Biasing circuit for radio frequency power amplifier

Abstract

The invention discloses a biasing circuit for a radio frequency power amplifier, which comprises a large-signal self-adaptive linearization unit and a temperature feedback unit, the temperature feedback unit comprises a third transistor, a fourth transistor, a first resistor, a second resistor, a second capacitor and a third capacitor, the base electrode of the third transistor is connected with the large-signal self-adaptive linearization unit, and the base electrode of the fourth transistor is connected with the large-signal self-adaptive linearization unit; the emitter of the third transistor is connected with one end of the third capacitor, the other end of the third capacitor is connected with the base of the fourth transistor, and the collector of the fourth transistor is connected with one end of the second capacitor and one end of the second resistor. According to the biasing circuit for the radio frequency power amplifier, the offset of a quiescent working point of a radio frequency power tube can be compensated, linearization of output voltage is achieved, temperature compensation is carried out on the radio frequency power tube, mutual interference with a main path is reduced, and the working stability of the radio frequency amplifier is improved.

Description

Technical Field

[0001] This invention relates to the field of integrated circuits, and more specifically to a bias circuit for a radio frequency power amplifier. Background Technology

[0002] With the gradual maturation of technologies such as 5G, 6G, and Wi-Fi 7, the concept of the Internet of Things (IoT), connecting everything, is gradually entering the public eye. As one of the foundations of this technology, the power amplifier technology of the radio frequency (RF) front-end chip directly determines the wireless communication distance, signal quality, and power consumption of terminal devices, making it one of the most crucial components of the entire RF system. Faced with increasingly demanding technical specifications and a continuously expanding communication equipment market, there is an urgent need for power amplifiers with superior performance.

[0003] For a power amplifier chip, the main factors affecting its high linear power output are the series of reactions that occur in the transistors under high-power operating conditions. These include bias point drift caused by increasing the input voltage and a decrease in output power due to the increased internal operating temperature of the transistors under high-power conditions. To improve RF chips, the first step is to study methods to stabilize the bias point under varying input power; the second is to address the problem of output power changes caused by temperature variations.

[0004] Traditional bipolar transistor power amplifier bias circuits typically consist of two resistors connected in series to divide the voltage, such as... Figure 1 The power amplifier shown. Figure 1 In the circuit, resistors R1 and R2 provide bias current to the power transistor HBT. At room temperature (300K), the saturation current of the power transistor HBT is typically 26mA. Since the base current of the power transistor HBT is very small, it can be ignored. Therefore, the collector current Ic of the power transistor HBT can be expressed by equation (1) (V T Vbias is the voltage of the power transistor HBT as a function of temperature, and Vbias is the output voltage of the power transistor HBT. (1) By selecting appropriate resistor values ​​R1 and R2, the relationship between the bias circuit and the gain can be made less closely related. However, the collector current Ic of the power transistor HBT has an exponential correlation with the resistance values ​​of the bias circuit R1 and R2, and the collector current Ic is very sensitive to the accuracy of the resistor values. Even when using high-precision resistors, the output voltage Vbias of the bias circuit still has an exponential correlation with the collector current Ic, and changes in the bias circuit voltage have a significant impact on the quiescent operating point of the power transistor HBT.

[0005] Figure 1Besides the unstable output voltage Vbias, the power amplifier shown also exhibits the following issues: as the input increases, the transconductance of the power transistor HBT decreases, causing the HBT's quiescent operating point to shift (e.g., ...). Figure 2 The shift from P2 to P3 causes a series of problems such as reduced or even collapsed gain and phase distortion, thus deteriorating the circuit performance.

[0006] Variations in the transconductance (gm) of the power transistor (HBT) itself can lead to amplitude and phase distortion of the output signal, degrading the linearity of the entire system. As mentioned above, when the power transistor (HBT) operates at the peak power of the input signal, the high-power signal output by the power amplifier is distorted. Typically, the bias circuit, under high-power input conditions, will keep the power transistor (HBT) operating in the amplification region while preventing it from entering the saturation region. Therefore, to prevent the power transistor (HBT) from deviating from its quiescent operating point in the amplification region, the bias circuit needs to detect the main path input power and provide feedback compensation. Figure 2 The current ΔIC and voltage ΔVBE are shown. To eliminate the influence of the resistive element mentioned above on the output current of the bias circuit, the bias circuit generally adopts a current mirror structure to provide a stable bias current. The specific structure is as follows... Figure 3 As shown, this bias circuit structure is simple, requiring only three transistors to build the bias circuit and form a temperature-dependent negative feedback network, thus achieving temperature stability. Furthermore, the current changes caused by the temperature sensitivity of different transistors can be adjusted by changing resistor R3 to select the appropriate negative feedback.

