a power supply voltage of a power amplifier composing the amplifying device, under the condition that the first amplitude correction value is kept constant, on the basis of amplitude information on the input signal so as to supply a power supply voltage by which an output of the power amplifier becomes a saturated state; a procedure for calculating, as a second amplitude correction value, the second amplitude coefficient at a time when an amplitude amplification factor becomes constant which is the ratio of an amplitude of the output signal to an amplitude of the input signal; and a procedure for compensating phase difference between the input signal and the output signal by using the phase correction value and controlling the amplitude amplification factor to be kept constant by using the first amplitude correction value and the second amplitude correction value.

Effect of the Invention

According to the amplifying device and the method for controlling the same of the present invention, it is possible to realize the low distortion characteristics and the highly-efficient operation of the amplifying device simultaneously.

DESCRIPTION OF EMBODIMENTS

The exemplary embodiments of the present invention will be described with reference to drawings below.

The First Exemplary Embodiment

FIG. 1is a block diagram showing a configuration of an amplifying device100in accordance with the first exemplary embodiment of the present invention. The amplifying device100, which is an amplifying device with Envelope Tracking system, includes a power amplifier (PA)110and a power supply voltage modulation unit120modulating a power supply voltage of the power amplifier110. The amplifying device100further includes a first pre-distorter unit130disposed in the preceding stage of the power amplifier110, a second pre-distorter unit140disposed in the preceding stage of the power supply voltage modulation unit120, and a control unit150. The first pre-distorter unit130outputs to the power amplifier (PA)110a modulated signal S11obtained by adding a phase compensation amount and an amplitude adjustment amount to an input signal S10. The second pre-distorter unit140obtains amplitude information S20on the input signal of the amplifying device100from an input side and controls the power supply voltage modulation unit120on the basis of the amplitude information S20. The control unit150controls the operation of the first pre-distorter unit130and the second pre-distorter unit140. The power amplifier110inputs the modulated signal S11from the first pre-distorter unit130and outputs an output signal S12which is obtained by amplifying the modulated signal S11.

The control unit150includes a phase control unit (AM-PM)160, a first amplitude control unit (AM-AM1)170, and a second amplitude control unit (AM-AM2)180. The phase control unit (AM-PM)160controls the phase compensation amount in the first pre-distorter unit130by using a phase coefficient P10. Here, the phase compensation amount is defined as a phase amount to compensate a distortion due to the non-linearity in output phase characteristics to input amplitudes (AM-PM characteristics).

The first amplitude control unit (AM-AM1)170controls the amplitude adjustment amount in the first pre-distorter unit130by using a first amplitude coefficient P11. The second amplitude control unit (AM-AM2)180controls the operation of the second pre-distorter unit140by using a second amplitude coefficient P12. Here, the first amplitude control unit170cooperates with the second amplitude control unit180so that an amplitude amplification factor may become constant which is the ratio of the amplitude of the output signal S12to the amplitude of the input signal S10of the amplifying device100. At this time, since the output amplitude characteristics to the input amplitude (AM-AM characteristics) become a linear relationship, the distortion due to non-linearity in the amplitude characteristics of the amplifying device100is compensated.

As mentioned above, in the amplifying device100of the exemplary embodiment, the first amplitude control unit170cooperates with the second amplitude control unit180to compensate the distortion in the amplitude characteristics of the amplifying device100. That is to say, the second amplitude control unit180enables the power amplifier110to operate with high efficiency by controlling the second pre-distorter unit140. And then, the first amplitude control unit170controls the first pre-distorter unit130, so that the first pre-distorter unit130may output the modulated signal to compensate the distortion characteristics of the power amplifier110in this operating condition. As a result, according to the amplifying device100of the exemplary embodiment, it is possible to realize the low distortion characteristics and the highly-efficient operation simultaneously.

FIG. 1shows the case in which the second pre-distorter unit140obtains the amplitude information S20on the input signal from the input side separately from the input signal S10. However, it is not limited to this; it is also acceptable for the second pre-distorter unit140to obtain the amplitude information from the input signal S10through an envelope detector.

Next, the control unit150in the amplifying device100according to the exemplary embodiment will be described in more detail. The phase control unit (AM-PM)160calculates, as a phase correction value, a phase coefficient at the time when the phase difference between the input signal and the output signal becomes minimized, and controls the phase compensation amount in the first pre-distorter unit130on the basis of the phase correction value.

