JP2018050351A - Temperature control circuit for crystal oscillator with thermostatic chamber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a temperature control circuit capable of achieving a stable output frequency by suppressing an adverse effect of fluctuations in a power supply voltage for stable temperature control.SOLUTION: The temperature control circuit is configured so that an operational amplifier 10 outputs a difference between a reference voltage input into a plus terminal and a voltage corresponding to a temperature from a thermistor input into a minus terminal and so that a PNP type power transistor Tr1 inputs an output from the operational amplifier 10 into a base and to control an electric current of a heater resistor connected with an emitter, and includes a bridge resistor circuit whose one end is connected with a power supply voltage and the other end is grounded and in which a part of the power supply voltage is added to a reference voltage input into the plus terminal of the operational amplifier, thereby maintaining a voltage between the base and the emitter of the PNP type power transistor Tr1 constant even if the power supply voltage fluctuates.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a temperature control circuit of a crystal oscillator with a thermostatic bath, and more particularly to a temperature control circuit capable of stabilizing the output frequency by suppressing the influence of fluctuations in power supply voltage and performing stable temperature control.

[Description of Prior Art: FIG. 3]
The Oven Controlled Crystal Oscillator (OCXO) contains an oscillation element such as a crystal resonator and a peripheral circuit such as a temperature control circuit in the thermostat, and keeps the temperature inside the thermostat constant. As a result, the influence of an external temperature change is suppressed and the output frequency is stabilized.

An example of a temperature control circuit used in a conventional crystal oscillator with a thermostat will be described with reference to FIG. FIG. 3 is a circuit diagram showing an example of a temperature control circuit of a conventional crystal oscillator with a thermostatic bath.
As shown in FIG. 3, a conventional OCXO temperature control circuit basically includes a thermistor (TH), an operational amplifier 10, a power transistor Tr1, a heater resistor HR, a power supply voltage Vcc, and a stabilized power supply Vreg. It has.

Each part and connection relation of the conventional temperature control circuit will be specifically described.
The thermistor TH is a temperature-sensitive element whose resistance value varies with temperature, detects the temperature of the oscillation element, and outputs a voltage corresponding to the temperature.
A stabilized power supply Vreg is applied to one end of the thermistor TH via a resistor R1, and the other end is grounded. One end of the thermistor TH is input to the minus (−) terminal (inverted input terminal) of the operational amplifier 10 via the resistor R4.

  The stabilized power supply Vreg is applied to one end of series-connected resistors R2 and R3 provided in parallel to the thermistor TH, the other end is grounded, and the point between the resistors R2 and R3 is a plus (+ ) Terminal (non-inverting input terminal) and is a reference voltage.

  Further, the output of the operational amplifier 10 is input to the base of the power transistor Tr1 through the resistor R6 and is fed back to the negative terminal of the operational amplifier 10 through the resistor R5.

The heater resistance HR generates heat according to the flowing current.
The power supply voltage Vcc is applied to one end of the heater resistor HR, the other end of the heater resistor HR is connected to the emitter of the power transistor Tr1, and the collector of the power transistor Tr1 is grounded.
The power transistor Tr1 is a PNP transistor, and the output of the operational amplifier 10 is applied to the base via R6.
A P-channel MOSFET (Metal-Oxide Semiconductor Field-Effect Transistor) may be used as the power transistor Tr1.

  In the temperature control circuit having the above configuration, the operational amplifier 10 amplifies and outputs the difference between the reference voltage and the voltage corresponding to the temperature of the crystal resonator from the thermistor, and applies the voltage of the difference to the base of the power transistor Tr1. Then, a current flows according to the voltage between the base and the emitter, and the heater resistor HR and the power transistor Tr1 generate heat to keep the temperature in the thermostatic chamber constant.

[Changes in power supply voltage]
Incidentally, when a PNP transistor is used as the power transistor Tr1 as in the temperature control circuit shown in FIG. 3, when the power supply voltage Vcc fluctuates rapidly, the voltage between the base and the emitter of the power transistor Tr1 changes abruptly. As a result, the current flowing through the heater resistor fluctuates greatly temporarily, and the temperature control of the thermostat may become unstable.

