1. Field of the Invention
The present invention relates to a high frequency power amplifier, and more specifically, to a high frequency power amplifier used in microwave or millimetric-wave telecommunications equipment for mobile communications or satellite communications.
2. Description of Related Art
In conventional high frequency power amplifiers used in microwave or millimetric-wave telecommunications equipment for mobile communications or satellite communications, it is well known that the efficiency of transistor operation is higher if the load at the frequencies of not only the fundamental waves but also higher harmonics of the output circuit of a transistor is controlled, as compared with the case where only the load of fundamental waves is controlled. Here, the fundamental waves are the waves that have the lowest frequency, and the higher harmonics are a series of waves, each of which has a frequency that is an integer multiple of the fundamental frequency.
It has been reported that there are the optimal load conditions for high-efficiency operation in input high frequency loads. For example, Japanese Patent No. 2695395 titled xe2x80x9cHigh Frequency Power Amplifierxe2x80x9d discloses that the control of input-side higher harmonics is effective for improving drain efficiency; the input-side higher harmonic control circuit has a resonance frequency with respect to frequencies lower than the frequency of the 2nd harmonic; there are optimal load conditions in the input impedance range of (0+j4xcexa9), (0+j25xcexa9), (5+j25xcexa9), and (5+j4xcexa9); and the efficiency of operation can be higher when the impedance of the 2nd harmonic is set in a low range. Here, higher harmonics, each of which has a frequency that is an odd-number multiple of the fundamental frequency, are called odd number higher harmonics; and higher harmonics, each of which has a frequency that is an even-number multiple of the fundamental frequency, are called even number higher harmonics.
Japanese Patent Laid-Open No. 7-22872 titled Electric Power Amplifier discloses that it is effective to make the load condition of input/output higher harmonics a short-circuit load in order to achieve high-efficiency operation in a hetero-junction bipolar transistor, and that, as in the above-described Japanese Patent No. 2695395, the efficiency of the transistor can be improved by setting a low impedance load. It is disclosed that there is no or little effect of odd number order higher harmonics, in particular of a 3rd higher harmonic.
As described above, conventional circuit configurations for realizing high efficiency operation of transistors in a high frequency power amplifier have a problem in that the circuit configurations are limited to make the input-side even-number higher harmonic load of the impedance matching circuit a short-circuit load.
Furthermore, such a high frequency power amplifier has a problem in that the higher the frequency of a signal, that is the higher the order of the harmonics, the smaller the amplitude of the higher harmonics reflected from higher harmonic processing circuit until the higher harmonics reach the input end of the transistor due to propagation loss in a line, and sufficient reflection cannot be obtained.
Therefore, an object of the present invention is to solve the above-described problems, and to provide a high frequency power amplifier that can improve the efficiency of transistor operation without limiting the input-side higher harmonic load of an impedance matching circuit to a short-circuit load.
Another object of the present invention is to provide a high frequency power amplifier that can increase the quantity of the reflection of higher harmonics.
According to a first aspect of the present invention, there is provided a high frequency power amplifier, comprising: a transistor for amplifying signals; and an input-side impedance matching circuit connected to an input side of the transistor, wherein the input-side impedance matching circuit makes impedance substantially open load with respect to even number order higher harmonics of a fundamental wave of a high frequency signal.
According to a second aspect of the present invention, there is provided a high frequency power amplifier, comprising: a transistor for amplifying signals; and an input-side impedance matching circuit connected to an input side of the transistor, wherein the input-side impedance matching circuit makes impedance substantially short-circuit load with respect to odd number order higher harmonics of a fundamental wave of a high frequency signal.
According to a third aspect of the present invention, there is provided a high frequency power amplifier, comprising: a front stage transistor; a rear stage transistor; and an inter-stage impedance matching circuit connected between the front stage transistor and the rear stage transistor for matching impedances, wherein higher harmonics generated in the front stage transistor is inputted into the rear stage transistor, and a higher harmonic load of the rear stage transistor is adjusted by the inter-stage impedance matching circuit.
According to a fourth aspect of the present invention, there is provided a high frequency power amplifier comprising a transistor for amplifying signals divided into cell units that operate in parallel, wherein each cell unit comprises an input-side impedance matching circuit and an output-side impedance matching circuit, and each cell unit adjusts a higher harmonic load of a basic frequency viewed from a direction of the transistor.
The above and other objects, effects, features and advantages of the present invention will become more apparent from the following description of the embodiments thereof taken in conjunction with the accompanying drawings.