JP2006311485A - Radio transmitter and amplifier - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enable transmission with low power consumption either when only one transmission system is used or when a plurality of transmission systems are used. <P>SOLUTION: A radio transmitter comprises first and second modulators for generating modulated signals, first and second amplifiers for power-amplifying the modulated signals to generate respective power-amplified signals, and first and second antennas for emitting the power-amplified signals as electric waves into air. The radio transmitter further comprises a first circuit provided between the first and second modulators and the first and second power amplifiers, and a second circuit provided between the first and second power amplifiers and the first and second antennas. When only the first modulator is used to perform communication, paths of the first and second circuits are set so that the first and second amplifiers are configured to serve as a Doherty amplifier. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a radio transmitter and an amplifier used in a radio communication system.

  In recent years, various techniques have been proposed in order to improve the data transmission rate in a wireless communication system. One of them is a technology called MIMO (Multi-Input, Multi-Output).

  MIMO is a technology that transmits radio waves using multiple analog transmission systems, each including an antenna, and similarly receives and communicates using multiple reception systems. In addition, the transmission speed can be improved by utilizing a phenomenon called multipath fading in which radio waves are irregularly reflected in a building or the like.

  As an example, the configuration of a MIMO transmitter having two transmission systems that are conventionally used includes a baseband unit, a first modulation unit that modulates a baseband modulation signal output from the baseband unit, and a second modulation. Output from the first power amplifier, the second power amplifier, the first power amplifier, and the second power amplifier that amplify the modulated signals output from the first, second, and second modulation sections, respectively. Including a first antenna and a second antenna that radiate signals as radio waves.

  MIMO is a technology that improves the transmission speed by utilizing a phenomenon called multipath fading as described above, so if there are a transmitter and a receiver in an open area with good visibility, the transmission speed is It may not improve. In such a case, communication using only one transmission system without using MIMO may be effective from the viewpoint of power consumption because the number of operation circuits is reduced. Further, in the area where the conventional system is provided, there may be a case where it is necessary to notify each terminal communicating with the conventional system of the reason why the own device will perform the MIMO transmission from now on. In such a case, even a MIMO transmitter having a plurality of transmission systems is required to have a function that enables communication by operating only one transmission system. In the following explanation, to simplify the explanation, when a MIMO transmitter transmits MIMO using multiple transmission systems, it is called “MIMO transmission” and when only one transmission system is operated to transmit a signal. Will be referred to as “during non-MIMO transmission”.

  Even in non-MIMO transmission, in order to make the signal level received on the receiver side the same as in MIMO transmission, the power level output from the transmitter must be the same level in MIMO transmission and non-MIMO transmission. is there. In such a case, the wireless communication system defines the power level signal that the transmitter should output for power amplifiers used in non-MIMO transmission among the power amplifiers provided in the plurality of transmission systems constituting the MIMO transmitter. The ability to output within the specified distortion range is required.

  Now, when the maximum output power level that should be output by the transmitter is X [W] and N transmission systems are used during MIMO transmission, the power amplifier used during non-MIMO transmission is a distortion specification specified by the wireless system. It must be possible to output a signal with the output of X [W] while satisfying. On the other hand, the maximum output power level that each power amplifier should output during MIMO transmission is X / N [W] when the same power amplifier is used. Considering the case where a MIMO transmitter does not transmit non-MIMO (MIMO transmission), each power amplifier needs to be able to output a signal with a maximum output of X / N [W] while satisfying the distortion specifications specified by the wireless communication system The difference between the maximum output levels of one power amplifier is (N-1) * X / N [W] when non-MIMO transmission is performed and when non-MIMO transmission is performed.

  That is, in a MIMO transmitter having N transmission systems, when performing non-MIMO transmission, the power amplifier is required to output a signal at a signal level N times that during MIMO transmission.

  In general, a power amplifier increases in operating efficiency as an output level approaches a saturated output level, but distortion characteristics deteriorate. On the contrary, as the output level becomes smaller than the saturation level, the distortion characteristic is improved, but the operation efficiency is deteriorated. In order to satisfy the distortion characteristics, operating the output level of the power amplifier lower than the saturation output level is called “backoff”, and the difference between the saturation output level and the actual output level is expressed as “backoff amount”. " When the power amplifier performs the back-off operation, the operation efficiency deteriorates. Therefore, in the MIMO transmitter that performs non-MIMO transmission as described above, the power amplifier performs an inefficient operation when performing MIMO transmission.

  In order to make it easy to understand the relationship between the backoff amount of the power amplifier and the operation efficiency, the conventional MIMO transmitter (baseband unit, first and second modulation units, first and second power amplifiers, first and second amplifiers) described above is used. Taking the second antenna as an example, a case where the transmission power of the transmitter required by the wireless communication system is 18 dBm (63 mW) and the distortion specification to be satisfied by the transmitter is −30 dBc or less will be specifically described.

  During MIMO transmission, both the first power amplifier and the second power amplifier are operating, and the two power amplifiers output signals with half the power to be transmitted by the transmitter. Therefore, the two power amplifiers output signals with a transmission power of half of 18 dBm, that is, 15 dBm (32 mW). Further, at this time, the first power amplifier and the second power amplifier need to have a distortion level of −30 dBc or less.

  On the other hand, if only one transmission system including, for example, the first modulation unit, the first power amplifier, and the first antenna is used during non-MIMO transmission, the first power amplifier is 18 dBm during non-MIMO transmission. It is required that a signal can be output with electric power. At this time, the distortion level of the first power amplifier must be -30 dBc or less.

  Currently, class AB or class B amplifiers are often used as small power amplifiers for wireless communication terminals. Here, there is no problem whether the amplifier used for the description is a class AB amplifier or a class B amplifier, and therefore, a class B amplifier will be described as an example. The class B amplifier theoretically has the highest operating efficiency at the saturation output level, and the operating efficiency decreases as the output level decreases. On the other hand, the distortion level increases as the output level approaches the saturated output level.

  As described above, the power amplifier needs to perform a back-off operation in order to keep the distortion level below a specified value, but the required back-off amount also depends on the modulation method of the modulation signal transmitted by the transmitter. Here, in order to simplify the explanation in an easy-to-understand manner, explanation will be made assuming that a specific back-off amount for satisfying the specification that the distortion level is −30 dBc or less is 10 dB.

  Now, the power level for non-MIMO transmission is 18 dBm, and the backoff amount required to obtain the distortion characteristics that meet the specifications is 10 dB, so the saturation output level required for the first power amplifier is 28 dBm . FIG. 16 shows the theoretical characteristics of the output power versus efficiency of a class B amplifier with a saturation output level of 28 dBm and an operating efficiency at saturation output of 45%. The horizontal axis is the output power level, and the vertical axis is the operating efficiency. In this case, the operating efficiency when the first power amplifier is operating at an output level of 18 dBm is 14%.

  On the other hand, during MIMO transmission, since the output level of the first power amplifier is 15 dBm, the operating efficiency is 10% from the characteristics shown in FIG. 16, and the operating efficiency is 4% lower than when output at 18 dBm. To do. When the same second power amplifier as the first power amplifier is used, the operating efficiency of the second power amplifier is also 10%.

As explained above, when it is necessary to perform non-MIMO transmission in a transmitter for MIMO transmission, it is necessary to provide a power amplifier with a high saturation output level, which increases the back-off amount of the power amplifier during MIMO transmission As a result, the operation efficiency deteriorates and the power consumption of the transmitter increases.
JP 2004-179822 JP High-Linearity RF Amplifier Design (by Peter B. Kenington) Microwave Technology Introductory Course (Basic) Eiji Mori CQ Publisher Junghyun KIM, et al., “A Highly-Integrated Doherty Amplifier for CDMA Handset Applications Using an Active Phase Splitter”, IEEE Microwave and Wireless Components Letters, vol. 15, No. 5, MAY 2005.

