Radio frequency power detection circuit applied to power amplifier

Abstract

The invention discloses a radio frequency power detection circuit applied to a power amplifier, which comprises a detection unit and an amplification unit, an external radio frequency signal is input into the detection unit, when the voltage value of the external radio frequency signal is greater than a set value, the detection unit is used for grounding the input external radio frequency signal, and the amplification unit is used for amplifying the external radio frequency signal. When the voltage value of the external radio frequency signal is smaller than a set value, the detection unit inputs the external radio frequency signal into the amplification unit; the amplification unit amplifies the signal output by the detection unit, converts the amplified signal into a voltage signal and outputs the voltage signal; and a filtering subunit is also arranged on the amplification unit, and when the voltage of the output signal of the output end is reduced, the filtering subunit discharges to reduce the voltage reduction trend of the output signal. The output voltage and the input signal power of the detection circuit change linearly, the accurate signal power value of the power amplifier can be obtained through the output voltage value of the detection circuit, and the detection precision of the output power of the power amplifier is improved.

Description

Technical Field

[0001] The present invention relates to the field of radio frequency detection, and more specifically to a radio frequency power detection circuit applied to a power amplifier. Background Art

[0002] RF power detection circuit is indispensable in RF power amplifier. The principle of RF power detection circuit is to convert AC power signal into DC voltage signal. Through RF power detection circuit, the output of RF power signal can be known, so as to accurately judge the working state of RF power amplifier.

[0003] Among them, peak detection technology is a commonly used detection method in the RF power detection process. The peak detection circuit established using this technology first performs half-wave or full-wave rectification on the signal, and then uses the charging and discharging characteristics of the capacitor to maintain the peak value of the rectified output DC signal to obtain a smooth DC signal. The amplitude of the DC signal is the peak value of the input signal.

[0004] The RF power detection circuit used in the commonly used peak detection technology is as follows: Figure 1 As shown, the RF power detection circuit is composed of a transistor HBT1 connected with a rectifier diode and a low-pass filter connected in parallel with RC (resistor R1 and capacitor C1). Figure 1 The transistor HBT1 in the middle is connected by a diode as a half-wave rectifier diode. The circuit converts the AC signal into a voltage signal close to DC, thereby completing the function of RF signal power detection.

[0005] Among them, the value of the RC low-pass filter should meet the following conditions:

[0006] (1) Time constant Here c is the frequency of the high-frequency carrier, that is, the capacitor C1 is approximately short-circuited to the high-frequency carrier, so as to filter out the high-frequency signal and make the output voltage tend to be flat;

[0007] (2) is the period of the modulation signal, and the time constant is smaller than the period of the modulation signal, that is, the low-pass filter allows low-frequency modulation signals to pass.

[0008] Please refer to Figure 2 , Figure 2 for Figure 1 The graph of the output voltage and input power of the RF power detection circuit is shown in FIG. Figure 2As shown, the solid line a is the curve of the output voltage of the power detection circuit changing with the signal power, while the dotted line b is an ideal linear straight line. Obviously, the relationship between the output voltage and the input signal power is not linear. The main reason is that as the input signal power increases, the conduction voltage VBE of the diode-connected transistor HBT1 decreases with the increase of the input current; the emitter junction of the transistor HBT1 is a nonlinear device; so that the output voltage of the RF power detection circuit does not change linearly with the signal power. Therefore, it is difficult to judge the output power of the power amplifier from the output voltage value, and the accuracy of the obtained result is not high; in addition, when the input RF signal is a half-wave signal, it is difficult to detect the changing output voltage value through the above detection circuit, so the input signal power cannot be detected.

[0009] Therefore, it is necessary to provide an improved radio frequency power detection circuit applied to a power amplifier to overcome the above-mentioned defects. Summary of the invention

[0010] The purpose of the present invention is to provide a radio frequency power detection circuit applied to a power amplifier. The output voltage of the detection circuit of the present invention varies linearly with the input signal power, and a precise signal power value can be accurately obtained through the output voltage value of the detection circuit, thereby improving the detection accuracy of the power amplifier output power.

