JP4901804B2 - High frequency power amplifier - Google Patents

Description

  The present invention relates to a high-frequency power amplifier, and more particularly to a high-frequency power amplifier suitable for amplifying a transmission signal used in a high-frequency band such as a third generation mobile phone or a wireless LAN system.

  A circuit diagram of a conventional high-frequency power amplifier is shown in FIG. In FIG. 4, 110 is an input matching circuit, 120 is an output matching circuit, and 130 is a bias circuit.

  In the case of this high-frequency power amplifier, a matching circuit for impedance conversion corresponding to the operating frequency is required at the input / output terminals, an input matching circuit 110 is provided on the base side of the power amplification bipolar transistor Q1, and output is provided on the collector side. A matching circuit 120 is provided. Since this high-frequency power amplifier is a linear amplifier, the bias point of the power amplification bipolar transistor Q1 is generally set to an operating point of class A or class AB, and the DC voltage supplied from the DC power supply E1 is The signal is input to the base terminal of the power amplification bipolar transistor Q1 through the bias circuit 130. The DC voltage from the DC power supply E2 is supplied to the collector terminal of the power amplification bipolar transistor Q1 via the output matching circuit 120.

  In a communication device such as a wireless LAN, an input signal is not always turned on at the time of transmission of the system, but a burst operation that repeats an on state in which an input signal is input and an off state in which no input signal is input is performed. . In an off state in which no input signal is input, in order to reduce power consumption of the system, a method of using a high-frequency power amplifier in synchronization with a burst operation is often used. In the conventional high frequency power amplifier of FIG. 4, the DC power supply E1 is turned on / off in synchronization with the burst operation, but the DC power supply E2 is always turned on.

  In the above high-frequency power amplifier, the bipolar transistor Q1 changes its power amplification factor due to its own thermal response when the DC power supply E1 is turned on in a pulse operation and immediately after being turned on and after the time has elapsed for a while. However, the power amplification factor becomes larger after a certain period of time than immediately after turning on and falls within a certain value (see, for example, Non-Patent Document 1).

  In a wireless LAN system or the like, there is a monitor area other than transmission data for monitoring power immediately after the DC power source E1 is turned on. Using the power value in the monitor region, the receiving side analyzes the amplitude data or phase data of the digitally modulated signal after a certain time has elapsed and demodulates the signal. For example, FIG. 5A shows the time response of the output signal and the power monitor timing of the demodulated signal when the resistor R1 and the capacitor C1 are not provided from the high frequency power amplifier. As shown in FIG. 5A, when the power amplification factor of the actual data area is larger than that at the time of power monitoring immediately after the DC power supply E1 is turned on, the deviation from the reference monitor value becomes larger, and the receiver side The demodulated signal contains many errors, and accurate signal demodulation cannot be performed.

  Therefore, in the conventional high-frequency power amplifier, as shown in FIG. 4, a circuit in which a resistor R1 and a capacitor C1 as an example of a capacitance element are connected in parallel is connected in series between a DC power supply E1 and a bias circuit 130. An insertion method is generally used. In this case, an instantaneous current flows into the bias circuit 130 via the capacitor 1 immediately after the DC power supply E1 is turned on, and the same voltage as the DC voltage of the DC power supply E1 is applied to the bias circuit 130. The voltage value applied to the bias circuit 130 gradually decreases according to the time constant determined by the resistor R1 and the capacitor C1, and finally becomes a value corresponding to a voltage drop due to the current flowing through the resistor R1. Therefore, immediately after the power is turned on, the amplifier is applied with the DC voltage of the DC power supply E1, the bias point is set high, and the power amplification factor is increased. However, the current flows through the resistor R1 with time, and the voltage drops. It operates at the bias point, and the power amplification factor becomes small. Thereby, the correction of the power amplification factor by the thermal response is performed.

  The final voltage value supplied to the bias circuit 130 is smaller than the voltage value of the DC power source E1 by the amount of voltage drop due to the current flowing through the resistor R1. When the voltage value supplied to the bias circuit 130 is small, it is necessary to make the resistance value of the resistor R1 as small as possible in order to secure a value that can sufficiently operate the high-frequency power amplifier. However, if the resistance value of the resistor R1 is made as small as possible, the capacitance value of the capacitor C1 is also made small, and the time constant is too small, as shown in FIG. It can no longer be obtained.

  For this reason, it is necessary to increase the capacitance value of the capacitor C1, but when the capacitance value of the capacitor C1 is increased, the overshoot of the output signal before the power monitoring becomes too large as shown in FIG. 5C.

