Power amplifier

A power amplifier based on EER technology or ET technology extracts an amplitude-modulated component from a modulated signal as an input signal which includes the amplitude-modulated component and a phase-modulated component, and decomposes the amplitude-modulated component into two control signals whose product is proportional to the amplitude-modulated component. One of the control signals is amplified by a highly efficient amplifier, and thereafter is used to amplitude-modulate an output from an RF amplifier. The other control signal is converted by a pulse modulator into a rectangular-wave signal, which is then mixed with the phase-modulated component or the modulated signal and input to the RF amplifier.

TECHNICAL FIELD

The present invention relates to a power amplifier with high linearity and power efficiency, primarily for use in wireless communication devices.

BACKGROUND ART

Power amplifiers for transmission which are included in wireless communication devices consume much electric power among other components in the wireless communication devices. Therefore, improving the power efficiency of power amplifiers is an important task to be accomplished in the development of wireless communication devices. In recent years, the wireless communication standards have seen mainstream efforts directed to an amplitude modulation scheme for improving the spectral efficiency. According to the amplitude modulation scheme, since strict requirements are imposed on signal distortions, power amplifiers need to be operated in a high backoff (low input power) state for better linearity. However, if a power amplifier is operated in the high backoff state, then the power amplifier has its power efficiency lowered. Recently, EER (Envelope Elimination and Restoration) has been intensively researched as a technology for increasing the power efficiency of power amplifiers and keeping linearity between input and output signals.

The EER technology is a scheme for amplifying highly efficiently an input signal (modulated signal) including an amplitude-modulated (AM) component and a phase-modulated (PM) component. Specifically, only the PM component that is left by removing the AM component from the input signal is amplified, and the amplified PM component is amplitude-modulated with the removed AM component, thereby linearly amplifying the input signal and restoring the original waveform thereof.FIG. 1shows a configuration of a power amplifier according to the background art which is based on the EER technology.

FIG. 1is a block diagram showing the configuration of the power amplifier according to the background art which is based on the EER technology.

As shown inFIG. 1, the power amplifier according to the background art which is based on the EER technology comprises signal generating circuit147, RF (Radio Frequency) amplifier109, pulse modulator104, driver amplifier116, switching amplifier105, low-pass filter106, and bandpass filter107.

Signal generating circuit147extracts an AM component included in an input signal, and outputs the extracted AM component as amplitude component signal111through terminal145to pulse modulator104. Signal generating circuit147also extracts a PM component included in the input signal, and outputs the extracted PM component as phase component signal112through terminal146to RF amplifier109.

Pulse modulator104pulse-modulates amplitude component signal111to generate a rectangular-wave signal, and outputs the rectangular-wave signal to driver amplifier116.

According to the rectangular-wave signal output from pulse modulator104, driver amplifier116drives switching amplifier105to amplify the rectangular-wave signal efficiently. The amplified rectangular-wave signal is smoothed by low-pass filter106, and then supplied through terminal142to RF amplifier109.

RF amplifier109comprises transistor101, input power supply circuit108, and output power supply circuit140. RF amplifier109amplifies phase component signal112output from signal generating circuit147. An output signal from RF amplifier109is amplitude-modulated with the smoothed rectangular-wave signal supplied from switching amplifier105through low-pass filter106and terminal142, i.e., amplified amplitude component signal114.

Input power supply circuit108that is connected to the gate of transistor101is usually supplied with a constant DC voltage from a power supply device, not shown, through terminal141.

The signal amplified by RF amplifier109(output signal115) is processed by bandpass filter107to remove unwanted band components therefrom, and then supplied through terminal144to an antenna device, not shown, or the like.

FIG. 2is a block diagram showing a configurational example of the signal generating circuit shown inFIG. 1, andFIG. 3is a block diagram showing another configurational example of the signal generating circuit shown inFIG. 1. Signal generating circuit147shown inFIG. 2is of a configuration optimum for an application wherein an RF signal is input to input terminal143of the power amplifier, and signal generating circuit147shown inFIG. 3is of a configuration that is optimum for an application wherein a baseband signal is input to input terminal143of the power amplifier.

Signal generating circuit147shown inFIG. 2comprises amplitude detector103for extracting an AM component from an RF signal as an input signal and outputting the extracted AM component as amplitude component signal111, and limiter102for removing the AM component of the input signal. Amplitude detector103extracts the AM component of the input signal (RF signal) input from terminal143, and outputs the extracted AM component as amplitude component signal111from terminal145. Limiter102removes the AM component of the input signal (RF signal) input from terminal143, and outputs phase component signal112, which represents a remaining PM component, from terminal146. Signal generating circuit147shown inFIG. 2also includes delay corrector153which is capable of adjusting the delay time difference between amplitude component signal111and phase component signal112.

Signal generating circuit147shown inFIG. 3comprises baseband signal processing circuit150and VCO151. Baseband signal processing circuit150should preferably comprise a DSP (Digital Signal Processor) and a D/A (digital-to-analog) converter. Baseband signal processing circuit150outputs amplitude component signal111, which represents the AM component of the baseband signal as the input signal, to terminal145, and also outputs a phase component signal, which represents the PM component of the baseband signal, to VCO151. In baseband signal processing circuit150, the DSP calculates and extracts the AM component of the baseband signal input from terminal143according to a digital processing process, and the D/A converter converts the AM component into an analog signal and thereafter outputs the analog signal as amplitude component signal111from terminal145. Furthermore, the DSP calculates and extracts the PM component of the baseband signal input from terminal143according to a digital processing process, and the D/A converter converts the PM component into an analog signal and thereafter outputs the analog signal as a phase component signal from terminal145. Baseband signal processing circuit150controls VCO151with the same phase component signal.

VCO151is controlled by the phase component signal from baseband signal processing circuit150to output a phase component signal which has been up-converted into an RF signal.

With the power amplifier shown inFIG. 1, signal generating circuit147outputs phase component signal112with sufficiently large electric power to keep transistor101of RF amplifier109saturated state in operation at all times. The drain of transistor101of RF amplifier109is supplied with amplitude component signal114through terminal142and output power supply circuit140to amplitude-modulate phase component signal112amplified by transistor101with amplitude component signal114. Therefore, the power amplifier can amplify the input signal with high power efficiency and maintain linearity between the input and output signals.

On the other hand, ET (Envelope Tracking) is known as another technology for increasing the power efficiency of power amplifiers and keeping linearity between input and output signals.

The ET technology is a scheme for amplifying an input signal including an AM component and a PM component, extracting the AM component of the input signal, and amplitude-modulating the amplified signal with the extracted AM component for thereby increasing the power efficiency and keeping linearity between input and output signals.FIG. 4shows the configuration of a power amplifier according to the background art which is based on the ET technology.

FIG. 4is a block diagram showing the configuration of the power amplifier according to the background art which is based on the ET technology.

As shown inFIG. 4, the power amplifier according to the background art which is based on the ET technology is different from the power amplifier based on the EER technology shown inFIG. 1as to configurational and operational details of signal generating circuit148. The configurational and operational details of the other components are the same as those of the power amplifier based on the EER technology shown inFIG. 1and will not be described below. InFIG. 4, components other than signal generating circuit148are denoted by the same reference characters as those of the power amplifier shown inFIG. 1.

Signal generating circuit148extracts an AM component included in an input signal, and outputs the extracted AM component as amplitude component signal111through terminal145to pulse modulator104. Signal generating circuit148outputs modulated signal149that is proportional to the amplitude of the input signal which includes the AM component and a PM component, through terminal146to RF amplifier109.

FIG. 5is a block diagram showing a configurational example of the signal generating circuit shown inFIG. 4, andFIG. 3is a block diagram showing another configurational example of the signal generating circuit shown inFIG. 4. Signal generating circuit148shown inFIG. 5is of a configuration that is optimum for an application wherein an RF signal is input to input terminal143of the power amplifier, and the signal generating circuit shown inFIG. 6is of a configuration that is optimum for an application wherein a baseband signal is input to input terminal143of the power amplifier.

Signal generating circuit148shown inFIG. 5comprises amplitude detector103for extracting an AM component from an RF signal as an input signal and for outputting the extracted AM component as amplitude component signal111. Amplitude detector103extracts the AM component of the input signal (RF signal) input from terminal143, and outputs the extracted AM component as amplitude component signal111from terminal145. The input signal input from terminal143is supplied to amplitude detector103and is also output as modulated signal149from terminal146. Signal generating circuit148shown inFIG. 5also includes delay corrector153which is capable of adjusting the delay time difference between amplitude component signal111and modulated signal149.

Signal generating circuit148shown inFIG. 6comprises baseband signal processing circuit150and quadrature modulator152. In baseband signal processing circuit150, the DSP calculates and extracts the AM component of the baseband signal input from terminal143according to a digital processing process, and the D/A converter converts the AM component into an analog signal and thereafter outputs the analog signal as amplitude component signal111from terminal145. Furthermore, the D/A converter converts the input baseband signal into an analog signal and thereafter outputs the analog signal to quadrature modulator152.

