JP5970275B2 - High stability oscillator - Google Patents

Description

  The present invention relates to an oscillator that outputs a highly stable frequency.

  As an oscillator that outputs a high-stability frequency, for example, a piezoelectric resonator, a crystal resonator, and a resonance element such as an LC (inductor-capacitor) resonance circuit are provided, and the resonance element is connected to the oscillation circuit. Some output an oscillation signal corresponding to the resonance frequency. In particular, the crystal oscillator has high stability of the resonance frequency as a resonance element, and the crystal oscillator, which is an oscillator using the crystal oscillator, has a highly stable output frequency, and is used in various electronic devices. And widely used as a reference source for time.

  Although the frequency stability of the crystal oscillator is high, the resonance frequency of the crystal oscillator changes slightly depending on the temperature, so in order to obtain a constant frequency with high stability regardless of the temperature by the crystal oscillator In some way, the temperature effect on the crystal must be removed.

  As a crystal oscillator that outputs a higher stability frequency, there is an Oven-Controlled Crystal Oscillator (OCXO) that contains at least a crystal unit in a thermostat that is maintained at a constant temperature by temperature control. is there. In the crystal oscillator with a thermostat, the temperature of the crystal resonator is maintained at a constant high temperature regardless of the ambient temperature, so that a frequency with extremely high stability can be obtained.

  Also, a temperature-compensated crystal oscillator that measures the ambient temperature, calculates the compensation amount from the measured ambient temperature based on the frequency temperature characteristics of the crystal unit, and feeds back the compensation amount to the oscillation circuit. (TCXO: Temperature Compensated Crystal Oscillator). In a temperature-compensated crystal oscillator, for example, it is possible to change the load capacitance value according to the compensation amount by using the fact that the oscillation frequency changes minutely by changing the value of the load capacitance connected to the crystal resonator in the oscillation circuit. Therefore, a constant oscillation frequency can be obtained regardless of the ambient temperature.

  Although the crystal oscillator with a thermostat has the advantage of being able to output a very high frequency of stability, it is necessary to heat the thermostat with a heater in order to maintain the thermostat at a constant temperature (generally, The temperature is sufficiently higher than room temperature), and there is a problem that power consumption is large. Another problem is that it takes several minutes to several tens of minutes as a startup time until the inside of the thermostatic chamber reaches a specified temperature and stabilizes after the power is turned on, and the output frequency is not stable during that time. If you try to use the crystal oscillator with a thermostatic bath whenever you need it, there is a problem of start-up time, so you need to keep the crystal oscillator with a thermostatic bath operating even when you don't use it. Consumption increases. In order to alleviate the problem of large power consumption of such a crystal oscillator with a thermostat, Patent Document 1 uses a thermostat having a heater, but in some cases, it is not a constant temperature but an ambient temperature. A configuration is disclosed in which the temperature of the thermostatic chamber is controlled so as to be a temperature determined by a certain relationship.

  On the other hand, the temperature-compensated crystal oscillator does not use a thermostatic chamber heated by a heater, and thus has an advantage that power consumption is small and it can be used immediately after power-on. However, there is a problem that the stability of the output frequency is worse by, for example, one digit or more as compared with the crystal oscillator with a thermostatic bath. In addition, if temperature compensation is to be performed with high accuracy, it is necessary to perform compensation up to higher-order components in the frequency temperature characteristics, and the configuration of the temperature compensation circuit for generating the compensation amount becomes large, and the temperature compensation circuit The amount of work for adjusting to the optimum point becomes enormous and requires time. When the ambient temperature changes greatly, sufficient temperature compensation cannot be performed in the vicinity of the upper and lower limits of the change range, and the frequency stability may decrease. Patent Document 2 discloses a temperature-compensated crystal oscillator in which, for example, when the ambient temperature is extremely low, the temperature of the crystal unit is raised to a temperature range in which the heater is operated and temperature compensation can be reliably performed. ing. Patent Document 3 discloses a temperature-compensated crystal oscillator in which a heater is incorporated in a crystal oscillator in order to shorten the adjustment time of the temperature-compensation circuit, and the temperature compensation circuit can be adjusted while the crystal unit is heated by the heater. Is disclosed.

  In the above description, the crystal oscillator with temperature chamber and the temperature-compensated crystal oscillator have been described. Even in an oscillator using an oscillation element other than a crystal oscillator, the oscillation element is accommodated in the temperature chamber to obtain a highly stable oscillation frequency. A configuration and a configuration in which a compensation amount is obtained from a measured value of the ambient temperature based on the frequency temperature characteristic of the oscillation element, and the oscillation frequency is compensated to obtain a highly stable oscillation frequency can be considered. Also in this case, the configuration using the thermostatic chamber outputs a higher stability frequency than the configuration of the temperature compensation type, but the power consumption is large and the startup time is also long.

