Bias circuit for RF amplifier

Abstract

The present invention discloses a bias circuit of a radio frequency amplifier, including a first voltage stabilizing circuit, the first voltage stabilizing circuit including a first triode, a second triode, a third triode, a first resistor, a second resistor, a third resistor, a fourth resistor, a fifth resistor, a capacitor and an inductor; wherein, it also includes a second voltage stabilizing circuit, the second voltage stabilizing circuit including a sixth resistor, a fourth triode and a fifth triode, another external voltage is input to one end of the sixth resistor, the other end of the sixth resistor is respectively connected to the other end of the first resistor, the collector of the fourth triode, and the base of the fourth triode; the emitter of the fourth triode is respectively connected to the collector of the fifth triode and the base of the fifth triode, and the emitter of the fifth triode is grounded. The bias circuit of the radio frequency amplifier of the present invention enhances the ability to stabilize the output voltage of the bias circuit and the quiescent current of the radio frequency amplifier under the condition of changes in the external input voltage, and improves the compatibility of the bias circuit with the external input voltage tolerance.

Description

Technical Field

[0001] The present invention relates to the field of radio frequency microwaves, and more particularly to a bias circuit of a radio frequency amplifier. Background Art

[0002] Usually the RF amplifier circuit includes an input matching circuit IMN, a bias circuit BIAS, a RF power amplifier PA and an output matching circuit OMN, such as Figure 1 As shown, the input matching circuit IMN, the RF power amplifier PA and the output matching circuit OMN are connected in sequence, the bias circuit BIAS is connected to the matching circuit IMN and the RF power amplifier PA at the same time, and the RF signal input port IN is connected to the input matching circuit IMN, and the RF signal output port OUT is connected to the output matching circuit IMN. The bias circuit BIAS provides a bias voltage for the RF power amplifier PA. The conventional commonly used bias circuit BIAS structure is as follows: Figure 2 As shown, the bias circuit BIAS is composed of transistors Q1, Q2, Q3, resistors R1, R2, R3, R4, R5, inductor L1, and capacitor C1. The circuit part that plays a major role in reducing the bias point change caused by the fluctuation of the external input voltage VCC1 is composed of transistors Q1, Q2, Q3, resistors R1, R2, R3, and R4. The working principle of this part of the circuit is: when the voltage VCC1 increases, the base voltage of the transistor Q2 increases, and the emitter voltage of the transistor Q1 increases, which eventually leads to an increase in the bias voltage of the RF power amplifier PA. However, due to the increase in the base voltage of the transistor Q1, the base voltage of the transistor Q3 will increase, thereby reducing the increment of the base voltage of the transistor Q2, and then reducing the change in the bias voltage of the RF power amplifier PA. Vice versa, therefore, when VCC1 changes, this part of the circuit can stabilize the output voltage of the bias circuit and the quiescent current of the PA.

[0003] In the above RF amplifier circuit, due to the insufficient ability to stabilize the output voltage of the bias circuit and the quiescent current of the PA, when the voltage VCC1 changes greatly, the output voltage of the bias circuit BISA changes greatly or the quiescent current of the RF power amplifier PA changes greatly. Therefore, when the voltage VCC1 tolerance is large, it is difficult to stabilize the quiescent current of the RF power amplifier PA within an acceptable range, which makes it difficult for various performance indicators of the PA (P1dB, efficiency, linearity, etc.) to fall within the pre-set range.

[0004] Therefore, it is necessary to provide an improved bias circuit for an RF amplifier to enhance the ability to stabilize the bias circuit output voltage and the quiescent current of the RF power amplifier under the condition of external input voltage changes, and to improve the compatibility of the bias circuit with external input voltage tolerance. Summary of the invention

[0005] The objective of the present invention is to provide a bias circuit of a radio frequency amplifier. The bias circuit of the radio frequency amplifier of the present invention enhances the ability to stabilize the output voltage of the bias circuit and the quiescent current of the radio frequency amplifier under the condition of changes in the external input voltage, thereby improving the compatibility of the bias circuit with the external input voltage tolerance.

[0006] To achieve the above-mentioned object, the present invention provides a bias circuit of a radio frequency amplifier, comprising a first voltage stabilizing circuit, wherein the first voltage stabilizing circuit comprises a first triode, a second triode, a third triode, a first resistor, a second resistor, a third resistor, a fourth resistor, a fifth resistor, a capacitor and an inductor, wherein the emitter of the first triode is connected to the inductor through the fifth resistor, and the inductor outputs a bias voltage to the radio frequency amplifier; the emitter of the second triode is connected to the third resistor through the fourth resistor; the emitter of the third triode is connected to the second resistor, and its collector is connected to one end of the first resistor connection; an external voltage is input to the collectors of the second and third triodes; the capacitor is connected to the base connector of the first triode; wherein, it also includes a second voltage stabilizing circuit, the second voltage stabilizing circuit includes a sixth resistor, a fourth triode and a fifth triode, another external voltage is input to one end of the sixth resistor, the other end of the sixth resistor is respectively connected to the other end of the first resistor, the collector of the fourth triode, and the base of the fourth triode; the emitter of the fourth triode is respectively connected to the collector of the fifth triode and the base of the fifth triode, and the emitter of the fifth triode is grounded.

