阅读说明：本技术 偏置电路及射频功率放大器 (Bias circuit and radio frequency power amplifier ) 是由 彭振飞 徐柏鸣 苏强 于 2021-03-30 设计创作，主要内容包括：本申请公开了一种偏置电路及射频功率放大器。其中,偏置电路包括：控制环路,用于向射频功率放大器的输入端输出偏置电流；调节电路,用于在确定所述控制环路输出的偏置电流能够满足第一条件的情况下,基于米勒效应调节所述控制环路的环路带宽,以使所述控制环路的稳定性和噪声抑制度满足第二条件。采用本申请的方案,射频功率放大器的输入信号的带宽增大时,在保证偏置电流能够补偿射频功率放大器的基极电流,使得所述基极电流不随输入信号的功率的增大而降低,从而抑制射频功率放大器的幅度调制对幅度调制(AM-AM)失真的前提下,能够减少偏置电路可能产生的电路振荡及噪声对射频功率放大器接收信号时的灵敏度的影响,提升射频功率放大器的性能。(The application discloses a bias circuit and a radio frequency power amplifier. Wherein, the bias circuit includes: the control loop is used for outputting bias current to the input end of the radio frequency power amplifier; and the adjusting circuit is used for adjusting the loop bandwidth of the control loop based on the Miller effect under the condition that the bias current output by the control loop can meet a first condition, so that the stability and the noise suppression degree of the control loop meet a second condition. By adopting the scheme of the application, when the bandwidth of the input signal of the radio frequency power amplifier is increased, the base current of the radio frequency power amplifier can be compensated by the bias current, so that the base current is not reduced along with the increase of the power of the input signal, and the influence of circuit oscillation and noise possibly generated by the bias circuit on the sensitivity of the radio frequency power amplifier in receiving the signal can be reduced on the premise of inhibiting the amplitude modulation of the radio frequency power amplifier from distorting the amplitude modulation (AM-AM), and the performance of the radio frequency power amplifier is improved.)

1. A bias circuit, comprising:

the control loop is used for outputting bias current to the input end of the radio frequency power amplifier;

the adjusting circuit is used for adjusting the loop bandwidth of the control loop based on the Miller effect under the condition that the bias current output by the control loop can meet a first condition, so that the stability and the noise suppression degree of the control loop meet a second condition; wherein the content of the first and second substances,

the first condition characterizes that the bias current can compensate a base current of the radio frequency power amplifier, so that the base current is not reduced along with the increase of the power of an input signal;

the second condition characterizes that a phase margin of the control loop is greater than or equal to 45 degrees and a noise suppression degree of the control loop enables noise of the radio frequency power amplifier to be less than or equal to a noise threshold.

2. The bias circuit of claim 1, wherein the adjustment circuit comprises a miller cell; the adjustment circuit adjusts a loop bandwidth of the control loop based on a Miller effect of the Miller unit.

3. The bias circuit of claim 2, wherein the miller cell is connected in parallel with a first transistor of the control loop; wherein the content of the first and second substances,

the control loop comprises the first transistor, a second transistor and a first resistor; the collector of the first transistor is connected with the base of the second transistor; an emitter of the second transistor is connected with one end of the first resistor; the other end of the first resistor is connected with a base electrode of the first transistor; an external current source inputs a current to the control loop through a first node between the first transistor and the second transistor; the control loop converts the input current into the bias current and outputs the bias current to the input end of the radio frequency power amplifier through the emitter of the second transistor.

4. The bias circuit of claim 3, wherein the Miller cell comprises a first capacitor.

5. The bias circuit of claim 4, wherein the first capacitance is a variable capacitance.

6. The bias circuit of claim 4, wherein the adjustment circuit further comprises a second resistor; the first capacitor and the second resistor are connected with the first transistor in parallel; wherein the content of the first and second substances,

the adjusting circuit adjusts the transmission zero point of the control loop through the second resistor so that the stability of the control loop meets a third condition; the transmission zero is introduced by the first transistor in parallel with the first capacitor; the third condition characterizes a phase margin of the control loop to be greater than or equal to 45 degrees.

7. The bias circuit of claim 6, wherein the first capacitor and the second resistor are connected in parallel with the first transistor through a collector and a base of the first transistor.

8. The bias circuit of claim 6, wherein the adjustment circuit further comprises a third resistor; the third resistor is connected with the first transistor in series; wherein the content of the first and second substances,

the adjusting circuit isolates a radio frequency signal for the first transistor through the third resistor, so that the radio frequency signal cannot be coupled to the first transistor through the first capacitor and the second resistor; the radio frequency signal is transmitted to the bias circuit through an input of the radio frequency power amplifier.

9. The bias circuit of claim 8, wherein the third resistor is in series with a collector of the first transistor.

10. The bias circuit according to any one of claims 3 to 9, further comprising a fourth resistor; the bias current is output to the input end of the radio frequency power amplifier through the fourth resistor; wherein the content of the first and second substances,

the bias circuit attenuates the radio-frequency signal transmitted through the input end of the radio-frequency power amplifier through the fourth resistor; isolating the radio-frequency signal attenuated by the fourth resistor for the first transistor through the first resistor, so that the radio-frequency signal attenuated by the fourth resistor is transmitted to the second transistor;

under the action of the radio-frequency swing of the radio-frequency signal attenuated by the fourth resistor, the bias current output by the transmitting stage of the second transistor is changed along with the change of the power of the radio-frequency signal through the detection effect of the second transistor.

