Output protection circuit for power amplifier and radio frequency device

Abstract

The invention relates to an output protection circuit for a power amplifier and a radio frequency device. The output protection circuit comprises a power detection module and a protection module, the input end of the power detection module is connected with the output end of the power amplifier, the output end is connected with the input end of the protection module, and the power detection module is used for obtaining detection voltage of the output end of the power amplifier and generating driving voltage; the output end of the protection module is connected with the input end of the power amplifier and is used for adjusting bias voltage input to the input end of the power amplifier according to the driving voltage; when the detection voltage is larger than a preset threshold value, the driving voltage generated by the power detection module enables the protection module to be conducted, and the bias voltage of the input end of the power amplifier is reduced through the protection module. The problem that in the prior art, the area of a clamping diode is increased, so that the circuit layout is larger is solved, meanwhile, the defect that protection voltages of diode protection are different at different temperatures is overcome, and the protection sensitivity is improved.

Description

Technical Field

[0001] The present invention is applicable to the technical field of radio frequency amplification, and in particular relates to an output protection circuit and a radio frequency device for a power amplifier. Background Art

[0002] In smart devices such as mobile phones, power amplifiers are used to output power to antennas. However, the antenna does not always maintain the same impedance when working. When the device is close to a wall or in a basement, the antenna will deviate from its original impedance. This impedance deviation of the antenna will cause impedance mismatch of the power amplifier and increase the voltage swing at the output point of the power amplifier, which will eventually cause the power tube to break down.

[0003] At present, in order to prevent the power tube from being broken down in the event of impedance deviation, a clamping circuit is generally formed by using several diodes at the output end of the power amplifier to protect the power tube and prevent the output voltage of the power tube from being too high and being broken down. Figure 1 As shown, Figure 1 The power amplifier includes two stages. The first stage amplifier is composed of capacitor sC1, resistor sR1, power tube sQ1 and inductor sL1. The second stage amplifier is composed of capacitor sC2, resistor sR2, power tube sQ2 and inductor sL2. Among them, the output matching network is designed outside the power amplifier, and diodes D1~D8 form a protection circuit to provide protection for the output of the power amplifier.

[0004] However, if Figure 1 In the technical solution shown, the area requirement of the protection circuit is relatively large, which will cause the area of ​​the amplifier circuit die to increase. At the same time, since the turn-on voltage of the diode is affected by temperature, when the temperature rises, the voltage of the diode decreases. At this time, the protection circuit will turn on in advance, so that the output voltage is clamped by the diode, thereby affecting the output power of the power amplifier; when the temperature drops, the voltage of the diode increases. At this time, the protection circuit requires a higher voltage to turn on, which makes the protection voltage of the power amplifier insufficient, the protection circuit does not work, and the power amplifier will still be broken down when the output voltage is high. Summary of the invention

[0005] The present invention aims to solve the technical problem that the existing power amplifier using a clamp diode protection circuit is easily affected by the circuit area and temperature and thus has protection failure.

[0006] In order to solve the above technical problems, in a first aspect, the present invention provides an output protection circuit for a power amplifier, comprising a power detection module and a protection module; The input end of the power detection module is used to connect to the output end of the power amplifier, the output end of the power detection module is connected to the input end of the protection module, and the power detection module is used to obtain the detection voltage output by the output end of the power amplifier and generate a driving voltage according to the detection voltage; The output end of the protection module is used to connect to the input end of the power amplifier, and the protection module is used to adjust the bias voltage input to the input end of the power amplifier according to the magnitude of the driving voltage; When the detection voltage acquired by the power detection module is greater than a preset threshold, the driving voltage generated by the power detection module turns on the protection module, and reduces the bias voltage of the input end of the power amplifier via the protection module.

[0007] Furthermore, the power detection module includes a first transistor, a second transistor, a third transistor, a first resistor, a second resistor, a third resistor, a fourth resistor, a fifth resistor, a first capacitor and a second capacitor, wherein: The first end of the first resistor is connected to the output end of the power amplifier as the input end of the power detection module, and the second end of the first resistor is connected to the first end of the first capacitor; The second end of the first capacitor is respectively connected to the output end of the first transistor, the first end of the second resistor and the first end of the third resistor; The second end of the second resistor is connected to an external bias voltage; The input end of the first transistor is connected to the second end of the third resistor and the first end of the fourth resistor respectively; The second end of the fourth resistor is connected to the first end of the second capacitor and the input end of the second transistor respectively; The second terminal of the second capacitor is grounded; The output end of the second transistor is connected to the first end of the fifth resistor and the input end of the third transistor respectively; The second end of the fifth resistor is connected to the external bias voltage; The output end of the third transistor is connected to the external bias voltage, and the ground end of the third transistor serves as the output end of the power detection module.