  As described above, in a transmitter for MIMO transmission, when a signal can be transmitted using only one transmission system, it is necessary to provide a power amplifier with a high saturation output level. This causes a problem that the power consumption of the transmitter increases during MIMO transmission.

  The present invention provides a radio transmitter and an amplifier capable of transmitting with low power consumption in both cases of transmission using only one transmission system and transmission using a plurality of transmission systems.

A radio transmitter according to an aspect of the present invention includes a first and a second modulation unit that modulates an input signal to generate a modulated signal, and a first that amplifies the modulated signal to generate a power amplified signal. And a second power amplifier, and first and second antennas that each radiate a power amplification signal as a radio wave in space, and further, a modulation signal from the first modulation unit is used as the first power. A first path that outputs to the amplifier and outputs the modulation signal from the second modulation unit to the second power amplifier, and separates the modulation signal from the first modulation unit and outputs one modulation signal to the second power amplifier; A first circuit having a second path for outputting the other modulation signal to the first power amplifier to the second power amplifier, and path switching means for switching the first and second paths; The power amplification signal from one power amplifier is converted into the first amplifier. And a third path for outputting the power amplification signal from the second power amplifier to the second antenna and a power amplification signal from the first and second power amplifiers at a synthesis point. A fourth path including impedance conversion means on the path of the power amplification signal from the first power amplifier that is output to the first or second antenna toward the combination point, and the third and fourth When performing the first communication using both the first and second modulators, the first circuit is switched to the first path. A control signal to be set to the first circuit path switching means, a control signal to set the second circuit to the third path is supplied to the path switching means of the second circuit, , The first and second modulation units When performing the second communication using only the first modulation unit, a control signal for setting the first circuit to the second path is supplied to the path switching unit of the first circuit, A control unit that supplies a control signal for setting the second circuit to the fourth path to the path switching unit of the second circuit.
An amplifier according to one aspect of the present invention outputs first and second power amplifiers and a first input signal to the first power amplifier and outputs a second input signal to the second power amplifier. A first path, a second path for separating the first input signal and outputting one separated input signal to the first power amplifier and the other separated input signal to a second power amplifier; A first path switching means for switching between the first and second paths; a third path for outputting the first and second power amplification signals input from the first and second power amplifiers; A fourth path for combining and outputting the first power amplification signal and the second power amplification signal via a conversion means at a combining point; and a second path switching means for switching the third and fourth paths. And comprising.

  According to the present invention, transmission can be performed with low power consumption in both cases of transmission using only one transmission system and transmission using a plurality of transmission systems.

  First, how the present inventors have made the present invention will be described.

  For example, a Doherty amplifier shown in Non-Patent Document 1 (High-Linearity RF Amplifier Design (Peter B. Kenington)) is known as a technique for reducing the efficiency deterioration during the back-off operation of the amplifier described in the background art.

  The Doherty amplifier includes a main amplifier and a sub-amplifier. A power divider (demultiplexer) for distributing power to the main amplifier and the sub-amplifier, an impedance conversion circuit for converting a load impedance for the main amplifier, and an output from the sub-amplifier. And a power combiner (synthesizer) for combining the outputs of the main amplifier and the sub-amplifier. FIG. 8 shows an example of the configuration of a Doherty amplifier having one main amplifier and one sub-amplifier. In the figure, 81 is a power divider, 82 is a power combiner, 83 is a main amplifier, 84 is a sub-amplifier, 85 is a 1/4 wavelength line (used as a phase adjustment circuit), 86 is a 1/4 wavelength line (impedance conversion circuit) , 87 is a control circuit, 88 is a variable attenuator, 89 is a power detector (detector), 90 is a bias circuit, 91 is a signal input terminal, and 92 is a signal output terminal. The quarter wavelength line 85 is for adjusting a phase shift caused by the insertion of the quarter wavelength line 86. The control circuit 87 is for controlling the amount of attenuation of the variable attenuator 88 for adjusting the bias of the sub-amplifier 84 and the input signal level to the sub-amplifier according to the signal level detected by the power detector 89. . Note that the control circuit 87, the power detector 89, the variable attenuator 88, and the bias circuit 90 can be eliminated by subjecting the sub-amplifier 84 to class-C bias. In principle, it is possible to realize a Doherty amplifier even when the number of amplifiers is not two as shown in FIG. 8, but three or more. However, in this description, a Doherty amplifier having two amplifiers will be described as an example for easy understanding.

  The Doherty amplifier operates such that only the main amplifier operates when the output signal level is low, and the sub-amplifier starts to operate as the output power increases, so power consumption when the output level is low can be reduced. It is possible to reduce deterioration in operating efficiency when the amplifier is performing a back-off operation. Further, since the output power of the Doherty amplifier is the sum of the output power of the main amplifier and the sub amplifier, the output level can be increased to the sum of the power levels that can be output by the main amplifier and the sub amplifier. The operation principle of such a Doherty amplifier will be described below.

  The basic operation of the Doherty amplifier is that when the input signal level is below a certain value, only the main amplifier is operated to perform an amplification operation, and when it exceeds a certain value, the sub-amplifier is also operated. is there. Note that the signal level at which the sub-amplifier begins to operate will be described in the detailed operation description to be described later. That is, when transistors with the same size (saturation level are equal) are used for the main amplifier and sub-amplifier, a transistor with substantially half the size is used when the signal input level is low, and the transistor size is doubled when the input signal level is high. The operation will be increased. As described above, the transistor size is apparently reduced at the time of low output, thereby increasing the operation efficiency of the transistor. At the time of high output, the transistor size is apparently increased to increase the saturation output.

  Further, in the Doherty amplifier, when the sub-amplifier starts to operate and supplies power to the output load, an effect called “active load pull effect” is obtained, in which the output load to the main amplifier changes and is observed. Due to this effect, the main amplifier can operate with a high impedance load with high operating efficiency when the output is low, and can perform an amplification operation with a low impedance load that provides a high output when the sub amplifier starts operating.

  Hereinafter, the operation of the Doherty amplifier will be described in more detail.

  The Doherty amplifier shown in FIG. 8 detects the signal input level using the detector 89, turns on the sub-amplifier 84 when the level of the input signal exceeds a certain value, and turns on the main amplifier 83 and the sub-amplifier 84. Amplification is performed by both amplifiers. However, changing the bias condition for the sub-amplifier 84 according to the input signal level with the above configuration not only requires complicated control but also increases the circuit scale, so that the sub-amplifier ON / OFF control is particularly accurate. The above configuration is rarely used except when necessary. In recent years, a method has been used in which a sub-amplifier is biased exclusively in class C and automatically turned on as the input signal level increases. However, the basic operation is the same except that the bias control of the sub-amplifier is automatically performed or the input signal level is monitored. Therefore, the operation of the Doherty amplifier having the configuration shown in FIG. 8 will be described below. Will be explained. In the following description, it is assumed that the sizes of both amplifiers 83 and 84 are equal. That is, at the time of maximum output when both amplifiers 83 and 84 are operating, both amplifiers 83 and 84 output signals of the same level.

  First, the operation when only the main amplifier 83 operates and the sub-amplifier 84 is in the OFF state and the signal input level is low will be described.

  A signal is input from the signal input terminal 91, and the signal is equally distributed to the path 1 and the path 2 by the power distributor 81. It is assumed that the signal input level is a low level that does not require the sub-amplifier 84 to be turned on. At this time, the sub-amplifier 84 is in an OFF state, and no signal amplification operation is performed. Thus, the bias circuit 90 supplies a bias voltage (usually 0 V) for turning off the sub-amplifier 84, and the attenuation amount of the attenuator 88 is set to a sufficiently large attenuation amount of about −30 dB. As the power divider 81 shown in FIG. 8, a hybrid type or a resistance divider can be used. Here, a power divider using a distributed constant line is used as an example.

