JP5380319B2 - Power amplifier - Google Patents

Description

  The present invention relates to a power amplification device.

  The SNG (Satellite News Gathering) system is a system that collects broadcast program materials such as TV news using an artificial satellite. SNG portable earth stations such as SNG in-vehicle stations and Flyaway (portable earth stations not for in-vehicle use) are installed at ground bases for collecting broadcast program materials. In such an SNG portable earth station, a solid state power amplifier (SSPA) that uses a field effect transistor (FET) as a power amplifier for amplifying a transmission signal to transmission power may be employed. Many.

  The SNG system is required to transmit high-quality video material at a high bit rate. Therefore, the transmission of video material for broadcasting with a large amount of information is performed in a wide band, and the required EIRP (Equivalent Isotropicaly Radiated Power) is also increased. For this reason, a high power SSPA that uses a gallium nitride-based high electron mobility transistor (GaN HEMT) to realize a saturation power number of 100 W class is also provided for broadcasters.

  Satellite communication in the SNG system is generally performed in the C band (4 G to 8 GHz band) and the Ku band (12 G to 18 GHz band). In order to achieve the high gain of about 60 dB required in the SNG system, the FET Must be cascaded in cascade. In addition, the power amplification unit of the high power SSPA provides sufficient back-up of the operating point of the FET by distributing the signals by arranging the FETs in parallel at the final stage of the cascade connection so that the desired radio characteristics are satisfied during high power transmission. Secured off.

  Since the gain of the FET varies depending on the ambient temperature, a compensation function for making the gain constant is required particularly when cascaded. For example, Patent Document 1 describes a technique in which a temperature sensor is disposed in the vicinity of a main amplifier circuit and a distortion signal amplifier circuit, and the temperature of a heat generating element of each circuit and an element having a large characteristic change due to temperature is monitored. In this technique, gain characteristics depending on the temperature of each element are stored in advance in a lookup table, and temperature compensation is performed.

Japanese Patent Laying-Open No. 2007-82016 (paragraph 0014, FIG. 1)

  However, in the SSPA for satellite communication that performs communication in the Ku band or the like, when a plurality of FETs are arranged in parallel in order to distribute the input signal to a plurality of systems, due to the high frequency, due to substrate accuracy and adjustment tolerances. The distribution loss of each output port of the distributor may vary. If the operating points of the cascade-connected final stage FETs vary, the amount of heat generated by each FET also varies. For this reason, a temperature difference may occur between the FETs arranged in parallel. As in the technique described in Patent Document 1, in a method in which one temperature sensor is arranged in the vicinity of the amplifier circuit and the temperature at one point is detected, gain fluctuation due to a temperature change other than the location where the temperature is detected cannot be corrected.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a power amplifying apparatus that stably compensates for gain fluctuations due to fluctuations in temperature distribution.

  A power amplifying device according to an embodiment of the present invention includes a plurality of cascade-connected field effect transistors, wherein a plurality of field-effect transistors are arranged in parallel in the final stage of the cascade connection. Field effect transistors, a plurality of temperature sensors provided in the vicinity of at least two or more field effect transistors among the plurality of field effect transistors at the final stage of cascade connection, and gains of the plurality of field effect transistors And a control means for controlling the variable attenuator based on the temperature detection results of the plurality of temperature sensors.

  According to the present invention, it is possible to provide a power amplifying apparatus that stably compensates for gain fluctuation due to temperature distribution fluctuation.

The block diagram which shows the structure of the power amplifier which concerns on one Embodiment of this invention. The figure which shows an example of the relationship between a frequency and a gain in the case of calculating a gain compensation amount based on the temperature detection result of one FET, and amplifying a small signal. The figure which shows an example of the relationship between a frequency and a gain in the case of calculating a gain compensation amount based on the temperature detection result of one FET same as FIG. 2, and amplifying a large signal. The figure which shows an example of the temperature detection result of FET by each temperature sensor at the time of amplification of a small signal. The figure which shows an example of the temperature detection result at the time of amplifying the signal in the example of FIG. 4 to a large signal. The figure which shows an example of the temperature detection result in the case of performing the same large signal amplification as the example of FIG. The figure which shows an example of the relationship between a frequency and a gain in the case of amplifying a large signal with the power amplifier which concerns on this embodiment.

  Hereinafter, embodiments of a power amplifying device according to the present invention will be described with reference to the drawings.