[0011] To achieve the above-mentioned purpose, the present invention provides a radio frequency power detection circuit applied to a power amplifier, which includes a detection unit and an amplification unit. An external radio frequency signal is input into the detection unit. When the voltage value of the external radio frequency signal is greater than a set value, the detection unit grounds the input external radio frequency signal. When the voltage value of the external radio frequency signal is less than the set value, the detection unit inputs the external radio frequency signal into the amplification unit. The amplification unit amplifies the signal output by the detection unit and converts the amplified signal into a voltage signal for output. A filtering subunit is also provided on the amplification unit. When the voltage of the output signal at the output end decreases, the filtering subunit discharges to reduce the trend of the output signal voltage decreasing.

[0012] Preferably, the detection unit includes a first capacitor and a first transistor, one end of the first capacitor is connected to the external input end, and the other end is connected to the base of the first transistor, the first transistor is connected in a diode manner and connected to the amplification unit, and the emitter of the first transistor is grounded.

[0013] Preferably, the detection unit further includes a first resistor, one end of the first resistor is connected to the external input end, and the other end of the first resistor is connected to one end of the first capacitor.

[0014] Preferably, the amplification unit includes three resistors, a fourth resistor, a fifth resistor, a second transistor and a second capacitor. The second capacitor and the fifth resistor are connected in parallel to form a filter subunit and are connected to the emitter of the second transistor, and the collector of the second transistor is also connected to the output end; one end of the third resistor and the fourth resistor are both connected to an external power supply, and the other end of the fourth resistor is connected to the collector of the second transistor; the other end of the third resistor is commonly connected to the base of the second transistor and connected to the collector of the first transistor.

[0015] Preferably, the amplifying unit further comprises a second resistor, one end of the second resistor is connected to the base of the first transistor, and the other end of the second resistor is connected to the base of the second transistor.

[0016] Preferably, the RF power detection circuit applied to the power amplifier also includes an emitter follower unit, which includes a seventh resistor, an eighth resistor, a ninth resistor, a tenth resistor and a third transistor; the base of the third transistor is connected to the collector of the second transistor, one end of the seventh resistor is connected to another external power supply, and the other end is connected to the collector of the third transistor; one end of the eighth resistor and the ninth resistor are both connected to the emitter of the third transistor, the other end of the ninth resistor and one end of the tenth resistor are connected to the output end, and the other ends of the eighth resistor and the tenth resistor are both grounded.

[0017] Preferably, the emitter follower unit further includes a sixth resistor, one end of the sixth resistor is connected to the collector of the second transistor, and the other end of the sixth resistor is connected to the base of the third transistor.

[0018] Preferably, the ratio of the resistance value of the third resistor to the resistance value of the second resistor is greater than 100.

[0019] Compared with the prior art, the radio frequency power detection circuit applied to the power amplifier of the present invention is provided with a detection unit and an amplification unit, and a filtering subunit is also provided on the amplification unit, so that the half-wave signal in the input radio frequency signal is screened out by the detection unit, and the amplification unit amplifies the screened half-wave signal and converts it into a voltage output, so that the input radio frequency signal can be detected through the output voltage; in addition, when the voltage of the output signal at the output end decreases, the filtering subunit discharges to reduce the trend of the output signal voltage decrease, so as to ensure the linear relationship between the input and output of the entire detection circuit, and further ensure the accuracy of detecting the input signal power through the output voltage.

[0020] 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

[0021] Figure 1The figure is a schematic diagram of the structure of a radio frequency power detection circuit in the prior art.

[0022] Figure 2 for Figure 1 Input and output graphs of the circuit shown.