11. The bias circuit of any of claims 3 to 9, wherein the first resistor is a variable resistor.

12. The bias circuit of claim 10, further comprising a second capacitance; one end of the second capacitor is grounded, and the other end of the second capacitor is connected with the base electrode of the second transistor; wherein the content of the first and second substances,

the bias circuit enables the radio-frequency signal which is transmitted to the second transistor and is attenuated by the fourth resistor to be short-circuited to the ground through the second capacitor.

13. A radio frequency power amplifier, characterized in that the input of the radio frequency power amplifier is provided with the bias circuit of any one of claims 1 to 12.

14. The rf power amplifier of claim 13, wherein the rf power amplifier is a multi-stage cascaded rf power amplifier; wherein the content of the first and second substances,

the input end of each stage is provided with the bias circuit.

Technical Field

The present application relates to the field of integrated circuit technologies, and in particular, to a bias circuit and a radio frequency power amplifier.

Background

Compared with the Long Term Evolution (LTE) system of the fourth Generation mobile communication technology (4G, 4th Generation), the New air interface (NR, New Radio) system of the fifth Generation mobile communication technology (5G, 5th Generation) has a higher requirement on the data transmission rate, and needs to use a modulation signal with wider bandwidth to transmit data, and takes the frequency band N41 (2490 megahertz (MHz) to 2690 MHz) as an example, the maximum modulation signal bandwidth is extended from 40MHz to 100MHz, which provides a New challenge for the design of the Radio frequency power amplifier in the mobile terminal, and how to improve the performance of the Radio frequency power amplifier becomes a problem to be solved urgently.

Disclosure of Invention

In order to solve the related art problems, embodiments of the present application provide a bias circuit and a radio frequency power amplifier.

The technical scheme of the embodiment of the application is realized as follows:

an embodiment of the present application provides a bias circuit, including:

the control loop is used for outputting bias current to the input end of the radio frequency power amplifier;

the adjusting circuit is used for adjusting the loop bandwidth of the control loop based on the Miller effect under the condition that the bias current output by the control loop can meet a first condition, so that the stability and the noise suppression degree of the control loop meet a second condition; wherein the content of the first and second substances,

the first condition characterizes that the bias current can compensate a base current of the radio frequency power amplifier, so that the base current is not reduced along with the increase of the power of an input signal;

the second condition characterizes that a phase margin of the control loop is greater than or equal to 45 degrees and a noise suppression degree of the control loop enables noise of the radio frequency power amplifier to be less than or equal to a noise threshold.

In the above scheme, the adjusting circuit includes a miller unit; the adjustment circuit adjusts a loop bandwidth of the control loop based on a Miller effect of the Miller unit.

In the above solution, the miller unit is connected in parallel with the first transistor of the control loop; wherein the content of the first and second substances,

the control loop comprises the first transistor, a second transistor and a first resistor; the collector of the first transistor is connected with the base of the second transistor; an emitter of the second transistor is connected with one end of the first resistor; the other end of the first resistor is connected with a base electrode of the first transistor; an external current source inputs a current to the control loop through a first node between the first transistor and the second transistor; the control loop converts the input current into the bias current and outputs the bias current to the input end of the radio frequency power amplifier through the emitter of the second transistor.

In the above scheme, the miller cell includes a first capacitor.

In the above scheme, the first capacitor is a variable capacitor.

In the above solution, the adjusting circuit further includes a second resistor; the first capacitor and the second resistor are connected with the first transistor in parallel; wherein the content of the first and second substances,

the adjusting circuit adjusts the transmission zero point of the control loop through the second resistor so that the stability of the control loop meets a third condition; the transmission zero is introduced by the first transistor in parallel with the first capacitor; the third condition characterizes a phase margin of the control loop to be greater than or equal to 45 degrees.

In the above solution, the first capacitor and the second resistor are connected in parallel to the first transistor through the collector and the base of the first transistor.

In the above solution, the adjusting circuit further includes a third resistor; the third resistor is connected with the first transistor in series; wherein the content of the first and second substances,

the adjusting circuit isolates a radio frequency signal for the first transistor through the third resistor, so that the radio frequency signal cannot be coupled to the first transistor through the first capacitor and the second resistor; the radio frequency signal is transmitted to the bias circuit through an input of the radio frequency power amplifier.

In the above solution, the third resistor is connected in series with the collector of the first transistor.

In the above scheme, the bias circuit further includes a fourth resistor; the bias current is output to the input end of the radio frequency power amplifier through the fourth resistor; wherein the content of the first and second substances,

the bias circuit attenuates the radio-frequency signal transmitted through the input end of the radio-frequency power amplifier through the fourth resistor; isolating the radio-frequency signal attenuated by the fourth resistor for the first transistor through the first resistor, so that the radio-frequency signal attenuated by the fourth resistor is transmitted to the second transistor;

under the action of the radio-frequency swing of the radio-frequency signal attenuated by the fourth resistor, the bias current output by the transmitting stage of the second transistor is changed along with the change of the power of the radio-frequency signal through the detection effect of the second transistor.

In the above scheme, the first resistor is a variable resistor.