  FIG. 1 is a block diagram showing a configuration of a power amplifier according to an embodiment of the present invention. As shown in FIG. 1, the power amplifier 10 according to the present embodiment is provided on a cooler (heat sink) 20. This power amplifier 10 is configured as an SPPA used for amplification of transmission power in an SNG portable earth station, for example.

  The power amplifier 10 includes a variable attenuator 11, temperature sensors 12 to 15, a control circuit 16, a plurality of field effect transistors (FETs), and distributors D-1 to D-7. Each of the plurality of FETs is a gallium arsenide FET, for example, and has a function of amplifying an input signal. FIG. 1 shows a six-stage cascade connection of these FETs. As the distributors D-1 to D-7, for example, branch line type distributors for high-frequency circuits can be used.

  An input signal input from the input terminal passes through the variable attenuator 11 and is supplied to the FET1 to FET3. FET1 to FET3 correspond to the first to third stages of cascade connection, respectively. The signal output from the FET 3 is distributed to two systems by the distributor D-1, and is supplied to the fourth stage FET 4-1 and FET 4-2, respectively.

  The output from the FET 4-1 is further divided into two systems by the distributor D- 2 and supplied to the fifth-stage FET 5-1 and the FET 5-2, respectively. Further, the output from the FET 4-2 is further divided into two systems by the distributor D- 3 and supplied to the fifth-stage FET 5-3 and the FET 5-4, respectively.

  Similarly, the output from the FET 5-1 is distributed to two systems by the distributor D-4, and is supplied to the sixth stage FET 6-1 and FET 6-2. The output from the FET 5-2 is distributed to two systems by the distributor D-5 and supplied to the sixth stage FET 6-3 and FET 6-4. The output from the FET 5-3 is distributed to two systems by the distributor D-6, and is supplied to the sixth stage FET 6-5 and FET 6-6. The output from the FET 5-4 is distributed to two systems by the distributor D-7, and is supplied to the sixth stage FET 6-7 and FET 6-8.

  As described above, in the power amplifier 10 shown in FIG. 1, the FETs 6-1 to 6-8 are arranged in parallel at the sixth stage, which is the final stage of the cascade. Input signals are distributed to eight systems in the sixth stage. The input signals distributed to the eight systems are output from the FETs 6-1 to 6-8, then synthesized again and output from the output terminals.

  Although FIG. 1 shows a six-stage cascade connection as an example, the number of cascade stages is not limited to this. For example, another FET may be cascade-connected between FET2 and FET3. FIG. 1 shows an example in which an input signal is distributed and amplified into eight systems, but the number of systems to be distributed is not limited to this. The input signal may be further distributed to a large number (or a small number) of systems.

  The temperature sensor 12 is provided in the vicinity of the final stage FET 6-1 and detects the temperature of the FET 6-1. The temperature sensor 13 is provided in the vicinity of the FET 6-3 and detects the temperature of the FET 6-3. Similarly, the temperature sensor 14 is provided in the vicinity of the FET 6-5 and detects the temperature of the FET 6-5. The temperature sensor 15 is provided in the vicinity of the FET 6-7 and detects the temperature of the FET 6-7. Each detected temperature is transmitted to the control circuit 16.

  In FIG. 1, four temperature sensors are shown as an example, but a larger number of temperature sensors may be provided to detect the temperature of other FETs in the final stage. Information on the temperature detected by each temperature sensor is transmitted to the control circuit 16.

  The control circuit 16 calculates a gain compensation amount based on the temperature detection results of the temperature sensors 12 to 15 and controls the variable attenuator 11 so that the gain of the entire power amplifier 10 is compensated by the calculated gain compensation amount.

  It is widely known that the temperature gradient of the gain of a gallium arsenide FET is 0.015 [dB / ° C.]. For this reason, the gain of the gallium arsenide FET increases when the temperature is low and decreases when the temperature is high. Not only gallium arsenide FETs but also silicon crystals and gallium nitride materials have similar temperature characteristics.

The gain fluctuation ΔG when the FETs are connected in multiple stages in a cascade is generally expressed by equation (1).

  In Equation (1), X represents the number of cascade stages, and ΔT represents a temperature change.

For example, in the case where 10 stages of gallium arsenide FETs are connected in cascade, if a temperature change of −20 ° C. to 60 ° C. occurs, the gain variation is obtained as 12 [dB] from the equation (2).

