Power amplifier and radio wave transmitter having the same

A power amplifier (10) comprises: an A/D converter (11) for converting, to a time discrete signal, an envelope signal included in a high-frequency modulated signal and including only an amplitude modulated component of the high-frequency modulated signal; a switching amplifier (12) for amplifying the output signal of the A/D converter (11); a low-pass filter (13) for removing high frequency noise from the output signal of the switching amplifier (12); a plurality of high-frequency power amplifiers (15-1 to 15-n) for receiving the output signal of the low-pass filter (13) as a power supply and for amplifying a carrier signal included in the high-frequency modulated signal; and a power controller (14) for adjusting the average power of the output signal of the power amplifier (10) by controlling the total gains of the plurality of high-frequency power amplifiers (15-1 to 15-n).

TECHNICAL FIELD

The present invention relates to a power amplifier and a radio wave transmitter having the same, and particularly, to a power amplifier and a radio wave transmitter having the same, which do not entail a change in SNR (Signal to Noise Ratio) of an output signal even if an average power of the output signal is changed.

BACKGROUND ART

In recent years, radio communications, such as those based on portable telephones and the like, employ a modulation scheme which demonstrates a high frequency utilization efficiency and a large peak-to-average power ratio (PAPR).

In the field of radio communications, for amplifying a modulated signal including an amplitude modulated component using an AB-class amplifier which has been conventionally employed, sufficient back-off must be taken in order to maintain the linearity of an output signal. Generally, this back-off is required to be at least in the order of PAPR.

On the other hand, the AB-class amplifier exhibits a power efficiency which reaches a maximum at output saturation, and becomes lower as the back-off increases. As such, a modulated signal having larger PAPR encounters larger difficulties in increasing the power efficiency of a power amplifier.

A polar modulation type power amplifier is representative of a power amplifier for highly efficiently amplifying such a modulated signal which has large PAPR. The polar modulation type power amplifier amplifies a high-frequency modulated signal for radio communications, which is generated on the basis of polar coordinate components of amplitude and phase. Also, polar modulation type power amplifiers include one which is particularly referred to as an EER (Envelope Elimination and Restoration) type power amplifier. The EER type power amplifier is configured to substitute for an AB-class amplifier.

FIG. 1shows the configuration of an RF (Radio Frequency) transmitter as an exemplary radio wave transmitter which comprises an associated polar modulation type power amplifier.

The RF transmitter shown inFIG. 1comprises digital baseband unit201, analog baseband unit205, and EER-type power amplifier214.

Digital baseband unit201generates three types of signals, i.e., a power control signal, an I-signal, and a Q-signal which are delivered to analog baseband unit205through power control signal output terminal202, I-signal output terminal203, and Q-signal output terminal204, respectively.

In analog baseband unit205, the I-signal delivered from I-signal output terminal203is applied to and converted to an analog signal by DA (Digital-to-Analog) converter206. Likewise, the Q-signal delivered from Q-signal output terminal204is applied to and converted to an analog signal by DA converter210.

The I-signal and Q-signal converted to analog signals are multiplied by signals supplied from local oscillator208through phase shifter209, by mixer207and mixer211, respectively. In this event, the signal supplied from phase shifter209to mixer211has a phase delayed by 90° from the signal supplied from phase shifter209to mixer207.

The output signal of mixer207and the output signal of mixer211are added by adder212to generate a high-frequency modulated signal. The high-frequency modulated signal delivered from adder212is amplified by variable gain amplifier213, and then delivered to EER-type power amplifier214. In this event, the gain of variable gain amplifier213is varied in accordance with a power control signal delivered from power control signal output terminal202.

In EER-type power amplifier214, the high-frequency modulated signal delivered from variable gain amplifier213is applied to envelope detector215and limiter219. Envelope detector215extracts an envelope signal from the high frequency modulated signal input thereto. The envelope signal extracted by envelope detector215is linearly amplified in an amplification path which is provided with AD (Analog-to-Digital) converter216, switching amplifier217, and low-pass filter218. Limiter219extracts a phase modulated signal, which presents a substantially uniform envelope, from the high-frequency modulated signal input thereto, and delivers the phase modulated signal to high-frequency power amplifier220. High-frequency power amplifier220is supplied with the envelope signal delivered from low-pass filter218as a power supply, and amplifies the phase modulated signal delivered from limiter219by multiplying the same by the power supply. The thus amplitude modulated output signal is delivered from signal output terminal221.

EER-type power amplifier214can increase the power efficiency because it can employ switching amplifier217which is highly efficient in the amplification of the envelope signal, and because the multiplication processing can be highly efficiently performed in high-frequency power amplifier220.

A signal band handled by envelope detector215is similar to a signal band for the output signal of variable gain amplifier213, and typically ranges approximately from several hundreds of kHz to several tens of MHz. Accordingly, the envelope signal can be amplified by a D-class amplifier or the like, which comprises AD converter216for generating a bit stream signal such as PDM (Pulse Density Modulation) or the like, switching amplifier217, and low-pass filter218, ideally without causing a power loss.

Meanwhile, high-frequency power amplifier220is operating in a saturation region with the output signal of low-pass filter218which is being supplied as a power supply. Generally, high-frequency power amplifier220is characterized by operating at the highest power efficiency when the output is saturated.

With the foregoing configuration, the power efficiency of EER-type power amplifier214is given by the product of the power efficiency of switching amplifier217with the power efficiency of high-frequency power amplifier220, and theoretically, high-frequency power amplifier220provides the highest efficiency at all times.

Alternatively, polar modulation type power amplifiers have been proposed for performing amplitude modulation in different ways, other than EER-type power amplifier214shown inFIG. 1. As an example,FIG. 2shows the configuration of a polar modulation type power amplifier described in Patent Document 1.

The polar modulation type power amplifier shown inFIG. 2performs amplitude modulation by switching the number of saturated amplification units304which are set to an operable state (is turned on) among a plurality of saturated amplification units304.

