JP2006319533A - Amplifier - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an amplifier which can effectively suppress AM-PM distortion and is compact and low-cost. <P>SOLUTION: A Doherty amplifier is provided with: a distortion pre-compensating circuit 7 in the preceding stage of an input distributing circuit 2; and a distortion pre-compensating circuit 9 in the preceding stage of a peak amplifier 4 respectively. An input signal from an input terminal 1 is distributed by the input distributing circuit 2 to a carrier amplifier 3 and a peak amplifier 4, and amplified only by the carrier amplifier 3 until the carrier amplifier 3 gets saturated, but when the carrier amplifier 3 gets saturated, the peak portion of the input signal above the level at which the carrier amplifier 3 gets saturated is amplified. However, the AM-PM distortion caused by the carrier amplifier 3 is compensated by the distortion pre-compensating circuit 7 and the AM-PM distortion caused by the peak amplifier 4 is compensated by the distortion pre-compensating circuit 7 and distortion pre-compensating circuit 9. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an amplifier used for a transmitter of a base station of a mobile phone system, and more particularly to a low distortion and high linearity amplifier.

  In a mobile phone system base station or the like, in order to transmit an RF (Radio Frequency) signal, the RF transmission signal is amplified by a power amplifier. In this case, since distortion occurs in the power amplifier of such a high-frequency signal, an attenuator for amplitude compensation and a phase shifter for phase compensation are provided in front of the power amplifier, and transmission before power amplification by the power amplifier is performed. Amplitude distortion and phase distortion are detected from the signal and the transmission signal after power amplification, and the compensation characteristic of the attenuator is adjusted according to the detected amplitude distortion, and the compensation characteristic of the phase shifter is adjusted according to the detected phase distortion. A technique has been proposed in which the amplitude and phase distortion of the power amplifier are suppressed by adjusting (see, for example, Patent Document 1).

  On the other hand, recently, a high-efficiency Doherty amplifier has attracted attention as a high-output power amplifier for such high-frequency signals. This was first proposed to improve the output efficiency of a high-frequency output power amplifier (see Non-Patent Document 1, for example).

  FIG. 2 is a diagram showing a circuit configuration of the Doherty amplifier, where 1 is an input terminal, 2 is an input distribution circuit, 3 is a carrier amplifier, 4 is a peak amplifier, 5 is an output synthesis circuit, and 6 is an output terminal.

  In the figure, a Doherty amplifier includes an input distribution circuit 2 that distributes a signal input from an input terminal into two, a carrier amplifier 3 that amplifies one output signal of the input distribution circuit 2, and the input distribution circuit 2. The peak amplifier 4 amplifies the other output signal, and the output combining circuit 5 that combines the output signals of the carrier amplifier 3 and the peak amplifier 4 and outputs them from the output terminal 6.

  The input distribution circuit 2 distributes the input signal from the input terminal 1 into two, supplies one distributed signal to the carrier amplifier 3, and transmits the other distributed signal at a quarter wavelength (λ / 4). It is supplied to the peak amplifier 4 through the path 2a.

  The carrier amplifier 3 and the peak amplifier 4 have the same characteristics, but the carrier amplifier 3 operates in class A, class AB, and class B, and the peak amplifier 4 operates in class C, so that the carrier amplifier 3 is saturated. At the same time, the peak amplifier 4 performs an amplification operation. That is, when the signal supplied from the input distribution circuit 2 is in an amplitude range that does not saturate with the carrier amplifier 3, the carrier amplifier 3 amplifies and outputs this signal, but the peak amplifier 4 is in the off state and outputs the signal. Do not output. When the level of the input signal reaches a level at which the carrier amplifier 3 is saturated, the peak amplifier 4 starts amplification for a portion of the input signal that exceeds the level at which the carrier amplifier 3 is saturated (hereinafter referred to as a peak portion). Above the level at which the carrier amplifier 3 is saturated, the carrier amplifier 3 further increases the output while maintaining the saturation due to the decrease in the output impedance, and the peak amplifier 4 amplifies and outputs the peak portion.

