JPH0147046B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a power amplifier for a mobile phone for a car phone in which overvoltage, surge voltage, etc. are a problem.

First, a power amplifier used in a conventional mobile phone mobile device will be explained with reference to FIG. The power amplifier shown in FIG. 1 is an example in which the first stage transistor amplifier TR1 is of class B or class AB, and the power supply voltage is controlled. The power amplifier is a multistage connection of transistor amplifiers TR1 to TRn, and a portion of the high frequency output is extracted from the final stage by a coupler 2. This detected high frequency output is amplified by an OP amplifier. The OP amplifier is configured so that when the high frequency output increases, the output decreases. Therefore, when the high frequency output is about to change in this way, the first transistor 5 operates in the non-conducting direction, and the second transistor 3 also operates in the non-conducting direction, and the transistor amplifier
The automobile battery voltage applied to TR1 is controlled to decrease. As a result, the amplification degree of the transistor amplifier TR1 decreases, and the high frequency output of the transistor amplifier TRn is suppressed to a constant value. When the high frequency output changes in the direction of decreasing, the control opposite to the above is performed by the feedback loop composed of the OP amplifier and the first and second transistors, and the amplification degree of the transistor amplifier TR1 is As a result, the high frequency output of the transistor amplifier TRn is also held at a constant value.

In the above configuration, when there is no high wave output, the output of the OP amplifier is maximum, and the first and second transistors are completely conductive, so the transistor amplifier TR1 receives overvoltage/surge voltage from the automobile battery. A voltage containing this will be directly applied.

Normally, no problem occurs if the transistor amplifier operates in class A mode, but in this case, since the transistor amplifier TR1, which is power-controlled, operates in class B or AB mode, there is a risk of overcurrent damage.

An object of the present invention is to provide a power amplifier for a mobile phone for a mobile phone in which the power supply voltage is controlled to a transistor amplifier operating in class B or AB class. An object of the present invention is to provide an overvoltage/surge voltage protection circuit that can protect against surge voltages.

In order to achieve the above object, the overvoltage/surge voltage protection circuit in a high frequency power amplifier according to the present invention connects a plurality of transistor amplifiers in multiple stages, extracts a part of the high frequency output from the final stage, and uses the extracted output to control the first transistor. A high-frequency power amplifier for a mobile phone for a mobile phone that maintains the high-frequency output at a predetermined value by controlling the power supply voltage of a transistor amplifier operating in class B or class AB among the transistor amplifiers by a second transistor. Inserting a Zener diode between the first and second transistors,
When the power supply voltage applied to the transistor amplifier rises above a certain value due to the absence of the high frequency output, the bias of the first transistor is made shallow by detecting the power supply voltage with the Zener diode, The voltage applied to the transistor amplifier is fixed to a constant value by suppressing the base current of the second transistor.

According to the above configuration, the power supply voltage is controlled,
A transistor amplifier operating in class B or class AB can be protected from overvoltage and surge voltage of an automobile battery, and the object of the present invention can be completely achieved.

Hereinafter, the present invention will be explained in more detail with reference to the drawings. FIG. 2 is a circuit diagram showing an embodiment of a high frequency power amplifier equipped with an overvoltage/surge voltage protection circuit according to the present invention. In the figure, except for the Zener diode 13 inserted between the emitter of the first transistor 4 and the collector of the second transistor 3, the other circuit configurations are the same as in FIG. 1, a feedback loop 11, and an overvoltage/surge voltage protection circuit. When the final stage of power amplifier 1 has a high frequency output, as explained in Fig. 1, the base current of the second transistor is controlled, and as a result, the transistor amplifier TR1 operates in class B or class AB.
power supply voltage is controlled. If there is no high-frequency output in the final stage, the output of the OP amplifier is at its maximum, so the first and second transistors are also completely conductive. However, when the collector voltage of the second transistor 3 exceeds the threshold of the Zener diode 13, the Zener diode starts operating.

Due to this operation of the Zener diode, a current flows through the path of the automobile battery, the second transistor 3, the Zener diode 13, and the emitter resistor 5 of the first transistor 4, and the emitter voltage is increased. Therefore, the bias of the first transistor 4 becomes shallower, and its collector current decreases, so that the base current of the second transistor 3 also decreases. As a result, the collector current of transistor 3 is suppressed, and the collector voltage of transistor 3 (Zener voltage+emitter voltage of transistor 4) is suppressed to a constant value.

As described above in detail, according to the present invention,
The collector voltage of the second transistor, which increases when there is no high-frequency output, is detected by a Zener diode,
By suppressing the collector voltage of the second transistor to a constant value by the first transistor, B
It operates in class or AB class, and is effective in protecting transistor amplifiers whose power supply voltage is controlled from overvoltages and surge voltages of automobile batteries.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an example of a power amplifier of a conventional mobile phone for a mobile phone, and FIG. 2 is a circuit diagram showing an embodiment of a power amplifier including an overvoltage/surge voltage protection circuit according to the present invention. DESCRIPTION OF SYMBOLS 1... Power amplifier, 2... Coupler, 3... Second transistor, 4... First transistor, 5, 6,
7, 8, 9, 10...Resistance, 7...OP amplifier, 11
...Feedback loop, 12...Protection circuit, 13
...Zener diode.

Claims (1)

[Claims] 1. A plurality of transistor amplifiers are connected in multiple stages, a part of the high frequency output is extracted from the final stage, and the first transistor is controlled by the extracted output,
Furthermore, in the high frequency power amplifier of the mobile phone for a car phone, the high frequency output is maintained at a predetermined value by controlling the power supply voltage of a transistor amplifier operating in class B or class AB among the transistor amplifiers by a second transistor. A Zener diode is inserted between the first and second transistors, and when the power supply voltage applied to the transistor amplifier rises above a certain value due to the absence of the high frequency output, the power supply voltage is connected to the Zener diode. The high frequency device is characterized in that the voltage applied to the transistor amplifier is fixed at a constant value by shallowly biasing the first transistor by detecting it and suppressing the base current of the second transistor. Overvoltage/surge voltage protection circuit for power amplifiers.