Analog automatic level control circuit with high power stability

Abstract

The application provides an analog automatic level control circuit with high power stability, comprising a main link, a feedback loop with a constant temperature island, a constant temperature circuit and a high-stability DAC reference circuit; the main link comprises a voltage-controlled attenuator 1, a voltage-controlled attenuator 2, an amplifier and a coupler connected in sequence; the feedback loop with the constant temperature island comprises a detection circuit and an RC comparison and integration loop; one output of the coupler is connected to the input of the detection circuit; the output of the detection circuit is connected to the input of the RC comparison and integration loop; the output of the RC comparison and integration loop is connected to the voltage-controlled attenuator 1 and the voltage-controlled attenuator 2; the constant temperature circuit is arranged at the feedback loop and is used for obtaining the ambient temperature of the feedback loop and generating heat to adjust the ambient temperature according to the ambient temperature; and the high-stability DAC reference circuit is connected to the RC comparison and integration loop and is used for providing the reference voltage to the RC comparison and integration loop. The application solves the problem that the output power of the ALC circuit fluctuates greatly with high and low temperatures through simple hardware circuit design.

Description

Technical Field

[0001] This application relates to the field of radio frequency and microwave technology, and in particular to an analog automatic level control circuit with high power stability. Background Technology

[0002] Automatic Level Control (ALC) circuits are power control circuits that enable adjustable system output power. Within a certain range, ALC circuits can maintain a constant output power even when input power changes or system components age. They are widely used in radar, communications, and other fields, playing a crucial role, especially in instrumentation. For example, in analog signal sources, they are the core circuit determining the output power specifications. Currently, most ALC circuits suffer from low output power stability, particularly poor temperature stability under varying high and low temperature environments. Summary of the Invention

[0003] To address the shortcomings of the prior art, this application provides a high-power-stability analog automatic level control circuit that solves the problem of large fluctuations in ALC circuit output power under high and low temperature conditions through simple hardware circuit design.

[0004] To achieve the above objectives, the present invention employs the following techniques:

[0005] A high-power-stability analog automatic level control circuit includes a main link, a feedback loop with a temperature-controlled island, a temperature-controlled circuit, and a high-stability DAC reference circuit.

[0006] The main link includes a voltage-controlled attenuator 1, a voltage-controlled attenuator 2, an amplifier, and a coupler connected in sequence. The voltage-controlled attenuator 1 is used to attenuate the power of the input signal, the voltage-controlled attenuator 2 is used to adjust the amplitude of the attenuated signal, the amplifier is used to amplify the amplitude-adjusted signal, and the coupler is used to split the amplified signal into two outputs. One output of the coupler is the output signal, and the other output is the feedback signal.

[0007] The feedback loop with a constant temperature island includes a detector circuit, an RC comparison and integration loop, and a coupler. The input of the detector circuit is connected to the other output of the coupler, and the output of the detector circuit is connected to the input of the RC comparison and integration loop. The detector circuit is used to convert the feedback signal into a detector voltage signal and provide it to the RC comparison and integration loop. The output of the RC comparison and integration loop is connected to voltage-controlled attenuators 1 and 2. The RC comparison and integration loop is used to compare and integrate the detector voltage signal with a reference voltage and output a control voltage signal to voltage-controlled attenuators 1 and 2 to control the attenuation of voltage-controlled attenuators 1 and 2.

[0008] Furthermore, the RC comparator-integrator loop includes resistors R1, R2, and R3, capacitors C1, C2, C3, and C4, and operational amplifier OP1. The inverting input of operational amplifier OP1 is connected to one end of capacitor C1 and the output of the detector circuit through resistor R1, and the other end of capacitor C1 is grounded. The non-inverting input of operational amplifier OP1 is connected to one end of capacitor C2 and the reference voltage output of the high-stability DAC reference circuit through resistor R2, and the other end of capacitor C2 is grounded. Capacitor C4 is connected in parallel between the inverting input and output of operational amplifier OP1. One end of resistor R3 is connected to the output of operational amplifier OP1, and the other end serves as the control voltage signal output of the RC comparator-integrator loop, and is connected to ground through capacitor C3.

[0009] A constant temperature circuit is located at the feedback loop to acquire the ambient temperature of the feedback loop and adjust the ambient temperature by generating heat accordingly. Further, the constant temperature circuit includes a temperature sensing element, a constant temperature chip, and a heating element connected in sequence. The temperature sensing element collects the ambient temperature and converts it into a temperature voltage signal, which is then provided to the constant temperature chip. The constant temperature chip outputs a heating control voltage to the heating element based on the temperature voltage signal, causing the heating element to generate heat and adjust the ambient temperature. In practice, the feedback loop and the temperature sensing element are located at the center of a circuit board, while the heating element is located on the bottom surface of the circuit board, forming a small island.

