JP2003347863A - Power-amplifying circuit and communication device using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a small-sized power-amplifying circuit with low distortion and high efficiency which can reduce phase distortions in medium power signaling range, without degrading amplitude distortion property in near saturated power condition, and to provide a communication device using it. <P>SOLUTION: A negative feedback circuit 13 is connected between a signal input terminal and a signal output terminal of a power amplifier 12. The negative feedback circuit 13 has a serial connection circuit, including series-connected diode D1 and a first capacitance element C11, and a second capacitance element C12 connected between an anode of the diode D1 and a ground. Impedance of the diode D1 depends on the signal voltage generated at its both ends. By controlling the characteristics of the negative feedback of the negative feedback circuit 13 with respect to the power amplifier 12 due to an input signal power, gain fluctuation of the power amplifier 12 is reduced and phase distortion is reduced through the second capacitance element C12. <P>COPYRIGHT: (C)2004,JPO

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power amplifier circuit and a communication device using the same, and more particularly, to a power amplifier circuit used for a communication device such as a portable telephone and a transmission device requiring low distortion amplification. And a communication device using the same.

[0002]

2. Description of the Related Art In today's and future wireless communication systems such as mobile phones and wireless LAN systems, QPSK (Quadrat) is used.
ure Phase Shift Keying; OFDM (Or
Digital modulation / demodulation such as thogonal Frequency Division Multiplex (orthogonal frequency division multiplex) has become mainstream. Power amplifier circuits used in these wireless communication systems are required to operate with low distortion. In addition, high efficiency operation is required for the power amplifier circuit in order to reduce the power consumption of the battery driven terminal. As an amplification device used in such a power amplification circuit, a bipolar transistor or a field effect transistor using a semiconductor such as silicon or gallium arsenide is used. These bipolar transistors and field-effect transistors have the characteristic that the efficiency increases as the operation approaches the saturation operation.However, in the saturation operation region, amplitude distortion and phase distortion increase, so that high efficiency operation and low distortion operation are traded. Off relationship. In order to overcome this trade-off, a method of applying negative feedback to a power amplifier is known.

FIG. 5 shows a general negative feedback type power amplifier circuit. In FIG. 5, reference numeral 32 denotes an input signal power Pin
33 is a negative feedback circuit having a negative feedback amount β.
By applying parallel negative feedback between the input and output of the negative feedback circuit 33, a negative feedback power amplifier circuit 31 is configured. In the power amplifier 32 shown in FIG. 5, as the input signal power Pin increases and the output signal power Pout approaches saturation, the increase in the output signal power becomes smaller than the increase in the input signal power. Gain G2 (Pin) gradually decreases.

[0004] This decrease in gain is what is called amplitude distortion.
When amplifying a modulated wave input signal that causes harmonic distortion and changes the instantaneous amplitude of the carrier, the gain differs for each instantaneous carrier amplitude, and the amplified output signal Is distorted, which causes communication failure such as an increase in power leaked to an adjacent channel. On the other hand, the gain G3 (Pin) of the negative feedback type power amplifier circuit 31 in which the power amplifier 32 is negatively fed back by the feedback amount β by the negative feedback circuit 33 is:

(Equation 1) It becomes. As is clear from the above (Equation 1), the gain is 1 / (1 + G2 (Pin), due to the negative feedback loop gain G2 (Pin) β, compared to G2 (Pin) when no negative feedback is applied. β), the G2 (Pin) decreases and the loop gain decreases near the saturation output due to an increase in the input signal power Pin.

[0005] Therefore, the above-mentioned factor increases as the input signal power Pin increases, and the gain G3 due to the increase in the input signal power Pin near the saturation output when negative feedback is applied.
As shown in FIG. 6, the decrease of (Pin) becomes more gradual than that of G2 (Pin) where no negative feedback is applied. Near the saturation output, negative feedback is applied if the same output signal power Pout is applied. If the distortion is small compared to the case where there is no distortion, and if the distortion is at the same level, an operation closer to saturation can be performed, so that the efficiency is improved.

However, as can be seen by differentiating the above (Equation 1) with the input signal power Pin,

(Equation 2) By applying the factor 1 / (1 + G2 (Pin) β) ² <1, negative feedback is applied to the power amplifier, whereby a decrease in the gain of the power amplifier in the saturation region can be suppressed.
Since G2 (Pin) / dPin <0, dG3 (Pin) / dPi
n <0, and the gain tends to decrease when the input signal power Pin increases, although it is slower than when no negative feedback is applied, as in the case where no negative feedback is applied.

