Shortwave power amplifier drain valley voltage detection circuit and voltage regulation method

Abstract

The present invention discloses a short-wave power amplifier drain valley voltage detection circuit and voltage regulation method, which includes a drain input port, a DC detection network, an AC negative voltage detection network, an addition amplifier and a detection output port; the drain input port is respectively connected to the input ends of the DC detection network and the AC negative voltage detection network; the output end of the DC detection network and the output end of the AC negative voltage detection network are connected to an input end of the addition amplifier; the output end of the addition amplifier is connected to the detection output port. The present invention realizes the detection and collection of the valley voltage of the drain of the power amplifier tube, provides an adjustment basis for the automatic adjustment system of the drain power supply voltage, and thus improves the efficiency of the power amplifier under load mismatch conditions.

Description

[Technical field]

[0001] The invention belongs to the technical field of radio frequency circuits, and in particular relates to a shortwave power amplifier drain valley voltage detection circuit and a voltage regulation method. [Background technology]

[0002] Shortwave power amplifiers are essential devices in shortwave communications, electronic countermeasures, and detection transmitters, providing the system with the necessary RF output power.

[0003] The shortwave frequency band covers 2MHz to 30MHz, which is close to 4 octaves. The transmitting equipment is a typical broadband system. The power amplifier often faces harsh load conditions. The typical load standing wave ratio will reach more than 2.5, and the reflection phase angle is distributed within 360°.

[0004] Severe load mismatch will lead to the loss of control of the performance of the power amplifier technology, one of which is the deterioration of efficiency. Low efficiency will increase heat consumption, increase the core temperature of the power tube, reduce reliability, and even damage the power tube. On the other hand, it will increase system power consumption and increase operating costs.

[0005] Figure 1(a) shows the drain efficiency of a typical power amplifier circuit at a load standing wave ratio of 2.5 and different reflection phase angles. It can be seen that as the load conditions change, the drain efficiency will drop from 65% to below 30%, and the heat loss will increase by nearly 5 times.

[0006] At present, the main technical solutions to deal with load mismatch are to increase the design margin and adopt automatic protection measures. Obviously, a large design margin will cause too much redundancy, which is not conducive to the miniaturization and lightness of the equipment; and the automatic protection measures only prevent equipment damage in extreme cases, and cannot fundamentally improve the performance of the power amplifier. If the design margin is insufficient, it will lead to frequent shutdown protection, affecting normal operation. Both measures cannot avoid the increase in operating costs.

[0007] To deal with the problem of reduced efficiency caused by load mismatch, the method of adjusting the power supply voltage can also be used. According to the working principle of the power tube, one of the mechanisms that causes the efficiency of the amplifier circuit to decrease is that the alternating voltage swing of the power tube drain is reduced due to load changes, and the dynamic range under the current DC power supply conditions is not fully utilized. Figure 1 (b) and Figure 1 (c) respectively show the voltage waveform of the power tube drain at the highest and lowest efficiency. It can be seen from the waveform that in the case of high efficiency, the voltage valley value reaches 0V and has a longer time share; while in the case of low efficiency, the lowest point of the valley voltage is 6V, there is still a large room for decline, and the valley duration is short. At this time, reducing the DC supply voltage of the drain can improve the efficiency without affecting the signal quality. Experiments have shown that under the conditions shown in Figure 1 (c), when the voltage is reduced from the original 48V to 36V, the drain efficiency is increased from 26% to 40%.

[0008] The adjustment of the supply voltage needs to be able to be automatically performed according to the load changes in order to be practical in engineering. Although there are no technical obstacles to testing the load vector reflection coefficient of the power amplifier, the implementation complexity is relatively high, and the measurement point is generally at the transmitter outlet. For high-power transmitters, there is a long RF path from the transmitter output port to the power amplifier circuit drain, which requires a cumbersome calibration process.

[0009] Currently, there is no relevant valley voltage detection circuit, nor an automatic voltage adjustment system based on the valley voltage. Therefore, it is necessary to provide a new short-wave power amplifier drain valley voltage detection circuit and voltage adjustment method to solve the above technical problems. [Summary of the invention]

[0010] One of the main purposes of the present invention is to provide a short-wave power amplifier drain valley voltage detection circuit, which realizes the valley voltage detection and collection of the power amplifier tube drain, provides an adjustment basis for the drain power supply voltage automatic adjustment system, and thus improves the efficiency of the power amplifier under load mismatch conditions.