Quadrature modulator152up-converts the baseband signal output from baseband signal processing circuit150into an RF frequency signal, and outputs the RF frequency signal as modulated signal149from terminal146.

With the power amplifier shown inFIG. 4, signal generating circuit148outputs modulated signal149with sufficiently large electric power to keep transistor101of RF amplifier109saturated state in operation at all times, thereby enabling RF amplifier109to have the function of limiter102shown inFIG. 2. Specifically, the power amplifiers based on the EER technology and the ET technology operate according to common principles except that the PM component of the input signal is input to RF amplifier109according to the EER technology and modulated signal149including the AM component and the PM component is input to RF amplifier109according to the ET technology. Therefore, the power amplifier based on the ET technology can also amplify the input signal with high power efficiency and maintain linearity between the input and output signals.

If the power amplifier shown inFIG. 1orFIG. 4is employed to power-amplify an RF signal having a bandwidth of several MHz such as those used in the W-CDMA (Wideband Code Division Multiple Access) communication process, then driver amplifier116and switching amplifier105need to perform a switching operation in a frequency range from several tens to several hundreds MHz. Furthermore, if the EER technology and the ET technology are applied to power amplifiers provided in radio base stations, then it is necessary for switching amplifier105to output a high voltage of several tens of volts. According to the present device and circuit technologies, however, driver amplifier116and switching amplifier105that operate under a high voltage of several tens of volts have a switching rate that is limited to about several hundreds kHz at maximum. A scheme for avoiding such an operational limitation on driver amplifier116and switching amplifier105has been proposed by JP-A No. 2005-244950, for example.

FIG. 7is a block diagram showing another configurational example of the power amplifier according to the background art which is based on the EER technology. The power amplifier shown inFIG. 7is illustrated in FIG. 24 of JP-A No. 2005-244950.

Data generator301shown inFIG. 7outputs an amplitude component signal and a phase component signal of a transmission signal. The phase component signal is added to an RF signal by angle modulator303and output to amplitude modulator305. The amplitude component signal is decomposed into a low-frequency amplitude component signal and a high-frequency amplitude component signal by frequency discriminator302. Amplitude modulator305amplitude-modulates the phase component signal with a high-frequency amplitude component signal generated by high-frequency voltage controller304, and amplitude modulator307amplitude-modulates the phase component signal with a low-frequency amplitude component signal generated by low-frequency voltage controller306. According to this arrangement, high-frequency voltage controller304may have relatively small output power though the operating frequency thereof is high, and low-frequency voltage controller306may have a relatively low operating frequency though the output power thereof is large. Therefore, high-frequency voltage controller304and low-frequency voltage controller306shown inFIG. 7do not need to have both high-voltage output and fast switching operation, but may be realized by the present device and circuit technologies.

However, the above power amplifiers according to the background art are problematic in that the power efficiency of RF amplifier109shown inFIGS. 1 and 4is lowered when the voltage (power supply voltage) supplied to output power supply circuit140of RF amplifier109is lowered.FIG. 8shows power efficiency characteristics when the RF amplifier109shown inFIG. 1is supplied with a constant power supply voltage (when it is in conventional operation), and also shows power efficiency characteristics when the RF amplifier109shown inFIG. 1is in EER operation.

As shown inFIG. 8, RF amplifier109has its power efficiency made better when it is in EER operation than when it is in conventional operation. However, even when RF amplifier109is in EER operation, the power efficiency thereof is low at the time that the output power thereof is small. The reduction in the power efficiency of RF amplifier109at the time that the output power thereof is small is responsible to a reduction in the average power efficiency of the overall power amplifying circuit.

The power amplifiers according to the background art are also disadvantageous in that the power efficiency of switching amplifier105shown inFIGS. 1 and 4is lowered when the output voltage (average voltage) of switching amplifiers105is lowered. As with the reduction in the power efficiency of RF amplifier109described above, the reduction in the power efficiency of switching amplifier105is responsible for a reduction in the average power efficiency of the overall power amplifying circuit.

Specifically, in the case where the amplitude component of the input signal has a large dynamic range and the output power of the power amplifier is small, the power efficiency of the RF amplifier and the switching amplifier of the power amplifiers according to the background art based on the EER technology and the ET technology is lowered and cannot be sufficiently improved.

Furthermore, if the power amplifiers according to the background art shown inFIGS. 1 and 4are employed to power-amplify an RF signal having a wide bandwidth, then driver amplifier116and switching amplifier105needs to have both high-voltage output and a fast switching operation. However, such requirements cannot be met by the present device technologies. Accordingly, the power amplifiers shown inFIGS. 1 and 4have a limited range of applications.

The power amplifier shown inFIG. 7does not require driver amplifier116and switching amplifier105to have both high-voltage output and fast switching operation. However, the arrangement has a problem in that a signal representative of the input signal which is highly accurately restored cannot be produced as the output signal.

According to the arrangement shown inFIG. 7, when amplitude modulator307is saturated state in operation, the output amplitude of amplitude modulator307is nearly independent of the output amplitude of amplitude modulator305. Therefore, the output signal of amplitude modulator307does not reflect the amplitude of the high-frequency amplitude component signal generated by high-frequency voltage controller304. Conversely, when amplitude modulator307is linearly operated, the output amplitude of amplitude modulator307is virtually unchanged by the low-frequency amplitude component signal generated by low-frequency voltage controller306. Therefore, the output signal of amplitude modulator307does not reflect the amplitude of the low-frequency amplitude component signal generated by low-frequency voltage controller306. Consequently, since the output signal reflects only either the amplitude component signals generated by high-frequency voltage controller304or low-frequency voltage controller306, it is difficult to produce a signal representative of the input signal which is highly accurately restored, as the output signal.

SUMMARY

It is an object of the present invention to provide a power amplifier based on the EER technology and the ET technology which is capable of amplifying a signal with good power efficiency and accurately restoring the signal.

To achieve the above object, there is provided in accordance with the present invention a power amplifier for amplifying a modulated signal including an amplitude-modulated component and a phase-modulated component, comprising:

a decomposing circuit for decomposing said amplitude-modulated component into two control signals whose product is proportional to said amplitude-modulated component;

a mixing circuit for mixing one of the decomposed control signals with said phase-modulated component;

an amplifying circuit for amplifying the other of the decomposed control signals; and

an RF amplifier for amplifying a signal output from said mixing circuit, amplitude-modulating the amplified signal with an output signal from said amplifying circuit, and outputting the amplitude-modulated signal.

There is also provided a power amplifier for amplifying a modulated signal including an amplitude-modulated component and a phase-modulated component, comprising:

a decomposing circuit for decomposing said amplitude-modulated component into two control signals whose product is proportional to said amplitude-modulated component;

a mixing circuit for mixing one of the decomposed control signals with said modulated signal;

an amplifying circuit for amplifying the other of the decomposed control signals; and

an RF amplifier for amplifying a signal output from said mixing circuit, amplitude-modulating the amplified signal with an output signal from said amplifying circuit, and outputting the amplitude-modulated signal.

EXEMPLARY EMBODIMENT

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

FIG. 9is a block diagram showing a configurational example of a power amplifier according to the present invention.

As shown inFIG. 9, the power amplifier according to the present invention comprises decomposition circuit1, mixing circuit2, amplifying circuit3, and RF amplifier4.

Decomposition circuit1decomposes an AM component included in an input signal into two control signals whose product has a value proportional to the AM component.

If the EER technology described above is applied, then mixing circuit2mixes one of the control signals decomposed by decomposition circuit1with a PM component included in the input signal. If the ET technology described above is applied, then mixing circuit2mixes one of the control signals decomposed by decomposition circuit1with the input signal (modulated signal).

Amplifying circuit3amplifies the other control signal decomposed by decomposition circuit1, and outputs the amplified control signal to RF amplifier4.

RF amplifier4amplifies a signal output from mixing circuit2, amplitude-modulates the amplified signal with the output signal from amplifying circuit3, and outputs the amplitude-modulated signal.

Specific examples of decomposition circuit1, mixing circuit2, amplifying circuit3, and RF amplifier4of the power amplifier shown inFIG. 9will be described below based on the first through fourth exemplary embodiments.

First Exemplary Embodiment

FIG. 10is a block diagram showing a configuration of a power amplifier according to a first exemplary embodiment.FIG. 11is a waveform diagram showing signal waveforms in principal portions of the power amplifier shown inFIG. 10.FIG. 12is a graph showing the frequency characteristics of the signals shown inFIG. 11.FIG. 10shows a configurational example of the power amplifier based on the EER technology described above.