FIG. 7 is a circuit diagram of a conventional power amplifier circuit. As shown in FIG. 7, a negative feedback circuit is provided with a control terminal for the amount of negative feedback, and a control voltage corresponding to the input signal power is used. A high-frequency power amplifier that controls the gain by controlling the amount of negative feedback is disclosed in Japanese Patent Application Laid-Open No. 1-174005. In FIG. 7, FET1 is a field effect transistor, A2 is a first input terminal connected to the gate of the field effect transistor FET1, A3 is an output terminal connected to the drain of the field effect transistor FET1, and A4 is the field effect transistor FET1. Power supply terminals A8 and A9 connected to the drain in parallel with the output terminal A3 via the resistor A5 are resistors, and divide the power supply voltage to apply a constant voltage to the gate of the field effect transistor FET1.

In FIG. 7, A10 is a varactor diode connected between the gate and the drain of the FET 1, and a second input terminal A6 is connected via a resistor A7. The varactor diode A10 forms a negative feedback circuit between the first input terminal A2 and the output terminal A3. In this power amplifying circuit, the capacitance of the varactor diode A10 is changed by changing the AGC voltage applied to the second input terminal A6 according to the power input to the first input terminal A2. Adjust the amount of feedback.

[0009]

By the way, in the negative feedback type power amplifier circuit shown in FIG. 5, it is necessary to set a large feedback amount β in order to suppress a decrease in gain until the operation becomes closer to saturation. Yes, the gain itself is reduced, and the power added efficiency (P
There is a problem of lowering AE (Power Added Efficiency).

Further, in the negative feedback amplifier shown in FIG. 7, an additional AGC voltage generating means for controlling the amount of feedback is required and an input signal power detecting means is required. There is a problem that the circuit configuration becomes complicated and miniaturization of the amplifier becomes difficult.

In order to solve these problems, the present applicant has a negative feedback circuit which is connected between a signal input terminal and a signal output terminal of a power amplifier and whose impedance depends on a signal voltage generated at both ends. (Japanese Patent Application No. 2000-359218) has been proposed. Note that this power amplifier circuit is described for the purpose of making the present invention easier to understand, and is not a known technology and not a conventional technology.

According to the above power amplifier circuit, it is possible to suppress a decrease in gain of the power amplifier due to an increase in input signal power in a state close to the saturation power, that is, a so-called amplitude distortion. However,
In the power amplifier circuit provided with the negative feedback circuit, the amplitude distortion in the saturation operation region is improved, but there is a problem that the phase distortion characteristic in the middle output signal power region is deteriorated.

It is an object of the present invention to provide a small, low-distortion, and high-efficiency power amplifier capable of suppressing the phase distortion in a medium output signal power range without deteriorating the amplitude distortion characteristic near the saturation power. An object of the present invention is to provide a circuit and a communication device using the circuit.

[0014]

To achieve the above object, a power amplifier circuit according to the present invention comprises a power amplifier and a negative feedback circuit connected between a signal input terminal and a signal output terminal of the power amplifier. It has. Further, the negative feedback circuit has a series connection circuit in which a non-linear element and a first capacitance element are connected in series, and a second capacitance element that grounds the non-linear element. It depends on the signal voltage developed across it.

In the power amplifier circuit having the above-described configuration, the impedance of the nonlinear element of the negative feedback circuit depends on the signal voltage generated at both ends thereof, and the signal voltage increases as the input signal power increases. Therefore, the amount of negative feedback to the power amplifier becomes variable depending on the input signal power, and by adjusting the variable characteristics, the gain variation of the power amplifier due to an increase or decrease of the input signal power or the output signal power near the desired output signal power. Can be suppressed,
It becomes possible to reduce the amplitude distortion near the desired output. In the power amplifier circuit according to the present invention, the nonlinear element of the negative feedback circuit is grounded by the capacitance element, but the capacitance element reduces the phase distortion in the middle output signal power range.

More preferably, the impedance of the negative feedback circuit is increased as the signal voltage amplitude at both ends thereof increases, so that the gain of the power amplifier decreases in the saturation operation region where the gain of the input signal decreases as the input signal power increases. , It is possible to suppress the decrease in the gain in the above-mentioned saturation operation region, and it is possible to achieve both low distortion operation and high efficiency operation of the power amplifier. Therefore, it is possible to reduce power consumption in a high output (close to saturation operation) state where the power amplifier occupies a large proportion in the communication terminal, which greatly contributes to the reduction in power consumption of the communication terminal.