  FIG. 9 shows an example of a power distributor using distributed constant lines. The power divider of the distributed constant line shown in FIG. 9 is specifically a transmission line 93 having a quarter wavelength length at a desired frequency. R1 is a load representing a circuit connected to the input signal terminal side (having a value equal to the impedance of the circuit), R2 is a load representing the main amplifier 83 (having a value equal to the input impedance of the main amplifier), R3 is 1 A load representing a quarter wavelength line 85 (having a value equal to the characteristic impedance of the quarter wavelength line).

  The signal input to the attenuator 88 is consumed as heat. On the other hand, the signal input to the main amplifier 83 is power amplified by the main amplifier 83 and output from the signal output terminal 92 via the quarter wavelength line 86 and the power combiner 82.

  Here, the output load of the main amplifier 83 is considered. The power divider shown in FIG. 9 can also be used as a power combiner if the input and output are reversed, so the power combiner 82 shown in FIG. 8 is the same as the 1/4 wavelength line power divider shown in FIG. Use things. As shown in FIG. 10, the output load for the main amplifier 83 looking to the right from the point B in FIG. 8 is that the impedance of the load resistor R4 connected to the signal output terminal 92 is two 1/4 wavelength lines 94, 86. Observed as (via XΩ). Therefore, when the signal input level is low and the sub-amplifier 84 is in the OFF state, the output load on the main amplifier 83 is XΩ.

  Next, a case where the main amplifier 83 is saturated and the sub amplifier 84 performs an amplification operation will be described.

  A signal input from the signal input terminal 91 is equally distributed to the path 1 and the path 2 by the power distributor 81. The attenuation amount of the attenuator 88 decreases as the input signal level increases, and is finally controlled to be a sufficiently small attenuation amount. Further, the bias for the sub-amplifier 84 is controlled according to the input signal level, and is finally controlled so as to have the same bias condition as that of the main amplifier 83.

  The signals input to the main amplifier 83 and the sub-amplifier 84 are amplified, synthesized by the power combiner 82, and then output from the signal output terminal 92.

  Here, output load conditions for the main amplifier 83 and the sub-amplifier 84 will be described. Now, the load conditions on the output side of the main amplifier 83 and the sub-amplifier 84 are as shown in FIG.

  When only the main amplifier 83 is operating and no signal is output from the sub-amplifier 84, the output load on the main amplifier 83 is XΩ as described with reference to FIG. However, when the sub-amplifier 84 starts to operate and the sub-amplifier 84 starts to supply a signal to the load R4 connected to the signal output terminal 92, the output load to the main amplifier 83 starts to gradually decrease from XΩ. Finally, when the sub-amplifier 84 outputs a signal with the same output power as the main amplifier 83, that is, to supply the same level signal to the output load R4 connected to the signal output terminal 92. When this happens, the output load on the main amplifier 83 is observed as if it were half of XΩ. Due to such a change in output load, the main amplifier 83 can increase the output power level while maintaining a high operating efficiency while maintaining a saturated state when the sub-amplifier 84 starts to operate.

  FIG. 12 shows the load movement, output current, and output voltage of the main amplifier 83 when the sub-amplifier 84 starts to operate. L1 indicates a load line when the sub-amplifier 84 is OFF, and L2 indicates a load line when both amplifiers are operating at the maximum output. I11 indicates an output current when the sub-amplifier 84 is OFF, and I12 indicates an output current when both amplifiers are operating at the maximum output. As shown in Figure 12, the main amplifier 83 increases the output power level by changing the output load from high impedance to low impedance, and increasing the output current amplitude while the output voltage amplitude remains constant. It becomes possible to make it. The amplitude of the current output from the main amplifier 83 is doubled from when the sub-amplifier 84 is in an OFF state until the same signal level as that of the main amplifier 83 is output. Therefore, the output signal level when the main amplifier 83 and the sub amplifier 84 finally output signals at the same level is four times the signal level output when only the main amplifier 83 is operating.

  On the other hand, the output load for the sub-amplifier 84 is parallel to the output impedance of the main amplifier 83 connected via the 1/4 wavelength line 86 and the load R4 connected via the 1/4 wavelength line 94. become. However, when the signal level supplied to the R4 load connected to the signal output terminal 92 by the sub-amplifier 84 increases, the output load to the sub-amplifier 84 gradually begins to be observed as a large impedance. When a signal is output with the same output power as that of the main amplifier 83, it is observed that the impedance is higher than the impedance when the sub amplifier is not operating.

  As described above, when signals are input from two signal sources to one output load, the phenomenon as if the impedance of the output load is changed is called an “active load pull effect”. The active load pull effect means that when a signal is supplied from one signal source (current source 1 in FIG. 13) to one output load R0 as shown in FIG. In FIG. 13, when a signal is supplied from the current source 2) to the same output load R0, the output load for the current source 1 increases and the output load for the current source 2 decreases.

That is, in FIG. 13, the output load R11 for the current source 1 is
R11 = V1 / I1 = R0 * (I1 + I2) / I1 = R0 + R0 * I2 / I1, and therefore when I2 increases, R11 increases. The output load R12 for the current source 2 is
R12 = V2 / I2 = R0 * (I1 + I2) / I2 = R0 + R0 * I1 / I2, so that when I2 increases, R12 decreases.

  With this active load pull effect and 1/4 wavelength line 86, the Doherty amplifier operates with high efficiency by setting the output load on the main amplifier to high impedance at low output, and low impedance at high output, thereby reducing distortion. Make it work.

  Here, Figure 14 shows the operating efficiency of a Doherty amplifier that uses two Class B amplifiers with a saturation output level half that of the Class B amplifier whose characteristics are shown in Figure 16, that is, a saturation output level of 25 dBm, as the main amplifier and sub amplifier. The theoretical characteristics of are shown. The horizontal axis is output power, and the vertical axis is operating efficiency. The efficiency characteristics shown in FIG. 14 are those when the input signal is a CW (continuous wave) wave (an unmodulated wave). Since a modulated signal is used in an actual wireless communication system, the efficiency characteristics shown in Fig. 14 vary depending on the type of the modulated signal, but the Doherty amplifier performs a back-off operation compared to a normal class B amplifier Sometimes the operating efficiency is excellent. Therefore, here, description will be made using the efficiency characteristics of the CW wave. For comparison, the operating efficiency of the class B amplifier shown in FIG. 16 is indicated by a broken line. From FIG. 14, it can be seen that the Doherty amplifier has about 12% higher operating efficiency at the time of 10 dB backoff than the Class B amplifier. As explained earlier, the output level at which the main amplifier and sub-amplifier eventually become saturated is 4 times the output level when only the main amplifier is saturated, that is, 6 dB higher. In a Doherty amplifier in which transistors of the same size are used for the sub-amplifier and the output load on the main amplifier changes to twice as large, the efficiency characteristic as shown in FIG. 14 is obtained.

  There are two peaks in this efficiency characteristic for the following reason. Generally, the operation efficiency of a transistor increases as it approaches saturation operation. Therefore, in the Doherty amplifier, when the main amplifier approaches the saturation operation, the efficiency peak once, and both the main amplifier and the sub-amplifier operate, and when both amplifiers are saturated, the efficiency peak again.

  As described above, the Doherty amplifier can improve the operation efficiency at the time of low output as compared with a normal single-ended amplifier.

  However, if the Doherty amplifier is used as it is for the power amplifier of the MIMO transmitter, the size of the power amplifier becomes very large, leading to an increase in the size and cost of the radio unit of the transmitter. For example, when a Doherty amplifier consisting of one main amplifier and one sub-amplifier is used as a power amplifier for a MIMO transmitter having two transmission systems, the total number of amplifiers used is four. Since two power distributors, impedance converters, and phase adjusters are required, the circuit size of the power amplifier increases by a factor of about two.