Special table 2008-507174 JP 2009-182881 A JP 2009-246658 A

  An oscillator using an oscillation element, such as a crystal oscillator, is used in various electronic devices, and a crystal oscillator with a thermostat or a temperature-compensated crystal oscillator is selected according to the frequency stability required for the electronic device. For example, a base station application in mobile communication requires a very stable frequency source, and conventionally, there has been no choice but to select a crystal oscillator with a thermostatic bath. However, in recent years, it has become possible to receive and use radio waves of extremely stable frequencies from GPS (Global Positioning System) satellites, and it is possible to use GPS radio waves. Therefore, even in the use of a communication base station, it is not always necessary to use a crystal oscillator with a thermostatic bath, and the use of a temperature compensated crystal oscillator is sufficient. However, a quartz oscillator with a thermostat is still being selected in the communication base station for the existence of a time zone in which the radio wave from the GPS satellite cannot be used or when the base station is adjusted. As the crystal oscillator with a thermostatic chamber continues to be used, it is difficult to reduce power consumption at the communication base station.

  In this way, there are devices that must keep the quartz crystal oscillator with a constant temperature bath operating due to the demand for high stability frequency in a short period of time, which increases the power consumption of the device. Connected to. In addition to this, the temperature compensated crystal oscillator has insufficient frequency stability, but there are applications in which the frequency stability is not as high as that of the thermostatic bath crystal oscillator. This means that the frequency is output with the same level of stability as the temperature compensated crystal oscillator at normal times, and when necessary, the frequency is output with the same high level of stability as the crystal oscillator with a thermostatic bath, It shows that there is a need for a crystal oscillator with reduced overall power consumption. Similarly, even for an oscillator that uses an oscillation element other than a crystal unit, there is a need for an oscillator that can further increase the stability of the oscillation frequency when the need arises and suppresses the overall power consumption. To do.

  Accordingly, an object of the present invention is to provide an oscillator that outputs a high stability frequency, outputs a higher stability frequency when necessary, and suppresses the overall power consumption. It is in.

  An oscillator according to the present invention is an oscillator that includes a resonant element and an oscillation circuit that uses the resonant element and outputs a frequency corresponding to the resonant element, and includes a temperature sensor that measures the temperature of the resonant element, and a temperature of the resonant element. Based on the temperature adjustment unit to be adjusted, the temperature control circuit for driving and controlling the temperature adjustment unit based on the temperature measured by the temperature sensor so that the temperature of the resonance element becomes a constant temperature, and the frequency temperature characteristic of the resonance element The temperature compensation circuit calculates the compensation amount for temperature compensation from the temperature measured by the temperature sensor and supplies it to the oscillation circuit. Based on the external signal, the temperature control circuit and the temperature adjustment unit are operated to keep the temperature of the resonant element constant. Oscillation circuit that performs constant temperature mode based on compensation amount without operating temperature control circuit and temperature adjustment unit. Has a temperature compensation mode is to operate, a switch-mode control circuit, the.

  In the oscillator of the present invention, the resonant element is, for example, a crystal resonator, and when the crystal resonator is used as the resonant element, the oscillator is configured as a crystal oscillator. Further, the temperature adjustment unit may be constituted by a heater having only a function of raising temperature, or may be constituted by an element (for example, a Peltier element) having both functions of raising and lowering temperature.

  In the present invention, the oscillator is provided with a temperature compensation circuit for performing temperature compensation of the oscillation frequency in accordance with the temperature of the resonant element based on the frequency temperature characteristic of the resonant element, and temperature adjustment for maintaining the resonant element at a constant temperature. A unit (such as a heater or a Peltier element) and a temperature control circuit are provided. In addition, a temperature control mode for operating the oscillation circuit while maintaining the resonant element at a constant temperature by operating the temperature adjustment unit and the temperature control circuit according to an external signal, and the temperature adjustment unit and the temperature control circuit are provided. Only the temperature compensation is performed without operating, and the temperature compensation mode for operating the oscillation circuit is switched. As a result, according to the present invention, it is possible to reduce power consumption as a temperature compensation mode in which the temperature adjustment unit is not operated during normal times, and particularly as a temperature control mode in which the temperature adjustment unit is operated when necessary. High frequency output can be obtained.

