ALC power closed-loop control circuit capable of preventing power overshoot

Abstract

The utility model provides an ALC power closed-loop control circuit capable of preventing power overshoot. The ALC power closed-loop control circuit comprises a radio frequency channel and a closed-loop control circuit, wherein the radio frequency channel is provided with a radio frequency input end and a radio frequency output end; the circuit also comprises a preset gain voltage, a diode D8 and an operational amplifier U2B. The output end of the operational amplifier U2A is connected with the cathode of a diode D8, the anode of the diode D8 is connected with the preset gain voltage and then connected with the in-phase end of an operational amplifier U2B connected according to a follower, and the output end of the operational amplifier U2B is connected with a radio frequency channel. According to the utility model, the preset gain voltage and the follower are added on the original ALC circuit, so that the gain variation range of the power amplifier is relatively small when a relatively large signal is initially input, the generated power overshoot is relatively small, and even the power overshoot is not generated.

Description

Technical Field

[0001] The utility model relates to the field of radio frequency circuits, in particular to an ALC power closed-loop control circuit for preventing power overshoot in a radio frequency circuit adopting analog power closed-loop control. Background Technique

[0002] The current radio frequency ALC (Automatic Level Control) power closed-loop control circuit generally adopts analog power closed-loop control, which has the advantages of simple application, easy control and strong adaptability.

[0003] Currently, common analog power closed-loop control circuits, such as Figure 1 shown, couple the power detection voltage feedback signal at the radio frequency output end by using a directional coupler. It has a very big defect, that is, it will generate power overshoot. As Figure 1 shown, in the initial state of the circuit, the power detection voltage coupled by the directional coupler is 0V. Since the operational amplifier U2 is in a differential open-loop amplification state, then U2 will output an extreme voltage, that is, the supply voltage of the operational amplifier, 12VDC. Then, the analog voltage-controlled attenuator in the radio frequency channel is in the minimum attenuation state, that is, the maximum positive bias. At this time, on the radio frequency channel, when a relatively large excitation signal comes from RFin, after passing through the analog voltage-controlled attenuator D5 and the analog voltage-controlled attenuator D6 and entering the radio frequency power amplifier A1 for amplification, it will output a maximum power, that is, overshoot is generated.

[0004] Especially in the high-excitation state, a very high power overshoot will be generated. Due to the limitation of its circuit, this overshoot is inevitable, which will cause a power impact on the subsequent devices and reduce the reliability of the overall circuit. Content of the Utility Model

[0005] The purpose of the utility model is to provide a MOS tube voltage switch protection circuit to ensure that when there is an input at a low voltage, the high voltage can always be in the output state; when the low voltage is turned off, the high voltage can be in the off state, so as to avoid the product being burned by overcurrent of the high voltage due to a large current during application.

[0006] The technical solution adopted by the present utility model to achieve its technical purpose is as follows: An ALC power closed-loop control circuit for preventing power overshoot, which includes a radio frequency channel with a radio frequency input end and a radio frequency output end, and a closed-loop control circuit; the closed-loop control circuit includes a power detection voltage led out from the radio frequency output end, an operational amplifier U2A, a resistor R3, a resistor R4, and a capacitor C9; the operational amplifier U2A, the resistor R3, the resistor R4, and the capacitor C9 are connected to form a differential amplification circuit, and the power detection voltage and a power reference voltage are respectively connected to the inverting end and the non-inverting end of the operational amplifier U2A through the resistor R4 and the resistor R3; it further includes a preset gain voltage, a diode D8, and an operational amplifier U2B; the output end of the operational amplifier U2A is connected to the cathode of the diode D8, and the anode of the diode D8 is connected to the non-inverting end of the operational amplifier U2B connected in a follower manner after being connected to the preset gain voltage, and the output end of the operational amplifier U2B is connected to the radio frequency channel.

[0007] Further, in the above-mentioned ALC power closed-loop control circuit for preventing power overshoot: it further includes a current-limiting resistor R5 and a current-limiting resistor R6; the current-limiting resistor R5 is connected in series between the preset gain voltage and the anode of the diode D8, and the current-limiting resistor R6 is connected in series between the anode of the diode and the non-inverting end of the operational amplifier U2B.