[0023] Figure 3 The figure is a schematic diagram of the structure of the radio frequency power detection circuit applied to the power amplifier of the present invention.

[0024] Figure 4 for Figure 3 Dynamic equivalent circuit diagram of the amplification unit in the circuit structure shown.

[0025] Figure 5 for Figure 3 Input and output curve diagram of the RF power detection circuit shown. DETAILED DESCRIPTION

[0026] Embodiments of the present invention are now described with reference to the accompanying drawings, in which similar element numbers represent similar elements. As described above, the present invention provides a radio frequency power detection circuit applied to a power amplifier, wherein the output voltage of the detection circuit of the present invention varies linearly with the input signal power, and the output voltage value of the signal can be accurately detected and an accurate signal power value can be obtained, thereby improving the detection accuracy of the radio frequency output power.

[0027] Please refer to Figure 3 , Figure 3 FIG. 1 is a schematic diagram of the structure of a radio frequency power detection circuit applied to a power amplifier of the present invention. Figure 3As shown, the radio frequency power detection circuit applied to the power amplifier of the present invention includes a detection unit and an amplification unit. The external radio frequency signal is input into the detection unit through the input terminal IN. When the voltage value of the external radio frequency signal is greater than the set value, the detection unit grounds the input external radio frequency signal, that is, the external radio frequency signal directly reaches the ground through the detection unit. When the voltage value of the external radio frequency signal is less than the set value, the detection unit inputs the external radio frequency signal into the amplification unit, that is, the half-wave signal in the external radio frequency signal is screened out by the detection unit for subsequent detection operations; the amplification unit amplifies the half-wave signal output by the detection unit and converts the amplified signal into a voltage signal Output; As mentioned above, the signal input to the amplifying unit is a half-wave signal. The voltage and power corresponding to the half-wave signal are very small and generally difficult to detect. Therefore, it is amplified by the amplifying unit to facilitate detection of the voltage or power of the half-wave signal and obtain accurate detection results; a filtering subunit is also provided on the amplifying unit. When the voltage of the output signal at the output terminal OUT decreases, the filtering subunit discharges to reduce the trend of the output signal voltage decrease, thereby ensuring that the output voltage value changes linearly with the power of the input RF signal, so that the accurate power of the RF signal can be obtained by detecting the output voltage value, thereby realizing power detection of the RF signal output by the power amplifier.

[0028] Specifically, the detection unit includes a first capacitor C1 and a first transistor Q1, one end of the first capacitor C1 is connected to the external input terminal IN, and the other end is connected to the base of the first transistor Q1, so that the external input terminal IN inputs the radio frequency signal to the detection unit through the first capacitor C1; the first transistor Q1 is connected in a diode manner and connected to the amplification unit, and the emitter of the first transistor Q1 is grounded; as described above, when the voltage value of the external radio frequency signal is greater than the set value, the detection unit grounds the input external radio frequency signal, and the set value is the difference between the on-voltage of the first transistor Q1 and the bias voltage loaded thereon, such as Figure 3As shown, when the voltage value of the external RF signal is greater than the set value so that the first transistor Q1 is turned on, the RF signal input through the first capacitor C1 directly flows into the ground through the emitter of the first transistor Q1. On the contrary, if the voltage value of the external RF signal is less than the set value, the RF signal input through the first capacitor C1 is input into the amplification unit through the collector of the first transistor Q1; thus, in the present invention, the half-wave signal is screened out by the first transistor Q1 for processing. Wherein, the detection unit also includes a first resistor R1, one end of the first resistor R1 is connected to the external input end, and the other end is connected to one end of the first capacitor C1; the first resistor R1 is set so that the RF signal is input to the first transistor Q1 through the first resistor, so that the voltage of the RF signal when it is input to the first transistor Q1 can be adjusted through the first resistor, so as to screen out the half-wave signal that meets the design requirements.