[0010] The high-stability DAC reference circuit is connected to the RC comparison and integration loop and is used to provide the reference voltage to the RC comparison and integration loop. Further, the high-stability DAC reference circuit includes a DAC circuit connected to the RC comparison and integration loop, an FPGA connected to the DAC circuit, and a bandgap reference source. The bandgap reference source is used to provide a voltage signal to the DAC circuit as a reference, and the FPGA is used to generate a digital signal to control the DAC circuit to output a reference voltage to the RC comparison and integration loop based on the voltage signal provided by the bandgap reference source.

[0011] The beneficial effects of this invention are as follows:

[0012] 1. By placing both the detector circuit and the RC comparison and integration loop on a temperature-controlled island, the output signal power can be stably detected by the detector circuit without being affected by changes in ambient temperature. At the same time, a bandgap reference source is used for the reference voltage to further ensure the stability of the control voltage. This solves the problem of large fluctuations in the output power of the ALC circuit under high and low temperature conditions, and the temperature stability can reach ±0.005dB / ℃.

[0013] 2. An RC comparison and integration loop is used as the feedback loop, a large capacitor is used as the integrating element, and an RC filter circuit is added at both the input and output terminals. Compared with the existing first-order or second-order comparison loops, the significant advantage of this circuit is its stability, which greatly reduces loop noise and makes the output power very stable. Especially when there are large temperature fluctuations, it can slow down the change of the detector voltage at the input terminal and reduce the impact of temperature fluctuations on the output power.

[0014] 3. It adopts a constant temperature chip + heating element as the main means of temperature control. Compared with other traditional constant temperature circuits, it has high temperature control accuracy and temperature stability can reach ±0.01℃. Moreover, it is a pure analog circuit and does not require digital control. Attached Figure Description

[0015] Figure 1 This is a block diagram of the analog automatic level control circuit structure according to an embodiment of this application.

[0016] Figure 2 This is a block diagram of the constant temperature circuit structure according to an embodiment of this application.

[0017] Figure 3 This is a circuit block diagram of the RC comparison integrator loop according to an embodiment of this application.

[0018] Figure 4 This is a side view of the spatial location of the constant temperature island according to an embodiment of this application.

[0019] Figure 5 This is a top view of the spatial location of the constant temperature island in an embodiment of this application. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the implementation methods of the present invention will be described in detail below with reference to the accompanying drawings. However, the embodiments described in this invention are only some embodiments of the present invention, and not all embodiments.

[0021] This application provides an analog automatic level control circuit with high power stability, such as... Figures 1-2 As shown, it includes the main link, a feedback loop with a temperature-controlled island, a temperature-controlled circuit, and a high-stability DAC reference circuit.

[0022] The main link consists of a voltage-controlled attenuator 1, a voltage-controlled attenuator 2, an amplifier, and a coupler connected in sequence. The input signal is first transmitted to the voltage-controlled attenuator 1, which attenuates the power of the input signal. The attenuated signal then enters the voltage-controlled attenuator 2, which adjusts the amplitude of the attenuated signal. The amplifier amplifies the amplitude-adjusted signal, and the amplified signal is transmitted to the coupler. The coupler splits the amplified signal into two outputs: one output signal and the other output signal, which serves as a feedback signal provided to the feedback loop with a temperature-controlled island.

[0023] The feedback loop with a constant temperature island includes a detector circuit, an RC comparison and integration loop, and a coupler. The input of the detector circuit is connected to the other output of the coupler, and the output of the detector circuit is connected to the input of the RC comparison and integration loop. The detector circuit is used to convert the feedback signal into a detector voltage signal VDET, which is provided to the RC comparison and integration loop. The output of the RC comparison and integration loop is connected to voltage-controlled attenuators 1 and 2. The RC comparison and integration loop is used to compare and integrate the detector voltage signal VDET with a reference voltage and output a control voltage signal Vctrl to voltage-controlled attenuators 1 and 2 to control the attenuation of voltage-controlled attenuators 1 and 2.