As shown inFIG. 2A, the first amplitude control unit (AM-AM1)170takes control so that the amplitude amplification factor in an overall range of the amplitude of the input signal may become equal to or larger than a reference amplitude amplification factor k which is an amplitude amplification factor at the time when the amplitude of the input signal is maximum. At this time, in the characteristics of the output amplitude to the input amplitude, as shown inFIG. 2B, the output amplitude in an overall range of the input amplitude becomes equal to or larger than a value on the line whose slope is equal to k (reference amplitude amplification factor). And then, the first amplitude control unit (AM-AM1)170calculates the first amplitude coefficient at this time as a first amplitude correction value, and controls the amplitude adjustment amount in the first pre-distorter unit130on the basis of the first amplitude correction value.

The second amplitude control unit (AM-AM2)180calculates, as a second amplitude correction value, a second amplitude coefficient at the time when the amplitude amplification factor becomes constant in an overall range of the amplitude of the input signal under the condition that the first amplitude correction value is constant. The second amplitude control unit180controls the operation of the second pre-distorter unit140on the basis of the second amplitude correction value.

Here, as shown inFIG. 3, it is possible to adopt a configuration in which the control unit150further includes a switching decision unit190and a switching unit191, and the first amplitude control unit170includes a shaping function calculation unit171and a first amplitude coefficient calculation unit172. The shaping function calculation unit171outputs, to the first amplitude coefficient calculation unit172, an input modulated signal S13which is obtained by applying a shaping function to the input signal. Here, the shaping function is a function whose output value is equal to or larger than an input value for all input values. Although a shaping function whose input/output characteristics are expressed by a convex shape will be described below as an example, it is not limited to this. The first amplitude coefficient calculation unit172calculates, as a first amplitude correction value, a first amplitude coefficient by which an amplitude difference between the input modulated signal S13and the output signal S12is minimized. At this time, the first amplitude control unit170controls the amplitude adjustment amount in the first pre-distorter unit130on the basis of the first amplitude correction value. As a result, the first pre-distorter unit130outputs the modulated signal S11by which the input/output amplitude characteristics of the amplifying device100becomes like a convex shape determined by the shaping function.

The switching decision unit190obtains, from the first amplitude coefficient calculation unit172, amplitude difference information S14which represents the amplitude difference between the input modulated signal S13and the output signal S12, and makes switching decision on the basis of the amplitude difference information S14. The switching unit191switches an operating condition of the first amplitude control unit170and the second amplitude control unit180on the basis of the result of the switching decision. Specifically, for example, when deciding that the amplitude difference exceeds a predetermined threshold value, the switching decision unit190outputs a switching instruction signal S15to the switching unit191. When the switching unit191receives the switching instruction signal S15, the switching unit191can switch the operating condition of the first amplitude control unit170and the operating condition of the second amplitude control unit180.

The second amplitude control unit180controls the power supply voltage modulation unit120through the second pre-distorter unit140. At this time, the power supply voltage modulation unit120controls the power supply voltage so that each output of the power amplifier110may become a saturated state in the overall range of the input amplitude. Specifically, the amplitude of the power supply voltage is reduced until the output of the power amplifier110becomes a saturated state. That is to say, the second amplitude control unit180calculates, as the second amplitude correction value, the second amplitude coefficient at the time when the power supply voltage modulation unit120supplies the power supply voltage which makes the output of the power amplifier110become a saturated state, and controls the operation of the second pre-distorter unit140on the basis of the second amplitude correction value.

Here, as mentioned above, the modulated signal S11having the convex-shaped input/output amplitude characteristics is input into the power amplifier110from the first pre-distorter unit130. Since the amplitude of the output signal S12decreases when the output of the power amplifier110becomes a saturated state, it is possible to keep constant the amplitude amplification factor which is the ratio of the amplitude of the output signal S12to the amplitude of the input signal S10, by controlling the power supply voltage by means of the above-mentioned configuration.

As mentioned above, the amplifying device100according to the exemplary embodiment has the configuration in which the first amplitude control unit170cooperates with the second amplitude control unit180so that the amplitude amplification factor, which is the ratio of the amplitude of the output signal to the amplitude of the input signal, may be controlled to become constant. Therefore, it becomes possible to compensate the distortion due to the non-linearity of the output amplitude to the input amplitude, under the condition that the power amplifier110operates with high efficiency in the saturation region.

Next, the operation of the amplifying device100according to the present exemplary embodiment will be described.FIG. 4is a sequence diagram to illustrate the operations of the amplifying device100. First, the control unit150initializes each coefficient of the phase control unit (AM-PM)160, the first amplitude control unit170, and the second amplitude control unit (AM-AM2)180(step S101).