[0029] The amplifying unit includes a third resistor R3, a fourth resistor R4, a fifth resistor R5, a second transistor Q2 and a second capacitor C2. The second capacitor C2 and the fifth resistor R5 are connected in parallel to form a filter subunit and connected to the emitter of the second transistor Q2. The collector of the second transistor Q2 is also connected to the output terminal OUT. The signal input to the amplifying unit is amplified and then output through the collector of the second transistor Q2. The filter subunit is a low-pass filter network to filter out low-frequency signals in the amplifying unit. When the emitter voltage of the second transistor Q2 decreases (the voltage across the fifth resistor R5 decreases), the second capacitor C2 will discharge, thereby suppressing the trend of the emitter voltage of the second transistor Q2 to decrease, and further suppressing the trend of the collector voltage of the second transistor Q2 to decrease, so that a slowly changing voltage signal can be obtained from the collector of the second transistor Q2 of the amplifying unit. One end of the third resistor R3 and the fourth resistor R4 are both connected to an external power source V1, and the other end of the fourth resistor R4 is connected to the collector of the second transistor Q2; the other end of the third resistor R3 is commonly connected to the base of the second transistor Q2 and connected to the collector of the first transistor Q1, so as to provide a bias current and a bias voltage for the first transistor Q1 through the external power source V1; wherein the aforementioned setting value is the difference between the on-voltage and the bias voltage of the first transistor Q1. The amplification unit also includes a second resistor R2, one end of the second resistor R2 is connected to the base of the first transistor Q1, and the other end of the second resistor R2 is connected to the base of the second transistor Q2; by setting the second resistor R2, the bias current applied to the first transistor Q1 by the external power source V1 is more controllable, so that the first transistor Q1 can obtain a suitable bias voltage to accurately control the on or off of the first transistor Q1.

[0030] As a preferred embodiment of the present invention, the RF power detection circuit applied to the power amplifier also includes an emitter follower unit, which includes a seventh resistor R7, an eighth resistor R8, a ninth resistor R9, a tenth resistor R10 and a third transistor Q3; the base of the third transistor Q3 is connected to the collector of the second transistor Q2, one end of the seventh resistor R7 is connected to another external power supply V2, and the other end is connected to the collector of the third transistor Q3; one end of the eighth resistor R8 and the ninth resistor R9 are both connected to the emitter of the third transistor Q3, the other end of the ninth resistor R9 and one end of the tenth resistor R10 are connected to the output end OUT, and the other ends of the eighth resistor R8 and the tenth resistor R10 are both grounded; the third transistor Q3 rectifies the voltage signal output by the amplification unit, and the rectified voltage is adjusted by the eighth resistor R8, the ninth resistor R9 and the tenth resistor R10 to output a final voltage value from the output end OUT, so that the voltage value of the output end OUT can well correspond to the power value of the input RF signal. In addition, the emitter follower unit also includes a sixth resistor R6, one end of the sixth resistor R6 is connected to the collector of the second transistor Q2, and the other end is connected to the base of the third transistor Q3. The current and voltage input to the base of the third transistor Q3 can be adjusted through the sixth resistor R6 so that the third transistor Q3 can be normally turned on and output voltage.

[0031] Please refer to Figure 4 , describing the working principle of the radio frequency power detection circuit applied to the power amplifier of the present invention: when the external radio frequency signal is input into the first transistor Q1 as the detection diode through the first capacitor C1, when the total voltage after the voltage of the external radio frequency signal is superimposed with the DC bias voltage (the bias voltage added to the first transistor Q1 by the external power supply V1 through the third resistor R3 and the second resistor R2) is greater than the conduction voltage of the first transistor Q1, the first transistor Q1 is turned on, and the external radio frequency signal is directly connected to the ground through the first transistor Q1; and when the total voltage after the voltage of the external radio frequency signal is superimposed with the DC bias voltage is less than the conduction voltage of the first transistor Q1. When the voltage is turned on, the input external RF signal is input to the amplification unit through the collector of the first transistor Q1; in the detection unit, since the bias voltage added to the first transistor Q1 by the external power supply V1 through the third resistor R3 and the second resistor R2 is fixed, but the power of the input external RF signal is different and its voltage value is also different, so the base voltage (total voltage) superimposed on the first transistor Q1 is also different, that is, the half-wave signal continues to flow into the subsequent circuit through the conduction of the first transistor Q1; wherein, the first resistor R1 with a suitable resistance value is selected to ensure that the signal input to the first transistor Q1 is a small signal.

