Bias Circuit

Abstract

The present invention discloses a bias circuit which mainly includes a first voltage stabilizing circuit, the first voltage stabilizing circuit includes 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 sixth resistor and a capacitor, the emitter of the first triode is connected to the fifth resistor, and the fifth resistor outputs a bias voltage to a 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 sixth resistor; wherein, it also includes a second voltage stabilizing circuit, the second voltage stabilizing circuit includes a seventh resistor and a fourth triode, an external voltage is input to one end of the seventh resistor, and the other end of the seventh resistor is respectively connected to the collector of the fourth triode and the base of the fourth triode; the emitter of the fourth triode is connected to the base of the third triode. The bias circuit of the present invention can have a relatively strong ability to stabilize static current when the external voltage changes and the ambient temperature changes.

Description

Technical Field

[0001] The present invention relates to the field of radio frequency microwaves, and more particularly to a bias circuit applied to 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. Specifically, 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, R6, 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, and resistors R6, R2, R3, and R4.

[0003] When using a traditional bias circuit, the quiescent current of the RF power amplifier PA is significantly affected by the external power supply voltage and ambient temperature. The quiescent current of the RF power amplifier PA has a great influence on its gain, P1dB, efficiency, linearity and other indicators. Therefore, changes in the external power supply voltage and ambient temperature may cause the performance of the RF power amplifier PA to deteriorate. Figure 2 In the scheme shown, the only path that can stabilize the static current of the RF power amplifier PA when the external voltage VCC1 changes is: VCC1, Q2 collector, Q2 emitter, Q3 base, Q3 collector, Q1 base, Q1 emitter, and finally to the output terminal B1 of the bias circuit BIAS. However, the change in the external voltage VCC1 produces a very small amount of in-phase change on the base of the transistor Q3, so the ability of the above scheme to stabilize the static current of the RF power amplifier PA when the external voltage VCC1 changes can be basically ignored; and when the ambient temperature changes, the above scheme cannot adjust the temperature change at all, so the stability of its static battery under different temperature conditions may be relatively poor.

[0004] Therefore, it is necessary to provide an improved bias circuit for a radio frequency amplifier so as to have a stronger ability to stabilize the static current when the external voltage changes and the ambient temperature changes. Summary of the invention

[0005] The object of the present invention is to provide a bias circuit applied to a radio frequency amplifier. The bias circuit of the present invention can have a relatively strong ability to stabilize static current when the external voltage changes and the ambient temperature changes.

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

[0007] Preferably, the fourth transistor is connected in a diode manner.

[0008] Compared with the prior art, the bias circuit of the present invention further includes a second voltage stabilizing circuit, so that when the external voltage VCC1 changes, the bias circuit has a trend opposite to the change in the quiescent current of the radio frequency power amplifier PA caused by the change in the external voltage VCC1, thereby achieving the purpose of stabilizing the quiescent current of the radio frequency power amplifier PA. In addition, the bias circuit utilizes the principle that the on-state voltage of the transistor BE junction decreases with temperature to achieve stabilization of the quiescent current of the radio frequency power amplifier PA when the temperature changes.

[0009] 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

[0010] Figure 1 It is a structural block diagram of a radio frequency amplifier in the prior art.

[0011] Figure 2 FIG. 4 is a structural diagram of a bias circuit in the prior art.

[0012] Figure 3 4 is a structural diagram of the bias circuit of the present invention.

[0013] Figure 4It is a comparison diagram of the output current of the bias circuit of the prior art and the present invention. DETAILED DESCRIPTION

[0014] 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, and the bias circuit of the present invention has a relatively strong ability to stabilize static current when the external voltage changes and the ambient temperature changes.

[0015] Please refer to Figure 3 , Figure 3 The structure diagram of the bias circuit of the present invention. The bias circuit of the present invention is applied to a radio frequency amplifier. As shown in the figure, the bias circuit 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 sixth resistor R6 and a capacitor C1; the emitter of the first transistor Q1 is connected to the fifth resistor R5, and the fifth resistor R5 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 sixth resistor R6, and an external voltage VCC1 is input to the other end of the sixth resistor; another external voltage VCC2 is input to the collectors of the second transistor Q2 and the third transistor Q3 through the first resistor R1; the capacitor C1 is connected to the base of the first transistor Q1. In the present invention, the structure and functional characteristics of the first voltage stabilizing circuit are the same as 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 seventh resistor R7 and a fourth transistor Q4; an external voltage VCC1 is input into one end of the seventh resistor R7, and the other end of the seventh resistor R7 is respectively connected to the collector of the fourth transistor Q4 and the base of the fourth transistor Q4; the emitter of the fourth transistor Q4 is connected to the base of the third transistor Q3. Through the above-mentioned second voltage stabilizing circuit, when the external voltage VCC1 changes, the bias circuit has an opposite trend to the change of the static current of the RF power amplifier PA caused by the change of the external voltage VCC1, thereby achieving the purpose of stabilizing the static current of the RF power amplifier PA. And the bias circuit uses the principle that the conduction voltage of the transistor BE junction decreases with temperature to achieve stabilization of the static current of the RF power amplifier PA when the temperature changes.