  As described above, the variation in the gain of the SSPA can be expressed by a function corresponding to the temperature change. For this reason, if the temperature change inside SSPA can be detected, the amount of gain to be compensated can be calculated from equation (1).

  However, in the power amplifier 10 in which a plurality of FETs are arranged in parallel in order to distribute the input signal to a plurality of systems, the dividers D-1 to D- are caused due to substrate accuracy and adjustment tolerance when a high-frequency signal is amplified. The distribution loss of each output port 7 may vary.

  If the operating points of the cascade-connected final stage FETs (FET6-1 to FET6-8) in the power amplifier 10 vary, the amount of heat generated by each FET also varies. In addition, individual differences in the amount of heat generated also occur due to differences in FET characteristics such as thermal resistance between flange and junction, power efficiency, and the like. Furthermore, since the high-frequency circuit pattern and the FET have frequency characteristics, the tendency of variation in the amount of generated heat varies depending on the frequency.

  In a power amplifier in which a plurality of FETs are arranged in parallel in the final stage of the cascade, variations in the amount of heat generated depending on the individual differences of devices and the frequency tend to be significant. Therefore, in the method in which only the temperature change at one point in the power amplifier 10 is detected and the variable attenuator 11 is changed, the gain cannot be stabilized in a short time. Also, since the amount of heat generated by each FET varies by changing the frequency and circuit settings, it is difficult to uniquely determine an appropriate temperature detection point.

  When gain compensation is performed by detecting the temperature of only an FET with a small amount of heat generation, even if an appropriate gain compensation amount can be calculated based on the formula (1) for a specific frequency, the frequency characteristics of the FET are different for different frequencies. Depending on the gain, the gain may deteriorate.

  FIG. 2 is a diagram illustrating an example of a relationship between frequency and gain when a gain compensation amount is calculated based on a temperature detection result of one FET and a small signal is amplified. FIG. 3 is a diagram illustrating an example of the relationship between frequency and gain when a gain compensation amount is calculated based on the temperature detection result of the same FET as in FIG. 2 and a large signal is amplified.

  As shown in FIG. 2, at the time of amplification of a small signal, an appropriate gain G1 can be obtained similarly at the frequency f1 with a small amount of heat generation and the frequency f2 with a large amount of heat generation. However, when a large signal is amplified, gain degradation occurs according to the frequency characteristics of the FET that is the target of temperature detection. That is, an appropriate gain G1 can be obtained by gain compensation at a frequency f1 with a small amount of heat generation, but a gain compensation amount becomes insufficient at a frequency f2 with a large amount of heat generation, and only a gain G2 smaller than G1 can be obtained.

  On the other hand, since the power amplifier 10 according to the present embodiment includes the plurality of temperature sensors 12 to 15, temperature changes can be detected at a plurality of temperature detection points. Therefore, it is possible to detect the temperature change of the FET according to the individual difference between the FETs arranged in parallel with higher sensitivity.

  The control circuit 16 monitors the plurality of FETs in the final stage in parallel, and calculates an average value of the detected temperatures of the plurality of FETs. Then, the gain compensation amount is calculated from the equation (1) based on the calculated average temperature. The variable attenuator 11 is controlled according to the gain compensation amount calculated based on the average temperature of each FET. Therefore, in the power amplifier 10 according to the present embodiment, temperature gain compensation can be performed without being affected by variations in temperature changes due to circuit patterns, individual differences in FETs, or frequencies. Furthermore, by averaging the temperature detection results of the temperature sensors 12 to 15, it is possible to remove the influence of variations in the detection accuracy of the temperature sensors.

  The temperatures of the respective FETs detected by the temperature sensors 12 to 15 usually take different values due to variations due to circuit patterns of the power amplifier 10 and individual differences among the FETs, variations due to frequencies, and variations in temperature detection accuracy.

  FIG. 4 is a diagram illustrating an example of the temperature detection result of the FET by each temperature sensor when a small signal is amplified. As shown in FIG. 4, the detected temperature varies for each FET. FIG. 5 is a diagram illustrating an example of a temperature detection result when the signal in the example of FIG. 4 is amplified to a large signal. As shown in FIG. 5, the temperature difference between the FETs increases during large signal amplification.