As shown inFIG. 10, the power amplifier according to the first exemplary embodiment comprises signal generating circuit447, RF (Radio Frequency) amplifier409, first pulse modulator420, first driver amplifier421, second pulse modulator404, second driver amplifier416, switching amplifier405, low-pass filter406, mixer423, and bandpass filter407

Signal generating circuit447extracts an AM component included in an input signal, outputs first control signal418generated from the AM component through terminal453to first pulse modulator420, and outputs second control signal419generated from the AM component through terminal445to second pulse modulator404. In the present exemplary embodiment, if it is assumed that the AM component of the input signal is denoted by a(t), then signal generating circuit447outputs amplitude component a1(t), which has a smaller dynamic range than AM component a(t) and satisfies the relationship: a(t) proportional to a1(t) a2(t), as first control signal418to first pulse modulator420, and also outputs amplitude component a2(t) as second control signal419to second pulse modulator404. Signal generating circuit447also extracts a PM component included in the input signal, and outputs the extracted PM component as phase component signal412through terminal446to RF amplifier409. Signal generating circuit447should preferably have a function to adjust the delay time difference between first control signal418and phase component signal412and the delay time difference between second control signal419and phase component signal412.

First pulse modulator420pulse-modulates first control signal418to generate a rectangular-wave signal having a constant amplitude, and outputs the rectangular-wave signal to first driver amplifier421. First pulse modulator420may comprise a PWM (Pulse Width Modulation) modulator, a delta modulator, a delta-sigma modulator, or the like. First pulse modulator420may comprise any circuit insofar as it can convert first control signal418output from signal generating circuit447into a rectangular-wave signal having a constant amplitude.

First driver amplifier421amplifies the rectangular-wave signal output from first pulse modulator420and supplies the amplified rectangular-wave signal to mixer423. If first pulse modulator420is capable of outputting a signal which is intensive enough to drive mixer423, then first driver amplifier421may be dispensed with.

Second pulse modulator404pulse-modulates second control signal419to generate a rectangular-wave signal, and outputs the rectangular-wave signal to second driver amplifier416. Second pulse modulator404may comprise a PWM (Pulse Width Modulation) modulator, a delta modulator, a delta-sigma modulator, or the like, as with first pulse modulator420.

Second pulse modulator416drives switching amplifier405according to the rectangular-wave signal output from second pulse modulator404, and switching amplifier405current-amplifies the rectangular-wave signal efficiently. The amplified rectangular-wave signal is smoothed by low-pass filter406, and supplied through terminal442to RF amplifier409. Switching amplifier405may comprise an amplifier capable of amplifying the rectangular-wave signal with high power efficiency, e.g., a class-D amplifier, a class-E amplifier, a class-S amplifier, or the like. If second pulse modulator404is capable of outputting a signal which is intensive enough to drive switching amplifier405, then second driver amplifier416may be dispensed with.

Mixer423mixes the phase component signal output from signal generating circuit447with the rectangular-wave signal output from first driver amplifier421, and outputs the mixed signal to RF amplifier409.

RF amplifier409, which comprises transistor401, input power supply circuit408, and output power supply circuit440, amplifies output signal426from mixer423. At this time, the output signal from RF amplifier409is amplitude-amplified with the smoothed rectangular-wave signal supplied from switching amplifier405through low-pass filter406and terminal442, i.e., amplified amplitude component signal414. Input power supply circuit408that is connected to the gate of transistor401is supplied with a constant DC voltage from a power supply device, not shown, through terminal441, as with the background art. Transistor401may be either a field-effect transistor or a bipolar transistor.

The output signal amplified by RF amplifier409(output signal415) is processed by bandpass filter407to remove unwanted band components therefrom, and then supplied through terminal444to an antenna device, not shown, or the like.

FIG. 13is a block diagram showing a configurational example of the signal generating circuit shown inFIG. 10, andFIG. 14is a block diagram showing another configurational example of the signal generating circuit shown inFIG. 10. Signal generating circuit447shown inFIG. 13is of a configuration that is optimum for an application wherein an RF signal is input to the power amplifier shown inFIG. 10, and signal generating circuit447shown inFIG. 14is of a configuration that is optimum for an application wherein a baseband signal is input to the power amplifier shown inFIG. 10.

Signal generating circuit447shown inFIG. 13comprises amplitude detector403for extracting an AM component from an RF signal as an input signal, limiter402for removing the AM component of the input signal, and signal separator417afor decomposing the AM component extracted from the input signal by amplitude detector403. Signal generating circuit447shown inFIG. 13also includes delay corrector454which is capable of adjusting the delay time difference between the AM component extracted from the input signal by amplitude detector403and a PM component extracted by limiter402.

Amplitude detector403extracts the AM component of the input signal (RF signal) input from terminal443, and outputs the extracted AM component to signal separator417a. Signal separator417adecomposes AM component a(t) of the input signal into amplitude components a1(t), a2(t) which satisfy the relationship: a(t) proportional to a1(t) a2(t), outputs first control signal418having amplitude component a1(t) to terminal453, and outputs second control signal419having amplitude component a2(t) to terminal445. Limiter402removes the AM component of the input signal (RF signal) input from terminal443, and outputs phase component signal412, which represents a remaining PM component, from terminal446.

Signal separator417amay be implemented by a digital signal processor (DSP) including logic circuits, an A/D (analog-to-digital) converter, and a D/A (digital-to-analog) converter, an arithmetic circuit comprising an analog circuit, or the like.

Signal generating circuit447shown inFIG. 14comprises baseband signal processing circuit450and VCO451. Baseband signal processing circuit450should preferably comprise a DSP and a D/A converter. In baseband signal processing circuit450, the DSP calculates and extracts amplitude components a1(t), a2(t) which satisfy the relationship: a(t) proportional to a1(t) a2(t) from AM component a(t) of the baseband signal input from terminal443according to a digital processing process, and the D/A converter converts amplitude components a1(t), a2(t) into analog signals, and thereafter outputs amplitude component a1(t) as first control signal418to terminal453and outputs amplitude component a2(t) as second control signal419to terminal445. Furthermore, the DSP calculates and extracts the PM component of the baseband signal input from terminal443according to a digital processing process, and the D/A converter converts the PM component into an analog signal and thereafter outputs the analog signal as a phase component signal from terminal145. Baseband signal processing circuit450should preferably have a function, implemented by the DSP, to calculate and correct the delay time difference between the AM and PM components of the baseband signal.

VCO451is controlled by an output signal from baseband signal processing circuit450to output a phase component signal which has been up-converted into an RF signal.

InFIG. 10, signal generating circuit447has a D/A converter for outputting first control signal418and second control signal419as analog signals. However, if signal generating circuit447includes signal separator417acomprising a DSP shown inFIG. 13or baseband signal processing circuit450shown inFIG. 14, then signal generating circuit447may output first control signal418and second control signal419as digital signals. In this case, first pulse modulator420and second pulse modulator404may include respective D/A converters. Baseband signal processing circuit450and signal separator417aof signal generating circuit447may include the functions of first pulse modulator420and second pulse modulator404. In this case, first pulse modulator420and second pulse modulator404may be dispensed with.

With the power amplifier according to the first exemplary embodiment shown inFIG. 10, first control signal418is added to phase component signal412by mixer423. Such a function may be realized by RF amplifier478shown inFIG. 15. The power amplifier shown inFIG. 15is of a configuration wherein RF amplifier4of the power amplifier shown inFIG. 9includes mixing circuit2.

RF amplifier478shown inFIG. 15is of the same configuration as RF amplifier409shown inFIG. 10, and comprises transistor471, input power supply circuit472, and output power supply circuit473.

If RF amplifier478shown inFIG. 15is used in place of mixer423, then phase component signal412may be input from terminal476shown inFIG. 15and the rectangular-wave signal output from first driver amplifier421may be input to input power supply terminal474or to output power supply terminal475shown inFIG. 15. In this case, a signal representative of phase component signal412and the rectangular-wave signal that are mixed with each other is produced from terminal477.

Since RF amplifier409shown inFIG. 10provides high power efficiency when saturated state in operation, the input signal applied to RF amplifier409should desirably have electric power high enough to saturate RF amplifier409in operation. However, when RF amplifier409is saturated state in operation, the output signal of RF amplifier409does not reflect the amplitude component of the input signal of RF amplifier409. Accordingly, first control signal418is converted into rectangular-wave signal422having a constant amplitude, and rectangular-wave signal422is added to phase component signal412by mixer423and then input to RF amplifier409. By thus processing first control signal418, it is possible for the output signal of RF amplifier409to reflect the amplitude component of first control signal418.

