JPH04217103A - Microwave band amplifier - Google Patents

Abstract

PURPOSE:To reduce non-linear distortion by a small scale and simple circuit concerning the microwave band amplifier to obtain high output power in a microwave band. CONSTITUTION:At the microwave band amplifier equipped with an amplifying means 11 to amplify a prescribed input signal and to obtain the output signal of prescribed power, a demultiplexing filter means 13 is arranged in the preceding step of the amplifying means 11 and provided to demultiplex the input signal to plural paths, a non-linear distortion generating means 15 is provided with a gain different from that of the amplifying means 11 and non-linearity approximate to that of the amplifying means 11 in respect to the input signal applied through the demultiplexing filter means 13, and a synthesizing means 17 is provided to synthesize non-linear distortion generated at the amplifying means 11 and the non-linear distortion generating means 15 while inverting the phases.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a microwave band amplifier that obtains large output power in the microwave band.

0002

2. Description of the Related Art High-output amplifiers in the microwave band can be used even at input signal levels that reach the saturated output level, since nonlinear distortion hardly occurs when, for example, an unmodulated carrier wave signal is amplified. However, the microwave that is normally amplified (hereinafter referred to as "main signal") is modulated by some kind of signal and includes multiple frequency components. Therefore, in a high-output amplifier, nonlinear distortion of a frequency given by the sum and difference of harmonic components of these frequency components occurs due to the nonlinearity of the amplification element.

[0003] The main energy of such nonlinear distortion is when the frequencies of the components included in the main signal are f1 and f2 (≒f
1), (2f1 - f2) and (2
f2 − f1) is the intermodulation distortion of the frequency (hereinafter referred to as
This is called "third-order distortion." ) and generally increases with input power at the output of a high-power amplifier. Therefore, the upper limit of the input power level of a high-power amplifier is determined by the level of third-order distortion allowed at its output.

By the way, the main methods for reducing such nonlinear distortion include an output backoff method and a predistortion method. The output back-off method generally utilizes the fact that the slope of the amplifier's input/output characteristics in the linear region is ``1'' for the main signal, but ``3'' for the third-order distortion component. However, by using an amplifier configured using an amplification element that can provide a large saturation output level at a low input level, third-order distortion can be effectively reduced.

However, in such a method, the configuration of each amplifier circuit is simple and small-scale, but in order to ensure that the level difference between the main signal and the third-order distortion is larger than a predetermined value, the level of the input signal is adjusted. is limited to a predetermined value or less, and cascade connections are performed for the purpose of obtaining a predetermined output power, making it impossible to increase power efficiency. In addition, power efficiency can be improved by setting the operating point of the amplifier element to class B or class C, but if the amplifier element is a GaAs FET, the bias cannot be set because the withstand voltage of the gate against reverse bias is low. In some cases, when a bipolar transistor is used as an amplification element, the amount of nonlinear distortion generated increases. Furthermore, depending on the type of amplification element, a sufficient saturation output level may not be obtained in some cases.

[0006] Therefore, the output back-off method cannot be adopted in many cases, and the predistortion method, which can reliably reduce nonlinear distortion, is currently widely used in high-output amplifiers in the microwave band. FIG. 6 is a diagram showing an example of the configuration of a microwave band amplifier using the predistortion method.

In the figure, the input signal is input to a linearizer 60.
is applied to the amplifier 61 via the amplifier 61, the output of which provides an output signal with a predetermined power. In the linearizer 60, an input signal is applied to a terminal a of a 90-degree hybrid 62, and its terminal b is connected to a terminal a of a 90-degree hybrid 63. 9
A terminal c of the 0 degree hybrid 63 is connected to the input of the amplifier 61. Terminal c of 90 degree hybrid 62 is connected to terminal a of 90 degree hybrid 64, and terminal b thereof is connected to terminal b of 90 degree hybrid 67 via attenuator 651 and amplifier 661. 90 degree hybrid 6
Terminal c of 7 is connected to terminal b of 90 degree hybrid 63. Terminal c of the 90 degree hybrid 64 is connected to the amplifier 662
and 90 degree hybrid 6 through attenuator 652
It is connected to terminal a of 7. 90 degree hybrid 62,6
Each terminal d of 3, 64, and 67 is connected to a resistor 681.
, 682 , 683 , 684 . Note that all of these 90 degree hybrids have terminal a
, b, c, and d are arranged in this order on a ring-shaped line provided inside the terminal, and the main signal component of the input signal has a phase shift of 0.5π radian on the line between each adjacent terminal. have characteristics.

