JPH0147926B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a high-frequency transistor power amplifier that improves instability caused by abnormal phenomena such as spurious oscillations due to load fluctuations. Conventionally, as a means for improving the instability of high frequency transistor power amplifiers, for example, J. Vidkjaer;
IEEE Journal of Solid-State Circuits, Vol.
SCll, No. 5 pages 703-712 and RCA Solid
State, 74 DataBook Series SSD−205B page
253, etc., have been used, but in most cases, a resistor is inserted into a bias circuit or a matching circuit to reduce the amplification gain inherent in the transistor in order to stabilize the transistor. For this reason, it has not been possible to design a high-frequency transistor power amplifier that has good stability against load fluctuations on the input side and output side, and also has high gain and high efficiency. Generally, high-frequency transistor power amplifiers are designed so that the input power supply side and the output load side are terminated with ideal characteristic impedance (for example, 50Ω with no frequency characteristics). However, when actually used, an excitation amplifier, an isolator, etc. are connected to the input side, and an isolator, wave generator, antenna, etc. are connected to the output side. Therefore, in the operating frequency band, the termination conditions are almost the same as those at the time of design. However, outside the band, the termination conditions are quite different from those at the time of design. In particular, due to differences in out-of-band termination conditions on the input side, unstable phenomena such as oscillation often occur due to load fluctuations on the output side. The cause of such oscillation will be briefly explained using a transistor class C power amplifier as an example. In a transistor class C power amplifier, when a relatively large high frequency signal is input, the transistor is excited, and the input high frequency signal is not only amplified, but also a wide frequency range from extremely low frequencies to the frequency of class C operation. It has amplification ability over a wide range of areas. Therefore, oscillation occurs due to the feedback capacitance inside the transistor, the termination conditions on the input side and the output side, and the amplification effect. If the load on the input or output side of the amplifier can be made resistive over a wide frequency range and at a value that does not cause oscillation, oscillation will not occur. The method of simply inserting had a large effect on the operating frequency and was accompanied by serious performance deterioration such as a reduction in amplification gain. The present invention has been made to eliminate the above-mentioned conventional drawbacks, and includes a circuit in which wave generators each having a cut-off frequency lower than the operating frequency of a high-frequency transistor power amplifier and a resistor-terminated wave generator are connected in series and parallel to each other. It is an object of the present invention to provide a high-frequency transistor power amplifier that can be inserted into the input side or the output side, hardly impairs the inherent performance of the transistor, and has good stability against load fluctuations. Embodiments of the high frequency transistor power amplifier of the present invention will be described below with reference to the drawings. 1st
The figure is a block diagram showing the configuration of one embodiment. 1 in FIG. 1 is an input power supply side terminal, which is connected to the input side of the high-pass waveform generator 2. In FIG. Further, 3 is a resistor, one end of which is grounded, and the other end connected to the input end of the low-pass waveform generator 4. The output terminal of the high-pass waveform generator 2 and the output terminal of the low-pass waveform generator 2 are connected to the input terminal of a power amplifier 6 (hereinafter referred to as an amplifier) constituted by a high-frequency transistor. When looking from the input terminal 5 of the amplifier 6 to the input power supply side terminal 1, the high-pass waveform generator 2 is configured to appear high impedance below a cutoff frequency lower than the operating frequency of the amplifier 6. Furthermore, the low-pass waveform generator 4 also has a cut-off frequency lower than the operating frequency of the amplifier 6. Therefore, at a frequency lower than the above-mentioned operating frequency, even if the load conditions at the stage before the input power supply side terminal 1 change, the resistor 3 is always visible when looking at the input power supply side terminal 1 from the input terminal 5. It is something. FIG. 2 is a circuit diagram showing the configuration of a specific embodiment of the high frequency transistor power amplifier of the present invention based on the block diagram of FIG. 1, and shows parts other than the amplifier 6. The high-pass waveform generator 2 is composed of an inductance element _L1 and a capacitance element _C2 . That is, the inductance element
One end of _L1 is grounded, and the other end and one end of capacitance element _C2 are connected to input power supply side terminal 1. The other end of the capacitance element _C2 is connected to the input terminal 5. Further, the resistor 3 is a resistor R ₅ , one end of which is grounded and the other end connected to the input terminal 5 via the inductance element L ₃ of the low-pass waveform generator 4 . The connection point between the resistor _R5 and the inductance element _L3 is the capacitance element of the low-pass waveform generator 4.
Grounded through _C4 . The values of each element in FIG. 2 are selected as shown in Table 1 below.