Further, according to the present invention, no additional input signal power detection means and additional negative feedback amount control means are required, and the power amplifier circuit can be reduced in size.

In one embodiment of the present invention, a diode is used as the non-linear element, and the negative feedback circuit is constituted by a series connection circuit of a diode and a first capacitance element and a second capacitance element.
Since the diode has variable impedance characteristics with respect to the signal voltage at both ends, the impedance of the negative feedback circuit depends on the signal voltage amplitude generated at both ends.

Therefore, the amount of negative feedback to the power amplifier becomes variable depending on the input signal power, and by adjusting the above-mentioned variable characteristics, the power amplifier by increasing or decreasing the input signal power or output signal power near the desired output signal power. Can be suppressed, and the amplitude distortion near the desired output can be reduced. Further, since the DC path between the output terminal and the input terminal of the power amplifier by the negative feedback circuit is cut off by the capacitance element, the bias state of the power amplifier is not disturbed. Further, since the diode is grounded via the second capacitance element, the second capacitance element reduces phase distortion in the middle output signal power range. Further, according to the power amplifier of this embodiment, there is no need to apply a DC bias to the diode, no additional bias circuit for the diode is required, and additional input signal power detection means and additional negative power. Since the feedback amount control means is not required, the size of the power amplifier circuit can be reduced.

Further, in the power amplifying circuit of one embodiment, a base-emitter junction and a base-collector junction of a bipolar transistor may be used as the diode. For example, a bipolar transistor or a field effect transistor using a semiconductor such as silicon or gallium arsenide is used as an amplifying device of the power amplifier circuit of this embodiment. In this case, if a bipolar transistor is used as the amplifying device, it can be formed on the same semiconductor substrate as the bipolar transistor as the diode, so that the power amplifier circuit can be downsized.

Further, in the power amplification circuit of one embodiment, a junction between two terminals of the gate, drain and source of the field effect transistor may be used as the diode.
In this case, if a field-effect transistor is used as the amplifying device, it can be formed on the same semiconductor substrate as the field-effect transistor as a diode, so that the power amplifier circuit can be reduced in size.

Further, the communication device of the present invention can realize a communication device with low distortion and high efficiency by using the above-described power amplifier circuit.

[0023]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a power amplifier circuit according to the present invention and a communication device using the same will be described in detail with reference to the illustrated embodiments.

[First Embodiment] FIG. 1 shows a power amplifier circuit according to a first embodiment of the present invention. As shown in FIG. 1, the power amplifier circuit 1 according to the first embodiment includes a power amplifier 12 and a negative feedback circuit 13 connected between a signal input terminal and a signal output terminal of the power amplifier 12. ing. The negative feedback circuit 13 includes a diode D1 having an anode connected to a signal input terminal of the power amplifier 12, and a first capacitance element C11 connected between a cathode of the diode D1 and a signal output terminal of the power amplifier 12.
And a second capacitance element C12 connected between the anode of the diode D1 and the ground. The diode D1 and the first capacitance element C11 constitute a series connection circuit.

Since the diode D1 has a variable impedance characteristic with respect to the signal voltage at both ends, the impedance of the negative feedback circuit 13 depends on the signal voltage generated at both ends. Therefore, the amount of negative feedback to the power amplifier 12 becomes variable depending on the input signal power, and by adjusting the variable characteristic, the power amplifier circuit 1 increases or decreases the input signal power or output signal power near the desired output signal power. Can be suppressed, and the amplitude distortion of the power amplifier circuit 1 in the vicinity of the desired output signal power can be reduced.

Since the DC path between the output terminal and the input terminal of the power amplifier 12 by the negative feedback circuit 13 is cut off by the first capacitance element C11, the bias state of the power amplifier 12 may be disturbed. Absent.

Further, by optimizing the capacitance value of the second capacitance element C12 grounding the diode D1, the phase distortion in the middle output signal power region can be reduced.

The power amplifier circuit 1 of the first embodiment
According to No. 1, there is no need to apply a DC bias to the diode D1, no additional bias circuit for the diode D1 is required, and additional input signal power detection means and additional negative feedback amount control means. Is unnecessary. Therefore, the size of the power amplifier circuit 11 can be reduced.