[0008] Further, in the above-mentioned ALC power closed-loop control circuit for preventing power overshoot: the power detection voltage is to extract a small part of the radio frequency power signal by using a directional coupler U1 at the radio frequency output end of the radio frequency channel for power detection.

[0009] Further, in the above-mentioned ALC power closed-loop control circuit for preventing power overshoot: it further includes a detection diode D7, which rectifies the signal extracted by the directional coupler U1 into a DC signal.

[0010] Further, in the above-mentioned ALC power closed-loop control circuit for preventing power overshoot: it further includes a choke coil L6, and the choke coil L6 is arranged between the output end of 2U2B and the radio frequency channel.

[0011] Further, in the above-mentioned ALC power closed-loop control circuit for preventing power overshoot: at least a first analog voltage-controlled attenuator, a second analog voltage-controlled attenuator, and a radio frequency power amplifier are sequentially arranged on the radio frequency channel; the first analog voltage-controlled attenuator and the second analog voltage-controlled attenuator are arranged on both sides of the choke coil L6.

[0012] Further, in the above-mentioned ALC power closed-loop control circuit for preventing power overshoot: the first analog voltage-controlled attenuator is a dual-tube common-cathode PIN diode D5, and the second analog voltage-controlled attenuator is a dual-tube common-cathode PIN diode D6;

[0013] The cathode of the dual - cathode common PIN diode D5 is connected to the RF input terminal, one anode is connected to one anode of the dual - cathode common PIN diode D6, and the other anodes of the dual - cathode common PIN diode D5 and the dual - cathode common PIN diode D6 are grounded through the filter capacitors C6 and C7 respectively; the cathode of the dual - cathode common PIN diode D6 is connected to the RF power amplifier A1.

[0014] Further, in the above - mentioned ALC power closed - loop control circuit for preventing power overshoot: there are also included a bias resistor R1 and a bias resistor R2. The bias resistor R1 is grounded between the dual - cathode common PIN diode D5 and the RF input terminal on the RF channel, and the bias resistor R2 is grounded between the dual - cathode common PIN diode D6 and the RF power amplifier A1 on the RF channel.

[0015] In the present utility model, on the basis of the original ALC circuit, a preset gain voltage and a follower are added, which ensures that when a relatively large signal is input at the beginning, the change range of the power amplifier gain is small, and thus the power overshoot generated is small, or even no power overshoot may occur.

[0016] The present utility model will be further described below in conjunction with the drawings and specific embodiments. Description of the Drawings

[0017] Fig. Figure 1 is the schematic diagram of the ALC circuit in the prior art;

[0018] Fig. Figure 2 is the schematic diagram of the ALC power closed - loop control circuit for preventing power overshoot in Embodiment 1 of the present utility model. Specific Embodiments

[0019] This embodiment is an ALC power closed - loop control circuit for preventing power overshoot. On the basis of the original ALC circuit (automatic power level control), an initial ATT control voltage is added, which ensures that when a relatively large signal is input at the beginning, the change range of the power amplifier gain is small, and thus the power overshoot generated is small, or even no power overshoot may occur.

[0020] As Figure 2 shown, the ALC power closed - loop control circuit for preventing power overshoot in this embodiment includes an RF channel with an RF input terminal and an RF output terminal and a closed - loop control circuit; the closed - loop control circuit includes a power detection voltage led out from the RF output terminal, an operational amplifier U2A, a resistor R3, a resistor R4, and a capacitor C9; the operational amplifier U2A, the resistor R3, the resistor R4, and the capacitor C9 are connected to form a differential amplifier circuit. The capacitor C9 is the integration capacitor of the operational amplifier, and its function is to filter and buffer the forward bias voltage on the analog ATT (D5, D6), ensuring that no self - excitation oscillation occurs during the adaptive adjustment process of the closed - loop voltage.

[0021] The power detection voltage and a power reference voltage are respectively connected to the inverting terminal and the non-inverting terminal of operational amplifier U2A through resistor R4 and resistor R3; it further includes a preset gain voltage, diode D8, and operational amplifier U2B; the output terminal of operational amplifier U2A is connected to the cathode of diode D8, and the anode of diode D8 is connected to the non-inverting terminal of operational amplifier U2B connected in a follower configuration after being connected to the preset gain voltage, and the output terminal of operational amplifier U2B is connected to the RF channel. It also includes current-limiting resistor R5 and current-limiting resistor R6; current-limiting resistor R5 is connected in series between the preset gain voltage and the anode of diode D8, and current-limiting resistor R6 is connected in series between the anode of the diode and the non-inverting terminal of operational amplifier U2B. Here, operational amplifier U2A, together with capacitor C9, resistor R3, and resistor R4, forms a differential amplifier circuit, which performs open-loop amplification on the voltage difference between its positive terminal (non-inverting terminal) and negative terminal (inverting terminal). Operational amplifier U2B functions as an emitter follower.

