JP2008109391A - Temperature-compensated piezoelectric oscillator and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a temperature-compensated piezoelectric oscillator capable of appropriately suppressing an oscillation frequency deviation with a simple circuit configuration when attached to a main body apparatus such as an image forming apparatus. <P>SOLUTION: The oscillator includes: an oscillation circuit provided with a piezoelectric oscillator 101 and varactors 104 and 105; a temperature detection circuit 111 for dividing a battery supply voltage by a temperature sensitive element 112; and a switching circuit provided with an FET 116 for outputting the divided voltage by the temperature sensitive element 112 to the varactors 104 and 105 when the power of a main body to which the oscillator is attached is supplied and for canceling voltage division by the temperature sensitive element 112 while the power of the main body is cut off. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a temperature-compensated piezoelectric oscillator that compensates the frequency-temperature characteristics of a piezoelectric oscillator, and an image forming apparatus including the oscillator.

  In an image forming apparatus such as a facsimile machine or a multifunction machine and other electronic devices, a piezoelectric oscillator such as a crystal oscillator is used as a real time clock. Facsimile uses RTC as facsimile transmission / reception time, and multi-function machines use it for displaying the main unit time. Since the oscillation frequency of the piezoelectric oscillator changes depending on the temperature, it is necessary to compensate the frequency-temperature characteristic in order to suppress a time lag. For example, the allowable range of time deviation in a facsimile is 60 s / month.

  In the image forming apparatus, a certain correction is performed by software so that the frequency deviation becomes the first by estimating the use method and the use temperature. However, when the microprocessor is driven by the main power supply, correction cannot be performed when the microprocessor is turned off, and a deviation of about 120 s / month may occur depending on the use method and use temperature.

Also, in a piezoelectric oscillator having a temperature compensation circuit, in general, temperature compensation is performed by applying a compensation voltage generated using a temperature sensitive element such as a thermistor to a varicap having a VCXO (Voltage Controlled Crystal Oscillator) structure. Is going. By changing the capacity of the varicap according to the ambient temperature, the load capacity seen from the piezoelectric oscillator is changed, thereby suppressing the oscillation frequency deviation. For example, Patent Document 1 describes a digitally controlled temperature compensated crystal oscillator.
JP-A-6-318820

  If correction is to be performed both when the ambient temperature is low and when it is high using a variable capacitance element such as a varicap, for example, it is necessary to create a quadratic function by connecting two varicaps in series. Creating a quadratic or higher function makes it more sensitive to component variations, and the variation tends to increase as the number of components increases.

  The present invention has been made in view of such a problem in the conventional technology, and when attached to a main device such as an image forming apparatus, the oscillation frequency deviation can be appropriately suppressed by a simple circuit configuration. An object of the present invention is to provide a temperature-compensated piezoelectric oscillator and an image forming apparatus including the oscillator.

  In order to achieve the above object, a temperature compensated piezoelectric oscillator provided by the present invention includes an oscillation circuit having a piezoelectric oscillator and a variable capacitance element, a temperature detection circuit that divides a battery power supply voltage by a temperature sensitive element, and When the power source of the main body to which the oscillator is attached is turned on, the divided voltage by the temperature sensitive element is output to the variable capacitance element, and while the power source of the main body is turned off, the voltage divided by the temperature sensitive element is output. And a switching circuit for releasing the pressure.

  According to another aspect of the present invention, an image forming apparatus including the above-described temperature compensated piezoelectric oscillator is provided.

  According to the above configuration, when the power of the main body is turned on and the inside of the main body is at a relatively high temperature, temperature compensation is performed using the divided voltage by the temperature sensing element, and the power of the main body is cut off. When the inside is near room temperature where the frequency deviation is small, the temperature compensation by the temperature sensing element is not canceled and it is not performed, so within the appropriate range without increasing the number of parts such as variable capacitance elements depending on the temperature range. Oscillation frequency deviation can be suppressed.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In this embodiment, it is assumed that the present invention is embodied as an RTC temperature-compensated crystal oscillator used for main unit time display of a multifunction machine. In the multi-function device, the RTC is operated independently by a battery, and even when the power source of the multi-function device main body is turned off, the RTC measures time for displaying the main body time.

  FIG. 1 is a diagram illustrating an example of a circuit configuration of a temperature-compensated crystal oscillator according to the present embodiment. This temperature compensated crystal oscillator includes a crystal oscillator 101 having a tuning fork-shaped crystal oscillation piece. An amplifier circuit having an inverter 102 and a feedback resistor 103 is connected to the crystal oscillator 101. These operate as a Pierce CB oscillation circuit and perform continuous oscillation.

