Analog automatic level control circuit with high power stability

Abstract

The invention provides an analog automatic level control circuit with high power stability. The analog automatic level control circuit comprises 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 which are connected in sequence; the feedback loop with the constant-temperature island comprises a detection circuit and an RC comparison integral loop, the input of the detection circuit is connected with the other path of output of the coupler, the output of the detection circuit is connected with the input of the RC comparison integral loop, and the output of the RC comparison integral loop is connected with 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 acquiring the environment temperature of the feedback loop and heating according to the environment temperature so as to adjust the environment temperature; and the high-stability DAC reference circuit is connected with the RC comparison integral loop and is used for providing the reference voltage for the RC comparison integral loop. Through simple hardware circuit design, the problem that the output power of the ALC circuit fluctuates greatly along with high and low temperature conditions is solved.

Description

Technical Field

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

[0002] The automatic level control (ALC) circuit is a power control circuit that can realize the adjustable output power of the system. Within a certain range, when the input power changes or the system components age, the ALC circuit can keep the output power unchanged. It is widely used in radar, communication and other fields, especially in instruments and meters. For example, in analog signal sources, it is the core circuit that determines the output power index. At present, most ALC circuits have the problem of low output power stability, especially when the high and low temperature environment changes, the temperature stability of the output power is very poor. Summary of the invention

[0003] In order to solve the above-mentioned deficiencies of the prior art, the present application provides an analog automatic level control circuit with high power stability, which solves the problem that the output power of the ALC circuit fluctuates greatly with high and low temperature conditions through simple hardware circuit design.

[0004] In order to achieve the above object, the present invention adopts the following technologies: The invention discloses 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.

[0005] 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 divide the amplified signal into two outputs, one output of the coupler is an output signal, and the other output is a feedback signal.

[0006] The feedback loop with a constant temperature island includes a detection circuit and an RC comparison integration loop, a coupler, the input of the detection circuit is connected to another output of the coupler, the output of the detection circuit is connected to the input of the RC comparison integration loop, the detection circuit is used to convert the feedback signal into a detection voltage signal and provide it to the RC comparison integration loop, the output of the RC comparison integration loop is connected to voltage-controlled attenuator 1 and voltage-controlled attenuator 2, and the RC comparison integration loop is used to compare and integrate the detection voltage signal with a reference voltage and then output a control voltage signal to voltage-controlled attenuator 1 and voltage-controlled attenuator 2 to control the attenuation of voltage-controlled attenuator 1 and voltage-controlled attenuator 2.

[0007] Furthermore, the RC comparison integral loop includes a resistor R1, a resistor R2, a resistor R3, a capacitor C1, a capacitor C2, a capacitor C3, a capacitor C4 and an operational amplifier OP1, the inverting input terminal of the operational amplifier OP1 is connected to one end of the capacitor C1 and the output of the detection circuit through the resistor R1, the other end of the capacitor C1 is grounded, the non-inverting input terminal of the operational amplifier OP1 is connected to one end of the capacitor C2 and the reference voltage output terminal of the high-stability DAC reference circuit through the resistor R2, the other end of the capacitor C2 is grounded, the capacitor C4 is connected in parallel between the inverting input terminal and the output terminal of the operational amplifier OP1, one end of the resistor R3 is connected to the output terminal of the operational amplifier OP1, and the other end serves as the control voltage signal output terminal of the RC comparison integral loop, and is connected to the ground through the capacitor C3.

[0008] The constant temperature circuit is arranged at the feedback loop, and is used to obtain the ambient temperature of the feedback loop, and generate heat according to the ambient temperature to adjust the ambient temperature; further, the constant temperature circuit includes a temperature sensor element, a constant temperature chip, and a heating element connected in sequence, the temperature sensor element is used to collect the ambient temperature and convert it into a temperature voltage signal to provide to the constant temperature chip, and the constant temperature chip is used to output a heating control voltage to the heating element according to the temperature voltage signal, so that the heating element generates heat to adjust the ambient temperature; wherein, during implementation, the feedback loop and the temperature sensor element are located at the center of the surface of a circuit board, the heating element is located at the bottom of the circuit board, and this part of the circuit board is a small island.

