A control circuit for a power amplifier

Abstract

The present invention discloses a control circuit of a power amplifier, comprising a first voltage-controlled current source coupled to the collector of a current mirror tube, wherein the collector current of the current mirror tube is positively correlated with the collector current of the output transistor of the power amplifier; and a second voltage-controlled current source coupled to the base of the current mirror tube, wherein the control voltage of the second voltage-controlled current source follows the collector voltage of the current mirror tube. The present invention uses the mirror current of the output current of the power amplifier to be controlled to control the output current of the power amplifier to be controlled, thereby realizing the output power control of the power amplifier in a way of indirectly controlling the output power, avoiding the use of expensive off-chip precision resistors and saving costs.

Description

Technical Field

[0001] The invention relates to a control circuit of a power amplifier. Background Art

[0002] A power amplifier is a device that can amplify the voltage or power of an input signal. It is composed of electron tubes or transistors, power transformers and other electrical components. It is widely used in various devices such as communications, broadcasting, radar, television, and automatic control.

[0003] The output power of the power amplifier needs to be controlled within a specific range. Taking the cellular data RF front end of a mobile phone as an example, its power amplifier system currently needs to output up to 33dBm of power. The battery needs to provide ampere-level current to the power amplifier. If the output power of the power amplifier is not properly controlled, it is easy to cause serious heat dissipation problems. Therefore, it is of great significance to develop a method that can control the output power of the power amplifier so that it is within a specific range. Summary of the invention

[0004] The object of the present invention is to provide a control circuit of a power amplifier which can effectively control the output power of the power amplifier.

[0005] To achieve the purpose of the present invention, the control circuit of the power amplifier provided herein includes a first voltage-controlled current source coupled to the collector of a current mirror tube, the collector current of the current mirror tube is positively correlated with the collector current of the output transistor of the power amplifier; and a second voltage-controlled current source coupled to the base of the current mirror tube, the control voltage of the second voltage-controlled current source follows the collector voltage of the current mirror tube.

[0006] Preferably, the first voltage-controlled current source generates a first bias current exponentially related to the control voltage according to an input control voltage, and the first bias current is coupled to the collector of the current mirror tube.

[0007] Preferably, the control voltage is input into the first voltage-controlled current source after being subjected to exponential change by an exponential function generator.

[0008] Preferably, the first voltage-controlled current source includes a first field effect transistor M1, a second field effect transistor M2 and a third field effect transistor M3, the control voltage is loaded on the gate of the first field effect transistor M1, the drain of the first field effect transistor M1 is connected to the drain of the second field effect transistor M2, and the gate of the second field effect transistor M2 is connected to the gate of the third field effect transistor M3; the source of the first field effect transistor M2 and the source of the third field effect transistor M3 are connected to the power supply VCC, and the output of the drain of the third field effect transistor M3 is coupled to the collector of the current mirror tube; the gate of the second field effect transistor M2 is connected to the drain of the second field effect transistor M2, and the third field effect transistor M3 is the current mirror tube of the second field effect transistor M2.

[0009] Preferably, the number of the second field effect transistors M2 is 1 / N times the number of the third field effect transistors M3.

[0010] Preferably, the second voltage-controlled current source generates a second bias current according to the collector voltage of the current mirror tube and a preset fixed voltage, the second bias current is coupled to the base of the current mirror tube, and the second bias current is positively correlated with the collector voltage of the current mirror tube.

[0011] Preferably, it also includes a filter resistor, a first end of the filter resistor is coupled to the base of the current mirror tube, and a second end of the filter resistor is coupled to the base of the output transistor of the power amplifier.

[0012] Preferably, it further comprises a filter capacitor, a first end of the filter capacitor is connected to the second end of the filter resistor and the base of the output transistor of the power amplifier, and a second end of the filter capacitor is grounded.

[0013] Beneficial effects of the present invention: The present invention utilizes the mirror current of the output current of the power amplifier to be controlled to control the output current of the power amplifier to be controlled, thereby achieving output power control of the power amplifier by indirectly controlling the output power, avoiding the use of expensive off-chip precision resistors and saving costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The drawings herein are incorporated into and constitute a part of the specification, showing embodiments consistent with the present invention, and together with the specification, are used to explain the principles of the present invention. Obviously, the drawings described below are only some embodiments of the present invention, and for those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative work. In the drawings:

[0015] Figure 1 A circuit diagram of a control circuit provided by the present invention;

[0016] Figure 2A circuit diagram of a first voltage-controlled current source provided by the present invention. DETAILED DESCRIPTION

[0017] Example embodiments will now be described more fully with reference to the accompanying drawings. However, example embodiments can be implemented in many forms and should not be construed as limited to the examples set forth herein; rather, these embodiments are provided so that the present invention will be more comprehensive and complete and fully convey the concept of the example embodiments to those skilled in the art.

