JP3035921B2 - High frequency power amplifier - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-frequency power amplifier, and more particularly to a circuit that prevents emitter-base reverse bias breakdown due to application of excessive input power in a common-emitter class AB power amplifier circuit. About.

[Conventional technology]

2. Description of the Related Art Conventionally, as a class AB power amplifier circuit using a common emitter transistor, there is a circuit shown in FIG. This circuit is connected to the strip line 7 as a load between the ground emitter transistor Q ₁ is a power supply terminal 3, the bias resistors R _1, R _2, and bias voltage divided by the temperature compensation diode D ₁ is, It is connected to the base of the transistor Q ₁ through a strip line 6. This circuit is connected to an input terminal 1 and an output terminal 3 via coupling capacitors C ₁ and C ₂ , respectively. That is, in this circuit, the voltage applied to the power supply terminal 3 is divided by the bias resistors R ₁ and R ₂ , and the divided voltage is applied to the base of the transistor 1 via the strip line 6.

[Problems to be solved by the invention]

Conventional class AB power amplifier circuit described above, when the voltage applied to the power supply terminal 3 is low, the base voltage of the transistor Q ₁ is lowered. At this time, when applying the excessive input power to the base of the transistor Q _1, the emitter-base of the transistor Q ₁ is reverse biased, since exceeding the emitter-base breakdown voltage BV _EBO, the transistor Q ₁ is the reverse bias breakdown There is a problem of causing.

An object of the present invention is to solve such a problem and prevent a voltage higher than the emitter-base breakdown voltage of the transistor from being applied even when excessive input power is applied to the base of the transistor, thereby preventing damage to the transistor. It is an object of the present invention to provide a high-frequency power amplifying device in which the high frequency power is prevented.

[Means for solving the problem]

In the high frequency power amplifier of the present invention, the power supply voltage is divided by a bias resistor and applied to the base as a bias voltage.
In a high-frequency power amplifier including a class AB emitter-grounded transistor, a directional coupler connected between a base of the transistor and a signal input terminal, and an input from the signal input terminal through one terminal of the directional coupler. A rectifier circuit that detects a part of the input signal and outputs the output voltage as an output voltage via a diode, a diode that is coupled to the anode side, grounds the cathode side, and maintains the voltage on the anode side at a constant voltage, Voltage supply means for superimposing the voltage on the anode side on the bias voltage and applying the voltage to the base.

〔Example〕

 Next, the present invention will be described with reference to the drawings.

FIG. 1 shows a circuit diagram of one embodiment of the present invention. This embodiment, on the base side of the transistor Q _1, and connect the directional coupler 8 for the high frequency power detection, the detected high frequency power diode D _2, a capacitor C _3, the bias voltage through the high-frequency choke L ₁ It is to be added. That is, a portion of the high frequency input power detected by the directional coupler 8 is converted into direct current during the energization of the diode D _2. The direct current, high-frequency choke coil L ₁ of the high-frequency signal blocking
The flow is energized to the diode D _1. This diode D ₁
Current flowing through are adjusting the coupling degree of the high frequency input to flow several mA or more fixed, to keep the potential of the diode D ₁ at a substantially constant potential (about 0.7V~0.8V).

On the other hand, the current flowing through the bias resistors R ₁ and R ₂
Voltage decreases As you lower the adding to, the voltage becomes smaller applied between the bias resistor R ₂ terminals, since the applied voltage of about 0.7~0.8V to the diode D ₁ as previously described, the base potential of the transistor Q ₁ is always 0.7~0.8V
That is, the transistor can be prevented from being damaged.

〔The invention's effect〕

As described above, according to the present invention, the input power is detected by the high-frequency input power detection coupler connected to the base of the transistor, and a current is caused to flow to the diode connected to the base of the transistor by this power. By obtaining a constant potential on the anode side, the base potential of the transistor can be kept constant.Thus, even when the power supply voltage is low, the base potential of the transistor becomes constant, and the reverse bias breakdown between the emitter and the base due to the excessive input power can be prevented. There is an effect that it can be stopped.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a high-frequency power amplifier according to a first embodiment of the present invention, and FIG. 2 is a circuit diagram of an example of a conventional high-frequency power amplifier. 1 ... input terminal, 2 ... output terminal, 3 ... power supply terminal, 6,
7 ... strip line, 8 ... directional coupler, C ₁ , C ₂ ...
... coupling capacitor, C ₃ ...... capacitors, D _1, D ₂ ...... diodes, L ₁ ...... high-frequency choke coil, Q ₁ ...... transistor, R _1, R ₂ ...... bias resistor, R3 ...... resistance.

Claims (1)

(57) [Claims] 1. A high-frequency power amplifier including a class-AB grounded-emitter transistor for dividing a power supply voltage by a bias resistor and applying the divided voltage to a base as a bias voltage, wherein a direction connected between a base of the transistor and a signal input terminal is provided. A rectifier circuit for detecting a part of an input signal input from the signal input terminal from one terminal of the directional coupler and outputting the output signal as an output voltage via a diode; and coupling the output voltage to the anode side. A diode that is provided with a cathode side to maintain the voltage on the anode side at a constant voltage;
A high-frequency power amplifier, comprising: voltage supply means for superimposing the anode-side voltage on the bias voltage and applying the voltage to the base.