A temperature stabilization circuit for radio frequency power amplifier

Abstract

The present invention relates to the technical field of radio frequency power amplifiers, and specifically to a temperature stabilization circuit of a radio frequency power amplifier, including an output stage transistor array and an output stage bias circuit; the transistor bases of the output stage transistor array are weighted in the manner of 1, 21, 22…2n…22, 21, 1 to perform series resistance, and the output stage transistor array is connected to the output stage bias circuit through series resistance. The present invention utilizes the resistance value between the power tube and the bias circuit to introduce power tube voltage regulation, thereby reducing the temperature change caused by the order of power tube distribution arrangement. The temperature regulation circuit effectively suppresses the change of linearity with temperature. The optimized design of the overall circuit structure can effectively improve the temperature control accuracy of a single power tube in a cascade amplifier, improve the stability of the entire amplifier, extend the service life of the device, and reduce losses.

Description

Technical Field

[0001] The invention relates to the technical field of radio frequency power amplifiers, and in particular to a temperature stabilization circuit of a radio frequency power amplifier. Background Art

[0002] In modern wireless communication systems, RF power amplifiers are key components for wireless transmission of RF signals, and power control chips are important components of RF power amplifier modules. RF power amplifier chips are the core of the power amplifier module, and their main function is to amplify the modulated RF signal to the required power value. However, due to the change in the junction voltage drop of the power transistor caused by temperature changes, the output power of the RF power amplifier is greatly affected by temperature, resulting in a significant change in the output power of the power amplifier at different temperatures, which increases the difficulty and complexity of power control.

[0003] RF power amplifiers usually use heterojunction bipolar transistors (HBT), complementary metal oxide semiconductor transistors (CMOS), high electron mobility transistors (HEMT), etc. as amplifying transistors, which are called power tubes. Power tubes require a certain DC voltage and / or DC current when working, which is called biasing. If the bias circuit provides a DC voltage to the power tube, it is called a voltage biasing method. If the bias circuit provides a DC current to the power tube, it is called a current biasing method. Most of the existing RF power amplifiers use voltage biasing. However, new generation communication standards such as 4G and 5G have put forward new performance requirements for RF power amplifiers. Traditional voltage biased RF power amplifiers can no longer meet the new performance requirements. Therefore, current biased RF power amplifiers have begun to receive attention. An important problem that needs to be solved for RF power amplifiers using current biasing is temperature compensation.

[0004] In the temperature control circuit based on the power amplifier, we often use the temperature compensation circuit to reduce the influence of temperature on the circuit. The first method of temperature compensation for RF power amplifier is that the power control circuit collects the temperature information T of the RF power amplifier, and converts the temperature information T into the temperature compensation amount through the temperature compensation function f(T). The control circuit converts the control signal Vramp into the control VCCO (Veamp) and then superimposes it with the temperature compensation amount f(T) to obtain the final power control signal VCC = VCCO (Vramp) + f(T). The control circuit transmits the final power control signal VCC to the power amplifier to control the output power of the power amplifier. The second method is to perform temperature compensation on the constant bias current, or to convert the constant bias voltage into current and then perform temperature compensation, and provide the base of the power tube with a temperature-compensated bias current.

[0005] The current temperature compensation circuit has received extensive attention. The general temperature compensation circuit is to perform temperature compensation on a constant bias current, or convert a constant bias voltage into a current and then perform temperature compensation, and then provide a temperature-compensated bias current for the base of the power tube. However, this temperature adjustment method is only for temperature compensation of all transistors. In a complex multi-stage amplifier, because many transistors are required, and after the transistors are arranged in order, the temperature of transistors in different order in a certain level of power amplifier will be different due to thermal effects. If only the temperature compensation circuit is used, it can only control the temperature change of the power amplifier as a whole, which will cause a short board effect, low accuracy, and cause waste.

[0006] Based on the analysis of traditional temperature regulation circuits, this paper proposes a new type of temperature regulation circuit, which directly controls the resistance of a single transistor, thereby accurately and effectively avoiding the influence of thermal effects on the power amplifier, reducing the influence of temperature on linearity, reducing the output power changes caused by temperature changes, improving stability, and solving reliability problems such as overheating and burning. Summary of the invention

[0007] In view of the deficiencies in the prior art, the present invention discloses a temperature stabilization circuit for a radio frequency power amplifier. The present invention directly controls the resistance of a single transistor, thereby accurately and effectively avoiding the influence of thermal effects on the power amplifier, reducing the influence of temperature on linearity, reducing output power changes caused by temperature changes, improving stability, and solving reliability problems such as overheating and burning.

[0008] The present invention is achieved through the following technical solutions:

[0009] A temperature stabilization circuit for a radio frequency power amplifier comprises an output stage transistor array and an output stage bias circuit; the characteristic is that: the transistor bases of the output stage transistor array are weighted in a manner of 1, 21, 22 ... 2n ... 22, 21, 1 to perform series resistance, and the output stage transistor array is connected to the output stage bias circuit via the series resistance.

[0010] Preferably, the transistor increases the direct current negative feedback of the transistor through a resistor connected in series with the base, reduces the current of the transistor, and delays the display of the Kirk effect.