[0018] In order to control the output power of a power amplifier, the present invention provides a control circuit of a power amplifier including a first voltage-controlled current source and a second voltage-controlled current source G1. Figure 1 As shown, the first voltage-controlled current source is coupled to the collector of the current mirror tube T2, and the collector current I2 of the current mirror tube T2 is positively correlated with the collector current I1 of the output transistor T1 of the power amplifier; the second voltage-controlled current source G1 is coupled to the base of the current mirror tube T2, and the control voltage of the second voltage-controlled current source G1 follows the collector voltage of the current mirror tube T2. The collector current I2 of the current mirror tube T2 and the collector current I1 of the output transistor T1 of the power amplifier are in a mirror relationship, and the collector current I1 of the output transistor T1 of the power amplifier can be controlled by controlling the collector current I2 of the current mirror tube T2, so as to achieve the purpose of controlling the output power.

[0019] In this article, the first voltage-controlled current source generates a first bias current exponentially related to the control voltage Vramp according to the input control voltage Vramp, and the first bias current is coupled to the collector of the current mirror tube T2. The control voltage Vramp is exponentially converted by an exponential function generator, and the output current exponentially related to the control voltage Vramp is used to control the first voltage-controlled current source to output a first bias current proportional to the control voltage Vramp. The first voltage-controlled current source couples the output first bias current to the collector of the current mirror tube T2, where the collector current I2 of the current mirror tube T2 is in a mirror relationship with the collector current I1 of the output transistor T1 of the power amplifier, and the output power of the power amplifier is controlled by the collector current I1 of the output transistor T1 of the power amplifier, and is therefore also controlled by the control voltage Vramp.

[0020] In a specific embodiment, the first voltage-controlled current source may be a voltage-controlled current source G0. Figure 2As shown, it includes a second field effect transistor M2 and a third field effect transistor M3, wherein the first field effect transistor M1 constitutes an exponential function generator, and the second field effect transistor M2 and the third field effect transistor M3 constitute a voltage-controlled current source G0. The control voltage Vramp is firstly converted to an exponential by the exponential function generator, and the output current I3 is exponentially related to the control voltage Vramp. I3=k*(Vramp-Vth) 2 =k*(Vramp 2 -2Vth*Vramp+Vth 2 ), where k is a constant; I and e x The Taylor series expansion of is consistent, so the current I3 is exponentially related to the control voltage Vramp. Then, the current I3 passes through the first voltage-controlled current source to output a first bias current I that is a multiple of the current I3, I=N*I3. In another specific embodiment, the first voltage-controlled current source may also include an exponential function generator and a voltage-controlled current source G0. Figure 2 As shown, it includes a first field effect transistor M1, a second field effect transistor M2 and a third field effect transistor M3, wherein the first field effect transistor M1 constitutes an exponential function generator, and the second field effect transistor M2 and the third field effect transistor M3 constitute a voltage-controlled current source G0. Figure 2 As shown, the control voltage Vramp is loaded on the gate of the first field effect tube M1, the drain of the first field effect tube M1 is connected to the drain of the second field effect tube M2, the gate of the second field effect tube M2 is connected to the gate of the third field effect tube M3, and the drain of the second field effect tube M2; the source of the second field effect tube M2 and the source of the third field effect tube M3 are connected to the power supply VCC, and the output of the drain of the third field effect tube M3 is exponentially related to the control voltage Vramp. The first bias current is coupled to the collector of the current mirror tube T2; the third field effect tube M3 is the current mirror tube of the second field effect tube M2. Among them, the number of tubes of the second field effect tube M2 is 1 / N times the number of tubes of the third field effect tube M3, ensuring that the current I output by the third field effect tube M3 is N times the output current of the second field effect tube M2, and N is a natural number greater than 1.

[0021] The control voltage Vramp is loaded on the gate of the first field effect transistor M1. After being processed by the first field effect transistor M1, the second field effect transistor M2 and the third field effect transistor M3, the first bias current I is output. The first bias current I can be expressed as: I=N*I3=N*k*(Vramp-Vth) 2 =N*k*(Vramp 2 -2Vth*Vramp+Vth 2 ), where k is a constant; I and e x The Taylor series expansion of is consistent, so the first bias current I is exponentially related to the control voltage Vramp.

[0022] In this article, the second voltage-controlled current source G1 generates a second bias current according to the collector voltage of the current mirror tube T2 and the preset fixed voltage Vb, and the second bias current is coupled to the base of the current mirror tube T2 and / or the base of the output transistor T1 of the power amplifier. The second bias current I2 is positively correlated with the collector voltage of the current mirror tube T2. The second bias current I2 provides a base current of appropriate size for the current mirror tube T2 and the output transistor T1 of the power amplifier. When the control voltage Vramp remains unchanged, the current of the first voltage-controlled current source G0 will also try to remain unchanged. At this time, if the collector current I1 of the output transistor T1 of the power amplifier and the collector current I2 of the current mirror tube T2 of the power amplifier increase due to some other reasons, the collector voltage of the current mirror tube T2 will decrease, causing the second bias current generated by the second voltage-controlled current source G1 to decrease, making the base current of the output transistor T1 and the current mirror tube T2 of the power amplifier smaller, thereby preventing the collector current I1 of the output transistor T1 of the power amplifier and the collector current I2 of the current mirror tube T2 from increasing, thereby preventing the power amplifier from being burned out.