At the first stage, the control unit150controls the operation of the first pre-distorter unit130by using the phase coefficient calculated by the phase control unit (AM-PM)160and the first amplitude coefficient calculated by the first amplitude control unit170. That is to say, the phase coefficient determines the phase compensation amount to the input signal in the first pre-distorter unit130, and the first amplitude coefficient determines the amplitude adjustment amount to the input signal.

The phase control unit (AM-PM)160synchronizes the input signal and the output signal of the amplifying device100, and updates the phase coefficient so that the phase difference between the synchronized input and output signals may be minimized (step S102). And then, the phase correction value is calculated which is the phase coefficient to minimize the phase difference (step S103). The phase compensation amount in the first pre-distorter unit130is determined by the phase correction value. At this time, it is possible to use the LMS (Least Mean Square) algorithm in order to calculate the phase correction value, for example.

The first amplitude control unit (AM-AM1)170generates the input modulated signal by applying the shaping function to the input signal of the amplifying device100, and synchronizes the input modulated signal and the output signal. The first amplitude coefficient is updated so that the amplitude difference between the input modulated signal and the output signal synchronized each other may be minimized (step S104). And then, the first amplitude correction value is calculated which is the first amplitude coefficient to minimize the amplitude difference between the input modulated signal and the output signal (step S105). The amplitude adjustment amount in the first pre-distorter unit130is controlled by using the first amplitude correction value so that the input/output characteristics of the amplifying device100may become identical with the shaping function. At this time, it is also possible to use the LMS algorithm in order to calculate the first amplitude correction value. In the present exemplary embodiment, as shown inFIG. 5A, the function (y=f(x) in the figure) is used as the shaping function which is convex upward over the straight line of y=x. However, it is not limited to this, as shown inFIG. 5B, it is possible to use as the shaping function any function which satisfies the condition that the output y is equal to or greater than every input x, that is, y≧x (y=g(x) in the figure).

When the switching decision unit190decides that the amplitude difference in the first amplitude control unit (AM-AM1)170has been at a minimum, for example, it outputs the switching instruction signal to the switching unit191. And then, when the switching unit191receives the switching instruction signal, it switches the operation state of the first amplitude control unit (AM-AM1)170and the operation state of the second amplitude control unit (AM-AM2)180. That is to say, the first amplitude control unit (AM-AM1)170is put into a stopped state (OFF) (step S106), and the second amplitude control unit (AM-AM2)180is put into an operating state (ON) (step S107). Accordingly, the first amplitude correction value becomes constant, and the input/output amplitude characteristics of the first pre-distorter unit130, which are determined on the basis of the first amplitude correction value, are fixed (step S108). The switching decision unit190can be configured so that it may decide that the amplitude difference has been at a minimum when a value of the amplitude difference between the input modulated signal and the output signal, for example, an average value of the amplitude difference exceeds a predesignated threshold value.

At the next second stage, the second amplitude control unit (AM-AM2)180controls the operation of the second pre-distorter unit140by updating the second amplitude coefficient. That is to say, the second pre-distorter unit140controls the power supply voltage modulation unit120on the basis of the second amplitude coefficient and determines the amplitude of the power supply voltage of the power amplifier110. Specifically, the second amplitude control unit (AM-AM2)180updates the second amplitude coefficient so that the power supply voltage modulation unit120may supply the power supply voltage by which the output of the power amplifier110becomes a saturated state decreasing the amplitude of power supply voltages (step S109). If the output of the power amplifier110becomes a saturated state, the amplitude of the output signal decreases. Therefore, it is possible to turn eventually the output signal having the convex input/output amplitude characteristics at the end of the first stage into that having the linear input/output characteristics in which the ratio of the amplitude of the output signal to the amplitude of the input signal becomes constant. The second amplitude control unit (AM-AM2)180calculates the second amplitude coefficient at this time as the second amplitude correction value (step S110), and controls the operation of the second pre-distorter unit140on the basis of the second amplitude correction value.

At the second stage, the phase control unit (AM-PM)160also updates the phase coefficient so that the phase difference between the input signal and the output signal may be minimized may be minimum (step S111), and calculates the phase correction value which is the phase coefficient to minimize the phase difference (step S112).