With the power amplifier according to the first exemplary embodiment, furthermore, the drain of transistor401of RF amplifier409is supplied with amplitude component signal414through terminal442and output power supply circuit440to amplitude-modulate the signal amplified by transistor401with amplitude component signal414, as with the power amplifier according to the background art shown inFIG. 1. As shown inFIG. 11, amplitude modulation causes RF amplifier409to output signal425that is generated by multiplying phase component signal412by rectangular-wave signal422and by multiplying the product by output signal (output power supply modulation signal)414from low-pass filter406.

As shown inFIG. 12, signal425output from RF amplifier409has such frequency characteristics that amplified and reproduced baseband signal component428has central frequency fc with spurious components429a,429bcaused by rectangular-wave signal422in the opposite side bands thereof.

As signal425output from RF amplifier409passes through bandpass filter407which has a frequency band wider than frequency band428of the baseband signal and which is capable of removing spurious components429a,429bcaused by rectangular-wave signal422, unwanted spurious components429a,429badded to signal425output from RF amplifier409are removed, thereby producing desired RF signal415which is representative of the linearly amplified input signal.

As described above, the power amplifier according to the first exemplary embodiment reduces the dynamic ranges of first control signal418and second control signal419so as to be smaller than the dynamic range of AM component a(t) of the original input signal. Therefore, the average output voltage of switching amplifier405and the output voltage of RF amplifier409are prevented from being lowered, thus preventing the power efficiency of RF amplifier409and switching amplifier405from being lowered.

Inasmuch as first control signal418is converted into the rectangular-wave signal having the constant amplitude and the rectangular-wave signal is input to RF amplifier409, the information of first control signal418is not lost, but is properly reflected in the output signal of RF amplifier409even when RF amplifier409is saturated state in operation.

The power amplifier according to the present exemplary embodiment thus produces, as the output signal, a signal representative of the waveform of the input signal that is restored more accurately than with the power amplifier according to the background art shown inFIG. 7which does not reflect a portion of the amplitude component signal and which fails to reproduce the signal properly.

For example,FIGS. 16 and 17show signal waveforms in principal portions of the power amplifier according to the present exemplary embodiment wherein an RF signal (central frequency of 1.95 GHz) that is amplitude-modulated with a sine wave having a frequency of 100 kHz is applied as the input signal, and first control signal (a1(t))418and second control signal (a2(t))419are related to each other by a1(t)=a2(t) proportional to sqrt(a(t)) where sqrt(a(t)) represents a root (e.g., a square root) of a(t).

FIG. 16is a waveform diagram showing the waveforms of AM component a(t) of the input signal and first control signal418and second control signal419.

As shown inFIG. 16, with the power amplifier according to the present exemplary embodiment, first control signal (a1(t))418and second control signal (a2(t))419have a dynamic range smaller than AM component a(t) of the input signal. Specifically, whereas the amplitude component of the input signal has a maximum/minimum ratio of 3.0, first control signal (a1(t))418and second control signal (a2(t))419have a reduced maximum/minimum ratio of 1.7. Accordingly, the average output voltage of switching amplifier405and the output voltage of RF amplifier409are prevented from being lowered, thus preventing the power efficiency of RF amplifier409and switching amplifier405from being lowered.

When a1(t)=a2(t) proportional to sqrt(a(t)) is satisfied, first control signal (a1(t))418and second control signal (a2(t))419satisfy the relationship: a(t) proportional to a1(t)a2(t). Therefore, the power amplifier shown inFIG. 10is capable of accurately restoring original AM component a(t)) from first control signal418and second control signal419.

FIG. 17is a waveform diagram showing the AM waveform of an input/output signal (RF) of the power amplifier shown inFIG. 10.

It can be seen fromFIG. 17that with the power amplifier according to the present exemplary embodiment, if the input signal is multiplied by a given constant to match the output signal in scale, then their waveforms are essentially in conformity with each other, indicating that the input signal is linearly amplified.

First control signal (a1(t))418and second control signal (a2(t))419are not limited to the relationship: a1(t)=a2(t) proportional to sqrt(a(t)), but may be of the relationship: a1(t) proportional to [a(t)]n1, a2(t) proportional to [a(t)]n2(n1+n2=1), for example. It is desirable that n1, n2<1 in order to satisfy the condition that amplitude components a1(t), a2(t) have a smaller dynamic range than AM component a(t).

Moreover, first control signal (a1(t))418and second control signal (a2(t))419may be set as shown inFIG. 18.

For example, predetermined threshold value arefis set for AM component a(t). If a(t) is smaller than threshold value aref, then first control signal418may be set to a value proportional to a(t) and second control signal419may be set to constant value aref2. If a(t) is equal to or greater than threshold value aref, then first control signal418may be set to constant value aref1and second control signal419may be set to a value proportional to a(t).

In other words, when a(t) is equal to or greater than threshold value aref, then first control signal418is set to a constant value, and when a(t) is smaller than threshold value aref, then first control signal418is set to a value proportional to a(t). When a(t) is equal to or greater than threshold value aref, then second control signal419is set to a value proportional to a(t), and when a(t) is smaller than threshold value aref, then second control signal419is set to a constant value.

Inasmuch as first control signal418and second control signal419thus set have a smaller dynamic range than original AM component a(t), the output voltage of switching amplifier405and the output voltage of RF amplifier409are prevented from being lowered, thus preventing the power efficiency of RF amplifier409and switching amplifier405from being lowered. As first control signal (a1(t))418and second control signal (a2(t))419satisfy the relationship: a(t) proportional to a1(t) a2(t), the input signal is linearly amplified. The same operation is realized even if a1(t) and a2(t) are switched around.

First control signal418and second control signal419are not limited to the values set as described above, but may have any value insofar as first control signal418and/or second control signal419has a smaller dynamic range than original AM component a(t) (provided a(t) proportional to a1(t) a2(t)).

FIG. 19is a block diagram showing a first modification of the power amplifier according to the first exemplary embodiment.FIG. 20is a waveform diagram showing signal waveforms in principal portions of the power amplifier shown inFIG. 19.FIG. 21is a graph showing the frequency characteristics of the signals shown inFIG. 19.FIG. 19shows a configurational example of the power amplifier based on the EER technology.

The power amplifier shown inFIG. 19is different from the configuration shown inFIG. 10in that mixer423is omitted from the configuration shown inFIG. 10, phase component signal412output from signal generating circuit447is input to RF amplifier409, and rectangular-wave signal422that is output from first driver amplifier421is input to RF amplifier409. Rectangular-wave signal422is applied to the gate of transistor401through terminal441and input power supply circuit408.

When transistor401is turned on and off by rectangular-wave signal422, the power amplifier shown inFIG. 19adds rectangular-wave signal422to phase component signal412as with the power amplifier shown inFIG. 10.

According to this arrangement, as shown inFIG. 20, RF amplifier409also outputs signal425that is generated by multiplying phase component signal412by rectangular-wave signal422and by multiplying the product by output signal (output power supply modulation signal)414from low-pass filter406.

As shown inFIG. 21, signal425output from RF amplifier409has frequency characteristics such that amplified and reproduced baseband signal component428has central frequency fc with spurious components429a,429bcaused by rectangular-wave signal422in the opposite side bands thereof.

With the power amplifier shown inFIG. 19, as with the power amplifier shown inFIG. 10, signal generating circuit447outputs first control signal418(a1(t)) and second control signal419(a2(t)) which have a smaller dynamic range than AM component a(t) and satisfy the relationship: a(t) proportional to a1(t) a2(t), so that the output voltage of switching amplifier405and the output voltage of RF amplifier409are prevented from being lowered, thus preventing the power efficiency of RF amplifier409and switching amplifier405from being lowered. The power amplifier shown inFIG. 19allows the waveform of the input signal to be restored in the output signal with higher accuracy than with the power amplifier according to the background art shown inFIG. 7. Furthermore, since the power amplifier shown inFIG. 19requires no mixer423, it is made up of a smaller number of parts, and hence consumes a lower amount of electric power and is manufactured at a lower cost than the power amplifier shown inFIG. 10.

FIG. 22is a block diagram showing a second modification of the power amplifier according to the first exemplary embodiment.FIG. 22shows a configurational example of the power amplifier based on the ET technology.

The power amplifier based on the ET technology is different from power amplifier based on the EER technology shown inFIG. 10as to configurational and operational details of signal generating circuit447. The configurational and operational details of the other components are the same as those of the power amplifier based on the EER technology shown inFIG. 10and will not be described below. InFIG. 22, the components that make up the power amplifier are denoted by the same reference characters as those of the power amplifier shown inFIG. 10.

