Automatic power control circuit with constant temperature control function

Abstract

The invention provides an automatic power control circuit with a constant temperature control function. The automatic power control circuit comprises a variable gain amplifier, a directional coupler, an integrating circuit, a detection circuit and a constant temperature control circuit, the variable gain amplifier amplifies the power of the microwave signal to P1, and outputs the microwave signal of P1 to the directional coupler; the directional coupler outputs a 0.9 P1 microwave signal, and the other 0.1 P1 microwave signal is coupled to the detection circuit; the detection circuit converts 0.1 P1 power of the coupled microwave signal into a direct current level, and outputs a converted level value V0 to the integrating circuit; the constant temperature control circuit automatically controls the temperature of the detection circuit at a preset temperature fixed point in a heating mode; the integrating circuit compares the conversion level value V0 output by the detection circuit with a reference level value V1 input from the outside to control the increase and decrease of the output control level Vt; the control level Vt is used for controlling the gain of the variable gain amplifier; according to the invention, the output signal power in the microwave emission system can be automatically controlled.

Description

An automatic power control circuit with constant temperature control function Technical Field

[0001] This invention belongs to the field of power control circuit technology, and relates to an automatic power control circuit with constant temperature control function. Background Technology

[0002] Automatic power control (ALC), a commonly used negative feedback control circuit, is widely applied in instruments, microwave transmitters, power amplifiers, radar, and other applications. Its working principle is as follows: the input microwave signal passes through a variable gain amplifier and then through a directional coupler for output; the coupler transmits a small portion of the signal power to a detector, which converts the microwave power signal into a DC level; this DC level then passes through an operational amplifier, is compared with a reference level, and generates a gain control level; finally, the gain control level controls the gain of the variable gain amplifier, thereby controlling the amplifier's output power. This process is a closed-loop negative feedback control process, with the detector being the key component; its operational stability determines the stability of the final power output. The detector works by using a diode to convert the high-frequency microwave signal into a DC level. Diodes are temperature-sensitive elements; temperature changes cause changes in the converted voltage level (temperature drift), which in turn affects the final output power. Summary of the Invention

[0003] The purpose of this invention is to at least solve one of the problems existing in the prior art.

[0004] Therefore, the present invention provides an automatic power control circuit with constant temperature control function, which can automatically control the output signal power in a microwave transmitting system.

[0005] The technical solution of this invention is as follows:

[0006] An automatic power control circuit with constant temperature control function includes: a variable gain amplifier, a directional coupler, an integrator circuit, a detector circuit, and a constant temperature control circuit;

[0007] The variable gain amplifier is used to amplify the power of the input microwave signal to P1, and output the microwave signal with the power amplified to P1 to the directional coupler.

[0008] The directional coupler amplifies the power to 0.9P1 of the microwave signal output in P1, and the remaining 0.1P1 microwave signal is coupled to the detector circuit.

[0009] The detection circuit is used to convert the 0.1P1 power of the coupled microwave signal into a DC level, and output the converted DC level value, i.e., the converted level value V0, to the integrator circuit.

[0010] The constant temperature control circuit automatically controls the temperature of the detector circuit at a preset fixed temperature point by heating.

[0011] The integrating circuit, implemented using an operational amplifier, compares the converted level value V0 output from the detector circuit with the externally input reference level value V1. When the converted level value V0 is greater than the externally input reference level value V1, the operational amplifier outputs a control level V. t Increase; when the conversion level V0 is less than the external input reference level V1, the operational amplifier output control level V t Decrease; when the conversion level V0 equals the external input reference level V1, the operational amplifier output control level V t Unchanged; the control level V output of the operational amplifier remains unchanged. t Used to control the gain of a variable gain amplifier, control level V t As the gain is gradually increased, the power of the microwave signal output by the variable gain amplifier decreases uniformly; the control level V t As the gain is gradually reduced, the power of the microwave signal output by the variable gain amplifier increases uniformly.

