Voltage reference circuit for RF amplifiers

Abstract

This invention provides a voltage reference circuit for an RF amplifier, which is connected to the RF amplifier via a linearization circuit. It includes a first voltage divider and a second voltage divider. The first voltage divider is composed of a first resistor and is connected to the base of the bias transistor in the linearization circuit. The second voltage divider is also connected to the base of the bias transistor in the linearization circuit and includes a second transistor and a third transistor connected in a diode configuration. The second voltage divider further includes an adjustment unit connected to the second transistor, the third transistor, and the linearization circuit. The adjustment unit can adjust the magnitude of the output current of the bias circuit to compensate for the quiescent current of the power amplifier due to temperature variations. This voltage reference circuit for an RF amplifier can dynamically adjust the drive current output from the bias circuit to the RF amplifier according to temperature changes, improving the temperature compensation effect of the bias circuit on the amplifier.

Description

Technical Field

[0001] This invention relates to the field of radio frequency microwaves, and more specifically to a voltage reference circuit for a radio frequency amplifier. Background Technology

[0002] With the development of wireless communication technology, signal modulation technology has become increasingly complex, placing higher demands on the linear output power of the power amplifier, a core component in the transmitter.

[0003] In conventional RF amplifier systems, as input power increases, the power transistor operates under large-signal conditions. Due to the nonlinear capacitance and the rectification effect of the PN junction (diode), the voltage between the base and emitter of the power transistor decreases with increasing input power, causing amplitude and phase modulation distortion and a decrease in linearity. Simultaneously, temperature changes also alter the base and collector currents of the power transistor, and the current gain decreases with rising temperature. Furthermore, the PN junction turn-on voltage decreases with increasing temperature, causing a change in the power transistor's quiescent operating point and deteriorating the power amplifier's output performance.

[0004] To address the aforementioned issues, bias circuits are typically configured for RF amplifier systems to compensate for performance degradation caused by temperature variations and increased input power, thereby improving the linear output power of the power amplifier.

[0005] like Figure 1 The diagram shown illustrates the connection between a prior art bias circuit and an RF amplifier. The entire bias circuit consists of a linearization circuit and a voltage reference circuit.

[0006] The linearization circuit consists of transistor HBT1, capacitor C1, resistor R1, and resistor Rb. Transistor HBT1 has the same characteristics as transistor HBT0 in the RF amplifier and is used to compensate for the drop in base-emitter voltage of transistor HBT0 (which acts as a power transistor) due to increased input power. Resistor Rb and capacitor C1 are used to adjust the amount of RF signal entering the bias circuit.

[0007] like Figure 1 As shown: When the amplifier is working, as the input signal RFI increases, the linearity of the amplifier gradually decreases with the change in the operating state of transistor HBT0. It is necessary to provide additional compensation current through the bias circuit to improve the linearity of the circuit. Due to transistor HBT1 and capacitor C1, the radio frequency signal flows into the bias circuit through resistor R1. Then, due to the rectification effect of the base-emitter diode of transistor HBT1, the rectified radio frequency signal is converted into a DC signal and flows into transistor HBT0, providing compensation for the circuit and improving the linearity of the circuit.

[0008] The voltage reference circuit consists of two voltage dividers used to stabilize the base voltage of transistor HBT1, thereby regulating the emitter drive current of transistor HBT1. Additionally, commonly used voltage reference circuits (bias circuits) consist of... Figure 2 As shown.

[0009] like Figure 2 As shown, the voltage reference circuit consists of two base-emitter diodes, HBT2 and HBT3 (forming a transistor with its base and collector connected together) and a resistor R2. Resistor R2 is a variable voltage divider used to control the base potential of transistor HBT1. Adjusting the resistance value of resistor R2, thereby adjusting the drive current output by the bias circuit.

