JPH0374526B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an amplifier protection circuit for protecting an amplifying element of a power amplifier from load fluctuations.

In recent years, the output of fully fixed power amplifiers has increased,
In the VHF band, units exceeding 1KW are in practical use. Furthermore, as high-efficiency power amplifiers that are smaller and more energy efficient, products that do not use circulators, increase the efficiency of the amplifier element, and minimize output circuit loss are also being used. I'm getting used to it. However, in power amplifiers that do not use this circulator, the amplifier element may be destroyed due to the reflected wave power caused by load fluctuations.To prevent this, the power amplifier is configured to detect the reflected wave power and amplify the power. It was necessary to take protective measures such as lowering the input signal level of the device and lowering the power supply voltage.

An example of an amplifier protection circuit that has been conventionally used as the above-mentioned protection means is as shown in FIG. The power amplifier 1 includes an amplifier section 2 and an output terminal 1.
A directional coupler 3 is provided between the detection circuit 2 and the detection circuit 2.
0 and a control section 30. The reflected wave power is taken out from the reflected wave power detection terminal 13 of this directional coupler 3 and controlled by the voltage detected by the wave detector.

However, this control voltage varies depending on the location of the impedance mismatch that occurs between the output terminal 13 of the power amplifier 1 and the antenna. As shown in FIG. 2, the power changes depending on the distance from P ₁ to P ₂ . Therefore, the detection of the reflected power becomes inaccurate, resulting in a drawback that the control section 30 malfunctions.

The present invention aims to improve such conventional drawbacks and provide an amplifier protection circuit that detects the ratio of the traveling wave to the reflected wave that is always constant even if the position of the mismatched portion changes. Specifically, it includes a directional coupler that is coupled to the output line of the power amplifier and has a traveling wave power detection terminal and a reflected wave power detection terminal, and a high frequency signal from the reflected wave power detection terminal of the directional coupler. a first detection circuit that receives the signal and detects a DC component corresponding to the reflected wave power; and a distributor that receives the high frequency signal from the traveling wave detection terminal of the directional coupler and divides the high frequency signal into two predetermined distributions. a level adjuster that receives the output of one of the dividers and adjusts the high-frequency signal to a specified level; and a second detector that receives the output of the level adjuster and detects a DC component corresponding to the output power. a differential amplifier that receives the outputs of the first and second detection circuits; a third detection circuit that receives the other output of the distributor and detects a prescribed level; and from the third detection circuit. It is an object of the present invention to provide an amplifier protection circuit comprising: a control section that is controlled by the output signal of the differential amplifier only when a signal of the differential amplifier is detected;

The present invention will be explained below based on an embodiment shown in FIG. In addition, in the following, common reference numerals are given to parts common to the conventional one, and duplicate explanations will be omitted.

In the figure, 20 is a directional coupler, 21 is a distributor, 22
23 is a level adjuster that adjusts the level of traveling wave power; 24 is a second detection circuit that detects a DC component that corresponds to the output power of the level adjuster 23; Detection circuit, 2
5 is a third detection circuit for detecting whether the traveling wave power is at a specified level; 26 is a differential amplifier; and 27 is a control section. Reference numeral 28 indicates a reflected power detection terminal of the directional coupler, and 29 indicates a traveling wave power detection terminal of the directional coupler 20.

Here, the high frequency signal from the reflected wave power detection terminal 28 of the directional coupler 20 is sent to one input terminal of the differential amplifier 26 via the first detection circuit 22 which outputs a DC component corresponding to the reflected wave power. join. Further, the high frequency signal from the traveling wave power detection terminal 29 of the directional coupler 20 is divided into prescribed distributions by the distributor 21, and one of the signals is converted into reflected wave power that does not destroy the amplifying element of the power amplifier 1. Adjust the level adjuster 23 so that the corresponding VSWR (voltage standing wave ratio, hereinafter omitted) is achieved.
Adjusted by

This adjusted high frequency signal is applied to the other input terminal of the differential amplifier 26 via the second detection circuit 24 which detects the output corresponding to the power indicated by the signal. In other words, the output of the differential amplifier 26 corresponds to the ratio of the traveling wave power to the reflected wave power, that is, the VSWR of the load, and this output signal is transmitted to the control unit 27.
sent to.

By the way, when power amplifiers 1 are used in parallel to obtain large amounts of power, it is often the case that one power amplifier is starting up temporarily due to variations in the start-up of the power amplifiers 1. Other power amplifiers may not start up properly. In this state, before one power amplifier starts up, other power amplifiers that have already started up output, and that signal goes around through the combiner, causing its own traveling wave to become 0. , a signal from the output terminal is input, and the output of the differential amplifier 26 gives a signal to the control unit 27 as if the VSWR were infinite. Therefore, if left as is, the control unit 27 will perform protective actions such as lowering the output of the power amplifier or stopping the output, which will cause the reflected wave power detection circuit 22 to malfunction. In order to prevent such malfunctions, a second device is installed to detect whether the other traveling wave power distributed by the distributor 21 is at a specified level (a level that does not destroy the amplifying element of the amplifier 2 even if the traveling wave power is totally reflected). The signal is sent to the control section 27 via the third detection circuit 25. As a result, the control section is operated by the output signal of the differential amplifier 26 only when the traveling wave power is at a certain level or higher, and performs the above-mentioned protective operation against the reflected wave power. .

Since the amplifier protection circuit according to the present invention is as described above, there is no error such as the reflected wave power changing depending on the location of the mismatched part, accurate detection is possible, and it has a great effect on improving reliability. Effects can be obtained.

[Brief explanation of drawings]

Figure 1 is a block diagram of a power amplifier using a conventional amplifier protection circuit, and Figure 2 is a characteristic showing changes in the output power of the reflected wave power detection terminal of the directional coupler due to changing the distance of the reflection point. 3 and 3 are block diagrams of a power amplifier including one embodiment of the present invention. 1: Power amplifier, 2: Amplifier, 3: Directional coupler, 11: Input terminal, 12: Output line, 13:
Output terminal, 14: Reflected wave power detection terminal, 20: Detection circuit, 21: Distributor, 22: First detection circuit, 2
3: Level adjuster, 24: Second detection circuit, 25:
Third detection circuit, 26: differential amplifier, 27: control section, 28: reflected wave power detection terminal, 29: traveling wave power detection terminal, 30: control section.

Claims (1)

[Claims] 1. A power amplifying section that receives a high frequency input signal, amplifies the power, and supplies the amplified output to an output line, and a directional coupler that is coupled to the output line and has a traveling wave power detection terminal and a reflected wave power detection terminal. a first detection circuit that receives a high frequency signal from a reflected wave power detection terminal of the directional coupler and detects a DC component corresponding to the reflected wave power; and a first detection circuit that receives a high frequency signal from a traveling wave detection terminal of the directional coupler. a distributor that divides the high-frequency signal into two predetermined distributions; a level adjuster that receives the output of one of the dividers and adjusts the high-frequency signal to a predetermined level; a second detection circuit that detects a DC component corresponding to the output power; a differential amplifier that receives the outputs of the first and second detection circuits; and a third detection circuit that receives the output of the other one of the dividers and detects a specified level. an amplifier protection circuit comprising: a detection circuit; and a control section that controls the level of the high-frequency input signal to the power amplification section based on the output signal of the differential amplifier only when a signal from the third detection circuit is detected. .