[0012] Furthermore, the constant temperature control circuit includes: comparator U1A, N-channel MOSFET Q1, power resistor R5, NTC resistor R6, and proportional voltage divider resistor R10;

[0013] The power resistor R5 generates heat when energized, and the generated heat is used to heat the detector in the detection circuit.

[0014] The resistance of NTC resistor R6 changes with the temperature t of the detector in the detector circuit, causing the voltage across NTC resistor R6 to change with temperature t; the resistance of NTC resistor R6 is R6(t).

[0015] The proportional voltage divider resistor R10 and the NTC resistor R6 are used together to generate the temperature voltage divider V+; V+ = 3.3V * R6(t) / (R6(t) + R10);

[0016] Comparator U1A is used to compare the temperature voltage divider V+ with the temperature threshold voltage V-: when the temperature t of the detector is less than the preset temperature fixed point, V+ > V-, and comparator U1A outputs a high level; when the temperature t of the detector is greater than or equal to the preset temperature fixed point, V+ < V-, and comparator U1A outputs 0V.

[0017] The N-channel MOSFET Q1 is used to control the on / off state of the power resistor R5 for heating the detector. When the comparator U1A outputs a high level, the N-channel MOSFET Q1 is turned on, and the power resistor R5 is energized and generates heat. When the comparator U1A outputs 0V, the N-channel MOSFET Q1 is turned off, and the power resistor R5 is de-energized and does not generate heat.

[0018] Furthermore, the constant temperature control circuit also includes: proportional voltage divider resistor R4 and proportional voltage divider resistor R7;

[0019] The proportional voltage divider resistors R4 and R7 are used together to generate the temperature threshold voltage V-; V- = 3.3V * R4 / (R4 + R7).

[0020] Furthermore, the constant temperature control circuit also includes: resistor R8 and capacitor C10;

[0021] The resistor R8 and capacitor C10 form a delay circuit used for debouncing and adjusting the response time.

[0022] Furthermore, the constant temperature control circuit also includes: resistor R9, resistor R11, and capacitor C9;

[0023] R9 is a current-limiting resistor; C9 is a decoupling capacitor; R11 is a pull-down resistor.

[0024] Furthermore, the connection relationship of the constant temperature control circuit is as follows: one end of the NTC resistor R6 is connected to one end of the proportional voltage divider resistor R4, the other end of the NTC resistor R6 is connected to one end of the proportional voltage divider resistor R10, and the other end of the proportional voltage divider resistor R10 is connected to the 3.3V power supply.

[0025] The common terminal of NTC resistor R6 and proportional voltage divider resistor R4 is grounded. The other end of proportional voltage divider resistor R4 is connected to one end of proportional voltage divider resistor R7. The other end of proportional voltage divider resistor R7 is connected to a 3.3V power supply.

[0026] The common terminal of NTC resistor R6 and proportional voltage divider resistor R10 is connected to port 3 of comparator U1A through resistor R9, and the common terminal of proportional voltage divider resistor R4 and proportional voltage divider resistor R7 is connected to port 4 of comparator U1A.

[0027] The fifth terminal of comparator U1A is connected to one end of capacitor C9, and the other end of capacitor C9 is grounded; the common terminal of capacitor C9 and the fifth terminal of comparator U1A is connected to a 3.3V power supply.

[0028] The first port of comparator U1A is connected to the first port of N-channel MOSFET Q1 through resistor R8. One end of resistor R11 is connected to the common terminal of the first port of comparator U1A and resistor R8, and the other end of resistor R11 is connected to the second port of comparator U1A. One end of capacitor C10 is connected to the common terminal of resistor R8 and the first port of N-channel MOSFET Q1. The other end of capacitor C10 is connected to the common terminal of resistor R11 and the first port of comparator U1A, and this end is grounded.

[0029] The second port of the N-channel MOSFET Q1 is connected to the 12V power supply ground, the third port of the N-channel MOSFET Q1 is connected to one end of the power resistor R5, and the other end of the power resistor R5 is connected to the 12V power supply.

