JP2004134823A - High frequency amplifier - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a high frequency amplifier capable of sufficiently reducing the operating current at a small output without deteriorating the linearity of the amplifier independently of the magnitude of the output power. <P>SOLUTION: The bases of a bipolar transistor 1 whose emitter size is larger and a bipolar transistor 1 whose emitter size is smaller are connected through capacitors 3, 4 in terms of an RF, and a power source 16 applies a bias to the collectors of the bipolar transistors 1, 2 through a collector power supply 15 such as a quarter-wavelength line. Bias power supply circuits 5, 6 respectively supply a bias to the bipolar transistors so that the respective base levels are equal to each other, an input matching circuit 7 converts the input impedance of the bipolar transistors with respect to the input impedance such as 50Ω, an output matching circuit 8 sets the impedance viewed from the bipolar transistors so that desired power can be extracted across a 50Ω load, and an external control circuit 9 turns ON/OFF the bias power supplies 5, 6 depending on the magnitude of the output power being a requirement of the high frequency amplifier. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a high-frequency transistor, particularly to a high-frequency amplifier using a bipolar transistor.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, a high-frequency amplifier configured using, for example, a bipolar transistor for wireless communication is designed so that current consumption of the entire amplifier is minimized at a desired output power.
[0003]
In particular, in the case of high-frequency amplifiers used for transmission of digital mobile phones, the linearity of the high-frequency amplifier is controlled so as to suppress the amplification distortion that causes unnecessary radiation in order to avoid leakage to adjacent channels. Is designed so that the current consumption is minimized in a state where is secured.
[0004]
The above-described conventional high-frequency amplifier will be described below with reference to the drawings.
FIG. 5 is an explanatory diagram of the configuration and operation of a conventional high-frequency amplifier, and FIG. 5B shows the relationship between the output power and the current consumption of the high-frequency amplifier. As shown in FIG. 5B, the operating current in the low power region where the output power is lower than, for example, 10 dBm becomes substantially equal to the bias current of the transistor of the high-frequency amplifier, and the input power to the input side of the high-frequency amplifier is further reduced. However, it cannot be reduced below this current value.
[0005]
In general, in a high-frequency amplifier, in order to secure linearity in a high power region where output power is higher than, for example, 10 dBm and to improve distortion characteristics, it is necessary to operate a transistor in a class-A operation by operating a transistor at a bias point. , It is necessary to set the bias current large so as to be の of the high frequency current amplitude. In this case, current consumption at the time of low power operation increases.
[0006]
Therefore, in the case of a high-frequency power amplifier used for transmission of a mobile phone, the transistor operates in a class AB operation in which the bias point is shallower and a bias current value is lower than that in the class A operation in consideration of efficiency at the maximum output and linearity. However, even in this case, the current consumption at low power is a problem.
[0007]
When a high-frequency amplifier having the above characteristics is used in a wireless communication system, particularly a system in which the output of a terminal is frequently switched by a distance between base stations or a user, such as a CDMA system, the high-frequency amplifier is used. The power is rarely used at the designed maximum power, and the frequency of use at low power with low power load efficiency increases. For this reason, in such a system, the high-frequency amplifier is configured so that the current at low power can be reduced by adjusting the bias current of the transistor according to the output power.
[0008]
FIG. 5A shows a configuration example of a conventional high-frequency amplifier. The voltage source 16 supplies a bias to the collector of the bipolar transistor 1 through a collector current supply circuit 15 such as a λ / 4 wavelength line. A bias supply circuit 5 supplied with a voltage from a variable voltage source 17 is connected to the base of the bipolar transistor 1 to supply a bias. By changing the voltage of the variable voltage source 17 according to the output power, the base current is changed and the bias current is adjusted.
[0009]
When the input impedance is, for example, 50Ω, the input matching circuit 7 converts the input impedance of the bipolar transistor 1 to 50Ω, and the output matching circuit 8 outputs the output impedance when the load impedance on the output side is, for example, 50Ω. , The impedance as viewed from the output side of the bipolar transistor 1 is set so as to extract desired power to the 50Ω load. Reference numeral 13 denotes a high-frequency power input terminal, and 14 denotes a high-frequency power output terminal.
[0010]
FIG. 5C shows output power-current consumption characteristics when the bias current of the high frequency amplifier shown in FIG. 5A is changed by changing the bias voltage.
[0011]
[Problems to be solved by the invention]
However, in the above-described conventional high-frequency amplifier, when the method of changing the bias current of the transistor according to the output power is used, for example, by reducing the bias current, as shown in FIG. The operating current at the time of low power is reduced, but at the same time, as shown in FIG. On the other hand, in order to ensure sufficient linearity, it is necessary to increase the bias current, and there is a problem in that the reduction of the operating current at low power is limited.