[0008] Furthermore, the protection module includes a fourth transistor, a sixth resistor, a seventh resistor, an eighth resistor and a third capacitor, wherein: The first end of the sixth resistor serves as the input end of the protection module, and the second end of the sixth resistor is connected to the first end of the third capacitor and the input end of the fourth transistor respectively; The second end of the third capacitor is grounded; The output end of the fourth transistor is connected to the first end of the eighth resistor, and the ground end of the fourth transistor is connected in series with the seventh resistor and then grounded; The second end of the eighth resistor serves as the output end of the protection module.

[0009] Furthermore, the current flowing into the input terminal of the first transistor is defined as I in , the detection voltage is Vout, and the resistance of the first resistor is R 1 , the capacitive reactance of the first capacitor is 1 / sC 1 , the equivalent transconductance of the first transistor is 1 / g m1 , satisfying the following relationship: I in = Vout / (R 1 + 1 / sC 1 + 1 / g m1 ).

[0010] Furthermore, the first transistor, the second transistor and the third transistor are all triodes; the base of the first transistor serves as the input terminal of the first transistor, the emitter of the first transistor serves as the ground terminal of the first transistor, and the collector of the first transistor serves as the output terminal of the first transistor; The base of the second transistor serves as the input terminal of the first transistor, the emitter of the second transistor serves as the ground terminal of the first transistor, and the collector of the second transistor serves as the output terminal of the second transistor; The base of the third transistor serves as the input terminal of the third transistor, the emitter of the third transistor serves as the ground terminal of the third transistor, and the collector of the third transistor serves as the output terminal of the third transistor.

[0011] Furthermore, the fourth transistor is a triode; the base of the fourth transistor serves as the input end of the fourth transistor, the emitter of the fourth transistor serves as the ground end of the fourth transistor, and the collector of the fourth transistor serves as the output end of the fourth transistor.

[0012] In a second aspect, the present invention further provides a radio frequency device, comprising the output protection circuit for a power amplifier and a power amplifier as described above.

[0013] Furthermore, the power amplifier includes a multi-stage power amplification unit, the input end of the output protection circuit is connected to the output end of the last stage power amplification unit in the multi-stage power amplification unit, and the output end of the output protection circuit is connected to the input end of the last stage power amplification unit in the multi-stage power amplification unit.

[0014] The beneficial effect achieved by the present invention is that an output protection circuit for a power amplifier is proposed. The protection circuit structure proposed by the present invention realizes output current detection and bias voltage adjustment of the output power amplifier based on a transistor, overcoming the problem of the prior art that the area of ​​the clamping diode is increased to make the circuit layout larger, while avoiding the disadvantage that the protection voltage of the diode protection is different at different temperatures, thereby improving the sensitivity of the protection. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 is a schematic diagram of an output protection circuit provided by the prior art; Figure 2 is a schematic structural diagram of an output protection circuit for a power amplifier provided by an embodiment of the present invention; Figure 3 It is a schematic diagram of the rectification signal waveform of the first transistor in the output protection circuit provided in an embodiment of the present invention.

[0016] Figure 4 It is a structural schematic diagram of a radio frequency amplification circuit in a radio frequency device provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0017] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0018] For details, please refer to Figure 2 , Figure 2 1 is a schematic diagram of a structure of an output protection circuit for a power amplifier provided in an embodiment of the present invention, wherein the output protection circuit 100 for a power amplifier comprises a power detection module 101 and a protection module 102; The input end of the power detection module 101 is used to connect to the output end of the power amplifier, the output end of the power detection module 101 is connected to the input end of the protection module 102, and the power detection module 101 is used to obtain the detection voltage output by the output end of the power amplifier, and generate the driving voltage VDET according to the detection voltage Vout; The output end of the protection module 102 is used to connect to the input end of the power amplifier, and the protection module 102 is used to adjust the bias voltage input to the input end of the power amplifier according to the magnitude of the driving voltage; When the detection voltage Vout obtained by the power detection module 101 is greater than a preset threshold, the driving voltage VDET generated by the power detection module 101 turns on the protection module 102 , and reduces the bias voltage of the input end of the power amplifier via the protection module 102 .