[0007] Preferably, the bias circuit of the radio frequency amplifier further includes a seventh resistor, one end of the seventh resistor is connected to the other end of the sixth resistor, and the other end of the seventh resistor is connected to the base of the fourth transistor.

[0008] Preferably, the bias circuit of the radio frequency amplifier further includes an eighth resistor, one end of the eighth resistor is connected to the emitter of the fourth transistor, and the other end of the eighth resistor is connected to the base of the fifth transistor.

[0009] Preferably, the fourth transistor and the fifth transistor are both NPN transistors.

[0010] Compared with the prior art, the bias circuit of the radio frequency amplifier of the present invention further includes a second voltage stabilizing circuit, so that when the external input voltage VCC1 increases, the current flowing through the fourth triode increases rapidly, the voltage drop across the sixth resistor increases, and the increment of the collector voltage of the fourth triode as the external voltage VCC1 increases is reduced; conversely, when the external voltage VCC1 decreases, the current flowing through the fourth triode decreases rapidly, the voltage drop across the sixth resistor decreases, and the decrease of the collector voltage of the fourth triode as the external voltage VCC1 decreases is reduced. Therefore, the second voltage stabilizing circuit has a direct voltage stabilizing function for the change of the external voltage VCC1, stabilizes the output voltage of the entire bias circuit, and improves the compatibility of the bias circuit with the external input voltage tolerance.

[0011] The present invention will become more apparent from the following description taken in conjunction with the accompanying drawings, which are used to illustrate embodiments of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 It is a structural block diagram of a radio frequency amplifier in the prior art.

[0013] Figure 2 It is a structural diagram of the bias circuit of the radio frequency amplifier in the prior art.

[0014] Figure 3 It is a structural diagram of the bias circuit of the radio frequency amplifier of the present invention.

[0015] Figure 4 It is a comparison diagram of the output current of the bias circuit of the prior art and the present invention. DETAILED DESCRIPTION

[0016] Embodiments of the present invention are now described with reference to the accompanying drawings, in which like element numbers represent like elements. As described above, the present invention provides a bias circuit for a radio frequency amplifier, which enhances the ability to stabilize the output voltage of the bias circuit and the quiescent current of the radio frequency amplifier under the condition of a change in the external input voltage, and improves the compatibility of the bias circuit with the external input voltage tolerance.

[0017] Please refer to Figure 3 , Figure 3 The structure diagram of the bias circuit of the radio frequency amplifier of the present invention. As shown in the figure, the bias circuit of the radio frequency amplifier of the present invention includes a first voltage stabilizing circuit and a second voltage stabilizing circuit. The first voltage stabilizing circuit includes a first transistor Q1, a second transistor Q2, a third transistor Q3, a first resistor R1, a second resistor R2, a third resistor R3, a fourth resistor R4, a fifth resistor R5, a capacitor C1 and an inductor L1; the emitter of the first transistor Q1 is connected to the inductor L1 through the fifth resistor R5, and the inductor L1 outputs a bias voltage to the radio frequency amplifier PA (such as through the output node B1). Figure 1 As shown); the emitter of the second transistor Q2 is connected to the third resistor R3 through the fourth resistor R4; the emitter of the third transistor Q3 is connected to the second resistor R2, and its collector is connected to one end of the first resistor R1; an external voltage VCC2 is input to the collectors of the second transistor Q2 and the third transistor Q3; the capacitor C1 is connected to the base of the first transistor Q1; the structure and functional characteristics of the first voltage stabilizing circuit are similar to those of the bias circuit of the prior art (such as Figure 2 The same as shown in the figure is not described in detail here. For details, please refer to Figure 2 and Figure 3 The second voltage stabilizing circuit includes a sixth resistor R6, a fourth transistor Q4 and a fifth transistor Q5; another external voltage VCC1 is input to one end of the sixth resistor R6, and the other end of the sixth resistor R6 is respectively connected to the other end of the first resistor R1, the collector of the fourth transistor Q4, and the base of the fourth transistor Q4; the emitter of the fourth transistor Q4 is respectively connected to the collector of the fifth transistor Q5 and the base of the fifth transistor Q5, and the emitter of the fifth transistor Q5 is grounded. Through the above second voltage stabilizing circuit, when the external input voltage VCC1 increases, the current flowing through the fourth transistor Q4 increases rapidly, and the voltage drop across the sixth resistor R6 increases, which eventually reduces the increment of the collector voltage of the fourth transistor Q4 as the external voltage VCC1 increases; on the contrary, when the external voltage VCC1 decreases, the current flowing through the fourth transistor Q4 decreases rapidly, and the voltage drop across the sixth resistor R6 decreases, which eventually reduces the decrease of the collector voltage of the fourth transistor Q4 as the external voltage VCC1 decreases. Therefore, the second voltage stabilizing circuit has a direct voltage stabilizing function for changes in the external voltage VCC1, thereby stabilizing the output voltage of the entire bias circuit.