[0012]
In particular, in high-frequency amplifiers using current-driven bipolar transistors, the bias point fluctuates greatly with an increase in input power due to the effect of the transistor output load circuit. The deterioration of the properties is remarkable.
[0013]
FIG. 5D shows a case where the bias voltage of the bipolar transistor 1 of the high-frequency amplifier shown in FIG. 5A is changed by the variable voltage source 17 through the bias supply circuit 5 to change the bias current to the base. This shows that the output power-gain characteristics of the graph indicate that the lower the bias current, the greater the linearity degradation.
[0014]
The present invention solves the above-mentioned conventional problems, and provides a high-frequency amplifier capable of sufficiently reducing the operating current at low output without deteriorating the linearity of the amplifier regardless of the magnitude of output power. provide.
[0015]
[Means for Solving the Problems]
In order to solve the above problem, a high frequency amplifier of the present invention is configured using a bipolar transistor, amplifies input high frequency power by the bipolar transistor, and outputs the amplified high frequency power through a load circuit connected to the output side of the bipolar transistor. In the high frequency amplifier, a plurality of bipolar transistors having different emitter sizes are used as the bipolar transistors, each collector of the plurality of bipolar transistors is connected to one, each emitter is grounded, and each base is DC-separated from each other. And a bias supply control unit that is formed on the same semiconductor chip as the bipolar transistor or on a different semiconductor chip for each of the bases and individually controls on / off of the supply of a bias to the base. Control means Characterized by being configured to on-off control the bias supply according to the magnitude of the output power.
[0016]
As described above, the bias supply to the base is individually turned on / off according to the magnitude of the output power, and the bipolar transistors having different emitter sizes are switched to operate. By supplying a fixed bias current corresponding to the emitter size based on the bias current value, the bias current can be reduced in the low power region without changing the bias point.
[0017]
BEST MODE FOR CARRYING OUT THE INVENTION
The high-frequency amplifier according to claim 1 of the present invention is configured using a bipolar transistor, amplifies the input high-frequency power by the bipolar transistor, and outputs the amplified high-frequency power through a load circuit connected to the output side of the bipolar transistor. In the amplifier, a plurality of bipolar transistors having different emitter sizes are used as the bipolar transistors, each collector of the plurality of bipolar transistors is connected to one, each emitter is grounded, and each base is DC-separated from each other. And a bias supply control means formed on the same semiconductor chip as the bipolar transistor or on a different semiconductor chip for each of the bases and individually controlling on / off of the bias supply to the base. The output power Configured to on-off control of the bias supply according to the magnitude.
[0018]
A high-frequency amplifier according to a second aspect is configured such that the load circuit according to the first aspect has a load impedance switching function using an external voltage.
The high-frequency amplifier according to claim 3, wherein the high-frequency amplifier is configured using a bipolar transistor, amplifies the input high-frequency power by the bipolar transistor, and outputs the amplified high-frequency power through a load circuit connected to the output side of the bipolar transistor. As the bipolar transistors, a plurality of bipolar transistors having different emitter sizes are used, the collectors of the plurality of bipolar transistors are connected through the load circuit in a state where they are DC-separated from each other, each emitter is grounded, and each base is connected to each other. Bias supply control means which is connected in a state of being separated in direct current and is formed on the same semiconductor chip as the bipolar transistor or on a different semiconductor chip for each of the bases and individually controls on / off of bias supply to the base. ,Previous A bias supply control unit, the bias supply configured to on-off control in accordance with the magnitude of the output power, the load circuit is configured to have a load impedance switching function according to at least one or more external voltage.
[0019]
A high-frequency amplifier according to a fourth aspect has a configuration in which the high-frequency amplifier according to the first, second, or third aspect is connected in multiple stages as one power amplifier.
In the high-frequency amplifier according to claim 5, one or more multi-stages of the high-frequency amplifier according to claim 1 or 2 or 3 are connected as one power amplifier, and the gain is variably controlled by an external voltage in a preceding stage thereof. The configuration is such that a variable gain high frequency amplifying unit is connected.
[0020]
As described above, this high-frequency amplifier uses two or more bipolar transistors whose bases are connected to each other in a dc-separated manner, and individually controls on / off of the bias supply to each base. It is characterized by having means.
[0021]
Hereinafter, for simplicity of description, a case having two bases will be described.