As described above, since the capacitance value of the capacitor C1 cannot be increased and the resistance value of the resistor R1 cannot be reduced too much, the voltage drop due to the resistor R1 cannot be ignored when the voltage of the DC power supply E1 is lowered, and the amplifier itself operates. Therefore, a sufficient bias voltage cannot be obtained. That is, the above high frequency power amplifier has a problem that it is not easy to cope with low voltage operation.
Sang-Woong Yoon, "Static and Dynamic Error Vector Magnitude Behavior of 2.4 GHz-Power Amplifier (Static and Dynamic Error Vector Magnitude Behavior of 2.4 -GHz Power Amplifier), IEEE TRANSACTIONS ON MICROWAVE THEORY AND TECHNIQUES, USA, I Triple E (IEEE), April 2007 (APRIL 2007) ), 55 (VOL. 55), No. 4 (NO. 4), p. 643-647

  Therefore, an object of the present invention is to provide a high-frequency power amplifier that is supplied with a DC voltage from a DC voltage source whose output is turned on and off in synchronization with a burst operation, and has a simple configuration to increase the power amplification factor after the DC voltage source is turned on. An object of the present invention is to provide a high-frequency power amplifier capable of reducing the voltage while achieving optimal communication by optimal correction.

In order to solve the above problems, a high-frequency power amplifier according to the present invention provides:
A high frequency power amplifier in which an external DC voltage source is turned on and off according to a burst operation that repeats a state in which an input signal is input and a state in which the input signal is not input, and a DC voltage is supplied from the external DC voltage source,
A power amplifying unit that is formed of at least one power amplification bipolar transistor and amplifies the input signal;
A reference voltage generating circuit for generating a reference voltage from a DC voltage supplied from the external DC voltage source;
A bias current amplifying unit which is formed of at least one bipolar transistor and supplies a bias current to the base of the power amplifying bipolar transistor of the power amplifying unit based on the reference voltage from the reference voltage generating circuit; Prepared,
Upper Symbol reference voltage generating circuit includes a first bipolar transistor of emitter-grounded DC voltage is applied to the collector via a first resistance from the external DC voltage source, the collector and base of said first bipolar transistor A second bipolar transistor connected to the base and emitter of the first bipolar transistor and having a DC voltage applied to the collector. The emitter of the second bipolar transistor is connected via a second resistor. Connected to the ground potential, a capacitor is connected in parallel to the second resistor, and the reference voltage is output from the emitter of the second bipolar transistor to the bias current amplifier .
Immediately after the external DC voltage source is turned on, the reference voltage becomes 0 V, and after the bias current supplied from the bias current amplification unit to the power amplification bipolar transistor increases,
As time elapses after the external DC voltage source is turned on, the reference voltage from the reference voltage generation circuit increases, and the bias current supplied from the bias current amplifier to the power amplification bipolar transistor decreases. characterized in that it.

  According to the high frequency power amplifier having the above configuration, immediately after the external DC voltage source is turned on, an instantaneous current flows through a capacitor connected in parallel to the second resistor. Therefore, the emitter of the second bipolar transistor of the reference voltage generating circuit The resistance value to ground is 0Ω. At this time, since the reference voltage from the reference voltage generation circuit is lowered in the bias current amplification unit, the bias current input to the base of the power amplification bipolar transistor of the power amplification unit increases. Therefore, the bias point of the power amplifying bipolar transistor of the power amplifying unit increases, and the power amplification factor increases. Then, with the passage of time, the current flowing through the capacitor decreases and becomes only the current flowing through the second resistor. Therefore, the resistance value between the emitter of the second bipolar transistor of the reference voltage generation circuit and the ground is the resistance value of only the second resistor. In this case, since the reference voltage from the reference voltage generation circuit is increased in the bias current amplification unit, the bias current input to the base of the power amplification bipolar transistor is reduced, and the power amplification bipolar transistor of the power amplification unit is reduced. The bias point decreases and the power amplification factor decreases.

  As described above, when the time elapses after the external DC voltage source is turned on, the power amplification factor becomes smaller than that immediately after the external DC voltage source is turned on, but the power amplification factor approaches the subsequent data area, and an error occurs on the receiving side. Less demodulation is possible. As a result, in a high-frequency power amplifier that is supplied with a DC voltage from a DC power supply whose output is turned on and off in synchronization with the burst operation, the power amplification factor after turning on the DC voltage source is optimally corrected with a simple configuration. It is possible to realize a high-frequency power amplifier capable of reducing the voltage while realizing simple communication.