As with the power amplifier shown inFIG. 10, signal generating circuit447shown inFIG. 22extracts an AM component included in an input signal, outputs first control signal418generated from the AM component through terminal453to first pulse modulator420, and outputs second control signal419generated from the AM component through terminal445to second pulse modulator404. If it is assumed that the AM component of the input signal is denoted by a(t), then signal generating circuit447outputs amplitude component a2(t), which has a smaller dynamic range than AM component a(t) and satisfies the relationship: a(t) proportional to a1(t) a2(t), as first control signal418to first pulse modulator420, and also outputs amplitude component a2(t) as second control signal419to second pulse modulator404. Signal generating circuit447shown inFIG. 22also outputs modulated signal410that is proportional to the amplitude of the input signal which includes the AM component and a PM component, through terminal446to mixer423. Signal generating circuit447should preferably have a function to adjust the delay time difference between first control signal418and phase component signal412and the delay time difference between second control signal419and phase component signal412.

FIG. 23is a block diagram showing a configurational example of the signal generating circuit shown inFIG. 22, andFIG. 24is a block diagram showing another configurational example of the signal generating circuit shown inFIG. 22. Signal generating circuit447shown inFIG. 23is of a configuration that is optimum for an application wherein an RF signal is input to input terminal443of the power amplifier, and signal generating circuit447shown inFIG. 24is of a configuration that is optimum for an application wherein a baseband signal is input to input terminal143of the power amplifier.

Signal generating circuit447shown inFIG. 23comprises amplitude detector403for extracting an AM component from an RF signal as an input signal, and signal separator417afor decomposing the AM component extracted from the input signal by amplitude detector403. The input signal input from terminal443is supplied to amplitude detector403and is also output as modulated signal410from terminal446.

Amplitude detector403extracts the AM component of the input signal (RF signal) input from terminal443, and outputs the extracted AM component to signal separator417a. Signal separator417adecomposes AM component a(t) of the input signal into amplitude components a1(t), a2(t) which satisfy the relationship: a(t) proportional to a1(t) a2(t), outputs first control signal418having amplitude component a1(t) to terminal453, and outputs second control signal419having amplitude component a2(t) to terminal445.

Signal separator417amay be implemented by a digital signal processor (DSP) including logic circuits, an A/D (analog-to-digital) converter, and a D/A converter, an arithmetic circuit comprising an analog circuit, or the like.

Signal generating circuit447shown inFIG. 23also includes delay corrector454which is capable of adjusting the delay time difference between the AM component extracted from the input signal by amplitude detector403and modulated signal410that is output to terminal446.

Signal generating circuit447shown inFIG. 24comprises baseband signal processing circuit450and quadrature modulator452. In baseband signal processing circuit450, the DSP calculates and extracts amplitude components a1(t), a2(t) which satisfy the relationship: a(t) proportional to a1(t) a2(t) from AM component a(t) of the baseband signal that is input from terminal443according to a digital processing process, and the D/A converter converts amplitude components a1(t), a2(t) into analog signals, and thereafter outputs amplitude component a1(t) as first control signal418to terminal453and outputs amplitude component a2(t) as second control signal419to terminal445. Furthermore, the D/A converter converts the baseband signal input from terminal443into an analog signal and thereafter outputs the analog signal to quadrature modulator452. Baseband signal processing circuit450should preferably have a function, implemented by the DSP, to calculate and correct the delay time difference between control signals418,419and the baseband signal output to quadrature modulator452.

Quadrature modulator452up-converts the baseband signal output from baseband signal processing circuit450into an RF frequency signal, and outputs the RF frequency signal as modulated signal410from terminal445.

InFIG. 22, signal generating circuit447has a D/A converter for outputting first control signal418and second control signal419as analog signals. However, if signal generating circuit447includes signal separator417acomprising a DSP shown inFIG. 23or baseband signal processing circuit450shown inFIG. 24, then signal generating circuit447may output first control signal418and second control signal419as digital signals. In this case, first pulse modulator420and second pulse modulator404may include respective D/A converters. Baseband signal processing circuit450and signal separator417aof signal generating circuit447may include the functions of first pulse modulator420and second pulse modulator404. In this case, first pulse modulator420and second pulse modulator404may be dispensed with.

As with the power amplifier shown inFIG. 10, the arrangement shown inFIG. 22outputs first control signal418(a1(t)) and second control signal419(a2(t)) which have a smaller dynamic range than AM component a(t) of the input signal (provided that the relationship: a(t) proportional to a1(t) a2(t) is satisfied) to first pulse modulator420and second pulse modulator404. Therefore, the average output voltage of switching amplifier405and the output voltage of RF amplifier409are prevented from being lowered, thus preventing the power efficiency of RF amplifier409and switching amplifier405from being lowered.

Inasmuch as first control signal418is converted into the rectangular-wave signal with the constant amplitude and the rectangular-wave signal is input to RF amplifier409, the information of first control signal418is not lost, but is properly reflected in the output signal of RF amplifier409even when RF amplifier409is saturated state in operation.

The power amplifier according to the present exemplary embodiment thus restores the waveform of the input signal in the output signal more accurately than with the power amplifier according to the background art shown inFIG. 7which does not reflect a portion of the amplitude component signal and fails to reproduce the signal properly.

FIG. 25is a block diagram showing a third modification of the power amplifier according to the first exemplary embodiment.FIG. 25shows a configurational example of the power amplifier based on the ET technology.

The power amplifier shown inFIG. 25is different from the configuration shown inFIG. 22in that mixer423is omitted from the configuration shown inFIG. 22, modulated signal410that is output from signal generating circuit447is input to RF amplifier409, and rectangular-wave signal422output from first driver amplifier421is input to RF amplifier409. Rectangular-wave signal422is applied to the gate of transistor401through terminal441and to input power supply circuit408.

When transistor401is turned on and off by rectangular-wave signal422, the power amplifier shown inFIG. 25adds rectangular-wave signal422to modulated signal410as with the power amplifier shown inFIG. 22.

As with the power amplifier shown inFIG. 22, signal generating circuit447outputs first control signal418(a1(t)) and second control signal419(a2(t)) which have a smaller dynamic range than AM component a(t) and satisfy the relationship: a(t) proportional to a1(t) a2(t), so that the output voltage of switching amplifier405and the output voltage of RF amplifier409are prevented from being lowered, thus preventing the power efficiency of RF amplifier409and switching amplifier405from being lowered. The power amplifier shown inFIG. 25allows the waveform of the input signal to be restored in the output signal with higher accuracy than with the power amplifier according to the background art shown inFIG. 7. Furthermore, since the power amplifier shown inFIG. 25requires no mixer423, it is made up of a smaller number of parts, and hence consumes a lower amount of electric power and is manufactured at a lower cost than the power amplifier shown inFIG. 22.

The power amplifier according to the present exemplary embodiment extracts an amplitude-modulated component from an input signal (modulated signal) which include amplitude-modulated and phase-modulated components, decomposes the amplitude-modulated component into two control signals whose product is proportional to the amplitude-modulated component, modulates the output power supply of the RF amplifier with one of the control signals (second control signal), converts the other control signal (first control signal) into a rectangular-wave signal having a constant amplitude, and modulates the input signal of the RF amplifier with the rectangular-wave signal. Therefore, the information of the first control signal is not lost, but is properly reflected in the output signal of the RF amplifier even when the RF amplifier is saturated state in operation.

The power amplifier according to the present exemplary embodiment thus produces, as the output signal, a signal representative of the waveform of the input signal that is restored more accurately than with the power amplifier according to the background art shown inFIG. 7which does not reflect a portion of the amplitude component signal and fails to reproduce the signal properly.

Consequently, there are provided power amplifiers based on EER technology and ET technology which are capable of amplifying a signal with good power efficiency and restoring the signal accurately.

With the power amplifier according to the present exemplary embodiment, since first control signal418and second control signal419(or either one of them) have a smaller dynamic range than original AM component a(t), the average output voltage of switching amplifier405and the output voltage of RF amplifier409are prevented from being lowered, thus preventing the power efficiency of RF amplifier409and switching amplifier405from being lowered.

Second Exemplary Embodiment

A power amplifier according to a second exemplary embodiment will be described below with reference to the drawings.

The power amplifier according to the second exemplary embodiment is different from the power amplifier according to the first exemplary embodiment shown inFIG. 10as to configurational and operational details of signal generating circuit447. The configurational and operational details of the other components are the same as those of the power amplifier according to the first exemplary embodiment shown inFIG. 10and will not be described below.

As with the power amplifier shown inFIG. 10, signal generating circuit447according to the present exemplary embodiment extracts an AM component included in an input signal, outputs first control signal418generated from the AM component through terminal453to first pulse modulator420, and outputs second control signal419generated from the AM component through terminal445to second pulse modulator404. According to the present exemplary embodiment, if it is assumed that the AM component of the input signal is denoted by a(t), then signal generating circuit447outputs amplitude component as(t), which has a smaller dynamic range than AM component a(t) and satisfies the relationship: a(t) proportional to as(t)af(t), as first control signal418to first pulse modulator420, and also outputs amplitude component af(t) as second control signal419to second pulse modulator404. as(t) represents a low-frequency component of AM component a(t), and af(t) represents the remaining frequency component produced by removing as(t) from a(t) (af(t) proportional to a(t)/as(t)). Signal generating circuit447according to the present exemplary embodiment also extracts a PM component included in the input signal and outputs the extracted PM component as phase component signal412through terminal446to RF amplifier409. Signal generating circuit447according to the present exemplary embodiment should preferably have a function to adjust the delay time difference between first control signal418and phase component signal412and the delay time difference between second control signal419and phase component signal412.