  The output signal of the carrier amplifier 3 is combined with the output signal of the peak amplifier 4 through the 1/4 wavelength transmission line 5 a in the output combining circuit 5 and output from the output terminal 6. The quarter wavelength transmission line 5a is for efficiently combining the output signal of the carrier amplifier 3 with the output signal of the peak amplifier 4. At this time, the output signal of the carrier amplifier 3 and the output of the peak amplifier 4 are used. As described above, the input distribution circuit 2 is provided with the 1/4 wavelength transmission path 2a so that the signal is synthesized in phase.

  In this way, the Doherty amplifier amplifies the peak portion at a higher level with another amplifier (the above-mentioned peak amplifier 4) as an auxiliary amplifier even if the amplifier (the above-mentioned carrier amplifier 3) which mainly functions is saturated. Since it is configured to synthesize and output the output signals of these two amplifiers, it has attracted attention as a high-output power amplifier that has excellent amplification efficiency and can be used from low frequencies to millimeter waves.

  By the way, in the amplifier, the gain and phase change with respect to the level of the input signal, which causes distortion. In the case of the Doherty amplifier, even if the carrier amplifier and the peak amplifier 4 are amplifiers having the same characteristics, The amplifiers are operated in class A, class AB or class B, and the peak amplifier is operated in class C. Since these two amplifier classes are different, the distortion generated in each amplifier is different, and the output signals of these amplifiers are different. The output signal of the Doherty amplifier obtained by the synthesis loses the linearity with respect to the input signal.

  In the Doherty amplifier, as a method of improving the linearity deterioration due to the gain change of the amplifier with respect to the signal level, a gain compensator is conventionally provided in the front stage of the peak amplifier, and the gain change of the peak amplifier corresponding to the signal level is set to this gain. A technique for compensating with a compensator has been proposed (see, for example, Patent Document 2).

  In addition, in the Doherty amplifier, as a method for improving linearity deterioration due to a change in the output phase of the amplifier with respect to the signal level (hereinafter, this phase distortion is referred to as AM (amplitude) −PM (phase) distortion), Each of the peak amplifiers 4 is provided with a pre-distortion compensation circuit in the preceding stage, and the AM-PM distortion of the carrier amplifier and the peak amplifier corresponding to the signal level is compensated by these pre-distortion amplifier circuits, and the linearity of the Doherty amplifier is increased. An improved technique has also been proposed (see, for example, Patent Document 3).

As described above, since the Doherty amplifier can obtain a high output with high linearity by reducing distortion, application to a power amplifier of a transmitter such as a base station of a mobile phone system is attracting attention. .
JP2003-273659 WHDoherty “A New High Efficiency Power Amplifier for Modulated Waves”, Proc.IRE, Vol.24, No.9, Sept. 1936 JP 2004-221646 A JP2004-222151

  By the way, in the technique described in Patent Document 2, the carrier amplifier and the peak amplifier have the same characteristics. Therefore, the gain of the peak amplifier becomes smaller than the ideal gain. This is to compensate for the lack of gain.

  On the other hand, in an amplifier, AM-PM distortion occurs according to the level of the signal to be processed. For this reason, in a Doherty amplifier using two amplifiers, a carrier amplifier and a peak amplifier, AM-PM distortion occurs in each of these amplifiers. In the technique described in Patent Document 3, a predistortion compensation circuit is provided for each of the carrier amplifier and the peak amplifier so as to suppress AM-PM distortion of the carrier amplifier and the peak amplifier.

  However, since the carrier amplifier operates in class A, class AB, or class B, the peak amplifier operates in class C, so that the AM-PM distortion of the peak amplifier is larger than that of the carrier amplifier (that is, depending on the input level). The phase changes greatly). For this reason, in the technique described in Patent Document 3, it is necessary for the predistortion circuit for correcting AM-PM distortion of the peak amplifier to correct such greatly varying AM-PM distortion. There is a problem in that the configuration of the Doherty amplifier becomes large due to the need for a distortion compensation circuit, resulting in high cost and high power consumption.

  An object of the present invention is to provide a high-output power amplifier that can eliminate such problems and can effectively suppress AM-PM distortion, and is small in size, low in cost, and low in power consumption.