It is sectional drawing which shows an example of a structure of the oscillator of one Embodiment of this invention. FIG. 2 is a block diagram showing a circuit configuration of the oscillator shown in FIG. 1.

  Next, a preferred embodiment of the present invention will be described with reference to the drawings.

  As shown in FIG. 1, the oscillator 1 according to this embodiment has a configuration in which a circuit board 3, a circuit unit 4, a resonance element 5, and a temperature adjustment unit 6 are accommodated in a container 2. The container 2 is made of a heat-resistant resin or metal, and includes, for example, a base and a cover. The container 2 may be airtight or non-airtight.

  The temperature adjustment unit 6 adjusts the temperature of the resonant element 5 and is constituted by, for example, a heater having only a temperature raising function or a Peltier element having both a temperature raising and lowering function. The temperature adjustment unit 6 is provided on the upper surface or the back surface of the circuit board 3. The resonant element 5 is, for example, a crystal resonator, and is disposed in contact with the temperature adjustment unit 6 so that the temperature thereof can be changed by the temperature adjustment unit 6. In the illustrated example, the resonant element 5 is a crystal resonator including, for example, a surface-mounted container, and is attached to the surface of the temperature adjustment unit 6. If, for example, a unit having a chamber is used as the temperature adjustment unit 6, the resonance element 5 is accommodated in the chamber. As will be described later, the circuit unit 4 includes an oscillation circuit using a resonance element 5 and is provided on the circuit board 3 as, for example, a one-chip IC (integrated circuit). The circuit unit 4 may be composed of a plurality of individual (discrete) parts. Furthermore, a plurality of foot patterns 7 used when the oscillator 1 is mounted on a substrate of an electronic device are formed on the base portion of the container 2, and these foot patterns 7 are formed on the circuit substrate 3 through conductive paths. Connected. In the drawing, the foot pattern 7 is shown as a conductive film terminal for surface mounting, but the foot pattern 7 may be a lead wire.

  FIG. 2 shows the circuit configuration of the oscillator 1 including the internal configuration of the circuit unit 4. A temperature sensor 8 for measuring the temperature of the resonant element 5 is provided. The temperature sensor 8 is disposed, for example, at the junction interface between the temperature adjustment unit 6 and the resonance element 5 or inside the container of the resonance element 5. The circuit unit 4 includes an oscillation circuit 11 that is electrically connected to the resonance element 5 and oscillates at the resonance frequency of the resonance element 5, and a temperature from the temperature measured by the temperature sensor 8 based on the frequency temperature characteristics of the resonance element 5. Based on a temperature compensation circuit 12 that obtains a compensation amount for compensation and outputs a signal representing the compensation amount to the oscillation circuit 11 and a temperature measured by the temperature sensor 8 so that the temperature of the resonant element 5 becomes a constant temperature. A temperature control circuit 13 for driving and controlling the temperature adjustment unit 6 and the operation of the oscillator 1 are controlled. In particular, mode control for switching between a temperature control mode and a temperature compensation mode, which will be described later, in accordance with an external control signal. A circuit 14 and a buffer circuit 15 connected to the output of the oscillation circuit 11 in order to reduce the influence from the external circuit are provided. The output of the buffer circuit 15 is connected to the frequency output terminal 16, and the oscillation frequency output of the oscillator 1 can be obtained from this frequency output terminal 16. A control terminal 17 connected to the mode control circuit 14 is provided for input / output of control signals. Each of the frequency output terminal 16 and the control terminal 17 is electrically connected to the corresponding foot pattern 7.

  Next, the temperature control mode and the temperature compensation mode will be described.

  In the temperature control mode, the temperature control circuit 13 and the temperature adjustment unit 6 are operated, and the temperature adjustment unit 6 is driven based on the temperature measured by the temperature sensor 8, thereby setting the temperature of the resonant element 5 to a constant temperature. In this mode, the oscillation circuit 11 is operated to oscillate and output a frequency with higher stability. In this mode, for example, the temperature adjustment unit 6 including a heater is operated to maintain the temperature of the resonant element 5 at a temperature considerably higher than room temperature (for example, 85 ° C.), so that power consumption increases.

  On the other hand, the temperature compensation mode is a mode in which the temperature control circuit 13 and the temperature adjustment unit 6 are not operated. In this mode, the temperature compensation is performed from the temperature measured by the temperature sensor 8 based on the frequency temperature characteristics of the resonant element 5. The circuit 12 obtains a compensation amount for temperature compensation, and supplies a compensation signal indicating the compensation amount to the oscillation circuit 11. At this time, the temperature of the resonant element 5 becomes the ambient temperature if the influence of the heat generation of the circuit in the oscillator 1 is ignored, and similarly changes if the ambient temperature changes. For example, the oscillation circuit 11 oscillates at a temperature compensated frequency by changing the value of the load capacitance connected to the resonance element 5 in accordance with the compensation signal. The frequency-temperature characteristic of the resonant element 5 is measured in advance from the change in the oscillation frequency when the oscillation circuit 11 is oscillated using the resonant element 5 while changing the temperature. The measured frequency temperature characteristics are stored in advance in, for example, a memory or the like in the temperature compensation circuit 12. In the temperature compensation mode, since the temperature adjustment unit 6 is not operated, the power consumption is small, but the frequency stability is worse than that in the temperature control mode.

  As is apparent from the above description, the temperature control mode and the temperature compensation mode correspond to the operation of the thermostat crystal oscillator and the temperature compensated crystal oscillator, respectively, if the resonant element 5 is a crystal resonator. The present invention is characterized in that the mode control circuit 14 switches between the temperature control mode and the temperature compensation mode in accordance with a control signal given from the outside. In order to prevent the output frequency from changing when the mode is switched, the temperature compensation circuit 12 continues to operate even in the temperature control mode, and the oscillation circuit 11 is based on the compensation signal from the temperature compensation circuit 12. To oscillate.

  The timing of switching between the temperature compensation mode and the temperature control mode will be described.

  In a system that requires a frequency with extremely high stability during normal operation, the temperature control mode is set during normal operation, but it is in standby mode (the power is on but a high-stability frequency output is not required). Sometimes switching to the temperature compensation mode can be considered. By doing so, the temperature adjustment unit 6 is not operated during standby, so that power saving can be realized.

  In base station applications, etc., it is possible to operate in temperature compensation mode during normal operation where high frequency stability is not required, and to switch to temperature control mode during maintenance periods where relatively high frequency stability is required. . In this case, since the period for operating in the temperature compensation mode becomes longer, the use of the oscillator according to the present embodiment compared to the case of using a crystal oscillator with a thermostatic bath as in the prior art can greatly reduce power consumption as a whole. Achieved.

  Alternatively, for applications that require a relatively short time before the output frequency reaches a certain degree of stability, a certain degree of frequency stability is ensured by operating in the temperature compensation mode at startup, and then the temperature control mode is entered. A method of use is also conceivable in which switching is made to converge to a higher frequency stability.

  As described above, according to the oscillator of this embodiment, a particularly stable frequency can be obtained when necessary, and the power consumption as a whole can be reduced.

  DESCRIPTION OF SYMBOLS 1 ... Oscillator, 2 ... Container, 3 ... Circuit board, 4 ... Circuit part, 5 ... Resonance element, 6 ... Temperature adjustment unit, 7 ... Foot pattern, 8 ... Temperature sensor, 11 ... Oscillation circuit, 12 ... Temperature compensation circuit, DESCRIPTION OF SYMBOLS 13 ... Temperature control circuit, 14 ... Mode control circuit, 15 ... Buffer circuit, 16 ... Frequency output terminal, 17 ... Control terminal.

Claims (4)

An oscillator comprising a resonance element and an oscillation circuit using the resonance element and outputting a frequency according to the resonance element,
A temperature sensor for measuring the temperature of the resonant element;
A temperature adjustment unit for adjusting the temperature of the resonant element;
A temperature control circuit that drives and controls the temperature adjustment unit based on the temperature measured by the temperature sensor so that the temperature of the resonant element becomes a constant temperature;
A temperature compensation circuit for obtaining a compensation amount for temperature compensation from the temperature measured by the temperature sensor based on the frequency temperature characteristics of the resonant element and supplying the compensation circuit to the oscillation circuit;
Based on an external signal, the temperature control mode in which the temperature control circuit and the temperature adjustment unit are operated to operate the oscillation circuit with the temperature of the resonant element as the constant temperature, and the temperature control circuit and the temperature adjustment unit are operated. A mode control circuit that switches between a temperature compensation mode in which only the temperature compensation based on the compensation amount is performed and the oscillation circuit is operated, and
Having an oscillator. The temperature control mode is set during normal operation, and is switched to the temperature compensation mode when the power is turned on but in a standby time that does not require a high-stability frequency output as compared with the normal operation. The oscillator described in 1. The oscillator according to claim 1, wherein the temperature compensation mode is set during normal operation, and the temperature control mode is switched during a period in which higher frequency stability is required than during normal operation . The oscillator according to any one of claims 1 to 3, wherein the temperature adjustment unit includes an element having a function of raising and lowering temperature.

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