[0010] In the above Figure 2 In this circuit, the emitter current of transistor HBT1 drives power transistor HBT0, while the operating state of transistor HBT1 is controlled by its base voltage Vbe1. The formula for the bias circuit drive current is:

[0011] Ib = I e1 =I b1 +I c1 ≈I b1 (1+β)

[0012] Ib1 is determined by the voltage reference circuit. The diode and resistor R2 constitute the voltage reference circuit. By adjusting the voltage reference circuit, the base voltage and current of transistor HBT1 are controlled, thereby controlling the output current of the bias circuit.

[0013] Resistor R2 and the two diodes are located in the voltage V2 branch, forming a series structure that divides the voltage between them. The base of HBT1 is located at the voltage divider node of R2 and the two diodes, and the base voltage Vbe1 of HBT1 is the same as the voltage divider potential of the two diodes. According to Kirchhoff's voltage and current laws, we can obtain:

[0014] V be1 =2V Diode =V2-R2*I2

[0015] I2 = I3 + I4

[0016] V be1 =2V Diode =V² - r² * (I³ + I⁴)

[0017] V2 is a fixed external input voltage because current I3 is much greater than current I4. Since current I3 is determined by the diode die area, voltage Vbe1 is determined by the resistance value of resistor R2 and the diode die area (the base-emitter diode formed by the transistor). The entire bias current is adjusted by regulating the value of R2 and the die area (the base-emitter diode formed by the transistor) to control the bias output current.

[0018] Due to the inherent limitations of chip manufacturing foundries' processes, the transistor die area cannot be modified at will, resulting in significant design constraints. With a fixed die area, relying solely on resistor R2 to control the output current significantly reduces adjustment precision. Furthermore, the temperature compensation effect of the bias circuit will fluctuate dramatically with changes in the resistance value of R2.

[0019] Additionally: Increased temperature leads to increased base current Ib0 of transistor HBT0 and emitter current Ie1 of transistor HBT1 (decreasing temperature has the opposite effect). The negative feedback device suppressing current changes in the current Ib branch is the ballast resistor Rb. As the branch current Ib increases, the voltage drop across resistor Rb increases, the Vce voltage of transistor HBT0 decreases, and the branch current Ib decreases. Furthermore, the larger the resistance value of Rb, the better the negative feedback suppression effect. However, the resistance value of Rb also participates in adjusting the magnitude of the bias circuit drive current, and this relationship is negatively correlated. Additionally, in the linearization circuit, resistor Rb plays a role in adjusting the magnitude of the coupled RF signal and cannot be increased indefinitely.

[0020] The resistor R2 acts as the temperature negative feedback in the current I2 branch. Specifically, the base current Ib1 (I4) of transistor HBT1 increases with temperature, and the diode branch current I3 also increases with temperature. This leads to an increase in the branch current I2, an increase in the voltage across resistor R2, a decrease in the diode reference voltage, a decrease in the bias voltage Vbe1 of transistor HBT1, a decrease in current Ie2, and a decrease in the branch current Ib. Furthermore, the higher the value of resistor R2, the better the negative feedback suppression effect. Since resistor R2 participates in controlling the output current of the bias circuit, and its resistance value is negatively correlated with the current magnitude, the trade-off between the two will lead to a worse temperature compensation effect, especially under conditions of high output current.

[0021] In summary, the temperature compensation effect of this voltage reference circuit is poor, especially under the condition of high output current of power transistor HBT0, the compensation effect is extremely poor.

[0022] Therefore, it is necessary to provide an improved voltage reference circuit for radio frequency amplifiers to overcome the above-mentioned defects. Summary of the Invention

[0023] The purpose of this invention is to provide a voltage reference circuit for an RF amplifier. The voltage reference circuit of this invention can dynamically adjust the drive current output from the bias circuit to the RF amplifier, thereby improving the temperature compensation effect of the bias circuit on the amplifier.