[0019] Specifically, in the embodiment of the present invention, the preset threshold is the maximum voltage value that the power amplifier can maintain during normal operation. When the preset threshold is exceeded, the power amplifier is easily broken down. Therefore, it is necessary to implement circuit protection according to the preset threshold. During implementation, according to actual needs or in order to improve redundancy, the preset threshold may also be slightly lower than the maximum voltage value that the power amplifier can maintain during normal operation. Figure 2 As shown, in the embodiment of the present invention, the power detection module 101 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 first capacitor C1 and a second capacitor C2, wherein: The first end of the first resistor R1 is connected to the output end of the power amplifier as the input end of the power detection module 101, and the second end of the first resistor R1 is connected to the first end of the first capacitor C1; The second end of the first capacitor C1 is respectively connected to the output end of the first transistor Q1, the first end of the second resistor R2 and the first end of the third resistor R3; The second end of the second resistor R2 is connected to the external bias voltage VBIAS1; The input end of the first transistor Q1 is connected to the second end of the third resistor R3 and the first end of the fourth resistor R4 respectively; The second end of the fourth resistor R4 is connected to the first end of the second capacitor C2 and the input end of the second transistor Q2 respectively; The second end of the second capacitor C2 is grounded; The output end of the second transistor Q2 is connected to the first end of the fifth resistor R5 and the input end of the third transistor Q3 respectively; The second end of the fifth resistor R5 is connected to the external bias voltage VBIAS1; The output end of the third transistor Q3 is connected to the external bias voltage VBIAS1 , and the ground end of the third transistor Q3 is connected to the input end of the protection module 102 as the output end of the power detection module 101 .

[0020] The protection module 102 includes a fourth transistor Q4, a sixth resistor R6, a seventh resistor R7, an eighth resistor R8 and a third capacitor C3, wherein: The first end of the sixth resistor R6 is connected to the output end of the power detection module 101 as the input end of the protection module 102, and the second end of the sixth resistor R6 is connected to the first end of the third capacitor C3 and the input end of the fourth transistor Q4 respectively; The second end of the third capacitor C3 is grounded; The output end of the fourth transistor Q4 is connected to the first end of the eighth resistor R8, and the ground end of the fourth transistor Q4 is connected in series with the seventh resistor R7 and then grounded; The second end of the eighth resistor R8 is connected to the input end of the power amplifier as the output end of the protection module 102 .

[0021] The first transistor Q1, the second transistor Q2, the third transistor Q3, and the fourth transistor Q4 in the embodiment of the present invention are all implemented based on triodes. At this time, the base of the triode is used as the input terminal, the collector is used as the output terminal, and the emitter is used as the ground terminal. It can be understood that in other embodiments, the first transistor Q1, the second transistor Q2, the third transistor Q3, and the fourth transistor Q4 can also be implemented based on MOS. At this time, the gate of the triode is used as the input terminal, the source is used as the output terminal, and the drain is used as the ground terminal. When the transistor type is the same, the technical effect achieved is the same, and the embodiment of the present invention does not impose specific restrictions on this.

[0022] In the embodiment of the present invention, the current flowing into the input terminal of the first transistor Q1 is defined as I in , the detection voltage is Vout, and the resistance of the first resistor R1 is R 1 , the capacitive reactance of the first capacitor C1 is 1 / sC 1 , the equivalent transconductance of the first transistor Q1 is 1 / g m1 , satisfying the following relationship: I in = Vout / (R 1 + 1 / sC 1 + 1 / g m1 ).

[0023] Based on the above circuit structure, in an embodiment of the present invention, the first capacitor C1 is input as an input capacitor, and it and the first resistor R1 as an attenuation resistor jointly introduce the input signal into the first transistor Q1, wherein the first transistor Q1 is used as a rectifier tube for rectifying the input sinusoidal signal to convert it into a DC signal, and then the second resistor R2 and the third resistor R3, the fourth resistor R4 included in the filtering network, the second capacitor C2 and the second transistor Q2 convert the filtered DC signal into an output voltage V2. When the power of the input signal increases, the voltage V1 at the second end of the first capacitor C1 will decrease, and the voltage V2 will increase, thereby driving the third transistor Q3 to increase the driving voltage VDET output by it.