The absolute value of the impedance between A1 and B1 of the negative feedback circuit 3 and the rate of change in impedance between A1 and B1 due to the non-linearity of the diode D1 also depend on the capacitance value of the first capacitance element C11. In particular,
When the capacitance value is reduced, the amount of feedback decreases and the gain of the power amplification circuit 1 increases, while the amount of change in the amount of feedback with respect to the input signal power Pin decreases. Therefore, the capacitance value of the first capacitance element C11 is appropriately set according to the gain, output, and distortion characteristics required as design items of the amplifier.

[Second Embodiment] FIG. 2 shows a power amplifier circuit according to a second embodiment of the present invention. As shown in FIG. 2, the power amplifier circuit 21 of the second embodiment includes a power amplifier 22 and a negative feedback circuit 23 connected between a signal input terminal and a signal output terminal of the power amplifier 22. ing. The negative feedback circuit 23 includes a bipolar transistor T whose base is connected to a signal input terminal of the power amplifier 22.
r1, a first capacitance element C12 connected between the emitter of the bipolar transistor Tr1 and the signal output terminal of the power amplifier 22, and a second capacitance element C12 connected between the base of the bipolar transistor Tr1 and ground. And a capacitance element C22. The collector and base of the bipolar transistor Tr1 are connected.

In the power amplifier circuit 21 of the second embodiment, the diode D1 of the power amplifier circuit 11 of the first embodiment shown in FIG. 1 is constituted by a junction between the base and the emitter of the bipolar transistor Tr1, and The base of the bipolar transistor Tr1 is connected to a second capacitance element C22.
Through the ground.

The absolute value of the impedance between A2 and B2 of the negative feedback circuit 23 and the rate of change of the impedance between A2 and B2 due to the non-linearity of the junction between the base and the emitter of the bipolar transistor Tr1 are determined by the first capacitance element C21.
Also depends on the capacitance value. Therefore, the capacitance value of the first capacitance element C21 is appropriately set according to gain, output, and distortion characteristics required as design items of the amplifier.

Although the collector and the base of the bipolar transistor Tr1 are short-circuited in the second embodiment, the collector may be open.

The junction between the base and the collector of the bipolar transistor Tr1 may be used as the diode. Further, a field effect transistor is used instead of the bipolar transistor Tr1, and the bipolar transistor Tr1 is used.
The gate, drain, and source of the field effect transistor may be connected to the base, collector, and emitter respectively, and a junction between the gate and source or between the gate and drain may be used as the diode.

The power amplifier circuit 21 of the second embodiment is
It has the same operation and effect as the power amplifier circuit of the first embodiment.

[Third Embodiment] FIG. 3 shows the result of studying the effect of the power amplifier circuit of the present invention. The effect of the presence or absence of the second capacitance element C22 in FIG. 2 on the phase distortion of the power amplifier was calculated. It is a simulation result. The power amplifier circuit studied here is a two-stage amplifier using the configuration of the power amplifier circuit shown in FIG. 2 of the second embodiment as the first stage. Further, the signal amplifying transistor and the bipolar transistor Tr1 have an HBT (H
eterojunction Bipolar Transistor (heterojunction bipolar transistor) was used. Here, the signal frequency is 5.
25GHz, collector voltage is 3.0V, base voltage is 2.
7V is set. This simulation was performed by a commonly used harmonic balance analysis.

It has been confirmed by calculation that the phase distortion is smaller when the second capacitance element C22 (= 2 pF) is grounded than when the second capacitance element C22 is not provided. As a result of examination, in the case of this power amplifier circuit, the capacitance value of the second capacitance element C22 is 2 pF
The degree is optimal. Note that the second capacitance element C
When the capacitance value of 22 is 2 pF or less, the phase distortion approaches (deteriorates) the case where the second capacitance element C22 is not provided. Conversely, the phase distortion does not change when the capacitance value of the second capacitance element C22 is 2 pF or more.

From the viewpoint of reducing the size of the power amplifier circuit, it is preferable that the second capacitance element C22 is smaller. In order to achieve both the reduction of the phase distortion and the miniaturization of the power amplifier circuit, the capacitance value of the second capacitance element C22 is optimally about 2 pF as the third embodiment. However, the optimum capacitance value of the second capacitance element C22 changes depending on characteristics of a transistor, a capacitance element, and the like used in the negative feedback circuit.