[0011] Preferably, the resistance value of the series resistor is determined by combining circuit simulation and thermal simulation.

[0012] Preferably, the temperature control circuit of the temperature stabilization circuit controls the temperature change of the transistor through a temperature and power supply voltage compensation circuit.

[0013] Preferably, the manner of the transistor base series resistance of the output stage transistor array can be determined by the thermal effect on the transistor and the arrangement position of the transistor.

[0014] The beneficial effects of the present invention are:

[0015] 1. Control the impact of transistor temperature changes by introducing temperature and power supply voltage compensation circuits. Directly use the connection characteristics of the bias circuit and the transistor, set different resistance values ​​at the place where the bias circuit connects to the transistor, use resistors R of different values ​​for different combinations, and use these different combinations to affect the bias current of the transistor or affect the bias voltage to change the bias current.

[0016] 2. This circuit directly controls a specific transistor based on the thermal effect of the transistor and the temperature changes caused by the different arrangement positions of the transistor. It has high precision and stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0018] Figure 1 It is the distribution heat effect diagram of the present invention;

[0019] Figure 2 It is a temperature control circuit diagram of the present invention;

[0020] Figure 3 It is a diagram of an output stage transistor array of a conventional radio frequency power amplifier of the present invention;

[0021] Figure 4 It is a schematic diagram of the output stage bias circuit of a conventional radio frequency power amplifier of the present invention;

[0022] Figure 5 is a schematic diagram of a temperature control circuit of a power amplifier of the present invention;

[0023] Figure 6 It is a specific implementation diagram of the power amplifier temperature control circuit of the present invention. DETAILED DESCRIPTION

[0024] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0025] Example 1

[0026] In view of the above-mentioned situation where the temperature of the parallel output device is different, this paper proposes a temperature control circuit based on the RF power amplifier. First, we introduce the classic solution: temperature compensation circuit. This classic method is to perform temperature compensation on the constant bias current, or to convert the constant bias voltage into current and then perform temperature compensation to provide the base of the power tube with a temperature-compensated bias current. However, this method is only for the case where M=1. If M is greater than 5, considering the distributed thermal effect mentioned above, it can only control the temperature change of the power amplifier as a whole, which will cause a short board effect, low accuracy, and waste.

[0027] Therefore, this paper proposes a ballast resistor network, that is, different transistors are connected to different resistance values ​​(such as Figure 2 ), and the resistance changes with the temperature in a gradient, so that the temperature change can be accurately controlled, the linearity change caused by the temperature change can be reduced, the stability can be improved, and the unreliability problems such as overheating and burning can be prevented. Compared with the previous methods, the present invention takes into account the temperature change of each transistor and proposes a solution, which can be accurate to a single transistor, avoid unnecessary waste, and reduce the impact of temperature on linearity, so as to have a good compromise between efficiency and linearity, and improve stability and prevent unreliability problems such as overheating and burning.

[0028] The RF power amplifier chip is the core part of the power amplifier module. Its main function is to amplify the modulated RF signal to the required power value. Therefore, when the power amplifier is in normal operation, it will generate a large output power, causing the transistor to heat up. The heating of the transistor will further cause the current to increase. As the current increases, it can be known that the power will further increase, which will fall into a vicious cycle. The temperature rises, the power increases, the power increases, and the temperature rises again, which will eventually cause the transistor to overheat and burn out the power amplifier.

[0029] For a multi-stage power amplifier, in order to output a relatively high power value, multiple parallel output devices are required. The number of parallel output devices is referred to as M. The so-called number of parallel output devices is the number of transistors required for a first-stage power amplifier, and the temperature of parallel output devices is different. Figure 1 As shown in the figure, the temperature of the transistor in the middle is higher than that of the transistors on the side. This is because the temperature of the transistor in the middle will increase due to its own operation, and the transistors on the left and right sides will generate a certain amount of radiation when working, affecting its temperature change. Therefore, the temperature of the parallel output device will present a temperature change graph with the highest temperature in the middle and a gradient change to both sides.

[0030] Example 2

[0031] like Figure 3 Figure 4 The output stage transistor array of a traditional power amplifier arranges many transistors in parallel to synthesize the output power. The base or gate is connected to a compensated voltage or current bias circuit through the same ballast resistor. The advantage of this structure is that the layout is simple, but it can easily lead to uneven temperature distribution between transistors. When the power amplifier is working, the transistor generates heat, causing the turn-on voltage of the PN junction to decrease. Under fixed external bias conditions, this will cause the bias current of the transistor to increase, which further increases the temperature of the transistor. The unstable characteristics of the transistor require that it must be connected to a thermal stabilization resistor. The traditional thermal stabilization resistor introduces negative feedback at the base level, which can effectively alleviate the thermal instability of the transistor and keep the amplifier stable as a whole. However, for Figure 3 In the transistor array shown, when the power amplifier is working, each array not only generates heat itself, but is also affected by the heat dissipated by the adjacent transistors. Taking the case of three transistors in parallel as an example, when working at the same time, the temperature of the middle transistor is higher than the transistors on both sides, which results in a lower PN junction turn-on voltage of the middle transistor. Under the same external bias and thermal resistance conditions, the middle transistor will draw more current from the bias circuit, resulting in a decrease in the base current of the other two transistors, which will cause the temperature difference between the three transistors to continue to expand. The final effect of this positive feedback is that the conduction current of the middle transistor occupies most of the overall circuit current, showing the Kirk effect prematurely, while the current of the other two transistors is low. The performance of the entire power amplifier is significantly deteriorated.