[0024] To achieve the above objectives, the present invention provides a voltage reference circuit for an RF amplifier. The voltage reference circuit is connected to the RF amplifier via a linearization circuit. The voltage reference circuit and the linearization circuit constitute the bias circuit of the RF amplifier to provide bias current. It includes a first voltage divider and a second voltage divider. The first voltage divider is composed of a first resistor and is connected to the base of the bias transistor of the linearization circuit to adjust and control the base-emitter junction voltage of the bias transistor. The second voltage divider is connected to the base of the bias transistor of the linearization circuit to provide a reference voltage for the base-emitter junction of the bias transistor. The second voltage divider includes a second transistor and a third transistor connected in a diode configuration. The second voltage divider further includes an adjustment unit connected to the second transistor, the third transistor, and the linearization circuit. The adjustment unit can adjust the magnitude of the output current of the bias circuit to compensate for the quiescent current of the power amplifier due to temperature variations.

[0025] Preferably, the adjustment unit includes a second resistor and a fourth transistor, the fourth transistor being connected in series with the second transistor and the third transistor, and the second resistor being connected in parallel with the second transistor which is connected in a diode manner.

[0026] Preferably, the collector of the fourth transistor is connected to the emitter of the second transistor, and its emitter is connected to the collector of the third transistor. One end of the second resistor is connected to the linearization circuit, and the other end is connected to the base of the fourth transistor.

[0027] Preferably, the fourth transistor is placed near the RF amplifier to acquire the temperature change of the RF amplifier in real time.

[0028] Preferably, the second transistor and the third transistor are placed near the power transistor RF amplifier to obtain the temperature change of the power transistor RF amplifier in real time.

[0029] Preferably, the resistance of the second resistor is much smaller than the equivalent resistance of the second transistor connected in a diode manner.

[0030] Preferably, the current flowing through the second resistor is much greater than the current flowing through the second transistor connected in a diode configuration.

[0031] Compared with the prior art, the voltage reference circuit for the RF amplifier of the present invention, by adding an adjustment unit to the second voltage divider, can control the magnitude of the current flowing through the adjustment unit by adjusting the resistance value of the adjustment unit during the design process, thereby controlling the base voltage of the bias transistor, thereby achieving the purpose of adjusting the output current of the bias circuit, realizing the compensation of the static current of the power transistor of the amplifier, and improving the temperature compensation effect of the bias circuit for the RF amplifier.

[0032] 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

[0033] Figure 1 This is a block diagram showing the connection between the bias circuit and the RF amplifier in the prior art.

[0034] Figure 2 This is a schematic diagram of the connection between the bias circuit and the RF amplifier in the prior art.

[0035] Figure 3 This is a block diagram showing the connection between the voltage reference circuit and the radio frequency amplifier of the present invention.

[0036] Figure 4 This is a schematic diagram of the connection between the voltage reference circuit and the radio frequency amplifier of the present invention.

[0037] Figure 5 This is a simulation comparison curve of the output current of the power amplifier of the present invention and the output current of the power amplifier of the prior art. Detailed Implementation

[0038] Embodiments of the present invention will now be described with reference to the accompanying drawings, in which similar element reference numerals represent similar elements. As described above, the present invention provides a voltage reference circuit for an RF amplifier. This voltage reference circuit for an RF amplifier can dynamically adjust the drive current output from the bias circuit to the RF amplifier, thereby improving the temperature compensation effect of the bias circuit on the RF amplifier.

[0039] Please refer to Figure 3 , Figure 3This is a block diagram showing the connection between the voltage reference circuit and the radio frequency amplifier of the present invention. As shown, the voltage reference circuit of the present invention is connected to the radio frequency amplifier through a linearization circuit. The voltage reference circuit and the linearization circuit constitute the bias circuit of the radio frequency amplifier to provide a bias current Ib for the radio frequency amplifier. The linearization circuit includes a voltage divider resistor Ra, a ballast resistor Rb, a bias transistor HBT1, and a capacitor C1. One end of the voltage divider resistor Ra is connected to an external power supply V1, and the other end is connected to the collector of the bias transistor HBT1. The emitter of the bias transistor HBT1 is connected to one end of the ballast resistor Rb, and the other end of the ballast resistor Rb is connected to the base of the power transistor HBT0 of the radio frequency amplifier, and the bias current Ib is input to the power transistor HBT0. The base of the bias transistor HBT1 is connected to one end of the capacitor C1 and the voltage reference circuit, and the other end of the capacitor C1 is grounded.