In the above scheme, the bias circuit further includes a second capacitor; one end of the second capacitor is grounded, and the other end of the second capacitor is connected with the base electrode of the second transistor; wherein the content of the first and second substances,

the bias circuit enables the radio-frequency signal which is transmitted to the second transistor and is attenuated by the fourth resistor to be short-circuited to the ground through the second capacitor.

The embodiment of the application also provides a radio frequency power amplifier, and the input end of the radio frequency power amplifier is provided with the bias circuit in any scheme.

In the above scheme, the rf power amplifier is a multistage cascaded rf power amplifier; wherein the content of the first and second substances,

the input end of each stage is provided with the bias circuit.

The bias circuit and the radio frequency power amplifier provided by the embodiment of the application, the bias circuit comprises: the control loop is used for outputting bias current to the input end of the radio frequency power amplifier; the adjusting circuit is used for adjusting the loop bandwidth of the control loop based on the Miller effect under the condition that the bias current output by the control loop can meet a first condition, so that the stability and the noise suppression degree of the control loop meet a second condition; wherein the first condition characterizes that the bias current is capable of compensating a base current of the radio frequency power amplifier such that the base current does not decrease with an increase in power of an input signal; the second condition is characterized in that the phase margin of the control loop is greater than or equal to 45 degrees, and the noise suppression degree of the control loop can enable the noise of the radio frequency power amplifier to be less than or equal to a noise threshold value; the bias circuit is arranged at the input end of the radio frequency power amplifier. In the scheme of the embodiment of the application, the bias circuit includes a loop structure, so that the bias circuit has the characteristic of low baseband impedance, in other words, the bias circuit provides a low baseband impedance path for the radio frequency Power amplifier, so that the memory effect of the radio frequency Power amplifier caused by the baseband impedance can be reduced (i.e., can be suppressed), and thus the deterioration of the Adjacent Channel Power Ratio (ACPR) of the output signal of the radio frequency Power amplifier caused by the memory effect can be reduced, the distortion of the output signal of the radio frequency Power amplifier is reduced, and the performance of the radio frequency Power amplifier is further improved. Meanwhile, adjusting the loop bandwidth of the control loop by using an adjusting circuit under the condition that the bias current output by the control loop can meet a first condition so that the stability and the noise suppression degree of the control loop meet a second condition; therefore, when the bandwidth of the input signal of the radio frequency power amplifier is increased, the base current of the radio frequency power amplifier can be compensated by the bias current, so that the base current is not reduced along with the increase of the power of the input signal, the stability and the noise suppression degree of a control loop included in the bias circuit can be considered on the premise of restraining amplitude modulation (AM-AM) distortion of the radio frequency power amplifier (AM-AM distortion refers to the distortion of the output signal of the radio frequency power amplifier relative to the input signal in amplitude), the influence of circuit oscillation and noise possibly generated by the bias circuit on the sensitivity of the radio frequency power amplifier when receiving the signal is reduced, and the performance of the radio frequency power amplifier is further improved.

Drawings

FIG. 1 is a schematic diagram illustrating asymmetry in third-order intermodulation of an RF power amplifier according to the related art;

FIG. 2 is a schematic diagram of a bias circuit in the related art;

FIG. 3 is a schematic diagram of another bias circuit in the related art;

fig. 4 is a diagram illustrating a frequency response of the impedance of the bias circuit 300 in the related art in the entire frequency band;

FIG. 5 is a schematic diagram of the loop gain of the bias circuit 300 in the related art;

FIG. 6 is a diagram illustrating phase margins of a bias circuit 300 according to the related art;

FIG. 7 is a schematic diagram of a bias circuit according to an embodiment of the present disclosure;

FIG. 8 is a schematic diagram of another embodiment of a bias circuit;

FIG. 9 shows an exemplary embodiment of the present invention in which the impedance of the bias circuit 700 is dependent on the parallel capacitance C₇Schematic illustration of a variation;

FIG. 10 shows the loop gain of the bias circuit 700 as a function of the shunt capacitance C according to an embodiment of the present application₇Schematic illustration of a variation;

FIG. 11 is a graph of phase margin versus shunt capacitance C for a bias circuit 700 in accordance with an embodiment of the present invention₇Schematic illustration of a variation;

FIG. 12 shows an embodiment of the present application in which an RF signal passes through a parallel capacitor C₇And a parallel resistor R₄Is coupled to T₅A schematic diagram of (a);

fig. 13 is a schematic structural diagram of a radio frequency power amplifier according to an embodiment of the present application.

Detailed Description

The present application will be described in further detail with reference to the following drawings and examples.

The radio frequency power amplifier in the mobile terminal generally comprises an input matching circuit, an output matching circuit, an amplifier tube, a bias circuit and the like, wherein the impedance of frequency response devices such as an inductor, a capacitor and the like is consistent only in a limited frequency bandwidth, in a 5G NR system, along with the widening of the bandwidth of a modulation signal, the impedance response of the radio frequency power amplifier on different frequencies is different, so that the modulation signal is superimposed with additional amplitude and phase change, and the third-order intermodulation component IM3 is asymmetric, namely the radio frequency power amplifier has a memory effect.