In the microwave band amplifier having such a configuration, the amplifier 61 alone amplifies the main signal component to a predetermined level and outputs it (Fig. 7■), and due to the nonlinearity of the amplifying element, Nonlinear distortion (third-order distortion) occurs (Fig. 7 ■). In the linearizer 60, a part of the input signal is passed through the terminal b of the 90 degree hybrid 62 to the 90 degree hybrid 63.
The signal is outputted from terminal c (Fig. 8), and its phase is shifted by 1.5π radians with respect to the input signal.

Furthermore, since the attenuators 651 and 652 have the same attenuation, the amplifiers 661 and 662 have the same gain, and their phase shifts are sufficiently small, the main signal is
There is a phase shift of 3 radians in the path leading to the terminal c of the 90 degree hybrid 67 via the terminal c of the 90 degree hybrid 62 and 90 degree hybrid 64. Moreover, the main signal is 2 in the path leading to the terminal c of the 90 degree hybrid 67 via the terminal b of the 90 degree hybrid 62 and the 90 degree hybrid 64.
Shift the phase in radians. Therefore, 90 degree hybrid 6
At terminal c of No. 7, the main signal component is canceled by the above-mentioned phase difference.

Furthermore, the amplifier 661 is an attenuator 651
The amplifier 662 is placed after the attenuator 652.
These amplifiers are provided with main signals of different levels. Therefore, the level of nonlinear distortion (third-order distortion) generated in these amplifiers varies depending on the difference in the rate of change between the main signal component and the third-order distortion component in their input/output characteristics.

[0011] This level difference is not canceled out by the difference in phase shift due to the above-mentioned path difference and the attenuation amount of the attenuator 652, and third-order distortion at a predetermined level is output to the terminal c of the 90-degree hybrid 67. be done. In this way, the phase of the third-order distortion output from the linearizer 40 is opposite to the third-order distortion output when the input signal is directly applied to the amplifier 61, as shown in FIG. The levels are set to be the same. Therefore, the third-order distortion described above is canceled out at the output of the amplifier 61 (Fig. 9
).

0012

[Problems to be Solved by the Invention] However, in such a conventional configuration, as mentioned above, the configuration of the linearizer is complicated, making it difficult to design, and the circuit scale is large, requiring a large mounting space. there were. An object of the present invention is to provide a microwave band amplifier that can reduce nonlinear distortion using a small-scale and simple circuit.

[0013]

[Means for Solving the Problems] FIG. 1 is a block diagram of the principle of the present invention. The present invention amplifies a predetermined input signal,
In a microwave amplifier equipped with an amplifying means 11 for obtaining an output signal of a predetermined power, the microwave amplifier is arranged before the amplifying means 11,
A demultiplexing means 13 that demultiplexes an input signal into a plurality of routes, and a gain that is different from that of the amplification means 11 for the input signal provided through the demultiplexing means 13, and a non-linearity of the amplification means 11. nonlinear distortion generating means 15 having approximate nonlinearity;
It is characterized by comprising a combining means 17 which combines the nonlinear distortions generated by the amplifying means 11 and the nonlinear distortion generating means 15 in opposite phases.

[0014]

[Operation] In the present invention, the nonlinear distortion generating means 15 sends out an output signal at a different level from the amplifying means 11 according to its gain, and has nonlinearity similar to the nonlinearity of the amplifying means 11. , generates nonlinear distortion including the main energy of the nonlinear distortion generated from the amplifying means 11. The combining means 17 cancels out these nonlinear distortions by combining them in opposite phases, but the output signal is not canceled out due to the above-mentioned level difference and is sent out at a predetermined level.