[0024] Furthermore, when the detection voltage Vout increases, the current I flowing into the first transistor Q1 inAlso increases accordingly. During the implementation process, since the equivalent transconductance of the first transistor Q1 is small, the current relationship can be simplified to: I in = Vout / (R 1 + 1 / sC 1 ); In the implementation process, the input current I required by the first transistor Q1 can be obtained by designing the size of R1 and C1. in The first transistor Q1 is used as a rectifier, please refer to Figure 3 , Figure 3 : is a schematic diagram of the rectified signal waveform of the first transistor Q1 provided in an embodiment of the present invention, wherein V0 is the added current I in The following waveform, the dotted line Vdc is the current I in The waveform when Vav is zero, and the current I in When the current is not zero, the average voltage of V0 is input to the first transistor Q1 when the current is positive half-wave. Since the first transistor Q1 discharges a strong current, the amplitude of the positive half-wave is limited at point V0. When the current is negative half-wave, the first transistor Q1 cannot provide current, and the current is drawn from R2, resulting in a decrease in voltage V1. It can be seen that when the current I in When it is not zero, Vav is lower than Vdc. A low Vav voltage means that the voltage V1 will also decrease, and then the current flowing into the second transistor Q2 will decrease. After the Q2 current decreases, the voltages V2 and VDET will increase. When VDET reaches a certain voltage, the fourth transistor Q4 will be turned on. At this time, the bias voltage of the power amplifier is pulled down and the output amplitude is reduced, thereby protecting the power amplifier from voltage breakdown.

[0025] An embodiment of the present invention further provides a radio frequency device, comprising the output protection circuit 100 for a power amplifier and a power amplifier as described in the above embodiment.

[0026] When the power amplifier includes only one stage, the connection method of the output protection circuit 100 for the power amplifier is as described in the above embodiment, which will not be repeated here.

[0027] When the power amplifier includes a multi-stage power amplification unit, illustratively, Figure 4 As shown, Figure 4: is a structural schematic diagram of a radio frequency amplification circuit in a radio frequency device provided by an embodiment of the present invention, wherein the power amplifier comprises a first-stage power amplification unit PA1 and a second-stage power amplification unit PA2, a fourth capacitor C4 is used as an input matching capacitor of the first-stage power amplification unit PA1, VBIAS2 is connected in series with a resistor R9 as a bias voltage of the first-stage power amplification unit PA1, VCC1 provides power for the output end of the first-stage power amplification unit PA1, and L1 is used as an input inductor of the first-stage power amplification unit PA1; a fifth capacitor C5 is used as an input matching capacitor of the second-stage power amplification unit PA2, VBIAS3 is connected in series with a resistor R10 as a bias voltage of the second-stage power amplification unit PA2, VCC2 provides power for the output end of the second-stage power amplification unit PA2, and L2 is used as an input inductor of the second-stage power amplification unit PA2; the power amplifier further comprises an output matching network, and the power amplifier receives a radio frequency signal RFIN through the fourth capacitor C4 and performs secondary amplification, and then outputs a radio frequency amplified signal RFOUT through the output matching network; The input end of the output protection circuit 100 is connected to the output end of the last power amplifier unit (i.e., the second power amplifier unit PA2) in the multi-stage power amplifier unit, and the output end of the output protection circuit 100 is connected to the input end of the last power amplifier unit (i.e., the second power amplifier unit PA2) in the multi-stage power amplifier unit. Since the output matching circuit processes the signal output by the second power amplifier unit PA2, the output protection circuit 100 for the power amplifier in the embodiment of the present invention directly collects and detects the output end signal of the second power amplifier unit PA2, thereby realizing the output protection function.

[0028] The beneficial effect achieved by the present invention is that an output protection circuit for a power amplifier is proposed. The protection circuit structure proposed by the present invention realizes output current detection and bias voltage adjustment of the output power amplifier based on a transistor, overcoming the problem of the prior art that the area of ​​the clamping diode is increased to make the circuit layout larger, while avoiding the disadvantage that the protection voltage of the diode protection is different at different temperatures, thereby improving the sensitivity of the protection. It should be noted that, in this article, the terms "include", "comprises" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, an element defined by the sentence "comprises a ..." does not exclude the existence of other identical elements in the process, method, article or device including the element.

[0029] The embodiments of the present invention are described above in conjunction with the accompanying drawings. What is disclosed is only the preferred embodiment of the present invention. However, the present invention is not limited to the above-mentioned specific implementation manner. The above-mentioned specific implementation manner is only illustrative rather than restrictive. Under the enlightenment of the present invention, ordinary technicians in this field can also make many forms and equivalent changes without departing from the scope of protection of the purpose of the present invention and the claims, all of which are within the protection of the present invention.