[Conventional power fluctuation characteristics: Fig. 4]
An example of power supply fluctuation characteristics in a conventional temperature control circuit will be described with reference to FIG. FIG. 4 is a characteristic diagram showing an example of power supply fluctuation characteristics in a conventional temperature control circuit.
As shown in FIG. 4, when the power supply voltage (Vcc) fluctuates, the current consumption value of the temperature control circuit fluctuates abruptly at the changing timing, and steep falling and rising are recognized. This indicates that the control of the oven is temporarily broken and unstable.

[Related technologies]
In addition, as a prior art regarding the temperature control circuit of the crystal oscillator with a thermostat, Unexamined-Japanese-Patent No. 2001-117645 "Temperature control circuit" (Toyo Tsushinki Co., Ltd., patent document 1), Unexamined-Japanese-Patent No. 2005-165630 "Temperature" Control circuit and thermostatic chamber type piezoelectric oscillator using the same ”(Toyo Tsushinki Co., Ltd., Patent Document 2), Japanese Patent Application Laid-Open No. 2012-253660,“ Quartz Oscillator with Thermostatic Chamber ”(Nippon Denpa Kogyo Co., Ltd., Patent Document 3) JP 2012-257195 A “Cooling Temperature Control Circuit for Crystal Oscillator with Thermostatic Bath” (Nippon Radio Industry Co., Ltd., Patent Document 4).

  In Patent Document 1, in a temperature control circuit, an output of a differential amplifier that fluctuates according to fluctuations in a power supply voltage is input to the base of a transistor, and a part of the emitter output is negatively fed back to the input of the differential amplifier. Have been described.

  In Patent Document 2, in the temperature control circuit, a capacitor C7 is connected between the drain of the power FET and the + input of the differential amplifier IC, and the drain current of the power FET is rapidly changed by an integration circuit using the capacitor C7. It is described that suppresses.

  In Patent Document 3, in a crystal oscillator with a thermostatic chamber, a resistance for adjusting sensitivity is provided, and a temperature of a control target due to a change in ambient temperature corresponding to a difference in ZTC (zero temperature coefficient point) temperature for each crystal resonator. It is described to prevent the change of.

  In Patent Document 4, in the temperature control circuit, the first digital potentiometer adjusts the vertex temperature of the crystal resonator, and the second digital potentiometer changes the resistance value so as to cancel the temperature gradient of the first digital potentiometer. It is described that.

JP 2001-117645 A JP 2005-165630 A JP 2012-253660 A JP2012-257195A

  As described above, in the conventional temperature control circuit using the PNP type transistor as the power transistor, the emitter voltage of the power transistor varies according to the variation of the power supply voltage, and accordingly, the voltage between the base and the emitter varies. As a result, the temperature control of the thermostatic chamber becomes unstable.

  Note that Patent Documents 1 and 2 are configured to feed back to a differential amplifier using a transistor output that has changed due to fluctuations in the power supply voltage, and directly reflect the power supply voltage to the operational amplifier without using the output of the power transistor. That is not described. Similarly, it is not described in Patent Documents 3 and 4.

  The present invention has been made in view of the above circumstances, and suppresses fluctuation of the voltage between the base and the emitter of the PNP type power transistor due to fluctuation of the power supply voltage, realizes stable temperature control, and improves frequency characteristics. An object of the present invention is to provide a temperature control circuit capable of performing the above.

The present invention for solving the problems of the above conventional example is a temperature control circuit for a crystal oscillator with a thermostat, which detects the temperature in the thermostat and outputs a voltage corresponding to the detected temperature, and a reference An operational amplifier having a positive terminal to which a voltage is input and a negative terminal to which the thermistor is connected, which outputs a difference between voltages input to both terminals, and a PNP power transistor which is input based on an output from the operational amplifier; one end connected to the power supply voltage, a heater resistance and the other end is connected to the emitter of the PNP power transistor, one end is connected to the power supply voltage, the other end is grounded, the part of the supply voltage, plus the operational amplifier And a bridge resistor circuit for adding to the reference voltage input to the terminal .