As described above, in the amplifying device100according to the present exemplary embodiment, the power amplifier110operates with high efficiency by the second amplitude control unit180controlling the second pre-distorter unit140. The first amplitude control unit170controls the first pre-distorter unit130so that it may output the modulated signal which compensates the distortion characteristics of the power amplifier110in this operation state. In addition, the phase control unit (AM-PM)160constantly controls the first pre-distorter unit130so that the phase difference between the input signal and the output signal may be at a minimum. By means of such configuration, according to the present exemplary embodiment, it becomes possible to compensate both of the amplitude difference and the phase difference between the input signal and the output signal under the condition that the power amplifier110operates with high efficiency in the saturation region.

In the above-mentioned description, the amplifying device100has the configuration including the power amplifier110, the power supply voltage modulation unit120, the first pre-distorter unit130, the second pre-distorter unit140, and the control unit150. Here, it is also acceptable that the first pre-distorter unit130, the second pre-distorter unit140, and the control unit150compose a control device for the power amplifier. In this case, the same effect as that of the amplifying device100according to the present exemplary embodiment can also be obtained by means of the configuration including the control device for the power amplifier, the power supply voltage modulation unit120, and the power amplifier110. The control device for the power amplifier can be implemented by an ASIC (Application Specific Integrated Circuit), for example.

It is also acceptable to make a computer execute above each step. That is to say, it is possible to make a computer execute a procedure for updating a phase coefficient determining a phase compensation amount to an input signal of an amplifying device so that a phase difference between the input signal and an output signal of the amplifying device may be minimized; a procedure for calculating a phase correction value which is a phase coefficient to minimize the phase difference; a procedure for generating an input modulated signal by applying to the input signal a function whose output value is equal to or greater than an input value for every input value; a procedure for updating a first amplitude coefficient determining an amplitude adjustment amount to the input signal so that an amplitude difference between the input modulated signal and the output signal may be minimized; a procedure for calculating a first amplitude correction value which is the first amplitude coefficient to minimize an amplitude difference between the input modulated signal and the output signal; a procedure for updating a second amplitude coefficient determining an amplitude of a power supply voltage of a power amplifier composing the amplifying device, under the condition that the first amplitude correction value is kept constant, on the basis of amplitude information on the input signal so as to supply a power supply voltage by which an output of the power amplifier becomes a saturated state; a procedure for calculating, as a second amplitude correction value, the second amplitude coefficient at a time when an amplitude amplification factor becomes constant which is the ratio of an amplitude of the output signal to an amplitude of the input signal; and a procedure for compensating phase difference between the input signal and the output signal by using the phase correction value and controlling the amplitude amplification factor to be kept constant by using the first amplitude correction value and the second amplitude correction value. In this case, it is possible to use a programmable logic calculating circuit (logic block) as the computer and implement it by means of a field programmable gate array (FPGA) and the like.

The Second Exemplary Embodiment

Next, the second exemplary embodiment of the present invention will be described.FIG. 6is a block diagram showing the configuration of an amplifying device200in accordance with the present exemplary embodiment. The amplifying device200, which is an amplifying device with Envelope Tracking system, includes the power amplifier (PA)110and the power supply voltage modulation unit120modulating the power supply voltage of the power amplifier110. The amplifying device200further includes the first pre-distorter unit130disposed in the preceding stage of the power amplifier110, the second pre-distorter unit140disposed in the preceding stage of the power supply voltage modulation unit120, and a control unit250.

The first pre-distorter unit130outputs to the power amplifier (PA)110the modulated signal S11obtained by adding a phase compensation amount and an amplitude adjustment amount to the input signal S10. The second pre-distorter unit140obtains the amplitude information S20on the input signal of the amplifying device200from the input side and controls the power supply voltage modulation unit120on the basis of the amplitude information S20. The control unit250controls the operation of the first pre-distorter unit130and the second pre-distorter unit140. The power amplifier110inputs the modulated signal S11from the first pre-distorter unit130and outputs the output signal S12which is obtained by amplifying the modulated signal S11. The configuration mentioned above is similar to that of the amplifying device100according to the first exemplary embodiment.

InFIG. 6, a configuration is illustrated in which the second pre-distorter unit140obtains the amplitude information S20from the input signal S10through an envelope detector (not shown in the figure) and the like. And the amplifying device200is configured to include a delay device203delaying the input signal in the preceding stage of the control unit250in order to synchronize the input signal and the output signal of the amplifying device200.