  Therefore, the present inventors have suppressed the increase in size and cost of equipment as much as possible, and in any case of transmission using only one transmission system and transmission using a plurality of transmission systems. As a result of trying to realize a wireless transmitter capable of transmitting with low power consumption and making efforts, the present invention was conceived. Hereinafter, embodiments of the present invention will be described in detail.

  FIG. 1 shows an embodiment of a wireless transmitter of the present invention. In the figure, 1 is a first modulation unit, 2 is a first power amplifier, 3 is a first antenna, 4 is a second modulation unit, 5 is a second power amplifier, 6 is a second antenna, 7 Is a first circuit, 8 is a second circuit, 9 is a baseband unit, and 10 is a control signal. In the present embodiment, the control signal is supplied from the baseband 9, but a control unit that supplies the control signal may be separately provided and supplied from the control unit.

  In this embodiment, in a MIMO transmitter having two transmission systems, when a signal needs to be transmitted using only one transmission system, a Doherty amplifier is configured using two power amplifiers, A signal is transmitted using a modulation unit and one antenna.

  In the following, a radio communication system in which the frequency of the transmission signal is 2 GHz and the output level of the signal output from the transmitter is 18 dBm is taken as an example, when transmitting with MIMO and using only one transmission system The specific operation of the embodiment of the present invention will be described.

  In the present embodiment, the output impedance of the first modulation unit 1 and the second modulation unit 4 is 50Ω, the input / output impedance of the first power amplifier 2 is also 50Ω, and the first antenna Assume that the input impedance of the third and second antennas 6 is also 50Ω. For the second power amplifier 5, the input / output impedance is 50Ω at the time of MIMO transmission, which is the same operating condition as the first power amplifier 2, but only one transmission system that operates as a sub-amplifier of the Doherty amplifier is used. , It is assumed that the input impedance is 50Ω, but the output impedance is sufficiently higher than 50Ω.

  First, a case where the transmitter performs MIMO transmission will be described.

  A baseband modulation signal is input from the baseband unit 9 to the first modulation unit 1 and the second modulation unit 4. The first modulation unit 1 and the second modulation unit 4 convert the input baseband modulation signal into a 2 GHz RF modulation signal to be transmitted by the transmitter and output it. Here, the modulation scheme used for signal modulation is not specifically specified since it is not the essence of the present invention, but modulation schemes such as 16QAM and OFDM used in wireless communication systems in recent years are conceivable. .

  FIG. 2 shows an example of a specific configuration common to the first modulation unit 1 and the second modulation unit 4 in the present embodiment. In the figure, 31 is a low-pass filter, 32 is a quadrature modulator, 33 is a band-pass filter, 34 is a driver amplifier, and 35 is a control signal distribution means. The baseband signal modulated by the baseband unit 9 is input to the quadrature modulator 32 via the low-pass filter 31, up-converted to a radio frequency of 2 GHz, and then driver amplifier via the band-pass filter 33. Input to 34, amplified and output. The low-pass filter 31, the quadrature modulator 32, and the driver amplifier 34 in the first modulation unit 1 and the second modulation unit are supplied with the control signal supplied from the baseband unit 9 through the control signal distribution unit 35. When the transmitter performs MIMO transmission, both the first modulation unit 1 and the second modulation unit 4 are in an operating state, and when the transmitter performs non-MIMO transmission, the configuration of the circuit 7 and the circuit 8 Depending on, either the first modulation unit 1 or the second modulation unit 4 is controlled so as to be in a resting state. In the case of the configuration of the present embodiment, the second modulation unit 4 is controlled so as to be in a dormant state. The control signal distribution means 35 may be a register that stores a control signal when the control signal is supplied from the baseband unit 9 as serial data, for example, and distributes the control signal to each unit when a trigger signal is supplied. It is done. In the present embodiment, the signal level output from the first modulation unit 1 and the second modulation unit 4 is specifically set to 5 dBm for easy understanding.

  Signals output from the first modulation unit 1 and the second modulation unit 4 are input to the circuit 7. FIG. 3 shows an example of the circuit 7. Reference numerals 41 and 42 are quarter wavelength lines having a characteristic impedance of 35Ω, reference numeral 43 is a quarter wavelength line having a characteristic impedance of 50Ω (1/4 + n wavelength line (n is 0 or any natural number)), and 44 and 45 are switches. The switches 44 and 45 are controlled by a control signal output from the baseband unit 9.

  Now, because the transmitter is performing MIMO transmission, the circuit 7 uses the first power amplifier 2 and the second power amplifier 5 as the signals output from the first modulation unit 1 and the second modulation unit 4, respectively. To output to In this embodiment, in the switch 44, the terminal A and the terminal B are connected, and the terminal C and the terminal D are connected. In the switch 45, the terminal G and the terminal F are connected, and the terminal E and the terminal H operate so as to be opened.

  At this time, let us consider the impedance that penetrates the circuit 7 side from the first modulation section 1. The impedance at the intersection I of the 1/4 wavelength line 43 having a characteristic impedance of 50Ω connected to the intersection I is opened because the other end of the line is short-circuited at the terminal C of the switch 44. In addition, the input impedance 50Ω of the first power amplifier 2 is converted to 25Ω by the 1/4 wavelength line 42 having the characteristic impedance of 35Ω, but is further converted by the 1/4 wavelength line 41 having the other characteristic impedance of 35Ω. Converted to 50Ω. Therefore, the impedance of the first modulation unit 1 that is inserted into the circuit 7 side is equal to the input impedance 50Ω of the first power amplifier 2, and the circuit 7 is connected to the first modulation unit 1 and the first power amplifier. 2, the signal output from the first modulation unit 1 without the power loss due to the impedance mismatch is the same as when the first modulation unit 1 and the first power amplifier 2 are directly connected. To the power amplifier 2.

  On the other hand, the impedance of the second modulation unit 4 that is inserted into the circuit 7 is equal to the input impedance 50Ω of the second power amplifier 5 because the terminal A and the terminal B of the switch 44 are connected.

  Thus, the signals output from the first modulation unit 1 and the second modulation unit 4 are input to the first power amplifier 2 and the second power amplifier 5, respectively.

  Here, the insertion loss in the circuit 7 is considered. The signal input from the first modulation unit 1 passes through two quarter-wave lines having a characteristic impedance of 35Ω and one switch, and is input to the first power amplifier 2. The signal input from the second modulation unit 4 passes through one switch and is input to the second power amplifier 5. When the 1/4 wavelength line is formed on a ceramic substrate or the like, the insertion loss is about 0.2 dB at 2 GHz, and the switch insertion loss is about 1 to 2 dB. Therefore, the insertion loss of the switch is more dominant than the insertion loss of the quarter wavelength line, and the insertion loss in the two signal paths formed by the circuit 7 is approximately equal to about 1 to 2 dB. If the insertion loss of the 1/4 wavelength line cannot be ignored, it is possible to correct the difference in insertion loss between the two signal paths by inserting the 1/2 wavelength line into the output of the switch 44. In this embodiment, it is assumed that there is no insertion loss of the circuit 7 in order to simplify the explanation of the operation. Even if the insertion loss of the circuit 7 is 2 dB, there is no contradiction in the explanation by describing the gains of the first power amplifier 2 and the second power amplifier 5 as 2 dB higher values, respectively.

  Signals input to the first power amplifier 2 and the second power amplifier 5 are amplified from the first antenna 3 and the second antenna 6 to a desired transmission power of 15 dBm. Now, since the signal level output from the first modulation unit 1 and the second modulation unit 4 is 5 dBm, the power gain of the first power amplifier 2 and the second power amplifier 5 is specifically 10 dB respectively. It is. That is, the bias condition is set such that the second power amplifier 5 has the same gain as the first power amplifier 2 by the control signal given from the baseband unit 9.

