JP2013065961A - Power amplification device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a power amplification device that has a high impedance and a spurious emission reduction effect at frequencies outside a modulation band of a main signal and a frequency range of intermodulation products.SOLUTION: According to an embodiment, the power amplification device comprises: an FET 103 for power-amplifying an input signal to a transmission signal containing a first signal and a second signal; a first decoupling element 104 for reducing an inductor component of the transmission signal output from the FET 103; a power circuit 200 for supplying driving power to the FET 103; a second decoupling element 300 for cutting off an RF component output from an output terminal 106 of the FET with respect to the power circuit 200; and a filter 400 connected between the first decoupling element 104 and the second decoupling element 300, and having a predetermined first impedance in a modulation band of the first signal and a frequency range of intermodulation products of the output signal of the FET and a second impedance outside the modulation band of the first signal and the frequency range of intermodulation products.

Description

  Embodiments described herein relate generally to a power amplifying apparatus such as a solid-state power amplifier for wireless equipment.

  Solid-state power amplifiers for wireless equipment are X-band, Ku-band, and Ka-band instead of traveling wave tube amplifiers (TWTA) that use a traveling wave tube, which is a type of vacuum tube, in the power amplifier of the power amplifier. Solid state power amplifiers (SSPA) using FETs (Field Effect Transistors) are becoming widespread even in high power applications such as high frequency regions. The reason behind this is the increase in efficiency and power consumption of power amplification FETs, and in particular, with the advent of FETs (GaN HEMTs) that use gallium nitride (GaN) materials, the SSPA Transmission output has improved dramatically.

  By the way, radio equipment is required to have radio wave quality that conforms to the standards of the Radio Law, and one of them is the provision of spurious that is an unnecessary wave. When looking at the radio equipment as a whole, spurious sources are generated when the oscillator carrier leaks in a device using an oscillator such as a modulator or frequency converter, or when the intermodulation product of a power amplifier is used. In addition, the main signal harmonic is also common. These spurious components are required to be equivalent to or higher than the standards required by the Radio Law as radio equipment.

JP-A-8-204472

By the way, in order to reduce spurious, a method using a filter circuit assembled by passive circuits such as a bandpass filter, a low-pass filter, and a high-pass filter is generally used. However, the passive circuit has the following problems in use. is there.
(1) The main signal is attenuated by the filter passage loss.
(2) For high power use, it is necessary to consider heat generation due to passage loss.
(3) When the frequency of the main signal is not fixed, it is difficult to reduce spurious near the main signal.

On the other hand, it is conceivable to use an active filter using active elements. However, with an active filter,
(1) The main signal is attenuated by the filter passage loss.

  (2) When the frequency of the main signal is not fixed, it is difficult to reduce spurious in the vicinity of the main signal.

  An object of the present invention is to provide a power amplifying device having a high impedance and a spurious reduction effect at a frequency outside the frequency range of the modulation band of the main signal and the intermodulation product.

  According to the embodiment, the signal level of the input signal from the input terminal provided in the package having the input terminal and the output terminal is smaller than that of the first signal having the predetermined frequency difference and the first signal. A FET (Field Effect Transistor) that amplifies power to an RF (Radio Frequency) band transmission signal including two signals and supplies the amplified signal to the output terminal, and a first output that reduces the inductor component of the transmission signal output from the FET. A decoupling element, a power supply circuit that supplies driving power to the FET in the package, a second decoupling element that cuts an RF component output from the output terminal to the power supply circuit, and a first decoupling element And a second decoupling element, and a predetermined first impedance in the frequency domain of the intermodulation product of the modulation band of the first signal and the output signal of the FET. Thus, it is possible to provide a power amplifying apparatus including a filter having a second impedance higher than the first impedance outside the frequency band of the first signal modulation band and the intermodulation product.

1 is a schematic configuration diagram showing an SNG system as an embodiment. The frequency characteristic figure of an output signal when a 2 wave signal source is input into a power amplifier. The figure which shows the generation principle of Capture Effect in the model which amplifies two waves of a large signal and a small signal in common. The operation characteristic figure of FET. The equivalent circuit diagram of FET which shows generation | occurrence | production of Vds. The figure which shows the component of the output signal which amplified two waves. The figure which shows the quantity of small signal suppression. The triaxial plot figure of suppression amount (DELTA) P of a spurious (f_small). The equivalent circuit diagram of FET at the time of mounting a filter. The figure which shows the example which suppresses the inductor component by the line length of a bias, and improves small signal suppression. The figure which shows the low impedance and high impedance of a filter. FIG. 3 is an equivalent circuit diagram of the power amplification device according to the present embodiment.