[0018] Please refer to Figure 3 As a preferred embodiment of the present invention, the bias circuit further includes a seventh resistor R7 and an eighth resistor R8; one end of the seventh resistor R7 is connected to the other end of the sixth resistor R6, and the other end thereof is connected to the base of the fourth triode Q4; one end of the eighth resistor R8 is connected to the emitter of the fourth triode Q4, and the other end thereof is connected to the base of the fifth triode Q5. As can be seen from the above, the collector and base of the fourth triode Q4 are connected through the seventh resistor R7, and the collector and base of the fifth triode Q5 are connected through the eighth resistor R8, so that the second voltage stabilizing circuit can be equivalent to a diode.

[0019] As another preferred embodiment of the present invention, the fourth transistor Q4 and the fifth transistor Q5 are both transistors of the same type, both of which are NPN transistors; thus, the present invention is easier to implement.

[0020] Combine the following Figure 3Describe the working principle of the second voltage stabilizing circuit of the bias circuit of the radio frequency amplifier of the present invention: As can be seen from the above, the second voltage stabilizing circuit can be equivalent to a diode. When the equivalent diode (the second voltage stabilizing circuit) is turned on, the dynamic resistance Rt of the equivalent diode (the second voltage stabilizing circuit) is:

[0021] Rt≈1 / g m4 +1 / g m5 ;

[0022] Among them, g m4 is the transconductance of the fourth transistor Q4, g m5 is the transconductance of the fifth transistor Q5.

[0023] When the external voltage VCC1 changes (the change in the external voltage VCC1 is recorded as VE), the change in the output voltage VF of the second voltage stabilizing circuit is approximately:

[0024] VF≈VE*(1 / g m4 +1 / g m5 ) / (R6+1 / g m4 +1 / g m5 );

[0025] Since the resistance value of the sixth resistor R6 is much larger than Rt (≈1 / g m4 +1 / g m5 ), so that the change VF of the output voltage of the second voltage stabilizing circuit is much smaller than the change VE of the external voltage VCC1; therefore, even when the tolerance of the external voltage VCC1 is large, the bias circuit of the present invention can stabilize its output voltage and the quiescent current of the RF amplifier PA within an acceptable range, thereby achieving the purpose of voltage stabilization.

[0026] Further, please refer to Figure 4 , Figure 4 The following is a comparison of the output current of the bias circuit of the prior art and the present invention. As shown in the figure, when the external voltage VCC1 increases from 2.96V to 3.63V, the quiescent current of the RF amplifier PA in the conventional solution changes from 46mA to 65mA, with a change of 19mA; while under the same conditions, the quiescent current of the RF calculator PA in the present invention solution changes from 52mA to 62mA, with a change of 10mA. It can be seen that under the same voltage change of the external voltage VCC1, the quiescent current change of the PA in the present invention solution is close to half of that of the conventional solution, and the voltage stabilization effect is significantly better.

[0027] The present invention is described above in conjunction with the best embodiment, but the present invention is not limited to the above disclosed embodiment, but should cover various modifications and equivalent combinations based on the essence of the present invention.

Claims

1. A bias circuit for a radio frequency amplifier, comprising a first voltage stabilizing circuit, wherein the first voltage stabilizing circuit comprises a first triode, a second triode, a third triode, a first resistor, a second resistor, a third resistor, a fourth resistor, a fifth resistor, a capacitor and an inductor, wherein the emitter of the first triode is connected to the inductor through the fifth resistor, and the inductor outputs a bias voltage to the radio frequency amplifier; the emitter of the second triode is connected to the third resistor through the fourth resistor, and the base of the second triode is connected to the collector of the third triode; the emitter of the third triode is connected to one end of the second resistor, and its collector is connected to one end of the first resistor, the base of the third triode is connected to one end of the third resistor, and the other ends of the second resistor and the third resistor are both grounded; an external voltage is input to the collectors of the second triode and the first triode; one end of the capacitor is connected to the base of the first triode, and the other end of the capacitor is grounded; characterized in that It also includes a second voltage stabilizing circuit, which includes a sixth resistor, a fourth transistor and a fifth transistor. Another external voltage is input to one end of the sixth resistor, and the other end of the sixth resistor is respectively connected to the other end of the first resistor, the collector of the fourth transistor, and the base of the fourth transistor; the emitter of the fourth transistor is respectively connected to the collector of the fifth transistor and the base of the fifth transistor, and the emitter of the fifth transistor is grounded.

2. The bias circuit of the radio frequency amplifier according to claim 1, characterized in that: It also includes a seventh resistor, one end of which is connected to the other end of the sixth resistor, and the other end of which is connected to the base of the fourth transistor.

3. The bias circuit of the radio frequency amplifier according to claim 2, characterized in that: An eighth resistor is also included, one end of the eighth resistor is connected to the emitter of the fourth transistor, and the other end of the eighth resistor is connected to the base of the fifth transistor.

4. The bias circuit of the radio frequency amplifier according to claim 3, characterized in that: The fourth transistor and the fifth transistor are both NPN transistors.

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