[0032] In order to effectively solve this problem and improve the overall performance of the power amplifier, this paper proposes a temperature control circuit based on each transistor.

[0033] like Figure 5As shown, since the temperature of the transistor in the middle position is higher, the self-heating effect of transistor 2 is more obvious. At this time, more resistors are connected in series at its base to increase the DC negative feedback of transistor 2. In this way, the current of transistor 2 will not be higher due to the higher temperature, preventing it from showing the Kirk effect earlier due to excessive current. The performance of all transistors is more balanced, so there will be no waste of current and deterioration of the performance of the power amplifier. In the specific circuit implementation, the number of base series resistors can be weighted in the manner of 1, 21, 22...2n...22, 21, 1. For example, the base series resistor of transistor 1 is 1, the base series resistor of transistor 2 is 2, and the base series resistor of transistor 3 is 1. Figure 6 A specific implementation method.

[0034] Example 3

[0035] like Figure 6 The circuit shown is a specific implementation of the power amplifier temperature control circuit. Among the five transistors arranged in parallel, the middle transistor should be the hottest. If a traditional temperature control circuit is used, the current flowing through the middle transistor is likely to be much larger than the transistors on both sides. In special cases, the middle transistor may flow 90% of all currents. The gain of the transistor itself is reduced due to the widening of the base region, and the performance of the power amplifier will be significantly deteriorated. The temperature control circuit structure proposed in this article can effectively avoid this problem. The current of the power amplifier flows through the five transistors more evenly, and the performance of any transistor will not deteriorate prematurely.

[0036] The specific way to load the resistor depends on the specific situation, and it is not necessary to follow the 1, 21, 22...2n...22, 21, 1 method. Because the temperature of the transistor is related to its own emission and the heat conduction of the adjacent transistor. The heat conduction of the adjacent transistor is related to the size of the transistor and the distance between the transistors. Under the condition that the transistor generates a lot of heat and the adjacent transistors are very close, the resistor in series with the base of the transistor close to the middle should be larger to control the temperature of the middle transistor. Correspondingly, if the situation is the opposite, the series resistance value can also be reduced accordingly. It is a reasonable solution to use circuit simulation and thermal simulation together to determine the base series resistance value of each transistor.

[0037] The present invention proposes a novel high-precision temperature regulation circuit with a simple structure. First: by introducing a temperature and power supply voltage compensation circuit to control the influence of temperature changes on the transistor. Directly utilize the connection characteristics between the bias circuit and the transistor, set different resistance values ​​at the place where the bias circuit is connected to the transistor, use resistors R of different values ​​for different combinations, and use these different combinations to affect the bias current of the transistor or affect the bias voltage to change the bias current. Second: the circuit directly controls a specific transistor for the temperature changes caused by the thermal effect of the transistor and the different arrangement positions of the transistor, with high precision and high stability.

[0038] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A temperature stabilization circuit for a radio frequency power amplifier, comprising an output stage transistor array and an output stage bias circuit; characterized in that: The transistor bases of the output stage transistor array are connected to series resistors, and the series resistors connected to the bases are connected according to 1, 2 1 , 2 2 …2 n …2 2 , 2 1 , weighted in the manner of 1, the output stage transistor array is connected to the output stage bias circuit through a series resistor; the transistor is connected to the base in series with a resistor so that the resistance value changes with the temperature in a gradient, thereby reducing the linearity change caused by temperature change, improving stability, and increasing the DC negative feedback of the transistor, reducing the current of the transistor, and finally causing the transistor delay to show the Kirk effect; The temperature control circuit of the temperature stabilization circuit controls the temperature change of the transistor through the temperature and power supply voltage compensation circuit, wherein the temperature control circuit includes a first resistor, a first bias transistor, a second bias transistor and a third bias transistor, one end of the first resistor and the collector of the third bias transistor are connected to the bias power supply voltage, the other end of the first resistor is respectively connected to the collector of the first bias transistor and the base of the third bias transistor, the collector of the first bias transistor is connected to the base of the first bias transistor, the emitter of the first bias transistor is connected to the collector of the second bias transistor, the collector of the second bias transistor is connected to the base of the second bias transistor, the emitter of the second bias transistor is grounded, and the emitter of the third bias transistor provides a bias current to the series resistor.

2. The temperature stabilization circuit of the radio frequency power amplifier according to claim 1, characterized in that: The resistance value of the series resistor is determined by combining circuit simulation and thermal simulation.

3. The temperature stabilization circuit of the radio frequency power amplifier according to claim 1, characterized in that: The manner of the series resistance of the transistor bases of the output stage transistor array may be determined by the thermal effect on the transistors and the arrangement positions of the transistors.

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