[0009] The high-stability DAC reference circuit is connected to the RC comparison integration loop and is used to provide the reference voltage to the RC comparison integration loop; further, the high-stability DAC reference circuit includes a DAC circuit connected to the RC comparison integration loop, an FPGA and a bandgap reference source connected to the DAC circuit, the bandgap reference source is used to provide a voltage signal to the DAC circuit for 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 integration loop based on the voltage signal provided by the bandgap reference source.

[0010] The beneficial effects of the present invention are: 1. The detection circuit and RC comparison integral loop are placed on a constant temperature island to ensure that the output signal power can be stably detected by the detection circuit and is not affected by ambient temperature changes. At the same time, the reference voltage uses a bandgap reference source to further ensure the stability of the control voltage, solving the problem of large fluctuations in the output power of the ALC circuit under high and low temperature conditions. The temperature stability can reach ±0.005dB / ℃; 2. Use RC comparison integral loop as feedback loop, use large capacitor as integral element, and add RC filter circuit at both input and output ends. Compared with the existing first-order or second-order comparison loop, the significant advantage of this circuit is stability, which greatly reduces loop noise and can make the output power very stable. Especially when the temperature fluctuates greatly, it can slow down the change of the detection voltage at the input end and reduce the influence of temperature fluctuation on the output power. 3. Constant temperature chip + heating element is used as the main means of constant temperature. Compared with other traditional constant temperature circuits, it has high constant temperature accuracy and temperature stability can reach ±0.01℃. It is a pure analog circuit and does not require digital control. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 It is a structural block diagram of an analog automatic level control circuit according to an embodiment of the present application.

[0012] Figure 2 It is a structural block diagram of the constant temperature circuit of an embodiment of the present application.

[0013] Figure 3 It is a circuit structure block diagram of the RC comparison integration loop of an embodiment of the present application.

[0014] Figure 4 It is a schematic side view of the spatial position of the constant temperature island in an embodiment of the present application.

[0015] Figure 5 It is a top view schematic diagram of the spatial position of the constant temperature island in an embodiment of the present application. DETAILED DESCRIPTION

[0016] To make the objectives, technical solutions and advantages of the embodiments of the present invention more clear, the implementation modes of the present invention are described in detail below with reference to the accompanying drawings. However, the embodiments described in the present invention are only part of the embodiments of the present invention, rather than all the embodiments.

[0017] The present application embodiment provides an analog automatic level control circuit with high power stability, such as Figure 1-Figure 2 As shown, it includes a main link, a feedback loop with a constant temperature island, a constant temperature circuit and a high-stability DAC reference circuit.

[0018] The main link includes 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 is used to attenuate the power of the input signal. The power-attenuated signal enters the voltage-controlled attenuator 2, which is used to adjust the amplitude of the attenuated signal. The amplifier is used to amplify the amplitude-adjusted signal. The amplified signal is transmitted to the coupler, which is used to divide the amplified signal into two outputs. One output of the coupler is the output signal, and the other output is the feedback signal, which is provided to the feedback loop with a constant temperature island.

[0019] The feedback loop with a constant temperature island includes a detection circuit and an RC comparison integration loop, a coupler, the input of the detection circuit is connected to another output of the coupler, the output of the detection circuit is connected to the input of the RC comparison integration loop, the detection circuit is used to convert the feedback signal into a detection voltage signal VDET and provide it to the RC comparison integration loop, the output of the RC comparison integration loop is connected to the voltage-controlled attenuator 1 and the voltage-controlled attenuator 2, the RC comparison integration loop is used to compare and integrate the detection voltage signal VDET with a reference voltage and then output a control voltage signal Vctrl to the voltage-controlled attenuator 1 and the voltage-controlled attenuator 2 to control the attenuation of the voltage-controlled attenuator 1 and the voltage-controlled attenuator 2.