  An example of the first power amplifier 2 and the second power amplifier 5 in the present embodiment is shown in FIGS. 6 and 7, respectively. In FIG. 6, 60 is an input matching circuit, 61 is a base bias circuit using an emitter follower, 62 is a collector bias circuit, 63 is a grounded emitter amplifier circuit, and 64 is an output matching circuit. In FIG. 7, 70 is an input matching circuit, 71 is a base bias circuit using an emitter follower controlled by a control signal, 72 is a collector bias circuit, 73 is a grounded emitter amplifier circuit, and 74 is an output matching circuit.

  In the present embodiment, the configurations of the first power amplifier 2 and the second power amplifier 5 are basically the same. However, the only difference is whether or not a base bias circuit using an emitter follower for supplying a base bias current to the grounded emitter amplifier circuits 63 and 73 is controlled by a control signal.

  In the present embodiment, when performing MIMO transmission, the first power amplifier 2 and the second power amplifier 5 each perform class AB operation, and during non-MIMO transmission, the first power amplifier 2 is class AB. The second power amplifier 5 operates in class C. That is, the base bias current of the first power amplifier 2 shown in FIG. 6 is the same during MIMO transmission and non-MIMO transmission. On the other hand, the base bias current of the second power amplifier 5 shown in FIG. 7 is the base bias current supplied to the grounded emitter amplifier circuit 73 by the base bias circuit 71 using the emitter follower according to the control signal given from the baseband unit 9. Is supplied so that the grounded-emitter amplifier circuit 73 operates in class AB during MIMO transmission, and is supplied so that the grounded-emitter amplifier circuit 73 operates in class C during non-MIMO transmission. The base bias circuit 71 using the emitter follower for the second power amplifier 5 of the present embodiment shown in FIG. 7 supplies the grounded emitter amplifier circuit 73 with the voltage value of the control signal given by the baseband unit 9 itself. It is possible to control the base bias current. Therefore, specifically, the operation of the grounded emitter amplifier circuit 73 can be changed from class AB to class C by lowering the control voltage supplied to the base bias circuit 71 using the emitter follower from the voltage value at the time of MIMO transmission. it can.

  Thus, the signals output from the first power amplifier 2 and the second power amplifier 5 are input to the circuit 8.

  An example of the circuit 8 is shown in FIG. In the figure, 50 is a 1/4 wavelength line with a characteristic impedance of 50Ω (1/4 + n wavelength line (n is 0 or any natural number)), 51 and 52 are 1/4 wavelength lines with a characteristic impedance of 35Ω, 53, 54, 55 Is a switch. The switches 53, 54 and 55 are controlled by a control signal output from the baseband unit 9.

  Since the transmitter performs MIMO transmission, the circuit 8 outputs the signals output from the first power amplifier 2 and the second power amplifier 5 to the first antenna 3 and the second antenna 6, respectively. To work. In this embodiment, in the switch 53, the terminal J and the terminal L are connected, and the terminal M and the terminal K are opened. In the switch 54, the terminal Q and the terminal R are connected, in the switch 55, the terminal P and the terminal O are connected, and the terminal N is opened.

  At this time, let us consider the impedance that penetrates the circuit 8 side from the first power amplifier 2. The impedance at the intersection T of the 1/4 wavelength line 50 having a characteristic impedance of 50 Ω connected to the intersection T is short-circuited at the other end of the line because the terminal P and the terminal O of the switch 55 are connected, and thus opened. . Then, since the terminal Q and the terminal R of the switch 54 are connected, the impedance that penetrates the circuit 8 side from the first power amplifier 2 becomes equal to the input impedance 50Ω of the first antenna 3.

  On the other hand, let us consider the impedance that penetrates the circuit 8 side from the second power amplifier 5. At the intersection S, since the terminal K in the switch 53 and the terminal N in the switch 55 are open, two 1/4 wavelength lines having a characteristic impedance of 35Ω are connected. In addition, the input impedance 50Ω of the second antenna 6 is converted to 25Ω by the 1/4 wavelength line 52 having the characteristic impedance of 35Ω, but the original 50Ω is converted by the 1/4 wavelength line 51 having another characteristic impedance of 35Ω. Therefore, the input impedance of the second antenna 6 becomes 50Ω. Therefore, the impedance of the circuit 8 side from the second power amplifier 5 is equal to the input impedance 50Ω of the first antenna 6, and the circuit 8 is connected to the second power amplifier 5 and the second antenna 6. Even if it is provided in between, the signal output from the second power amplifier 5 without power loss due to impedance mismatch is the same as when the second power amplifier 5 and the second antenna 6 are directly connected. Is input.

  Here, as in the case of the circuit 7, the insertion loss of the circuit 8 is considered. The signal input from the first power amplifier 2 passes through one switch and is input to the first antenna 3. The signal input from the second power amplifier 5 passes through two quarter-wave lines having a characteristic impedance of 35Ω and one switch, and is input to the second antenna 6. As in the case of the circuit 7, the insertion loss of the switch is more dominant than the insertion loss of the quarter wavelength line, and the insertion loss in the two signal paths formed by the circuit 8 is approximately equal to 1 to 2 dB. It will be about. If the insertion loss of the 1/4 wavelength line cannot be ignored, it is possible to reduce the difference in insertion loss between the two signal paths by inserting the 1/2 wavelength line at the input of the switch 54. As in the case of the circuit 7, it is assumed that there is no insertion loss of the circuit 8 in order to simplify the description.

  As described above, a signal with an output level of 15 dBm is output from each of the first antenna 3 and the second antenna 6, and a signal is output at an output level of 18 dBm for the entire transmitter.

  Next, when a signal is transmitted using only one transmission system, that is, when a Doherty amplifier is configured using two power amplifiers and a signal is transmitted using one modulation unit and one antenna Will be described.

  In the present embodiment, it is assumed that the first modulation unit 1 is used as the modulation unit and the second antenna 6 is used as the antenna. The operation until a signal is input from the baseband unit 9 to the circuit 7 is the same as the operation of the first modulation unit 1 during MIMO transmission described above. The signal output from the first modulation unit 1 is input to the circuit 7.

  Here, the operation of the circuit 7 will be described first.

  In FIG. 3, the circuit 7 distributes the signal input from the first modulation unit 1 to the first power amplifier 2 and the second power amplifier 5 in accordance with the control signal supplied from the baseband unit 9. To operate as a power distribution circuit. Specifically, in the switch 44, the terminal B and the terminal C are connected, and the terminal A and the terminal D are opened. The switch 45 operates so that the terminal E and the terminal F are connected and the terminal G and the terminal H are connected.

  At this time, at the intersection I, the 1/4 wavelength line 42 having a characteristic impedance of 35Ω with the other end short-circuited and the 1/35 of the characteristic impedance 35Ω connected to the first modulation unit 1 having the other end of the output impedance of 50Ω. 4 wavelength line 41, first power amplifier 2 with input impedance of 50Ω, and 1/4 wavelength line 43 with characteristic impedance of 50Ω connected at the other end to second power amplifier 5 with output impedance of 50Ω become.

  Considering the state of impedance matching at the intersection point I, the impedance of the 1/4 wavelength line 42 having a characteristic impedance of 35Ω with the other end short-circuited is large enough to be regarded as an open state, and the other end is the first impedance with an output impedance of 50Ω. The 1/4 wavelength line 41 with a characteristic impedance of 35Ω connected to the modulation unit 1 of 1 becomes 25Ω, and the first power amplifier 2 with an input impedance of 50Ω and the second power amplifier 5 with the other end having an output impedance of 50Ω. Since the 1/4 wavelength line 43 having a characteristic impedance of 50Ω connected to is connected, the matching can be achieved with an impedance of 25Ω. As a result, the signal output from the first modulation unit 1 is distributed to the first power amplifier 2 and the second power amplifier 5, and the phase of the signal input to the second power amplifier 5 is the first. A power distributor is formed such that the phase is delayed by 90 ° compared to the phase of the signal input to one power amplifier 2.