[0030] Furthermore, the detection circuit and the constant temperature control circuit are arranged on the same circuit board;

[0031] The detection circuit is arranged on the front of the circuit board and includes a detector, an adjustable attenuator, and a temperature sensor. The detector is used to convert the 0.1P1 power of the input microwave signal into a DC level value V0. The adjustable attenuator is used to adjust the power of the input microwave signal so that the detector is in a linear operating state. The temperature sensor is used to measure the temperature of the circuit board.

[0032] The NTC resistor R6 of the constant temperature control circuit is located at the detector location; the other components of the constant temperature control circuit are located on the back of the circuit board.

[0033] Furthermore, the power resistor R5 of the constant temperature control circuit is located in the center of the back of the circuit board. The heat dissipation surface area of ​​the power resistor R5 is 1 / 2 of the area of ​​the circuit board. When the power resistor R5 is powered on, it generates heat, which is conducted to the detector through the heat conduction holes on the circuit board to heat the detector.

[0034] Furthermore, when the detector circuit converts the 0.1P1 power of the microwave signal into a DC level, the logarithm of the 0.1P1 power of the microwave signal is proportional to the converted level value V0.

[0035] Furthermore, when the control level V output by the integrating circuit... t When the voltage is 0V, the power of the microwave signal output by the variable gain amplifier is at its maximum.

[0036] By applying the above technical solution, the present invention has the following beneficial effects:

[0037] (1) This invention proposes an automatic power control circuit with constant temperature control function for automatic control of output signal power in microwave transmission system. The difference from the traditional automatic power control circuit is that: in this invention, an automatic constant temperature control circuit is added to the key part of the circuit - the detector circuit, which can keep the working temperature of the detector at a preset temperature point (generally a fixed temperature point between 40℃ and 50℃), ensuring that the detector works at a constant temperature, thereby suppressing the temperature drift characteristics of the logarithmic detector and improving the accuracy of automatic power control.

[0038] (2) The automatic temperature control circuit of the present invention is integrated with the detector circuit on a single circuit board. It has a compact structure, low power consumption, and sensitive and rapid temperature adjustment. By using heating, the temperature of the detector is controlled at a constant temperature (higher than the ambient temperature), thereby suppressing the temperature drift characteristics of the detector. Attached Figure Description

[0039] The accompanying drawings, which form part of this specification, are provided to further illustrate embodiments of the invention and, together with the textual description, explain the principles of the invention. It is obvious that the drawings described below are merely some embodiments of the invention, and those skilled in the art can obtain other drawings based on these drawings without any creative effort.

[0040] Figure 1 is a schematic diagram of the present invention;

[0041] Figure 2 is a schematic diagram of the automatic constant temperature control circuit of the present invention;

[0042] Figure 3 is a layout diagram of the automatic constant temperature control circuit and the detection circuit of the present invention on the circuit board. (a) is a front view of the circuit board, and (b) is a back view of the circuit board.

[0043] Among them, 1-detector, 2-adjustable attenuator, 4-temperature sensor, 5-variable gain amplifier, 6-directional coupler, 7-detection circuit, 8-constant temperature control circuit, 9-integrating circuit, and 10-operational amplifier. Detailed Implementation

[0044] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit the present invention or its application or use. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0045] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments according to this application. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0046] Unless otherwise specifically stated, the relative arrangement, numerical expressions, and values ​​of the components and steps set forth in these embodiments do not limit the scope of the invention. It should also be understood that, for ease of description, the dimensions of the various parts shown in the drawings are not drawn to actual scale. Techniques, methods, and devices known to those skilled in the art may not be discussed in detail, but where appropriate, such techniques, methods, and devices should be considered part of the specification. In all examples shown and discussed herein, any specific values ​​should be interpreted as merely exemplary and not as limitations. Therefore, other examples of exemplary embodiments may have different values. It should be noted that similar reference numerals and letters in the following figures denote similar items; therefore, once an item is defined in one figure, it need not be further discussed in subsequent figures.