[0011] The present invention achieves the above-mentioned purpose through the following technical scheme: a shortwave power amplifier drain valley voltage detection circuit, which includes a drain input port, a DC detection network, an AC negative voltage detection network, an adding amplifier and a detection output port; the drain input port is respectively connected to the input ends of the DC detection network and the AC negative voltage detection network; the output end of the DC detection network and the output end of the AC negative voltage detection network are connected to an input end of the adding amplifier; the output end of the adding amplifier is connected to the detection output port.

[0012] Furthermore, the DC detection network includes two voltage-dividing resistors R1 and R2 connected in series, one end of the resistor R1 is connected to the drain input port, one end of the resistor R2 is grounded, and the terminals connecting the resistors R1 and R2 form the output end of the DC detection network.

[0013] Furthermore, the DC detection network also includes an operational amplifier N1; the terminal connecting the resistor R1 and the resistor R2 is connected to the positive input terminal of the operational amplifier N1; the negative input terminal of the operational amplifier N1 is connected to the output terminal of the operational amplifier N1 to form a follower; the output terminal of the operational amplifier N1 forms the output terminal of the DC detection network.

[0014] Furthermore, the AC negative voltage detection network includes a DC blocking capacitor C1, a resistor R3, a resistor R4, a detection diode D1, a capacitor C2 and a resistor R5; the drain input port is connected to one end of the DC blocking capacitor C1, and the other end of the DC blocking capacitor C1 is connected to one end of the resistor R3; the resistor R3 and the resistor R4 are connected in series and then grounded; the terminal where the resistors R3 and R4 are connected to each other is connected to the cathode of the detection diode D1; the anode of the detection diode D1 is respectively connected to the capacitor C2 and the resistor R5; the capacitor C2 and the resistor R5 are connected to the ground in parallel; the anode of the detection diode D1 forms the output end of the AC negative voltage detection network.

[0015] Furthermore, the AC negative voltage detection network also includes an operational amplifier N2; the anode of the detection diode D1 is connected to the positive input terminal of the operational amplifier N2; the negative input terminal of the operational amplifier N2 is connected to its output terminal to form a follower; the output terminal of the operational amplifier N2 forms the output terminal of the AC negative voltage detection network.

[0016] Furthermore, the AC negative voltage detection network includes a DC blocking capacitor C1, a resistor R3, a resistor R4, a detection diode D1 and a capacitor C2; the drain input port is connected to one end of the DC blocking capacitor C1, and the other end of the DC blocking capacitor C1 is connected to one end of the resistor R3; the resistor R3 and the resistor R4 are connected in series and then grounded; the terminal where the resistors R3 and R4 are interconnected is connected to the cathode of the detection diode D1; the anode of the detection diode D1 is connected to one end of the capacitor C2, and the connection end forms the output end of the AC negative voltage detection network; the other end of the capacitor C2 is connected to the output end of the DC detection network.

[0017] Furthermore, the AC negative pressure detection network also includes a capacitor C5 and a capacitor C6; the resistor R3 is connected in parallel with the capacitor C5, and the resistor R4 is connected in parallel with the capacitor C6.

[0018] Furthermore, the adding amplifier has two input terminals and one output terminal, and includes an operational amplifier N3, a resistor R6 and a resistor R7; the two input terminals of the adding amplifier are respectively connected to the positive input terminal of the operational amplifier N3 through the resistor R6 and the resistor R7; the negative input terminal of the operational amplifier N3 is grounded through a resistor R8, and is connected to its output terminal through a resistor R9; the output terminal of the operational amplifier N3 forms the detection output terminal of the detection circuit and is connected to the detection output port.

[0019] Furthermore, the drain input port is located on the printed circuit board near the root of the drain of the power transistor and is electrically connected to the drain of the power transistor.

[0020] Another object of the present invention is to provide a method for adjusting the drain DC supply voltage of a shortwave power amplifier, which adjusts the drain DC supply voltage of the power amplifier accordingly according to the drain valley voltage value of the power amplifier detected by the above-mentioned detection circuit.