  In order to achieve the above object, the present invention provides an input distribution circuit that distributes an input signal, a carrier amplifier that amplifies one output signal of the input distribution circuit, and the carrier signal using the other output signal of the input distribution circuit. An amplifier comprising a peak amplifier for amplifying a peak of a level equal to or higher than an input level at which the amplifier is saturated, and an output combining circuit for combining the output signal of the carrier amplifier and the output signal of the peak amplifier, A first distortion compensation circuit for distortion compensation of the carrier amplifier is provided on the input side, and a first distortion compensation circuit for compensating for distortion of the peak amplifier is provided between the input distribution circuit and the peak amplifier together with the first distortion compensation circuit. Two distortion compensation circuits are provided, and the first and second phase compensation circuits give phases in the same direction as the input level increases.

  According to the present invention, the first distortion compensation circuit for compensating for the distortion of the carrier amplifier, together with the second distortion compensation circuit provided for compensating for the distortion of the peak amplifier, to compensate for the distortion of the peak amplifier. Since it is used, the second distortion compensation circuit does not need to have a large circuit configuration that compensates for the distortion of the peak amplifier by itself, and the distortion of the peak amplifier can be effectively suppressed. It becomes possible.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a circuit configuration diagram showing an embodiment of an amplifier according to the present invention, in which 7 is a predistortion circuit, 8 is a drive amplifier, 9 is a predistortion circuit, and 10 and 11 are drive amplifiers. The parts corresponding to those in FIG.

  In the figure, a predistortion compensation circuit 7 and a drive amplifier 8 are provided in series between an input terminal 1 and an input distribution circuit 2, and a drive amplifier 10 is provided between the input distribution circuit 2 and the carrier amplifier 3. , And a predistortion compensation circuit 9 and a drive amplifier 11 are provided in series between the input distributor 2, the peak amplifier 4, and the capacity.

  The predistortion circuit 7 has a distortion compensation characteristic for compensating for at least AM-PM distortion in the carrier amplifier 3 in a non-saturated state, and the AM generated in the carrier amplifier 3 in the signal input from the input terminal 1. -Add AM-PM distortion (hereinafter referred to as compensation distortion) that cancels PM distortion (that is, opposite). The predistortion circuit 9 has a compensation characteristic for compensating for the AM-PM distortion generated in the peak amplifier 4 together with the predistortion circuit 7, and the distortion compensation circuit 7 adds compensation distortion. Then, AM-PM distortion (hereinafter referred to as compensation distortion) is added to the signal subjected to distortion compensation so that the AM-PM distortion generated in the peak amplifier 4 can be canceled. Such predistortion compensation circuits 7 and 9 can be small current circuits composed of, for example, Schottky diodes, small signal transistors, FETs, and the like.

  In such a configuration, the signal input from the input terminal 1 is added with compensation distortion for canceling AM-PM distortion generated in the carrier amplifier 3 by the predistortion compensation circuit 7, and the level is adjusted by the drive amplifier 8. The signal is supplied to the input distribution circuit 2 and distributed to the carrier amplifier 3 side and the peak amplifier 4 side. The signal A distributed to the carrier amplifier 3 side is level-adjusted by the drive amplifier 10 and then amplified by the carrier amplifier 3. The signal B distributed to the peak amplifier 4 side is supplied to the predistortion circuit 9. In this predistortion compensation circuit 9, compensation distortion is further added to the signal B to which compensation distortion has been added in the predistortion circuit 7 so that AM-PM distortion generated in the peak amplifier 4 is canceled. Is done. The signal B output from the predistortion circuit 9 is supplied to the peak amplifier 4 after the level is adjusted by the drive amplifier 11.

  Here, the bias is set so that the carrier amplifier 3 operates in class A, class AB or class B, and the peak amplifier 4 operates in class C. Until the carrier amplifier 3 is saturated, Although the peak amplifier 4 is in a cut-off state, when the carrier amplifier 3 reaches saturation, the peak amplifier 4 suddenly increases its output and operates to compensate for the insufficient gain of the carrier amplifier 3.

  Note that the carrier amplifier 3 and the peak amplifier 4 are amplified by, for example, the same type (same type name) semiconductor device, and the AM-PM characteristics have the same tendency (for example, the phase increases as the level increases, even if the bias is different). Are monotonously shifted in the same direction). For example, in the case of LDMOS, when the input level is small, the AM-PM characteristic is flat, but the phase delay becomes remarkable from around a certain value.