[0047] This embodiment discloses an automatic power control circuit with constant temperature control function, as shown in Figure 1, including: a variable gain amplifier 5, a directional coupler 6, an integrator circuit 9, a detector circuit 7, and a constant temperature control circuit 8;

[0048] The variable gain amplifier 5 amplifies the power of the input microwave signal to P1, and outputs the amplified microwave signal to the directional coupler 6; the gain of the power amplification is controlled by the input control level V. t The size is controlled; the control level V t When the voltage is 0V, the power of the microwave signal output by the variable gain amplifier 5 is at its maximum. As the control level V increases... tAs the gain increases, the power of the microwave signal output by the variable gain amplifier 5 decreases uniformly; the control level V t As the gain gradually decreases, the power of the microwave signal output by the variable gain amplifier 5 increases uniformly.

[0049] The directional coupler 6 amplifies the power to 0.9P1 of the microwave signal output in P1, and the remaining 0.1P1 microwave signal is coupled to the detector circuit 7.

[0050] The detector circuit 7 is used to convert the 0.1P1 power of the coupled microwave signal into a DC level, and output the converted DC level value, i.e., the converted level value V0, to the integrator circuit 9; wherein, the logarithm of the 0.1P1 power of the microwave signal is proportional to the converted level value V0.

[0051] The constant temperature control circuit 8 automatically controls the temperature of the detector circuit 7 at a preset fixed temperature point by heating.

[0052] The integrating circuit 9, implemented by the operational amplifier 10, compares the conversion level value V0 output by the detector circuit 7 with the externally input reference level value V1. When the conversion level value V0 is greater than the externally input reference level value V1, the control level V0 output by the operational amplifier 10 is increased. t The voltage increases by a fixed ratio; when the conversion level V0 is less than the externally input reference level V1, the control level V output by operational amplifier 10 increases. t The voltage decreases by a fixed ratio; when the conversion level V0 equals the externally input reference level V1, the control level V output by operational amplifier 10 decreases. t The control level V output of operational amplifier 10 remains unchanged. t Used to control the gain of variable gain amplifier 5.

[0053] The detector circuit 7 and the constant temperature control circuit 8 are arranged on the same circuit board.

[0054] Referring to Figure 3, the detection circuit 7 is arranged on the front of the circuit board. The detection circuit 7 includes a detector 1, an adjustable attenuator 2, and a temperature sensor 4. The detector 1 is used to convert the 0.1P1 power of the input microwave signal into a DC level value V0. The adjustable attenuator 2 is used to adjust the power of the input microwave signal so that the detector 1 is in a linear working state. The temperature sensor 4 is used to measure the temperature of the circuit board for monitoring.

[0055] Referring to Figure 2, the constant temperature control circuit 8 includes: comparator U1A, N-channel MOSFET Q1, power resistor R5, NTC resistor R6, proportional voltage divider resistors R4, R7, and R10, resistors R8, R9, and R11, capacitors C9 and C10; wherein, the NTC resistor R6 is located near the detector 1; the other components of the constant temperature control circuit 8 are located on the back of the circuit board;

[0056] The connection relationship of the constant temperature control circuit 8 is as follows: one end of the NTC resistor R6 is connected to one end of the proportional voltage divider resistor R4, the other end of the NTC resistor R6 is connected to one end of the proportional voltage divider resistor R10, and the other end of the proportional voltage divider resistor R10 is connected to the 3.3V power supply.

[0057] The common terminal of NTC resistor R6 and proportional voltage divider resistor R4 is grounded. The other end of proportional voltage divider resistor R4 is connected to one end of proportional voltage divider resistor R7. The other end of proportional voltage divider resistor R7 is connected to a 3.3V power supply.

[0058] The common terminal of NTC resistor R6 and proportional voltage divider resistor R10 is connected to port 3 of comparator U1A through resistor R9, and the common terminal of proportional voltage divider resistor R4 and proportional voltage divider resistor R7 is connected to port 4 of comparator U1A.