[0040] In the linearization circuit, when the RF amplifier is operating, as the input signal RFin increases, the base potential Vbe0 of the power transistor HBT0 decreases. The linearity gradually decreases with the change in the operating state of the power transistor HBT0, requiring the linearization circuit to compensate for the voltage drop. Simultaneously, the bias current needs to be increased with increasing power, thereby increasing the collector current. The impedance of the voltage reference circuit to the left of node Vbe1 is much higher than the impedance of capacitor C1 at the RF frequency. All RF signals at node Vbe1 flow to capacitor C1. Controlling the value of capacitor C1 controls the amount of RF signal flowing to the voltage reference circuit. Meanwhile, the ballast resistor Rb is located on the coupled RF signal branch, and the resistance of the ballast resistor Rb can also control the amount of RF signal flowing to the voltage reference circuit. Due to the rectification effect of the base-emitter diode of the bias transistor HBT1, the rectified RF signal is converted into a DC signal and flows into the base circuit of the power transistor HBT0. As a result, the output bias current Ib is increased, and the voltage division on the ballast resistor Rb is increased, which leads to a decrease in the base-emitter voltage of the bias transistor HBT1, thereby compensating for the base bias voltage drop of the power transistor HBT0. Therefore, the linearization circuit provides voltage compensation for the RF amplifier, thereby improving the linearity of the circuit.

[0041] The voltage reference circuit is used to control the base potential of the bias transistor HBT1, adjust the output current Ib of the bias circuit, thereby controlling the output current ICC of the power transistor HBT0. It also has a temperature compensation negative feedback effect, which suppresses the change of the output current of the power transistor HBT0 with the temperature value. The voltage reference circuit includes a first voltage divider and a second voltage divider. The first voltage divider is composed of a first resistor R1 and is connected to the base of the bias transistor HBT1 in the linearization circuit. It can dynamically adjust and control the base-emitter junction voltage of the bias transistor HBT1 based on the induced current of the second voltage divider sensing the temperature change of the power transistor, thus providing temperature compensation negative feedback. The second voltage divider is connected to the base of the bias transistor HBT1 in the linearization circuit to provide a base-emitter junction reference voltage for the bias transistor HBT1. In addition, in this invention, the second voltage divider is placed near the RF amplifier (power transistor HBT0) to obtain the temperature change of the power transistor HBT0 in real time and work with the first voltage divider to dynamically adjust the base-emitter junction voltage of the bias transistor HBT1 to achieve temperature compensation for the power transistor HBT0. The term "near" in this invention means that, under the premise of meeting the basic requirements of circuit design and layout, the second voltage divider is placed as close as possible to the power transistor HBT0 to obtain its temperature change information more accurately. In this invention, the second voltage divider includes a second transistor HBT2 and a third transistor HBT3 connected in a diode configuration; wherein, a transistor connected in a diode configuration means that the base and collector of the transistor are connected together, specifically as follows: Figure 4 As shown.

[0042] Specifically, the second voltage divider further includes an adjustment unit, which is connected to the second transistor HBT2, the third transistor HBT3, and the linearization circuit. Specifically, one end of the first resistor R1 is connected to another external power supply V2, and the other end is connected to the collector of the second transistor HBT2. The collector of the second transistor HBT2 is connected to its base and to the base of the bias transistor HBT1, and its emitter is connected to the adjustment unit. The collector of the third transistor HBT3 is connected to its base and to the adjustment unit, and its emitter is grounded. In this invention, the adjustment unit can adjust the output current of the bias circuit to compensate for the quiescent current of the power amplifier due to temperature changes, while also enhancing the temperature sensing capability of the second voltage divider and improving the temperature compensation negative feedback effect of the first voltage divider.