[0021] Compared with the prior art, the beneficial effects of the short-wave power amplifier drain valley voltage detection circuit and voltage regulation method of the present invention are as follows: by measuring the AC valley voltage value of the power tube drain, it is possible to know whether the dynamic range of the power tube is fully used under the current load condition, and then it can directly reflect whether the current power supply voltage is appropriate, providing a basis for automatically adjusting the DC power supply voltage of the power tube drain, greatly simplifying the implementation process; the power tube drain is input to the DC detection network and the AC negative voltage detection network; the DC detection network is proportional to the drain DC voltage through resistor voltage division, filtering and buffering; the AC negative voltage detection network is connected to the DC isolation capacitor after the DC isolation capacitor. A detector diode is used to obtain the negative peak value of the AC component; the outputs of the DC detection network and the AC negative voltage detection network are connected to the input of the summing amplifier, and the two detection voltages are added and amplified to obtain the drain valley voltage detection value; this scheme detects the DC and AC components of the drain separately, optimizes the AC negative voltage detection circuit, and improves the detection accuracy and efficiency of the power amplifier drain voltage; the circuit is simple and convenient to implement, with a small size, and can be arranged near the power tube drain; the circuit is simple, compact, and easy to implement, and can accurately measure the valley voltage of the power tube drain, so as to know whether the dynamic range of the power tube is fully used, and provide a basis for automatic adjustment of the power supply voltage.

Brief Description of the Drawings

[0022] Figure 1(a) shows the variation of the shortwave power amplifier drain efficiency with the reflection phase when the load standing wave ratio is 2.5 (frequency is 30MHz);

[0023] Figure 1(b) shows the drain voltage waveform at the highest efficiency;

[0024] Figure 1(c) shows the drain voltage waveform at the lowest efficiency;

[0025] Figure 2 A functional block diagram of an embodiment of the present invention;

[0026] Figure 3 One of the circuit schematics of an embodiment of the present invention;

[0027] Figure 4 The second circuit diagram of the embodiment of the present invention;

[0028] Figure 5 The third circuit diagram of the embodiment of the present invention;

[0029] Figure 6 Schematic diagram of the installation position of an embodiment of the present invention. [Specific implementation method]

[0030] Embodiment 1:

[0031] This embodiment is a short-wave power amplifier drain valley voltage detection circuit. The principle block diagram of the embodiment is as follows: Figure 2 As shown, it includes a drain input port 1, a DC detection network 2, an AC negative voltage detection network 3, an adder amplifier 4, and a detection output port 5. The input ends of the DC detection network 2 and the AC negative voltage detection network 3 are connected in parallel and connected to the drain input port 1; the output end of the DC detection network 2 is connected to one input end of the adder amplifier 4, and the output end of the AC negative voltage detection network 3 is connected to the other input end of the adder amplifier 4; the output end of the adder amplifier 4 serves as a detection output end of a short-wave power amplifier drain valley voltage detection circuit of the present invention.

[0032] The circuit diagram of this implementation is as follows Figure 3 As shown. The DC detection network 2 includes a voltage divider circuit formed by resistors R1 and R2 connected in series, a filter capacitor C3, a follower formed by an operational amplifier N1, and an output filter capacitor C4; wherein one end of the voltage divider resistor R1 is connected to the drain input port 1, and the other end is connected in series with the resistor R2 and grounded; the filter capacitor C3 is connected in parallel with the resistor R2; the terminal where the resistor R1 and the resistor R2 are connected to each other is connected to the positive input end of the operational amplifier N1; the output end of the operational amplifier N1 is connected to its negative input end; one end of the filter capacitor C4 is connected to the output end of the operational amplifier N1, and the other end is grounded; the output end of the operational amplifier N1 forms the output end of the DC detection network 2.

[0033] In another embodiment, please refer to Figure 4 The DC detection network 2 includes a voltage divider circuit formed by resistors R1 and R2 connected in series and a filter capacitor C3; wherein one end of the voltage divider resistor R1 is connected to the drain input port 1, and the other end is connected in series with the resistor R2 and grounded; the filter capacitor C3 is connected in parallel with the resistor R2; the terminals connecting the resistors R1 and R2 form the output end of the DC detection network 2.