[0059] The fifth terminal of comparator U1A is connected to one end of capacitor C9, and the other end of capacitor C9 is grounded; the common terminal of capacitor C9 and the fifth terminal of comparator U1A is connected to a 3.3V power supply.

[0060] The first port of comparator U1A is connected to the first port of N-channel MOSFET Q1 through resistor R8. One end of resistor R11 is connected to the common terminal of the first port of comparator U1A and resistor R8, and the other end of resistor R11 is connected to the second port of comparator U1A. One end of capacitor C10 is connected to the common terminal of resistor R8 and the first port of N-channel MOSFET Q1. The other end of capacitor C10 is connected to the common terminal of resistor R11 and the first port of comparator U1A, and this end is grounded.

[0061] The second port of the N-channel MOSFET Q1 is connected to the 12V power supply ground, the third port of the N-channel MOSFET Q1 is connected to one end of the power resistor R5, and the other end of the power resistor R5 is connected to the 12V power supply.

[0062] Among them, the resistance value of NTC resistor R6 changes with temperature t, and its resistance value can be written as R6(t). NTC resistor R6 is used to convert the temperature of the detector into the voltage division value on both sides of R6.

[0063] Proportional voltage divider resistors R4 and R7 are used together to generate the temperature threshold voltage V-; proportional voltage divider resistor R10 and NTC resistor R6 are used together to generate the temperature voltage V+.

[0064] V-=3.3V*R4 / (R4+R7); V+=3.3V*R6(t) / (R6(t)+R10);

[0065] The comparator U1A is used to compare and calculate the temperature threshold voltage V- and the temperature divider voltage V+. When V+>V-, it outputs a high level; otherwise, it outputs 0V.

[0066] R9 is a current-limiting resistor;

[0067] C9 is a decoupling capacitor; R11 is a pull-down resistor;

[0068] R8 and C10 form a delay circuit for debouncing and adjusting response time;

[0069] The power resistor R5 is located in the center of the back of the circuit board. The heat dissipation surface area of ​​the power resistor R5 is 1 / 2 of the circuit board area. When the power resistor R5 is powered on, it generates heat, which is conducted to the detector through the heat conduction holes on the circuit board to heat the detector; wherein, R5 = 10Ω.

[0070] The N-channel MOSFET Q1 is used to control the on / off state of the power resistor R5 for heating the detector. When the comparator U1A outputs a high level, the N-channel MOSFET Q1 is turned on, and the power resistor R5 is energized and generates heat. When the comparator U1A outputs 0V, the N-channel MOSFET Q1 is turned off, and the power resistor R5 is de-energized and does not generate heat.

[0071] Therefore, (1) the working principle of the constant temperature control circuit 8 is as follows:

[0072] The resistance of the NTC resistor R6 decreases with increasing temperature and increases with decreasing temperature. Assuming the detector temperature needs to be stably controlled at 40℃, and the NTC resistor R6 at 40℃ can be denoted as R6(40℃), then appropriate proportional voltage divider resistors R4, R7, and R10 should be selected to ensure V- = V+.

[0073] 3.3V*R4 / (R4+R7)=3.3V*R6(40℃) / (R6(40℃)+R10);

[0074] After the constant-temperature control circuit 8 is powered on in a room-temperature environment, since the temperature is less than 40°C, at this time, the resistance value of the NTC resistor R6 is greater than R6(40°C), V+>V-, then the comparator U1A outputs a high level, the N-channel MOS transistor Q1 conducts, and the current flows into the power resistor R5. The power resistor R5 is energized to generate heat; the heat is conducted to the detector and at the same time to the NTC resistor R6. The temperature of the NTC resistor R6 rises, and its resistance value gradually decreases until the resistance value of the NTC resistor R6 decreases to R6(40°C). At this time, the temperature of the detector is 40°C, V- = V+, the comparator U1A outputs 0V, the N-channel MOS transistor Q1 is turned off, and the power resistor R5 is de-energized and no longer generates heat;

[0075] When the temperature of the detector continuously rises from 40°C, then V+<V-, the comparator U1A still outputs 0V, the N-channel MOS transistor Q1 remains off, the power resistor R5 stops heating, and the temperatures of the detector and the NTC resistor R6 start to decrease; when the temperature is lower than 40°C and V+>V- is satisfied, the above heating process is repeated.