Illustratively, the input signal at the rf power amplifier is a constant amplitude two-tone signal (the corresponding two frequencies can be respectively expressed as f)₁And f₂And f is₁<f₂) Based on the expansion of the nonlinear polynomial of the radio frequency power amplifier, it can be determined that: the third-order non-linear product of the radio frequency power amplifier comprises a third-order current vector I₃，I₃Containing 2f₁-f₂And 2f₂-f₁(i.e. I)₃The corresponding two frequencies can be denoted as 2f₁-f₂And 2f₂-f₁) Radio frequency power amplifier at 2f₁-f₂Impedance response at frequency point and 2f₂-f₁Impedance response at frequency point is substantially uniform, and 2f₁-f₂Corresponding current vector sum 2f₂-f₁Corresponding current vectors are similar; the contributing parts of the second-order nonlinear products of the rf power amplifier mainly include: second order current vector I₁、I₂And I₄(ii) a Wherein, I₁And I₂For baseband envelope signals, respectively containing f₁-f₂And f₂-f₁(i.e. I)₁And I₂The two frequencies respectively corresponding can be denoted as f₁-f₂And f₂-f₁），f₁-f₂Corresponding current vector sum f₂-f₁The corresponding current vectors are equal in magnitude but different in phase; i is₄Is a second harmonic signal, including 2f₁And 2f₂(i.e. I)₄The corresponding two frequencies can be denoted as 2f₁And 2f₂) Radio frequency power amplifier at 2f₁Impedance response at frequency point and 2f₂Impedance response at frequency point is substantially uniform, and 2f₁Corresponding current vector sum 2f₂Corresponding current vectors are similar. As shown in FIG. 1, the third-order intermodulation product IM3 is the current vector I₁、I₂、I₃And I₄The upper sideband IM3_ Up and the lower sideband IM3_ Low are asymmetric, i.e. the rf power amplifier has memory effect.

When the radio frequency power amplifier is designed for a scene with a narrow modulation signal bandwidth (that is, the maximum modulation signal bandwidth is less than or equal to 20 MHz), because the frequency response of the impedance of each node in the radio frequency power amplifier is relatively consistent and the memory effect is weak, the interstage impedance and the load impedance of the radio frequency power amplifier can be designed in a region which is compatible with both ACPR and efficiency, so that the problem that the ACPR of an output signal is deteriorated due to the nonlinear amplification characteristic of the radio frequency power amplifier under the condition of large signal (that is, signal with large power) input is solved.

When the radio frequency power amplifier is designed for a scene with a wider modulation signal bandwidth (that is, the maximum modulation signal bandwidth is greater than or equal to 40 MHz), the frequency response difference of the impedance of each node in the radio frequency power amplifier is increased along with the widening of the modulation signal frequency band, and the displayed memory effect is more serious, that is, three-order intermodulation has obvious asymmetry, so that the ACPR of an output signal is deteriorated. At this time, if the linear power of the radio frequency power amplifier is increased by reducing the load impedance when designing the narrow band radio frequency power amplifier (i.e. the radio frequency power amplifier designed for the scene with narrower modulation signal bandwidth), only the third order current vector I can be reduced₃The distortion introduced, for a second order current vector I₁、I₂And I₄The distortion improvement is weak, so that the ACPR improvement effect is not good, and the power consumption of the rf power amplifier tends to become unacceptable (e.g., the power consumption exceeds the budget).

To reduce the influence of memory effect on ACPR, the second-order current vector I can be reduced₁、I₂And I₄The distortion is brought into consideration, and the current vector I is reduced by manufacturing a baseband, a second-order frequency and low resistance and the like at the input and output nodes of the radio frequency power amplifier₁、I₂And I₄Amplitude generated by impedance flowing through these nodes, thereby improving RF power amplifierThe condition of deterioration of the output signal ACPR.

Specifically, a bias network with low baseband impedance can be used for realizing low impedance of baseband frequency at an input node of the radio frequency power amplifier and suppressing the current vector I₁And I₂Is measured. As shown in fig. 2, the radio frequency power amplifier includes: input matching capacitor C₁Amplifying transistor T₁Output matching inductor L₁、L₂And L₃Capacitor C₂、C₃And C₄And a bias circuit 200. Radio frequency signals pass through RFin and C₁Enter into T₁Amplifying, and passing through output matching circuit (including L)₁、L₂、L₃、C₂、C₃And C₄) Output to Rfout. Wherein the bias circuit 200 comprises an isolation resistor R₁Transistor T₂、T₃And T₄And a capacitor C₅(ii) a The bias circuit 200 converts the current Ib1 input by the external current source into a bias current I_em3And through R₁To the input of the rf power amplifier, the impedance Zin1 of the node a in the bias circuit 200 (i.e., the baseband impedance of the bias circuit 200) can be expressed by the following equation:

（1）

wherein R is_e3Represents T₃The emitter via resistance of (a) can be calculated by the following equation:

（2）

wherein VT represents T₃Thermal voltage of (I)_em3Represents T₃The bias current of (1). Illustratively, R₁Taking 15 ohms (Ohm), VT is about 26 millivolts (mV) at room temperature, transistor T₁Has a bias current of 100 milliamperes (mA), I_em3About 0.6 mA; at this time, R_e3About 43ohm (i.e., 26mV/0.6 mA), Zin1 is about 58ohm (i.e., 43 o)hm +15 Ohm). It can be seen that the baseband impedance of the bias circuit 200 is relatively high, which cannot effectively improve the deterioration of the ACPR output signal.