  To this oscillation circuit, varicaps 104 and 105 which are variable capacitance elements are connected. By controlling the voltage applied to the varicaps 104 and 105 and changing the load capacitance of the oscillation circuit, the oscillation frequency of the crystal oscillator 101 is adjusted. As the voltage applied to the varicaps 104 and 105 increases, the capacity decreases, and as the voltage decreases, the capacity increases. The load capacity is a capacity component included in a closed loop from one end of the crystal oscillator 101 to the other end. In addition to the varicaps 104 and 105, the closed loop includes capacitors 106 and 107 having fixed capacitances and DC cut capacitors 108 and 109. Further, a resistor 110 is provided between the oscillation circuit and the DC cut capacitor 109 in order to suppress overtones.

  The temperature detection circuit 111 outputs a control voltage to the varicaps 104 and 105 of such a voltage-controlled oscillation circuit. Here, the temperature detection circuit 111 has a voltage dividing circuit in which the thermistor 112 as a temperature sensitive element is arranged on the low pressure side. The battery power supply voltage is applied to the voltage dividing circuit, and the battery power supply voltage is divided by the ratio of the resistance value of the fixed resistor 113 arranged on the high voltage side and the resistance value of the thermistor 112. The thermistor 112 is disposed in the vicinity of the crystal oscillator 101. When the ambient temperature of the crystal oscillator 101 increases, the resistance value decreases, and when the ambient temperature decreases, the resistance value increases. As the resistance value of the thermistor 112 changes, the divided voltage that is the voltage at the connection point between the thermistor 112 and the fixed resistor 113 changes according to the ambient temperature of the crystal oscillator 101. This divided voltage is output to the varicaps 104 and 105 via the resistors 114 and 115, respectively.

  In the temperature compensated crystal oscillator according to this embodiment, when the power supply of the multi-function device main body to which the oscillator is attached is turned on, the divided voltage by the thermistor 112 is output to the varicaps 104 and 105, and While the power supply is cut off, the switching circuit for releasing the partial pressure by the thermistor 112 is provided. Here, as the switching circuit, a MOSFET 116 is disposed between the thermistor 112 and the ground. The source of the P-channel FET 116 is connected to one end of the thermistor 112, and the drain is grounded.

  The gate of the FET 116 is connected to the main body power supply. The main body power supply voltage is divided by resistors 117 and 118, and the divided voltage is supplied to the gate by a capacitor 119. The FET 116 operates as a switching element and is turned on when the power source of the multi-function peripheral is turned on to ground the low voltage end of the thermistor 112. Further, the FET 116 is turned off while the main body power supply is cut off. For this reason, the divided voltage by the thermistor 112 is output to the varicaps 104 and 105 only while the main body power is turned on, and temperature compensation is performed. On the other hand, when the main body power supply is disconnected, the voltage division by the thermistor 112 is released, and the maximum voltage by the battery power supply voltage is output to the varicaps 104 and 105. In this case, temperature compensation is not performed. This is because it is considered that the oscillation frequency deviation is small when the power source of the multi-function peripheral is turned off.

  When the power supply of the multi-function peripheral is turned off, the temperature range is normally considered to be 10 ° C to 40 ° C. In an environment where a multifunction device is actually used in an office or the like, the office or the like is often not operating when the power of the multifunction device is turned off. In this case, the inside of the multifunction machine in which the crystal oscillator is disposed is also near the normal temperature, and the temperature is considered not to deviate significantly from the multifunction machine specification temperature range of 10 ° C. to 40 ° C. On the other hand, when the MFP is powered on, the office is in operation, so the ambient temperature is often around 25 ° C., and the internal temperature of the device is higher than that, for example, It is conceivable that the temperature becomes as high as 60 ° C.

  As described above, since the internal temperature of the multifunction device changes greatly between when the power is turned on and when it is not turned on, the operating temperature range is expanded to, for example, 10 ° C. to 60 ° C., and the multifunction device has a large oscillation frequency deviation depending on the method of use. turn into. In addition, since there is a temperature deviation of about −45 ppm (120 s / month) at 60 ° C., it is difficult to satisfy the rule of 60 s / month. Further, if the varicap tries to correct the case of low temperature and high temperature, the number of parts increases and it becomes difficult to suppress the influence of variation.