[0007] exist Figure 3 In this transistor HBT1, the emitter current IE is related to the load resistance R3; if the resistance R3 increases, the current IE decreases. In a simple resistive load emitter follower, these two effects cancel each other out. However, due to the DC offset of the transistor HBT1 itself, the difference between the input and output of the transistor HBT1 should not be constant within the expected swing.

[0008] Meanwhile, transistor HBT3 couples the temperature signal. However, since transistors HBT0 and HBT1, acting as signal couplers, allow some of the main path signal to flow into transistor HBT3, they cannot transmit the actual signal. Temperature changes causing voltage and current variations in the temperature module superimposed on the main path interference signal affect the temperature feedback output voltage Vbias input to the main path. Simultaneously, the DC signal in the temperature feedback circuit also flows into the main path through resistor R3. When the temperature feedback circuit starts operating, these changing DC signals directly affect the linearity of the main path.

[0009] Therefore, it is necessary to provide an improved bias circuit for RF power amplifiers to overcome the above-mentioned defects. Summary of the Invention

[0010] The purpose of this invention is to provide a bias circuit for an RF power amplifier. The bias circuit of this invention can compensate for the offset of the static operating point of the RF power transistor, suppress interference from other signals, achieve linearization of the output voltage, and perform temperature compensation for the RF power transistor, thereby improving the operating stability of the RF amplifier.

[0011] To achieve the above objectives, the present invention provides a bias circuit for an RF power amplifier, comprising a large-signal adaptive linearization unit and a temperature feedback unit. The large-signal adaptive linearization unit is connected to the base of the power transistor of the power amplifier to compensate for the changing trend of the base bias voltage of the power transistor. The temperature feedback unit is connected to the large-signal adaptive linearization unit to compensate for the current change of the power transistor caused by temperature changes. The temperature feedback unit includes a third transistor, a fourth transistor, a first resistor, a second resistor, a second capacitor, and a third capacitor. The base of the third transistor is connected to the large-signal adaptive linearization unit, and its collector is connected to an external power supply voltage. The emitter of the third transistor is connected to one end of the third capacitor, and the other end of the third capacitor is connected to the base of the fourth transistor. The collector of the fourth transistor is connected to one end of the second capacitor and one end of the second resistor. The other end of the second capacitor is connected to the base of the third transistor. The emitter of the fourth transistor is grounded. The other end of the second resistor is connected to the base of the third transistor. One end of the first resistor is connected to the base of the third transistor, and the other end is connected to another power supply voltage.

[0012] Preferably, the large-signal adaptive linearization unit includes a second transistor, a first capacitor, and a load resistor. The gate of the second transistor is connected to the gate of the third transistor, its emitter is connected to one end of the load resistor, the other end of the load resistor is connected to the gate of the power transistor, the collector of the second transistor is connected to an external power supply voltage, one end of the first capacitor is connected to the gate of the second transistor, and the other end is grounded.

[0013] Preferably, the large-signal adaptive linearization unit further includes an inductor, one end of which is connected to the base of the power transistor, and the other end of which is connected to the other end of the load resistor.

[0014] Preferably, the bias circuit for the RF power amplifier further includes a filter unit connected between an external power supply voltage and the collectors of the second and third transistors.

[0015] Preferably, the filter unit includes a third resistor and a fourth capacitor. One end of the third resistor and the fourth capacitor are both connected to an external current and voltage. The other end of the third resistor is connected to the collectors of the second transistor and the third transistor. The other end of the fourth capacitor is grounded.

[0016] Preferably, the fourth transistor is located adjacent to the power transistor.

[0017] Compared with the prior art, the bias circuit for the RF power amplifier of the present invention, by setting the temperature feedback unit, senses the temperature change of the power transistor in real time and adjusts the magnitude of the bias current output from the bias circuit to the power transistor, thereby achieving temperature compensation for the power transistor and making the output signal of the power transistor more stable and reliable. In addition, by having the base-emitter voltage of the second transistor of the large signal adaptive linearization unit follow the change of the base-emitter voltage of the power transistor, the trend of the change of the base-emitter voltage of the power transistor is slowed down, and the linearity of the entire power amplifier is improved.