The bias circuit 200 may be modified to further reduce the baseband impedance of the bias circuit and thereby improve the degradation of the output signal ACPR of the rf power amplifier. As shown in fig. 3, the bias circuit 300 includes: transistor T₅And T₆Isolation resistor R₂And R₃And a capacitor C₆. Under the condition that no radio frequency signal is input into the radio frequency power amplifier, the bias circuit 300 converts the current Ib1 input by the external current source into the appropriate static bias current I_em6And through a resistor R₂And outputting the signal to the input end of the radio frequency power amplifier. The bias circuit 300 passes through R in the case where there is an rf signal input to the rf power amplifier₂Blocking most of the rf signal from leaking from the bias circuit (i.e. attenuating the rf signal transmitted through the input of the rf power amplifier, R)₂May take a small value, such as 15 Ohm) and pass through R₃Is T₅Base low-resistance point isolation of₂Attenuated RF signal (to improve isolation of RF signal, R)₃Is more critical, and usually needs to take a larger value, such as 2000 Ohm) so as to be R₂The attenuated RF signal is transmitted to T₆By being R₂The attenuated RF signal, if the RF signal is a large signal (i.e. a signal with large power), T₆The emitter of (2) has a certain radio frequency swing which passes through T₆The detection effect of the BE junction of (1) makes the bias voltage of the BE junction small, thereby making T₆I of emitter output_em6Increase (i.e. I)_em6Increases with increasing power of the input signal of the radio frequency power amplifier), T can be compensated for₁The base voltage is reduced along with the increase of the power of the input signal, the AM-AM distortion of the radio frequency power amplifier under large signal is restrained, and simultaneously, C₆(one may take a small value, such as 3 picofarads (pF)) at T₆The base forms a low RF resistance, and the bias circuit 300 passes through C₆Make transmission to T₆Is R₂The attenuated radio frequency signal is shorted to ground. At this time, the impedance Zin2 of node a in the bias circuit 300 (i.e., the baseband impedance of the bias circuit 300) may be expressed by the following equation:

（3）

where ω denotes the angular frequency, C_be5Represents T₅Base capacitor of C_be6Represents T₆Beta represents the current amplification coefficient of the transistor, and is usually 80-150; g_m5And g_m6Respectively represents T₅And T₆Transconductance of (1).

In practical application, consider C_be5、C_be6And C₆Is small and can be ignored in the fundamental frequency range, so equation (3) can be simplified as the following equation:

（4）

thus, at R₂And R in FIG. 2₁All of which are 15 ohms, the baseband impedance of the bias circuit 300 is only 15 ohms, while the baseband impedance of the bias circuit 200 is 58 ohms. It can be seen that the baseband impedance of the bias circuit 300 is further reduced compared to the bias circuit 200, so that the problem of deterioration of the output signal ACPR of the rf power amplifier can be further improved.

In practical applications, as shown in fig. 4, the bias circuit 300 may exhibit very low baseband impedance characteristics within a baseband signal bandwidth of 100 MHz. Due to T₁Equivalent to being in parallel with node A, the impedance of node A (i.e., the baseband impedance Zin2 of the bias circuit 300) is typically on the order of 15 ohms and T is typically about 15 ohms at baseband frequencies within 100MHz₁Impedance (which may be denoted as Zin _ T)₁) Is typically on the order of 40-50 Ohm. Thus, T₁Second order non-linear current vector I generated at input node D as shown in FIG. 3₁And I₂Most of the passing impedance is moreThe low bias circuit 300 shorts to ground, reducing the incoming T₁Second order non-linear current vector I₁And I₂To achieve the suppression of the current vector I₁And I₂The purpose of the non-linear contribution of (c).

However, in practical applications, the bias circuit 300 has the following problems:

first, loop stability is poor. Specifically, in practical applications, the loop gain of the bias circuit 300 is shown in fig. 5, while the phase margin of the bias circuit 300 is shown in fig. 6 due to R₃It needs to take a larger value to effectively be T₅Base low-resistance point isolation of₂Attenuated RF signal (if R₃Is small in value, R₃The isolation effect on the radio frequency signal becomes poor, T₆The detection compensation effect of (3) can be weakened, the radio frequency power amplifier can have obvious AM-AM distortion under large signals, and the ACPR of the radio frequency power amplifier is obviously degraded), and R₃The larger the value of (A), R₃And C_be5The more advanced the phase shift of the fed signal is due to the Resistor-capacitor (RC) network formed. Illustratively, in the case where the loop gain of the bias circuit 300 is 0, the phase of the signal fed back to the node B may vary by-135 degrees compared to the signal input to the node C; if the phase of the signal at node B changes by-180 degrees from the phase of the signal at node C, the loop of the bias circuit 300 will form positive feedback, causing the bias circuit 300 to oscillate; although the-135 degrees has a 45 degree margin compared with the-180 degrees, the phase of the signal at the node B is easily changed from the phase of the signal at the node C by the 45 degree margin under the conditions of high and low temperature, high and low voltage or process fluctuation; in other words, the loop of the bias circuit 300 has poor stability and there is a risk of circuit oscillation.