[0022] In the ALC power closed-loop control circuit for preventing power overshoot in this embodiment: the power detection voltage extracts a small part of the RF power signal at the RF output terminal RFout of the RF channel using directional coupler U1 for power detection. Here, directional coupler U1 can extract a small part of the RF power signal for power detection. It also includes detection diode D7, which rectifies the signal extracted by directional coupler U1 into a DC signal. Detection diode D7 can convert the RF signal into a DC signal, and the larger the input power, the larger the output level. In the feedback loop (detection loop), capacitor C8 is a filter / storage capacitor, and it forms a standard diode detection circuit with detection diode D7. It also includes choke coil L6, which is arranged between the output terminal of 2U2B and the RF channel. The function of choke coil L6 is to provide a DC bias for the first analog voltage-controlled attenuator and the second analog voltage-controlled attenuator, and at the same time block the RF signal from entering the operational amplifier.

[0023] In the embodiment, at least a first analog voltage-controlled attenuator, a second analog voltage-controlled attenuator, and an RF power amplifier are sequentially arranged on the RF channel; the first analog voltage-controlled attenuator and the second analog voltage-controlled attenuator are arranged on both sides of choke coil L6. The first analog voltage-controlled attenuator is dual-tube common-cathode PIN diode D5, and the second analog voltage-controlled attenuator is dual-tube common-cathode PIN diode D6.

[0024] The cathode of the dual - cathode PIN diode D5 is connected to the RF input terminal RFin. One anode of D5 is connected to one anode of the dual - cathode PIN diode D6. The other anodes of the dual - cathode PIN diode D5 and the dual - cathode PIN diode D6 are grounded through the filter capacitors C6 and C7 respectively. The cathode of the dual - cathode PIN diode D6 is connected to the RF power amplifier A1. In this embodiment, the amplifier A1 is for illustrative purposes here. It can be single - stage or multi - stage. Here, the series equivalent resistance of the dual - cathode PIN diode D5 and the dual - cathode PIN diode D6 decreases as the forward - bias current increases. Thus, the attenuation of the RF signal is controlled by controlling their forward - bias current. The filter capacitors C6 and C7 filter out the RF reflection signals generated on the PIN diodes. Their values are based on the frequency of the RF signal, and their function is to allow the RF signal (alternating current) to pass through.

[0025] In this embodiment, it also includes a bias resistor R1 and a bias resistor R2. The bias resistor R1 is grounded between the dual - cathode PIN diode D5 and the RF input terminal (RFin) on the RF channel. The bias resistor R2 is grounded between the dual - cathode PIN diode D6 and the RF power amplifier A1 on the RF channel. The bias resistors R1 and R2 are the bias resistors for the analog ATT. Their function is to form a bias loop with the bias voltage on the analog ATT (D5, D6) to determine the operating state of the analog ATT.

[0026] The working process of this embodiment:

[0027] 1. When the circuit is in the initial state, there is no signal input at the RF input terminal RFin at this time, that is, the output of the "power detection voltage" is 0V. Then, the difference between the positive and negative input terminals of the input operational amplifier U2A is the largest, which is the power reference voltage. Since it is in an open - loop amplification state, the output voltage of the output terminal of the operational amplifier U2A is the largest, that is, the supply voltage of the operational amplifier, 12VDC. At the same time, the output terminal of the operational amplifier U2A is connected to another "gain preset voltage" through a switching diode D8. When the output voltage of the operational amplifier U2A is smaller than the gain preset voltage, the diode D8 is in the off state. At this time, only the gain preset voltage takes effect. Therefore, at this time, the gain of the RF channel is in the preset state, not maximized.

[0028] 2. When the RF excitation comes, since the gain of the RF channel is in the preset state and the analog ATT has a certain attenuation, the excitation entering the amplifier is relatively small. Therefore, the power overshoot generated is relatively small or even non - existent.