The amplifying device200according to the present exemplary embodiment differs from the amplifying device100according to the first exemplary embodiment in the configuration of the control unit250. Here, the control unit250includes a phase control unit (AM-PM)260, a first amplitude control unit (AM-AM1)270, and a second amplitude control unit (AM-AM2)280. The control unit250is configured to control the first pre-distorter unit130and the second pre-distorter unit140respectively by using look up tables (LUT).

That is to say, the phase control unit (AM-PM)260includes a first look up table263in which a phase coefficient to determine a phase compensation amount in the first pre-distorter unit130is recorded. The first amplitude control unit (AM-AM1)270includes a second look up table273in which a first amplitude coefficient to determine an amplitude adjustment amount in the first pre-distorter unit130is recorded. And, the second amplitude control unit (AM-AM2)280is configured to include a third look up table283in which a second amplitude coefficient to determine the operation of the second pre-distorter unit140is recorded.

The case will be described as an example below in which the amplifying device200is used for a transmission device which up-converts a baseband signal and transmits the up-converted signal. In this case, it is possible to adopt a configuration in which an up-converter301is disposed between the first pre-distorter unit130and the power amplifier (PA)110and a down-converter302is disposed between the output of the power amplifier (PA)110and the control unit250.

InFIG. 7, the configuration of the control unit250is illustrated in more detail. The phase control unit (AM-PM)260includes a phase coefficient calculation unit262and the first look up table263. The first amplitude control unit270includes a shaping function calculation unit271, a first amplitude coefficient calculation unit272, and the second look up table273. And, the second amplitude control unit (AM-AM2)280includes a second amplitude coefficient calculation unit282and the third look up table283. In addition, the control unit250includes an input signal processing unit251carrying out a scaling and an amplitude/phase separation of the input signal, an output signal processing unit252carrying out a scaling and an amplitude/phase separation of the output signal, and a switching control unit290. The switching control unit290switches an operating condition of the first amplitude control unit270and an operating condition of the second amplitude control unit280.

Next, the operation of the amplifying device200according to the present exemplary embodiment will be described in detail with reference toFIGS. 6 to 10. As shown inFIG. 6, the input signal S10in baseband is modulated by the first pre-distorter unit130, and then, up-converted by the up-converter301and input into the power amplifier (PA)110. The output signal S12, which is output from the power amplifier (PA)110after amplification, is transmitted through an antenna. A part of the output signal S12is attenuated by a coupler and the like, down-converted by the down-converter302, and then input into the control unit250.

Meanwhile, a part of the input signal S10in baseband is input into an envelope detector (not shown in the figure) or the like, and the amplitude information S20is extracted from the input signal S10. The second pre-distorter unit140controls the power supply voltage modulation unit120on the basis of the amplitude information S20and the second amplitude coefficient. The power supply voltage modulation unit120modulates the power supply voltage of the power amplifier110.

By delaying the input signal S10, the delay device203synchronizes the input signal (x(t+τ)) inputting into the control unit250and the output signal (y(t)). A delay amount t in the delay device203is obtained by calculating a correlation coefficient between the input signal and the output signal.

The control unit250calculates each coefficient by using the synchronized input and output signal, and updates values in each look up table. Specifically, as shown inFIG. 7, the phase coefficient calculation unit262calculates the phase coefficient and updates the value in the first look up table263. The first amplitude coefficient calculation unit272calculates the first amplitude coefficient and updates the value in the second look up table273. And, the second amplitude coefficient calculation unit282calculates the second amplitude coefficient and updates the value in the third look up table283.

When the output value of the first amplitude coefficient calculation unit272falls below a predetermined threshold value, the switching control unit290switches the operating condition of the first amplitude control unit (AM-AM1)270and the operating condition of the second amplitude control unit (AM-AM2)280. That is to say, the first amplitude control unit (AM-AM1)270is put into a stopped state (OFF), and the second amplitude control unit (AM-AM2)280is put into an operating state (ON).

The phase control unit (AM-PM)260determines the phase compensation amount in the first pre-distorter unit130by means of the phase coefficient recorded in the first look up table263. The first amplitude control unit (AM-AM1)270determines the amplitude adjustment amount in the first pre-distorter unit130by means of the first amplitude coefficient recorded in the second look up table273. And, the second amplitude control unit (AM-AM2)280determines the operation of the second pre-distorter unit140by means of the second amplitude coefficient recorded in the third look up table283.

Next, a procedure for calculating each coefficient recorded in each look up table in the control unit250will be described.FIG. 8is a block diagram showing a part of the configuration of the control unit250, corresponding to a case for controlling the first pre-distorter unit130.FIG. 9is a block diagram showing another part of the configuration of the control unit250, corresponding to a case for controlling the second pre-distorter unit140. And,FIG. 10is a sequence diagram to illustrate the operations of the control unit250.