  Thus, the signal output from the circuit 7 is distributed and input to the first power amplifier 2 and the second power amplifier 5.

  Next, the operation of the circuit 8 will be described.

  In FIG. 4, the circuit 8 outputs signals output from the first power amplifier 2 and the second power amplifier 5 to the second antenna 6 in accordance with a control signal supplied from the baseband unit 9. It is controlled to operate. Specifically, in the switch 53, the terminal J and the terminal K are connected, and the terminal L and the terminal M are connected. In the switch 54, the terminals Q and R are opened. In the switch 55, the terminal P and the terminal N are connected, and the terminal O is opened.

  At this time, at the intersection S, the 1/4 wavelength line 51 having a characteristic impedance of 35Ω with the other end short-circuited and the 1/50 of the characteristic impedance 50Ω connected to the first power amplifier 2 having the other end of the output impedance of 50Ω. The 4 wavelength line 50, the 1/4 wavelength line 52 having a characteristic impedance of 35Ω, the other end of which is connected to the second antenna 6 having an input impedance of 50Ω, and the second power amplifier 5 having an output impedance of 50Ω are connected. Become.

  Considering the state of impedance matching at the intersection S, the impedance of the 1/4 wavelength line 51 with the characteristic impedance of 35Ω with the other end short-circuited is large enough to be considered as an open state, and the other end is the first with the output impedance of 50Ω. The 1/4 wavelength line 50 with a characteristic impedance of 50Ω connected to the power amplifier 2 of 1 is 50Ω, and the second power amplifier 5 whose output impedance is sufficiently large with respect to 50Ω and the other end output A quarter wavelength line 52 having a characteristic impedance of 35Ω connected to the second antenna 6 having an impedance of 50Ω is connected. At this time, since the output impedance of the second power amplifier 5 is assumed to be sufficiently larger than 50Ω in this embodiment, impedance matching is not achieved at the intersection S in the above state. When a signal is output from the sub-amplifier due to the “load pull effect”, it is necessary to consider the effect observed when the output load on the power amplifier changes, so that the impedance matching can be obtained at the intersection S due to the “active load pull effect”. No problem if designed to. As a result, after the signal output from the first power amplifier 2 has a phase delayed by 90 ° compared to the signal input from the second power amplifier 5, the first power amplifier 2 and the second power amplifier 2 Thus, a power combiner is formed such that the signals output from the power amplifier 5 are added together.

  Here, a circuit formed by the circuit 7, the first power amplifier 2, the second power amplifier 5, and the circuit 8 at the time of non-MIMO transmission in the present embodiment described above is illustrated in FIG. become. Comparing FIG. 5 and FIG. 8, the first power amplifier 2 is the main amplifier 83, the second power amplifier 5 is the sub-amplifier 84, the 1/4 wavelength line 41 having the characteristic impedance of 35Ω in the circuit 7 is the power distributor 81, A 1/4 wavelength line 43 having a characteristic impedance of 50Ω is a 1/4 wavelength line 85, a 1/4 wavelength line 50 having a characteristic impedance of 50Ω in the circuit 8 is a 1/4 wavelength line 86, and a 1/4 wavelength line 52 having a characteristic impedance of 35Ω. This is the same as the circuit configuration of the Doherty amplifier in which the power combiner 82 is used. A 1/4 wavelength line (phase adjusting means) 43 having a characteristic impedance of 50Ω is for adjusting a phase delay caused by insertion of the 1/4 wavelength line 50 having a characteristic impedance of 50Ω. The intersection point S corresponds to, for example, a composite point. Note that, as described above, in this embodiment, a class C biased amplifier is used as the sub-amplifier, so that the control circuit 87, the power detector 89, the variable attenuator 88, and the bias circuit 90 in FIG. 8 are not necessary.

  Therefore, the control signal is sent from the baseband unit 9 to the second power amplifier 5 so that the second power amplifier 5 is class-C biased, so that the circuit 7, the first power amplifier 2, and the second power amplifier 5 The circuit formed by the second power amplifier 5 and the circuit 8 operates as a Doherty amplifier that amplifies the signal output from the modulation unit 1.

  In the Doherty amplifier, only the main amplifier operates when the input signal level is low, and the sub-amplifier starts to operate as the input signal level increases. In the present embodiment, the second power amplifier 5 used as a sub-amplifier is a class C amplifier, and is operated so that the bias current gradually increases as the input signal increases, and an ON state having a gain is obtained. In addition, the output load on the main amplifier when only the main amplifier is operating is a high value for high-efficiency operation, but when the sub-amplifier starts operating, the output load values for the main amplifier and the sub-amplifier are respectively A phenomenon called “active load pull effect” observed to change occurs, and when the 1/4 wavelength line 50 is used as an impedance converter as in this embodiment, the value of the output load for the main amplifier Lowers, allowing higher power operation.

  The basic operating principle of the Doherty amplifier as described above is described in detail in the cited document 1, and also explained in the background art section. Therefore, here, when the first power amplifier 2 and the second power amplifier 5 output signals at a maximum output level of 15 dBm, the circuit 7, the first power amplifier 2, and the second power amplifier, respectively. Only the operation of the Doherty amplifier formed by 5 and the circuit 8 will be described.

  The signal input from the first modulation unit 1 is distributed to the first power amplifier 2 and the second power amplifier 5 by the power distributor formed by the circuit 7.

  The gains of the first power amplifier 2 and the second power amplifier 5 in the present embodiment are assumed to have the same gain of 10 dB both during MIMO transmission and during non-MIMO transmission. That is, at the time of non-MIMO transmission, the gain of the second power amplifier 5 biased with class C has a characteristic of 10 dB. At this time, the signal level output from the first modulation unit 1 is specifically 8 dBm.

  In the present embodiment, the gains of the first power amplifier 2 and the second power amplifier 5 are set to be equal in MIMO transmission and non-MIMO transmission. Therefore, the output power level of the first modulation unit 1 is 3 dB higher in non-MIMO transmission than in the case of MIMO transmission. This is the same with the conventional transmitter when the gain of the power amplifier is the same during MIMO transmission and during non-MIMO transmission as in this embodiment. That is, the increase in power consumption due to the output level of the first modulation unit 1 being increased by 3 dB is the same between the conventional transmitter and the present embodiment.

  In the present embodiment, since the first power amplifier 2 and the second power amplifier 5 have the same gain as described above, the first power amplifier 2 and the second power amplifier 5 have the same level, respectively. Are equally distributed. That is, a signal of 5 dBm is input to each of the first power amplifier 2 and the second power amplifier 5.

  The signals input to the first power amplifier 2 and the second power amplifier 5 are power amplified and output to the circuit 8 at an output level of 15 dBm. At this time, the first power amplifier 2 and the second power amplifier 5 are input with the same level signal as the MIMO transmission described above, and output the same level signal. Therefore, the operating efficiencies of the first power amplifier 2 and the second power amplifier 5 are the same as in MIMO transmission.

  In the circuit 8, since a power combiner is formed, the signals output from the first power amplifier 2 and the second power amplifier 5 are added together, and the second antenna is output as a signal having an output level of 18 dBm. Input to 6.

  As described above, a signal with an output level of 18 dBm is output from the second antenna 6, and a signal is output with the same output level of 18 dBm as the transmitter when transmitting MIMO.

  FIG. 15 shows another configuration example of the first circuit 7. The first circuit 100 includes an isolation circuit 101 that can ensure isolation between output terminals and generates a phase difference of 90 degrees between output signals.