[0020] Preferably, Figure 3 As shown, the RC comparison integral loop includes a resistor R1, a resistor R2, a resistor R3, a capacitor C1, a capacitor C2, a capacitor C3, a capacitor C4 and an operational amplifier OP1, an inverting input terminal of the operational amplifier OP1 is connected to one end of the capacitor C1 and the output of the detection circuit through the resistor R1, and the other end of the capacitor C1 is grounded, a non-inverting input terminal of the operational amplifier OP1 is connected to one end of the capacitor C2 and the reference voltage output terminal of the high-stability DAC reference circuit through the resistor R2, the other end of the capacitor C2 is grounded, and the capacitor C4 is connected in parallel between the inverting input terminal and the output terminal of the operational amplifier OP1, one end of the resistor R3 is connected to the output terminal of the operational amplifier OP1, and the other end is used as the control voltage signal output terminal of the RC comparison integral loop, and is connected to the ground through the capacitor C3.

[0021] Among them, the detection voltage enters the resistor R1 through the filter capacitor C1, and then enters the inverting input terminal of the operational amplifier OP1; the reference voltage enters the resistor R2 through the filter capacitor C2, and then enters the non-inverting input terminal of the operational amplifier OP2; the voltages of the inverting input terminal and the non-inverting input terminal are compared and then pass through the integrating capacitor C4 to the operational amplifier OP2, and then are filtered again through the resistor R3 and the capacitor C3 to obtain the control voltage signal; wherein the integrating capacitor uses a large capacitor of uF level. Compared with the existing first-order or second-order comparison loop, the significant advantage of this circuit is stability. The first-order or second-order comparison loop is very easy to cause circuit oscillation, and it is easy to form power overshoot when there is external environmental interference or temperature changes. The circuit of this example reduces noise through RC filtering at the input and output ends, and at the same time cooperates with large capacitor integration to achieve a very small loop bandwidth, which can make the output control voltage very stable, thereby making the power very stable, especially when the temperature fluctuates greatly, it can slow down the change of the detection voltage at the input end and reduce the influence of temperature fluctuation on the output power.

[0022] The constant temperature circuit is arranged at the feedback loop, and is used to obtain the ambient temperature of the feedback loop, and generates heat according to the ambient temperature to adjust the ambient temperature. 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 is used to collect the ambient temperature and convert it into a temperature voltage signal to provide to the constant temperature chip. The constant temperature chip is used to output a heating control voltage Vh to the heating element according to the temperature voltage signal, so that the heating element generates heat to adjust the ambient temperature. Optionally, the temperature sensing element adopts a thermistor, and the heating element adopts a heating resistor. The constant temperature chip adopts ADN8830. Wherein, during implementation, if Figure 4 and Figure 5 As shown, the feedback loop and the thermistor are located at the center of the surface of the circuit board, and the heating resistor is located on the bottom of the circuit board. This part of the circuit board is a small island, and a constant temperature island space is formed under the action of the constant temperature circuit; compared with the existing constant temperature circuit, such as the transistor-controlled power tube heating circuit, the circuit has extremely high constant temperature accuracy, simple control, and simple circuit; the constant temperature circuit can make 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°C, and the temperature stability can reach ±0.01°C.

[0023] The high-stability DAC reference circuit is connected to the RC comparison integral loop, and is used to provide the reference voltage to the RC comparison integral loop. Optionally, the high-stability DAC reference circuit includes a DAC circuit connected to the RC comparison integral loop, an FPGA connected to the DAC circuit, and a bandgap reference source, the bandgap reference source is used to provide a high-stability voltage signal 5V for 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 integral loop based on the voltage signal provided by the bandgap reference source, and the reference voltage has a unique corresponding relationship with the output power. Among them, the DAC circuit can use the DAC chip LTC1668, and the bandgap reference source can use REF70. Since the reference of the DAC is the bandgap reference source, the maximum drift of the voltage is 2ppm / ℃, so the reference voltage generated by the DAC circuit is very stable and hardly changes with temperature.

[0024] The present embodiment provides an analog automatic level control circuit with high power stability. The detection circuit and the RC comparison integral loop are placed on a constant temperature island to ensure that the output signal power can be stably detected by the detection circuit and is not affected by ambient temperature changes. The RC comparison integral loop is used as a feedback loop, a large capacitor is used as an integral element, and an RC filter circuit is added to the input and output ends at the same time, which greatly reduces the loop noise and makes the output power very stable. At the same time, the reference voltage uses a bandgap reference source to further ensure the stability of the control voltage, solve the problem of large fluctuations in the output power of the ALC circuit under high and low temperature conditions, and compared with other traditional constant temperature circuits, it has high constant temperature accuracy and a temperature stability of ±0.01°C. It is a pure analog circuit and does not require digital control.