First, the control unit250initializes each coefficient of the phase control unit (AM-PM)260, the first amplitude control unit (AM-AM1)270, and the second amplitude control unit (AM-AM2)280. That is to say, in the phase control unit (AM-PM)260, the value of the phase coefficient recorded in the first look up table (LUT)263is initialized (step S201inFIG. 10). In the first amplitude control unit (AM-AM1)270, the value of the phase coefficient recorded in the second look up table (LUT)273is initialized, and a predetermined shaping function is set in the shaping function calculation unit271(step S202). And, in the second amplitude control unit (AM-AM2)280, an initial value for the second amplitude coefficient is set in the third look up table (LUT)283(step S203). The initial value at this time is set so that the output of the power amplifier110may not become a saturated state under the operating condition of the power amplifier110which is determined by the control of the second pre-distorter unit140.

Next, with reference toFIG. 8andFIG. 10, a procedure for updating each coefficient recorded in the first look up table263and the second look up table273which control the operation of the first pre-distorter unit130will be described (procedure1inFIG. 10).

As shown inFIG. 8, the control unit250includes the input signal processing unit251and the output signal processing unit252. The input signal processing unit251and the output signal processing unit252scale the amplitude so that the maximum value of the amplitude may become equal to one in each baseband data stream of the input signal and the output signal for a certain time period. After being scaled, an amplitude component (r) and a phase component (θ) are separated and output respectively.

The phase coefficient calculation unit262performs calculations using the LMS (Least Mean Square:) algorithm so that the phase difference may be at a minimum between a phase value in the input signal (θx(t+τ)) and a phase value in the output signal (θy(t)). And then, the phase coefficient recorded in the first look up table263is updated by the updated value of the phase coefficient (Δθ) at this time (step S204).

Meanwhile, with respect to the amplitude component (r), first, the shaping function calculation unit271applies the shaping function having the convex input/output characteristics to the input signal (rx(t+τ)), and outputs an input modulated signal (rx′(t+τ)) to the first amplitude coefficient calculation unit272. The first amplitude coefficient calculation unit272performs calculations using the LMS algorithm so that the amplitude difference may be at a minimum between the input modulated signal (rx′(t+τ)) and the amplitude component of the output signal (ry(t)). And then, the first amplitude coefficient recorded in the second look up table273is updated by the updated value of the first amplitude coefficient (Δr) at this time (step S205).

Here, as shownFIG. 5A, the function (y=f(x) in the figure) is used as the shaping function which is convex upward over the straight line of y=x, which is used in the first exemplary embodiment. That is to say, the function is used which represents a curve (y=f(x) inFIG. 5A) located upward over the straight line (y=x inFIG. 5A) which connects a point corresponding to a set of the minimum values of the input/output (0, 0) to a point corresponding to a set of the maximum values (1, 1), if each range of the input x and the output y is equal to or more than zero and less than or equal to one ([0, 1] to [0, 1]). Expressing this condition in mathematical form, the shaping function f satisfies the following numerical formulae.
f(0)=0,f(1)=1
f(a)>a(0<a<1)
Specifically, it is possible to use y=sin(πx/2) as the shaping function, for example.

Specifically, updating each coefficient mentioned above can be carried out as follows, for example. First, the phase coefficient calculation unit262and the first amplitude coefficient calculation unit272calculate an address value “p” of each look up table corresponding to the amplitude of the input signal (x(t+τ)) into the control unit250. Then, the value of each look up table is updated by adding the updated values of Δθ and Δr to the values in the corresponding address “p” of the first look up table263and the second look up table273respectively.

By repeating the processing for updating the phase coefficient, the phase correction value is calculated that is a phase coefficient by which the phase difference between the input signal and the output signal of the amplifying device200is minimized (step S206). And, by repeating the processing for updating the first amplitude coefficient, the first amplitude correction value is calculated that is a first amplitude coefficient by which the amplitude difference between the input modulated signal and the output signal is minimized (step S207). At this time, the relation between the input modulated signal after being shaped (rx′(t+τ)) and the output signal (ry(t)) become a linear relationship. However, the relation between the input modulated signal before being shaped (rx(t+τ)) and the output signal (ry(t)) is not linear, so the output signal remains distorted at this time.