[0018] The invention will become clearer from the following description, taken in conjunction with the accompanying drawings, which are used to explain embodiments of the invention. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the circuit structure of an existing bipolar transistor power amplifier.

[0020] Figure 2 for Figure 1 The graph shows the static operating point of the circuit.

[0021] Figure 3 This is a schematic diagram of an existing power amplifier circuit with a temperature compensation structure.

[0022] Figure 4 This is a schematic diagram of the bias circuit for an RF power amplifier according to the present invention.

[0023] Figure 5 This is a comparison of simulation curves between the bias circuit of the present invention for an RF power amplifier and the bias circuit of the prior art. Detailed Implementation

[0024] Embodiments of the present invention will now be described with reference to the accompanying drawings, in which similar element reference numerals denote similar elements. As described above, the present invention provides a bias circuit for an RF power amplifier. This bias circuit can compensate for the offset of the quiescent operating point of the RF power transistor, achieve linearization of the output voltage, perform temperature compensation for the RF power transistor, reduce mutual interference with the main path, and improve the operating stability of the RF amplifier.

[0025] Please refer to Figure 4 , Figure 4This is a schematic diagram of the bias circuit for a radio frequency power amplifier according to the present invention. The specific structure and working principle of the radio frequency amplifier are well known to those skilled in the art and will not be described in detail here. Figure 4 As shown, the bias circuit for an RF power amplifier of the present invention mainly includes a large-signal adaptive linearization unit and a temperature feedback unit. The large-signal adaptive linearization unit is connected to the base of the power transistor HBT1 of the power amplifier to compensate for the changing trend of the base bias voltage of the power transistor HBT1. The temperature feedback unit is connected to the large-signal adaptive linearization unit to compensate for the current change of the power transistor HBT1 caused by temperature changes. This improves the linearity and stability of the output signal of the entire RF amplifier.

[0026] Specifically, the temperature feedback unit includes a third transistor HBT3, a fourth transistor HBT4, a first resistor R1, a second resistor R2, a second capacitor C2, and a third capacitor C3. The base of the third transistor HBT3 is connected to the large-signal adaptive linearization unit, and its collector is connected to an external power supply voltage VCC. The emitter of the third transistor HBT3 is connected to one end of the third capacitor C3, and the other end of the third capacitor C3 is connected to the base of the fourth transistor HBT4. The collector of the fourth transistor HBT4 is connected to one end of the second capacitor C2 and the second resistor R2. The other end of the second capacitor C2 is connected to the base of the third transistor HBT3. The emitter of the fourth transistor HBT4 is grounded. The other end of the second resistor R2 is connected to the base of the third transistor HBT3. One end of the first resistor R1 is connected to the base of the third transistor HBT3, and the other end is connected to another power supply voltage VDD. In this invention, the power supply voltage VCC and another power supply voltage VDD are the voltages that allow each transistor in the bias circuit to operate in the appropriate linear region at the static operating point, and these are common technical solutions in the field, so they will not be described in detail here. In a preferred embodiment of the present invention, the fourth transistor HBT4 is positioned adjacent to the power transistor HBT1 to sense the temperature change of the power transistor HBT1 in real time, thereby changing its own voltage and current accordingly. Specifically, when the power of the input RF signal RFin increases, the temperature of the power transistor HBT1 rises, and its on-state voltage VBE1 (base-emitter voltage) decreases. This causes the fourth transistor HBT4, adjacent to the power transistor HBT1, to sense the temperature change of the power transistor HBT1 in real time and follow the change. Consequently, the quiescent current IC4 of the fourth transistor HBT4, which is adjacent to the power transistor HBT1, also increases. This, in turn, increases the current flowing through the second resistor R2, which leads to a decrease in the base current of the third transistor HBT3. As a result, the bias current flowing into the main path (power amplifier circuit) through the large signal adaptive linearization unit decreases, ultimately causing a corresponding decrease in the voltage of the output amplified signal RFout. This achieves temperature compensation for the power transistor HBT1, thereby improving the stability of the output amplified signal RFout. Simultaneously, the second capacitor C2 and the third capacitor C3 are connected to the base and collector of the fourth transistor HBT4, which acts as a temperature sensor. This prevents the input radio frequency signal RFin from coupling into the fourth transistor HBT4, thereby interfering with its feedback temperature signal and ensuring the effectiveness of the temperature feedback unit in compensating for the temperature of the power transistor HBT1. Typically, in a transistor, IC = β × IB, and the β value of a common transistor is 120. Therefore, even a slight change in the base current can have a significant impact on the output current IC, making the base clearly have a greater influence on the output signal.As described in the background art, when the bias circuit of an existing power amplifier is working, some of the main path signal will enter the temperature sensing transistor through the radio frequency signal coupled with the temperature sensing transistor (such as the fourth transistor HBT4), thereby affecting the normal operation of the temperature feedback unit. In this invention, the fourth transistor HBT4, which is a temperature sensing transistor, can simultaneously suppress the flow of radio frequency signals into the fourth transistor HBT4 by adding a third capacitor C3 to its base, adding a second capacitor C2 and a second resistor R2 in parallel to its collector, so as to ensure the temperature compensation effect of the power transistor HBT1. Moreover, the DC feedback signal of the fourth transistor HBT4 can flow into the base of the second transistor HBT2 and the third transistor HBT3 connected through the second resistor R2, thereby realizing the transmission of the temperature feedback signal.