[0025] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Obviously, those skilled in the art can make various changes and modifications to the present application without departing from the spirit and scope of the present application.

Claims

1. An analog automatic level control circuit with high power stability, characterized in that: It includes the main link, feedback loop with thermostatic island, thermostatic circuit and high-stability DAC reference circuit; The main link includes a voltage-controlled attenuator 1, a voltage-controlled attenuator 2, an amplifier, and a coupler connected in sequence, one output of the coupler is an output signal, and the other output is a feedback signal; The feedback loop with a constant temperature island includes a detection circuit and an RC comparison integral loop, the input of the detection circuit is connected to another output of the coupler, the output of the detection circuit is connected to the input of the RC comparison integral loop, the detection circuit is used to convert the feedback signal into a detection voltage signal and provide it to the RC comparison integral loop, the output of the RC comparison integral loop is connected to the voltage-controlled attenuator 1 and the voltage-controlled attenuator 2, the RC comparison integral loop is used to compare and integrate the detection voltage signal with a reference voltage and then output a control voltage signal to the voltage-controlled attenuator 1 and the voltage-controlled attenuator 2 to control the attenuation of the voltage-controlled attenuator 1 and the voltage-controlled attenuator 2; The constant temperature circuit is arranged at the feedback loop, and is used to obtain the ambient temperature of the feedback loop, and to generate heat according to the ambient temperature to adjust the ambient temperature; The high-stability DAC reference circuit is connected to the RC comparison integration loop and is used to provide the reference voltage to the RC comparison integration loop.

2. The analog automatic level control circuit with high power stability according to claim 1, characterized in that: The constant temperature circuit includes a temperature sensing element, a constant temperature chip, and a heating element connected in sequence. The temperature sensing element is used to collect the ambient temperature and convert it into a temperature voltage signal and provide it to the constant temperature chip. The constant temperature chip is used to output a heating control voltage to the heating element according to the temperature voltage signal so that the heating element generates heat to adjust the ambient temperature.

3. The analog automatic level control circuit with high power stability according to claim 2, characterized in that: The feedback loop and the temperature sensing element are arranged at the center of the front side of a circuit board, and the heating element is arranged at the center of the back side of the circuit board.

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

5. The analog automatic level control circuit with high power stability according to claim 2, characterized in that: The constant temperature chip uses ADN8830.

6. The analog automatic level control circuit with high power stability according to claim 1, characterized in that: The RC comparison integral loop includes a resistor R1, a resistor R2, a resistor R3, a capacitor C1, a capacitor C2, a capacitor C3, a capacitor C4 and an operational amplifier OP1. The inverting input terminal of the operational amplifier OP1 is connected to one end of the capacitor C1 and the output of the detection circuit through the resistor R1, and the other end of the capacitor C1 is grounded. The non-inverting input terminal of the operational amplifier OP1 is connected to one end of the capacitor C2 and the reference voltage output terminal of the high-stability DAC reference circuit through the resistor R2, and the other end of the capacitor C2 is grounded. The capacitor C4 is connected in parallel between the inverting input terminal and the output terminal of the operational amplifier OP1. One end of the resistor R3 is connected to the output terminal of the operational amplifier OP1, and the other end serves as the control voltage signal output terminal of the RC comparison integral loop and is connected to the ground through the capacitor C3.

7. The analog automatic level control circuit with high power stability according to claim 1, characterized in that: The high-stability DAC reference circuit includes a DAC circuit connected to an RC comparison integral 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 for reference. The FPGA is used to generate a digital signal to control the DAC circuit to output a reference voltage to the RC comparison integral loop based on the voltage signal provided by the bandgap reference source.

8. The analog automatic level control circuit with high power stability according to claim 7, characterized in that: The DAC circuit uses the DAC chip LTC1668.

9. The analog automatic level control circuit with high power stability according to claim 7, characterized in that: The bandgap reference source uses REF70.

10. The analog automatic level control circuit with high power stability according to claim 1, characterized in that: 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 divide the amplified signal into two paths for output.

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