Second, the degree of noise suppression is poor. Specifically, in the 5G NR system, the baseband bandwidth of the bias circuit 300 is wide, and R is₃It is necessary to take a large value, which makes R₃The generated noise (i.e., thermal noise) cannot be well suppressed in the pass band of the bias circuit 300, and the noise current passes through T₅Amplified and fed into node B, and then passed through T₆Base superposed to bias current I_em6. It can be seen that the noise current will pass through T₁The nonlinear mixing is performed to both ends of the radio frequency signal, which causes noise degradation of the receiving frequency band of the radio frequency power amplifier, so that the radio frequency power amplifier cannot meet the requirement of the related communication protocol on the sensitivity of signal reception.

Based on this, in various embodiments of the present application, the bias circuit includes a control loop and an adjusting circuit, and the bias circuit outputs a bias current to the input terminal of the rf power amplifier by using the control loop, and since the bias circuit includes a loop structure, the bias circuit has a characteristic of low baseband impedance, in other words, the bias circuit provides a low baseband impedance path for the rf power amplifier, so that a memory effect of the rf power amplifier caused by the baseband impedance can be reduced (i.e., can be suppressed), thereby reducing ACPR degradation of an output signal of the rf power amplifier caused by the memory effect, reducing distortion of the output signal of the rf power amplifier, and further improving performance of the rf power amplifier. Meanwhile, the bias circuit utilizes the adjusting circuit to adjust the loop bandwidth of the control loop under the condition that the bias current output by the control loop can meet a first condition, so that the stability and the noise suppression degree of the control loop meet a second condition; the first condition characterizes that the bias current can compensate a base current of the radio frequency power amplifier, so that the base current is not reduced along with the increase of the power of an input signal; the second condition is characterized in that the phase margin of the control loop is greater than or equal to 45 degrees, and the noise suppression degree of the control loop can enable the noise of the radio frequency power amplifier to be less than or equal to a noise threshold value; therefore, when the bandwidth of the input signal of the radio frequency power amplifier is increased, the base current of the radio frequency power amplifier can be compensated by the bias current, so that the base current is not reduced along with the increase of the power of the input signal, and the AM-AM distortion of the radio frequency power amplifier is restrained.

An embodiment of the present application provides a bias circuit, as shown in fig. 7, the bias circuit 700 includes:

a control loop 701 for outputting a bias current to an input terminal of the radio frequency power amplifier;

an adjusting circuit 702, configured to, when it is determined that the bias current output by the control loop 701 can satisfy a first condition, adjust a loop bandwidth of the control loop 701 based on a miller effect so that stability and a noise suppression degree of the control loop 701 satisfy a second condition;

wherein the first condition characterizes that the bias current is capable of compensating a base current of the radio frequency power amplifier such that the base current does not decrease with an increase in power of an input signal;

the second condition characterizes that the phase margin of the control loop 701 is greater than or equal to 45 degrees and the noise suppression degree of the control loop 701 is such that the noise of the radio frequency power amplifier is less than or equal to a noise threshold.

Here, the control loop 701 functions as the loop (including T) of the bias circuit 300 shown in fig. 3₅、T₆And R₃) The function of (c).

In practical application, when the adjusting circuit 702 adjusts the loop bandwidth of the control loop 701 based on the miller effect, a value can be taken according to the maximum working bandwidth of the circuit, in other words, the maximum working bandwidth of the control loop 701 is adjusted. The smaller the value of the maximum working bandwidth is, the narrower the loop bandwidth of the control loop 701 is, the better the stability and the noise suppression degree of the control loop 701 are, but the worse the suppression of the radio frequency power amplifier on the memory effect caused by the baseband impedance is; the larger the value of the maximum working bandwidth is, the wider the loop bandwidth of the control loop 701 is, the worse the stability and noise suppression degree of the control loop 701 are, and the better the radio frequency power amplifier suppresses the memory effect caused by the baseband impedance.

In practical applications, the determining that the bias current output by the control loop 701 can satisfy the first condition may be understood as ensuring that the bias current output by the control loop 701 can satisfy the first condition, that is, in a case that the determining that the bias current output by the control loop 701 can satisfy the first condition, the adjusting circuit 702 adjusts the loop bandwidth of the control loop 701 based on the miller effect, so that the stability and the noise suppression degree of the control loop 701 satisfy the second condition. Here, based on the stability and noise suppression degree of the control loop 701 and the change rule of the suppression degree of the memory effect caused by the baseband impedance by the radio frequency power amplifier, the user may specifically set the second condition according to the requirement, so that the bias circuit 700 can give consideration to the baseband impedance bandwidth, the noise suppression degree, the circuit stability and the radio frequency performance.

Illustratively, the phase margin of the control loop 701 may be set to be greater than or equal to 60 degrees, and the noise threshold may be set according to the requirement of the communication protocol in the related art for the signal reception sensitivity of the radio frequency power amplifier. For example, for the frequency band N1 (uplink frequency band Transmission (TX): 1920MHz to 1980MHz, downlink frequency band Reception (RX): 2110MHz to 2170 MHz), the protocol requires that the signal reception sensitivity of the rf power amplifier is less than or equal to-98 decibel milliwatts (dBm) under the bandwidth of 10MHz, and in combination with the degree of suppression of the RX path output by the rf power amplifier to the N1 duplexer, it can be calculated that the noise requirement of the rf power amplifier in the RX frequency band is less than or equal to-135 dBm/Hz. In this case, the second condition may specifically include: the phase margin of the control loop 701 is greater than or equal to 60 degrees, and the noise suppression degree of the control loop 701 can enable the noise of the radio frequency power amplifier to be less than or equal to-135 dBm/Hz.