Further, according to the present invention, in the above temperature control circuit, the bridge resistor circuit is configured by a series circuit of a first resistor and a second resistor, and a point between the first resistor and the second resistor is an operational amplifier. It is connected to the positive terminal .

According to the present invention, in the above temperature control circuit, a point between the first resistor and the second resistor is connected to the plus terminal of the operational amplifier via a third resistor . .

According to the present invention, a temperature control circuit for a crystal oscillator with a thermostatic chamber, which detects the temperature in the thermostatic chamber and outputs a voltage corresponding to the detected temperature, a plus terminal to which a reference voltage is input, An operational amplifier that has a negative terminal to which the thermistor is connected , outputs a difference between voltages input to both terminals, a PNP power transistor that is input based on an output from the operational amplifier, and one end connected to the power supply voltage; The other end is connected to the emitter of the PNP-type power transistor, the other end is connected to the power supply voltage, the other end is grounded, and a part of the power supply voltage is added to the reference voltage input to the positive terminal of the operational amplifier since the temperature control circuit that includes a bridge resistor circuit, if the supply voltage fluctuates, and the emitter voltage of the base voltage of the PNP power transistor The voltage between the base and the emitter can be kept constant by changing the direction, and the output frequency signal can be stabilized by performing stable temperature control even when the power supply voltage changes suddenly. .

It is a circuit diagram of the temperature control circuit which concerns on embodiment of this invention. It is a characteristic view which shows the example of a power supply fluctuation characteristic of this temperature control circuit. It is a circuit diagram which shows the example of the temperature control circuit of the conventional crystal oscillator with a thermostat. It is a characteristic view which shows the example of a power supply fluctuation characteristic in the conventional temperature control circuit.

Embodiments of the present invention will be described with reference to the drawings.
[Outline of the embodiment]
The temperature control circuit for the crystal oscillator with a thermostatic bath according to the embodiment of the present invention uses the output of the operational amplifier that outputs the difference between the voltage corresponding to the temperature detected by the thermistor and the reference voltage as the base of the PNP type power transistor. Is a temperature control circuit in which a heater resistor is connected to the emitter, and a part of the power supply voltage is added to the reference voltage of the operational amplifier via the bridge resistor circuit. When the power supply voltage fluctuates, the PNP type By changing the base voltage of the power transistor in the same direction as the emitter voltage, the base-emitter voltage can be kept constant, and even if the power supply voltage changes suddenly, stable temperature control is performed and output. The frequency can be stabilized.

[Temperature Control Circuit According to Embodiment: FIG. 1]
A temperature control circuit of the thermostatic crystal oscillator according to the embodiment of the present invention will be described with reference to FIG. FIG. 1 is a circuit diagram of a temperature control circuit according to an embodiment of the present invention.
As shown in FIG. 1, the temperature control circuit (this temperature control circuit) according to the embodiment of the present invention has a thermistor (TH) and a basic part similar to the conventional temperature control circuit shown in FIG. , An operational amplifier 10, a PNP power transistor Tr1, a heater resistor HR, a power supply voltage Vcc, and a stabilized power supply Vreg.
As a feature of the temperature control circuit, a bridge resistor circuit 11 including a resistor R11, a resistor R12, and a resistor R13 is provided.

Since the connections other than the bridge resistor circuit 11 are the same as those in FIG. 3, the description thereof is omitted.
The bridge resistor circuit 11 includes a resistor R11 having one end connected to the power supply voltage Vcc, a resistor R12 having one end grounded, and a resistor R13 having one end connected to a point between the resistor R2 and the resistor R3. In this configuration, the other ends of R11, R12, and R13 are connected at one point.

The power supply voltage Vcc is branched and applied to one end of the resistor R11 of the bridge resistor circuit 11.
The branched power supply voltage Vcc is input to a point between the resistors R2 and R3 through a resistor R13 connected to a point between the resistors R11 and R12.