[0016] As a preferred embodiment of the present invention, the fourth transistor Q4 is connected in a diode manner, thereby making the present invention easier to implement.

[0017] Combine the following Figure 3 The working principle of the second voltage stabilizing circuit of the bias circuit of the radio frequency amplifier of the present invention is described as follows: the voltage generated by the external voltage VCC1 at the node A is recorded as VA, and VA can be simply equivalent to the output voltage after the external voltage VCC1 is divided by two equivalent resistors, and the voltage division ratio is recorded as r (r = VA / VCC1). Since the fourth transistor Q4 is a diode connection method, the voltage drop from the collector to the emitter of the fourth transistor Q4 will maintain a relatively stable value as the external voltage VCC1 changes. Therefore, the fourth transistor Q4 almost shifts the voltage of the external voltage VCC1 to a lower voltage value, and the voltage shift amount is relatively stable and is less affected by the change of the external voltage VCC1. Compared with the voltage division ratio r obtained by directly using two resistors to divide the external voltage VCC1, it will be larger. So that, when the change amount of the external voltage VCC1 is fixed, the change amount of VA is increased, thereby improving the bias circuit when the change amount of the external voltage VCC1 is larger. Can still effectively stabilize the static current of the radio frequency amplifier PA. The change in the external voltage VCC1 is in phase with the change in VA. VA is amplified by the emitter amplifier composed of the sixth resistor R6, the second resistor R2, and the third transistor Q3 to obtain VB (the voltage of node B). The change in VB is in phase with the change in VA. VB is passed through the emitter follower composed of the first transistor Q1, the first resistor R1, and the fifth resistor R5 to obtain VC (the voltage of node C). The change in VC is in phase with the change in VB, which ultimately causes the voltage change at the output terminal B1 of the bias circuit to be in phase with the change in the external voltage VCC1. Therefore, when the external voltage VCC1 increases, the quiescent current of the RF amplifier PA tends to increase, while the above loop tends to reduce the quiescent current of the PA, thereby stabilizing the quiescent current of the PA within a certain range; vice versa.

[0018] In addition, when the ambient temperature changes, the change in the quiescent current of the RF amplifier PA is in phase with the change in the ambient temperature. The change in voltage between the collector and the emitter of the fourth transistor Q4 is in phase with the change in ambient temperature, which causes the change in voltage of VA to be in phase with the change in ambient temperature, and ultimately causes the change in voltage at the output terminal B1 of the bias circuit to be in opposite phase with the change in ambient temperature. Therefore, when the ambient temperature rises, the quiescent current of the RF amplifier PA tends to increase, and the bias circuit of the present invention can make the quiescent current of the RF amplifier PA tend to decrease, thereby stabilizing the quiescent current of the RF amplifier PA within a certain range; and vice versa. Therefore, the bias circuit of the present invention can further reduce the change in the quiescent current of the RF amplifier PA when the ambient temperature changes.

[0019] Next, please refer to Figure 4 , Figure 4 It is a comparison chart 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 2.97V to 3.63V, the quiescent current of the RF amplifier PA in the traditional solution changes from 54mA to 75mA, and the change is 21mA; the quiescent current of the RF amplifier PA in the solution of the present invention changes from 64mA to 66mA, and the change is 2mA. Obviously, under the condition of the same external voltage VCC1 electrical change, the quiescent current change of the RF amplifier PA in the solution of the present invention is much smaller than that of the traditional solution, and the effect is more obvious. Therefore, the bias circuit of the present invention has a stronger ability to stabilize the quiescent current of the RF amplifier, and can ensure the stable operation of the entire RF amplifier.

[0020] The present invention has been described above in conjunction with the best embodiments, but the present invention is not limited to the embodiments disclosed above, but should cover various modifications and equivalent combinations based on the essence of the present invention.

Claims

1. A bias circuit, which is applied to a radio frequency amplifier, comprises 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 sixth resistor and a capacitor, wherein the emitter of the first triode is connected to the fifth resistor, and the fifth resistor outputs a bias voltage to the radio frequency amplifier; the emitter of the second triode is connected to one end of the fourth resistor, the other end of the fourth resistor is connected to one end of the third resistor, and the other end of the third resistor is grounded; the base of the second triode is connected to the base of the first triode and the collector of the third triode; the emitter of the third triode is connected to one end of the second resistor, and the other end of the second resistor is grounded; the collector of the third triode is connected to one end of the sixth resistor, and an external voltage is input to the other end of the sixth resistor; the base of the third triode is connected to the other end of the fourth resistor; another external voltage is input to the collectors of the first triode and the second triode through the first resistor; 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 seventh resistor and a fourth transistor. An external voltage is input into one end of the seventh resistor, and the other end of the seventh resistor is respectively connected to the collector of the fourth transistor and the base of the fourth transistor; the emitter of the fourth transistor is connected to the base of the third transistor.

2. The bias circuit according to claim 1, wherein: The fourth transistor is connected in a diode manner.

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