First, local oscillator303applies a phase modulated signal to each of the plurality of saturated amplification units304. On the other hand, an amplitude modulated signal is applied from modulated signal input terminal301, and is converted to a control signal for saturated amplification units304by amplitude controller306. The control signal from amplitude controller306determines whether each of a plurality of saturated amplification units304, arranged in parallel, should be set into an operable state or a sleep state (off-state). The phase modulated signals delivered from saturated amplification units304in the operable state are combined by output combiner circuit305, and delivered from output terminal302.

Here, the modulated signal delivered from output terminal302has an amplitude which is a sum total of the amplitudes of the phase modulated signals delivered from saturated amplification units304. Accordingly, the amplitude modulation can be performed by varying the number of saturated amplification units304which are in the operable state.

However, since the polar modulation type power amplifiers shown inFIGS. 1 and 2convert an envelope signal to a time discrete signal which is quantified through AD conversion, quantization noise occurs. In the polar modulation type amplifier, the quantization noise has a magnitude which is substantially uniform irrespective of output power, so that the output signal deteriorates in SNR particularly when the output power decreases more from a maximum power.

In the polar modulation type power amplifiers shown inFIGS. 1 and 2, the output signal varies in SNR depending on the output power for causes which are attributable to basic characteristics of the AD converter for use in amplification of the envelope signal.FIG. 3shows the relationship between an input power and SNR of an output signal in an ideal AD converter.

As shown inFIG. 3, in an ideal AD converter, SNR (dB) of an output signal can be represented by a first-order function of input power (dBm) within the range of output saturation. This fact is shown, for example, in Non-Patent Document 1, Non-Patent Document 2, and the like.

For the reason set forth above, when an envelope signal applied to an AD converter as an input signal has a lower average power, an envelope signal delivered from the AD converter will deteriorate in SNR.

For example, in W-CDMA based communications, the radio wave strength is adjusted in accordance with the distance between a base station and a portable terminal. Accordingly, a W-CDMA based radio wave transmitter requires a circuit for controlling the output power of a polar modulation type power amplifier.

In the radio wave transmitter shown inFIG. 1, the output power of EER-type power amplifier214is adjusted by variable gain amplifier213which is positioned antecedent to AD converter216. Consequently, since AD converter216is applied with an envelope signal with a varying average power, SNR will vary in the envelope signal amplification path.

Likewise, SNR also varies in the polar modulation type power amplifier shown inFIG. 2. For controlling the output power with the polar modulation type power amplifier shown inFIG. 2, it is necessary to vary the number of saturated amplification units304which are controlled to be in operable state by amplitude controller306. Amplitude controller306plays the same role as AD converter206shown inFIG. 1, and the number of bits representative of the magnitude of an envelope signal is represented by the number of saturated amplification units304which are in operable state. Accordingly, the relationship between the input power of the envelope signal and the SNR in the polar modulation type power amplifier shown inFIG. 2is the same as that shown inFIG. 3, so that the envelope signal varies in SNR due to variations in average power of the output signal.

As described above, in a power amplifier used in a radio wave transmitter, a change in the average power of an output signal causes the SNR to vary on an envelope signal amplification path, resulting in variations in SNR of the output signal. Particularly, the output signal tends to deteriorate in SNR when a power amplifier generates an output signal with reduced average power.

From the foregoing, the power amplifier has a challenge in maintaining SNR of the output signal substantially constant irrespective of the average power of the output signal.Patent Document 1: JP2005-86673A (FIG. 4).Non-Patent Document 1: “Systematic Design of Sigma-Delta Analog-to-Digital Converters,” authored by Ovidiu Bajdechi and Johan H. Huijsing, Kluwer Academic Publishers, p. 16, FIG. 2.6.Non-Patent Document 2: “Bandpass Sigma Delta Modulators,” authored by Jurgen van Engelen and Rudy van de Plassche, Kluwer Academic Publishers, p. 47, FIG. 4.7.

DISCLOSURE OF THE INVENTION

It is therefore an object of the present invention to provide a power amplifier and a radio wave transmitter having the same, which solve the problems described above.

A power amplifier of the present invention is provided for amplifying a high-frequency modulated signal. The power amplifier is characterized by comprising:

an AD converter for converting an envelope signal included in the high-frequency modulated signal, to a time discrete signal, where the envelope signal includes only an amplitude modulated component of the high-frequency modulated signal;

a switching amplifier for amplifying an output signal of the AD converter;

a low-pass filter for removing high-frequency noise from an output signal of the switching amplifier;

a plurality of high-frequency power amplifiers supplied with an output signal of the low-pass filter as a power supply for amplifying a carrier signal included in the high-frequency modulated signal; and

a power controller for controlling a total gain of the plurality of high-frequency power amplifiers, thereby adjusting an average power of an output signal of the power amplifier.

A first radio wave transmitter of the present invention is characterized by further comprising:

the power amplifier;

a digital baseband circuit for generating a power control signal, an I-signal, and a Q-signal; and

a polar coordinate conversion circuit for generating the envelope signal and the carrier signal based on the I-signal and the Q-signal delivered from the digital baseband circuit,

wherein the AD converter receives the envelope signal delivered from the polar coordinate conversion circuit,

the plurality of high-frequency power amplifiers receive the carrier signal delivered from the polar coordinate conversion circuit, and

the power controller receives the power control signal delivered from the digital baseband circuit, and conducts on/off control for the plurality of high-frequency power amplifiers based on the power control signal to adjust the average power of the output signal of the power amplifier.