  Thereby, in the first circuit 100, the isolation between the two output terminals can be ensured. Therefore, isolation between the input terminals of the first power amplifier 2 and the second power amplifier 5 is also ensured, and as a result, a Doherty amplifier is configured using the first power amplifier 2 and the second power amplifier 5. Since the input impedances of the two power amplifiers do not affect each other, the design of the power amplifier input matching circuit and the like can be made relatively easy.

  Further, the first circuit 100 adds a 90-degree phase difference between the output signals, so that the 1/4 wavelength line 41 having the characteristic impedance of 35Ω and the 1/4 wavelength having the characteristic impedance of 50Ω in the first circuit 7 of FIG. A function equivalent to that of the power distributor constituted by the line 43 is realized.

  Hereinafter, the first circuit 100 will be described in more detail.

  In FIG. 15, 101 is an isolation circuit that can provide isolation between output terminals and provides a 90-degree phase difference between output signals, 102 is a first switch circuit, 103 is a second switch circuit, and 104 is It is a terminator.

  For the isolation circuit 101, for example, a 3 dB branch line coupler described in Non-Patent Document 2 (Introduction to Microwave Technology (Basics) by Eiji Mori, CQ Publisher) can be used. Non-patent document 2 describes the configuration and design method of the 3 dB branch line coupler. When a 3 dB branch line coupler is used, according to Non-Patent Document 2, isolation between output terminals can be secured at 30 GHz or more at 1.5 GHz.

  The isolation circuit 101 includes, for example, Non-Patent Document 3 (Junghyun KIM, et al., “A Highly-Integrated Doherty Amplifier for CDMA Handset Applications Using an Active Phase Splitter”, IEEE Microwave and Wireless Components Letters, vol. 15). , No. 5, MAY 2005.), a phase shifter composed of semiconductor transistors can also be used. According to Non-Patent Document 3, 10 dB or more can be secured.

  The operation of the transmitter including the first circuit 100 is the same as that of the transmitter including the first circuit 7 except for the operation of the first circuit 100. Therefore, in the following, the operation of the first circuit 100 will be mainly described.

  First, a case where a transmitter including the first circuit 100 performs non-MIMIO transmission will be described. In FIG. 15, the first circuit 100 sends the signal input from the first modulation unit 1 to the first power amplifier 2 and the second power amplifier 5 in accordance with the control signal supplied from the baseband unit 9. It is controlled to operate as a power distribution circuit for distributing. Specifically, the first switch circuit 102 operates such that the terminals A and C and the terminals F and E are connected, and the second switch circuit 103 operates so that the terminals G and I are connected.

  Thus, the signal input from the first modulation unit 1 is demultiplexed into two signals with a phase difference of 90 degrees from each other at the same power level by the isolation circuit 101, and the first power amplifier 2 and the second power To the power amplifier 5.

  On the other hand, when the transmitter performs MIMO transmission, the first circuit 100 converts the signal input from the first modulation unit 1 into the first power amplifier according to the control signal supplied from the baseband unit 9. 2, and operates so as to output the signal input from the second modulation unit 4 to the second power amplifier 5. Specifically, the first switch circuit 102 operates so that the terminals A and B, the terminal D and the terminal E are connected, and the second switch circuit 103 operates so that the terminal H and the terminal I are connected.

  Thus, the signal input from the first modulation unit 1 is output to the first power amplifier 2, and the signal input from the second modulation unit 4 is output to the second power amplifier 5.

  The operation of the circuit constituting the transmitter other than the operation of the first circuit 100 described above is the case of the transmitter including the first circuit 7 in both cases of non-MIMO transmission and MIMO transmission. It is the same.

  As described above, in this embodiment, the first power amplifier 2 and the second power amplifier 5 provided in the transmitter have the same operation efficiency during MIMO transmission and during non-MIMO transmission. Therefore, in the conventional MIMO transmitter, when the same power amplifier is used, there is a problem that the operation efficiency of the power amplifier is deteriorated at the time of non-MIMO transmission, but this problem is avoided by implementing the present invention. It becomes possible to do.

  Further, in this embodiment, in a MIMO transmitter that is required to transmit a signal using only one transmission system, the saturation level of the power amplifier provided in each transmission system is the saturation required for MIMO transmission. It becomes possible to make it equal to the level. As a result, it is not necessary to increase the back-off amount of the power amplifier during MIMO transmission, so that power consumption during MIMO transmission can be reduced.

  Furthermore, in this embodiment, when a signal is transmitted using only one transmission system, a Doherty amplifier is configured by a plurality of power amplifiers included in the transmitter. It is possible to satisfy the transmission level to be output while satisfying the level.

  Due to the above effects, it is possible to realize a MIMO transmitter that needs to transmit a signal using only one transmission system in a small size and at a low price.

  In the present embodiment, as an example of the impedance conversion means and the phase adjustment means, a 1/4 wavelength line having a characteristic impedance of 50Ω is given as an example, and a switch is given as an example of the signal path switching means. The signal path switching means may be another circuit having the same effect as the quarter wavelength line and the switch, or the impedance value before and after conversion may be different from that of the present embodiment.

  In addition, when describing the operation of the first circuit 7 and the second circuit 8, the notation that “impedance matching can be obtained” was used. There is no problem even in a state where impedance matching is achieved to the extent that no trouble occurs in wireless communication (for example, the voltage standing wave ratio (VSWR) between circuits is about 2 or less).

  In addition, the second power amplifier 5 has been described by taking as an example a case where the output impedance is sufficiently higher than 50Ω in the class C bias state, but this is a case where the output impedance of the second power amplifier 5 is not sufficiently high. However, there is no problem because the Doherty amplifier can be realized by appropriately selecting the characteristic impedance value and the length of the 1/4 wavelength line used in the first circuit 7 and the second circuit 8.

  In addition, even if the first modulation unit 1 and the second modulation unit 4 are not configured as shown in FIG. 2, that is, if the circuit has a function capable of outputting a modulated radio frequency signal, the circuit shown in FIG. A configuration different from the configuration shown may be used.

  Further, the second power amplifier 5 has been described with an example in which the second power amplifier 5 is controlled by a control signal supplied from the baseband unit 9 so as to be a class C bias when transmitting by only one transmission system. This is a power amplifier in which the bias voltage and the drive level are adjusted by the control signal supplied from the baseband unit 9 according to the level of the input signal so that the power amplifier 5 of 2 can function as a sub-amplifier of the Doherty amplifier. It does not matter.

  In addition, the example in which the signal output from the first modulation unit 1 is equally distributed to the first power amplifier 2 and the second power amplifier 5 has been described, but the distribution ratio is not equal. There is no problem even if it exists.

  Further, the case where the gains of the first power amplifier 2 or the second power amplifier 5 are equal has been described as an example, but when the gains of the first power amplifier 2 and the second power amplifier 5 are not equal, Both or one of the first power amplifier 2 and the second power amplifier 5 may have a function of correcting the gain of a gain amplifier or an attenuator.

  Furthermore, when performing transmission power control in which the transmission power of the transmitter is changed according to the condition of the signal propagation path, a variable for making the output power variable in the first modulation unit 1 and the second modulation unit 4 This can be realized by having a circuit such as a gain amplifier.

  Further, in the present embodiment, a MIMO transmitter having two transmission systems is used. Similarly, when the present invention is implemented in a MIMO transmitter having three transmission systems, the first circuit and the second circuit are similarly applied. And three power amplifiers provided in three transmission systems, and by using these three power amplifiers as one main amplifier and two sub-amplifiers, a Doherty amplifier can be configured. It becomes possible to avoid the deterioration of the operation efficiency of the power amplifier.