  Hereinafter, the present embodiment will be described with reference to the drawings.

Prior to the description of the present embodiment, the principle of the small signal spurious reduction process will be described.
FIG. 1 is a schematic configuration diagram showing an SNG system as an example, and TS indicates a master station.

  First, the master station TS outputs encoded data to be transmitted to the modulator 11. The modulator 11 modulates the input encoded data by a predetermined modulation method, and supplies this modulated signal to the frequency converter 12.

  The frequency converter 12 converts the frequency of the modulated signal into an RF band and outputs the converted signal to the power amplifier 13. The power amplifier 13 amplifies the input RF signal to a predetermined transmission power level, and transmits the amplified signal (main signal) from the antenna 15 to the satellite via the satellite circuit via the RF circuit 14.

  Further, the master station TS generates a data signal (small signal) using, for example, a communication line. Similar to the main signal, this small signal is transmitted from the antenna 15 to the satellite via the satellite line via the modulator 11, the frequency converter 12, the power amplifier 13, and the RF circuit 14.

By the way, there is the following method as a method for reducing the spurious of the small signal.
FIG. 2 shows an output signal when a two-wave signal source is input to the power amplifier 13. When one main signal wave and one small spurious wave output from the modulator 11 and the frequency converter 12 connected to the preceding stage of the power amplifier 13 are input to the power amplifier 13, a third-order mutual signal is present in the vicinity of the main signal. In addition to the occurrence of modulation products, it can be seen that second harmonics, third harmonics, etc. are generated, but these unnecessary waves are less likely to cause problems because they are at a level sufficiently lower than the input spurious signal. . On the other hand, as a method for reducing spurious input to the power amplifier together with the main signal, there is known a plan using distortion of input / output linearity (AM-AM characteristic) of the power amplifier.

  The proposal using the distortion of the AM-AM characteristic (input / output linearity) of the power amplifier is a technique in which a small signal is suppressed due to the AM-AM characteristic in a power amplifier that amplifies two waves in common. Known as “Capture Effect”. Examples of books include Gerard Maral et al., SATELLITE COMMUNICATIONS SYSTEMS P.444-445.

FIG. 3 shows the principle of capture effect generation in a model in which two waves of a large signal and a small signal are commonly amplified by a device having a non-linear AM-AM characteristic. FIG. 3A shows an example of spurious reduction using the nonlinear characteristic of the AM-AM characteristic, and FIG. 3B shows an example where the AM-AM characteristic is good and the spurious is not reduced. When the operating point of the two waves of the large signal and small signal is on the linear part of the Pin-Pout characteristic, the output of the small signal does not decrease due to ON / OFF of the large signal input (FIG. 3B )).

  However, if the operating point of the small signal is on the pin-pout characteristic, but the operating point of the large signal is on the non-linear area of the pin-pout characteristic, the input of the large signal The phenomenon that the output of the small signal decreases due to ON / OFF of the signal occurs, and if the small signal is regarded as spurious, it is effective to reduce the spurious when it is commonly amplified with the large signal as the main signal (FIG. 3A). .

  However, as shown in FIG. 3, the spurious reduction using the Capture Effect phenomenon is expected to have an effect of only a few dB. In addition, since nonlinearity of AM-AM characteristics affects distortion characteristics such as IMD, it is generally considered that linearity is important, and a linearizer should be introduced to correct nonlinearity linearly. This is more common, and an active filter based on Capture Effect is not realistic.

  In addition to the Capture Effect effect, we propose a method for effectively reducing small signal spurious in elements with nonlinear AM-AM characteristics such as GaN HEMT.

  The FET operation varies from a high Idset to a Class A, Class AB, Class B, and Class C depending on the setting of the idle current (Idset) as shown in FIG. In the GaN HEMT operating in the AB class, the drain current Ids increases or decreases according to the increase or decrease of the output power Pout. At this time, when the impedance Z of the drain circuit is finite as shown in FIG. 5, Vds varies depending on Ids that varies depending on Z and Pout. Since the device parameter of the transistor depends on Vds, it is modulated by Vds, which creates a memory effect and constitutes an active filter that reduces small signal spurious.