As described with reference to FIG. 3, the point between the resistor R2 and the resistor R3 is connected to the stabilized power supply Vreg and to the + terminal of the operational amplifier 10 to supply a reference voltage.
That is, in this temperature control circuit, the power supply voltage Vcc is added to the reference voltage and supplied to the + terminal of the operational amplifier.

  Thereby, when the power supply voltage Vcc fluctuates, the emitter voltage of the power transistor Tr1 fluctuates accordingly, and the fluctuation is added to the reference voltage and reflected in the output of the operational amplifier 10, and the power transistor Tr1 When input to the base, the base voltage fluctuates in the same direction as the emitter voltage.

  Therefore, even if the power supply voltage Vcc fluctuates, the base-emitter voltage of the PNP type power transistor Tr1 can be kept constant, and the amount of current flowing through the heater resistor HR can be prevented from fluctuating greatly. It is.

[Characteristics of this temperature control circuit: Fig. 2]
Next, the power supply fluctuation characteristics of the temperature control circuit and the frequency stability of the thermostatic crystal oscillator using the temperature control circuit will be described with reference to FIG. FIG. 2 is a characteristic diagram showing an example of power supply fluctuation characteristics of the temperature control circuit.
As shown in FIG. 2, in this temperature control circuit, even if the power supply voltage Vcc fluctuates, the fluctuation of the consumption current is small and no steep falling or rising occurs.
Compared with the characteristics of the conventional temperature control circuit shown in FIG. 4, the characteristics are greatly improved, indicating that the control of the oven is stable.

[Effect of the embodiment]
According to the temperature control circuit according to the embodiment of the present invention, the operational amplifier 10 outputs the difference between the reference voltage output from the point between the resistors R2 and R3 and the voltage corresponding to the temperature from the thermistor, A PNP-type power transistor Tr1 is a temperature control circuit that inputs the output from the operational amplifier 10 and controls the current of the heater resistor connected to the emitter, one end of which is connected to the power supply voltage Vcc, and resistors R11 and R12 Are connected in series, and a point between the resistors R11 and R12 of the bridge resistor circuit 11 is connected to a point between the resistors R2 and R3 supplying the reference voltage via the resistor R13. Therefore, when the power supply voltage Vcc fluctuates, the base voltage of the PNP type power transistor Tr1 is changed in the same direction as the emitter voltage to Scan - the voltage between the emitter can be kept constant, there is an effect capable of stabilizing the output frequency by performing a temperature control of the power supply voltage Vcc is stabilized vary.

  The present invention is suitable for a temperature control circuit that can suppress the influence of fluctuations in the power supply voltage and perform stable temperature control to stabilize the output frequency.

  DESCRIPTION OF SYMBOLS 10 ... Operational amplifier 11 ... Bridge resistance circuit R1, R2, R3, R4, R5, R6, R11, R12, R13 ... Resistance, HR ... Heater resistance, TH ... Thermistor, Tr1 ... Power transistor

Claims (3)

A temperature control circuit for a crystal oscillator with a thermostatic bath,
A thermistor that detects the temperature in the thermostat and outputs a voltage corresponding to the detected temperature;
An operational amplifier having a positive terminal to which a reference voltage is input and a negative terminal to which the thermistor is connected, and outputting a difference between voltages input to both terminals;
A PNP-type power transistor that inputs the output from the operational amplifier as a base;
A heater resistor having one end connected to the power supply voltage and the other end connected to the emitter of the PNP-type power transistor;
A temperature control comprising: a bridge resistor circuit having one end connected to a power supply voltage, the other end grounded, and adding a part of the power supply voltage to a reference voltage input to a plus terminal of the operational amplifier circuit.   The bridge resistor circuit is configured by a series circuit of a first resistor and a second resistor, and a point between the first resistor and the second resistor is connected to a plus terminal of an operational amplifier. The temperature control circuit according to claim 1.   3. The temperature control circuit according to claim 2, wherein a point between the first resistor and the second resistor is connected to a plus terminal of the operational amplifier via a third resistor.

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