[0034] In this embodiment, please refer to Figure 3, the AC negative voltage detection network 3 includes a DC blocking capacitor C1, a series voltage-dividing resistor R3 and a resistor R4, a detector diode D1, a filter composed of a capacitor C2 and a resistor R5, and a follower composed of an operational amplifier N2. One end of the DC blocking capacitor C1 is connected to the drain input port 1, and the other end is connected to the voltage-dividing resistor R3; the other end of the voltage-dividing resistor R3 is connected in series with the voltage-dividing resistor R4 and then grounded; the terminals where the voltage-dividing resistor R3 and the resistor R4 are connected to each other are connected to the negative electrode of the detector diode D1; the positive electrode of the detector diode D1 is connected to the capacitor C2 and the resistor R5 respectively; the capacitor C2 and the resistor R5 are connected to the ground in parallel; the positive electrode of the detector diode D1 is also connected to the positive input terminal of the operational amplifier N2; the negative input terminal of the operational amplifier N2 is connected to its output terminal to form a follower; the output terminal of the operational amplifier N2 forms the output terminal of the AC negative voltage detection network 3.

[0035] In another embodiment, please refer to Figure 4 , the AC negative voltage detection network 3 includes a DC blocking capacitor C1, a series voltage dividing resistor R3 and a resistor R4, a detector diode D1, and a filter composed of a capacitor C2 and a resistor R5. One end of the DC blocking capacitor C1 is connected to the drain input port 1, and the other end is connected to the voltage dividing resistor R3; the other end of the voltage dividing resistor R3 is connected in series with the voltage dividing resistor R4 and then grounded; the terminal where the voltage dividing resistor R3 and the resistor R4 are connected to each other is connected to the cathode of the detector diode D1; the anode of the detector diode D1 is connected to the capacitor C2 and the resistor R5 respectively, and the capacitor C2 and the resistor R5 are connected in parallel to the ground; the anode of the detector diode D1 forms the output end of the AC negative voltage detection network 3.

[0036] In another embodiment, please refer to Figure 5 The AC negative voltage detection network 3 includes a DC blocking capacitor C1, a series voltage-dividing resistor R3 and a resistor R4, a detection diode D1 and a capacitor C2, wherein one end of the DC blocking capacitor C1 is connected to the drain input port 1, and the other end is connected to the voltage-dividing resistor R3; the other end of the voltage-dividing resistor R3 is connected in series with the voltage-dividing resistor R4 and then grounded; the terminals where the voltage-dividing resistor R3 and the resistor R4 are connected to each other are connected to the cathode of the detection diode D1; the anode of the detection diode D1 is connected to one end of the capacitor C2, and the connection end forms the output end of the AC negative voltage detection network 3; the other end of the capacitor C2 is connected to the output end of the DC detection network 2.

[0037] The AC negative voltage detection network 3 further includes a capacitor C5 and a capacitor C6; a resistor R3 is connected in parallel with the capacitor C5, and a resistor R4 is connected in parallel with the capacitor C6.

[0038] In this embodiment, the adding amplifier circuit 4 includes input resistors R6 and R7, an operational amplifier N3, and feedback voltage-dividing resistors R8 and R9; one end of the input resistor R6 is connected to the output end of the AC negative voltage detection network 3 (the output end of the operational amplifier N2, or the positive electrode of the detection diode D1, or the connection end of the detection diode D1 and the capacitor C2), and the other end is connected to the positive input end of the operational amplifier N3; one end of the input resistor R7 is connected to the output end of the DC detection network 2 (the output end of the operational amplifier N1, or the terminal where the resistor R1 and the resistor R2 are connected to each other), and the other end is connected to the positive input end of the operational amplifier N3; the feedback voltage-dividing resistor R9 is connected between the output end and the negative input end of the operational amplifier N3; one end of the feedback voltage-dividing resistor R8 is connected to the negative input end of N3, and the other end is grounded.

[0039] The output end of the operational amplifier N3 serves as the detection output end of the detection circuit of this embodiment and is connected to the detection output port 5 .