[0076] The temperature change is a slow change. The response time of the constant-temperature control circuit 8 to the temperature can be adjusted by adjusting the resistor R8 and the capacitor C10, so that the switching process of the N-channel MOS transistor Q1 proceeds slowly to avoid generating switching oscillations.

[0077] Due to the fast and sensitive temperature response of the NTC resistor R6, the constant-temperature control error of this constant-temperature control circuit 8 can reach ±1°C.

[0078] (2) The working principle of the automatic power control circuit is as follows:

[0079] Since the power of the microwave signal output from the directional coupler 6 is 0.9P1 (the remaining 0.1P1 of the microwave signal is used for coupling to the detection circuit 7), 0.9P1 is set as the target power of the final output;

[0080] When a microwave signal is input, the variable gain amplifier 5 amplifies the power of the microwave signal to the initial power P0 (P0 is not equal to P1). After the microwave signal with the initial power P0 passes through the directional coupler 6, the actual power of the output port is 0.9P0, and the actual power coupled to the detection circuit 7 is 0.1P0; the detection circuit 7 converts the power of the microwave signal with a power of 0.1P0 into a DC level value V0; when the target power of the final output needs to be controlled at 0.9P1, a DC voltage is applied to the reference level input port of the integration circuit 9, and the reference level value V1 of the DC voltage can be obtained through calibration (described below);

[0081] If P0 > P1, then V0 > V1, and the control level V output by the integration circuit 9 t gradually increases, V tThe increase in P0 causes the gain of variable gain amplifier 5 to gradually decrease, and P0 gradually decreases. The decrease in P0 causes V0 to gradually decrease; the decrease in V0 causes V... t The rate of increase gradually slows down until it approaches a constant value and remains unchanged. At this point, V1 = V0, the automatic power control circuit reaches a balance, and the final output power decreases from 0.9P0 to 0.9P1.

[0082] If P0 < P1, then V0 < V1, and the control level V output by the integrator circuit 9... t Gradually decrease, V t The decrease in gain causes the gain of variable gain amplifier 5 to gradually increase, P0 gradually increases, and the increase in P0 causes V0 to gradually increase; the increase in V0 causes V t The rate of decrease gradually slows down until it approaches a constant value and remains unchanged. At this point, V1 = V0, the automatic power control circuit reaches equilibrium, and the final output power increases from 0.9P0 to 0.9P1.

[0083] To avoid oscillation or instability caused by premature adjustment, the delay of the integrator circuit 9 can be reasonably adjusted according to the response time of the variable gain amplifier 5 and the detector circuit 7.

[0084] (3) Calibration of automatic power control circuit

[0085] Connecting a microwave power meter to the microwave signal output interface in Figure 1 enables calibration of the automatic power control circuit. The specific method is as follows:

[0086] a) Input a microwave signal and apply a DC voltage with a level of V2 (any appropriate value not exceeding the operating voltage of the integrator circuit 9) to the reference level input port;

[0087] b) Read the current stable power value P2 from the microwave power meter (the output power is stable due to the working principle described above);

[0088] c) Gradually increase or decrease V2, and the reading P2 of the microwave power meter changes synchronously; when P2 reaches the final output target power of 0.9P1, the level value V2 at this time is the reference level value V1.

[0089] The above process establishes the correspondence between the output power 0.9P1 and the reference level value V1, thereby achieving the calibration of the output power of the automatic power control circuit.