[0024] Preferred, such as Figure 3 As shown, the RC comparator-integrator loop includes resistors R1, R2, and R3, capacitors C1, C2, C3, and C4, and operational amplifier OP1. The inverting input of operational amplifier OP1 is connected to one end of capacitor C1 and the output of the detector circuit through resistor R1, and the other end of capacitor C1 is grounded. The non-inverting input of operational amplifier OP1 is connected to one end of capacitor C2 and the reference voltage output of the high-stability DAC reference circuit through resistor R2, and the other end of capacitor C2 is grounded. Capacitor C4 is connected in parallel between the inverting input and output of operational amplifier OP1. One end of resistor R3 is connected to the output of operational amplifier OP1, and the other end serves as the control voltage signal output of the RC comparator-integrator loop, and is connected to ground through capacitor C3.

[0025] The detected voltage passes through filter capacitor C1 and then resistor R1, before entering the inverting input of operational amplifier OP1. The reference voltage passes through filter capacitor C2 and then resistor R2, before entering the non-inverting input of operational amplifier OP2. The voltages at the inverting and non-inverting inputs are compared, then pass through integrating capacitor C4 to operational amplifier OP2, and finally pass through resistor R3 and capacitor C3 for further filtering to obtain the control voltage signal. A large uF capacitor is used for the integrating capacitor. Compared to existing first- or second-order comparator loops, this circuit's significant advantage is stability. First- or second-order comparator loops are prone to circuit oscillation, easily leading to power overshoot when there is external interference or temperature changes. The circuit in this example reduces noise through RC filtering at the input and output ends, and achieves a very small loop bandwidth through integration with a large capacitor, resulting in a very stable output control voltage and thus very stable power. Especially under conditions of large temperature fluctuations, it can slow down the change in the detected voltage at the input end, reducing the impact of temperature fluctuations on the output power.

[0026] A constant temperature circuit is located at the feedback loop to acquire the ambient temperature of the feedback loop and adjust the ambient temperature by generating heat accordingly. Optionally, the constant temperature circuit includes a temperature sensing element, a constant temperature chip, and a heating element connected in sequence. The temperature sensing element collects the ambient temperature and converts it into a temperature voltage signal, which is then provided to the constant temperature chip. The constant temperature chip outputs a heating control voltage Vh to the heating element based on the temperature voltage signal, causing the heating element to generate heat and adjust the ambient temperature. Optionally, the temperature sensing element is a thermistor, and the heating element is a heating resistor. The constant temperature chip is an ADN8830. In implementation, such as... Figure 4 and Figure 5 As shown, the feedback loop and thermistor are located at the center of the circuit board surface, and the heating resistor is located on the bottom surface of the circuit board. This part of the circuit board is a small island, which forms a constant temperature island space under the action of the constant temperature circuit. Compared with existing constant temperature circuits, such as transistor-controlled power tube heating circuits, this circuit has extremely high temperature control accuracy and is simple to control. The constant temperature circuit can keep the temperature of the feedback loop with the constant temperature island in a constant temperature state when the ambient temperature changes from -40 to 70℃, and the temperature stability can reach ±0.01℃.

[0027] A high-stability DAC reference circuit is connected to an RC comparator-integrator loop to provide the aforementioned reference voltage to the RC comparator-integrator loop. Optionally, the high-stability DAC reference circuit includes a DAC circuit connected to the RC comparator-integrator loop, an FPGA connected to the DAC circuit, and a bandgap reference source. The bandgap reference source provides a highly stable 5V voltage signal to the DAC circuit as a reference. The FPGA generates digital signals to control the DAC circuit to output a reference voltage to the RC comparator-integrator loop based on the voltage signal provided by the bandgap reference source. This reference voltage has a unique correspondence with the output power. The DAC circuit can use the DAC chip LTC1668, and the bandgap reference source can use REF70. Since the DAC reference is a bandgap reference source, the maximum voltage drift is 2ppm / ℃, so the reference voltage generated by the DAC circuit is very stable and hardly changes with temperature.

[0028] This embodiment provides a high-power-stability analog automatic level control circuit. It employs a configuration where both the detector circuit and the RC comparison-integration loop are placed on a temperature-controlled island, ensuring that the output signal power can be stably detected by the detector circuit, unaffected by ambient temperature changes. The RC comparison-integration loop serves as the feedback loop, using a large capacitor as the integrator, and RC filter circuits are added simultaneously at the input and output terminals, significantly reducing loop noise and resulting in highly stable output power. Furthermore, a bandgap reference voltage is used to further ensure the stability of the control voltage, solving the problem of large power fluctuations in ALC circuits under high and low temperatures. Compared to other traditional temperature-controlled circuits, it offers high temperature control accuracy, achieving a temperature stability of ±0.01℃. It is a purely analog circuit, requiring no digital control.