In one embodiment, the conditioning circuit 702 may include a miller cell; the adjustment circuit 702 adjusts the loop bandwidth of the control loop 701 based on the miller effect of the miller cells.

Specifically, the miller cell may be connected in parallel with a first transistor of the control loop 701; wherein the content of the first and second substances,

the control loop 701 may include the first crystalBody tube (i.e. T in figure 3)₅) A second transistor (i.e., T in FIG. 3)₆) And a first resistance (i.e., R in FIG. 3)₃) (ii) a The collector of the first transistor is connected with the base of the second transistor; an emitter of the second transistor is connected with one end of the first resistor; the other end of the first resistor is connected with a base electrode of the first transistor; an external current source inputs a current to the control loop 701 through a first node (i.e., node B in fig. 3) between the first transistor and the second transistor; the control loop 701 converts the input current into the bias current (i.e., I in fig. 3)_em6) And the output is output to the input end of the radio frequency power amplifier through the emitter of the second transistor.

In practical applications, the miller cell may include a capacitor and/or a transistor.

Based on this, in one embodiment, the miller cell includes a first capacitor.

In practical applications, in order to enhance the circuit flexibility, the first capacitor may be a variable capacitor (such as a voltage-controlled variable capacitor); alternatively, the first capacitor may include a plurality of capacitors with different capacitance values connected in parallel and/or in series with the switch, and the change of the capacitance value of the first capacitor may be realized by controlling the on or off of the switch.

In one embodiment, the regulating circuit 702 may further include a second resistor; the first capacitor and the second resistor are connected with the first transistor in parallel; wherein the content of the first and second substances,

the adjusting circuit 702 adjusts the transmission zero point of the control loop 701 through the second resistor, so that the stability of the control loop 701 meets a third condition; the transmission zero is introduced by the first transistor in parallel with the first capacitor; the third condition characterizes a phase margin of the control loop 701 being greater than or equal to 45 degrees.

In particular, in practical applications, the first capacitor and the second resistor may be connected in parallel to the first transistor through a collector and a base of the first transistor.

In practical application, as can be known from circuit analysis, before the second resistor is added, the frequency of the transmission zero introduced by the first capacitor can be calculated by the following formula:

（5）

wherein, ω is_zeroRepresenting the angular frequency of the transmission zero, g_m5Represents T₅Transconductance of (C)₇Representing the first capacitance. Since the transmission zero exists in the right half plane, the decrease of the loop gain is reduced, and the intersection point of the loop gain is extrapolated to be farther from the origin, which results in a decrease in the stability of the control loop 701. After the second resistor is added, the frequency of the transmission zero point can be calculated by the following formula:

（6）

wherein R4 represents the second resistance. The user can adjust R₄Is taken to be omega_zeroLess than or equal to 0, thereby pushing the transmission zero to the left half-plane, so that the stability of the control loop 701 is further improved, i.e. the stability of the bias circuit 700 is further improved.

In one embodiment, the adjusting circuit 702 may further include a third resistor; the third resistor is connected with the first transistor in series; wherein the content of the first and second substances,

the adjusting circuit 702 isolates the radio frequency signal for the first transistor through the third resistor, so that the radio frequency signal cannot be coupled to the first transistor through the first capacitor and the second resistor; the rf signal is transmitted to the bias circuit 700 through the input of the rf power amplifier.

In particular, in practical applications, the third resistor may be connected in series with the collector of the first transistor. The third resistor isolates the radio-frequency signal for the first transistor, so that the base electrode potential of the first transistor can be prevented from being reduced due to the radio-frequency signal, the emitter electrode potential of the second transistor can be prevented from being reduced, the AM-AM distortion of the radio-frequency power amplifier can be restrained, and the ACPR deterioration of the output signal of the radio-frequency power amplifier can be restrained.

In one embodiment, the bias circuit 700 may further include a fourth resistor (i.e., R in fig. 3)₂) (ii) a The bias current is output to the input end of the radio frequency power amplifier through the fourth resistor; wherein the content of the first and second substances,

the bias circuit 700 attenuates the rf signal transmitted through the input terminal of the rf power amplifier through the fourth resistor; isolating the radio-frequency signal attenuated by the fourth resistor for the first transistor through the first resistor, so that the radio-frequency signal attenuated by the fourth resistor is transmitted to the second transistor;

under the action of the radio-frequency swing of the radio-frequency signal attenuated by the fourth resistor, the bias current output by the transmitting stage of the second transistor is changed along with the change of the power of the radio-frequency signal through the detection effect of the second transistor.

In practical application, no radio frequency signal is transmitted to the second transistor under the condition that no radio frequency signal is input into the radio frequency power amplifier, so that the bias current is a static bias current; in a case that a radio frequency signal is input to the radio frequency power amplifier, the larger the power of the radio frequency signal is, the larger the radio frequency swing of the radio frequency signal attenuated by the fourth resistor is, so that the bias current is larger, in other words, the bias current increases with the increase of the power of the radio frequency signal. In this way, the AM-AM distortion of the radio frequency power amplifier can be suppressed, thereby suppressing ACPR deterioration of the output signal of the radio frequency power amplifier.