At the time of high power output, two bipolar transistors are turned on, or a bipolar transistor having a large base region is turned on, and the other is turned off. At the time of low power output, a bipolar transistor having a small base region is turned on, and the other is turned off. For example, if the same potential is applied to the base of the bipolar transistor through the bias supply control means, the bias current is determined by the emitter size of the bipolar transistor that is turned on.
[0022]
Therefore, as compared with the conventional case where the bias current is reduced without changing the size of the bipolar transistor, the bias supply to the base is individually turned on / off according to the magnitude of the output power, and the bipolar transistor having a different emitter size is operated by switching. By supplying a fixed bias current corresponding to the emitter size to the bipolar transistor during operation based on the bias current value per unit size of the emitter, the bias point is not changed in the low power region. , The bias current can be reduced.
[0023]
Hereinafter, a high-frequency amplifier according to an embodiment of the present invention will be specifically described with reference to the drawings.
(Embodiment 1)
The high-frequency amplifier according to the first embodiment of the present invention will be described in detail with reference to FIG.
[0024]
FIG. 1 is an explanatory diagram of the configuration and operation of the high-frequency amplifier according to the first embodiment, and FIG. 1A is a configuration example of the high-frequency amplifier. As shown in FIG. 1A, the bases of a bipolar transistor 1 having a large emitter size and a bipolar transistor 2 having a small emitter size are short-circuited in terms of RF (separated in terms of direct current) by capacitors 3 and 4. Connected. A voltage source 16 supplies a power supply bias to each collector of the bipolar transistor 1 and the bipolar transistor 2 through a collector current supply circuit 15 such as a λ / 4 wavelength line. Bias supply circuits 5 and 6 supply power for bias to different bipolar transistors so that their base potentials are equal.
[0025]
The input matching circuit 7 converts the impedance of the bipolar transistor to the input side impedance of, for example, 50Ω, and the output matching circuit 8 extracts the desired power for the load side impedance of, for example, 50Ω. The impedance matching as seen from the output side of the bipolar transistor is set.
[0026]
The external control circuit 9 is configured by, for example, a microprocessor to control the bias supply circuits 5 and 6 to be turned on and off according to the magnitude of the output power required for the high-frequency amplifier, and has a large power level (for example, an output power of 10 dBm or more). When the power level is low (for example, less than 10 dBm), only the bipolar transistor 2 with the smaller emitter size is turned on, and the bipolar transistor 1 with the larger emitter size is turned on. Turn off.
[0027]
The operating current at low power is determined by the ratio of the two emitter sizes. For example, if the emitter size ratio is 4: 1, the operating current at low power is reduced from 100 mA in the conventional example to 20 mA. It can be greatly reduced. The output power-current characteristics in this case are shown in FIG. As shown in the output power-gain characteristics of FIG. 1C, although the gain is discontinuous at the time of switching, it can be seen that the linearity in each power region is maintained.
[0028]
In the present embodiment, switching is performed for two bipolar transistors. However, if three or more bipolar transistors are used, more power regions can be set, and control in three or more multi-stages can be performed. It goes without saying that you can do it.
[0029]
Further, it goes without saying that bipolar transistors having different emitter sizes may be configured by connecting unit bipolar transistors having a small size in parallel in order to improve high-frequency characteristics.
(Embodiment 2)
Next, a high-frequency amplifier according to Embodiment 2 of the present invention will be described in detail with reference to FIG.
[0030]
FIG. 2 is an explanatory diagram of the configuration and operation of the high-frequency amplifier according to the second embodiment, and FIG. 2A is a configuration example of the high-frequency amplifier. As shown in FIG. 2A, bases of a bipolar transistor 1 having a large emitter size and a bipolar transistor 2 having a small emitter size are RF-connected by capacitors 3 and 4. A voltage source 16 supplies a power supply bias to the collector of the bipolar transistor 1 through a collector current supply circuit 15 such as a λ / 4 wavelength line. The bias supply circuits 5 and 6 supply bias to different bipolar transistors so that their base potentials are equal.
[0031]
The input matching circuit 7 converts the impedance of the bipolar transistor into 50Ω. An impedance switching circuit 10 that can be controlled by an external voltage using a PIN diode is connected to the output matching circuit 8.
[0032]
As in the first embodiment, the external control circuit 9 is, for example, a microprocessor that performs on / off control of the bias supply to each base through the bias supply circuits 5 and 6 according to the magnitude of the output power required for the high-frequency amplifier. When the power level is high (output power 10 dBm or more), both bipolar transistors are turned on. When the power level is low (output power less than 10 dBm), only the bipolar transistor 2 with the smaller emitter size is turned on, and the bipolar transistor with the larger emitter size is turned on. The transistor 1 is turned off.