[0040] The working principle of this embodiment is:

[0041] The voltage at the drain input port V d (t) is:

[0042] V d (t) = V d0 +V a (t+nT),

[0043] Where n is an integer, T is the RF signal period, V d0 is the DC component, V a (t) is the AC waveform. Then the valley value of the drain voltage V val for:

[0044] V val =min 0≤t≤T {V d (t)}=V d0 +min 0≤t≤T {V a (t)}

[0045] In the DC detection network 2, the drain voltage is divided by resistors R1 and R2, and then filtered by filter capacitor C3 to remove the AC component, obtaining the DC detection voltage V sd for:

[0046]

[0047] In the AC negative voltage detection network 3, capacitor C1 isolates the DC component, so resistors R3 and R4 divide the voltage to obtain the AC voltage Detector diode D1 to V a1(t) The negative voltage in the waveform is turned on, charging the filter capacitor C2, making the capacitor C2 present a negative voltage to the ground; the filter time constant τ composed of capacitor C2 and resistor R5 is selected = C2·R5>>T, then the capacitor C2 will maintain V a1 (t) is the lowest voltage, and the final detector diode D1 output voltage V sa for:

[0048]

[0049] Summing amplifier 4 converts V sd 、V sa After adding and amplifying, the final detection voltage V is obtained. s for:

[0050]

[0051] Select component parameter values ​​to satisfy:

[0052]

[0053] but

[0054]

[0055] That is, the detected output voltage is proportional to the valley voltage value. The proportionality coefficient can be adjusted by selecting resistors R9 and R8.

[0056] When using Figure 5 The specific implementation shown is different from the working principle of the present embodiment in that the input resistor R6 and the resistor R7 of the adding amplifier 4 are connected in series, which is equivalent to the filter resistance at the output end of the detection diode D1. Therefore, the time constant of the filter τ=(R6+R7)C2, and τ>>T should be ensured. Figure 5 The detection output result of the detection circuit shown is the same as that of this embodiment. Figure 5 The detection circuit shown in the figure, on the one hand, removes the operational amplifier N2 and the filter resistor R5, thereby simplifying the circuit; on the other hand, since one end of the filter capacitor C2 is connected to the DC detection output, the loop voltage difference of the detection diode D1 is increased, making the detection diode D1 more fully conductive, thereby increasing the sensitivity of the detection diode D1 and reducing the influence of the junction voltage drop.

[0057] Figure 6Schematic diagram of the layout position of the circuit of this embodiment. The detection circuit of this embodiment is designed and manufactured on a printed circuit board 52. The power tube 51 to be detected and the printed circuit board 52 are mounted on the surface of a metal substrate 53. The drain pin 511 of the power tube 51 is connected to the microstrip line 54 on the upper layer of the printed circuit board 52. A cavity 57 is processed on the metal substrate 53 below the output transformer 56. The microstrip line 54 is connected to the back of the printed circuit board 52 through a metalized via 55 at the root position close to the drain pin 511 and is placed in the cavity 57. The detection circuit of this embodiment is arranged on the back of the printed circuit board 52, and corresponds to the position of the cavity 57. The drain input terminal is connected to the metalized via 55.

[0058] In the frequency range of 2 to 30 MHz, the embodiment of the present invention selects R6=R7=20 kΩ, C2=560 pF, R3=R1=20 kΩ, R8=R9=10 kΩ, the detector diode D1 is a Schottky diode, and the operational amplifier adopts a universal model. Taking the valley detection output voltage of 0.7 V as a reference, the power supply voltage of the power amplifier is adjusted, and under the test conditions shown in FIG1 , the minimum efficiency of the power amplifier reaches more than 40%.

[0059] This embodiment measures the AC valley voltage value of the drain of the power tube, so that it can be known whether the dynamic range of the power tube is fully used under the current load condition, and can directly reflect whether the current power supply voltage is appropriate, providing a basis for automatically adjusting the DC power supply voltage of the drain of the power tube, greatly simplifying the implementation process; the drain of the power tube is input to the DC detection network and the AC negative voltage detection network; the DC detection network outputs a voltage proportional to the drain DC voltage through resistor voltage division, filtering and buffering; the AC negative voltage detection network uses a detection diode after the DC isolation capacitor to obtain the negative peak value of the AC component; the DC The outputs of the detection network and the AC negative voltage detection network are connected to the input of the summing amplifier, and the two detection voltages are added and amplified to obtain the drain valley voltage detection value; this scheme detects the DC and AC components of the drain separately, optimizes the AC negative voltage detection circuit, and improves the detection accuracy and efficiency of the power amplifier drain voltage; the circuit is simple and convenient to implement, with a small size, and can be arranged near the drain of the power tube; the circuit is simple, compact, and easy to implement, and can accurately measure the valley voltage of the power tube drain, so as to know whether the dynamic range of the power tube is fully used, and provide a basis for automatic adjustment of the power supply voltage.