The nonlinear distortion generating means 15 has the same structure as the amplifying means 11, except that it is constructed using an element that can obtain a predetermined nonlinearity and a gain for the input signal under predetermined operating conditions. be. Furthermore, the demultiplexing means 13 and the multiplexing means 17 are easily constructed without using active elements. Therefore, nonlinear distortion can be reduced using a small and simple circuit that can be implemented in a small space.

[0016]

Embodiments Hereinafter, embodiments of the present invention will be described in detail based on the drawings. FIG. 2 is a diagram showing an embodiment of the present invention. In the figure, the input signal is 90 degree hybrid 2
1, and its terminal b is connected to the coupling capacitor 2.
21 , is connected to terminal a of the 90-degree hybrid 24 via an amplifier 23 and a coupling capacitor 222 . 9
Terminal b of the 0 degree hybrid 24 provides an output signal. On the other hand, the terminal c of the 90 degree hybrid 21 is connected to the coupling capacitor 223, the amplifier 25 and the coupling capacitor 224.
It is connected to the terminal d of the 90-degree hybrid 24 via. Terminal d of the 90 degree hybrid 21 is grounded via a terminating resistor (resistance value = 50 Ω) 261, and terminal c of the 90 degree hybrid 24 is connected to a terminating resistor (resistance value = 50 Ω).
262 to ground.

The 90-degree hybrids 21 and 24 are constructed by arranging terminals a, b, c, and d in this order at regular intervals on a ring-shaped line, and the intervals are determined by the main signal component included in the input signal. In contrast, the length is set to λ/4. therefore,
In these hybrids, the main signal has a phase shift of 0.5π radians from each terminal to its adjacent terminal. Note that these hybrids are constructed from a hybrid ring circuit formed in a square shape using a microstrip line having a characteristic impedance of 50Ω on a printed circuit board on which each component of the high-output amplifier is mounted.

In the amplifier 23, the input signal is applied to the gate of the FET 281 via the microstrip line 271. A stub 291 for input matching and a bias circuit 301 are arranged at predetermined positions on the microstrip line 271 . The drain of FET 281 is connected to coupling capacitor 222 via microstrip line 311. A bias circuit 321 and a stub 331 for output matching are arranged at predetermined positions on the microstrip line 311 . The source of FET 281 is grounded through its case. The bias circuit 301 includes FET28
A power supply 341 supplying a bias voltage of 1 is connected. A power supply 351 that supplies a predetermined power supply voltage to the drain of the FET 281 is connected to the bias circuit 321 .

The configuration of the amplifier 25 is basically that of the amplifier 23.
is the same as Therefore, for its components:
The reference numerals of the corresponding components arranged in the amplifier 23 are shown with the suffixes changed to "2", and the explanation of their connection relationships will be omitted here. In addition, reference number 361 indicates the ground pattern connected to the terminating resistor 261,
Reference numeral 362 indicates a ground trace connected to terminating resistor 262.

Regarding the correspondence between this embodiment and the block diagram shown in FIG. 90 corresponding to the distortion generating means 15
The hybrid 24 corresponds to the multiplexing means 17. Figure 3~
FIG. 5 is a diagram showing the frequency spectrum of each part of the circuit of this embodiment.

The operation of this embodiment will be explained below with reference to FIGS. 2 to 5. The amplifier 23 is a 90 degree hybrid 2
amplifying the main signal component of the input signal provided through 1;
Outputs an output signal of a predetermined power (Fig. 3 ■). Furthermore, the amplifier 23 generates nonlinear distortion (third-order distortion) due to the nonlinearity of the FET 281 (FIG. 3), and the distorted wave component is output as part of the output signal.

In the amplifier 25, the voltage supplied from the power supply 352 is set to a value sufficiently smaller than the value supplied to a normal amplifier circuit, so the main signal component is not amplified and is output with small power (as shown in FIG. 4■). Also, FET282
For this purpose, an element having non-linearity (transfer characteristics) approximate to that of the FET 281 mounted in the amplifier 23 at the operating point set by the power supplies 342 and 352 is used. That is, the amplifier 25 generates third-order distortion having the same frequency component as the third-order distortion generated from the amplifier 23 (see FIG.
■).