[0043] Specifically, please refer to the following: Figure 4 , Figure 4This is a schematic diagram of the voltage reference circuit and its connection to the RF amplifier of the present invention. As shown in the figure, the adjustment unit includes a second resistor R2 and a fourth transistor HBT4. The fourth transistor HBT4 is connected in series with the second transistor HBT2 and the third transistor HBT3. The second resistor R2 is connected in parallel with the second transistor HBT2, which is connected in a diode configuration. Furthermore, the collector of the fourth transistor HBT4 is connected to the emitter of the second transistor HBT2, and its emitter is connected to the collector of the third transistor HBT3. One end of the second resistor R2 is connected to the linearization circuit, and the other end is connected to the base of the fourth transistor HBT4. In a preferred embodiment of the present invention, the fourth transistor HBT4 is placed near the RF amplifier (power transistor HBT0) to obtain the temperature change of the power transistor HBT0 in real time. In addition, in the present invention, the fourth transistor HBT4 and the power transistor HBT0 are of the same type and size, therefore, their temperature change characteristics are also the same as those of the power transistor HBT0. Compared with the traditional diode solution, the present invention has better temperature sensing capability, enhancing the temperature sensing capability of the second voltage divider.

[0044] The working principle of the adjustment unit in this invention is as follows:

[0045] The voltage at node Vbe1 is determined by the third transistor HBT3, which is connected to the regulating unit via a diode configuration. From Kirchhoff's voltage and current theorem, we can obtain:

[0046] V2=R1*I2+V Diode2 +Vce4+V Diode3

[0047] Vbe1=V Diode2 +Vce4+V Diode3 =V2-R1*I2

[0048] I2 = I3 + I4 + I5

[0049] Vbe1 = V2 - R1 * (I3 + I4 + I5)

[0050] Among them, V Diode2 With V Diode3 The second transistor HBT2 and the third transistor HBT3 are used as fixed voltage drops for diodes, respectively, and Vce4 is the voltage between the collector and emitter junction of the fourth transistor.

[0051] In this invention, the stable Kirchhoff current characteristic of the transistor (Ie = Ib + Ic) is mainly utilized to construct the parallel branch of the second transistor HBT2, which is connected to the diode via the second resistor R2. That is, the second resistor R2 and the second transistor HBT2 are connected in parallel. Furthermore, the resistance of the second resistor R2 is much smaller than the resistance of the diode (second transistor HBT2), so the current I3 in the branch containing the second resistor R2 is much larger than the current I4 in the branch containing the diode, and similarly much larger than the base current I5 of the bias transistor HBT1.

[0052] I3 >> I4 >> I5;

[0053] Since I2 equals the sum of I3, I4 and I5, and I3 >> I4 >> I5, the current I3 determines the value of the current I2.

[0054] And because:

[0055] V Diode2 +Vce4=R2*I3+Vbe4,

[0056] I3=(V Diode2 +Vce4-Vbe4) / R2;

[0057] When the temperature is constant, the above voltages are constant values, and the current I3 decreases as the resistance of the second resistor R2 increases.

[0058] Based on the above overall analysis: the increase in the resistance of the second resistor R2 causes the current I3 to decrease, the current I2 to decrease, which leads to a decrease in the voltage drop across the first resistor R1, thereby increasing the voltage Vbe1 and the emitter output current Ib of the bias transistor HBT1.

[0059] In this invention, by adjusting the resistance value of the second resistor R2, the output current Ib of the bias circuit is adjusted, thereby releasing the resistance value of the first resistor R1 of the first voltage divider, enabling it to reach the kiloohm level and enhancing the temperature negative feedback capability of the first voltage divider.

[0060] Please refer to the references. Figure 5 The following describes the temperature compensation principle of the voltage reference circuit for radio frequency amplifiers according to the present invention:

[0061] Due to changes in ambient temperature or self-heating effects, the temperature of power transistor HBT0 increases, and its base current Ib increases. At this time, the temperature of the fourth transistor HBT4, which acts as a temperature sensor, and the two diodes (second transistor HBT2 and third transistor HBT3), which also act as temperature sensors, rise near power transistor HBT0. This causes currents I3 and I4 in each branch to increase, resulting in an increase in current I2 across the first resistor R1. Consequently, the voltage drop across the first resistor R1 increases, the base potential Vbe1 of the bias transistor HBT1 decreases, and the bias current Ib decreases.