In practical application, in order to enhance the flexibility of the circuit, the first resistor may be a variable resistor, and the larger the resistance of the first resistor is, the better the effect of isolating the radio frequency signal attenuated by the fourth resistor is for the first transistor; the first resistor may include a plurality of resistors with different resistances connected in parallel and/or in series with the switch, and the variation of the resistance of the first resistor may be realized by controlling the on or off of the switch.

In one embodiment, the bias circuit 700 may further include a second capacitor (i.e., C in fig. 3)₆) (ii) a One end of the second capacitor is grounded, and the other end of the second capacitor is connected with the base electrode of the second transistor; wherein the content of the first and second substances,

the bias circuit 700 shorts the rf signal attenuated by the fourth resistor, which is transmitted to the second transistor, to ground through the second capacitor.

In practical applications, the bias circuit 700 provided in the embodiment of the present application may adopt the structure shown in fig. 8, and in fig. 8, the first capacitor is denoted by C₇And the second resistance is represented as R₄And the third resistance is represented as R₅. In addition, the impedance Zin3 of node A (i.e., the baseband impedance of the bias circuit 700) is dependent on the shunt capacitance C₇The variation of capacitance is shown in FIG. 9, the loop gain of the bias circuit 700 is a function of the parallel capacitance C₇The change in capacitance is shown in FIG. 10, with the phase margin of the bias circuit 700 following the parallel capacitance C₇The change in capacitance values is shown in fig. 11. T is₅Parallel resistor R₄Can connect the capacitors C in parallel₇The introduced transmission zero is pushed to the left half shaft (even if the frequency point of the transmission zero is shifted to the left), so that the stability of the bias circuit 700 is further improved, and meanwhile, the isolation resistor R is used₅The radio frequency signal of the node B can be compared with T₅The collector electrodes are isolated, and radio frequency signals are prevented from passing through the parallel capacitor C₇And a parallel resistor R₄Is coupled to T₅The base level of (c). As shown in fig. 12, if the rf signal passes through C₇And R₄Is coupled to T₅Is coupled to T₅Is passed through T₅The BE junction detection effect of (1) can make T₅The base potential decreases with the increase of the radio frequency signal, thereby enabling T₆The emitter potential also decreases, resulting in significant AM-AM distortion of the rf power amplifier at large signals, and thus in degradation of the ACPR. It can be seen that the bias circuit 700 provided by the embodiments of the present application includes the adjusting circuit 702 (i.e., C)₇、R₄And R₅) At the same isolation resistance R as compared to the bias circuit 300₃With the value of (a), the bias circuit 700 provided by the embodiment of the present application can obtain better noise performance and bias circuit stability.

In practical application, the isolation resistor R₃And a parallel capacitor C₇Is switchable, in other words R₃May be a variable resistor, C₇May be a variable capacitance. By varying R₃And/or C₇The values of the bias circuit are selected according to different modulation bandwidth signals, different baseband impedance bandwidths and noise suppression degrees of the bias circuit are selected, and the purpose of increasing the applicability and flexibility of the circuit can be achieved.

In practical applications, the Transistor in the embodiment of the present application may be a Heterojunction Bipolar Transistor (HBT), a Metal Oxide Semiconductor (MOS) Transistor, or a Bipolar Junction Transistor (BJT).

The embodiment of the application also provides a radio frequency power amplifier, wherein the bias circuit of any one of the above embodiments is arranged at the input end of the radio frequency power amplifier.

Illustratively, as shown in fig. 13, the radio frequency power amplifier may include: a bias circuit 700, an input matching circuit 1301, an amplification circuit 1302, and an output matching circuit 1303.

In one embodiment, the rf power amplifier may be a multi-stage cascaded rf power amplifier; wherein the content of the first and second substances,

the input end of each stage is provided with the bias circuit.

The bias circuit and the radio frequency power amplifier provided by the embodiment of the application have the following advantages:

first, the bias circuit includes a loop structure, which enables the bias circuit to have a characteristic of low baseband impedance, in other words, the bias circuit provides a low baseband impedance path for the rf power amplifier, so that a memory effect of the rf power amplifier caused by the baseband impedance can be reduced (i.e., can be suppressed), thereby reducing ACPR degradation of an output signal of the rf power amplifier caused by the memory effect, reducing distortion of the output signal of the rf power amplifier, and further improving performance of the rf power amplifier.

Secondly, in the 5G NR system, when the bandwidth of the input signal of the rf power amplifier is increased, on the premise that the bias current can compensate the base current of the rf power amplifier, so that the base current is not reduced with the increase of the power of the input signal, thereby suppressing the AM-AM distortion of the rf power amplifier, the stability and noise suppression degree of a control loop included in the bias circuit can be considered, the influence of circuit oscillation and noise that may be generated by the bias circuit on the sensitivity of the rf power amplifier when receiving the signal is reduced, and the performance of the rf power amplifier is further improved.

Thirdly, the circuit structure is simple, extra circuit cost cannot be introduced, and the design difficulty of the radio frequency power amplifier is reduced.

It should be noted that: "first," "second," and the like are used for distinguishing between similar elements and not necessarily for describing a particular sequential or chronological order.

The technical means described in the embodiments of the present application may be arbitrarily combined without conflict.

The above description is only a preferred embodiment of the present application, and is not intended to limit the scope of the present application.