[0029] The above description is only a preferred embodiment of this application and is not intended to limit this application. Obviously, those skilled in the art can make various modifications and variations to this application without departing from the spirit and scope of this application.

Claims

1. A high-power-stability analog automatic level control circuit, characterized in that, This includes the main link, a feedback loop with a temperature-controlled island, a temperature-controlled circuit, and a high-stability DAC reference circuit; The main link includes a first voltage-controlled attenuator, a second voltage-controlled attenuator, an amplifier, and a coupler connected in sequence. One output of the coupler is the output signal, and the other output is the feedback signal. The feedback loop with a constant temperature island includes a detector circuit and an RC comparison and integration loop. The input of the detector circuit is connected to the other output of the coupler, and the output of the detector circuit is connected to the input of the RC comparison and integration loop. The detector circuit is used to convert the feedback signal into a detector voltage signal and provide it to the RC comparison and integration loop. The output of the RC comparison and integration loop is connected to the first voltage-controlled attenuator and the second voltage-controlled attenuator. The RC comparison and integration loop is used to compare and integrate the detector voltage signal with a reference voltage and output a control voltage signal to the first voltage-controlled attenuator and the second voltage-controlled attenuator to control the attenuation of the first voltage-controlled attenuator and the second voltage-controlled attenuator. A constant temperature circuit is located at the feedback loop to acquire the ambient temperature of the feedback loop and adjust the ambient temperature by heating accordingly. The constant temperature circuit includes a temperature sensing element, a constant temperature chip, and a heating element connected in sequence. The temperature sensing element collects the ambient temperature and converts it into a temperature voltage signal, which is provided to the constant temperature chip. The constant temperature chip outputs a heating control voltage to the heating element based on the temperature voltage signal, so that the heating element heats up to adjust the ambient temperature. The feedback loop and the temperature sensing element are located at the center of the surface of a circuit board, and the feedback loop is spaced apart on both sides of the temperature sensing element. The heating element is located on the bottom surface of the circuit board and includes two spaced parts. The feedback loop and the temperature sensing element are positioned at the intervals between the two parts of the heating element, and the top view projection of each part of the heating element covers at least a portion of the feedback loop and the temperature sensing element. The high-stability DAC reference circuit is connected to the RC comparator-integrator loop and is used to provide the reference voltage to the RC comparator-integrator loop. The high-stability DAC reference circuit includes a DAC circuit connected to an RC comparison and integration loop, an FPGA connected to the DAC circuit, and a bandgap reference source. The bandgap reference source provides a voltage signal to the DAC circuit as a reference, and the FPGA generates a digital signal to control the DAC circuit to output a reference voltage to the RC comparison and integration loop based on the voltage signal provided by the bandgap reference source.

2. The high power stability analog automatic level control circuit according to claim 1, characterized in that, The temperature sensing element is a thermistor, and the heating element is a heating resistor.

3. The high power stability analog automatic level control circuit according to claim 1, characterized in that, The temperature control chip used is ADN8830.

4. The high power stability analog automatic level control circuit according to claim 1, characterized in that, The RC comparator-integrator loop includes resistors R1, R2, and R3, capacitors C1, C2, C3, and C4, and operational amplifier OP1. The inverting input of operational amplifier OP1 is connected to one end of capacitor C1 and the output of the detector circuit through resistor R1, while the other end of capacitor C1 is grounded. The non-inverting input of operational amplifier OP1 is connected to one end of capacitor C2 and the reference voltage output of the high-stability DAC reference circuit through resistor R2, while the other end of capacitor C2 is grounded. Capacitor C4 is connected in parallel between the inverting input and output of operational amplifier OP1. One end of resistor R3 is connected to the output of operational amplifier OP1, and the other end serves as the control voltage signal output of the RC comparator-integrator loop, and is connected to ground through capacitor C3.

5. The high power stability analog automatic level control circuit according to claim 1, characterized in that, The DAC circuit uses the LTC1668 DAC chip.

6. The high power stability analog automatic level control circuit according to claim 1, characterized in that, The bandgap reference source used is REF70.

7. The high power stability analog automatic level control circuit according to claim 1, characterized in that, The first voltage-controlled attenuator is used to attenuate the power of the input signal, the second voltage-controlled attenuator is used to adjust the amplitude of the attenuated signal, the amplifier is used to amplify the amplitude-adjusted signal, and the coupler is used to split the amplified signal into two output paths.

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