[0060] The above are only some embodiments of the present invention. For those skilled in the art, several modifications and improvements can be made without departing from the creative concept of the present invention, which all belong to the protection scope of the present invention.

Claims

1. A shortwave power amplifier drain valley voltage detection circuit, characterized in that: It includes a drain input port, a DC detection network, an AC negative voltage detection network, an adding amplifier and a detection output port; the drain input port is respectively connected to the input ends of the DC detection network and the AC negative voltage detection network; the output end of the DC detection network and the output end of the AC negative voltage detection network are connected to an input end of the adding amplifier; the output end of the adding amplifier is connected to the detection output port; The AC negative voltage detection network includes a DC blocking capacitor C1, a resistor R3, a resistor R4, a detector diode D1, a capacitor C5 and a capacitor C6; the drain input port is connected to one end of the DC blocking capacitor C1, and the other end of the DC blocking capacitor C1 is connected to one end of the resistor R3; the resistor R3 and the resistor R4 are connected in series and then grounded; the terminal where the resistor R3 and the resistor R4 are connected to each other is connected to the negative electrode of the detector diode D1; the resistor R3 is connected in parallel to the capacitor C5, and the resistor R4 is connected in parallel to the capacitor C6; The drain input port is arranged on the printed circuit board near the root of the drain of the power amplifier and is electrically connected to the drain of the power amplifier.

2. The shortwave power amplifier drain valley voltage detection circuit as claimed in claim 1, characterized in that: The DC detection network includes two voltage-dividing resistors R1 and R2 connected in series, one end of the resistor R1 is connected to the drain input port, one end of the resistor R2 is grounded, and the terminals connecting the resistors R1 and R2 form the output end of the DC detection network.

3. The shortwave power amplifier drain valley voltage detection circuit as claimed in claim 2, characterized in that: The DC detection network also includes an operational amplifier N1; the terminals connecting the resistor R1 and the resistor R2 are connected to the positive input terminal of the operational amplifier N1; the negative input terminal of the operational amplifier N1 is connected to the output terminal of the operational amplifier N1 to form a follower; the output terminal of the operational amplifier N1 forms the output terminal of the DC detection network.

4. The short-wave power amplifier drain valley voltage detection circuit as claimed in claim 1, characterized in that: The AC negative voltage detection network also includes a capacitor C2 and a resistor R5. The positive electrode of the detection diode D1 is connected to the capacitor C2 and the resistor R5 respectively. The capacitor C2 and the resistor R5 are connected to the ground in parallel. The positive electrode of the detection diode D1 forms the output end of the AC negative voltage detection network.

5. The short-wave power amplifier drain valley voltage detection circuit as claimed in claim 4, characterized in that: The AC negative voltage detection network also includes an operational amplifier N2; the anode of the detection diode D1 is connected to the positive input terminal of the operational amplifier N2; the negative input terminal of the operational amplifier N2 is connected to its output terminal to form a follower; the output terminal of the operational amplifier N2 forms the output terminal of the AC negative voltage detection network.

6. The short-wave power amplifier drain valley voltage detection circuit as claimed in claim 1, characterized in that: The AC negative voltage detection network also includes a capacitor C2. The positive electrode of the detection diode D1 is connected to one end of the capacitor C2, and the connection end forms the output end of the AC negative voltage detection network. The other end of the capacitor C2 is connected to the output end of the DC detection network.

7. The short-wave power amplifier drain valley voltage detection circuit according to any one of claims 1 to 6, characterized in that: The adding amplifier has two input terminals and one output terminal, and includes an operational amplifier N3, a resistor R6 and a resistor R7; the two input terminals of the adding amplifier are respectively connected to the positive input terminal of the operational amplifier N3 through the resistor R6 and the resistor R7; the negative input terminal of the operational amplifier N3 is grounded through a resistor R8, and is connected to its output terminal through a resistor R9; the output terminal of the operational amplifier N3 forms the detection output terminal of the detection circuit and is connected to the detection output port.

8. A method for regulating the drain DC supply voltage of a short-wave power amplifier, which is used to address the problem of reduced efficiency of the power amplifier caused by load mismatch, and is characterized by: A detection circuit as claimed in claim 1 is provided to detect the drain valley voltage of the power amplifier and adjust the drain DC supply voltage of the power amplifier accordingly according to the drain valley voltage.

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