A second radio wave transmitter of the present invention is characterized by further comprising:

the power amplifier;

a digital baseband circuit for generating a power control signal, an I-signal, and a Q-signal; and

a polar coordinate conversion circuit for generating the high-frequency modulated signal based on the I-signal and the Q-signal delivered from the digital baseband circuit, and further generating the envelope signal and the carrier signal based on the high-frequency modulated signal,

wherein the AD converter receives the envelope signal delivered from the polar coordinate conversion circuit,

a high-frequency power amplifier at a first stage among the plurality of high-frequency power amplifiers receives the carrier signal delivered from the polar coordinate conversion circuit, and

the power controller receives the power control signal delivered from the digital baseband circuit, and conducts switching control for the high frequency switches based on the power control signal to adjust the average power of the output signal of the power amplifier.

In the power amplifier of the present invention, the envelope signal is amplified by the AD converter, switching amplifier, and low pass filter, while the average power of the output signals of the power amplifiers is adjusted by the power controller, and the plurality of high-frequency power amplifiers.

In particular, in the power amplifier of the present invention, since the amplification of the envelope signal is performed independently of the adjustments to the average power of the output signals, the average power of the output signals is not adjusted antecedent to the AD converter which is located on an envelope signal amplification path.

Accordingly, the average power of the envelope signal, applied to the AD converter as an input signal, does not vary depending on the average power of the output signals, and remains substantially constant.

As a result, since the output signal of the AD converter presents a substantially constant SNR at all times, the power amplifier can generate an output signal with a substantially constant SNR at all times.

For the reasons set forth above, the power amplifier can advantageously maintain the SNR of its output signal substantially constant at all times independently of the average power of the output signal.

BEST MODE FOR CARRYING OUT THE INVENTION

In the following, the best mode for carrying out the present invention will be described with reference to the drawings.

Notably, while the following description will be given on the assumption that a power amplifier according to the present invention is a polar modulation type power amplifier, the present invention is not so limited but can be applied to an envelope tracking type power amplifier which performs an operation referred to as “envelope tracking.” In this respect, a description will be given later.

First Embodiment

FIG. 4shows the configuration of power amplifier10according to a first embodiment of the present invention.

As shown inFIG. 4, power amplifier10of this embodiment comprises AD converter11, switching amplifier12, low-pass filter13, power controller14, a plurality of high-frequency power amplifiers15-1˜15-n(n is an integer given by n≧2), and modulated signal output terminal16.

AD converter11is applied with an envelope signal which includes only an amplitude modulated component of a high-frequency modulated signal for use in radio communications for conversion of the same to a time discrete signal.

Switching amplifier12amplifies the output signal of AD converter11.

Low-pass filter13removes high-frequency noise from the output signal of switching amplifier12.

Each of the plurality of high-frequency power amplifiers15-1˜15-nare supplied with the output signal of low-pass filter13as a power supply, and used for amplifying a carrier signal included in the high-frequency modulated signal. While the plurality of high-frequency power amplifiers15-1˜15-nare arranged in parallel inFIG. 4, they can be alternatively arranged in series.

Power controller14controls a total gain of the plurality of high-frequency power amplifiers15-1˜15-nto adjust the average power of the output signal of power amplifier10. The output signal (modulated signal) whose average power has been adjusted by power controller14, is delivered from modulated signal output terminal16.

In power amplifier10of this embodiment, an envelope signal is amplified by AD converter11, switching amplifier12, and low-pass filter13. Specifically, AD converter11converts an envelope signal included in a high-frequency modulated signal to a time discrete signal, switching amplifier12amplifies the output signal of AD converter11, and low-pass filter13removes high-frequency noise from the output signal of switching amplifier12. The output signal of low-pass filter13is supplied to the plurality of high-frequency power amplifiers15-1˜15-nas a power supply.

On the other hand, the average power of the output signal of power amplifier10is adjusted by power controller14and a plurality of high-frequency power amplifiers15-1˜15-n. Specifically, the carrier signal included in the high-frequency modulated signal is amplified using the plurality of high-frequency power amplifiers15-1˜15-nwhich are supplied with the output signal of low-pass filter13as a power supply. In this event, power controller14controls the total gain of the plurality of high-frequency power amplifiers15-1˜15-nto adjust the average power of the output signal of power amplifier10.

Stated another way, power amplifier10of this embodiment amplifies the envelope signal and adjusts the average power of the output signal, independently of each other.

As such, even when the average power of the output signal of power amplifier10is adjusted, for example, for adjusting the radio wave strength in W-CDMA based communication, the average power of the output signal is not adjusted antecedent to AD converter11which is included in the envelope signal amplification path.

Consequently, the average power of the envelope signal applied to AD converter11as an input signal does not vary depending on the average power of the output signal, and is substantially constant at all times.

As a result, since the output signal of AD converter11presents a substantially constant SNR at all times, the SNR of the output signal of AD converter11can be maintained substantially constant.

FIG. 5shows the relationship between the average power of the output signal and ACPR (Adjacent Channel Power Ratio) of the output signal in power amplifier10of this embodiment.

In the polar modulation type power amplifiers shown inFIGS. 1 and 2, ACPR of the output signal increases as the average power of the output signal is reduced. This is caused by the fact that when an attempt is made to reduce the average power of the output signal, this reduction entails a need for reducing the average power of the input signal to the AD converter, which results in a reduction in SNR of the output signal of the AD converter.

In contrast, in power amplifier10of this embodiment, the average power of the output signal is adjusted by power controller14and the plurality of high-frequency power amplifiers15-1˜15-n, which are located on a path independent of the envelope signal amplification path which includes AD converter11, so that AD converter11is applied with an input signal which has a substantially constant average power, thus making ACPR of the output signal substantially constant at all times.

Second Embodiment

FIG. 6shows the configuration of a radio wave transmitter which comprises power amplifier110according to a second embodiment of the present invention.

The radio wave transmitter shown inFIG. 6comprises digital baseband unit101, polar coordinate conversion circuit105, and power amplifier110.