  In one embodiment, a third resistor is connected between the emitter of the second bipolar transistor of the reference voltage generation circuit and the second resistor.

  According to the above embodiment, by connecting the third resistor between the emitter of the second bipolar transistor of the reference voltage generating circuit and the second resistor, the instantaneous current flows through the capacitor immediately after the external DC voltage source is turned on. In order to be suppressed by the third resistor, the resistance value between the emitter of the second bipolar transistor of the reference voltage generation circuit and the ground is equal to or greater than the resistance value of the third resistor, and the power amplification factor does not increase too much. The overshoot of the output signal can be suppressed.

  As is apparent from the above, according to the high frequency power amplifier of the present invention, in a high frequency power amplifier in which the DC voltage of the DC power supply is turned on and off in synchronization with the burst operation, the power amplification after the DC power supply voltage is turned on with a simple configuration It is possible to realize a high-frequency power amplifier capable of reducing the voltage while realizing good communication by optimally correcting the rate.

  Hereinafter, the high-frequency power amplifier of the present invention will be described in detail with reference to embodiments shown in the drawings.

[First Embodiment]
FIG. 1 shows a circuit diagram of a high frequency power amplifier according to a first embodiment of the present invention. As shown in FIG. 1, the high-frequency power amplifier of the first embodiment includes an input matching circuit 10 having an input terminal A connected to the input side, a base connected to the output side of the input matching circuit 10, and an emitter. A power amplifying bipolar transistor Q1 as an example of a power amplifying unit connected to the ground potential, and an output matching circuit in which the collector and input of the power amplifying bipolar transistor Q1 are connected and the output side is connected to the output terminal B. 20. The high-frequency power amplifier includes a reference voltage generation circuit 30 that generates a reference voltage from a DC voltage supplied from a DC power supply E1 as an example of an external DC voltage source, and a reference voltage from the reference voltage generation circuit 30. And a bias current amplifier 40 for supplying a bias current to the base terminal of the bipolar transistor Q1. The DC power supply E1 is turned on and off in response to a burst operation in which an input signal is input and an input signal is not input.

  The reference voltage generation circuit 30 includes a resistor R2 (first resistor) having one end connected to the positive electrode side of the DC power supply E1, and a bipolar transistor Q2 (first bipolar transistor) having a collector connected to the other end of the resistor R2. ), A resistor R3 connected between the emitter of the bipolar transistor Q2 and the ground, and a bipolar transistor Q3 (first transistor) having a base connected to the collector of the bipolar transistor Q2 and an emitter connected to the base of the bipolar transistor Q2. 2 bipolar transistors), a resistor R1 (second resistor) connected between the emitter of the bipolar transistor Q3 and the ground, and a capacitor C1 connected in parallel to the resistor R1. The positive side of the DC power source E2 is connected to the collector of the bipolar transistor Q3.

  The bias current amplifying unit 40 includes a resistor R5 having one end connected to the positive electrode side of the DC power supply E1, a second end connected to the collector of the resistor R5, and an emitter having a base connected to the emitter of the bipolar transistor Q3. A grounded bipolar transistor Q4, a bipolar transistor Q5 having a base connected to the collector of the bipolar transistor Q3 and a collector connected to the positive side of the DC power supply E2, and a resistor R6 having one end connected to the emitter of the bipolar transistor Q5 have. The other end of the resistor R6 is connected to the base of the power amplification bipolar transistor Q1.

  The bipolar transistors Q1 to Q5 are NPN transistors.

As shown in FIG. 1, since a parallel circuit comprising a resistor R1 and a capacitor C1 is inserted on the emitter side of the bipolar transistor Q3, an instantaneous current flows through the capacitor C1 immediately after the DC power supply E1 is turned on. The resistance value between the emitter of transistor Q3 and ground appears to be 0Ω. At this time, the reference voltage output from the reference voltage generation circuit 30 becomes 0V, and in the bias current amplifier 40, the current flowing through the resistor R5 increases, and the base current of the DC transistor for DC amplification Q5 increases. For this reason, the bias current input to the base of the bipolar transistor Q1 for power amplification increases and the power amplification factor increases. Then, with the passage of time, the current flowing through the capacitor C1 decreases and becomes only the current flowing through the resistor R1. Therefore, the resistance value between the emitter of the bipolar transistor Q3 and the ground is the resistance value of only the resistor R1, and in this case, the bias current input to the base of the bipolar transistor Q1 for power amplification decreases .