[0023] Furthermore, the signal passing through the amplifier 25 has a frequency of 90
There is a delay of π/2 radians between the terminals b to c of the 90-degree hybrid 21 and between the terminals d to a of the 90-degree hybrid 24, respectively. Therefore, in the 90-degree hybrid 24, the third-order distortion component generated by the amplifier 23 is combined in opposite phase with the third-order distortion component of the same level generated by the amplifier 25, and canceled out (FIG. 5).

[0024] Such an amplifier 25 is simply constructed like the amplifier 23. Also, 90 degree hybrid 21
, 24 can also be easily constructed using only passive elements, and for example, even if the frequency is as low as several GHz, the wavelength shortening rate can be increased by using a material with high Q and high dielectric constant. Therefore, miniaturization is possible. Therefore, nonlinear distortion can be reduced with a small and simple circuit that can be implemented in a small space.

In this embodiment, the phase difference (π
radian) is obtained by dispersing each π/2 radian between the 90-degree hybrid 21, which operates as a demultiplexer, and the 90-degree hybrid 24, which operates as a multiplexer, but the dispersion ratio is limited in this way. isn't it. That is, for example, instead of the 90-degree hybrid 21, a duplexer with no phase difference between the output paths may be used, and the phase may be shifted all at once when combining the outputs of both amplifiers.

Furthermore, the amplifying element is not limited to FETs as in this embodiment, but bipolar transistors and other elements can be used as long as the desired amplifier can be constructed and the necessary frequency components and levels of nonlinear distortion can be obtained. may also be used.

[0027]

As explained above, the present invention uses a nonlinear distortion generating means with a simple configuration to generate a distorted wave corresponding to the main output energy of the nonlinear distortion output from the amplifying means, and The nonlinear distortion is reduced by combining these nonlinear distortions in opposite phases through a combining means that is simply configured using only passive elements.

That is, the configuration of the microwave band amplifier is simplified, and the mounting efficiency of a device including the amplifier can be improved.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of the principle of the present invention.

FIG. 2 is a diagram showing an embodiment of the present invention.

FIG. 3 is a diagram showing the frequency spectrum of the output signal of the amplifier 23.

FIG. 4 is a diagram showing the frequency spectrum of the output signal of the amplifier 25.

FIG. 5 is a diagram showing a frequency spectrum of an output signal of the circuit of this embodiment.

FIG. 6 is a diagram showing a configuration example of a microwave band amplifier using a predistortion method.

FIG. 7 is a diagram showing the frequency spectrum of the output signal of the amplifier 61 alone.

FIG. 8 is a diagram showing the frequency spectrum of the output signal of the linearizer 60 alone.

FIG. 9 is a diagram showing a frequency spectrum of an output signal of a conventional microwave band amplifier.

[Explanation of symbols]

11 Amplifying means 13 Demultiplexing means 15 Nonlinear distortion generating means 17 Multiplexing means 21, 24, 62, 63, 64, 67 90 degree hybrid 221, 222, 223, 224 Coupling capacitors 23, 25, 61, 661, 662 Amplifier 261 , 262 , 681 , 682 , 683
, 684 Termination resistor 271 , 272 , 311 , 312 Microstrip line 281 , 282 FET 291 , 292 , 331 , 332 Stub 301 , 302 , 321 , 322 Bias circuit 341 , 342 , 351 , 352 Power supply 361 , 362 Earth pattern 60 Linearizer 651, 652 Attenuator

Claims (1)

[Claims] 1. A microwave amplifier comprising an amplifying means (11) for amplifying a predetermined input signal to obtain an output signal of a predetermined power, the microwave amplifier being disposed before the amplifying means (11) and connected to a plurality of routes. demultiplexing means (13) for demultiplexing the input signal;
), which has a gain different from that of the amplifying means (11) with respect to the input signal applied via the demultiplexing means (13), and which is approximate to the nonlinearity of the amplifying means (11). a nonlinear distortion generating means (15) having a characteristic, and a combining means (17) for combining the nonlinear distortions generated by the amplifying means (11) and the nonlinear distortion generating means (15) in opposite phases.
A microwave band amplifier characterized by comprising: