A temperature control circuit for a constant temperature crystal oscillator and a constant temperature crystal oscillator

Abstract

The present invention relates to the technical field of oscillators, and provides a temperature control circuit for a constant temperature crystal oscillator and a constant temperature crystal oscillator. The temperature control circuit includes an operational amplifier adjustment circuit, a temperature control element and a sampling comparison circuit. The temperature control element includes a power tube Q1 and a fixed resistor R4. The output end of the operational amplifier adjustment circuit is connected to the base of the power tube Q1, the emitter of the power tube Q1 is connected to one end of the fixed resistor R4, the other end of the fixed resistor R4 is grounded, and the collector of the power tube Q1 serves as a voltage input end. The present invention adds a sampling comparison circuit to the temperature control circuit to realize that when the output voltage of the emitter of the power tube Q1 is different from the preset voltage, the sampling comparison circuit can timely correct the input voltage of the base of the power tube Q1, so that the constant temperature crystal oscillator has a more stable and accurate temperature characteristic.

Description

Technical Field

[0001] The present invention relates to the technical field of oscillators, and in particular to a temperature control circuit for a constant temperature crystal oscillator and a constant temperature crystal oscillator. Background Art

[0002] The constant temperature crystal oscillator is also called the constant temperature controlled crystal oscillator, abbreviated as constant temperature crystal oscillator. It is widely used in power, communications, satellite navigation, military radar and other fields because of its advantages such as highest stability, lowest aging level, and optimal phase noise level.

[0003] Existing constant temperature crystal oscillators are usually composed of structures such as a crystal resonator, an oscillation circuit, a voltage stabilization circuit and a temperature control circuit. The crystal resonator is placed in a specific constant temperature bath of the constant temperature crystal oscillator. The temperature of the constant temperature bath is controlled by the temperature control circuit to control the temperature of the crystal resonator within a constant range, thereby ensuring that the constant temperature crystal oscillator has a stable output frequency.

[0004] Conventional temperature control circuits for constant temperature crystal oscillators use a single-stage op amp PID temperature control mode to control the temperature of the constant temperature bath. Such temperature control circuits are composed of op amp adjustment circuits and power tubes. The thermistor in the op amp adjustment circuit senses the temperature of the constant temperature bath and outputs different input voltages to the power tube through a thermistor bridge to control the output power of the power tube set in the constant temperature bath. The temperature of the constant temperature bath is then adjusted through the power tube to ensure that the temperature of the constant temperature bath is relatively constant. However, due to the discreteness and thermal hysteresis of the thermistor itself, it can only roughly control the temperature of the constant temperature bath, resulting in poor temperature control effect and unstable temperature characteristics of the constant temperature crystal oscillator. Summary of the invention

[0005] The first object of the present invention is to provide a temperature control circuit for a constant temperature crystal oscillator, which is used to solve the technical problems that the temperature control effect of the temperature control circuit of the existing constant temperature crystal oscillator is poor and the temperature characteristics of the constant temperature crystal oscillator are unstable.

[0006] The second object of the present invention is to provide a constant temperature crystal oscillator to improve the temperature control accuracy of the constant temperature crystal oscillator and improve the temperature characteristics of the constant temperature crystal oscillator.

[0007] The purpose of the present invention is achieved through the following technical solutions:

[0008] On the one hand, the present invention provides a temperature control circuit, including an operational amplifier adjustment circuit, a temperature control element and a sampling comparison circuit, the temperature control element including a power tube Q1 and a fixed resistor R4, the output end of the operational amplifier adjustment circuit is connected to the base of the power tube Q1, the emitter of the power tube Q1 is connected to one end of the fixed resistor R4, the other end of the fixed resistor R4 is grounded, and the collector of the power tube Q1 serves as a voltage input end;

[0009] The sampling and comparing circuit includes a secondary operational amplifier OPA2, a MOS tube M1, a fixed resistor R3, a fixed resistor R5, a fixed resistor R6, a fixed resistor R7 and an adjustable resistor RR2;

[0010] One end of the fixed resistor R5 is connected to the emitter of the power tube Q1, and the other end thereof is respectively connected to one end of the fixed resistor R6 and the non-inverting input end of the secondary operational amplifier OPA2; the other end of the fixed resistor R6 is connected to the collector of the power tube Q1;

[0011] One end of the adjustable resistor RR2 is connected to one end of the fixed resistor R7 and the inverting input end of the secondary operational amplifier OPA2, and the other end of the fixed resistor R7 is grounded; the resistance value of the adjustable resistor RR2 is 1k-25kohm;

[0012] The output end of the secondary operational amplifier OPA2 is connected to one end of the fixed resistor R3, the other end of the fixed resistor R3 is connected to the G pole of the MOS tube M1, the S pole of the MOS tube M1 is grounded, and the D pole of the MOS tube M1 is connected to the base of the power tube Q1.

[0013] Optionally, the operational amplifier adjustment circuit includes a first-stage operational amplifier OPA1, a fixed resistor R1, a fixed resistor R2, an adjustable resistor RR1 and a thermistor Rt;

[0014] One end of the fixed resistor R1 is respectively connected to one end of the fixed resistor R2 and the inverting input end of the first-stage operational amplifier OPA1, and the other end of the fixed resistor R2 is grounded;

[0015] One end of the adjustable resistor RR1 is connected to one end of the thermistor Rt and the non-inverting input end of the first-stage operational amplifier OPA1, the other end of the adjustable resistor RR1 is connected to the other end of the fixed resistor R1, and the other end of the thermistor Rt is grounded;

[0016] The output end of the first-stage operational amplifier OPA1 is connected to the base of the power tube Q1.

[0017] Furthermore, the operational amplifier adjustment circuit also includes an adjustment capacitor C1 and a fixed resistor R8, one end of the adjustment capacitor C1 is connected to the inverting input terminal of the first-stage operational amplifier OPA1, the other end of the adjustment capacitor C1 is connected to one end of the fixed resistor R8, and the other end of the fixed resistor R8 is connected to the output terminal of the first-stage operational amplifier OPA1.

[0018] Optionally, the power tube Q1 is an NPN tube.

[0019] In another aspect, the present invention provides a constant temperature crystal oscillator, comprising:

[0020] A crystal resonator is placed in a constant temperature bath;

[0021] A control chip, comprising a processor and the temperature control circuit as described above, wherein the temperature control circuit is electrically connected to the processor;

[0022] Among them, the operational amplifier regulation circuit is used to output a corresponding input voltage to the base of the power tube Q1 according to the temperature of the constant temperature bath, and the power tube Q1 is arranged in the constant temperature bath to heat the constant temperature bath; the sampling and comparison circuit is used to collect the output voltage of the emitter of the power tube Q1 and compare it with the preset voltage; the processor can generate a control voltage signal according to the comparison result of the sampling and comparison circuit to control the sampling and comparison circuit to correct the input voltage of the base of the power tube Q1.

[0023] Optionally, the control chip also includes a voltage stabilizing circuit and an oscillation circuit, the voltage stabilizing circuit is electrically connected to the temperature control circuit and the oscillation circuit respectively, the oscillation circuit is electrically connected to the crystal resonator, and the oscillation circuit is electrically connected to the processor.

[0024] Optionally, the control chip also includes a frequency temperature compensation circuit, and the frequency temperature compensation circuit is electrically connected to the processor, the oscillation circuit and the voltage stabilization circuit respectively.

[0025] Optionally, the control chip also includes a FLASH memory, and the FLASH memory is electrically connected to the processor.

[0026] The technical solution of the embodiment of the present invention has at least the following advantages and beneficial effects:

[0027] The present invention adds a sampling and comparison circuit in the temperature control circuit. During the entire temperature control process, the sampling and comparison circuit can collect the output voltage of the emitter of the power tube Q1 in real time, and compare the output voltage of the emitter of the power tube Q1 with a preset voltage, so as to monitor a small change in the output voltage of the emitter of the power tube Q1. When there is a difference between the output voltage of the emitter of the power tube Q1 and the preset voltage, the sampling and comparison circuit can timely correct the input voltage of the base of the power tube Q1, so that the input voltage of the power tube Q1 meets the preset condition, and the output power of the power tube Q1 meets the preset requirement, thereby achieving more accurate control of the output power of the power tube Q1. Compared with the PID temperature control mode of the existing single-stage operational amplifier, the temperature regulation effect of the thermostatic bath is better, thereby making the thermostatic crystal oscillator have a more stable and accurate temperature characteristic. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments are briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without creative work.

[0029] Figure 1 A circuit schematic diagram of a temperature control circuit provided in Example 1 of the present invention;

[0030] Figure 2 The electrical principle block diagram of the oven-controlled crystal oscillator provided in Embodiment 2 of the present invention;

[0031] Figure 3 A circuit schematic diagram of an oscillator circuit provided in Embodiment 2 of the present invention;

[0032] Figure 4 A circuit schematic diagram of the basic structure of an oscillator circuit and a linear feedback model provided in Embodiment 2 of the present invention;

[0033] Figure 5 This is a circuit schematic diagram of a frequency temperature compensation circuit provided in Example 2 of the present invention.

[0034] Icons: 1-control chip, 10-temperature control circuit, 101-op amp adjustment circuit, 102-temperature control element, 103-sampling comparison circuit, 20-processor, 30-voltage stabilization circuit, 40-oscillation circuit, 50-frequency temperature compensation circuit, 60-FLASH memory, 2-crystal resonator. DETAILED DESCRIPTION

[0035] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Generally, the components of the embodiments of the present invention described and shown in the drawings here can be arranged and designed in various different configurations.

[0036] It should be noted that similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, further definition and explanation thereof is not required in subsequent drawings.

[0037] In the description of the present invention, it is also necessary to explain that, unless otherwise clearly specified and limited, the terms "set", "install", "connect", and "connect" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0038] Example 1

[0039] Considering that the existing constant temperature crystal oscillator usually uses the PID temperature control mode of a single-stage operational amplifier to adjust the temperature of the constant temperature bath, this temperature control method is affected by the characteristics of the thermistor itself, and can only roughly control the temperature of the constant temperature bath, and the temperature control effect is poor. To this end, this embodiment provides a temperature control circuit to solve the technical problems existing in the temperature control circuit in the prior art and improve the temperature control accuracy of the constant temperature bath.

[0040] Please refer to Figure 1 The temperature control circuit 10 includes an operational amplifier adjustment circuit 101, a temperature control element 102 and a sampling comparison circuit 103. The temperature control element 102 includes a power tube Q1 and a fixed resistor R4. The power tube Q1 can be, but is not limited to, an NPN tube. The emitter of the power tube Q1 is connected to one end of the fixed resistor R4, the other end of the fixed resistor R4 is grounded, and the collector of the power tube Q1 serves as a voltage input terminal. It should be noted that in order to adjust the temperature of the thermostatic bath through the power tube Q1, the power tube Q1 needs to be placed outside the thermostatic bath.

[0041] The output end of the operational amplifier adjustment circuit 101 is connected to the base of the power tube Q1, so as to output the corresponding input voltage to the base of the power tube Q1 through the operational amplifier adjustment circuit 101, so as to control the output power of the power tube Q1. Specifically, the operational amplifier adjustment circuit 101 includes a first-stage operational amplifier OPA1, a fixed resistor R1, a fixed resistor R2, an adjustable resistor RR1, a thermistor Rt, an adjustment capacitor C1 and a fixed resistor R8.

[0042] Among them, continue to refer to Figure 1One end of the fixed resistor R1 is respectively connected to one end of the fixed resistor R2 and the inverting input end of the first-stage operational amplifier OPA1, the other end of the fixed resistor R2 is grounded, and the other end of the fixed resistor R1 serves as a voltage input end; one end of the adjustable resistor RR1 is respectively connected to one end of the thermistor Rt and the non-inverting input end of the first-stage operational amplifier OPA1, the other end of the adjustable resistor RR1 is connected to the other end of the fixed resistor R1 (that is, the voltage input end of the fixed resistor R1), and the other end of the thermistor Rt is grounded; the output end of the first-stage operational amplifier OPA1 is connected to the base of the power tube Q1.

[0043] At this time, the fixed resistor R1, the fixed resistor R2, the adjustable resistor RR1 and the thermistor Rt together form a thermistor bridge to sense the temperature in the thermostat through the thermistor Rt, that is, in actual implementation, the thermistor Rt needs to be placed outside the thermostat, and the resistance of the thermistor Rt will change according to the change of the temperature of the thermostat, and then the corresponding input voltage is output to the power tube Q1 through the thermistor bridge to control the output power of the power tube Q1 to adjust the temperature of the thermostat. At the same time, considering that the temperature inflection point of the crystal is different, the temperature inflection point of the thermostat can be set by using the adjustable resistor RR1. For example, the resistance of the adjustable resistor RR1 in this embodiment is 3k-16kohm.

[0044] The adjusting capacitor C1 and the fixed resistor R8 are arranged between the inverting input terminal and the output terminal of the first-stage operational amplifier OPA1. At this time, one end of the adjusting capacitor C1 is connected to the inverting input terminal of the first-stage operational amplifier OPA1, the other end of the adjusting capacitor C1 is connected to one end of the fixed resistor R8, and the other end of the fixed resistor R8 is connected to the output terminal of the first-stage operational amplifier OPA1, so as to realize proportional-integral-differential feedback adjustment of the temperature control circuit 10 through the adjusting capacitor C1 and the fixed resistor R8, thereby ensuring that the temperature control circuit 10 has good control performance.

[0045] In order to achieve further precise control of the input voltage of the power tube Q1 and improve the temperature control accuracy of the constant temperature bath, the temperature control circuit 10 of this embodiment is newly added with a sampling and comparison circuit 103, so as to collect the output voltage of the emitter of the power tube Q1 through the sampling and comparison circuit 103, and compare the output voltage with the preset voltage. At this time, the sampling and comparison circuit 103 can correct the input voltage at the base of the power tube Q1 according to the comparison result, thereby achieving more precise control of the output power of the power tube Q1 and improving the temperature control accuracy.

[0046] Specifically, the sampling and comparing circuit 103 includes a secondary operational amplifier OPA2, a MOS tube M1, a fixed resistor R3, a fixed resistor R5, a fixed resistor R6, a fixed resistor R7 and an adjustable resistor RR2. Figure 1, one end of the fixed resistor R5 is connected to the emitter of the power tube Q1, and the other end of the fixed resistor R5 is respectively connected to one end of the fixed resistor R6 and the non-inverting input end of the secondary operational amplifier OPA2; the other end of the fixed resistor R6 is connected to the collector of the power tube Q1; the adjustable resistor RR2 is used to control the maximum current of the constant temperature crystal oscillator. For example, the resistance of the adjustable resistor RR2 is 1k-25kohm. At this time, one end of the adjustable resistor RR2 is respectively connected to one end of the fixed resistor R7 and the inverting input end of the secondary operational amplifier OPA2, the other end of the adjustable resistor RR2 is used as the voltage input end, and the other end of the fixed resistor R7 is grounded; the output end of the secondary operational amplifier OPA2 is connected to one end of the fixed resistor R3, the other end of the fixed resistor R3 is connected to the G pole of the MOS tube M1, the S pole of the MOS tube M1 is grounded, and the D pole of the MOS tube M1 is connected to the base of the power tube Q1.

[0047] The feedback circuit formed by the secondary operational amplifier OPA2 and the MOS tube M1 can collect the output voltage of the emitter of the power tube Q1 in real time, and compare the output voltage of the emitter of the power tube Q1 with the preset voltage, so as to monitor the small change of the output voltage of the emitter of the power tube Q1. When there is a difference between the output voltage of the emitter of the power tube Q1 and the preset voltage, the sampling and comparison circuit 103 can timely correct the input voltage of the base of the power tube Q1, so that the input voltage of the power tube Q1 meets the preset conditions, and ensures that the output power of the power tube Q1 meets the preset requirements, thereby achieving more accurate control of the output power of the power tube Q1, thereby improving the temperature control accuracy of the constant temperature bath.

[0048] It can be seen that the temperature control circuit 10 provided in this embodiment realizes the temperature adjustment of the constant temperature bath by the PID temperature control mode of the two-stage operational amplifier by adding a sampling and comparison circuit 103. Compared with the PID temperature control mode of the existing single-stage operational amplifier, the temperature adjustment effect of the constant temperature bath is better, thereby making the constant temperature crystal oscillator have a more stable and accurate temperature characteristic.

[0049] Example 2

[0050] On the basis of Embodiment 1, this embodiment provides a constant temperature crystal oscillator, which comprises a crystal resonator 2 and a control chip 1. The crystal resonator 2 is arranged in a constant temperature bath of a constant temperature crystal oscillator.

[0051] Please refer to Figure 2The crystal resonator 2 adopts an SMD packaged crystal resonator, and the control chip 1 includes a processor 20, a voltage stabilizing circuit 30, an oscillation circuit 40, a frequency temperature compensation circuit 50, a FLASH memory 60 and the temperature control circuit 10 as described in the above embodiment 1. By integrating the voltage stabilizing circuit 30, the oscillation circuit 40, the frequency temperature compensation circuit 50 and the temperature control circuit 10 into one control chip 1, the volume of the constant temperature crystal oscillator can be effectively reduced compared to a constant temperature crystal oscillator composed of discrete devices.

[0052] It should be noted that, in the temperature control circuit 10 described in the above embodiment 1, the adjustment capacitor C1 and the adjustment resistor R8 are both externally disposed outside the control chip 1, and the thermistor Rt is externally disposed inside the thermostatic bath and is arranged near the crystal resonator 2, so that the temperature inside the thermostatic bath can be sensed by the thermistor Rt and the accuracy of the temperature sensed by the thermistor Rt can be improved. The temperature control element 102 is also externally disposed outside the control chip 1, wherein the power tube Q1 is arranged inside the thermostatic bath, so that the power tube Q1 can be used to heat the thermostatic bath, thereby adjusting the temperature of the thermostatic bath.

[0053] Specifically, the voltage stabilizing circuit 30 is electrically connected to the temperature control circuit 10, the oscillation circuit 40 and the frequency temperature compensation circuit 50, respectively, so as to provide a stable output voltage to the temperature control circuit 10, the oscillation circuit 40 and the frequency temperature compensation circuit 50 through the voltage stabilizing circuit 30; the oscillation circuit 40 is electrically connected to the crystal resonator 2 to generate an oscillation signal, the oscillation circuit 40 is electrically connected to the processor 20, the frequency temperature compensation circuit 50 is electrically connected to the processor 20 and the oscillation circuit 40, respectively, the FLASH memory 60 is electrically connected to the processor 20 to store various parameter information of the control chip 1 through the FLASH memory 60, and the temperature control circuit 10 is electrically connected to the processor 20.

[0054] Among them, the operational amplifier adjustment circuit 101 of the temperature control circuit 10 is used to output a corresponding input voltage to the base of the power tube Q1 according to the temperature of the constant temperature bath, and the power tube Q1 is arranged in the constant temperature bath to heat the constant temperature bath; the sampling and comparison circuit 103 is used to collect the output voltage of the emitter of the power tube Q1 and compare it with a preset voltage, and the processor 20 can generate a control voltage signal according to the comparison result of the sampling and comparison circuit 103 to adjust the input voltage of the base of the power tube Q1 through the sampling and comparison circuit 103.

[0055] In this embodiment, the oscillation circuit 40 adopts a Colpitts oscillation circuit, and its circuit schematic diagram is shown in FIG. Figure 3 As shown, the basic structure of the Colpitts oscillator circuit is as follows Figure 4 As shown in (a), the linear feedback model of the Colpitts oscillator circuit is as follows Figure 4 As shown in (b), Figure 4The loop gain expression of the oscillator circuit 40 is obtained as follows:

[0056]

[0057] Where L is the inductance, R P is the parallel loss resistance, g m is the transistor transconductance.

[0058] According to the phase condition in Expression 1, the ratio of the real part to the imaginary part of the numerator is equal to the ratio of the real part to the imaginary part of the denominator, see Expression 2:

[0059]

[0060] At this time, the oscillation frequency ω is obtained osc for:

[0061]

[0062] Where Q represents the resonant cavity Q value, satisfying R p =ωLQ. Finally, according to Expression 3, the starting condition of the constant temperature crystal oscillator is:

[0063]

[0064] During actual operation, the processor 20 sends a corresponding oscillation control signal to the oscillation circuit 40 , so that the oscillation circuit 40 can generate and output an oscillation signal.

[0065] In order to more clearly and intuitively understand the temperature control principle of the constant temperature crystal oscillator provided in this embodiment, the temperature control process of the constant temperature crystal oscillator will be further explained below.

[0066] In the initial stage, the temperature of the thermostatic bath has not yet reached the preset control temperature. After power is turned on, the thermistor bridge has a large unbalanced output voltage. At this time, the operational amplifier regulation circuit 101 is in the maximum heating power state, that is, the current flowing through the power tube Q1 is the largest, so that the power tube Q1 is used to heat the thermostatic bath, so that the temperature of the thermostatic bath quickly reaches the preset control temperature.

[0067] When the temperature in the thermostatic bath reaches the preset control temperature, the thermistor bridge maintains a certain balanced output voltage. At this time, the operational amplifier adjustment circuit 101 is in the minimum heating power state, that is, the current flowing through the power tube Q1 is minimum, and the heat generated by the power tube Q1 is equal to the heat loss of the thermostatic bath under certain external conditions, thereby maintaining the internal temperature of the thermostatic bath relatively constant.

[0068] When the temperature inside the thermostatic bath changes due to the influence of the external environment, the resistance value of the thermistor Rt changes accordingly, thereby changing the relative balanced output voltage of the thermistor bridge to adjust the input voltage of the base of the power tube Q1, that is, to adjust the current flowing through the power tube Q1, so as to correct the change in the temperature inside the thermostatic bath.

[0069] At the same time, during the entire temperature control process, the sampling and comparison circuit 103 can collect the output voltage flowing through the emitter of the power tube Q1 in real time, and compare the output voltage with the preset voltage. If there is a difference between the output voltage and the preset voltage, at this time, the processor 20 can generate a control voltage signal according to the comparison result of the sampling and comparison circuit 103 to control the sampling and comparison circuit 103 to correct the input voltage of the base of the power tube Q1, thereby realizing the correction of the output power of the power tube Q1 and improving the temperature control accuracy of the constant temperature bath.

[0070] In addition, the control chip 1 of the constant temperature crystal oscillator of this embodiment is also equipped with a frequency temperature compensation circuit 50. At this time, the temperature sensor in the frequency temperature compensation circuit 50 is externally placed close to the crystal resonator 2 to monitor the temperature of the crystal resonator 2. At this time, the frequency temperature compensation circuit 50 can output a voltage to the voltage control terminal of the constant temperature crystal oscillator according to the temperature information detected by the temperature sensor to compensate for the frequency of the constant temperature crystal oscillator, thereby realizing the high-precision, high-frequency temperature characteristics of the constant temperature crystal oscillator.

[0071] Specifically, the circuit schematic diagram of the frequency temperature compensation circuit 50 is as follows: Figure 5 As shown, at this time, the frequency temperature compensation circuit 50 adjusts the amplification factor according to the linear range and center voltage of the varactor diode, that is, the slope of the linear first-order function; the compensation voltage slope can be adjusted by the adjustable resistor RR3, so as to meet the frequency temperature compensation of crystals with different temperature inflection points. For example, the resistance value of the adjustable resistor RR3 is 5k-50kohm.