[0023] The control circuit provided herein further includes a filter resistor RO, a first end of the filter resistor RO is coupled to the base of the current mirror tube T2, and a second end of the filter resistor R0 is coupled to the base of the output transistor T1 of the power amplifier.

[0024] The control circuit provided in this article also includes a filter capacitor C1 and a filter capacitor C0. The first end of the filter capacitor C1 is connected to the second end of the filter resistor R0 and the base of the output transistor of the power amplifier, and the second end of the filter capacitor C1 is grounded; the first end of the filter capacitor C0 is connected to the base of the current mirror tube T2, and the second end is grounded.

[0025] The resistor R0 and the capacitor C0 provide certain filtering characteristics to prevent RF signal crosstalk.

[0026] The output transistor T1 of the power amplifier described in this article refers to the first-level transistor with the largest current and the largest power in the power amplifier.

[0027] In this article, the output transistor T1 and the current mirror tube T2 of the power amplifier adopt the same size, but the number of the output transistor T1 of the power amplifier is N times that of the current mirror tube T2, where N is a natural number greater than 1, to ensure that the output current of the output transistor T1 of the power amplifier is N times the output current of the current mirror tube T2.

[0028] The first voltage-controlled current source, the second voltage-controlled current source G1, the filter resistor R0, the filter capacitor C0 and the filter capacitor C1 in the control circuit provided in this article can be distributed and arranged independently; or they can be integrated on a CMOS or SOI chip to achieve on-chip control.

[0029] The control circuit provided in this article uses a current mirror transistor to control the current of the main amplifier transistor of the power amplifier to indirectly control the output power, avoid the use of expensive off-chip precision resistors, and save costs; the second voltage-controlled current source G1 is used to control the base current of the output transistor T1 and the current mirror tube T2 of the power amplifier, thereby realizing negative feedback control of the collector current of the output transistor T1 of the power amplifier.

[0030] The present disclosure has been described by the above-mentioned relevant embodiments, but the above-mentioned embodiments are only examples for implementing the present disclosure. It must be pointed out that the disclosed embodiments do not limit the scope of the present disclosure. On the contrary, changes and modifications made without departing from the spirit and scope of the present disclosure are all within the scope of patent protection of the present disclosure.

Claims

1. A control circuit of a power amplifier, characterized in that: include: A first voltage-controlled current source generates a first bias current exponentially related to the control voltage according to an input control voltage, wherein the first bias current is coupled to the collector of a current mirror tube, and the collector current of the current mirror tube is positively correlated with the collector current of the output transistor of the power amplifier; a second voltage-controlled current source, generating a second bias current according to the collector voltage of the current mirror tube and a preset fixed voltage, wherein the second bias current is coupled to the current mirror tube and the base of the output transistor of the power amplifier; and a control voltage of the second voltage-controlled current source follows the collector voltage of the current mirror tube; This control circuit is used to achieve output power control of the power amplifier by indirectly controlling the output power when the control voltage Vramp remains unchanged. The control method is as follows: When the control voltage Vramp remains unchanged, the current of the first voltage-controlled current source remains unchanged. When the collector current of the output transistor of the power amplifier and the collector current of the current mirror tube increase, the collector voltage of the current mirror tube will decrease, resulting in a decrease in the second bias current generated by the second voltage-controlled current source, thereby reducing the base current of the output transistor of the power amplifier and the base current of the current mirror tube.

2. The control circuit according to claim 1, characterized in that: The control voltage is input into the first voltage-controlled current source after being subjected to exponential change by an exponential function generator.

3. The control circuit according to claim 1, characterized in that: The first voltage-controlled current source includes a first field effect transistor M1, a second field effect transistor M2 and a third field effect transistor M3, the control voltage is loaded on the gate of the first field effect transistor M1, the drain of the first field effect transistor M1 is connected to the drain of the second field effect transistor M2, and the gate of the second field effect transistor M2 is connected to the gate of the third field effect transistor M3; the source of the first field effect transistor M2 and the source of the third field effect transistor M3 are connected to the power supply VCC, and the output of the drain of the third field effect transistor M3 is coupled to the collector of the current mirror tube; the gate of the second field effect transistor M2 is connected to the drain of the second field effect transistor M2, and the third field effect transistor M3 is the current mirror tube of the second field effect transistor M2.

4. The control circuit according to claim 3, characterized in that: The number of the second field effect transistors M2 is 1 / N times the number of the third field effect transistors M3.

5. The control circuit according to claim 1, characterized in that: It also includes a filter resistor, a first end of the filter resistor is coupled to the base of the current mirror tube, and a second end of the filter resistor is coupled to the base of the output transistor of the power amplifier.

6. The control circuit according to claim 5, characterized in that: It also includes a filter capacitor, a first end of the filter capacitor is connected to the second end of the filter resistor and the base of the output transistor of the power amplifier, and a second end of the filter capacitor is grounded.

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