  As a result, the power amplification factor of the high-frequency power amplifier is smaller than that immediately after the DC power supply E1 is turned on. The time response of the output signal and the timing of signal monitoring at this time are shown in FIG. 2A. The rate approaches the subsequent data area, and demodulation with less error becomes possible. Further, since the DC voltage of the DC power supply E1 does not cause a voltage drop, it is possible to cope with a low voltage.

[Second Embodiment]
FIG. 3 shows a circuit diagram of the high-frequency power amplifier according to the second embodiment of the present invention. The high-frequency power amplifier according to the second embodiment has the same configuration as the high-frequency power amplifier according to the first embodiment except for the reference voltage generation circuit, and the same components are denoted by the same reference numerals and description thereof is omitted. .

  The reference voltage generation circuit 50 of the high-frequency power amplifier according to the second embodiment includes a resistor R2 (first resistor) having one end connected to the positive electrode side of the DC power supply E1, and a collector connected to the other end of the resistor R2. A base is connected to the bipolar transistor Q2 (first bipolar transistor), the resistor R3 connected between the emitter of the bipolar transistor Q2 and the ground, the collector of the bipolar transistor Q2, and the emitter is the base of the bipolar transistor Q2. Connected between the other end of the resistor R4 and the ground, the bipolar transistor Q3 (second bipolar transistor) connected to the resistor, the resistor R4 (third resistor) having one end connected to the emitter of the bipolar transistor Q3 A resistor R1 (second resistor) and a capacitor C1 connected in parallel to the resistor R1. Yes. The positive side of the DC power source E2 is connected to the collector of the bipolar transistor Q3.

  By inserting a parallel circuit composed of a resistor R1 and a capacitor C1 into a portion grounded via a resistor R4 from the emitter side of the bipolar transistor Q3, the capacitor C1 is connected to an instantaneous current immediately after the DC power supply E1 is turned on. Therefore, the resistance value between the emitter of the bipolar transistor Q3 and the ground appears only as the resistance value of the resistor R4. At this time, the reference voltage output from the reference voltage generation circuit 30 is a voltage drop of the resistance value of the resistor R4, and the current flowing through the resistor R5 is increased in the bias current amplifier 40, and the DC transistor for amplifying a DC transistor Q5 The base current increases. Therefore, the bias point of the power amplification bipolar transistor Q1 is increased, and the power amplification factor is increased. Then, with the passage of time, the current flowing through the capacitor C1 decreases and becomes only the current flowing through the resistor R1. Therefore, the resistance value between the emitter of the bipolar transistor Q3 and the ground is [resistance value of the resistor R1 + resistance value of the resistor R4]. In this case, the bias point of the bipolar transistor Q1 for power amplification is lowered.

  As a result, the power amplification factor of the high frequency power amplifier is smaller than that immediately after the DC power supply E1 is turned on. The time response of the output signal and the timing of signal monitoring at this time are shown in FIG. 2B. The rate approaches the subsequent data area, and demodulation with less error becomes possible. Further, since the DC voltage of the DC power supply E1 does not cause a voltage drop, it is possible to cope with a low voltage.

  In the high frequency power amplifier, a resistor R4 (third resistor) is connected between the emitter of the second bipolar transistor Q3 of the reference voltage generating circuit 50 and the resistor R1 (second resistor), thereby providing a DC power supply E1. Since the instantaneous current of the capacitor C1 is suppressed by the resistor R4 immediately after turning ON, the resistance value between the emitter of the second bipolar transistor Q3 of the reference voltage generation circuit 50 and the ground becomes the resistance value of the resistor R4, and the power The amplification factor does not become too large, and the overshoot of the output signal can be suppressed as shown in FIG. 2B.

  In the first and second embodiments, an NPN transistor is used. However, a circuit may be configured by using a PNP transistor. In this case, the power supply side and the ground potential are opposite in polarity.

  The bias current amplification unit 40 is not limited to the circuit configuration of the first and second embodiments, and the bias current is increased as the reference voltage from the reference voltage generation circuit is increased, while the bias current is decreased as the reference voltage is decreased. Any bias current amplifying unit having a circuit configuration may be used.

  Although specific embodiments of the present invention have been described, the present invention is not limited to the first and second embodiments described above, and various modifications can be made within the scope of the present invention.

