Temperature control circuit of self-adaptive heating and cooling constant temperature crystal oscillator

Abstract

The invention discloses a temperature control circuit of a self-adaptive heating and cooling constant temperature crystal oscillator, which is characterized in that on the basis of a traditional thermosensitive bridge and a heating circuit, a switch driving mode of a driving circuit is changed into a linear mode, that is, a linear voltage comparison circuit is added, and the linear voltage comparison circuit not only has a linear amplification function, but also has a PID (Proportion Integration Differentiation) calculation function. When the thermo-sensitive bridge is unbalanced, the thermo-sensitive bridge generates a voltage signal difference related to the temperature, the voltage difference is linearly amplified through the linear voltage comparison circuit, and after PID calculation, a thermoelectric cooler TEC of the heating / cooling circuit is driven to heat or cool a circuit board where the thermo-sensitive bridge is located. The linear comparison circuit is used for regulating and controlling the voltage difference and then controlling the heating / cooling circuit, the problem that temperature control fails when the external environment temperature exceeds the set temperature can be effectively solved, control is not in an on state or an off state any more and is related to the amplitude of the voltage difference, and therefore the temperature control precision is improved, and the temperature control efficiency is improved. And the temperature overshoot phenomenon is well inhibited.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of ovenized crystal oscillator, more specifically, to a self-adaptive temperature control circuit for an ovenized crystal oscillator. BACKGROUND

[0002] The main function of a crystal oscillator is to provide a system time (frequency) reference or timing reference, which is in the position of "heart" in an electronic system. The core device of a crystal oscillator, a crystal resonator, has a frequency-temperature characteristic, that is, the output frequency of the crystal resonator is easily affected by the external environment temperature. In order to solve the problem that the frequency of the crystal oscillator changes due to the influence of the external environment temperature on the crystal resonator, there are two ways: one is to use a temperature compensation method to offset the frequency drift caused by temperature; the other is to use a temperature control circuit combined with an oven to make the crystal resonator work at a constant temperature set. The crystal oscillator realized by this method is called an ovenized crystal oscillator (abbreviated as ovenized crystal).

[0003] The temperature control circuit of the conventional ovenized crystal oscillator, such as the Chinese invention patent with the patent number CN114545998B granted on July 19, 2022, discloses a self-adaptive protection temperature control circuit for an ovenized crystal oscillator and an implementation method. As shown in the figure, Figure 1 The operational amplifier N300 in the drive circuit for driving the heating power tube Q201 in the temperature control circuit only exists in the two states of on and off, so that the heating power tube Q201 works at the maximum heating power set before the bridge reaches the balance after the circuit is powered on, which has the problems of low temperature control precision and easy temperature overshoot. In addition, the existing temperature control circuit can only realize the heating function, and when the external environment temperature exceeds the set temperature, the temperature control circuit will fail.

[0004] In addition, although the drive circuit in the temperature control circuit as shown in the figure Figure 1 has introduced proportion and integration, but lacks the differentiation link, which has a certain influence on the temperature control precision. SUMMARY

[0005] The present application aims to overcome the shortcomings of the prior art and provide a self-adaptive temperature control circuit for an ovenized crystal oscillator to improve the temperature control precision, stability and reliability, suppress the temperature overshoot phenomenon, and adaptively increase and decrease the temperature to avoid the failure of the temperature control circuit.

[0006] To achieve the above-mentioned application purpose, the self-adaptive temperature control circuit for an ovenized crystal oscillator comprises:

[0007] A thermosensitive bridge composed of the thermistor RT300 and the precision resistors R300, R301 and R302;

[0008] characterized in that it further comprises:

[0009] A linear voltage comparison circuit composed of the operational amplifier A300, the resistors R303, R304, R305 and R306 and the capacitors C300 and C301, the precision resistors R301 and R302 form the fixed arm of the thermosensitive bridge, the voltage VCC is divided at the tap and input to the inverting input terminal of the operational amplifier A300 through the resistor R303, at the same time, the precision resistor R300 and the thermistor RT300 with negative temperature coefficient form the dynamic arm of the thermosensitive bridge, the voltage VCC is divided at the tap and input to the non-inverting input terminal of the operational amplifier A300 through the resistor R306, the division is related to temperature, when the thermosensitive bridge is unbalanced, a voltage difference related to temperature is generated at the two taps of the thermosensitive bridge and input to the non-inverting input terminal and the inverting input terminal of the operational amplifier A300 in the voltage comparison circuit, at the same time, the inverting input terminal of the operational amplifier A300 is connected to the output terminal through the resistor R305, forming a linear amplification circuit, at the same time, the inverting input terminal of the operational amplifier A300 is also connected to the output terminal through the capacitor C301 and the resistor R304, the capacitor C300 is connected in parallel to the resistor R303, in this way, the resistor R305 as the feedback resistor realizes proportional control, the capacitor C301 and the resistor R304 in series with the capacitor C301 realize integral control, and the capacitor C300 realizes differential control, so that the linear voltage comparison circuit has proportional-integral-differential calculation function while being linearly amplified.

[0010] A heating / cooling circuit composed of the operational amplifier A301, the operational amplifier A302, the resistors R308, R309, R310, R311 and the thermoelectric cooler TEC, the non-inverting input terminal of the operational amplifier A301 is connected to the output terminal of the linear voltage comparison circuit, i.e. the output terminal of the operational amplifier A300 through the resistor R307, the resistor R308 is connected between the output terminal of the operational amplifier A301 and the inverting input terminal of the operational amplifier A302, the non-inverting input terminal of the operational amplifier A302 is connected to one end of the voltage dividing resistors R310 and R311, the other end of the voltage dividing resistor R310 is connected to the reference voltage VREF, the other end of the voltage dividing resistor R311 is connected to ground, the output terminal of the operational amplifier A302 is connected to the inverting input terminal of the operational amplifier A302 through the resistor R309, the thermoelectric cooler TEC is connected between the output terminal of the operational amplifier A301 and the output terminal of the operational amplifier A302, and the reference voltage VREF is connected to the power input terminals of the operational amplifier A301 and the operational amplifier A302 respectively.​

[0011] The object of the present application is achieved as follows.

[0012] The adaptive temperature control circuit of the oven-controlled crystal oscillator of the present application is based on the traditional thermistor bridge and heating circuit, and the switch driving mode of the driving circuit is changed to linear mode, i.e., a linear voltage comparison circuit is added. The linear voltage comparison circuit has not only linear amplification function but also PID calculation function. The target temperature is set by adjusting the resistance parameter of the fixed arm of the thermistor bridge, and the thermistor bridge outputs a voltage related to the real-time environmental temperature. When the thermistor bridge is unbalanced, the thermistor bridge will generate a voltage signal difference related to the temperature. The voltage difference is linearly amplified and PID calculated by the linear voltage comparison circuit, and then the thermoelectric cooler TEC of the heating / cooling circuit drives the circuit board where the thermistor bridge is located to be heated or cooled. At the same time, the thermistor senses the temperature change. When the temperature is lower than the set temperature point, the TEC realizes the heating function. When the temperature is higher than the set temperature point, the TEC realizes the cooling function. When the set temperature is reached, the thermistor bridge and the linear voltage comparison circuit output constant voltage, and the heating / cooling circuit reaches the balance state, thereby achieving the purpose of temperature control. The voltage difference is regulated by the linear voltage comparison circuit in the present application, and then the thermoelectric cooler TEC is controlled. The control is no longer in the on and off states, but is related to the amplitude of the voltage difference, so that the temperature control precision is improved, and the temperature overshoot phenomenon is well inhibited.

[0013] Compared with the existing temperature control technology, the present application has the following advantages:

[0014] 1) The operational amplifier in the linear voltage comparison circuit of the present application works in a linear amplification state rather than a traditional switch state, so that the overshoot is inhibited.

[0015] 2) The linear voltage comparison circuit of the present application adopts proportional-integral-derivative (PID) calculation, which is more conducive to precise temperature control.

[0016] 3) The present application uses a thermoelectric cooler as a core temperature control execution element to accurately regulate the working temperature of the oven-controlled crystal oscillator. When the temperature of the oven-controlled crystal oscillator exceeds the set threshold, the element can actively start the refrigeration function to cool it down, and completely gets rid of the dependence on the traditional passive heat dissipation method.

[0017] 4) The double operational amplifier push-pull output driving circuit structure used in the present application can not only significantly improve the current driving load capacity, but also effectively enhance the stability of the circuit in the process of long-time continuous operation, thereby providing protection for the continuous and reliable work of the temperature control circuit. BRIEF DESCRIPTION OF DRAWINGS

[0018] ​​Figure 1 is a circuit schematic diagram of a temperature control circuit of a conventional constant temperature crystal oscillator;

[0019] Figure 2 is a circuit schematic diagram of a temperature control circuit of a constant temperature crystal oscillator according to the present application;

[0020] Figure 3 is a temperature control curve diagram of a temperature control circuit of a constant temperature crystal oscillator according to the present application;

[0021] Figure 4 is a temperature control curve diagram of a temperature control circuit of a constant temperature crystal oscillator according to the present application. DETAILED DESCRIPTION

[0022] The specific embodiments of the present application will now be described with reference to the drawings. It should be noted, however, that the description herein is intended to be illustrative only and is not intended to limit the scope of the present application. As such, there is no intention that the application be limited to the specific form set forth in the description.

[0023] Figure 2 is a circuit schematic diagram of a temperature control circuit of a constant temperature crystal oscillator according to the present application;

[0024] In the present embodiment, as shown in Figure 2 the temperature control circuit of the constant temperature crystal oscillator according to the present application comprises a thermistor bridge 1 composed of a thermistor and precision resistors, a linear voltage comparison circuit 2 connected to the thermistor bridge 1, and a heating / cooling circuit 3 connected to the linear voltage comparison circuit 2.

[0025] The thermistor bridge 1 is composed of a thermistor RT300 and precision resistors R300, R301 and R302. The precision resistor R300 and the thermistor RT300 of negative temperature coefficient constitute a dynamic arm, and the precision resistors R301 and R302 constitute a fixed arm.

[0026] The linear voltage comparison circuit 2 is composed of an operational amplifier A300, resistors R303, R304, R305 and R306. The reference voltage VREF1 is divided at the tap of the fixed arm and input to the inverting input terminal of the operational amplifier A300 through the resistor R303, while the reference voltage VREF1 is divided at the tap of the dynamic arm and input to the non-inverting input terminal of the operational amplifier A300 through the resistor R306. The division is temperature-dependent, and when the thermistor bridge is unbalanced, a voltage difference dependent on temperature is generated at the two taps of the thermistor bridge The linear voltage comparison circuit is connected to the in-phase input and reverse input of the operational amplifier A300, and the reverse input of the operational amplifier A300 is connected to the output through the resistance R305, forming a linear amplification circuit, and the reverse input of the operational amplifier A300 is also connected to the output through the capacitor C301 and the resistance R304, and the capacitor C300 is connected in parallel to the resistance R303, so that the resistance R305 as a feedback resistance realizes proportional control, the capacitor C301 and the resistance R304 connected in series realize integral control, and the capacitor C300 realizes differential control, so that the linear voltage comparison circuit has proportional-integral-differential calculation function while being linearly amplified.

[0027] The output of the operational amplifier A300 is connected to the heating / cooling circuit 3 through the resistance R307.

[0028] The heating / cooling circuit 3 is composed of the operational amplifier A301, the operational amplifier A302, the resistance R308, the resistance R309, the resistance R310, the resistance R311, the thermoelectric cooler TEC and the reference voltage VREF, the in-phase input of the operational amplifier A301 is connected to the output of the linear voltage comparison circuit, i.e. the output of the operational amplifier A300 through the resistance R307, the resistance R308 is connected between the output of the operational amplifier A301 and the reverse input of the operational amplifier A302, the in-phase input of the operational amplifier A302 is connected to one end of the voltage dividing resistance R310 and the voltage dividing resistance R311, the other end of the voltage dividing resistance R310 is connected to the reference voltage VREF, the other end of the voltage dividing resistance R311 is connected to the ground, the output of the operational amplifier A302 is connected to the reverse input of the operational amplifier A302 through the resistance R309, the thermoelectric cooler TEC is connected between the output of the operational amplifier A301 and the output of the operational amplifier A302, and the reference voltage VREF is connected to the power supply input of the operational amplifier A301 and the operational amplifier A302.

[0029] The working principle of the temperature control circuit is that the target temperature is set by adjusting the resistance parameter of the fixed arm of the thermosensitive bridge, the thermosensitive bridge outputs a voltage related to the real-time environmental temperature, when the bridge is unbalanced, the thermosensitive bridge will generate a temperature-related voltage difference The voltage difference is amplified by the linear voltage comparison circuit 2 and subjected to proportional-integral-differential (PID) operation, and the output voltage of the PID operation is connected to the heating / cooling circuit 3 through the resistor R307, to drive the heating / cooling circuit 3 to control the thermoelectric cooler TEC to heat or cool the circuit board on which the bridge is located. At the same time, the thermistor senses the temperature change, and when the temperature is lower than the set temperature point, the TEC realizes the heating function, and when the temperature is higher than the set temperature point, the TEC realizes the cooling function. When the set temperature is reached, the thermistor bridge, the linear voltage comparison circuit and the PID circuit all output a constant voltage, and the heating / cooling circuit reaches a balanced state.

[0030] In the specific implementation process, the negative temperature coefficient thermistor RT300 is in the same temperature field as the crystal oscillator module that needs to be controlled at a constant temperature, and the temperature of the constant temperature crystal oscillator is monitored in real time. By adjusting the parameters of the precision resistors R300, R301 or R302 in the thermistor bridge (calibrated before shipment according to the temperature characteristics of different crystal resonators), the target constant temperature value can be accurately set.

[0031] When the circuit is initially powered on, the negative temperature coefficient thermistor RT300 has a high resistance value due to the low sensed temperature, which corresponds to a high voltage division value, so that the positive input end voltage of the operational amplifier A300 is higher than the reverse input end, and the output level is accordingly raised. The signal drives the operational amplifier A301 in the heating / cooling circuit through the resistor R307, so that the output level of the operational amplifier A301 is raised, and then the output level of the operational amplifier A302 is lowered, finally driving the thermoelectric cooler to pass through a reverse current and starting the heating process of the constant temperature crystal oscillator. The operational amplifier A300 should be a chopper amplifier to suppress low-frequency noise and reduce the offset voltage, and the operational amplifier A301 and the operational amplifier A302 should be the same type of linear operational amplifier to suppress common-mode interference.

[0032] When the heating continues and the temperature rises to the set value, the resistance value of the thermistor RT300 just makes the bridge reach a balanced state, and the operational amplifier A300 will control the working current of the heating / cooling circuit to maintain dynamic balance. If the actual temperature is lower than the balanced temperature point, the voltage at the positive input end of the operational amplifier A300 is raised, the output voltage is increased, the heating / cooling circuit generates a reverse voltage, the thermoelectric cooler passes through a reverse current, and the temperature of the constant temperature crystal oscillator is raised through heating; if the actual temperature is higher than the balanced temperature point, the voltage at the same phase input end of the operational amplifier A300 is lower than that at the reverse input end, the operational amplifier A300 outputs a negative voltage, which promotes the heating / cooling circuit to generate a forward voltage, the thermoelectric cooler TEC passes through a forward current, and the temperature of the constant temperature crystal oscillator is lowered through cooling.

[0033] Resistors R303, R304, and R305, together with capacitors C300 and C301, constitute a proportional-integral-derivative (PID) control circuit. By adjusting their resistance and capacitance parameters, the system response speed can be improved, ensuring that the temperature control circuit responds quickly to the temperature changes of the constant temperature crystal oscillator, reducing steady-state temperature error, and effectively suppressing overshoot and oscillation phenomena.

[0034] Operational amplifiers A301 and A302 form a push-pull power drive circuit, which converts the output signal of the preceding voltage comparator circuit into a two-terminal signal, ensuring that the drive voltage can be positive or negative, thereby controlling the thermoelectric cooler (TEC) to cool or heat. At the same time, this structure also provides stronger current drive capability, ensuring long-term operational reliability.

[0035] Figure 3 This is a temperature control curve of the adaptive heating and cooling constant temperature crystal oscillator high-precision temperature control circuit of the present invention.

[0036] In this embodiment, as Figure 3 As shown, the overcharge temperature was 12°C, and the set temperature was reached in 48.63 seconds, after which it stabilized with almost zero fluctuation. This indicates that the present invention has high temperature control accuracy and strong stability, and effectively suppresses the overcharge phenomenon.

[0037] Figure 4 This is a cooling temperature control curve of the high-precision temperature control circuit of the adaptive heating and cooling constant temperature crystal oscillator of the present invention.

[0038] In this embodiment, as Figure 4 As shown, the overcharge temperature was 5°C, and the set temperature was reached in 37.14 seconds, after which it stabilized with almost zero fluctuation. This indicates that the present invention has high temperature control accuracy and strong stability, and effectively suppresses the overcharge phenomenon.

[0039] Although the illustrative specific embodiments of the present invention have been described above to enable those skilled in the art to understand the invention, it should be understood that the invention is not limited to the scope of the specific embodiments. For those skilled in the art, various changes are obvious as long as they are within the spirit and scope of the invention as defined and determined by the appended claims, and all inventions utilizing the concept of the present invention are protected.

Claims

1. A self-adaptive temperature control circuit for a temperature-controlled crystal oscillator, comprising: a thermistor bridge composed of a thermistor RT300, a precision resistor R300, a precision resistor R301, and a precision resistor R302; and characterized in that further comprising: a heating / cooling circuit composed of an operational amplifier A301, an operational amplifier A302, a resistor R308, a resistor R309, a resistor R310, a resistor R311, a thermoelectric cooler TEC, and a reference voltage VREF, wherein the non-inverting input terminal of the operational amplifier A301 is connected to the output terminal of a linear voltage comparator, i.e., the output terminal of an operational amplifier A300, through a resistor R307, the resistor R308 is connected between the output terminal of the operational amplifier A301 and the inverting input terminal of the operational amplifier A302, the non-inverting input terminal of the operational amplifier A302 is connected to one end of the resistor R310 and the resistor R311, the other end of the resistor R310 is connected to the reference voltage VREF, the other end of the resistor R311 is connected to ground, the output terminal of the operational amplifier A302 is connected to the inverting input terminal of the operational amplifier A302 through the resistor R309, the thermoelectric cooler TEC is connected between the output terminal of the operational amplifier A301 and the output terminal of the operational amplifier A302, and the reference voltage VREF is connected to the power supply input terminals of the operational amplifier A301 and the operational amplifier A302. The negative temperature coefficient thermistor RT300 is in the same temperature field as a crystal oscillator module that needs to be controlled in temperature, and monitors the temperature of the temperature-controlled crystal oscillator in real time. The operational amplifier A300 is a chopper amplifier, and the operational amplifier A301 and the operational amplifier A302 are linear operational amplifiers of the same type. The linear voltage comparison circuit consists of operational amplifier A300, resistance R303, resistance R304, resistance R305, resistance R306, and capacitor C300, capacitor C301. Precision resistance R301 and precision resistance R302 form the fixed arm of the thermosensitive bridge, which divides the voltage VCC at the tap and inputs the voltage to the inverting input terminal of operational amplifier A300 through resistance R303. At the same time, precision resistance R300 and negative temperature coefficient thermosensitive resistance RT300 form the dynamic arm of the thermosensitive bridge, which divides the voltage VCC at the tap and inputs the voltage to the non-inverting input terminal of operational amplifier A300 through resistance R306. The voltage difference at the two taps of the thermosensitive bridge is related to temperature when the thermosensitive bridge is unbalanced The non-inverting input terminal and the inverting input terminal of operational amplifier A300 in the voltage comparison circuit are connected to the voltage difference at the two taps of the thermosensitive bridge, at the same time, the inverting input terminal of operational amplifier A300 is connected to the output terminal through resistance R305, forming a linear amplification circuit, and the inverting input terminal of operational amplifier A300 is also connected to the output terminal through capacitor C301 and resistance R304. Capacitor C300 is connected in parallel to resistance R303. In this way, resistance R305 as the feedback resistance realizes proportional control, capacitor C301 and resistance R304 in series realize integral control, and capacitor C300 realizes derivative control, so that the linear voltage comparison circuit has proportional-integral-derivative calculation function while linearly amplifying. ​ 2. The self-adapting temperature control circuit for oven-controlled crystal oscillator with lift-up according to claim 1, wherein, ​ 3. The self-adapting temperature control circuit for an oven-controlled crystal oscillator according to claim 1, wherein, ​

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