FIG. 26is a block diagram showing a configurational example of a signal generating circuit for use in the power amplifier according to the second exemplary embodiment. Signal generating circuit447shown inFIG. 26is of a configuration that is optimum for an application wherein an RF signal is input to input terminal443of the power amplifier. The configuration shown inFIG. 26is optimum for use in the power amplifier according to the present exemplary embodiment which is based on the EER technology.

Signal generating circuit447shown inFIG. 26comprises amplitude detector403for extracting an AM component from an RF signal as an input signal, limiter402for removing the AM component of the input signal, low-pass filter427for allowing low-frequency component as(t) of AM component a(t) extracted from the input signal by amplitude detector403to pass trough, and signal generator417bfor generating remaining frequency component af(t) produced by removing as(t) from a(t).

Amplitude detector403extracts AM component a(t) of the input signal (RF signal) input from terminal443, and outputs the extracted AM component to low-pass filter427. Low-pass filter427allows a low-frequency component of AM component a(t) extracted by amplitude detector403to pass through, and outputs second control signal419having amplitude component as(t) to terminal445.

Signal separator417bgenerates af(t) which satisfies a(t) proportional to as(t)af(t), i.e., af(t) proportional to a(t)/as(t), from AM component a(t) of the input signal and low-frequency component as(t) output from low-pass filter427, and outputs first control signal418having amplitude component af(t) to terminal453. Limiter402removes the AM component of the input signal (RF signal) that is input from terminal443, and outputs phase component signal412, which represents a remaining PM component, from terminal446.

Signal separator417bmay be implemented by a digital signal processor (DSP) including logic circuits, an A/D (analog-to-digital) converter, and a D/A (digital-to-analog) converter, an arithmetic circuit comprising an analog circuit, or the like.

If a baseband signal is input to input terminal443of the power amplifier according to the present exemplary embodiment, then signal generating circuit447may comprise baseband signal processing circuit450and VCO451shown inFIG. 14. Baseband signal processing circuit450converts the input signal (baseband signal) input from terminal443into an analog signal, and up-converts the analog signal into an RF signal. Baseband signal processing circuit450then extracts an AM component of the RF signal, decomposes AM component a(t) into amplitude components as(t), af(t) which satisfy the relationship: a(t) proportional to as(t)af(t), outputs first control signal418having amplitude component af(t) to terminal453, and outputs second control signal419having amplitude component as(t) to terminal445. VCO451is controlled by a control voltage output from baseband signal processing circuit450to output phase component signal412that is equal to a PM component of the up-converted RF signal.

If signal generating circuit447of the power amplifier according to the present exemplary embodiment has signal generator417bwhich comprises a DSP shown inFIG. 26or baseband signal processing circuit450shown inFIG. 14, then signal generating circuit447may output first control signal418and second control signal419as digital signals. In this case, first pulse modulator420and second pulse modulator404may include respective D/A converters. Baseband signal processing circuit450and signal separator417aof signal generating circuit447may include the functions of first pulse modulator420and second pulse modulator404. In this case, first pulse modulator420and second pulse modulator404may be dispensed with.

With the power amplifier according to the second exemplary embodiment, as with the first exemplary embodiment, phase component signal412output from signal generating circuit447and the rectangular-wave signal output from first driver amplifier421are mixed with each other, and the output signal is input to RF amplifier409. The output signal of RF amplifier409is amplitude-modulated with output power supply modulation signal414which represents the amplified first control signal419. RF amplifier409thus outputs signal425that is generated by multiplying phase component signal412by rectangular-wave signal422and by multiplying the product by output signal (output power supply modulation signal)414from low-pass filter406.

As signal425that is output from RF amplifier409passes through bandpass filter407which has a frequency band that is wider than frequency band428of the baseband signal and that is capable of removing spurious components caused by rectangular-wave signal422, unwanted spurious components added to signal425output from RF amplifier409are removed, thereby producing desired RF signal415which is representative of the linearly amplified input signal.

With the power amplifier according to the second exemplary embodiment, since second control voltage419has a low frequency, second driver amplifier416and switching amplifier405can be operated at a high voltage of several tens of volts.

While first control signal418has as high a frequency as the AM component of the input signal, the input voltage of RF amplifier409may usually be of a relatively low voltage of several volts even when the output electric power is large as in the case where the power amplifier is used in wireless base stations. Consequently, it is possible to operate first driver amplifier418at a relatively low voltage and at a desired high frequency.

The power amplifier according to the second exemplary embodiment offers the same advantages as those of the first exemplary embodiment, and is additionally applicable to apparatus which require a wide band and high output electric power because switching amplifier405, first driver amplifier416, and second driver amplifier421do not need to perform both high-voltage operation and fast operation.

Each of the first through third modifications of the first exemplary embodiment can also be applied to the power amplifier according to the second exemplary embodiment, and, when applied, provides not only the advantages described with respect to the first exemplary embodiment, but also the advantages described above.

If the second modification and the third modification (ET technology) of the first exemplary embodiment are applied to the power amplifier according to the second exemplary embodiment, then signal generating circuit447may be of the configuration shown inFIG. 27or the configuration shown inFIG. 24. Signal generating circuit447shown inFIG. 27is of a configuration that is optimum for an application wherein an RF signal is input to the power amplifier according to the present exemplary embodiment.

Signal generating circuit447shown inFIG. 27comprises amplitude detector403for extracting an AM component from an RF signal as an input signal, low-pass filter427for allowing a low-frequency component as(t) of AM component a(t) extracted from the input signal by amplitude detector403to pass through, and signal generator417bfor generating remaining frequency component af(t) produced by removing as(t) from a(t).

The input signal input from terminal443is supplied to amplitude detector403and is also output as modulated signal410from terminal446.

Amplitude detector403extracts AM component a(t) of the input signal (RF signal) input from terminal443, and outputs the extracted AM component to low-pass filter427. Low-pass filter427allows a low-frequency component of AM component a(t) extracted by amplitude detector403to pass through, and outputs second control signal419having amplitude component as(t) to terminal445.

Signal separator417bgenerates af(t) which satisfies a(t) proportional to as(t)af(t), i.e., af(t) proportional to a(t)/as(t), from AM component a(t) of the input signal and low-frequency component as(t) output from low-pass filter427, and outputs first control signal418having amplitude component af(t) to terminal453.

Signal separator417bmay be implemented by a digital signal processor (DSP) including logic circuits, an A/D (analog-to-digital) converter, and a D/A (digital-to-analog) converter, an arithmetic circuit comprising an analog circuit, or the like.

If a baseband signal is input to input terminal443of the power amplifier according to the second modification and the third modification of the present exemplary embodiment, then signal generating circuit447may comprise baseband signal processing circuit450and quadrature modulator452shown inFIG. 24. Baseband signal processing circuit450converts the input signal (baseband signal) that is input from terminal443into an analog signal, and up-converts the analog signal into an RF signal. Baseband signal processing circuit450then extracts an AM component of the RF signal, decomposes AM component a(t) into amplitude components as(t), af(t) which satisfy the relationship: a(t) proportional to as(t)af(t), outputs first control signal418having amplitude component af(t) to terminal453, and outputs second control signal419having amplitude component as(t) to terminal445. Baseband signal processing circuit450also outputs a control signal for controlling the output signal of quadrature modulator452.

Quadrature modulator452outputs modulated signal410which is proportional to the amplitude of the up-converted RF signal from terminal446according to the control signal output from baseband signal processing circuit450.

Third Exemplary Embodiment

A power amplifier according to a third exemplary embodiment will be described below with reference to the drawings.

FIG. 28is a block diagram showing a configuration of a power amplifier according to the third exemplary embodiment.

As shown inFIG. 28, the power amplifier according to the third exemplary embodiment is different from the power amplifier according to the first exemplary embodiment shown inFIG. 10as to configurational and operational details of signal generating circuit447for generating first control signal418and second control signal419, pulse modulator404, and signal separator417a. The configurational and operational details of the other components are the same as those of the power amplifier according to the first exemplary embodiment and will not be described in detail below.

Signal generating circuit147according to the present exemplary embodiment is of the same configuration as the signal generating circuit according to the background art shown inFIG. 2or3, and extracts an AM component included in an input signal and outputs the extracted AM component as amplitude component signal111from terminal145.