  The mechanism of the active filter based on the differential modulation of the drain bias is as follows.

An input signal of two waves indicated by frequencies ω1 and ω2 is indicated by x in (Equation 1), and an amplified output signal y is indicated by (Equation 2).

  The elements generated from this equation are shown in FIG.

From (Equation 1) and (Equation 2), the signal f_large wave F _L having a large amplitude and the f_small wave F _H having a small amplitude are represented by (Equation 3) and (Equation 4). f_large is a main signal, and f_small indicates spurious.

Disassemble (Equation 3) and (Equation 4).

Focusing on the f_small wave F _H , there is a second-order distortion term in which the f_small signal component includes the f_large amplitude component A ₁ . This second-order distortion term is expressed by the following equation.

At this time, the difference between the signal levels of f_large and f_small is large and A ₂ << A ₁ , so that f_small with a small signal level is largely suppressed by the amplitude component of f_large with a large signal level. From these equations, it can be seen that the suppression ratio can be reduced by controlling the components of a ₂ (nonlinear) and E (envelope).

Focusing on the envelope (E), the causal relationship between the f characteristic of the bias circuit and the suppression amount ΔP is shown. The F _L of the large amplitude signal f_large and the F _H of the small amplitude f_small are expressed by (Equation 3-1) and (Equation 4-1), which are expressed by the fundamental wave a ₁ x and the secondary distortion a. _When it is decomposed into terms of ₂ x / 2 and third-order distortion a ₃ x / 4, it is expressed as follows.

(Expression 3-2) and (Expression 4-2) are outputs in which the input signal x expressed by (Expression 1-1) is input to (Expression 2).

Here, only the fundamental wave and E are considered.

Here, it is assumed that the f_small wave F _H is on the small signal side, and E is only a complex number.

If the level of the f_small wave F _H is increased to the same level as the f_large wave F _L , the following formula is obtained.

There is almost no suppression to the output of f_small. That, F_small when there is no level difference f_large wave F _L and F_small wave F _H is not suppressed, F_small is suppressed when there is a level difference between f_large wave F _L and f_large wave F _H, which is the envelope (E Therefore, the spurious (f_small) is effectively suppressed by adjusting the frequency characteristics of the bias circuit and enlarging the envelope of an arbitrary frequency region. FIG. 7 is a graph showing the amount of small signal suppression under the condition of Equation 5.

  Figure 8 shows the spurious (f_small) when GaN HEMT is used to input f_large that is assumed to be the main signal and f_small that is assumed to be spurious at a maximum difference of 500 MHz from 14.0 GHz to 14.5 GHz at 100 MHz intervals. It is a three-axis plot diagram of the suppression amount ΔP. As shown in FIG. 10 described later, the spurious is greatly suppressed by increasing the impedance outside the envelope frequency region of the drain bias circuit. This is more effective than reducing spurious due to Capture Effect caused only by AM-AM characteristics.

  As described above, the device parameter of the transistor depends on Vds. As shown in FIG. 5, by increasing the impedance Z of the drain circuit in a frequency region that is greater than or equal to the desired bandwidth of the main signal, the envelope increases and the variation in Vds increases. Thereby, the differential modulation Vds (t) of the drain bias shown in FIG. 5 works, a memory effect is generated, and the spurious component of the small signal is suppressed.

  From the above equation, focusing on the second-order distortion component, the factor of the envelope (E) was extracted. Drain bias circuit for the wavelength of the main signal in order to make it smaller within the frequency range of the modulation band of the main signal f_large and the main intermodulation product and larger outside the frequency range of the modulation band of the main signal f_large and the main intermodulation product It is conceivable to adjust the inductor component and the decoupling capacitor multiplier according to the line length.

  FIG. 9 is a schematic circuit diagram, and FIG. 10 shows the impedance of the bias circuit in the envelope frequency range. As shown in FIG. 9, an inductor L is connected between a decoupling element D1 connected to the drain terminal side of the FET and a decoupling element D2 on the power supply (24V) side.