Digital baseband unit101in turn comprises power control signal output terminal102, I-signal output terminal103, and Q-signal output terminal104. Polar coordinate conversion circuit105in turn comprises I-signal input terminal106, Q-signal input terminal107, envelope signal output terminal108, and phase modulated signal output terminal109. Power amplifier110in turn comprises AD converter111, switching amplifier112, low-pass filter113, power controller114, high-frequency power amplifiers115-1˜115-n(n is an integer given by n≧2), power combiner circuit116, and modulated signal output terminal117.

Digital baseband unit101generates a power control signal, an I-signal, and a Q-signal. The power control signal is delivered from power control signal output terminal102to power amplifier110. On the other hand, the I-signal and Q-signal are delivered to polar coordinate conversion circuit105from I-signal output terminal103and Q-signal output terminal104, respectively.

Polar coordinate conversion circuit105is applied with the I-signal and Q-signal from I-signal input terminal106and Q-signal input terminal107, respectively. Polar coordinate conversion circuit105generates a high-frequency modulated signal based on the I/Q signals applied thereto. Further, polar coordinate conversion circuit105generates an envelope signal which includes only an amplitude modulated component of the high-frequency modulated signal, and also generates a phase modulated signal as a carrier signal. The phase modulated signal includes only a phase modulated component of the high-frequency modulated signal, is up-converted to a carrier frequency band, and presents a substantially constant envelope. The envelope signal and phase modulated signal are respectively delivered from envelope signal output terminal108and phase modulated signal output terminal109to power amplifier110.

In power amplifier110, the envelope signal delivered from envelope signal output terminal108is applied to AD converter111. The power control signal delivered from power control signal output terminal102in turn is applied to power controller114. Further, the phase modulated signal delivered from phase modulated signal output terminal109is applied to high-frequency power amplifiers115-1˜115-n. The envelope signal applied to AD converter111has a substantially constant average power at all times. This is because the output power of power amplifier110is not controlled antecedent to AD converter111, but is controlled by way of a path different from the envelope signal amplification path. In contrast, in EER-type power amplifier214shown inFIG. 1, since the output power of EER-type power amplifier214is controlled by variable gain amplifier213antecedent to AD converter216, the average power of the envelope signal applied to AD converter216varies. For a similar reason, the average power of the phase modulated signal applied to high-frequency power amplifiers115-1˜115-nis also substantially constant at all times.

AD converter111converts the envelope signal delivered from envelope signal output terminal108to a time discrete signal which is delivered to switching amplifier112.

Switching amplifier112highly efficiently amplifies the time discrete signal applied thereto, and delivers the amplified time discrete signal to power supply terminals of high-frequency power amplifiers115-1˜115-nthrough low-pass filter113to remove high-frequency noise.

Power controller114individually generates control signals delivered to the plurality of high-frequency power amplifiers115-1˜115-nbased on the power control signal delivered from power control signal output terminal102.

The control signal delivered from power controller114determines that each of high-frequency power amplifiers115-1˜115-nis to enter an on-state or an off-state. High-frequency power amplifier115-1˜115-n, when in on-state, amplifies the phase modulated signal delivered from phase modulated signal output terminal109by multiplying the same by the envelope signal delivered from low-pass filter113for use as a power supply, to generate a modulated signal. On the other hand, high-frequency power amplifier115-1˜115-n, when in the off-state, does not generate a modulated signal, but remains in a sleep state. Output signals of high-frequency power amplifiers115-1˜115-nare combined by power combiner circuit116, and delivered from modulated signal output terminal117.

The I/Q signals and the modulated signal generated from the I/Q signals are signals which contain communication data. On the contrary, the power control signal is a signal for varying the average power of the output signal of power amplifier110in accordance with the distance between communication devices (for example, between a portable terminal and a base station when the portable terminal is a portable telephone).

Power amplifier110of this embodiment adjusts the average power of the output signal in terms of total output power of high-frequency power amplifiers115-1˜115-nwhich are in the on-state. In this way, AD converter111used to amplify an envelope signal is applied at all times with an envelope signal having a substantially constant average power because the average power of the output signal is not adjusted antecedent thereto. Accordingly, the envelope signal is converted to a time discrete signal with a substantially constant SNR by AD converter111.

Since AD converter111is a main noise source in power amplifier110of this embodiment, if the output signal of AD converter111presents a substantially constant SNR at all times, the modulated signal delivered from modulated signal output terminal117also presents a substantially constant SNR.

Notably, in power amplifier110of this embodiment, a method of designing/controlling high-frequency power amplifiers115-1˜115-ncan be modified in accordance with a desired output power.

For example, when all high-frequency power amplifiers115-1˜115-nare designed such that their saturated output powers are equal to one another, a proportional relationship is developed between the number of high-frequency power amplifiers115-1˜115-nin the on-state and the output power, thus making it easier to control the output power. In this event, power controller114converts the power control signal delivered from power control signal output terminal102to a value at one of (n+1) steps from zero to n, and controls high-frequency power amplifiers115-1˜115-nsuch that the converted value at one of (n+1) steps is equal to the number of high-frequency power amplifiers115-1˜115-nwhich are turned on.

As another example, it is also contemplated to design high-frequency power amplifiers115-1˜115-nsuch that their saturated output powers are respectively provided in the ratio of, such as 1:2:4: . . . :2(n−1). In doing so, the output power can be controlled in a range of zero to 2(n−1) times as large as the minimum step width of the output power. Here, the minimum step width of the output power is equal to the saturated power of high-frequency power amplifier115-1. In this event, power controller114converts the power control signal delivered from power control signal output terminal102to an n-bit signal, and controls high-frequency power amplifiers115-1˜115-nsuch that high-frequency power amplifier115-kis brought into the on-state when a k-th bit (1≦k≦n) counted from the least significant bit is “1” (High), and is brought into off-state when the k-th bit is “0” (Low).

Alternatively, in power amplifier110of this embodiment, the phase modulated signal delivered from phase modulated signal output terminal109may be replaced with a modulated signal which includes a phase modulated component and an amplitude modulated component of a high-frequency modulated signal. In this configuration, power amplifier110performs an operation referred to as “envelope tracking,” and behaves as an envelope tracking type power amplifier.

Third Embodiment

A power amplifier according to a third embodiment of the present invention is modified such that the average power of the output signal can be adjusted by a method other than the on/off control of high-frequency power amplifiers115-1˜115-n, as performed in the second embodiment.

FIG. 7shows the configuration of a radio wave transmitter which comprises power amplifier410according to the third embodiment of the present invention.

The radio wave transmitter shown inFIG. 7comprises digital baseband unit401, polar coordinate conversion circuit405, and power amplifier410, as is the case with the second embodiment.

Digital baseband unit401in turn comprises power control signal output terminal402, I-signal output terminal403, and Q-signal output terminal404. Polar coordinate conversion circuit405in turn comprises I-signal input terminal406, Q-signal input terminal407, envelope signal output terminal408, and phase modulated signal output terminal409. Power amplifier410in turn comprises variable gain amplifier418, AD converter411, switching amplifier412, low-pass filter413, power controller414, high-frequency variable gain amplifier419, high-frequency power amplifiers415-1˜415-n(n is an integer given by n≧2), power combiner circuit416, and modulated signal output terminal417.

Digital baseband unit401generates a power control signal, an I-signal, and a Q-signal. The power control signal is delivered from power control signal output terminal402to power amplifier401. The I-signal and Q-signal are delivered to polar coordinate conversion circuit405from I-signal output terminal403and Q-signal output terminal404, respectively.

Polar coordinate conversion circuit405is applied with the I-signal and Q-signal from I-signal input terminal406and Q-signal input terminal407, respectively. Polar coordinate conversion circuit405generates a high-frequency modulated signal based on the I/Q signals applied thereto. Further, polar coordinate conversion circuit405generates an envelope signal which includes only an amplitude modulated component of the high-frequency modulated signal, and also generates a phase modulated signal as a carrier signal. The phase modulated signal includes only a phase modulated component of the high-frequency modulated signal, is up-converted to a carrier frequency band, and presents a substantially constant envelope. The envelope signal and phase modulated signal are respectively delivered from envelope signal output terminal408and phase modulated signal output terminal409to power amplifier410.

In power amplifier410, the envelope signal delivered from envelope signal output terminal408is applied to variable gain amplifier418. The power control signal delivered from power control signal output terminal402in turn is applied to power controller414. The phase modulated signal delivered from phase modulated signal output terminal409in turn is delivered to high-frequency variable gain amplifier419.

Variable gain amplifier418is positioned antecedent to AD converter411. Variable gain amplifier418, whose gain is controlled by power controller414, delivers a power-adjusted envelope signal to AD converter411.

High-frequency variable gain amplifier419is positioned antecedent to high-frequency power amplifiers415-1˜415-n. Likewise, high-frequency variable gain amplifier419, whose gain is controlled by power controller414, delivers a power-adjusted phase modulated signal to high-frequency power amplifiers415-1˜415-n.

AD converter411converts the envelope signal delivered from variable gain amplifier418to a time discrete signal which is delivered to switching amplifier412.

Switching amplifier412highly efficiently amplifies the time discrete signal applied thereto, and delivers the amplified time discrete signal to power supply terminals of high-frequency power amplifiers415-1˜415-nthrough low-pass filter413to remove high-frequency noise.

Power controller414individually generates control signals delivered to variable gain amplifier418, high-frequency variable gain amplifier419, and the plurality of high-frequency power amplifiers415-1˜415-nbased on the power control signal delivered from power control signal output terminal402.

The control signal delivered from power controller414determines that each of high-frequency power amplifiers415-1˜415-nis to enter an on-state or an off-state. High-frequency power amplifier415-1˜415-n, when in the on-state, amplifies the phase modulated signal delivered from high-frequency variable gain amplifier419by multiplying the same by the envelope signal delivered from low-pass filter413for use as a power supply, to generate a modulated signal. On the other hand, high-frequency power amplifier415-1˜415-n, when in the off-state, does not generate the modulated signal, but remains in a sleep state. Output signals of high-frequency power amplifiers415-1˜415-nare combined by power combiner circuit416, and delivered from modulated signal output terminal417.

Power amplifier410of this embodiment comprises variable gain amplifier418and high-frequency gain amplifier419added to the configuration of the second embodiment and is modified such that the average power of the output signal can be adjusted by a method other than the on/off control of high-frequency power amplifiers415-1˜415-n. With this modification, the average power of the output signal can be adjusted with sufficient accuracy, while the linearity is not largely damaged, even if a reduced number of high-frequency power amplifiers415-1˜415-nare turned on.

FIG. 8shows the relationship between the input power of AD converter411and the output power at modulated signal output terminal417in power amplifier410of this embodiment.

As shown inFIG. 8, in power amplifier410of this embodiment, high-frequency power amplifiers415-1˜415-nare turned on/off when the output power is largely changed, and fine adjustments of the output power are made by varying the gain of variable gain amplifier418. By conducting the power control as shown inFIG. 8, variations in input power of AD converter411can be limited to a smaller range, as compared with variations in output power of modulated signal output terminal417. AD converter411provides an output signal with a higher SNR since the input power is larger (seeFIG. 3). Accordingly, the linearity (ACPR) of the modulated signal delivered from modulated signal output terminal417behaves as shown inFIG. 9in accordance with the magnitude of the output power.

Notably, in power amplifier410of this embodiment, a method of designing/controlling high-frequency power amplifiers415-1˜415-ncan be modified in accordance with a desired output power.

For example, when all high-frequency power amplifiers415-1˜415-nare designed such that their saturated output powers are equal to one another, a proportional relationship is developed between the number of high-frequency power amplifiers415-1˜415-nin the on-state and the output power, thus making it easier to control the output power. In this event, power controller414converts the power control signal delivered from power control signal output terminal402to a value at one of (n+1) steps from zero to n, and controls high-frequency power amplifiers415-1˜415-nsuch that the converted value at one of (n+1) steps is equal to the number of high-frequency power amplifiers415-1˜415-nwhich are turned on.