Amplitude component signal111output from signal generating circuit147is converted into a rectangular-wave signal (1-bit pulse signal)111ahaving a constant amplitude by pulse modulator404. 1-bit pulse signal111aconverted by pulse modulator404is decomposed into first control signal418and second control signal419by signal separator417a.

If it is assumed that the amplitude component of the input signal is represented by a(t) and 1-bit pulse signal111aby D[a(t)], then signal separator417adecomposes AM component a(t) of the input signal into 1-bit pulse signals D[a1(t)], D[a2(t)] which satisfy the above relationship: a(t) proportional to a1(t) a2(t). Signal separator417aoutputs 1-bit pulse signal D[a1(t)] as first control signal418to first driver amplifier421, and outputs 1-bit pulse signal D[a2(t)] as second control signal419to second driver amplifier416. Signal separator417amay comprise a DSP, for example.

In the power amplifier according to the first exemplary embodiment shown inFIG. 10, first control signal418and second control signal419comprise analog signals. According to the present exemplary embodiment, first control signal418and second control signal419comprise 1-bit pulse signals, respectively. However, as with the first exemplary embodiment, at least one of decomposed control signals a1(t), a2(t) is selected as having a smaller dynamic range than AM component a(t) of the original input signal. Pulse modulator404may comprise a PWM (Pulse Width Modulation) modulator, a delta modulator, a delta-sigma modulator, or the like. These modulators may be implemented by an analog circuit comprising an operational amplifier, a switched capacitor circuit, etc. in combination.

First driver amplifier421amplifies first control signal418output from signal separator417aand supplies amplified first control signal418to mixer428. If signal separator417ais capable of outputting a signal which is intensive enough to drive mixer423, then first driver amplifier421may be dispensed with.

Second driver amplifier416drives switching amplifier405according to the rectangular-wave signal (second control signal419) output from signal separator417a, and switching amplifier405current-amplifies the rectangular-wave signal efficiently. The amplified rectangular-wave signal is smoothed by low-pass filter106, and then supplied through terminal442to RF amplifier409. Switching amplifier405may comprise an amplifier capable of amplifying the rectangular-wave signal with high power efficiency, e.g., a class-D amplifier, a class-E amplifier, a class-S amplifier, or the like. If signal separator417ais capable of outputting a signal which is intensive enough to drive switching amplifier405, then second driver amplifier416may be dispensed with.

Mixer423mixes phase component signal412output from signal generating circuit447and the rectangular-wave signal output from first driver amplifier421with each other, and outputs the mixed signal to RF amplifier409.

RF amplifier409, which comprises transistor401, input power supply circuit408, and output power supply circuit440, amplifies output signal426from mixer423. At this time, the output signal from RF amplifier409is amplitude-amplified with the smoothed rectangular-wave signal supplied from switching amplifier405through low-pass filter406and terminal442, i.e., amplified second control signal414. Therefore, RF amplifier409outputs signal425that is generated by multiplying phase component signal412by rectangular-wave signal422and multiplying the product by output signal414from low-pass filter406.

As signal425output from RF amplifier409passes through bandpass filter407which has a frequency band that is wider than frequency band428of the baseband signal and that is capable of removing spurious components caused by rectangular-wave signal422, unwanted spurious components added to signal425output from RF amplifier409are removed, thereby producing desired RF signal415which is representative of the linearly amplified input signal.

As described above, the power amplifier according to the third exemplary embodiment reduces the dynamic ranges of first control signal418and second control signal419so as to be smaller than the dynamic range of AM component a(t) of the original input signal. Therefore, the average output voltage of switching amplifier405and the output voltage of RF amplifier409are prevented from being lowered, thus preventing the power efficiency of RF amplifier409and switching amplifier405from being lowered.

Inasmuch as first control signal418is converted into the rectangular-wave signal with the constant amplitude and the rectangular-wave signal is input to RF amplifier409, the information of first control signal418is not lost, but is properly reflected in the output signal of RF amplifier409even when RF amplifier409is saturated state in operation.

The power amplifier according to the present exemplary embodiment thus produces an output signal representative of the waveform of the input signal that is restored more accurately than with the power amplifier according to the background art shown inFIG. 7which does not reflect a portion of the amplitude component signal and fails to reproduce the signal properly.

With the power amplifier according to the present exemplary embodiment, both the input and output signals of signal separator417aare 1-bit digital signals. Therefore, signal separator417acan be implemented by a processing sequence performed by a DSP comprising a combination of a counter, a digital filter, logic operations, etc. Therefore, signal separator417ais advantageous in that it can flexibly decompose the input signal into control signals a1(t), a2(t).

Furthermore, since the power amplifier requires only one pulse modulator which is an analog circuit that requires a relatively large circuit area and that consumes relatively large electric power, the overall size and power consumption of the power amplifier can be reduced.

Each of the first through third modifications of the first exemplary embodiment can also be applied to the power amplifier according to the third exemplary embodiment, and, when applied, provides not only the advantages described with respect to the first exemplary embodiment, but also the advantages described above.

If the second modification and the third modification (ET technology) of the first exemplary embodiment are applied to the power amplifier according to the third exemplary embodiment, then the signal generating circuit may be of the configuration according to the background art shown inFIG. 5or6. Signal generating circuit148shown inFIG. 5is of a configuration that is optimum for an application wherein an RF signal is input to input terminal143of the power amplifier, and the signal generating circuit shown inFIG. 6is of a configuration that is optimum for an application wherein a baseband signal is input to input terminal143of the power amplifier.

According to the third exemplary embodiment, as described with respect to the second exemplary embodiment, amplitude component a(t) of the input signal can be decomposed by signal separator417ainto a low-frequency component (second control signal) D[as(t)] and a remaining frequency component (first control signal) D[af(t)] (af(t) proportional to a(t)/as(t)) produced by removing as(t) from a(t).

In this case, since both the input signal and the output signal comprise 1-bit digital signals, signal separator417acan be implemented by a processing sequence performed by a DSP comprising a combination of a counter, a digital filter, logic operations, etc. Other configurational and operational details are the same as those of the second exemplary embodiment, and will not be described below.

With a configuration which is a combination of the configuration according to the third exemplary embodiment and the configuration according to the second exemplary embodiment, since signal component as(t) included in second control signal419is of a low frequency, the average switching frequency of second control signal419is also low, making it possible to operate second driver amplifier416and switching amplifier405at a high voltage of several tens of volts. While first control signal418has as high a frequency as the AM component of the input signal, the input voltage of RF amplifier409may usually be of a relatively low voltage of several volts even when the output electric power is large as is the case where the power amplifier according to the present invention is used in wireless base stations. Consequently, it is possible to operate first driver amplifier418at a relatively low voltage and at a desired high frequency.

The combination of the configuration according to the third exemplary embodiment and the configuration according to the second exemplary embodiment is also applicable to apparatuses which require a wide band and high output electric power because, as described above, switching amplifier405, first driver amplifier416, and second driver amplifier421do not need to have both a high-voltage output and fast switching operation. Moreover, since the power amplifier requires only one pulse modulator which is an analog circuit that requires a relatively large circuit area and which consumes a relatively large amount of electric power, the overall size and power consumption of the power amplifier can be reduced.

Fourth Exemplary Embodiment

A power amplifier according to a fourth exemplary embodiment will be described below with reference to the drawings.

FIG. 29is a block diagram showing a configuration of a power amplifier according to the fourth exemplary embodiment.FIG. 29shows a configuration of a power amplifier according to the background art which is based on the EER technology.

As shown inFIG. 29, the power amplifier according to the fourth exemplary embodiment comprises signal generating circuit647, RF (Radio Frequency) amplifier609, first pulse modulator620, first driver amplifier621, mixer623, output power supply modulating circuit633, and band pass filter607.

Signal generating circuit647extracts an AM component included in an input signal, outputs first control signal618generated from the AM component through terminal653to first pulse modulator620, and outputs second control signal619generated from the AM component through terminal645to output power supply modulating circuit633.

According to the present exemplary embodiment, if it is assumed that the AM component of the input signal is represented by a(t), then amplitude component ae(t) which satisfies the relationship: a(t) proportional to ad(t)ae(t) is output as first control signal618to first pulse modulator620, and amplitude component ad(t) which has a higher ratio of a DC component to an AC component than AM component a(t) is output as second control signal619to output power supply modulating circuit633.

Second control signal619may be a signal which satisfies the relationship: ad(t) proportional to sqrt(a(t)). If it is assumed that the input signal is an RF signal according to the W-CDMA (downlink) scheme, then 63% of the electric power of amplitude component a(t) of the input signal is taken up by a DC component. If second control signal619comprises amplitude component ad(t) which satisfies the relationship: ad(t) proportional to sqrt(a(t)), then the proportion of a DC component in ad(t) is 86%. At this time, first control signal618satisfies ae(t) proportional to sqrt(a(t)) because of the relationship: a(t) proportional to ad(t)ae(t).