[Fourth Embodiment] FIG. 4 shows a configuration diagram of a fourth embodiment of the present invention. FIG. 4 is a block diagram of a basic configuration on the transmission side of the communication device. As shown in FIG. 4, the signal to be transmitted, which has been signal-processed by the signal processing circuit 111, is modulated by the modulator 112, and the driver amplifier 1
It is amplified at 14. After that, the transmission power amplification circuit 115
And is radiated from the antenna 117 through the transmission / reception switch 116. The modulator 112 is supplied with a reference signal from an oscillator 113.

In the digital modulation / demodulation system used in the current wireless communication system, information is carried in both the amplitude and the phase of a signal, so that a transmission power amplifier circuit is required to linearly amplify an input signal. The reason is that if the linearity of the transmission power amplifier circuit is impaired, distortion power caused by amplitude distortion and phase distortion leaks to an adjacent channel, and communication quality is degraded.

The transmission power amplifier circuit 11 of the fourth embodiment
5, the power amplifier circuit shown in the second embodiment is used, and by using the power amplifier circuit of the present invention for transmission of a communication device, it becomes possible to linearly amplify an input signal; It is possible to prevent communication quality deterioration of a system using the communication device.

The negative feedback circuit 11 of the first and second embodiments,
Reference numeral 21 denotes an example of a negative feedback circuit of the power amplifier circuit according to the present invention, which is not limited to the configuration shown in FIGS. The negative feedback circuit of the power amplifying circuit according to the present invention is provided as long as it has a series connection circuit in which a nonlinear element and a first capacitance element are connected in series, and a second capacitance element that grounds the nonlinear element. Good.

[0043]

As is clear from the above, according to the power amplifier circuit of the present invention, a small, low-distortion and high-efficiency power amplifier circuit required in a wireless communication system such as a cellular phone or a wireless LAN is realized. be able to.

Further, according to the communication device using the power amplifier circuit of the present invention, it is possible to realize a small, low-distortion and high-efficiency communication device.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a power amplifier circuit according to a first embodiment of the present invention.

FIG. 2 is a circuit diagram of a power amplifier circuit according to a second embodiment of the present invention.

FIG. 3 is a diagram showing a simulation result of a power amplifier circuit according to a third embodiment of the present invention.

FIG. 4 is a block diagram showing a basic configuration of a communication device according to a fourth embodiment of the present invention.

FIG. 5 is a circuit diagram of a general negative feedback power amplifier circuit.

FIG. 6 is a diagram showing the output signal power dependency of the gain of the power amplifier circuit.

FIG. 7 is a circuit diagram of a conventional power amplifier circuit.

[Explanation of symbols]

11,21 ... negative feedback type power amplifier circuit, 12,22 ... power amplifier, 13,23 ... negative feedback circuit, D1… Diode, Tr1: bipolar transistor, C11, C21: first capacitance element, C12, C22 ... second capacitance element, 111 ... signal processing circuit, 112 ... modulator, 114 ... Driver amplifier, 113 ... oscillator, 115 ... transmission power amplification circuit, 116 ... Transmission / reception switch 117 ... An antenna.

Continuation of front page    F term (reference) 5J090 AA01 AA41 CA25 CA26 CA36                       DN02 FA17 HA02 HA09 HA19                       HA21 HA25 HA29 HA30 HN23                       KA53 MA13 MN03 NN00 SA13                       TA01 TA03                 5J091 AA01 AA41 CA25 CA26 CA36                       FA17 HA02 HA09 HA19 HA21                       HA25 HA29 HA30 KA53 MA13                       SA13 TA01 TA03                 5J500 AA01 AA41 AC25 AC26 AC36                       AF17 AH02 AH09 AH19 AH21                       AH25 AH29 AH30 AK53 AM13                       AS13 AT01 AT03 ND02 NH23                       NM03 NN00

Claims (5)

[Claims] 1. A power amplifier circuit comprising: a power amplifier; and a negative feedback circuit connected between a signal input terminal and a signal output terminal of the power amplifier, wherein the negative feedback circuit includes a non-linear element A series connection circuit in which a first capacitance element is connected in series; and a second capacitance element grounding the non-linear element, wherein the impedance of the non-linear element depends on a signal voltage generated at both ends thereof. Characteristic power amplifier circuit. 2. The power amplifying circuit according to claim 1, wherein said non-linear element is a diode. 3. The power amplifying circuit according to claim 2, wherein the diode is a base of a bipolar transistor.
A power amplifier circuit comprising an emitter-junction and a base-collector junction. 4. The power amplifying circuit according to claim 2, wherein said diode is formed by a junction between two terminals of a gate, a drain and a source of a field effect transistor. . 5. A communication device using the power amplification circuit according to claim 1.