As another example, it is also contemplated to design high-frequency power amplifiers415-1˜415-nsuch that their saturated output powers are respectively provided in the ratio of, such as 1:2:4: . . . :2(n−1). In doing so, the output power can be controlled in a range of zero to 2(n−1) times as large as a minimum step width of the output power. Here, the minimum step width of the output power is equal to the saturated power of high-frequency power amplifier415-1. In this event, power controller414converts the power control signal delivered from power control signal output terminal402to an n-bit signal, and controls high-frequency power amplifiers415-1˜415-nsuch that high-frequency power amplifier415-kis brought into on-state when a k-th bit (1≦k≦n) counted from the least significant bit is “1” (High), and is brought into off-state when it is zero (Low).

High-frequency variable gain amplifier419serves to allow high-frequency power amplifiers415-1˜415-nto operate in an optimally saturated state. High-frequency power amplifiers415-1˜415-nalternatively enter a saturated state or a sleep state, where the linearity and efficiency vary in response to variations in average voltage of the power supply provided from low-pass filter413. Such variations in linearity and efficiency can be corrected for by adjusting the average input power of high-frequency power amplifiers415-1˜415-nby high-frequency variable gain amplifier419. However, no problem will arise as long as sufficient power is ensured to saturate high-frequency power amplifiers415-1˜415-n. Accordingly, high-frequency variable gain amplifier419is not an essential component for this embodiment, and can be omitted if phase modulated signal output terminal409is directly coupled to high-frequency power amplifiers415-1˜415-n.

Alternatively, in power amplifier410of this embodiment, the phase modulated signal delivered from phase modulated signal output terminal409may be replaced with a modulated signal which includes a phase modulated component and an amplitude modulated component of a high-frequency modulated signal. In this configuration, power amplifier410performs an operation referred to as “envelope tracking,” and behaves as an envelope tracking type power amplifier.

Fourth Embodiment

FIG. 10shows the configuration of a radio wave transmitter which comprises power amplifier510according to a fourth embodiment of the present invention.

The radio wave transmitter shown inFIG. 10comprises digital baseband unit501, polar coordinate conversion circuit505, and power amplifier510, as is the case with the second and third embodiments.

Digital baseband unit501in turn comprises power control signal output terminal502, I-signal output terminal503, and Q-signal output terminal504. Polar coordinate conversion circuit505in turn comprises I-signal input terminal506, Q-signal input terminal507, envelope signal output terminal508, and phase modulated signal output terminal509. Power amplifier510in turn comprises AD converter511, switching amplifier512, low-pass filter513, power controller514, high-frequency power pre-amplifier515, high-frequency switches516-1˜516-n(integer given by n≧1), high-frequency power amplifiers517-1˜517-n(integer given by n≧2), matching circuits518-1˜518-n(integer given by n≧1), and modulated signal output terminal519. Notably, in this embodiment, power amplifier510comprises a plurality (n+1) of high-frequency power amplifiers, where a high-frequency power amplifier at the first stage is particularly designated by high-frequency power pre-amplifier515, and the remaining ones are designated by high-frequency power amplifiers517-1˜517-n.

Digital baseband unit501generates a power control signal, an I-signal, and a Q-signal. The power control signal is delivered from power control signal output terminal502to power amplifier510. The I-signal and Q-signal are delivered to polar coordinate conversion circuit505from I-signal output terminal503and Q-signal output terminal504, respectively.

Polar coordinate conversion circuit505is applied with the I-signal and Q-signal from I-signal input terminal506and Q-signal input terminal507, respectively. Polar coordinate conversion circuit505generates a high-frequency modulated signal based on the I/Q signals applied thereto. Further, polar coordinate conversion circuit505generates an envelope signal which includes only an amplitude modulated component of the high-frequency modulated signal, and also generates a phase modulated signal as a carrier signal. The phase modulated signal includes only a phase modulated component of the high-frequency modulated signal, is up-converted to a carrier frequency band, and presents a substantially constant envelope. The envelope signal and phase modulated signal are respectively delivered from envelope signal output terminal508and phase modulated signal output terminal509to power amplifier510.

In power amplifier510, the envelope signal delivered from envelope signal output terminal508is applied to AD converter511. The power control signal delivered from power control signal output terminal502in turn is applied to power controller514. The phase modulated signal delivered from phase modulated signal output terminal509in turn is delivered to high-frequency power pre-amplifier515. The envelope signal applied to AD converter511has substantially constant average power at all times. This is because the output power of power amplifier510is not controlled antecedent to AD converter511, but is controlled by way of a path different from the envelope signal amplification path. For a similar reason, the signal applied to high-frequency power pre-amplifiers515also has a substantially constant average power at all times.

AD converter511converts the envelope signal delivered from envelope signal output terminal508to a time discrete signal which is delivered to switching amplifier512.

Switching amplifier512highly efficiently amplifies the time discrete signal applied thereto, and delivers the amplified time discrete signal to power supplies of high-frequency power pre-amplifier515and high-frequency power amplifiers517-1˜517-nthrough low-pass filter513for removing high-frequency noise.

Power controller514individually generates control signals delivered to high-frequency switches516-1˜516-nbased on the power control signal delivered from power control signal output terminal502.

High-frequency power pre-amplifier515amplifies the phase modulated signal delivered from phase modulated signal output terminal509by multiplying the same by the envelope signal delivered from low-pass filter513for use as a power supply, and delivers its output signal to following high-frequency switch516-1.