[0090] For ease of description, spatial relative terms such as "above," "on top of," "on the upper surface of," "above," etc., are used herein to describe the spatial positional relationship of a device or feature as shown in the figures to other devices or features. It should be understood that spatial relative terms are intended to encompass different orientations in use or operation beyond the orientation of the device as described in the figures. For example, if the device in the figures were inverted, a device described as "above" or "on top of" other devices or structures would subsequently be positioned as "below" or "under" other devices or structures. Thus, the exemplary term "above" can include both "above" and "below." The device may also be positioned in other different ways (rotated 90 degrees or in other orientations), and the spatial relative descriptions used herein will be interpreted accordingly.

[0091] Furthermore, it should be noted that the use of terms such as "first" and "second" to define components is merely for the purpose of distinguishing the corresponding components. Unless otherwise stated, the above terms have no special meaning and therefore should not be construed as limiting the scope of protection of this invention.

[0092] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. An automatic power control circuit with constant temperature control function, characterized in that, include: Variable gain amplifier, directional coupler, integrating circuit, detection circuit and constant temperature control circuit; The variable gain amplifier amplifies the power of the input microwave signal to P1, and outputs the amplified microwave signal to the directional coupler. The directional coupler outputs 0.9P1 of the amplified microwave signal to the P1 power level, and the remaining 0.1P1 microwave signal is coupled to the detector circuit. The detector circuit converts the 0.1P1 power of the coupled microwave signal into a DC level and outputs the converted DC level value, i.e., the conversion level value V0, to the integrator circuit. The constant temperature control circuit automatically controls the temperature of the detector circuit at a preset fixed temperature point through heating. The integrator circuit, implemented by an operational amplifier, compares the conversion level value V0 output by the detector circuit with the externally input reference level value V1. When the conversion level value V0 is greater than the externally input reference level value V1, the operational amplifier outputs a control level V. t Increase; when the conversion level V0 is less than the external input reference level V1, the operational amplifier output control level V t Decrease; when the conversion level V0 equals the external input reference level V1, the operational amplifier output control level V t Unchanged; the control level V output of the operational amplifier remains unchanged. t Used to control the gain of a variable gain amplifier, control level V t As the gain is gradually increased, the power of the microwave signal output by the variable gain amplifier decreases uniformly; the control level V t As the gain is gradually reduced, the power of the microwave signal output by the variable gain amplifier increases uniformly.

2. The automatic power control circuit with constant temperature control function as described in claim 1, characterized in that, The constant temperature control circuit includes: a comparator U1A, an N-channel MOSFET Q1, a power resistor R5, an NTC resistor R6, and a proportional voltage divider resistor R10. The power resistor R5 generates heat when energized, which is used to heat the detector in the detection circuit. The resistance of the NTC resistor R6 changes with the temperature t of the detector in the detection circuit, causing the voltage across the NTC resistor R6 to change with temperature t. The resistance of the NTC resistor R6 is R6(t). The proportional voltage divider resistor R10 works in conjunction with the NTC resistor R6 to generate a temperature-divided voltage V+; V+ = 3.3V * R6(t) / (R6(t) + R10). The comparator U1A compares the temperature voltage divider V+ with the temperature threshold voltage V-: when the detector temperature t < the preset fixed temperature point, V+ > V-, and the comparator U1A outputs a high level; when the detector temperature t ≥ the preset fixed temperature point, V+ < V-, and the comparator U1A outputs 0V; the N-channel MOSFET Q1 controls the on / off state of the power resistor R5 for heating the detector, that is, when the comparator U1A outputs a high level, the N-channel MOSFET Q1 is turned on, and the power resistor R5 is energized to generate heat; when the comparator U1A outputs 0V, the N-channel MOSFET Q1 is turned off, and the power resistor R5 is de-energized and does not generate heat.

3. The automatic power control circuit with constant temperature control function as described in claim 2, characterized in that, The constant temperature control circuit also includes: proportional voltage divider resistors R4 and R7; the proportional voltage divider resistors R4 and R7 work together to generate the temperature threshold voltage threshold V-; V- = 3.3V * R4 / (R4 + R7).