[0029] When the RF signal is amplified by the amplifier, the generated high-power RF signal is detected after being taken out by the directional coupler. The detected voltage is sent to the inverting terminal of the operational amplifier U2A. At this time, the voltage at the inverting terminal of the operational amplifier starts to increase from 0. Then its output control voltage will become smaller. As the power increases, the detected voltage also increases. Then the voltage entering the inverting terminal of the operational amplifier U2A is also larger, and the output voltage of the operational amplifier is smaller. When the power increases to a certain value and the output voltage of the operational amplifier U2A is less than "preset gain voltage - 0.5V", the diode D8 starts to conduct. At this time, the DC bias voltage entering the analog ATT (D5, D6) is clamped to the output voltage of U2A. At this time, the power control of the amplifier enters the closed-loop operation and the power stabilizes.

Claims

1. An ALC power closed-loop control circuit for preventing power overshoot, comprising a radio frequency channel having a radio frequency input terminal and a radio frequency output terminal and a closed-loop control circuit; the closed-loop control circuit comprises a power detection voltage derived from the radio frequency output terminal and an operational amplifier U2A, a resistor R3, a resistor R4, and a capacitor C9; the operational amplifier U2A, the resistor R3, the resistor R4, and the capacitor C9 are connected to form a differential amplifier circuit, and the power detection voltage and a power reference voltage are respectively connected to the out-of-phase terminal and the in-phase terminal of the operational amplifier U2A through the resistor R4 and the resistor R3; it is characterized in that: It also includes a preset gain voltage, a diode D8 and an operational amplifier U2B; the output terminal of the operational amplifier U2A is connected to the cathode of the diode D8, the anode of the diode D8 is connected to the preset gain voltage and then connected to the in-phase terminal of the operational amplifier U2B connected as a follower, and the output terminal of the operational amplifier U2B is connected to the RF channel.

2. The ALC power closed-loop control circuit for preventing power overshoot according to claim 1, characterized in that: It also includes a current limiting resistor R5 and a current limiting resistor R6; the current limiting resistor R5 is connected in series between the preset gain voltage and the anode of the diode D8, and the current limiting resistor R6 is connected in series between the anode of the diode and the in-phase terminal of the operational amplifier U2B.

3. The ALC power closed-loop control circuit for preventing power overshoot according to claim 1, characterized in that: The power detection voltage is obtained by extracting a small part of the RF power signal at the RF output end of the RF channel using a directional coupler U1 for power detection.

4. The ALC power closed-loop control circuit for preventing power overshoot according to claim 3, characterized in that: A detection diode D7 is also included to rectify the signal extracted by the directional coupler U1 into a DC signal.

5. The ALC power closed-loop control circuit for preventing power overshoot according to any one of claims 1 to 4, characterized in that: It also includes a choke coil L6, which is arranged between the output end of 2U2B and the radio frequency channel.

6. The ALC power closed-loop control circuit for preventing power overshoot according to claim 5, characterized in that: The RF channel is at least sequentially provided with a first analog voltage-controlled attenuator, a second analog voltage-controlled attenuator and a RF power amplifier; the first analog voltage-controlled attenuator and the second analog voltage-controlled attenuator are arranged on both sides of the choke coil L6.

7. The ALC power closed-loop control circuit for preventing power overshoot according to claim 6, characterized in that: The first analog voltage-controlled attenuator is a double-tube common-cathode PIN diode D5, and the second analog voltage-controlled attenuator is a double-tube common-cathode PIN diode D6; The cathode of the dual-tube common-cathode PIN diode D5 is connected to the RF input end, and one anode is connected to an anode of the dual-tube common-cathode PIN diode D6. The other anodes of the dual-tube common-cathode PIN diode D5 and the dual-tube common-cathode PIN diode D6 are grounded through filter capacitors C6 and C7 respectively; the cathode of the dual-tube common-cathode PIN diode D6 is connected to the RF power amplifier A1.

8. The ALC power closed-loop control circuit for preventing power overshoot according to claim 7, characterized in that: It also includes a bias resistor R1 and a bias resistor R2. The bias resistor R1 is on the RF channel and grounded between the double-tube common-cathode PIN diode D5 and the RF input terminal. The bias resistor R2 is on the RF channel and grounded between the double-tube common-cathode PIN diode D6 and the RF power amplifier A1.

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