High-frequency switches516-1˜516-nare one-input, two-output switches which are respectively connected antecedent to high-frequency power amplifiers517-1˜517-n. High-frequency switch516-1has an input terminal connected to high-frequency power pre-amplifier515, and a first output terminal connected to following high-frequency power amplifier517-1. High-frequency switch516-k(2≦k≦n) has an input terminal connected to preceding high-frequency power amplifier517-o(o=k−1), and a first output terminal connected to following high-frequency power amplifier517-k. Additionally, high-frequency switches516-k(1≦k≦n) have their respective second output terminals connected to matching circuit518-k.

High-frequency power amplifier517-k(1≦k≦n−1) amplifies the output signal of preceding high-frequency switch516-k, and delivers its output signal to following high-frequency switch516-m(m=k+1). High-frequency power amplifier517-namplifies the output signal of preceding high-frequency switch516-n, and delivers its output signal to modulated signal output terminal519.

High-frequency switch516-k(1≦k≦n−1) determines, in accordance with a control signal delivered from power controller514, whether a phase modulated signal delivered from high-frequency power pre-amplifier515should be amplified by high-frequency power amplifier517-kand sent to following high-frequency switch516-m(m=k+1) or whether the phase modulated signal should be delivered from modulated signal output terminal519through matching circuit518-k. When high-frequency switches516-kare all connected to high-frequency power amplifiers517-k, the phase modulated signal delivered from phase modulated signal output terminal509travels up to high-frequency switch516-n. In this event, high-frequency switch516-ndetermines, in accordance with a control signal delivered from power controller514, whether a phase modulated signal applied thereto should be amplified by high-frequency power amplifier517-nand delivered from following modulated signal output terminal519or whether the phase modulated signal should be delivered from modulated signal output terminal519through matching circuit518-n.

In power amplifier510of this embodiment, high-frequency power amplifiers517-1˜517-nare designed such that their saturated output powers increase at later stages.

For example, when high-frequency power amplifiers517-1˜517-nare designed such that their saturated output powers are provided in a ratio of, such as 1:A:A2. . . :A(n−1), step widths of output power are substantially constant on a decibel scale, thus facilitating the power control. Here, A is an arbitrary positive real number. In this event, power controller514converts a power control signal delivered from power control signal output terminal502to a logarithmic value which is further converted to a value at one of (n+1) steps from zero to n. When the value resulting from the conversion to the (n+1) steps is j−1 (1≦j≦n), power controller514controls high-frequency switches516-1˜516-nsuch that the phase modulated signal is delivered from modulated signal output terminal519through matching circuit518-j.

Since the gain of overall power amplifier510is determined by to which stages high-frequency power amplifiers517-1˜517-nare used, the average power of the output signal can be adjusted by selecting high-frequency switches516-1˜516-n. Also, like the second embodiment, since the average power of the envelope signal applied to AD converter511is a substantially constant at all times, the modulated signal delivered from modulated signal output terminal519presents a substantially constant SNR at all times.

Alternatively, in power amplifier510of this embodiment, the phase modulated signal delivered from phase modulated signal output terminal509may be replaced with a modulated signal which includes a phase modulated component and an amplitude modulated component of a high-frequency modulated signal. In this event, high-frequency power pre-amplifier515can be removed such that phase modulated output terminal509is directly coupled to high-frequency switch516-1. In this configuration, power amplifier510performs an operation referred to as “envelope tracking,” and behaves as an envelope tracking type power amplifier.

Fifth Embodiment

A power amplifier according to a fifth embodiment of the present invention is modified such that the average power of the output signal can be adjusted by a method other than the switching control of high-frequency switches516-1˜516-n, as performed in the fourth embodiment.

FIG. 11shows the configuration of a radio wave transmitter which comprises power amplifier610according to the fifth embodiment of the present invention.

The radio wave transmitter shown inFIG. 11comprises digital baseband unit601, polar coordinate conversion circuit605, and power amplifier610, as is the case with the second through fourth embodiments.

Digital baseband unit601in turn comprises power control signal output terminal602, I-signal output terminal603, and Q-signal output terminal604. Polar coordinate conversion circuit605in turn comprises I-signal input terminal606, Q-signal input terminal607, envelope signal output terminal608, and phase modulated signal output terminal609. Power amplifier610comprises variable gain amplifier620, AD converter611, switching amplifier612, low-pass filter613, power controller614, high-frequency variable gain amplifier621, high-frequency power pre-amplifier615, high-frequency switches616-1˜616-n(integer given by n≧1), high frequency power amplifiers617-1˜617-n(integer n≧1), matching circuits618-1˜618-n(integer given by n≧1), and modulated signal output terminal619. Notably, in this embodiment, power amplifier610comprises a plurality (n+1) of high-frequency power amplifiers, where a high-frequency power amplifier at the first stage is particularly designated by high-frequency power pre-amplifier615, and the remaining ones are designated by high-frequency power amplifiers617-1˜617-n.

Digital baseband unit601generates a power control signal, an I-signal, and a Q-signal. The power control signal is delivered from power control signal output terminal602to power amplifier610. The I-signal and Q-signal are delivered to polar coordinate conversion circuit605from I-signal output terminal603and Q-signal output terminal604, respectively.

Polar coordinate conversion circuit605is applied with the I-signal and Q-signal from I-signal input terminal606and Q-signal input terminal607, respectively. Polar coordinate conversion circuit605generates a high-frequency modulated signal based on the I/Q signals applied thereto. Further, polar coordinate conversion circuit605generates an envelope signal which includes only an amplitude modulated component of the high-frequency modulated signal, and also generates a phase modulated signal as a carrier signal. The phase modulated signal includes only a phase modulated component of the high-frequency modulated signal, is up-converted to a carrier frequency band, and presents a substantially constant envelope. The envelope signal and phase modulated signal are respectively delivered from envelope signal output terminal608and phase modulated signal output terminal609to power amplifier610.

In power amplifier610, the envelope signal delivered from envelope signal output terminal608is applied to variable gain amplifier620. The power control signal delivered from power control signal output terminal602in turn is applied to power controller614. The phase modulated signal delivered from phase modulated signal output terminal609in turn is delivered to high-frequency variable gain amplifier621.