[0033]
On the other hand, the impedance switching circuit 10 is controlled by the external control circuit 9 and is turned off when the power level is high, and the impedance viewed from the two devices shows almost the impedance characteristic of only the output matching circuit 8, but is turned on when the power level is low. The impedance seen from the device side shows an impedance conversion characteristic by the output matching circuit 8 and the impedance switching circuit 10 such that the impedance becomes higher than when the power level is high.
[0034]
In the first embodiment, the load circuit of the bipolar transistor is optimized when the power level is high, and the load circuit of the bipolar transistor 2 is not optimized when the power level is low.
[0035]
In contrast to the first embodiment, in the second embodiment, the load impedance of the bipolar transistor 2 is increased when the power level is low, and the impedance matching is improved. Current can be realized. The output power-current characteristics in this case are shown in FIG.
[0036]
By converting the impedance of the load circuit as viewed from the device side from 5Ω at high power to 20Ω at low power, the operating current near 10 dBm at low power level can be reduced by about 15 mA compared to the case of the first embodiment. it can.
[0037]
According to the present embodiment, a method of switching the impedance of only the load circuit without switching the transistor by the bias supply circuit as in the present embodiment can be considered, but generally the maximum efficiency is obtained by the emitter size of the bipolar transistor. Since the output power is determined, it is more advantageous to switch the transistors by the bias supply circuit as in the present embodiment, in order to realize a low current at a wide power level.
[0038]
In this embodiment, switching is performed for two bipolar transistors. However, if three or more bipolar transistors are used, more power regions can be set, and control in three or more multi-stages can be performed. It goes without saying that you can do it.
[0039]
Further, it goes without saying that bipolar transistors having different emitter sizes may be configured by connecting unit bipolar transistors having a small size in parallel in order to improve high-frequency characteristics.
(Embodiment 3)
Next, a high-frequency amplifier according to Embodiment 3 of the present invention will be described in detail with reference to FIG.
[0040]
FIG. 3 is a circuit block diagram showing a configuration of the high-frequency amplifier according to the third embodiment. As shown in FIG. 3, the bases of a bipolar transistor 1 having a large emitter size and a bipolar transistor 2 having a small emitter size are RF-connected by capacitors 3 and 4. A power supply bias is individually supplied to each collector of the bipolar transistor 1 and the bipolar transistor 2 by a voltage source 16 through a collector power supply circuit 15 such as a λ / 4 wavelength line. Bias supply circuits 5 and 6 supply bias to different bipolar transistors so that their base potentials are equal.
[0041]
The input matching circuit 7 converts the impedance of the bipolar transistor into 50Ω. In the output matching circuit 11 that combines the two output powers from the bipolar transistor 1 and the bipolar transistor 2 as inputs, it is possible to control the impedance switching by an external voltage by using a PIN diode on the output side of the small-sized bipolar transistor. A possible impedance switching circuit 10 is connected.
[0042]
The same effect can be obtained by the same switching method as in the second embodiment, but the difference from the second embodiment is that the impedance switching circuit 10 is connected to the load circuit of the bipolar transistor 2 having a low power output. Thus, at the time of low power, the current consumption at the time of high power can be reduced while obtaining the same effect as in the second embodiment. In an impedance switching circuit using a PIN diode, a loss due to the impedance switching circuit becomes a problem due to the capacitance and resistance components of the PIN diode.
[0043]
Since the loss of the impedance switching circuit used in the present embodiment is about 0.5 dB, when the output of the bipolar transistor is 30 dBm (collector voltage 3.5 V, collector efficiency 50%), the loss of the output circuit in the second embodiment. Causes the amplifier output to be 29.5 dBm, but in the present embodiment, the emitter size ratio is 29.9 dBm since the emitter size ratio is 4: 1. Comparing the efficiency difference in this case, a very large improvement effect of about 4% can be obtained.
[0044]
In this embodiment, switching is performed for two bipolar transistors. However, if three or more bipolar transistors are used, more power regions can be set, and control in three or more multi-stages can be performed. It goes without saying that you can do it.
[0045]
Further, it goes without saying that bipolar transistors having different emitter sizes may be configured by connecting unit bipolar transistors having a small size in parallel in order to improve high-frequency characteristics.
(Embodiment 4)
Next, a high-frequency amplifier according to Embodiment 4 of the present invention will be described in detail with reference to FIG.