Claims

1. An output protection circuit for a power amplifier, characterized in that: Including power detection module and protection module; The input end of the power detection module is used to connect to the output end of the power amplifier, the output end of the power detection module is connected to the input end of the protection module, and the power detection module is used to obtain the detection voltage output by the output end of the power amplifier and generate a driving voltage according to the detection voltage; The output end of the protection module is used to connect to the input end of the power amplifier, and the protection module is used to adjust the bias voltage input to the input end of the power amplifier according to the magnitude of the driving voltage; When the detection voltage acquired by the power detection module is greater than a preset threshold, the driving voltage generated by the power detection module turns on the protection module, and reduces the bias voltage of the input end of the power amplifier via the protection module.

2. The output protection circuit for a power amplifier according to claim 1, characterized in that: The power detection module includes a first transistor, a second transistor, a third transistor, a first resistor, a second resistor, a third resistor, a fourth resistor, a fifth resistor, a first capacitor and a second capacitor, wherein: The first end of the first resistor serves as the input end of the power detection module, and the second end of the first resistor is connected to the first end of the first capacitor; The second end of the first capacitor is respectively connected to the output end of the first transistor, the first end of the second resistor and the first end of the third resistor; The second end of the second resistor is connected to an external bias voltage; The input end of the first transistor is connected to the second end of the third resistor and the first end of the fourth resistor respectively; The second end of the fourth resistor is connected to the first end of the second capacitor and the input end of the second transistor respectively; The second terminal of the second capacitor is grounded; The output end of the second transistor is connected to the first end of the fifth resistor and the input end of the third transistor respectively; The second end of the fifth resistor is connected to the external bias voltage; The output end of the third transistor is connected to the external bias voltage, and the ground end of the third transistor serves as the output end of the power detection module.

3. The output protection circuit for a power amplifier according to claim 2, characterized in that: The protection module includes a fourth transistor, a sixth resistor, a seventh resistor, an eighth resistor and a third capacitor, wherein: The first end of the sixth resistor serves as the input end of the protection module, and the second end of the sixth resistor is connected to the first end of the third capacitor and the input end of the fourth transistor respectively; The second end of the third capacitor is grounded; The output end of the fourth transistor is connected to the first end of the eighth resistor, and the ground end of the fourth transistor is connected in series with the seventh resistor and then grounded; The second end of the eighth resistor serves as the output end of the protection module.

4. The output protection circuit for a power amplifier according to claim 2, characterized in that: Define the current flowing into the input terminal of the first transistor as I in , the detection voltage is Vout, the resistance of the first resistor is R1, the capacitive reactance of the first capacitor is 1 / sC1, and the equivalent transconductance of the first transistor is 1 / g m1 , satisfying the following relationship: I in = Vout / ( R1 + 1 / sC1 + 1 / g m1 )。 5. The output protection circuit for a power amplifier according to claim 2, characterized in that: The first transistor, the second transistor and the third transistor are all triodes; the base of the first transistor serves as the input terminal of the first transistor, the emitter of the first transistor serves as the ground terminal of the first transistor, and the collector of the first transistor serves as the output terminal of the first transistor; The base of the second transistor serves as the input terminal of the first transistor, the emitter of the second transistor serves as the ground terminal of the first transistor, and the collector of the second transistor serves as the output terminal of the second transistor; The base of the third transistor serves as the input terminal of the third transistor, the emitter of the third transistor serves as the ground terminal of the third transistor, and the collector of the third transistor serves as the output terminal of the third transistor.

6. The output protection circuit for a power amplifier according to claim 3, characterized in that: The fourth transistor is a triode; the base of the fourth transistor serves as the input end of the fourth transistor, the emitter of the fourth transistor serves as the ground end of the fourth transistor, and the collector of the fourth transistor serves as the output end of the fourth transistor.

7. A radio frequency device, characterized in that: The invention comprises an output protection circuit for a power amplifier and a power amplifier as described in any one of claims 1 to 6.

8. The radio frequency device according to claim 7, characterized in that: The power amplifier includes a multi-stage power amplification unit, the input end of the output protection circuit is connected to the output end of the last stage power amplification unit in the multi-stage power amplification unit, and the output end of the output protection circuit is connected to the input end of the last stage power amplification unit in the multi-stage power amplification unit.

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