[0062] That is, as the temperature T increases, the bias current Ib increases;

[0063] Meanwhile, as the temperature T rises, the current I3+I4 rises, the current I2 rises, the voltage Vbe1 falls, and the bias current Ib falls.

[0064] This enables temperature compensation for the bias current Ib.

[0065] Compared to traditional solutions, the adjustment unit of this invention allows for arbitrary adjustment of the resistance value of the first resistor R1, thereby achieving optimal temperature compensation for the entire bias circuit.

[0066] Furthermore, given that the die area of ​​the bias circuit in this invention is the same as that of the existing bias circuit, the output current is adjusted to approximately 260mA by adjusting their respective current regulation structures. The simulated current ICC curve as a function of temperature is shown below. Figure 5 As shown in the figure, the temperature ranges from -40℃ to 140℃. Simulation results show that in the existing bias circuit structure, the current ICC increases monotonically with increasing temperature, with a minimum current of 231mA and a maximum current of 304mA, a difference of 73mA, indicating highly unstable current ICC with temperature. In contrast, the current ICC curve of the bias circuit structure of this invention is basically flat, with a minimum current of 263mA and a maximum current of 275mA, a difference of only 12mA. Figure 5 In the diagram, the solid line represents the current curve of the present invention, and the dashed line represents the current curve of the prior art.

[0067] Comparing the two simulation data, the voltage reference circuit of the present invention enables the bias circuit to have better temperature compensation effect in the RF amplifier.

[0068] 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 voltage reference circuit for a radio frequency amplifier, the voltage reference circuit being connected to a radio frequency amplifier by a linearization circuit, the voltage reference circuit and the linearization circuit forming a biasing circuit for the radio frequency amplifier to provide a bias current for the radio frequency amplifier; It comprises a first voltage divider and a second voltage divider, the first voltage divider is composed of a first resistor and is connected with the base of a bias transistor of the linearization circuit to adjust the base-emitter junction voltage of the bias transistor; the second voltage divider is connected with the base of the bias transistor of the linearization circuit to provide the bias transistor with a reference voltage of the base-emitter junction, the second voltage divider comprises a second transistor, a third transistor connected in a diode mode; The collector of the bias transistor is connected with an external power supply through the voltage dividing resistor of the linearization circuit, and the emitter of the bias transistor is connected with the radio frequency amplifier through the ballast resistor of the linearization circuit, characterized in that the second voltage divider further comprises an adjusting unit, the adjusting unit is connected with the second transistor, the third transistor and the linearization circuit respectively, the adjusting unit can adjust the size of the output current of the bias circuit to compensate for the static current of the power amplifier changed due to temperature; the adjusting unit comprises a second resistor and a fourth transistor, the fourth transistor is connected in series with the second transistor and the third transistor, the second resistor is connected in parallel with the second transistor connected in a diode mode, and the fourth transistor is placed adjacent to the radio frequency amplifier to obtain the temperature change of the radio frequency amplifier in real time; the resistance value of the second resistor is much smaller than the equivalent resistance value of the second transistor connected in a diode mode.

2. The voltage reference circuit for a radio frequency amplifier of claim 1, wherein, The collector of the fourth transistor is connected with the emitter of the second transistor, the emitter of the fourth transistor is connected with the collector of the third transistor, one end of the second resistor is connected with the linearization circuit, and the other end of the second resistor is connected with the base of the fourth transistor.

3. The voltage reference circuit for a radio frequency amplifier of claim 2, wherein, The second transistor and the third transistor are placed adjacent to the power transistor of the radio frequency amplifier to obtain the temperature change of the power transistor of the radio frequency amplifier in real time.

4. The voltage reference circuit for a radio frequency amplifier of claim 3, wherein, The current flowing through the second resistor is much larger than the current flowing through the second transistor connected in a diode mode.

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