  FIG. 6 is a diagram illustrating an example of a temperature detection result when the same large signal amplification as that of the example of FIG. 5 is performed at a frequency different from that of the example of FIG. When the frequency varies, the amount of heat generated by each FET also varies according to the frequency characteristics of the circuit and the frequency characteristics of the FET. For this reason, even when the same large signal is amplified, the temperature detection result varies depending on the frequency as shown in FIGS. That is, the temperature distribution in the sixth stage of the same cascade varies, and the temperature differs for each FET.

  In the power amplifier 10 according to the present embodiment, the control circuit 16 calculates the average value of the detected temperatures of the temperature sensors 12 to 15 and determines the gain compensation amount. Therefore, for example, in the example shown in FIG. 4, the gain compensation amount is determined based on the average temperature T1. Further, the example of FIG. 5 and the example of FIG. 6 have the same temperature T2 although the temperature distribution is different. In either example, the control circuit 16 can determine the gain compensation amount based on the average temperature T2. Even in the case where the temperature detection result varies depending on the temperature distribution variation at one temperature detection point as in the examples of FIGS. 5 and 6, in this embodiment, compensation is performed based on the average temperature of the final stage FET. Therefore, it is possible to suppress variations in compensation amount.

  FIG. 7 is a diagram illustrating an example of the relationship between frequency and gain when a large signal is amplified by the power amplifier 10 according to the present embodiment. In the example shown in FIG. 3, when the large signal is amplified, the gain compensation amount is insufficient at the frequency f2 where the heat generation amount is large. However, in the power amplifier 10 according to the present embodiment, an appropriate gain compensation amount G ′ is appropriately calculated at the frequency f1 with a small amount of heat generation and the frequency f2 with a large amount of heat generation, and gain compensation can be performed with high accuracy.

  The control circuit 16 may calculate the average temperature by excluding the maximum value and the minimum value from the temperatures detected by the temperature sensors 12 to 15 and determine the gain compensation amount based on the average temperature. Alternatively, the control circuit 16 may calculate the average temperature by excluding the detected temperature outside the predetermined temperature range, and determine the gain compensation amount based on this normal air temperature. In addition, the control circuit 16 may calculate an average temperature by excluding a detected temperature that is greatly different from the detection results of other temperature sensors, and determine the gain compensation amount based on the average temperature. According to such a configuration, even when the temperature sensor detects an erroneous temperature (abnormal temperature) due to noise or the like, it is possible to perform control so that erroneous gain compensation based on the abnormal temperature is not performed.

  The present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the scope of the invention at the stage of implementation. Further, each of the embodiments includes inventions at various stages, and various inventions can be extracted by appropriately combining a plurality of disclosed constituent elements. For example, even if some constituent elements are deleted from all the constituent elements shown in one embodiment or the constituent elements shown in some embodiments are combined, they are described in the column of the problem to be solved by the invention. In the case where the problems described above can be solved and the effects described in the “Effects of the Invention” can be obtained, a configuration in which these constituent requirements are deleted or combined can be extracted as an invention.

  DESCRIPTION OF SYMBOLS 10 ... Power amplifier, 11 ... Variable attenuator, 12-15 ... Temperature sensor, 16 ... Control circuit, FET1-FET3 ... Field effect transistor, FET4-1-FET4-2 ... Field effect transistor, FET5-1-FET5- 4. Field effect transistor, FET6-1 to FET6-9, field effect transistor, D-1 to D7, distributor, 20 ... cooler.

Claims (4)

A variable attenuator that varies the input level of the input signal;
Multiple stages of field effect transistors are cascade-connected, and the final stage field effect transistors of each distribution system are arranged in parallel. Amplifying means for combining and outputting the output of
A plurality of temperature sensors that are arranged in the vicinity of two or more field effect transistors of the final stage field effect transistors and measure the respective ambient temperatures;
Control means for calculating an overall gain compensation amount of the amplifying means based on temperature detection results of the plurality of temperature sensors and controlling the variable attenuator based on the calculated gain compensation amount. Power amplification device. Before SL control means, the power amplifier according to claim 1, wherein the plurality of temperature sensors to calculate the average value of the temperatures detected, calculates the gain compensation amount based on the calculated average value.   The power amplifying apparatus according to claim 2, wherein the control unit calculates the average value by excluding a singular value from temperatures detected by the plurality of temperature sensors. The power amplifying apparatus according to claim 3, wherein the control unit excludes at least one of a maximum value and a minimum value from the temperatures detected by the plurality of temperature sensors as the singular value .

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