[0027] Furthermore, the large-signal adaptive linearization unit includes a second transistor HBT2, a first capacitor C1, and a load resistor R0. The gate of the second transistor HBT2 is connected to the gate of the third transistor HBT3, and its emitter is connected to one end of the load resistor R0. The other end of the load resistor R0 is connected to the gate of the power transistor HBT1. The collector of the second transistor HBT2 is connected to an external power supply voltage VCC. One end of the first capacitor C1 is connected to the gate of the second transistor HBT2, and the other end is grounded. When the RF power amplifier starts amplifying a high-power signal (the input RF signal RFin is a high-power signal), the input RF signal RFin enters the bias circuit through the load resistor R0 and the second transistor HBT2. As is well known, the bias circuit consists of multiple devices, and the emitter area of ​​each transistor in the bias circuit is much smaller than the emitter area of ​​the power transistor HBT1 in the main path (RF power amplifier) ​​(in practical applications, HBT1 consists of multiple transistors connected in parallel). Therefore, the impedance of the main path is much smaller than that of the bias circuit, so that only a portion of the RF signal RFin flows into the bias circuit, having very little impact on the main path signal. The magnitude of the signal flowing into the bias circuit through the main path is mainly affected by the load resistor R0 and the second transistor HBT2. If the overall impedance of the load resistor R0 and the second transistor HBT2 is large, it will suppress the inflow of the radio frequency signal. The inflowing radio frequency signal is converted into a DC signal after passing through the second transistor HBT2. Since the collector-base voltage VCB2 of the second transistor HBT2 is constant, its base-emitter voltage VBE2 decreases. The base-emitter voltage VBE1 of the power transistor HBT1 in the main path is as shown in equation (2): (2) Equation (2) shows that the base-emitter voltage VBE2 of the second transistor HBT2 compensates for the changing trend of the base bias voltage VBE1 of the power transistor HBT1. Since the bias voltage of the power transistor HBT1 is compensated, the trend of the transconductance of the power transistor HBT1 changing with the input signal is also compensated. Moreover, when the circuit is working, when a large signal is input, the base bias voltage VBE1 of the main path power transistor HBT1 increases, and at the same time, some radio frequency signals leak into the bias circuit. The base-emitter voltage VBE2 of the second transistor HBT2 has the same changing trend as the base bias voltage VBE1 of the power transistor HBT1. When the voltage VBE1 increases, the voltage VBE2 also increases. As can be seen from equation (2), the increase of the voltage VBE2 slows down the changing trend of the voltage VBE1. Therefore, the linearity of the output of the radio frequency amplifier is improved when a large signal is input.

[0028] In a preferred embodiment of the present invention, an inductor L1 is further provided in the large signal adaptive linearization unit. One end of the inductor L1 is connected to the base of the power transistor HBT1, and the other end is connected to the other end of the load resistor R0. The voltage L1 can completely suppress the flow of radio frequency signals into the bias circuit, adjust the influence of the bias circuit on the input impedance of the main path, and reduce the influence of the bias circuit structure on the main path.

