High frequency power amplifier

A high frequency power amplifier comprises: an amplifier that amplifies signals received from a first input terminal and outputs amplified signals to an output terminal; a bypass route that connects a second input terminal to the output terminal without passing through the amplifier; a capacitor having a first end connected to the amplifier, and a second end connected to the output terminal; a first switch having a first terminal connected to the second end of the capacitor and to the output terminal, and a second terminal connected to the bypass route; an inductor connected in parallel with the capacitor; a second switch connected in parallel with the capacitor, and connected in series with the inductor; and a control unit that turns off the first switch and the second switch at a high power level and turns on the first switch and the second switch at a low power level.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a high frequency power amplifier that switches between a route passing through the amplifier and a route bypassing the amplifier, specifically relates to a high frequency power amplifier that can reduce passing loss.

2. Background Art

A high frequency power amplifier that switches between a route passing through the amplifier and a route bypassing the amplifier has been proposed (for example, refer to Japanese Patent Laid-Open No. 2000-22559).

SUMMARY OF THE INVENTION

FIG. 5is a block diagram showing a reference example of a high frequency power amplifier. An amplifier10amplifies signals inputted from a first input terminal IN1and outputs the amplified signals to an output terminal OUT. A bypass route12connects a second input terminal IN2to the output terminal OUT without involving the amplifier10. The gate of the amplifier10is connected to the first input terminal IN1via an input matching circuit14, the drain of the amplifier10is connected to a power source terminal Vc via an inductor16, and the source of the amplifier10is grounded. One end of a capacitor34is connected to the drain of the amplifier10via an output matching circuit18, and the other end of the capacitor34is connected to the output terminal OUT. A switch36is controlled by a control unit28to connect the other end of the capacitor34to the output terminal OUT at the high power level, and to connect the bypass route12to the output terminal OUT at the low power level.

In the high frequency power amplifier shown inFIG. 5, since the signals outputted from the amplifier10at the high power level are outputted to the output terminal OUT via the switch36, there has been a problem that passing loss occurs in the switch36. In the circuit of Japanese Patent Laid-Open No. 2000-22559, there has been a problem that passing loss similarly occurs in the circulator present between the amplifier and the output terminal. Since passing loss in the switch36or the circulator must be compensated in the amplifier10, there has been a problem that operating current increases in comparison with a single amplifier having the same output power.

To solve the above-described problems, it is an object of the present invention to provide a high frequency power amplifier that can reduce passing loss.

According to one aspect of the present invention, a high frequency power amplifier comprises: an amplifier that amplifies signals inputted from a first input terminal and outputs the amplified signals to an output terminal; a bypass route that connects a second input terminal to said output terminal without involving said amplifier; a capacitor one of whose ends is connected to said amplifier, and the other of whose ends is connected to said output terminal; a first switch one of whose ends is connected to the other end of said capacitor and to said output terminal, and the other of whose ends is connected to said bypass route; an inductor connected in parallel with said capacitor; a second switch connected in parallel with said capacitor, and connected in series with said inductor; and a control unit that turns off said first switch and said second switch at a high power level and turns on said first switch and said second switch at a low power level.

According to the present invention, passing loss can be reduced.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

First Embodiment

FIG. 1is a block diagram showing a high frequency power amplifier according to the first embodiment. An amplifier10amplifies signals inputted from a first input terminal IN1and outputs the amplified signals to an output terminal OUT. A bypass route12connects a second input terminal IN2to the output terminal OUT without involving the amplifier10.

The gate of the amplifier10is connected to the first input terminal IN1via an input matching circuit14, the drain of the amplifier10is connected to a power source terminal Vc via an inductor16, and the source of the amplifier10is grounded. One end of a capacitor20is connected to the drain of the amplifier10via an output matching circuit18, and the other end of the capacitor20is connected to the output terminal OUT.

One end of a first switch22is connected to the other end of the capacitor20and the output terminal OUT, and the other end of the first switch22is connected to the bypass route12.

An inductor24is connected in parallel with the capacitor20. A second switch26is connected in parallel with the capacitor20, and connected in series with the inductor24. A control unit28controls ON/OFF of the first switch22and the second switch26.

The operation of the above-described high frequency power amplifier will be described. At the high power level, the control unit28turns the first switch22and the second switch26off. Since the second switch26is thus turned off, passing loss due to the second switch26has no effect. Also since the first switch22is thus turned off, the bypass route12side is isolated from the amplifier10side. Therefore, passing loss can be reduced. As a result, the operating current can be suppressed to the same degree as a single amplifier having the same output power. The capacitor20operates as a part of the output matching circuit18.

At the low power level, the control unit28turns the first switch22and the second switch26on. Signals inputted from the second input terminal IN2is outputted from the output terminal OUT without involving the amplifier10. At this time, the LC resonant circuit composed of the capacitor20and the inductor24is resonated by the frequency of the inputted signals, the impedance viewed from the bypass route12toward the amplifier10is elevated, and the amplifier10side is isolated from the bypass route12side. As a result, the passing loss of the bypass route12can be substantially suppressed to the only passing loss due to the first switch22.

Second Embodiment

FIG. 2is a block diagram showing a high frequency power amplifier according to the second embodiment. An inductor30is provided in place of the capacitor20in the first embodiment, and a capacitor32is provided in place of the inductor24in the first embodiment. Other parts of the configuration are the same as those of the first embodiment. Thereby, advantages equivalent to those from the first embodiment can be obtained.

Third Embodiment

FIG. 3is a block diagram showing a high frequency power amplifier according to the third embodiment. In place of the inductor24in the first embodiment, a plurality of inductors24(1) to24(n) are connected in parallel with the capacitor20. In place of the second switch26in the first embodiment, a plurality of second switches26(1) to26(n) are connected in parallel with the capacitor20, respectively, and connected in series with the plurality of inductors24(1) to24(n), respectively. The control unit28turns the first switch22and the plurality of second switches26(1) to26(n) on at the high power level, and turns the first switch22and the plurality of second switches26(1) to26(n) off at the low power level. Other parts of the configuration are the same as those of the first embodiment.

When the frequency band of signals inputted from the second input terminal IN2is wide, the design using a plurality of inductors24(1) to24(n) and a plurality of second switches26(1) to26(n) so as to overlap their resonant frequencies can reduce passing loss over a wide frequency band.

Fourth Embodiment

FIG. 4is a block diagram showing a high frequency power amplifier according to the fourth embodiment. In place of the capacitor32in the second embodiment, a plurality of capacitors32(1) to32(n) are connected in parallel with the inductor30. In place of the second switch26in the second embodiment, each of a plurality of second switches26(1) to26(n) is connected in parallel with the inductor30, and connected in series with each of the plurality of capacitors32(1) to32(n). The control unit28turns the first switch22and the plurality of second switches26(1) to26(n) off at the high power level, and turns the first switch22and the plurality of second switches26(1) to26(n) on at the low power level. Other parts of the configuration are the same as those of the first embodiment. Thereby, advantages equivalent to those from the third embodiment can be obtained.

The entire disclosure of a Japanese Patent Application No. 2008-096944, filed on Apr. 3, 2008 including specification, claims, drawings and summary, on which the Convention priority of the present application is based, are incorporated herein by reference in its entirety.