  However, since the temperature deviation is small near room temperature, the temperature compensated crystal oscillator according to the present embodiment does not perform temperature compensation when the power is turned off, but performs temperature compensation only when the power is turned on. This makes it possible to perform temperature compensation within an appropriate range with a simple circuit configuration without increasing the number of parts. For example, since it is sufficient for the multi-function device to satisfy 60 s / month, the frequency deviation can be suppressed within a range of about 20 ppm so as to satisfy it. In addition, since the influence of component variations can be suppressed, the variation of each multifunction product can be reduced. As a result, it is not necessary to make adjustments for individual products.

  FIG. 2 is a diagram showing an example of frequency temperature characteristics of the temperature compensated crystal oscillator. The horizontal axis indicates the ambient temperature [° C.], and the vertical axis indicates the oscillation frequency deviation [ppm]. The temperature characteristic of the varicap indicated by a broken line in this graph is a temporary representation of the compensation amount obtained by applying a voltage to the varicap as described above.

  In this example, the frequency temperature characteristics of the crystal oscillator are indicated by a thin dotted line and a thin solid line. In this embodiment, since a tuning fork type oscillator is used, the characteristic is represented by an upward convex quadratic function in this graph, and the vertex temperature is 25 ° C. Although the shape of the quadratic function has frequency temperature characteristics as described above, in the range of 10 ° C. to 40 ° C. in which the power source of the multi-function device is cut off, the frequency of the crystal oscillator is indicated by a thin dotted line. The deviation is −10 ppm or less. For this reason, the temperature characteristics of the entire oscillator when the power source of the main body is turned off are kept at −20 ppm or less as shown by the thick dotted line.

  On the other hand, when the power is turned on, the temperature inside the multi-function device is about 35 ° C. to 60 ° C. In this range, as shown by a thin solid line, the oscillation frequency deviation of the crystal oscillator greatly fluctuates. However, since temperature compensation is performed when the power is turned on, the temperature characteristics of the varicap also change in accordance with the oscillation frequency deviation of the crystal oscillator, as indicated by a thin broken line. The amount of compensation increases as the temperature rises. Therefore, even when the power is turned on, the frequency-temperature characteristic of the entire crystal oscillator can be suppressed within a range of about 20 ppm as shown by the bold solid line.

  As described above, in the temperature compensated crystal oscillator according to the present embodiment, the temperature compensation is not performed when the power of the multi-function device is turned off, and the temperature compensation is performed only when the power is turned on, thereby increasing the number of parts such as varicaps. And suppress the oscillation frequency deviation within an appropriate range. In addition, only when the temperature is high can be compensated, and the accuracy can be improved by narrowing the target temperature range.

  The embodiments described above do not limit the technical scope of the present invention, and various modifications and applications other than those already described are possible within the scope of the present invention. In the above example, a tuning fork type oscillator having a quadratic function characteristic is used. However, other types of piezoelectric oscillators may be used. For example, an AT cut oscillator having a cubic function characteristic may be used. Further, instead of switching the presence / absence of temperature compensation by turning on / off the main power supply, it is also possible to switch at the operating point of the image forming apparatus such as a sleep mode and a ready mode. Furthermore, the present invention can be applied to other image forming apparatuses such as facsimiles and printers in addition to multi-function machines, temperature compensated piezoelectric oscillators mounted on electronic devices other than image forming apparatuses, It can also be applied to electronic devices.

  According to the temperature-compensated piezoelectric oscillator and the image forming apparatus according to the present invention, the oscillation frequency deviation can be appropriately suppressed by a simple circuit configuration when attached to a main device such as an image forming apparatus, and image formation It is useful for various devices equipped with devices and other RTCs.

The figure which shows an example of the circuit structure of the temperature compensation type | mold crystal oscillator in this Embodiment Diagram showing an example of frequency temperature characteristics of temperature compensated crystal oscillator

Explanation of symbols

101 Crystal oscillator 102 Inverter 103 Feedback resistor 104, 105 Varicap (variable capacitance element)
111 Temperature Detection Circuit 112 Thermistor (Temperature Sensing Element)
116 FET

Claims (2)

A temperature compensated piezoelectric oscillator,
An oscillation circuit having a piezoelectric resonator and a variable capacitance element;
A temperature detection circuit that divides the battery power supply voltage by a temperature sensing element; and
When the power source of the main body to which the oscillator is attached is turned on, the divided voltage by the temperature sensing element is output to the variable capacitance element, and while the power source of the main body is cut off, the temperature sensing element A temperature-compensated piezoelectric oscillator comprising a switching circuit that releases partial pressure.   An image forming apparatus comprising the temperature compensated piezoelectric oscillator according to claim 1.

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