[0029] Furthermore, the bias circuit for an RF power amplifier of the present invention further includes a filtering unit connected between an external power supply voltage VCC and the collectors of the second transistor HBT2 and the third transistor HBT3. Specifically, the filtering unit includes a third resistor R3 and a fourth capacitor C4. One end of the third resistor R3 and the fourth capacitor C4 are both connected to the external power supply voltage VCC, the other end of the third resistor R3 is connected to the collectors of the second transistor HBT2 and the third transistor HBT3, and the other end of the fourth capacitor C4 is grounded. By setting the third resistor R3 and the fourth capacitor C4, the RF interference signal from the external power supply circuit can be suppressed from flowing into the bias circuit, thereby affecting the operating performance of the bias circuit.

[0030] Please refer to the references. Figure 5 , Figure 5 This is a comparison of simulation curves between the bias circuit of the present invention for an RF power amplifier and a prior art bias circuit; the dashed line represents the curve of the prior art bias circuit, and the solid line represents the curve of the bias circuit of the present invention for an RF power amplifier. The two bias circuits are configured to provide the same static operating point to the RF path power transistor, and the simulation environment is set to be completely identical. Figure 5 As shown, when a high-power radio frequency signal is input, the bias circuit gradually exhibits output power saturation and gain collapse, while the radio frequency circuit of the present invention maintains the preset output power of the main path power transistor under high-power signal conditions.

[0031] In summary, the advantages of the bias circuit for the RF power amplifier of the present invention become more apparent when the power of the input RF signal is large. As the input power increases, the static operating point of the entire circuit changes further, and the load impedance also changes further, which makes the bias circuit of the present invention more stable, thereby increasing the stability of the RF power amplifier.

[0032] The present invention has been described above in conjunction with the preferred embodiments, but the present invention is not limited to the embodiments disclosed above, but should cover various modifications and equivalent combinations made in accordance with the essence of the present invention.

Claims

1. A bias circuit for an RF power amplifier, comprising a large-signal adaptive linearization unit and a temperature feedback unit, wherein the large-signal adaptive linearization unit is connected to the base of a power transistor of the power amplifier to compensate for the changing trend of the base bias voltage of the power transistor; the temperature feedback unit is connected to the large-signal adaptive linearization unit to compensate for the current change of the power transistor caused by temperature changes; characterized in that, The temperature feedback unit includes a third transistor, a fourth transistor, a first resistor, a second resistor, a second capacitor, and a third capacitor. The base of the third transistor is connected to the large-signal adaptive linearization unit, and its collector is connected to an external power supply voltage. The emitter of the third transistor is connected to one end of the third capacitor, and the other end of the third capacitor is connected to the base of the fourth transistor. The collector of the fourth transistor is connected to one end of the second capacitor and the second resistor, and the other end of the second capacitor is connected to the base of the third transistor. The emitter of the fourth transistor is grounded, and the other end of the second resistor is connected to the base of the third transistor. One end of the first resistor is connected to the base of the third transistor, and the other end is connected to another power supply voltage.

2. The bias circuit for an RF power amplifier as described in claim 1, characterized in that, The large-signal adaptive linearization unit includes a second transistor, a first capacitor, and a load resistor. The gate of the second transistor is connected to the gate of the third transistor, its emitter is connected to one end of the load resistor, the other end of the load resistor is connected to the gate of the power transistor, the collector of the second transistor is connected to an external power supply voltage, one end of the first capacitor is connected to the gate of the second transistor, and the other end is grounded.

3. The bias circuit for an RF power amplifier as described in claim 2, characterized in that, The large-signal adaptive linearization unit also includes an inductor, one end of which is connected to the base of the power transistor, and the other end is connected to the other end of the load resistor.

4. The bias circuit for an RF power amplifier as described in claim 1, characterized in that, It also includes a filtering unit, which is connected between an external power supply voltage and the collectors of the second transistor and the third transistor.

5. The bias circuit for an RF power amplifier as described in claim 4, characterized in that, The filter unit includes a third resistor and a fourth capacitor. One end of the third resistor and the fourth capacitor are connected to an external current and voltage. The other end of the third resistor is connected to the collectors of the second transistor and the third transistor. The other end of the fourth capacitor is grounded.

6. The bias circuit for an RF power amplifier as described in claim 1, characterized in that, The fourth transistor is located adjacent to the power transistor.

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