That is, a high-frequency power amplifier in which an external DC voltage source is turned on and off according to a burst operation that repeats a state in which an input signal is input and a state in which the input signal is not input, and a DC voltage is supplied from the external DC voltage source. And
A power amplifying unit that is formed of at least one power amplification bipolar transistor and amplifies the input signal;
A reference voltage generating circuit for generating a reference voltage from a DC voltage supplied from the external DC voltage source;
A bias current amplifying unit which is formed of at least one bipolar transistor and supplies a bias current to the base of the power amplifying bipolar transistor of the power amplifying unit based on the reference voltage from the reference voltage generating circuit; Prepared,
The bias current amplifying unit increases the bias current as the reference voltage from the reference voltage generation circuit increases, and decreases the bias current as the reference voltage decreases.
In the reference voltage generation circuit, a first emitter-grounded bipolar transistor to which a DC voltage from the external DC voltage source is applied to a collector via a first resistor is connected to a collector and a base of the first bipolar transistor. And a second bipolar transistor in which a base and an emitter of the first bipolar transistor are connected and a DC voltage is applied to a collector, and the emitter of the second bipolar transistor is connected via a second resistor. Any device may be used as long as it is connected to the ground potential, a capacitor is connected in parallel to the second resistor, and the reference voltage is output from the emitter of the second bipolar transistor to the bias current amplifier.

  In the first and second embodiments described above, a high-frequency power amplifier including a power amplifier composed of one power amplification bipolar transistor is described. However, in order to amplify a larger power, a plurality of bipolar transistors connected in parallel are used. You may use for a power amplification part. Furthermore, in order to increase the amplification factor, a plurality of high-frequency power amplifiers may be connected in series, or a plurality of power amplification bipolar transistors may be connected in series.

FIG. 1 is a circuit diagram of a high frequency power amplifier according to a first embodiment of the present invention. FIG. 2A is a diagram showing time response and demodulated signal monitoring timing by the high-frequency power amplifier according to the first embodiment. FIG. 2B is a diagram showing time response and demodulated signal monitoring timing by the high-frequency power amplifier according to the second embodiment of the present invention. FIG. 3 is a circuit diagram of a high frequency power amplifier according to a second embodiment of the present invention. FIG. 4 is a circuit diagram showing a conventional first high-frequency power amplifier. FIG. 5A is a diagram illustrating the time response of the output signal and the monitor timing of the demodulated signal when there is no resistor and capacitor. FIG. 5B is a diagram showing the time response of the output signal and the monitor timing of the demodulated signal. FIG. 5C is a diagram showing the time response of the output signal and the monitor timing of the demodulated signal when the capacitance value of the capacitor is increased.

Explanation of symbols

Q1-Q5 ... Bipolar transistors R1-R6 ... Resistors C1 ... Capacitors E1, E2 ... DC power supply A ... Input terminal B ... Output terminal

Claims (2)

A high frequency power amplifier in which an external DC voltage source is turned on and off according to a burst operation that repeats a state in which an input signal is input and a state in which the input signal is not input, and a DC voltage is supplied from the external DC voltage source,
A power amplifying unit that is formed of at least one power amplification bipolar transistor and amplifies the input signal;
A reference voltage generating circuit for generating a reference voltage from a DC voltage supplied from the external DC voltage source;
A bias current amplifying unit which is formed of at least one bipolar transistor and supplies a bias current to the base of the power amplifying bipolar transistor of the power amplifying unit based on the reference voltage from the reference voltage generating circuit; Prepared,
Upper Symbol reference voltage generating circuit includes a first bipolar transistor of emitter-grounded DC voltage is applied to the collector via a first resistance from the external DC voltage source, the collector and base of said first bipolar transistor A second bipolar transistor connected to the base and emitter of the first bipolar transistor and having a DC voltage applied to the collector. The emitter of the second bipolar transistor is connected via a second resistor. Connected to the ground potential, a capacitor is connected in parallel to the second resistor, and the reference voltage is output from the emitter of the second bipolar transistor to the bias current amplifier .
Immediately after the external DC voltage source is turned on, the reference voltage becomes 0 V, and after the bias current supplied from the bias current amplification unit to the power amplification bipolar transistor increases,
As time elapses after the external DC voltage source is turned on, the reference voltage from the reference voltage generation circuit increases, and the bias current supplied from the bias current amplifier to the power amplification bipolar transistor decreases. A high frequency power amplifier. The high frequency power amplifier according to claim 1,
A high frequency power amplifier comprising a third resistor connected between an emitter of the second bipolar transistor of the reference voltage generating circuit and the second resistor.

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