The switching control unit290decides whether the updated value (Δr) of the first amplitude coefficient output from the first amplitude coefficient calculation unit272converges. If it is decided that the updated value (Δr) has converged, the first amplitude coefficient calculation unit272is put into a stopped state (OFF) (step S208), and the second amplitude coefficient calculation unit282is put into an operating state (ON) (step S209). That is to say, the processing moves from procedure1to procedure2inFIG. 10. At this time, the first amplitude correction value becomes constant, and the input/output amplitude characteristics of the first pre-distorter unit130, which are determined on the basis of the first amplitude correction value, are fixed (step S210). The decision of the convergence can be performed as below, for example. It is deemed that the updated value has converged if a value averaged N times of the absolute updated value (|Δr|) falls below a threshold value β. Here, N and β are parameters given beforehand.

By procedure1described above, the characteristics of the output phase to the input amplitude (AM-PM characteristics) of the amplifying device200is optimized so that the phase difference between the input signal and the output signal may be at a minimum. And, the characteristics of the output amplitude to the input amplitude (AM-AM characteristics) have come to show the similar characteristic curve to the shaping function. That is to say, at an end of procedure1, the AM-AM characteristics remain distorted. Since an optimization process is not carried out to the power supply voltage in procedure1, the amplifying device does not become optimum in the operating condition with respect to the efficient operation.

In calculating the first amplitude correction value mentioned above, if the LMS algorithm has not converged after a predetermined time (τ1) has passed, it is also acceptable to change the shaping function into a function more closely to the linearity and to restart the process from the initialization. Specifically, in stead of the original shaping function y=f(x), a function of y=(x+f(x))/2 can be used as a new shaping function, for example.

It is desirable for the second amplitude control unit (AM-AM2)280to put the power amplifier into a state just before the output saturation by controlling the second pre-distorter unit140after the second amplitude coefficient calculation unit282has been put into the operating state (ON). The condition in which the input/output characteristics of the power amplifier110are saturated is that the output amplitude of the power amplifier110becomes almost equal to the power supply voltage of the power amplifier110. An example of specific control method in this case will be described below.

FIG. 11is a diagram to illustrate a method for controlling the power supply voltage supplied to the power amplifier110, with the time on the horizontal axis and the voltage on the vertical axis. By means of the initial value of the second amplitude coefficient in the second amplitude control unit (AM-AM2)280, the power supply voltage modulation unit120supplies the power amplifier110with an initial power supply voltage Vdd0(t). The initial power supply voltage Vdd0(t) is set so as to have a predesignated positive offset v0large enough for the amplitude of the output signal v(t) of the power amplifier110. That is, it is expressed as
Vdd0(t)=v(t)+v0.

After the optimization of the first amplitude coefficient in above-mentioned procedure1has been completed, the voltage offset value v0in the power supply voltage is decreased by controlling the power supply voltage modulation unit120. At this time, for example, monitoring an amplification factor (gain) which is the ratio of the output signal to the input signal, the update of the voltage offset is stopped if a value of reduced gain against a range of reduced voltage offset v0exceeds a predetermined threshold value. If the offset value at this time is represented by v1, the power supply voltage is expressed as v(t)+v1. In this way, it is possible to set the power supply voltage at the state just before the output saturation of the power amplifier110.

Next, with reference toFIG. 9andFIG. 10, a procedure for updating the second amplitude coefficient recorded in the third look up table283which controls the operation of the second pre-distorter unit140will be described (procedure2inFIG. 10). Here, since the phase control unit (AM-PM)260carries out the same operation as that in the procedure1, the description of it is omitted.

FIG. 9is a block diagram showing a part of the configuration of the control unit250, corresponding to a case for controlling the second pre-distorter unit140. The second amplitude coefficient calculation unit282updates the second amplitude coefficient recorded in the third look up table (LUT)283by the updated value of the second amplitude coefficient (Ah) (step S211). At this time, the second amplitude coefficient calculation unit282updates the second amplitude coefficient so that the AM-AM characteristics in a distorted state at the end of procedure1may approach the linearity. That is to say, the power amplifier110is put into a state of the output saturation by attenuating the corresponding power supply voltage to the input amplitude having AM-AM characteristics without a linear relationship, by which the power amplifier110is controlled so that the output amplitude may decrease.