4. An automatic power control circuit with constant temperature control function as described in claim 3, characterized in that, The constant temperature control circuit also includes: resistor R8 and capacitor C10; resistor R8 and capacitor C10 form a delay circuit for debouncing and adjusting response time.

5. An automatic power control circuit with constant temperature control function as described in claim 4, characterized in that, The constant temperature control circuit also includes: resistor R9, resistor R11, and capacitor C9; R9 is a current-limiting resistor; C9 is a decoupling capacitor; and R11 is a pull-down resistor.

6. An automatic power control circuit with constant temperature control function as described in claim 5, characterized in that, The connection relationship of the constant temperature control circuit is as follows: one end of NTC resistor R6 is connected to one end of proportional voltage divider resistor R4, the other end of NTC resistor R6 is connected to one end of proportional voltage divider resistor R10, and the other end of proportional voltage divider resistor R10 is connected to the 3.3V power supply; the common terminal of NTC resistor R6 and proportional voltage divider resistor R4 is grounded, the other end of proportional voltage divider resistor R4 is connected to one end of proportional voltage divider resistor R7, and the other end of proportional voltage divider resistor R7 is connected to the 3.3V power supply; the common terminal of NTC resistor R6 and proportional voltage divider resistor R10 is connected to port 3 of comparator U1A through resistor R9, and the common terminal of proportional voltage divider resistor R4 and proportional voltage divider resistor R7 is connected to port 4 of comparator U1A; port 5 of comparator U1A is connected to one end of capacitor C9, and the other end of capacitor C9 is grounded. The common terminal of capacitor C9 and the 5th port of comparator U1A is connected to a 3.3V power supply. The 1st port of comparator U1A is connected to the 1st port of N-channel MOSFET Q1 through resistor R8. One end of resistor R11 is connected to the common terminal of the 1st port of comparator U1A and resistor R8, and the other end of resistor R11 is connected to the 2nd port of comparator U1A. One end of capacitor C10 is connected to the common terminal of resistor R8 and the 1st port of N-channel MOSFET Q1. The other end of capacitor C10 is connected to the common terminal of resistor R11 and the 1st port of comparator U1A, and this end is grounded. The 2nd port of N-channel MOSFET Q1 is connected to the 12V power supply ground. The 3rd port of N-channel MOSFET Q1 is connected to one end of power resistor R5, and the other end of power resistor R5 is connected to the 12V power supply.

7. An automatic power control circuit with constant temperature control function as described in claim 2, characterized in that, The detection circuit and the temperature control circuit are arranged on the same circuit board. The detection circuit is located on the front of the circuit board and includes a detector, an adjustable attenuator, and a temperature sensor. The detector is used to convert the 0.1P1 power of the input microwave signal into a DC level value V0. The adjustable attenuator is used to adjust the power of the input microwave signal so that the detector is in a linear operating state. The temperature sensor is used to measure the temperature of the circuit board. The NTC resistor R6 of the temperature control circuit is located at the location of the detector. The other components of the temperature control circuit are located on the back of the circuit board.

8. An automatic power control circuit with constant temperature control function as described in claim 7, characterized in that, The power resistor R5 of the constant temperature control circuit is located in the center of the back of the circuit board. The heat dissipation surface area of ​​the power resistor R5 is 1 / 2 of the area of ​​the circuit board. When the power resistor R5 is powered on, it generates heat, which is conducted to the detector through the heat conduction holes on the circuit board to heat the detector.

9. An automatic power control circuit with constant temperature control function as described in claim 1, characterized in that, When the detector circuit converts the 0.1P1 power of the microwave signal into a DC level, the logarithm of the 0.1P1 power of the microwave signal is proportional to the converted level value V0.

10. An automatic power control circuit with constant temperature control function as described in claim 1, characterized in that, When the control level V output by the integrating circuit t When the voltage is 0V, the power of the microwave signal output by the variable gain amplifier is at its maximum.

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