Variable gain amplifier620is positioned antecedent to AD converter611. Variable gain amplifier620, whose gain is controlled by power controller614, delivers a power-adjusted envelope signal to AD converter611.

High-frequency variable gain amplifier621is positioned antecedent to high-frequency power pre-amplifier615. Likewise, high-frequency variable gain amplifier621, whose gain is controlled by power controller614, delivers a power-adjusted modulated signal to high-frequency power pre-amplifier615.

AD converter611converts the envelope signal delivered from variable gain amplifier620to a time discrete signal which is delivered to switching amplifier612.

Switching amplifier612highly efficiently amplifies the time discrete signal applied thereto, and delivers the amplified time discrete signal to the power supply terminals of high-frequency power pre-amplifier615and high-frequency power amplifiers617-1˜617-nthrough low-pass filter613to remove high-frequency noise.

Power controller614individually generates control signals delivered to a plurality of variable gain amplifiers620, high-frequency variable gain amplifier621, and high-frequency power amplifiers616-1˜616-nbased on the power control signal delivered from power control signal output terminal602.

High-frequency power pre-amplifier615amplifies the phase modulated signal delivered from high-frequency variable gain amplifier621by multiplying the same by the envelope signal delivered from low-pass filter613for use as a power supply, and delivers the output signal to following high-frequency switch616-1.

High-frequency switches616-1˜616-nare one-input, two-output switches which are respectively connected antecedent to high-frequency power amplifiers617-1˜617-n. High-frequency switch616-1has an input terminal connected to high-frequency power pre-amplifier615, and a first output terminal connected to following high-frequency power amplifier617-1. High-frequency switch616-k(2≦k≦n) has an input terminal connected to preceding high-frequency power amplifier617-o(o=k−1), and a first output terminal connected to following high-frequency power amplifier517-k. Additionally, high-frequency switches616-k(1≦k≦n) have their respective second output terminals connected to matching circuit618-k.

High-frequency power amplifier617-k(1≦k≦n−1) amplifies the output signal of preceding high-frequency switch616-k, and delivers its output signal to following high-frequency switch616-m(m=k+1). High-frequency power amplifier617-namplifies the output signal of previous high-frequency switch616-n, and delivers its output signal to modulated signal output terminal619.

High-frequency switch616-k(1≦k≦n−1) determines, in accordance with a control signal delivered from power controller614, whether a phase modulated signal delivered from high-frequency power pre-amplifier615should be amplified by high-frequency power amplifier617-kand sent to following high-frequency switch616-m(m=k+1) or whether it should be delivered from modulated signal output terminal619through matching circuit618-k. When high-frequency switches616-kare all connected to high-frequency power amplifiers617-k, the phase modulated signal delivered from phase modulated signal output terminal609travels up to high-frequency switch616-n. In this event, high-frequency switch616-ndetermines, in accordance with a control signal delivered from power controller614, whether a phase modulated signal applied thereto should be amplified by high-frequency power amplifier617-nand delivered from following modulated signal output terminal619or whether the phase modulated signal should be delivered from modulated signal output terminal619through matching circuit618-n.

In power amplifier610of this embodiment, high-frequency power amplifiers617-1˜617-nare designed such that their saturated output powers increase at later stages.

For example, when high-frequency power amplifiers617-1˜617-nare designed such that their saturated output powers are provided in a ratio of, such as 1:A:A2. . . :A(n−1), step widths of output power are substantially constant on a decibel scale, thus facilitating power control. Here, A is an arbitrary positive real number. In this event, power controller614converts a power control signal delivered from power control signal output terminal602to a logarithmic value which is further converted to a value at one of (n+1) steps from zero to n. When the value resulting from the conversion to the (n+1) steps is j−1 (1≦j≦n), power controller614controls high-frequency switches616-1˜616-nsuch that the phase modulated signal is delivered from modulated signal output terminal619through matching circuit618-j.

Since the gain of overall power amplifier610is determined by to which stages high-frequency power amplifiers617-1˜617-nare used, the average power of the output signal can be adjusted by selecting high-frequency switches616-1˜616-n. Also, when the gain control is additionally conducted using variable gain amplifier620as is the case with the third embodiment, the relationship between the output power and the linearity can be established as shown inFIG. 9.

High-frequency variable gain amplifier621is provided for operating high-frequency power pre-amplifier615and high-frequency power amplifiers617-1˜617-nin an optimally saturated state. The linearity and efficiency of high-frequency power pre-amplifier615and high-frequency power amplifiers617-1˜617-nvary in response to variations in the average voltage of the power supply provided from low-pass filter613. Such variations in linearity and efficiency can be corrected for by adjusting the average input power of high-frequency power amplifiers617-1˜617-nby high-frequency variable gain amplifier621. However, no problem will arise in regard to operations as long as sufficient power is ensured to saturate high-frequency power pre-amplifier615. Accordingly, high-frequency variable gain amplifier621is not an essential component for this embodiment, and can be omitted if phase modulated signal output terminal609is directly coupled to high-frequency power pre-amplifier615.

Alternatively, in power amplifier610of this embodiment, the phase modulated signal delivered from phase modulated signal output terminal609may be replaced with a modulated signal which includes a phase modulated component and an amplitude modulated component of a high-frequency modulated signal. In this event, high-frequency power pre-amplifier615can be removed such that phase modulated output terminal609is directly coupled to high-frequency switch616-1. In this configuration, power amplifier610performs an operation referred to as “envelope tracking,” and behaves as an envelope tracking type power amplifier.

While the present invention has been described above with reference to some embodiments, the present invention is not limited to the foregoing embodiments. The present invention can be modified in configuration and details in various manners which can be understood by those skilled in the art to be within the scope of the present invention.

This application claims the priority based on Japanese Patent Application No. 2007-287282 filed Nov. 5, 2007, the disclosure of which is incorporated herein by reference in its entirety.