Second control signal619according to another example may be a signal which is represented by amplitude component a(t) and a DC component added thereto. In this case, first control signal618satisfies ae(t) proportional to (a(t)/ad(t) because of the relationship: a(t) proportional to ad(t)ae(t).

Second control signal619is not limited to the above examples, but may be any signal insofar as it has a higher ratio of a DC component to an AC component than AM component a(t).

Signal generating circuit647extracts a PM component included in an input signal, and outputs the extracted PM component as phase component signal612through terminal646to mixer623. As with the first exemplary embodiment and the second exemplary embodiment, signal generating circuit647according to the present exemplary embodiment should desirably have a function to adjust the delay time difference between first control signal618and phase component signal612and the delay time difference between second control signal619and phase component signal612.

First pulse modulator620pulse-modulates first control signal618to generate a rectangular-wave signal having a constant amplitude, and outputs the rectangular-wave signal to first driver amplifier621. First pulse modulator620may comprise a PWM (Pulse Width Modulation) modulator, a delta modulator, a delta-sigma modulator, or the like. First pulse modulator620may comprise any circuit insofar as it can convert first control signal618output from signal generating circuit647into a rectangular-wave signal having a constant amplitude.

First driver amplifier621amplifies the rectangular-wave signal output from first pulse modulator620and supplies the amplified rectangular-wave signal to mixer623. If first pulse modulator620is capable of outputting a signal which is intensive enough to drive mixer623, then first driver amplifier621may be dispensed with.

First low-pass filter628passes a low-frequency component of second control signal619(ad(t)) output from signal generating circuit647, and outputs the low-frequency component to second pulse modulator604.

Second pulse modulator604pulse-modulates second control signal619(low-frequency component) which has passed through first low-pass filter628to generate a rectangular-wave signal, and outputs the rectangular-wave signal to second driver amplifier616. Second pulse modulator604may comprise a PWM (Pulse Width Modulation) modulator, a delta modulator, a delta-sigma modulator, or the like, as with first pulse modulator620.

Second driver amplifier616drives switching amplifier605according to the rectangular-wave signal output from second pulse modulator604, and switching amplifier605current-amplifies the rectangular-wave signal efficiently. The amplified rectangular-wave signal is smoothed by second low-pass filter606, and supplied through adder632and terminal642to RF amplifier609. Switching amplifier605may comprise an amplifier capable of amplifying the rectangular-wave signal with high power efficiency, e.g., a class-D amplifier, a class-E amplifier, a class-S amplifier, or the like. Switching regulator635including second pulse modulator604, second driver amplifier616, and switching amplifier605may be replaced with a known DC/DC converter. If second pulse modulator604is capable of outputting a signal which is intensive enough to drive switching amplifier605, then second driver amplifier616may be dispensed with.

Subtractor634subtracts an output signal of adder634, which is fed-back through attenuator627, from second control signal619(ad(t)) output from signal generating circuit647, and outputs the subtraction result to linear amplifier624. Linear amplifier624amplifies the output signal from subtractor634, and outputs the amplified signal to adder632.

Adder632adds signal631output from second low-pass filter606and signal629output from linear amplifier624, and outputs the sum to RF amplifier609.

According to the present exemplary embodiment, second control signal619(ad(t)) output from signal generating circuit647is processed into corrective signal629for correcting a relatively high-frequency component by linear amplifier624having a feedback circuit, and corrective signal629is added to output signal631from second low-pass filter606by adder632, thereby producing signal614which represents first control signal619that is amplified with accuracy. The output signal from RF amplifier609is amplitude-modulated with signal614.

Mixer623mixes phase component signal612output from signal generating circuit647with the rectangular-wave signal output from first driver amplifier621, and outputs the mixed signal to RF amplifier409.

RF amplifier609, which comprises transistor601, input power supply circuit608, and output power supply circuit640, amplifies output signal626from mixer623. At this time, the output signal from RF amplifier609is amplitude-amplified with the corrected rectangular signal supplied from output power supply modulating circuit633, i.e., amplified amplitude component signal614. Input power supply circuit608that is connected to the gate of transistor601is supplied with a constant DC voltage from a power supply device, not shown, through terminal641, as with the background art. Transistor601may be either a field-effect transistor or a bipolar transistor.

The signal amplified by RF amplifier609(output signal625) is processed by bandpass filter607to remove unwanted band components therefrom, and then supplied through terminal644to an antenna device, not shown, or the like.

Signal generating circuit647shown inFIG. 29may be of the same configuration as the second exemplary embodiment shown inFIGS. 26 and 27, etc. or may be of a configuration including the baseband signal processing circuit shown inFIGS. 14 and 24, for example. Terminals443,445,446,453shown inFIGS. 14 and 24andFIGS. 26 and 27correspond to terminals643,645,646,653shown inFIG. 29. The configurational and operational details of signal generating circuit647are the same as the configurational and operational details described with respect to the first exemplary embodiment and the second exemplary embodiment, and will not be described below.

InFIG. 29, signal generating circuit647includes a D/A converter for outputting first control signal618and second control signal619as analog signals. However, if signal generating circuit647includes the signal separator comprising a DSP shown inFIG. 13or the baseband signal processing circuit shown inFIG. 14, then signal generating circuit647may output first control signal618and second control signal619as digital signals. In this case, first pulse modulator620and output power supply modulating circuit633may include respective D/A converters. The baseband signal processing circuit and the signal separator of signal generating circuit647may include the functions of first pulse modulator620and output power supply modulating circuit633. In this case, first pulse modulator620and output power supply modulating circuit633may be dispensed with.

In the power amplifier shown inFIG. 29, first control signal622is added to phase component signal612by mixer623. This function can also be realized by RF amplifier478shown inFIG. 15, as with the first exemplary embodiment.

If RF amplifier478shown inFIG. 15is used in place of mixer623, then phase component signal612may be input from terminal476shown inFIG. 15, and the rectangular-wave signal output from first driver amplifier621may be input to input power supply terminal474or output power supply terminal475.

Since RF amplifier609shown inFIG. 29provides high power efficiency when saturated state in operation, the input signal applied to RF amplifier609should desirably have electric power high enough to saturate state RF amplifier609in operation. However, when RF amplifier609is saturated state in operation, the output signal of RF amplifier609does not reflect the amplitude component of the input signal of RF amplifier609. Accordingly, first control signal618is converted into rectangular-wave signal622having a constant amplitude, and rectangular-wave signal622is added to phase component signal612by mixer623and then input to RF amplifier609. By thus processing first control signal618, it is possible for the output signal of RF amplifier609to reflect the amplitude component of first control signal618.

With the power amplifier according to the present exemplary embodiment, furthermore, the drain of transistor601of RF amplifier609is supplied with amplitude component signal614through terminal642and output power supply circuit640to amplitude-modulate the signal amplified by transistor601with amplitude component signal614. The amplitude modulation causes RF amplifier609to output signal625that is generated by multiplying phase component signal612by rectangular-wave signal622and by multiplying the product by output signal (output power supply modulation signal)614from second low-pass filter606.

According to the present exemplary embodiment, inasmuch as amplitude component ad(t) which satisfies the relationship: a(t) proportional to ad(t)ae(t) and which has a higher ratio of a DC component to an AC component than AM component a(t) is supplied as second control signal619to output power supply modulating circuit633, the amplitude of corrective signal629output from linear amplifier624is reduced. Therefore, the power amplifier can reduce the power consumption of the linear amplifier in addition to providing the advantages of the first exemplary embodiment and the second exemplary embodiment. Since the linear amplifier can have a low operating voltage, the linear amplifier can have a low cost.

FIG. 30is a block diagram showing a configuration of a first modification of the power amplifier according to the fourth exemplary embodiment,FIG. 31is a block diagram showing a configuration of a second modification of the power amplifier according to the fourth exemplary embodiment, andFIG. 32is a block diagram showing a configuration of a third modification of the power amplifier according to the fourth exemplary embodiment.

Each of the first through third modifications of the first exemplary embodiment can also be applied to the power amplifier according to the fourth exemplary embodiment, and, when applied, provides not only the advantages described with respect to the first exemplary embodiment, but also the advantages described above.

If the second modification and the third modification (ET technology) of the first exemplary embodiment are applied to the power amplifier according to the fourth exemplary embodiment, then signal generating circuit647may be of the configuration shown inFIG. 27or the configuration shown inFIG. 24. Signal generating circuit447shown inFIG. 27is of a configuration that is optimum for an application wherein an RF signal is input to the power amplifier according to the present exemplary embodiment.

This application is based upon and claims the benefit of priority from No. 2006-349724 filed on Dec. 26, 2006 and Japanese patent application No. 2007-310899 filed on Nov. 30, 2007, the disclosure of which is incorporated herein in its entirety by reference.