  FIG. 11 shows the filter characteristics when the inductor component is high and low. It turns out that it functions as a filter by making an inductor component high. Here, FIG. 11A shows the filter characteristics when the inductor component is high, and FIG. 11B shows the filter characteristics when the inductor component is low.

  Based on the above principle, the present embodiment will be described below.

  FIG. 12 is an equivalent circuit diagram of the power amplification device according to the present embodiment. Here, description will be made assuming that the power amplifier 13 is provided in the above-described FIG.

  An RF signal input to the package 100 of the internal match FET is supplied to the input terminal 101 and is amplified by the FET 103 via the LC circuit 102. An output signal from the drain terminal of the FET 103 is supplied to a decoupling element 104 including a resistor, a coil, and a capacitor, and an inductor component of the output signal is reduced. The output signal of the decoupling element 104 is taken out from the output terminal 106 via the LC circuit 105 and supplied to the subsequent RF circuit 14.

  Further, reference numeral 200 in FIG. 12 denotes a power supply circuit that supplies driving power to the FET 103 in the package 100. Further, a decoupling element 300 including a resistor, a coil, and a capacitor is connected between the power supply circuit 200 and the package 100 so as to be in parallel with the decoupling element 104.

  The decoupling element 300 serves as a low-pass filter that cuts the RF component from the output terminal 106 with respect to the power supply circuit 200. This prevents an output signal from the package 100 from entering the power supply circuit 200 with noise. Further, the capacitance value of the decoupling element 300 is larger than that of the decoupling element 104.

  By the way, in this embodiment, the filter 400 which consists of the inductor L is connected to the position within (lambda) / 4 wavelength of RF signal from the drain terminal of FET103. This filter 400 has a low impedance in the frequency band of the intermodulation product in the modulation band of the f_large signal and the output signal of the FET 103, and has a high impedance outside the frequency band of the modulation band of the f_large signal and the intermodulation product.

  Therefore, the RF signal output from the package 100 can suppress the envelope component of the difference frequency between f_large and f_small by the filter 400.

  As described above, in the above-described embodiment, the frequency range in which the spurious of the f_small signal is reduced follows the frequency of the f_large signal. A filter 400 that is small in the frequency domain of the intermodulation product in the output signal and large outside the frequency band of the f_large signal and the intermodulation product, that is, the inductor L, is connected between the decoupling element 104 and the decoupling element 300. For example, spurious near the f_large signal can be reduced.

(Other embodiments)
In addition, it is not limited to the above-described embodiment as it is, and in the implementation stage, the constituent elements can be modified and embodied without departing from the scope of the invention. In addition, various inventions can be formed by appropriately combining a plurality of components disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, constituent elements over different embodiments may be appropriately combined.

  DESCRIPTION OF SYMBOLS 11 ... Modulator, 12 ... Frequency converter, 13 ... Power amplifier, 14 ... RF circuit, 15 ... Antenna, 100 ... Package, 101 ... Input terminal, 102, 105 ... LC circuit, 103 ... FET, 104, 300 ... Decoupling Ring element 106... Output terminal 200... Power supply circuit 400.

Claims (5)

An RF (including a first signal having a predetermined frequency difference and a second signal having a signal level smaller than that of the first signal is provided in a package having an input terminal and an output terminal. FET (Field Effect Transistor) that amplifies the power to the transmission signal of the Radio Frequency) band and supplies it to the output terminal;
A first decoupling element that reduces and outputs an inductor component of a transmission signal output from the FET;
A power supply circuit for supplying driving power to the FET in the package;
A second decoupling element that cuts an RF component output from the output terminal to the power supply circuit;
Connected between the first decoupling element and the second decoupling element, with a predetermined first impedance in the frequency band of the intermodulation product in the modulation band of the first signal and the output signal of the FET, A power amplifying apparatus comprising: a filter having a second impedance higher than the first impedance outside the modulation band of the first signal and the frequency range of the intermodulation product.   The power amplifying apparatus according to claim 1, wherein the filter includes an inductor.   2. The power amplifying apparatus according to claim 1, wherein the capacitor values of the first and second decoupling elements are in a relationship of second decoupling element> first decoupling element. The first decoupling element is disposed inside the package;
The power amplifying apparatus according to claim 1, wherein the second decoupling element is disposed outside the package.   The power amplifying apparatus according to claim 1, wherein the first and second decoupling elements are composed of a plurality of elements.

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