  The AM-PM distortion generated in the carrier amplifier 3 is canceled by the compensation distortion added by the predistortion circuit 7, and the AM-PM distortion generated in the peak amplifier 4 is added by the predistortion circuits 7 and 9. Canceled by compensation distortion.

  When the carrier amplifier 3 is not saturated, the peak amplifier 4 is in an off state, so that the output signal of the carrier amplifier 3 is output from the output terminal 6 via the output synthesis circuit 5 as an output signal of the Doherty amplifier. Is output. Further, when the carrier amplifier 3 is saturated, a signal that increases rapidly from the peak amplifier 4 is output, and the output signal of the carrier amplifier 3 and the output signal of the peak amplifier 4 that compensates for the shortage are output by the output synthesis circuit 5. The signals are combined and output from the output terminal 6 as an output signal of the Doherty amplifier.

  Thus, according to this embodiment, AM-PM distortion in the carrier amplifier 3 and the peak amplifier 4 can be corrected efficiently, and low power consumption and high output power with low distortion and improved linearity can be obtained. An amplifier can be realized. For example, by using it as a power amplifier of a transmitter in a base station of a mobile phone system, it is possible to amplify high output power with low power consumption and excellent low distortion linearity.

  Here, the predistortion compensation circuit 7 compensates for AM-PM distortion over all levels of the input signal, and the predistortion compensation circuit 9 compensates for AM-PM distortion at least at a level at which the carrier amplifier 3 is saturated. Distortion characteristics. In the Doherty amplifier, near the level at which the peak amplifier 4 starts to operate, the predistortion compensation circuit 9 adjusts the bias and the like because the phase may be shifted in the opposite direction due to the influence of a change in the output impedance. Accordingly, it may be preferable to generate the predistortion at a level higher than the predistortion amplifier 7 (for example, a level 0 to 10 dB higher than the level at which the peak amplifier 4 starts to operate).

  For simplicity, the predistortion circuits 7 and 9 may have a circuit configuration having the same AM-PM distortion compensation characteristic. In this case, the peak amplifier 4 uses the AM− in the carrier amplifier 3. The distortion compensation is twice as much as the PM distortion compensation. For this reason, the AM-PM distortion compensation of the peak amplifier 4 does not require a predistortion circuit having a large distortion characteristic as in the technique described in Patent Document 3 above, and has a high output with low distortion and high linearity. A signal will be obtained. Of course, even if the predistortion compensation circuit 9 and the predistortion compensation circuit 7 have different compensation amounts, the predistortion compensation circuit 9 can use the AM-PM distortion of the peak amplifier according to the technique described in Patent Document 3 above. Therefore, the predistortion circuit can compensate for the above-mentioned distortion with a small amount of compensation and low power consumption.

  In FIG. 1, the drive amplifiers 8, 10, and 11 are for adjusting the signal level as described above, and are not necessarily required.

It is a circuit block diagram which shows one Embodiment of the amplifier by this invention. It is a circuit block diagram which shows a Doherty amplifier.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Input terminal 2 Input distribution circuit 2a 1/4 wavelength transmission line 3 Carrier amplifier 4 Peak amplifier 5 Output composition circuit 6 Output terminal 7 Predistortion compensation circuit 8 Drive amplifier 9 Predistortion compensation circuit 10,11 Drive amplifier

Claims (1)

An input distribution circuit that distributes an input signal, a carrier amplifier that amplifies one output signal of the input distribution circuit, and a peak component at a level equal to or higher than an input level at which the carrier amplifier saturates in the other output signal of the branch circuit In an amplifier comprising: a peak amplifier that amplifies the output of the carrier amplifier; and an output combining circuit that combines the output signal of the carrier amplifier and the output signal of the peak amplifier.
A first distortion compensation circuit for compensating for distortion of the carrier amplifier is provided on the input side of the input distribution circuit;
And a second distortion compensation circuit that compensates for distortion of the peak amplifier together with the first distortion compensation circuit between the input distribution circuit and the peak amplifier,
The amplifiers characterized in that the first and second distortion compensation circuits give phases in the same direction as the input level increases.

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