[Table] When input power supply side terminal 1 and input terminal 5 are terminated with 50Ω, the frequency characteristics of standing wave ratio and passing loss are as shown in Figs. 3 and 4. Characteristic a in FIG. 3 is the frequency characteristic of the voltage standing wave ratio as seen from the input power supply side terminal 1, and characteristic b is the frequency characteristic of the voltage standing wave ratio as seen from the input terminal 5. And the fifth
The figure is an equivalent circuit diagram of FIG. 2. Also, Figure 4 shows the frequency characteristics of the insertion loss in Figure 2,
This is a case where the input terminal 5 is viewed from the input power supply side terminal 1 and a case where the input power supply side terminal 1 is viewed from the input terminal 5. As shown in Figures 3 and 4,
In the 900MHz band, there is almost no passing loss, and the standing wave ratio is directional. Figure 6 (shows the frequency spectrum of the oscillation waveform of the amplifier before applying this invention) at a normal output load standing wave ratio of 2.5:1, with the horizontal axis representing the frequency and the vertical axis representing the relative value of amplitude. The operating frequency a is
900M which causes oscillation as shown in (900MHz)
When we conducted an experiment by connecting the circuit shown in Figure 2 to a Hz4W class amplifier as shown in Figure 1, no oscillation occurred even when the output load standing wave ratio was varied by 10:1 in total phase. In the description of this embodiment, a case has been described in which the circuit shown in FIG. 2 is applied to the input side of the amplifier 6, but the same effect can be obtained on the output side. In fact, when the circuit shown in Figure 2 was applied to the output side of the amplifier 6, the output load standing wave ratio was 5:1.
So, no oscillation occurred even with a total phase change. Further, application to interstage circuits of multistage amplifiers, etc. is also considered. FIG. 7 is a circuit diagram showing another embodiment of the present invention, in which illustration of the amplifier 6 is omitted as in the case of FIG. 2. In the case of FIG. 7, the inductance element 8 and the capacitance element 9 constitute a high-pass waveform 2,
One end of the inductance element 8 is grounded, and the other end is connected to the input power supply side terminal 1.
In addition, the capacitance element 9 is connected to the input power supply side terminal 1
and input terminal 5. Furthermore, the inductance element 10 and the capacitance element 11 are connected in parallel to form a band-stop waveform, one end of which is grounded via the resistor 3, and the other end connected to the input terminal 5.
In this band-elimination type waveform generator, the resistor 3 is not visible near the operating frequency of the amplifier 6, resulting in low passing loss, and the resistor 3 is visible outside the band. It goes without saying that the same effect can be expected even if the high-pass waveform generator 2 in FIG. 1 is replaced with a band-pass waveform generator. As described above, according to the high frequency transistor power amplifier of the present invention, a circuit in which a wave device having a cut-off frequency lower than the operating frequency of the high frequency transistor power amplifier and a resistor-terminated wave device are connected in series and parallel to each other is installed on the input side. Alternatively, since it is inserted on the output side, it is possible to create an amplifier that is extremely stable against fluctuations in the load standing wave ratio without reducing the gain of the transistor, making it suitable for applications such as mobile radio equipment. It is effective.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of an embodiment of the high frequency transistor power amplifier of the present invention, FIG. 2 is a circuit diagram of the specific embodiment of FIG. 1, and FIG.
Figure 4 is a frequency characteristic diagram of the voltage standing wave ratio seen from the input power supply terminal and input terminal of the high frequency transistor power amplifier in Figure 2. Figure 4 is a frequency characteristic diagram of insertion loss in the high frequency transistor power amplifier of Figure 2. Figure 2 is an equivalent circuit diagram of the high-pass waveform, resistor, and low-pass waveform in the high-frequency transistor power amplifier; Figure 6 is a diagram showing the spurious oscillation frequency spectrum of the amplifier before applying the present invention; FIG. 7 is a circuit diagram of another embodiment of the high frequency transistor power amplifier of the present invention. 1...Input power supply side terminal, 2...High-pass waveform generator,
3...Resistor, 4...Low-pass waveform generator, 5...Input terminal, 6...Amplifier, 7...Output terminal, L ₁ , L ₃ , 8,
10...Inductance element, C ₂ , C ₄ , 9, 11
...capacitance element.

Claims (1)

[Claims] 1 a power amplifier configured with a high-frequency transistor; a first wave amplifier having a cutoff frequency lower than the operating frequency of the power amplifier and connected in series with the power amplifier so as to pass only a frequency signal higher than the cutoff frequency; A second power amplifier having a cut-off frequency lower than the operating frequency and connected in parallel with the power amplifier with a resistor termination so as to take in a frequency signal lower than the cut-off frequency and guide it to the resistor termination.
and a circuit inserted on the input side or output side of the power amplifier.