  Also, in this embodiment, each power amplifier outputs wireless communication typified by distortion characteristics and noise characteristics when outputting a signal at the same level under the same operating conditions such as bias voltage or bias current and environmental temperature. The high frequency characteristics defined by the system are preferably at the same level.

  In the present embodiment, the first circuit, the second circuit, or both of them are configured by an inductor and a capacitor made by a semiconductor process, or an inductor and a capacitor of a chip component such as a multilayer ceramic capacitor or a thin film inductor. A lumped constant circuit and a switch may be included.

  In the present embodiment, the first circuit, the second circuit, and the plurality of power amplifiers may be MMICs manufactured by the same semiconductor process.

  In the present embodiment, each of the first circuit, the second circuit, and the plurality of power amplifiers, or any combination of these, is wired on the same ceramic substrate or resin substrate. It may be a module realized using a pattern, a chip component, or the like.

The figure which shows the structure of the transmitting apparatus as embodiment of this invention. FIG. 3 is a diagram illustrating an example of a first modulation unit and a second modulation unit. The figure which shows an example of a 1st circuit. The figure which shows an example of a 2nd circuit. The figure explaining that a Doherty amplifier is formed by the 1st circuit, the 2nd circuit, the 1st power amplifier, and the 2nd power amplifier, when transmitting a signal only by one transmission system. The figure which shows an example of a 1st power amplifier. The figure which shows an example of the 2nd power amplifier. The figure which shows the structure of a known Doherty amplifier. The figure which shows the power divider | distributor using a 1/4 wavelength distributed constant line. The figure explaining the output load of the main amplifier when only the main amplifier is operating. The figure explaining the output load of both amplifier when the main amplifier and the sub amplifier operate | move. The figure explaining the change of the output current of a main amplifier. The figure explaining the active load pull effect. The figure which shows the theoretical characteristic of the operating efficiency of the Doherty amplifier which consisted of two Class B amplifiers with half the saturation output level of Class B amplifier. The figure which shows the other structural example of a 1st circuit. The figure which shows the output power versus efficiency characteristic of the class B amplifier whose saturation output level is 28dBm and whose operation efficiency at the time of saturation output is 45% by theoretical value.

Explanation of symbols

1: First modulation unit 2: First power amplifier
3: First antenna 4: Second modulator
5: Second power amplifier 6: Second antenna
7: First circuit
8: Second circuit
9: Baseband part 10: Control signal

31: Low-pass filter
32: Quadrature modulator 33: Band pass filter
34: Driver amplifier 35: Control signal distribution means

41, 42: 1/4 wavelength line with characteristic impedance of 35Ω
43: 1/4 wavelength line with characteristic impedance of 50Ω
44, 45: Switch

50: 1/4 wavelength line with characteristic impedance of 50Ω
51, 52: 1/4 wavelength line with characteristic impedance of 35Ω
53, 54, 55: Switch

60: Input matching circuit 61: Base bias circuit using emitter follower
62: Collector bias circuit 63: Common emitter amplifier circuit
64: Output matching circuit

70: Input matching circuit
71: Base bias circuit using emitter follower controlled by control signal
72: Collector bias circuit 73: Grounded emitter amplifier circuit
74: Output matching circuit

81: Power distributor 82: Power combiner 83: Main amplifier
84: Sub-amplifier 85, 86: 1/4 wavelength line 7: Control circuit
88: Variable attenuator 89: Power detector

90: Bias circuit 91: Signal input terminal 92: Signal output terminal
93, 94: 1/4 wavelength line

100: First circuit 101: Isolation circuit
102: First switch circuit 103: Second switch circuit

Claims (17)

First and second modulators that each modulate an input signal to generate a modulated signal;
First and second power amplifiers that each amplify the modulated signal to generate a power amplified signal;
First and second antennas each radiating power amplification signals as radio waves in space,
further,
A first path for outputting a modulation signal from the first modulation unit to the first power amplifier and outputting a modulation signal from the second modulation unit to the second power amplifier; and A second path for separating the modulation signal from the modulation unit and outputting one modulation signal to the first power amplifier and the other modulation signal to the second power amplifier; and the first and second paths A first circuit having a path switching means for switching;
A third path for outputting a power amplification signal from the first power amplifier to the first antenna and outputting a power amplification signal from the second power amplifier to the second antenna; and A power amplification signal from the second power amplifier is synthesized at a synthesis point and output to the first or second antenna. The power amplification signal from the first power amplifier has an impedance on a path toward the synthesis point. A second circuit having a fourth path including conversion means and path switching means for switching between the third and fourth paths;
When performing first communication using both the first and second modulation units, a control signal for setting the first circuit to the first path is supplied to the path switching unit of the first circuit. And supplying a control signal for setting the second circuit to the third path to the path switching means of the second circuit,
On the other hand, when performing the second communication using only the first modulation unit among the first and second modulation units, a control signal for setting the first circuit to the second path is set to the first signal. Supplying to the path switching means of the first circuit, and supplying a control signal for setting the second circuit to the fourth path to the path switching means of the second circuit;
A control unit;
With wireless transmitter.   2. The radio transmitter according to claim 1, wherein the control unit supplies a bias control signal for controlling a bias voltage or a bias current of the second power amplifier to the second power amplifier.   When the first communication is executed, the control unit supplies a bias control signal for class AB amplification of the second power amplifier to the second power amplifier, and the second communication is executed. 3. The radio transmitter according to claim 2, wherein a bias control signal for class C amplification of the second power amplifier is supplied to the second power amplifier.   The radio transmitter according to claim 1, wherein the first power amplifier performs class AB amplification. 5. The radio transmitter according to claim 1, wherein the second path includes phase adjusting means on the path of the other modulation signal.   6. The radio transmitter according to claim 5, wherein the phase adjusting means is a 1/4 + n wavelength line (n is 0 or an arbitrary natural number).   The second path in the first circuit has a function of separating the modulated signal and a hybrid power that separates the input modulated signal into two so that the phase difference is 90 ° with each other as the phase adjusting means. The wireless transmitter according to claim 5, further comprising a distributor.   8. The radio according to claim 1, wherein the impedance conversion means on the fourth path in the second circuit is a ¼ + n wavelength line (n is 0 or an arbitrary natural number). Transmitter.   9. The radio transmitter according to claim 1, wherein the path switching unit in the first circuit or the path switching unit in the second circuit is configured by a switch.   9. The radio transmitter according to claim 1, wherein the first circuit, the second circuit, or both of them are configured by a lumped constant circuit and a switch. First and second power amplifiers;
A first path for outputting a first input signal to the first power amplifier and a second input signal to the second power amplifier;
A second path for separating the first input signal and outputting one separated input signal to the first power amplifier and the other separated input signal to the second power amplifier;
First path switching means for switching the first and second paths;
A third path for outputting the first and second power amplification signals respectively input from the first and second power amplifiers;
A fourth path for combining and outputting the first power amplification signal and the second power amplification signal via the impedance conversion means at a combining point;
Second path switching means for switching between the third and fourth paths;
With amplifier.   The amplifier according to claim 11, wherein the first power amplifier performs class AB amplification.   The amplifier according to claim 11, wherein the second path includes a phase adjusting unit on the path of the other separated signal.   14. The amplifier according to claim 13, wherein the phase adjusting means is a 1/4 + n wavelength line (n is 0 or an arbitrary natural number).   The second path includes, as a function of separating the input signal and the phase adjusting unit, a hybrid power distributor that separates the input signal into two so that the phase difference is 90 ° with respect to each other. 15. An amplifier according to claim 13 or 14, characterized in that:   16. The amplifier according to claim 11, wherein the impedance conversion means on the fourth path is a 1/4 + n wavelength line (n is 0 or an arbitrary natural number).   The amplifier according to any one of claims 11 to 16, wherein the first path switching unit or the second path switching unit is configured by a switch.

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