[0072] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A temperature control circuit for a constant temperature crystal oscillator, characterized in that: It includes an operational amplifier regulation circuit, a temperature control element and a sampling comparison circuit. The temperature control element includes a power tube Q1 and a fixed resistor R4. The output end of the operational amplifier regulation circuit is connected to the base of the power tube Q1. The emitter of the power tube Q1 is connected to one end of the fixed resistor R4. The other end of the fixed resistor R4 is grounded. The collector of the power tube Q1 serves as a voltage input end. The sampling and comparing circuit includes a secondary operational amplifier OPA2, a MOS tube M1, a fixed resistor R3, a fixed resistor R5, a fixed resistor R6, a fixed resistor R7 and an adjustable resistor RR2; One end of the fixed resistor R5 is connected to the emitter of the power tube Q1, and the other end thereof is respectively connected to one end of the fixed resistor R6 and the non-inverting input end of the secondary operational amplifier OPA2; the other end of the fixed resistor R6 is connected to the collector of the power tube Q1; One end of the adjustable resistor RR2 is connected to one end of the fixed resistor R7 and the inverting input end of the secondary operational amplifier OPA2, and the other end of the fixed resistor R7 is grounded; the resistance value of the adjustable resistor RR2 is 1k-25kohm; The output end of the secondary operational amplifier OPA2 is connected to one end of the fixed resistor R3, the other end of the fixed resistor R3 is connected to the G pole of the MOS tube M1, the S pole of the MOS tube M1 is grounded, and the D pole of the MOS tube M1 is connected to the base of the power tube Q1.

2. The temperature control circuit for a constant temperature crystal oscillator according to claim 1, characterized in that: The operational amplifier adjustment circuit includes a first-stage operational amplifier OPA1, a fixed resistor R1, a fixed resistor R2, an adjustable resistor RR1 and a thermistor Rt; One end of the fixed resistor R1 is respectively connected to one end of the fixed resistor R2 and the inverting input end of the first-stage operational amplifier OPA1, and the other end of the fixed resistor R2 is grounded; One end of the adjustable resistor RR1 is connected to one end of the thermistor Rt and the non-inverting input end of the first-stage operational amplifier OPA1, the other end of the adjustable resistor RR1 is connected to the other end of the fixed resistor R1, and the other end of the thermistor Rt is grounded; The output end of the first-stage operational amplifier OPA1 is connected to the base of the power tube Q1.

3. The temperature control circuit for a constant temperature crystal oscillator according to claim 2, characterized in that: The operational amplifier adjustment circuit also includes an adjustment capacitor C1 and a fixed resistor R8. One end of the adjustment capacitor C1 is connected to the inverting input end of the first-stage operational amplifier OPA1, the other end of the adjustment capacitor C1 is connected to one end of the fixed resistor R8, and the other end of the fixed resistor R8 is connected to the output end of the first-stage operational amplifier OPA1.

4. The temperature control circuit for a constant temperature crystal oscillator according to claim 1, characterized in that: The power tube Q1 is an NPN tube.

5. A constant temperature crystal oscillator, characterized in that: include: A crystal resonator is placed in a constant temperature bath; A control chip, comprising a processor and a temperature control circuit as claimed in any one of claims 1 to 4, wherein the temperature control circuit is electrically connected to the processor; Among them, the operational amplifier regulation circuit is used to output a corresponding input voltage to the base of the power tube Q1 according to the temperature of the constant temperature bath, and the power tube Q1 is arranged in the constant temperature bath to heat the constant temperature bath; the sampling and comparison circuit is used to collect the output voltage of the emitter of the power tube Q1 and compare it with the preset voltage; the processor can generate a control voltage signal according to the comparison result of the sampling and comparison circuit to control the sampling and comparison circuit to correct the input voltage of the base of the power tube Q1.

6. The oven controlled crystal oscillator according to claim 5, characterized in that: The control chip also includes a voltage stabilizing circuit and an oscillating circuit. The voltage stabilizing circuit is electrically connected to the temperature control circuit and the oscillating circuit respectively. The oscillating circuit is electrically connected to the crystal resonator, and the oscillating circuit is electrically connected to the processor.

7. The oven-controlled crystal oscillator according to claim 5, characterized in that: The control chip also includes a frequency temperature compensation circuit, which is electrically connected to the processor, the oscillation circuit and the voltage stabilization circuit respectively.

8. The oven controlled crystal oscillator according to claim 5, characterized in that: The control chip also includes a FLASH memory, which is electrically connected to the processor.

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