[0032] The current of the half-wave signal screened by the detection unit is amplified by the second transistor Q2 of the amplification unit and charges the second capacitor C2 when flowing through the emitter of the second transistor Q2. When the voltage amplitude across the fifth resistor R5 on the emitter of the second transistor Q2 starts to decrease from the maximum value, the second capacitor C2 discharges to suppress the change of the voltage amplitude. Figure 4 The figure shows the dynamic equivalent circuit of the amplification unit. In the present invention, the ratio of the resistance value of the third resistor R3 to the resistance value of the second resistor R2 is set to be greater than 100, that is, the third resistor R3 is much larger than the second resistor R2, so the AC signal flowing through the third resistor R3 can be approximately 0. Figure 4 The dynamic equivalent circuit shown can be obtained:

[0033] Δu e ≈Δi e R 5 ,

[0034] Δu c ≈Δi c (R 4 +R 5 );

[0035] because,

[0036] Δi e ≈Δi c =βΔi b

[0037] Among them, Δu e is the voltage change of the emitter of the second transistor Q2, Δi e is the current change of the emitter of the second transistor Q2, Δu c is the voltage change of the collector of the second transistor Q2. Therefore, Δi c is the current change Δi of the collector of the second transistor Q1 b is the current change of the base of the second transistor Q2;

[0038] therefore

[0039]

[0040] From the above formula, we can get that when the voltage change of the emitter of the second transistor Q2 is Δu e When it decreases, it will inevitably cause the voltage change Δu of the collector of the second transistor Q2 cDecreases; and from the above, it can be seen that when the voltage at the emitter of the second transistor Q2 decreases (the voltage across the fifth resistor R5 decreases), due to the discharge effect of the second capacitor C2, the change in voltage reduction will be suppressed, thereby causing the voltage change at the collector of the second transistor Q2 to decrease, so that a slowly changing voltage signal can be obtained from the collector of the second transistor Q2 of the amplifying unit.

[0041] The voltage signal output by the amplifier unit (the voltage signal output by the collector of the second transistor Q2) reaches the output terminal OUT through the emitter follower unit. The emitter follower unit further rectifies the voltage signal output by the amplifier unit through the base-emitter junction diode rectification characteristics of the third transistor Q3, and the output voltage value can be adjusted through the eighth resistor R8, the ninth resistor R9 and the tenth resistor R10. Thus, the power detection function of the power detection circuit is realized.

[0042] Depend on Figure 4 The dynamic equivalent circuit of the amplifier unit shown can be obtained by b The expression is:

[0043] Δu b =Δi b (R 2 +r be )+Δi e R 5

[0044] Therefore, the voltage amplification factor of the amplifier unit is:

[0045]

[0046] As is well known, the voltage amplification factor can be regarded as a constant value within the normal working range of the transistor. Therefore, the radio frequency power detection circuit applied to the power amplifier of the present invention has the characteristic of linear output.

[0047] Please refer to Figure 5 ,exist Figure 5 In, yes Figure 3 The input power PIN of the detection circuit shown is simulated from 0-20dBm, and the voltage-power curve can be obtained, as shown in Figure 5 shown in Figure 5 The horizontal axis is the input power PIN, and the vertical axis is the output voltage VOUT. The solid curve a is the simulation result, and the dotted curve b is the theoretical linear straight line. Figure 5 It can be seen that curve a and curve b are substantially overlapped; therefore, the output voltage and input power of the radio frequency power detection circuit applied to the power amplifier of the present invention are in a linear relationship.