Specifically, for example, it is possible to put the power amplifier110into an output saturated state by reducing the value in the third look up table (LUT)283corresponding to the input amplitude rx(t) in proportion to a difference value from the linearity (ry(t)−rx(t)). That is to say, the updated value (Δh(t)) corresponding to rx(t) is determined by the following formula.
Δh(t)=−α(ry(t)−rx(t))
Where α is a value given beforehand. It is possible to update the second amplitude coefficient by means of calculating an address value corresponding to the amplitude of the input signal (x(t+τ)), and adding the updated value Δh to a value in the corresponding address value in the third look up table (LUT)283, for example.

In this way, by repeating the processing for updating the second amplitude coefficient, it is possible to put the power amplifier110into the saturation state at each of the output amplitude. As a result, since the corresponding output amplitude is attenuated for each of the input amplitude, it is possible to move the AM-AM characteristics having the convex input/output characteristics at the end of the procedure1closer to the linear characteristics. And then, the second amplitude coefficient calculation unit282calculates, as the second amplitude correction value, a second amplitude coefficient at the time when the amplitude amplification factor, that is, the ratio of the amplitude of the output signal to the amplitude of the input signal, becomes constant over the entire range of the amplitude of the input signal (step S212). As a result, it is possible to obtain the low-distortion output signal in which both of the amplitude component and the phase component are corrected, in addition to the highly-efficient amplification operation utilizing the region where the input/output characteristics of the power amplifier110are saturated.

As described above, in the amplifying device200according to the present exemplary embodiment, the power amplifier110operates with high efficiency by the second amplitude control unit280controlling the second pre-distorter unit140. The first amplitude control unit270controls the first pre-distorter unit130so that it may output the modulated signal which compensates the distortion characteristics of the power amplifier110in this operation state. In addition, the phase control unit (AM-PM)260constantly controls the first pre-distorter unit130so that the phase difference between the input signal and the output signal may be at a minimum. By means of such configuration, according to the present exemplary embodiment, it becomes possible to compensate both of the amplitude difference and the phase difference between the input signal and the output signal under the condition that the power amplifier110operates with high efficiency in the saturation region.

Since the optimization of the second pre-distorter unit140according to the present exemplary embodiment is carried out by reducing the second amplitude coefficient, the calculation amount is small and the convergence time of the algorithm is short. Therefore, according to the present exemplary embodiment, the effect can be obtained that it is possible to optimize the amplifying device rapidly. In addition, according to the present exemplary embodiment, since the power amplifier operates in the saturation region, it is able to operate with higher efficiency than the related amplifying device.

The method for updating the coefficient recorded in the third look up table (LUT)283is not limited to the above-mentioned method. Another linearization method is also applicable such as a method for reducing a coefficient recorded in the near address simultaneously in order to keep the continuity of the look up table.

It is also acceptable to repeat the above-mentioned processing for updating the second amplitude coefficient until the distortion of the amplifying device200satisfies a predetermined standard value. For example, it is possible to repeat the processing until the adjacent-channel power ratio (ACPR) becomes equal to or less than −40 dB.

In calculating the second amplitude correction value mentioned above, if the distortion does not satisfy the predetermined standard value even after a predetermined time (τ2) has passed, it is thought that the influence of the distortion due to the output saturation is significant. Accordingly, it is also acceptable to change the shaping function into a function more closely to the linearity in order to relax the output saturation and to restart the process from the initialization. In this case, as is the case with procedure1, it is possible to use a function of y=(x+f(x))/2 as a new shaping function in stead of the original shaping function y=f(x), for example.

In the present exemplary embodiment, the case is described in which the look up table (LUT) method is used as the pre-distorter. However, it is not limited to this. It is also acceptable to use a pre-distorter employing a method for approximating a distortion correction amount by means of polynomial equations, or a method for performing computer processing by means of complex signals.

In the above-mentioned description, the amplifying device200has the configuration including the power amplifiers110, the power supply voltage modulation unit120, the first pre-distorter unit130, the second pre-distorter unit140, and the control unit250. Here, it is also acceptable that the first pre-distorter unit130, the second pre-distorter unit140, and the control unit250compose a control device for the power amplifier. In this case, the same effect as that of the amplifying device200according to the present exemplary embodiment can also be obtained by means of the configuration including the control device for the power amplifier, the power supply voltage modulation unit120, and the power amplifier110. The control device for the power amplifier can be implemented by an FPGA (Field Programmable Gate Array) or the like.

The present invention is not limited to the above-mentioned exemplary embodiments and can be variously modified within the scope of the invention described in the claims. It goes without saying that these modifications are also included in the scope of the present invention.

This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2010-283133, filed on Dec. 20, 2010, the disclosure of which is incorporated herein in its entirety by reference.

DESCRIPTION OF THE CODES