[0046]
FIG. 4 is an explanatory diagram of the configuration and operation of the high-frequency amplifier according to the fourth embodiment, and FIG. 4A is a configuration example of the high-frequency amplifier. In the high-frequency amplifier according to the fourth embodiment, as shown in FIG. 4A, a variable-gain high-frequency amplifier 12 whose gain can be variably controlled by an external voltage is connected in front of the high-frequency amplifier according to the first embodiment. I have.
[0047]
The operation other than that of the variable gain high frequency amplifying unit 12 is as described in the first embodiment. As described above, the impedance of the bipolar transistor 2 operating at a low power is insufficiently matched, so that the gain is reduced. The external control circuit 9 controls the variable gain high frequency amplifying unit 12 at the same time as the switching of the bipolar transistor so as to compensate for the decrease in gain at low power, thereby increasing the gain at low power. Conversely, when the power is high, the gain of the variable gain high frequency amplifying section 12 is reduced. FIG. 4B shows a gain-output power characteristic in this case.
[0048]
In this manner, a high-frequency amplifier with low power consumption and low gain fluctuation can be easily realized.
[0049]
【The invention's effect】
As described above, according to the present invention, the bias supply to the base is individually turned on / off according to the magnitude of the output power, and the bipolar transistors having different emitter sizes are switched to operate. By supplying a fixed bias current corresponding to the emitter size based on the bias current value per unit size of the emitter, the bias current can be reduced in the low power region without changing the bias point.
[0050]
Therefore, regardless of the magnitude of the output power, the operating current at the time of low power output can be sufficiently reduced without deteriorating the linearity of the amplifier, and unnecessary radiation due to distortion during amplification can be suppressed to the adjacent channel. Leakage can be reduced, and power consumption can be efficiently reduced according to the output power.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating the configuration and operation of a high-frequency amplifier according to a first embodiment of the present invention; FIG. 2 is a diagram illustrating the configuration and operation of a high-frequency amplifier according to a second embodiment of the present invention; FIG. 4 is a circuit block diagram illustrating a configuration of a high-frequency amplifier according to Embodiment 3. FIG. 4 is a diagram illustrating the configuration and operation of a high-frequency amplifier according to Embodiment 4 of the present invention. FIG. 5 is a diagram illustrating the configuration and operation of a conventional high-frequency amplifier. Explanation of code]
1 Bipolar transistor (large emitter size)
2 Bipolar transistor (small emitter size)
3, 4 Capacitor 5, 6 Bias supply circuit 7 Input matching circuit 8 Output matching circuit 9 External control circuit 10 Impedance switching circuit 11 Output matching circuit 12 Variable gain high frequency amplifier 13 High frequency power input terminal 14 High frequency power output terminal 15 Collector current supply Circuit 16 Voltage source 17 Variable voltage source

Claims (5)

In a high-frequency amplifier configured using a bipolar transistor, amplifying the input high-frequency power by the bipolar transistor and outputting the amplified power through a load circuit connected to the output side of the bipolar transistor, the bipolar transistor includes a plurality of transistors having different emitter sizes. The collectors of the plurality of bipolar transistors are connected to one another, the emitters are grounded, and the bases are connected in a state of being separated from each other in a direct current manner. And a bias supply control unit that is formed on the same semiconductor chip or a different semiconductor chip, and individually controls on / off of the bias supply to the base, wherein the bias supply control unit controls the bias supply according to the magnitude of the output power. On-off High-frequency amplifier, characterized by being configured such that Gosuru. 2. The high-frequency amplifier according to claim 1, wherein the load circuit has a load impedance switching function based on an external voltage. In a high-frequency amplifier configured using a bipolar transistor, amplifying the input high-frequency power by the bipolar transistor and outputting the amplified power through a load circuit connected to the output side of the bipolar transistor, the bipolar transistor includes a plurality of transistors having different emitter sizes. Using bipolar transistors, the collectors of the plurality of bipolar transistors are connected through the load circuit in a state where they are DC-separated from each other, each emitter is grounded, and each base is connected in a state where they are DC-separated from each other, A bias supply control unit formed on the same semiconductor chip as the bipolar transistor or a different semiconductor chip for each of the bases and individually controlling on / off of a bias supply to the base; and Large and small the bias supply configured to on-off control in response to said load circuit, high-frequency amplifier, characterized by being configured to have a load impedance switching function by external voltage to at least one or more. A high-frequency amplifier comprising a plurality of the high-frequency amplifiers according to claim 1, 2, or 3 connected as one power amplifier. One or more multi-stage high-frequency amplifiers according to claim 1 or claim 2 or 3 are connected as a single power amplifier, and a gain variable high-frequency amplification unit whose gain can be variably controlled by an external voltage is connected to a preceding stage thereof. A high-frequency amplifier characterized in that:

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