[0048] In summary, the RF power detection circuit applied to the power amplifier of the present invention filters out the half-wave signal in the input RF signal through the detection unit, and the amplification unit amplifies the filtered half-wave signal and converts it into a voltage output, so that the input RF signal can be detected through the output voltage; in addition, the discharge of the second capacitor C2 in the amplification unit is used to suppress the decreasing trend of the emitter voltage of the second transistor Q2, thereby suppressing the decreasing trend of the collector voltage of the second transistor Q2 and the output voltage of the output terminal OUT, thereby ensuring the linear relationship between the input and output of the entire detection circuit, and further ensuring the accuracy of detecting the input signal power through the output voltage.

[0049] 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 radio frequency power detection circuit applied to a power amplifier, characterized in that: It comprises a detection unit and an amplification unit, an external radio frequency signal is input into the detection unit, when the voltage value of the external radio frequency signal is greater than a set value, the detection unit grounds the input external radio frequency signal, when the voltage value of the external radio frequency signal is less than the set value, the detection unit inputs the external radio frequency signal into the amplification unit; the amplification unit amplifies the signal output by the detection unit, and converts the amplified signal into a voltage signal for output; a filtering subunit is also arranged on the amplification unit, when the voltage of the output signal at the output end decreases, the filtering subunit discharges to reduce the tendency of the output signal voltage decreasing.

2. The radio frequency power detection circuit for a power amplifier according to claim 1, characterized in that: The detection unit includes a first capacitor and a first transistor, one end of the first capacitor is connected to the external input end, and the other end is connected to the base of the first transistor, the first transistor is connected in a diode manner and connected to the amplification unit, and the emitter of the first transistor is grounded.

3. The radio frequency power detection circuit for a power amplifier according to claim 2, characterized in that: The detection unit further includes a first resistor, one end of which is connected to the external input end, and the other end of which is connected to one end of the first capacitor.

4. The radio frequency power detection circuit for a power amplifier according to claim 2, characterized in that: The amplification unit includes three resistors, a fourth resistor, a fifth resistor, a second transistor and a second capacitor. The second capacitor and the fifth resistor are connected in parallel to form a filter subunit and are connected to the emitter of the second transistor, and the collector of the second transistor is also connected to the output end; one end of the third resistor and the fourth resistor are both connected to an external power supply, and the other end of the fourth resistor is connected to the collector of the second transistor; the other end of the third resistor is commonly connected to the base of the second transistor and connected to the collector of the first transistor.

5. The radio frequency power detection circuit for a power amplifier as claimed in claim 4, characterized in that: The amplifying unit further includes a second resistor, one end of the second resistor is connected to the base of the first transistor, and the other end of the second resistor is connected to the base of the second transistor.

6. The radio frequency power detection circuit for a power amplifier according to claim 4, characterized in that: It also includes an emitter follower unit, which includes a seventh resistor, an eighth resistor, a ninth resistor, a tenth resistor and a third transistor; the base of the third transistor is connected to the collector of the second transistor, one end of the seventh resistor is connected to another external power supply, and the other end is connected to the collector of the third transistor; one end of the eighth resistor and the ninth resistor are both connected to the emitter of the third transistor, the other end of the ninth resistor and one end of the tenth resistor are connected to the output end, and the other ends of the eighth resistor and the tenth resistor are both grounded.

7. The radio frequency power detection circuit for a power amplifier according to claim 6, characterized in that: The emitter follower unit further includes a sixth resistor, one end of which is connected to the collector of the second transistor, and the other end of which is connected to the base of the third transistor.

8. The method according to claim 5, characterized in that: The ratio of the resistance value of the third resistor to the resistance value of the second resistor is greater than 100.

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